Old engine won't draw fuel/start/idle/RUN!
07-02-2007, 10:11 PM
#1
Thread Starter
Old engine won't draw fuel/start/idle/RUN!
Ok, the subject line was pretty broad but I'm not sure how else to put it. The engine in question is an old OS .45 FSR, once the most reliable engine in my collection. It would hand start easily, idle perfectly, and never gave me a bit of trouble. The last time it ran was 1990. I've since gotten back into the hobby and have installed this engine on a new airplane and it's giving me all kinds of fits.
First, it won't draw fuel when you choke it. In fact, you can watch it push fuel back through the fuel line towards the tank. I've removed the pressure line from the tank and blown into it gently to force fuel to the carb. The you choke it and the fuel goes back to the tank. I've opened the throttle fully, covered the carb and turned it with an electric starter. Nuthin...
Second, it won't hand start. It barely starts with an electric starter and then only if you open the throttle at least 3/4. This thing used to hand start on the first or second flip. Choke it a few times, turn it slowly by hand to feel the "bump" and then one good flip and it would purr away.
Third, when and if I can get it started it will run at full throttle nicely, but won't run below half. Below half it slows down and stops. When it does this the carb is open quite a ways, probably 1/8". It won't stay running unles the throttle barrel is open probably 1/2 way.
Here's what I've done.
I've taken the carb apart and replaced both rubber o-rings, the one on the high speed needle and the idle screw. I've cleaned out all passageways and there are no obstructions. I've disassembled the entire engine and cleaned all parts. The engine has great compression. I've replaced the glow plug (several times now). I'm running 15/18 fuel, new stuff too. I thought maybe my tank installation was too low so I removed the tank, connected it, set it so the top of the tank was about 1/2 inch higher than the carb, and still it won't draw fuel unless I lift the tank up even higher at which time gravity seems to take over and it flows fine.
No amount of fiddleing with the idle screw seems to make much of a difference. When it quits, it's always after I've warmed it up, run it to full throttle and adjusted the high speed needle. Sometimes it won't even start with an electric starter. Yes, my glow plug battery is fully charged and I've used a different one just to make sure.
Could I have assembled the engine incorrectly? Piston 180 degrees backwards? Would that make a difference? The liner is installed the only way it can go in. All gaskets are intact and in good shape. Could it be a tank issue? Fuel line ID? I've used up all the swear words I know, invented a few new ones, even threw a temper tantrum any 5 year old would be proud of, and still it refuses to be intimidated into running.
Before I buy a new engine and give up on this one, does anyone have any ideas? I usually am pretty good with engines but this one has me stumped.
Thanks!
Kurt
First, it won't draw fuel when you choke it. In fact, you can watch it push fuel back through the fuel line towards the tank. I've removed the pressure line from the tank and blown into it gently to force fuel to the carb. The you choke it and the fuel goes back to the tank. I've opened the throttle fully, covered the carb and turned it with an electric starter. Nuthin...
Second, it won't hand start. It barely starts with an electric starter and then only if you open the throttle at least 3/4. This thing used to hand start on the first or second flip. Choke it a few times, turn it slowly by hand to feel the "bump" and then one good flip and it would purr away.
Third, when and if I can get it started it will run at full throttle nicely, but won't run below half. Below half it slows down and stops. When it does this the carb is open quite a ways, probably 1/8". It won't stay running unles the throttle barrel is open probably 1/2 way.
Here's what I've done.
I've taken the carb apart and replaced both rubber o-rings, the one on the high speed needle and the idle screw. I've cleaned out all passageways and there are no obstructions. I've disassembled the entire engine and cleaned all parts. The engine has great compression. I've replaced the glow plug (several times now). I'm running 15/18 fuel, new stuff too. I thought maybe my tank installation was too low so I removed the tank, connected it, set it so the top of the tank was about 1/2 inch higher than the carb, and still it won't draw fuel unless I lift the tank up even higher at which time gravity seems to take over and it flows fine.
