Flathead

My Feedback: (11)

Well, stuff happens. Beautiful day, 60+ degrees, put the stock (no mods yet except for Electronic Ig) RYOBI on the test stand, starts right off, idling a little fast, so adjust needle, got the tach out, ouch, dang, got to ba little more careful, wonder why it started running rough, whats that funny red stuff on my finger. It's tough to type with a splint on my pinky that covers the 10 stiches it took to stop the bleeding. Totally destroyed the end of the 18 X 6-10 TOP FlIGHT. Guess I wll be out of action for awhile. MAMMA says no more until you are well enough to get the garden ready. Anyway, this is a stock engine with 2 narrow rings, The off-white reed valve plate off of a STIHL FS40, stock carb. E-I at 30 degrees. Only reading I got was 6540. More info when the swelling goes down

diceco

I fooled around on my CAD program tonight and made a full circle degree wheel of about the right size for our little engines. The automotive ones available are a bit too big. I hope it uploads in full scale. It's 6 inches in diameter. Let me know if it bombs.

diceco

To get it to print full size:

click link for full size below thumbnail in post. It will open in a new tab in the browser
save image
print image directly from file folder where you saved it.

That worked for me anyway.

I was not happy with the jagged lines of the previous wheel so I've replaced it with a high resolution version.

andrew66

for the timing wheel that i made, i just did a google image search. It took a few mins, but i found a suitable one kinda like yours. I just printed it off and used spray adhesive to glue it to an old beer box.
Its starting to get warm here again, and im going to build an actuall test stand then i will try and get some rpm numbers.
Hey combat, if u figure that u have too many (if thats possible) of those poulan engines, how much do you want for one? I have been looking around here for one, with no luck.

diceco

YIKES, WHAT A BUMMER!!! 10 STITCHES.....


I have a thought on the calibration/prop issue. I'm willing to donate my 18x8 Classic Master Airscrew prop for a community "standard" test prop. I think I can get it all packaged up and ready to ship with no more than a pound shipping weight. The shipping charge would then be $5 USPS Priority Mail for domestic addresses. I'm not sure what it would be to Mexico or Canada!

So... Each one of us would be responsible for only one shipping cost to ship it to the next interested party. We run our engine on the "standard" prop and take data for all to compare directly. Then we switch out the prop to our own prop and make a back to back comparision of the "standard" prop to our own prop to get an adjustment factor between the two. Now, after the "standard" prop has been shipped off somewhere else, if we make any changes to our motors it's performance can be referenced to the standard prop by applying the adjustment factor.

av8tor, you mentioned the problem with your spinner not fitting the prop hub. I assume with electronic ignition you are starting by hand flip. You could easily forgo the spinner for a test run up of any prop, right?

Too complicated? Any thoughts?

diceco

combatpilot

Ten stiches man that had to hurt. Did you hold your finger in pain and amazement and sheepishly look around to see if anyone saw you do it lol? Isnt it funny thats the first though in your head is man i hope nobody saw that.

Anyhow thats not a bad idea on the test prop. I am wondering how accurate the adjustment factor is gona be though.

I think your gona want something more rigid for your degree wheel. I used 1/4" plywood. I think 6 inches is about right. That gives good resolution and allows you to mount your needle off of the ignition coil boss



As far as a poulan engine I will give it to ya if you pay shipping. Let me take a pic and send it to ya so I can be sure we are talking the engine you want. Im sure I will get more in the future as they seem to be the most common engine. In a way its hard to belive you cant find one when i found so many lol. Heck if ya want a couple of them thats fine to.

I finally scored a cheap set of inline roller skates to rob the wheels off of for my test stand. I will give construction details of this as i get back to work on it. I may be monday though as today I had to work on the airfield mower to get it ready for the upcoming season and tommorow I have to go help with feild maintenance.

