Jim.Thompson

Done that, with little or no noticeable difference. I can still get it to cut out on idle down. Also, it is hard to start when hot.
Any tips for hard starting diagnosis?

Jim.Thompson

End of day report.


It's been a good day. I can now start the engine when it is cold and tune it to run nicely. I've got rid of the cutting out on idle down and the slow, mid-range and high speed mixture seems pretty good. Also, there was a high speed miss-fire occasionally earlier on; it is not occuring now.
Also, my right arm and shoulder are now not getting sore from swinging the prop; I am getting some old seldom used muscles back into condition.
That's the good news!

The not so good news is that the choke does not appear to working as it should. I have to slip the aircleaner off and charge the carb with 1 or 2 cc of fuel using a syringe. Then it will go after 6 or 8 swings of the propellor.
It still will not start when it is hot. It will fire and run weakly for a second or so, then run down and stop. It will do this repeatedly. It might be ok with a bit of throttle, but on my own I don't want to throttle it up while swinging the prop.

This project is alive again!

Gizmo-RCU

My Feedback: (27)

If the Choke has a little hole in it solder it closed, that will help the draw quite a bit. I had a RCEXEL ignition fail repeatedly at 7 mins., period, replaced it and all is good.

Jim.Thompson

Thanks for the tip Gizmo.
Any suggestions about the hot starting difficulty?

spaceworm

[QUOTE=Jim.Thompson;12244538]Thanks for the tip Gizmo.
Any suggestions about the hot starting difficulty?QUOTE] Is the carb thermally isolated from the engine? A hot carb may cause the fuel inside to.vaporize and affect running, and, especially,
hot starting since the engine will get hotter right after stopping, before cooling off.

Jim.Thompson

[QUOTE=spaceworm;12244574]The engine has the original Stihl rubber cylinder to carburettor hose or manifold. That is in it's current configuration. It may not stay that way. It's well insulated.

Gizmo-RCU

My Feedback: (27)

Jim,
I thought about this overnight (as I am an old guy I find my thoughts now differ from those of my younger days!) , I have seen spark plugs behave as you describe, breaking down when hot, DLE stock plugs are noted for this.......use a good NGK......what the heck! (I'll sleep better now!)

Jim.Thompson

I now have the engine installed in the plane and I started it up this morning. It will start (with some difficulty) and run, but still not well. It will only run with the low speed needles open 1/2 a turn and the high speed needle fully closed. Even then, it runs rich at low to mid- range throttle.
It seems to me, that the lever now needs to be bent a bit more to reduce the amount of fuel being supplied to the carb.
The best advice I can find about the fuel metering lever setting is in this WB manual. Walbro advises that there is no manual for the WJ model!
As can be seen in the screenshot from the Walbro WB manual, the lever is set from 3/64 to 1/6 inch. The setting that I now have it is slightly more than this, and it is still not possible to lean out the mixture at any range other than idle speed sufficiently.

I am hoping that one of you Walbro experienced people will provide a comment on the above.
From the Walbro manual:

Edit:
By mechanic buddy Barry has just called in and we collaborated on the next change to the engine/carb/exhaust. One thing he mentioned is that the big exhaust (that is very noisy) might be offering too little restriction. Tomorrow I will fit the original chainsaw exhaust and give it a go without changing anything else. If it is still the same, I will adjust the fuel metering lever down further. The engine is obvious getting far too much fuel. But we agreed that one change at a time is a good strategy.

Jim.Thompson

Thanks Gizmo. I have an NGK plug in it. (I think) I will check to make sure tomorrow.

Have you read my post #183 yet with todays report?
Judging from the boast you made some days ago about being able to fix it if you were here, I would expect you to have suggestions for the reasons we are observing the phenomena I describe above. I am assuming from your post to that effect that you have some experience with Walbro carburettors.
What conclusions would you draw?

spaceworm

Maybe send the engine to Gizmo? He seems to be the resident expert. Seriously! Good luck. Over and out. Sincerely, Richard

av8tor1977

My Feedback: (6)

Sorry, but your muffler is in no way a problem. It is a frustratingly persisting myth that engines "need back pressure". It is just not true. Off hand, the only benefit I can think of to back pressure is on a glow engine, to help keep the glow plug hot at idle, and this comes at a sacrifice in power. Before anyone says "what about an expansion chamber or other tuned exhaust?", those operate on reflected sonic waves, NOT back pressure.