No amount of fiddleing with the idle screw seems to make much of a difference. When it quits, it's always after I've warmed it up, run it to full throttle and adjusted the high speed needle. Sometimes it won't even start with an electric starter. Yes, my glow plug battery is fully charged and I've used a different one just to make sure.
Could I have assembled the engine incorrectly? Piston 180 degrees backwards? Would that make a difference? The liner is installed the only way it can go in. All gaskets are intact and in good shape. Could it be a tank issue? Fuel line ID? I've used up all the swear words I know, invented a few new ones, even threw a temper tantrum any 5 year old would be proud of, and still it refuses to be intimidated into running.
Before I buy a new engine and give up on this one, does anyone have any ideas? I usually am pretty good with engines but this one has me stumped.
Thanks!
Kurt
07-02-2007, 10:29 PM
#2
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RE: Old engine won't draw fuel/start/idle/RUN!
Have the engine mounted on the plane or a test bench. Remove the carb completely.
Drop a few drops of fuel into the carb opening. Flip several times to distribute the fuel. Apply glow heat and flip the prop. If it doesn't start in a few flips, you have a massive air leak somewhere.
Is there any chance that you were running crankcase pressure before you put the engine in storage and forgot about a now open to the atmosphere pressure nipple, or hole for same, in the crankcase?
If the engine did start with the few drops of prime, the problem is still in the carburetor, assuming that the fuel tank plumbing is okay. Some times it is easy to miss something obvious, or to keep making the same mistake.
It is rare, but it some times happens that an engine can have fine cylinder compression (upstroke), but have terrible crankcase compression. Yes, the crankcase has compression. The crankcase compression pushed the fuel charge up the bypass and into the cylinder. When the piston/rod reverse direction, the upward movement of the piston causes a negative pressure area to form in the crankcase, this is what pulls the fuel from the fuel tank. Duke Fox wrote an explanation citing circumstances where the cylinder compression could be fine, but if the fit/seal of the lower piston area was poor, the pumping action as the piston descended in the cylinder and sucking action of the piston ascending toward the top of its stroke could cause an engine not to run at all. No fuel draw, no pumping a fuel/air charge through the bypass into the cylinder, etc.
I forget if the OS .45F-SR has a Dykes ring or not. These can be difficult to diagnose if one is not aware of how they behave when the tension/fit has been lost.
Good luck solving the problem.
Ed Cregger
Drop a few drops of fuel into the carb opening. Flip several times to distribute the fuel. Apply glow heat and flip the prop. If it doesn't start in a few flips, you have a massive air leak somewhere.
Is there any chance that you were running crankcase pressure before you put the engine in storage and forgot about a now open to the atmosphere pressure nipple, or hole for same, in the crankcase?
If the engine did start with the few drops of prime, the problem is still in the carburetor, assuming that the fuel tank plumbing is okay. Some times it is easy to miss something obvious, or to keep making the same mistake.
It is rare, but it some times happens that an engine can have fine cylinder compression (upstroke), but have terrible crankcase compression. Yes, the crankcase has compression. The crankcase compression pushed the fuel charge up the bypass and into the cylinder. When the piston/rod reverse direction, the upward movement of the piston causes a negative pressure area to form in the crankcase, this is what pulls the fuel from the fuel tank. Duke Fox wrote an explanation citing circumstances where the cylinder compression could be fine, but if the fit/seal of the lower piston area was poor, the pumping action as the piston descended in the cylinder and sucking action of the piston ascending toward the top of its stroke could cause an engine not to run at all. No fuel draw, no pumping a fuel/air charge through the bypass into the cylinder, etc.
I forget if the OS .45F-SR has a Dykes ring or not. These can be difficult to diagnose if one is not aware of how they behave when the tension/fit has been lost.
Good luck solving the problem.