Oh yea also on the engine pile i found all the ryobis but one had what I consider to be the good high compression heads and none have the slits I keep hearing about. I still yet have to find one witht the slit. Only one engine has the two runner per side transfer port and low compression head. There is one cylinder in particular while even having the single ring piston it has great compression and is not scared in any way. I cant wait to try this one as my original cylinder had some minor scoring to it.

diceco

Ran the 12.7mm carb. The motor gained 150 rpm and 1/2 lb thrust going from a 9 mm carb. I guess I thought it might be a little more. I now have runs for 8 and 9 and 12.7 mm carbs.

8mm 7080 rpm 12.8 lbs
9mm 7220 rpm 13.5 lbs
12.7mm 7370rpm 14.0 lbs

The 12.7 mm carb was a bit more touchy to get running well. The mid range tends to run lean and the motor stalls out on a throttle dump. I may have to put up with a slightly rich low speed in order to get reliable transitions. That means it will load up if idled too long. For the stock porting on my motor, a 12.7 mm carb is probably more than needed. I'm real curious to see what combatpilot finds is the effect of raising the exhaust timing. It might be, with my current stock port timing setup, the flow through the motor could be improved and that big carb would show more promise.

When I get a chance I'll do some curve fitting to all the data I've got in attempt to smooth out the rather large scatter in the data.

diceco

Flathead

My Feedback: (11)

For all you out there that sometimes want to know the displacent of an engine, and can't remember the correct formula like me, go to
"WALLACE RACING" and put in the info and hit the button. NICE

combatpilot

Dieco I didnt have that problem at all with my carb. Is your carb brand new or is it a rebuild? mine would pull hard on the top end and then drop off after a little running at top speed. I finally figured out my needle valve lever wasent set properly and after readjusting it pulled hard on the top end and didnt drop at all. it also ran better on idle and transitioned very well. I didnt get a chance to see if the port timming helped as I was not able to test on the day I did the mod. all my test equipment seemed to fail.

Tommorow i should get back to work on my static thrust test stand.

Displacement is an easy formula. dia x dia x .7854 x stroke. to convert inches to cc there is 2.56 cm in an inch so 2.56 squared = 16.777216 so if you take your cubic inches and multiply it by 16.777216 you should get cc.

ie 5 cu inches multiplied by 16.777216 = 83.88608

Racinrc14

My Feedback: (7)

Hey Andrew, in your video, when the camera is full on frontal, does the crankshaft really move around like that, or is it an illusion? Are you using rubber mounts?

andrew66

That was caused by the make shift mount starting to fail. when i removed the engine from it that night, the plywood that joined the two halves was very weak. Thats another reason why im building an actuall test stand. Im going to make a universal mounting system so i will only have 4 bolt holes.
Hey combat, did u get my PM by chance?

diceco

Thanks for the tip.

It is a used carb but looks like it's had a rebuild kit put in it. I did have the covers off and it appeared the tang was even with the adjacent flat of the carb body which is what is recommended as a starting point if the official gage is not available. I'll look at it more carefully and even try to measure the drop from the outer part of the carb which is the way the official Walbro gage works. I've read that this setting may depend on which configuration of diaphragm is used but I've not found an actual measurement defined for the two different types.

diceco

combatpilot

Yea it may take a bit of trial and error to. I know i had to play with mine just a bit. they say the tang sould be even with or slightly below. if when running it goes lean and no amount of screw adustment helps you know then it needs to go up lol. This is a pretty crittical adjustment in this carb. there was a walbro tuning site listed erlier that ajnor posted.

http://tech.flygsw.org/walbro_tuneup.htm

They have some really great info on here.

Here is a small part of this article on the needle lever

This is the single most critical setting on a Walbro carb! Walbro offers a "setting gauge" to properly set the height of the lever for your particular carb. If you don't have one, the setting will be a trial & error adjustment and a real pain in the butt since you have to open up the carb to make the adjustment. For general purposes, the lever will be almost perfectly parallel to the carb base. This will get you close. If the lever is too high, your engine will tend to run a little erratic at idle. If the lever is too low, your idle will be OK but it will tend to run lean on midrange and highend. It may also run the float cavity "dry" at full throttle and die, regardless of your highspeed /lowspeed needle settings.