Keep after that regulator lever adjustment, it is critical. You might also have a look at the high speed check valve in the carb

You might also beg, borrow, steal, or make a pop off pressure checker and do a pop off pressure check.

Edit: Last thought..... You are putting the regulator chamber gasket on first, and then the diaphragm on top, then the cover right? Lots of people put them on backwards, then have "too rich" problems.

AV8TOR

av8tor1977

My Feedback: (6)

I haven't been following this thread, but I just went back and read some posts. This engine is problematic with two different carbs. That would make me change out all the ignition components as the next test.....

I had one engine that just was a bear to start. Took forever and a lot of finicking to get it to start. Bill from CH told me to try 6 volts on the ignition instead of 4.8, and then it ran perfectly. It was a weak ignition. An edgy hall sensor will drive you nuts as well...

AV8TOR

Jim.Thompson

Thanks for that clear and confident assertion AV.

Good. That confirms my suspicions.
I cannot find one of them in my model. The only reference that I have is a .pdf doc from Walbro for the WB model. They advise that it is (quote)"almost the same" (end quote). Manual for the WB model attached above.
I don't know how to do that. I will have to make one, do you have any suggestions of how I could make one? I am guessing, a low range, accurate pressure gauge (maybe a good tire gauge) and a relief valve etc.?
Affirmative!
Many thanks for joining the discussion with helpful information.

Jim.Thompson

[QUOTE=av8tor1977;12245481].................................................. ......

There is reason to suspect the hall sensor, for sure. However, When I do get enough fuel into the engine, it will fires almost immediately. I have been getting it started by priming a shot of 1 or 2 cc of fuel into the carb throat.
However, it does not account for the fact the fact that the engine will run (at a too rich state) at high revs with the high speed needle fully closed. In my understanding, this points to fuel regulation problems and not the ignition.
Do you agree.
I am now suspecting that the pop off pressure is not right.
I would go back to the original carb, but I have removed the welch plug and can not get one locally short of buying a full service kit.
Do you have a local source? It is a 3/8 inch aluminium welch plug.

Gizmo-RCU

My Feedback: (27)

Being half a world away it's not easy, If possible use the orig. carb. your local small engine repair shops goes thru kits by the gross and these kits contain extra parts that are not used or necessary many times as the kits are for a number of different Walbro carbs so there are always leftovers. Usually these are kept around for occasional use? Worth a try. I try and not to make changes if things are working.............you can find cheap Walbro clones on ebay, I just put one on a Zenoah G-26 that some one had
messed with the carb and screwed up, bent throttle arms and no telling what else. $16,00 including postage for one of these carbs, and the engine runs flawlessly! I bought the engine for $40.00 at a swap meet! Not sure what I will put it on but never could pass a bargain on an engine.

Jim.Thompson

The carb that is on it is an aftermarket clone Gizmo. My buddy Laurie (Warialda on the other thread) bought for me some time ago.

Jim.Thompson

I have actually made some progress this morning. Av8tor is on the money here it seems. I also have been suspecting that the pop off pressure might be the trouble, but did not know enough about it to tackle it.
I have two WJ57 carbs. So I pulled the fuel metering lever springs out of both of them and compared them. The new aftermarket one is noticeably weaker. This would cause a low pop off pressure and would explain why no matter where I bent the spring to, the engine could not be leaned out.
I now have the engine starting easily using the choke!
It will run ok and is good at mid-range and high rpm.
It will not idle and cuts out.
One of the suggestion in the Walbro chart for this, is sticking throttle butterfly. I will investigate after lunch.

Jim.Thompson

My mechanic buddy called in and loaned me a cooling system pressure checker which we figure will serve to check the pop off pressure of the fuel metering jet. He listened to it running while I was having difficulty getting it to take throttle without missing. He immediately suggested an ignition breakdown problem, which I agree. I was mistaking that for a fuel mixture problem all along. After we removed the spark plug, which looked a good colour, it measured .6 mm gap. Barry suggests to reduce that to around .4 mm and try that.
Order of events for the next session:
1. Do the pop off test.
2. If that test result is far out of parameters, adjust etc.
3. Change out ignition components as suggested by Av8tor above. I only have one hall sensor and I might have to order another one. Deliveries takes weeks etc.
4. Remove the engine from the plane and mount on the bench again. My old body is suffering from bending and squatting down to work on it in the plane.
5. If all the above unsuccessful, shelve the project until after our coming Manilla Slope flying festival in four weeks. I have a fleet of gliders to prepare etc.