Ed Cregger
07-02-2007, 11:02 PM
#3
Thread Starter
RE: Old engine won't draw fuel/start/idle/RUN!
ORIGINAL: Ed Cregger
Have the engine mounted on the plane or a test bench. Remove the carb completely.
Drop a few drops of fuel into the carb opening. Flip several times to distribute the fuel. Apply glow heat and flip the prop. If it doesn't start in a few flips, you have a massive air leak somewhere. I just went out to the garage and tried this - with a few drops, it did nothing but fire a couple times then nothing. With a whole lot more fuel dumped in it started after a couple flips and ran for about three seconds.
Is there any chance that you were running crankcase pressure before you put the engine in storage and forgot about a now open to the atmosphere pressure nipple, or hole for same, in the crankcase? Nope!
If the engine did start with the few drops of prime, the problem is still in the carburetor, assuming that the fuel tank plumbing is okay. Some times it is easy to miss something obvious, or to keep making the same mistake. Don't know what I could be doing wrong with the tank plumbing, the main line goes to the clunk and the pressure line goes to the fitting at the very top of the tank. It just won't draw fuel. Normally I'd think this would mean my idle mixture is too lean but I've gone full rich on the idle screw and it doesn't change anything.
It is rare, but it some times happens that an engine can have fine cylinder compression (upstroke), but have terrible crankcase compression. Yes, the crankcase has compression. The crankcase compression pushed the fuel charge up the bypass and into the cylinder. When the piston/rod reverse direction, the upward movement of the piston causes a negative pressure area to form in the crankcase, this is what pulls the fuel from the fuel tank. Duke Fox wrote an explanation citing circumstances where the cylinder compression could be fine, but if the fit/seal of the lower piston area was poor, the pumping action as the piston descended in the cylinder and sucking action of the piston ascending toward the top of its stroke could cause an engine not to run at all. No fuel draw, no pumping a fuel/air charge through the bypass into the cylinder, etc.
I forget if the OS .45F-SR has a Dykes ring or not. These can be difficult to diagnose if one is not aware of how they behave when the tension/fit has been lost. This is an ABC engine, don't know if that helps or hinders the diagnosis?
Good luck solving the problem.
Ed Cregger
Have the engine mounted on the plane or a test bench. Remove the carb completely.
Drop a few drops of fuel into the carb opening. Flip several times to distribute the fuel. Apply glow heat and flip the prop. If it doesn't start in a few flips, you have a massive air leak somewhere. I just went out to the garage and tried this - with a few drops, it did nothing but fire a couple times then nothing. With a whole lot more fuel dumped in it started after a couple flips and ran for about three seconds.
Is there any chance that you were running crankcase pressure before you put the engine in storage and forgot about a now open to the atmosphere pressure nipple, or hole for same, in the crankcase? Nope!
If the engine did start with the few drops of prime, the problem is still in the carburetor, assuming that the fuel tank plumbing is okay. Some times it is easy to miss something obvious, or to keep making the same mistake. Don't know what I could be doing wrong with the tank plumbing, the main line goes to the clunk and the pressure line goes to the fitting at the very top of the tank. It just won't draw fuel. Normally I'd think this would mean my idle mixture is too lean but I've gone full rich on the idle screw and it doesn't change anything.
It is rare, but it some times happens that an engine can have fine cylinder compression (upstroke), but have terrible crankcase compression. Yes, the crankcase has compression. The crankcase compression pushed the fuel charge up the bypass and into the cylinder. When the piston/rod reverse direction, the upward movement of the piston causes a negative pressure area to form in the crankcase, this is what pulls the fuel from the fuel tank. Duke Fox wrote an explanation citing circumstances where the cylinder compression could be fine, but if the fit/seal of the lower piston area was poor, the pumping action as the piston descended in the cylinder and sucking action of the piston ascending toward the top of its stroke could cause an engine not to run at all. No fuel draw, no pumping a fuel/air charge through the bypass into the cylinder, etc.