Racinrc14

My Feedback: (7)

Combat,

I mounted my ignition today with a little shadetree engineering. I'll try to get pics tomorrow night. Looks like I'm getting good spark, but anyone on here have any suggestions as to how far away the magnet can be from the pulse switch and still work okay? I've got a pretty good gap, I'd say about .035" without measuring it and seems to work fine. I noticed, however, that while rotating the crank back and forth with the magnet under the switch that it would 'miss' a spark here and there. Is this normal? I wasn't going full revolutions, just rocking it back and forth under the switch. I'm waiting for the JB Weld to cure now, but I am going to try and run this thing for the first time tomorrow. Here is my setup:

Older jug, two single large ports (and no 'slits'), large crankcase, factory 7.2mm carb, CDI set at 28deg, stock unmodified muffler, new piston (2 ring, no gap), cylinder base gasket installed (piston hits jug without it), non-recessed reed mount with stop set at 1/8" and no bends, except to get the reed to sit tight on the backplate with no gaps.

I have an 11mm carb to try after break-in and some initial test numbers. I am also looking for a decent muffler. Mine looks like it is crimped together, so I am reluctant to break it apart to gut it as it probably wont seal after getting it back together. Suggestions?

Racinrc14

My Feedback: (7)

Say guys, I forgot which inlet was the primer inlet?!?! I'm omitting the primer on mine. There's two inlets on my carb, on e on the needle side, and one w/bend on the other. It's a Zama, but similar to Walbros.

combatpilot

I am not sure without seeing it.


I as playing with mine and i noticed it didnt like much gap at all. I had my magnet stuck to a exacto knife blade and was just passing it over the pick up. It is polarity sensitive on the magnet as someone pointed out before. In my opinion I would set it up much like a mag ignition. .035 seems like a lot of gap. i use a bussiness card to set up my mags.

Ok this is just a prediction and a guess but i think your gona see an rpm of 6300-6400 rpm. I may bee off on this as im not sure what the cdi will do but it should be interesting.

I got a chance to work on my test stand today. here is what i got so far. I welded two angle iron pieces for the runners to a 3 inch piece of channel. I hope the pictures make sense and you can see where this is going. It will all become more clear when i get closer to completion which should be wensday and i should get to run another test to.









I am going to screw the rail trolleys to a piece of wood deck. I like the wood deck as it is easy to screw things to for different experiments.

av8tor1977

My Feedback: (6)

Well, it is "Hell for stout" that's for sure. Nice work and nice pics.

AV8TOR

av8tor1977

My Feedback: (6)

On that Zama carb, trace out the passages. The one that goes directly to the fuel pump diaphragm is the fuel "IN" connection. The other one will go to the regulator diaphragm area and can be plugged.

AV8TOR

combatpilot

I know I subscribe to the monolithic engineering sect. If I bend it everyones gona want one of my engines huh? I cant wait to finish it.

Racinrc14

My Feedback: (7)

Well, it runs, poorly.

I have some carb adjusting to do, but the ignition is running flawlessly. It will idle forever, but the high end and midrange are spotty. Also, after a wot run for a few seconds, the engine dies when pulling back to idle. I was hoping the needles would be ok since I haven't moved them since it was a weedie, and it ran good then. I put a rebuild kit in the carb during the conversion, so that should be okay. Looks like I have a leak at the backplate also, which I'm sure isn't helping. More to come after lunch....