Jim.Thompson

I am delighted to report that the engine is starting and running nicely now. Three problems were found. First of all, the fuel metering pop off pressure was far too low! It was around 10 psi. The recommendation for this model Walbro is 15 - 25 psi. I adjusted it up to around 20.
Second problem was the spark gap was too big. Late last night I measured it a bit more carefully and it was close to .68mm. My pal Barry was here who has just built a race car and described the same problem with his modified Zephyr engine. Spark failure/flame out with throttle. He adusted his plugs down to around .020 (approx .5 mm). I did the same to mine, and now it take fully throttle without any miss-firing. Easy starting too.
The third problem was a leaking connection of the rubber manifold to carburettor connection. It slipped out slightly after I remounted it and ran it for a while also. I will machine a thin walled, flanged spigot to go inside it on Monday when I go into the Mens Shed. That will located it internally and externally positively.
We had the engine running nicely at all throttle levels. It was idling well, until the manifold rubber started to slip again and leak.
This problem will be an easy fix.
Many thanks to Av8tor for the pop off pressure test tip. And to Al for the intake leak. To Barry for the spark plug gap suggestion. And of course to Zagnut for his endless patient technical descriptions and corrections. To Bogbeagle and to all the others who have hung in there on this thread throughout this tiresome and sometimes boring saga!
And a special thanks to Gizmo for boasting that he could fix it if he was here!

Jim.Thompson

I used a automotive cooling system pressure tester to test the pop off pressure of the carburettor fuel metering needle and spring assembly. I was able to push the pump handle in slowly, while watching and listening to the exposed needle and seat area. When it started to hiss I noted the pressure. It worked well. I will do a short video when I get to check the original carburettor in the same way.

edit:
I probably goes without saying that the very low pop off pressure is the reason that the engine would only run with the high speed needle fully closed. And it would not lean out properly. As a result, all my adjusting of the metering lever up and down was in vain; it did nothing!

Jim.Thompson

I checked the fuel metering pop off pressure using both of the springs that I have; one out of the old carburettor and the one out of the new one. Both provided a very low pop pressure!
A bit of speculation suggests to me that these springs could loose some of their temper over time and used etc. So it might be a good point to remember should similar symptoms be encountered with other diaphragm carburettors in the future.

Gizmo-RCU

My Feedback: (27)

Jim

I once installed a Carb and had the small vent hole on the manifold covered by the gasket (back wards). The engine ran up to about half throttle and then ran out of gas. If you engine has that small passage from the block thru the manifold to the carb it must be clear to allow the air flow it requires. Just another late night thought.

Jim.Thompson

I am concluding that I have the problems sorted Gizmo. I just need to run the engine in the plane again sometime tomorrow to proved that my repair of the carb mounting has in fact fixed the manifold leak. That's a good general tip and a good one to put into the inventory for future 2 stroke adventures. Not that I am planning on having too many!
Your tips have been useful, but don't seem to relate to the symptoms that I report.

Gizmo-RCU

My Feedback: (27)

REALLY difficult to sort out from afar especially when you are not hands-on. What I have passed on are things I have encountered in the past. And yes the plugged port allowed an engine of mine to run well up to about half throttle..........

Jim.Thompson

I've just had another tuning session with the engine mounted in the plane. I can get it to idle quite well. Then when I throttle up, it will not return to the idle. Revs reduce to something above idle. If I adjust the idle screw, it will idle down and then stop.

edit;
Two hours later:
I switched back to the original carburettor again after checking the pop off pressure.
It is running the best it ever has now with both needles fully closed! It is idling down nicely and taking throttle ok. Just running a bit rich at all throttle openings and revs.
I will have to bend the metering lever down more and give that another try.

Edit#2
Bending the lever did no good at all - again. I've been in this position before, and I'm going around in circles.
There is only one thing that can now be causing the above and that is the metering needle spring is too weak. (I did do the pop test and it seemed to check out within the specifications). However, I will stretch it 3 mm, replace it and try again next opportunity.

Another problem with the plane/engine combination is becoming evident. One of the batteries is running down in a rather short time. The elevators are vibrating at an alarming rate and at a large magnitude; I suspect that this is working the servos hard and draining the batteries. And the battery drain is only one consideration, needless to say; I hope the servos will take the punishment.