I forget if the OS .45F-SR has a Dykes ring or not. These can be difficult to diagnose if one is not aware of how they behave when the tension/fit has been lost. This is an ABC engine, don't know if that helps or hinders the diagnosis?
Good luck solving the problem.
Ed Cregger
07-07-2007, 12:46 PM
#4
Thread Starter
RE: Old engine won't draw fuel/start/idle/RUN!
Thanks for the ideas, Ed. I did as you suggested, removed the carb, put a few drops of fuel in and tried to start it. It would pop but not start. So I dumped in a whole lotta fuel, and it started and ran for about 3 seconds. You mentioned a massive air leak but I can't find anything. There was never a crank pressure tap that has been left open and all gaskets are good and screws are tight.
I disassembled the carb again, checked all parts for blockage, re-checked the new o-rings to see if they'd been damaged or had come out of position when I'd put it back together the first time, and all looked good.
This is an ABC engine so there is no ring, but I read another posting about an engine that had air leaking past the bearings and that was causing it not to start. I wonder if that could have happened in this case? I'm wondering if this is not more of a hard parts problem (piston, liner, bearings) than it is a gasket or carb issue... Regardless, I have what appears to be a perfectly good engine that will not run.
Odd...
Kurt
I disassembled the carb again, checked all parts for blockage, re-checked the new o-rings to see if they'd been damaged or had come out of position when I'd put it back together the first time, and all looked good.
This is an ABC engine so there is no ring, but I read another posting about an engine that had air leaking past the bearings and that was causing it not to start. I wonder if that could have happened in this case? I'm wondering if this is not more of a hard parts problem (piston, liner, bearings) than it is a gasket or carb issue... Regardless, I have what appears to be a perfectly good engine that will not run.
Odd...
Kurt
ORIGINAL: Ed Cregger
Have the engine mounted on the plane or a test bench. Remove the carb completely.
Drop a few drops of fuel into the carb opening. Flip several times to distribute the fuel. Apply glow heat and flip the prop. If it doesn't start in a few flips, you have a massive air leak somewhere.
Is there any chance that you were running crankcase pressure before you put the engine in storage and forgot about a now open to the atmosphere pressure nipple, or hole for same, in the crankcase?
If the engine did start with the few drops of prime, the problem is still in the carburetor, assuming that the fuel tank plumbing is okay. Some times it is easy to miss something obvious, or to keep making the same mistake.
It is rare, but it some times happens that an engine can have fine cylinder compression (upstroke), but have terrible crankcase compression. Yes, the crankcase has compression. The crankcase compression pushed the fuel charge up the bypass and into the cylinder. When the piston/rod reverse direction, the upward movement of the piston causes a negative pressure area to form in the crankcase, this is what pulls the fuel from the fuel tank. Duke Fox wrote an explanation citing circumstances where the cylinder compression could be fine, but if the fit/seal of the lower piston area was poor, the pumping action as the piston descended in the cylinder and sucking action of the piston ascending toward the top of its stroke could cause an engine not to run at all. No fuel draw, no pumping a fuel/air charge through the bypass into the cylinder, etc.
I forget if the OS .45F-SR has a Dykes ring or not. These can be difficult to diagnose if one is not aware of how they behave when the tension/fit has been lost.
Good luck solving the problem.
Ed Cregger
Have the engine mounted on the plane or a test bench. Remove the carb completely.
Drop a few drops of fuel into the carb opening. Flip several times to distribute the fuel. Apply glow heat and flip the prop. If it doesn't start in a few flips, you have a massive air leak somewhere.
Is there any chance that you were running crankcase pressure before you put the engine in storage and forgot about a now open to the atmosphere pressure nipple, or hole for same, in the crankcase?
If the engine did start with the few drops of prime, the problem is still in the carburetor, assuming that the fuel tank plumbing is okay. Some times it is easy to miss something obvious, or to keep making the same mistake.