Racinrc14

My Feedback: (7)

Ran her some more, but I can't get it to run right. To get it to stop four cycling on the high end, I have to turn in the high end needle to about 1/4 out. Also, when throttling back from wot, it leans out and dies. There is another threaded screw, looks like an adjustment of some sort, on the opposite side of the carb from the needles I can't figure out what it does. Any suggestions? I'll try to get pics uploaded tonight when I get home.

andrew66

it could be a prob with the low end needle. the low affects the high on these carbs. One thing i do if i have alot of troubles, i start from scratch (both needles out 1 1/4 turn) usually is a bit rich, but close enough to run without damage (ex. being too lean). But if no matter what u do, it still is tempermental, suspect an air leak of some sort. check all gaskets and crank seals.
PS
Also check that lever thingy under the diaphram. I cant remember what its called exactly. Aviatior and the other guys can give u better advice than i can. http://www.geistware.com/rcmodeling/...ine_tune_1.htm (this is also a very good site)

Racinrc14

My Feedback: (7)

Andrew, the problem is I can't get past the first step from that tuning guidance. It wont' lean out, no matter what I do, unless I run the H.S. screw almost all the way in, then it dies when returning to idle. Is it normal for the two screws to be way different from each other as far as how far they are turned out?

I ran it some more and I don't think I have any leaks. I used all new gaskets, including the extra gasket that goes behind the carb spacer. I haven't tried the carb cleaner trick, but that's next. Won't an air leak manifest itself as a lean condition? Seems like I'm having the opposite problem.

andrew66

I looked up what the lever thingy is, and its the needle valve lever. if the lever is bent too far up, it will flow too much fuel regardless of high or low speed needle settings. I have read that its supposed to be flush with the carb body.

combatpilot

Ok i have put this on here a hundred times and I dont know why you guys just wont read it. looks like andrew66 read it

http://tech.flygsw.org/walbro_tuneup.htm

If you read this you will realize pretty quickly that your fuel needle valve lever is set way to high. the thing you have to understand is the diapram and lever act together to act like a float bowl. if the lever is set to high the needle valve will not close and the fuel pump will charge the diapram chamber till the diapram can no longer move. at this point the diapram chamber will now be pressurised by the fuel pump. this raises the pressure in the diapram chamber to a pressure higher than atmosheric and you are now injecting the fuel in by fuel pump pressure. this is evident by having to almost close the needel valve. Ok so just like a float bowl in a regular carburator the fuel in the diapram chamber is at atmosperic pressure. sure it has a physical barrier that seperates the fuel and the atmosphere but the diapram is movable barrier where the back side or non fuel side is at atmosheric pressure. this pressure acts on the fuel through the diapram to push the fuel into the lower pressure area of the venturi. FUEL IS NOT DRAWN IN BY A VACUMME. a vacume is outer space and is something in your wifes closet. Things in nature flow from high to low in the path of least resistance. to prove this look at the cover for the diapram. notice the little hole in it. this vents the diapram to the atmospere just like a vent in the float bowl of a regular carburetor. Plug this hole and see what happens. I bet its gona run real lean as now there is no atmosperic air pressure to push the fuel into the venturi and push the diapram to where it opens the fuel needle valve. On regular aircraft this vent has an adjustable orfice and this is how they make a carb in flight mixture adjustable. by variying the size of the orfice you vary the force apllied to pushing the fuel into the venturi.

Ok on the flip side. If the valve is set to low the pressure differential between the fuel and the atmospere pressure required to move the diapram to where it will open tha valve will be to great and the engine will run lean.

Its your needle valve lever i will garuntee it. It is set to high. It needs to be just parrallel with the carb body or just a little lower as described in the link provided.

I WILL bet my dollars to your dog terds on this and if im wrong I will kiss your but on the state capitol lawn and give you two weeks to draw a crowd.

tkg

My Feedback: (1)

Not meaning to slam anybody, but the scariest words I hear over the phone is "I've/We/The club expert" just rebuild the carb and it won't run right......
The Walbro is very simple to use and rebuild, BUT it just as simple to screw it totally up.
The lever, the pop off pressure and the way the gaskets are stacked gives someone many chances to get it wrong.
On the pump side its the thin gasket first then the thick one. ON the regulator side its the other way around. Miss with the lever height and get ready for a real head banging season. Also if you havet the regulator side gaskets wrong it acts like the lever height is off, but of course its not.