It is rare, but it some times happens that an engine can have fine cylinder compression (upstroke), but have terrible crankcase compression. Yes, the crankcase has compression. The crankcase compression pushed the fuel charge up the bypass and into the cylinder. When the piston/rod reverse direction, the upward movement of the piston causes a negative pressure area to form in the crankcase, this is what pulls the fuel from the fuel tank. Duke Fox wrote an explanation citing circumstances where the cylinder compression could be fine, but if the fit/seal of the lower piston area was poor, the pumping action as the piston descended in the cylinder and sucking action of the piston ascending toward the top of its stroke could cause an engine not to run at all. No fuel draw, no pumping a fuel/air charge through the bypass into the cylinder, etc.
I forget if the OS .45F-SR has a Dykes ring or not. These can be difficult to diagnose if one is not aware of how they behave when the tension/fit has been lost.
Good luck solving the problem.
Ed Cregger
07-07-2007, 11:03 PM
#6
Thread Starter
RE: Old engine won't draw fuel/start/idle/RUN!
It rotates nice and smooth. Last time I used it (1990) it ran perfectly.
Kurt
Kurt
ORIGINAL: rainedave
This sort of sounds to me like something is out of round, warped or bent. How does it rotate with the plug out and the back cover removed?
David
This sort of sounds to me like something is out of round, warped or bent. How does it rotate with the plug out and the back cover removed?
David
07-08-2007, 03:30 AM
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RE: Old engine won't draw fuel/start/idle/RUN!
Does this engine have good compression?
Other than that the only thing I can think of is that the engine does not get any fuel, for some reason. I would also put a brand new glow plug in there Enya3.
Other than that the only thing I can think of is that the engine does not get any fuel, for some reason. I would also put a brand new glow plug in there Enya3.
07-08-2007, 04:46 AM
#8
RE: Old engine won't draw fuel/start/idle/RUN!
ORIGINAL: KurtS
... but I read another posting about an engine that had air leaking past the bearings and that was causing it not to start. I wonder if that could have happened in this case? ....
Kurt
... but I read another posting about an engine that had air leaking past the bearings and that was causing it not to start. I wonder if that could have happened in this case? ....
Kurt
Remove cylinderhead, rotate the crankshaft in rotation direction. You will feel a little force of compression in the crankcase while the crankshaft are rotated with fingers. You will hear "Poofff" from the sleeve when the transferport are opened. It means the sealing around the crankcase are good.
If not sound or too weak "Poofff" from crankcase pressure:
1. Check there are not damaged backcover gasked
2. There are not too much play between crankshaft and crankcase or too much scratches at crankshaft or crankcase bearing to generate leakage. Remove piston/sleeve and mount the backcover at place with gasked. Close the intake port (crankshaft rotatet 180 degree, then you will see the intake hole are closed) and fill the fuel in the crankcase. Can you see much leakage at short time, the play are too big, time to replace the engine or crankcase and crankshaft.
Little leakage at some hour are ok so long you can still hear "poofff" there. The engine are in good contidion.
07-08-2007, 12:33 PM
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RE: Old engine won't draw fuel/start/idle/RUN!
Am I the only one who thinks this might be as simple as old fuel having turned to glue in the carb while it sat, preventing fuel from flowing? Especially if Castor oil was involved? I would take a short piece of fuel tubing, put one end on the carb, and with the needles open, blow through it, and make sure the carb is not plugged . . . .
- Tim
- Tim
07-08-2007, 01:19 PM
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RE: Old engine won't draw fuel/start/idle/RUN!
Kurt,
If it won't prime when you choke it there is an air leak. Just being clear: when priming, if you don't remove your finger from the throttle opening at TDC you will be forcing crankcase pressure (from the downward motion of the piston) back through the carb and into the fuel line. Yep, fuel will flow backwards into the tank.
I have seen this happen to some of my engines. Chances are the leak is around the HS needle or you have a hole in your fuel line. After the first bit of trouble I never trusted the O-rings on the HS needle. I always, on every engine 2 and 4 stroke, put a piece of fuel tubing over the main needle where it enters the barrel. Every fuel barb gets one too.
I assume the carb is attached to the case the same way most of them are. Although you didn't mention it, I'm guessing the carb seat got a new o-ring too. Make sure you press somewhat firmly on the carb before tightening the retaining screw/nut. An airleak there will cause the same probs you're having.
It kinda sounds like the LS needle is screwed all the way in. Try opening it up 3-4 turns. If the LS needle is in too far you'll prematurely limit the fuel flow when it comes into play.
Good Luck,
Jeff
If it won't prime when you choke it there is an air leak. Just being clear: when priming, if you don't remove your finger from the throttle opening at TDC you will be forcing crankcase pressure (from the downward motion of the piston) back through the carb and into the fuel line. Yep, fuel will flow backwards into the tank.
I have seen this happen to some of my engines. Chances are the leak is around the HS needle or you have a hole in your fuel line. After the first bit of trouble I never trusted the O-rings on the HS needle. I always, on every engine 2 and 4 stroke, put a piece of fuel tubing over the main needle where it enters the barrel. Every fuel barb gets one too.
I assume the carb is attached to the case the same way most of them are. Although you didn't mention it, I'm guessing the carb seat got a new o-ring too. Make sure you press somewhat firmly on the carb before tightening the retaining screw/nut. An airleak there will cause the same probs you're having.
It kinda sounds like the LS needle is screwed all the way in. Try opening it up 3-4 turns. If the LS needle is in too far you'll prematurely limit the fuel flow when it comes into play.
Good Luck,
Jeff
07-09-2007, 12:51 AM
#11
Thread Starter
RE: Old engine won't draw fuel/start/idle/RUN!
Thanks for the replies, a couple of you have given me some good ideas of things things to look at.
One question I do have is, what does the brass idle screw really do? I'm talking the one that you see if you look it the throttle arm side of the carburetor. I know it's the idle adjustment and I'm assuming it is an air adjustment. What I'm not sure of is how it does this. I've of course taken the brass assembly out of the carb in order to replace the o-ring but other than it moving back and forth when you turn the screw slot end, I see no holes that coul be plugged, no orafices, nothing.
When I took the engine out of the box a couple months ago it was so varnished up after I obviously forgot to clean it before putting it into storage for 17 years that it was locked up solid. I had to use a lot of care, time, and chemicals to free it up so that it would turn over and also on the carb so that the barrel would rotate. All looks good now though, the bearings feel fine and the carb looks clean to me, but maybe there is something that is still plugged. As for an air leak, it would have to be something pretty large to cause this kind of extreme running issues I would think.
What I do know is that until the day it was put into storage, it ran perfectly so I am doubting that any physical problem with any hard parts like the crankcase or bearings exists. It's possible I know, but I'm still thinking carburetor.
Kurt
One question I do have is, what does the brass idle screw really do? I'm talking the one that you see if you look it the throttle arm side of the carburetor. I know it's the idle adjustment and I'm assuming it is an air adjustment. What I'm not sure of is how it does this. I've of course taken the brass assembly out of the carb in order to replace the o-ring but other than it moving back and forth when you turn the screw slot end, I see no holes that coul be plugged, no orafices, nothing.
When I took the engine out of the box a couple months ago it was so varnished up after I obviously forgot to clean it before putting it into storage for 17 years that it was locked up solid. I had to use a lot of care, time, and chemicals to free it up so that it would turn over and also on the carb so that the barrel would rotate. All looks good now though, the bearings feel fine and the carb looks clean to me, but maybe there is something that is still plugged. As for an air leak, it would have to be something pretty large to cause this kind of extreme running issues I would think.
What I do know is that until the day it was put into storage, it ran perfectly so I am doubting that any physical problem with any hard parts like the crankcase or bearings exists. It's possible I know, but I'm still thinking carburetor.
Kurt
07-09-2007, 03:08 AM
#12
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RE: Old engine won't draw fuel/start/idle/RUN!
ORIGINAL: KurtS
One question I do have is, what does the brass idle screw really do? I'm talking the one that you see if you look it the throttle arm side of the carburetor. I know it's the idle adjustment and I'm assuming it is an air adjustment. What I'm not sure of is how it does this. I've of course taken the brass assembly out of the carburettor in order to replace the O-ring but other than it moving back and forth when you turn the screw slot end, I see no holes that could be plugged, no orifices, nothing.
One question I do have is, what does the brass idle screw really do? I'm talking the one that you see if you look it the throttle arm side of the carburetor. I know it's the idle adjustment and I'm assuming it is an air adjustment. What I'm not sure of is how it does this. I've of course taken the brass assembly out of the carburettor in order to replace the O-ring but other than it moving back and forth when you turn the screw slot end, I see no holes that could be plugged, no orifices, nothing.
Your assumption is wrong.
That brass, conical, low-speed needle is the part-throttle fuel-metering device; not an air adjustment.
As you move the carburettor's throttle arm toward the idle position, the entire barrel shifts the the left (of the engine), along with that needle.
The needle enters the fuel nozzle and progressively make the fuel-orifice smaller. The further the throttle is closed - the deeper the low-speed needle goes into the nozzle and the smaller the fuel orifice becomes.
Opening the throttle has the exact opposite affect, of course.
That O-ring is there to prevent air from leaking in around the needle, but also to make this needle hold its setting better.
07-09-2007, 03:08 AM
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RE: Old engine won't draw fuel/start/idle/RUN!
I am not familiar with that carb to tell you how the idle adjust works, but you might want to take the needles out and just let it soak in some fuel for a day or so . . . that usually will soften up any crusties that may have formed in the carb. And as I mentioned before, try blowing through it as well - once the crap is soft, that will get it moved through. Even if the idle needle was set big time wrong, you should still be able to prime/draw fuel at wide open throttle . . .
- Tim
- Tim
07-09-2007, 04:34 AM
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RE: Old engine won't draw fuel/start/idle/RUN!
Some more thoughts...
You said you can get it started with an electric starter and the throttle 3/4 open or more? Once it's started, does it run at full throttle like it used to? If yes, then it's getting fuel through the needle.
Try this test. Put a clean piece of fuel line on the carb. Open the throttle all the way and start blowing through the fuel line. Then gradually close the carb. As it moves toward the idle position you should feel that it's a little harder to blow through, but you should be able to blow through it. If you get to a point where you can't blow through it any more then the low speed needle is screwed in too far. If there's no change at all, even a slight one, then the low speed needle might be too far out.
You mentioned that you changed the needle o-rings. What about the one between the carb and the crankcase? This can be a source of an air leak.
And finally, you mentioned something about using chemicals and cleaning off the varnish. You also said it was an ABC engine and something about it quitting, and not being able to start it again after it's warm. If you removed varnish from the piston, it's possible that the piston to liner fit is now too loose. With an ABC engine, when it's up to speed, the piston fit is looser. If you removed some built up varnish, the piston to liner fit is now looser than it was when you put it away. Compare the compression between when it's cold and when it's really warm.
You said you can get it started with an electric starter and the throttle 3/4 open or more? Once it's started, does it run at full throttle like it used to? If yes, then it's getting fuel through the needle.
Try this test. Put a clean piece of fuel line on the carb. Open the throttle all the way and start blowing through the fuel line. Then gradually close the carb. As it moves toward the idle position you should feel that it's a little harder to blow through, but you should be able to blow through it. If you get to a point where you can't blow through it any more then the low speed needle is screwed in too far. If there's no change at all, even a slight one, then the low speed needle might be too far out.
You mentioned that you changed the needle o-rings. What about the one between the carb and the crankcase? This can be a source of an air leak.
And finally, you mentioned something about using chemicals and cleaning off the varnish. You also said it was an ABC engine and something about it quitting, and not being able to start it again after it's warm. If you removed varnish from the piston, it's possible that the piston to liner fit is now too loose. With an ABC engine, when it's up to speed, the piston fit is looser. If you removed some built up varnish, the piston to liner fit is now looser than it was when you put it away. Compare the compression between when it's cold and when it's really warm.
07-11-2007, 09:43 AM
#15
Thread Starter
RE: Old engine won't draw fuel/start/idle/RUN!
Ah yes, I can see now that you are correct with your explaination, thanks! I took the entire engine apart again last night just to double check that I'd done it all correctly the last time and spent some time examining the carburetor. I can see the fuel orafice and how the idle adjustment screw moves over the top of it as the throttle opens and closes. Neat.
I did check too that the fuel orafice is not plugged with varnish and as was also suggested I blew through a piece fuel line and found that it does get harder to blow as the carb closes and the pressure required changes as you move the high speed needle. All seems to be working fine.
I have also checked and rechecked my tank, the fuel lines, and, well heck, everything! I'm still though missing something. Some little thing that when found will probably make me go "DUH" but man, I'm just stumped.
Kurt
Kurt,
Your assumption is wrong.
That brass, conical, low-speed needle is the part-throttle fuel-metering device; not an air adjustment.
As you move the carburettor's throttle arm toward the idle position, the entire barrel shifts the the left (of the engine), along with that needle.
The needle enters the fuel nozzle and progressively make the fuel-orifice smaller. The further the throttle is closed - the deeper the low-speed needle goes into the nozzle and the smaller the fuel orifice becomes.
Opening the throttle has the exact opposite affect, of course.
That O-ring is there to prevent air from leaking in around the needle, but also to make this needle hold its setting better.
I did check too that the fuel orafice is not plugged with varnish and as was also suggested I blew through a piece fuel line and found that it does get harder to blow as the carb closes and the pressure required changes as you move the high speed needle. All seems to be working fine.
I have also checked and rechecked my tank, the fuel lines, and, well heck, everything! I'm still though missing something. Some little thing that when found will probably make me go "DUH" but man, I'm just stumped.
Kurt
Kurt,
Your assumption is wrong.
That brass, conical, low-speed needle is the part-throttle fuel-metering device; not an air adjustment.
As you move the carburettor's throttle arm toward the idle position, the entire barrel shifts the the left (of the engine), along with that needle.
The needle enters the fuel nozzle and progressively make the fuel-orifice smaller. The further the throttle is closed - the deeper the low-speed needle goes into the nozzle and the smaller the fuel orifice becomes.
Opening the throttle has the exact opposite affect, of course.
That O-ring is there to prevent air from leaking in around the needle, but also to make this needle hold its setting better.
07-11-2007, 10:07 AM
#16
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RE: Old engine won't draw fuel/start/idle/RUN!
ORIGINAL: KurtS
I did check too that the fuel orafice is not plugged with varnish and as was also suggested I blew through a piece fuel line and found that it does get harder to blow as the carb closes and the pressure required changes as you move the high speed needle. All seems to be working fine.
I did check too that the fuel orafice is not plugged with varnish and as was also suggested I blew through a piece fuel line and found that it does get harder to blow as the carb closes and the pressure required changes as you move the high speed needle. All seems to be working fine.
07-11-2007, 10:15 AM
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RE: Old engine won't draw fuel/start/idle/RUN!
Do you still have good compression when the engine is warm, right after it quits? The symptoms you describe sound like worn piston/liner to me. Ross
07-11-2007, 11:39 AM
#18
RE: Old engine won't draw fuel/start/idle/RUN!
ORIGINAL: KurtS
I've disassembled the entire engine and cleaned all parts.
I've disassembled the entire engine and cleaned all parts.
David
