Jim.Thompson

A buddy of mine has given me some AvGas and has suggested I try it out in the Stihl.
Is there likely to be any detrimental affect on the engine using this high octane fuel? And is there any advantages?
I don't want to just try it out in ignorance.

Gizmo-RCU

My Feedback: (27)

I have used many gallons of non-ethanol 92 octane and do not think anymore is necessary, I see no advantage, our local Stihl dealers suggest that type of gas around here. Most of the commercial loggers in the area
go that way. Think I would stay away from the AV Gas even though I have never tried it nor do I know anyone who has. Your Beast will make more power than you need using conventional mixes. Lubrication is the most critical
component in my opinion.

Jim.Thompson

That is more or less what I thought Gizmo.
I will use the recommended Stihl oil mixed with unleaded petrol @ 50:1.

TFF

AV gas will run leaner than car gas so it requires different tuning . It also can be tough on rubber parts if they are the wrong compound.

Gizmo-RCU

My Feedback: (27)

My theory is stay with what is proven to work over the long haul. Your mix will work well, have burned a lot of it over the years. The old conventional mixes did require carbon removal from time to time. Not near as much
with the new Synthetic oils.

Jim.Thompson

Last time I was in our local Stihl agent shop, I noticed there was several varieties of Stihl oil. This is, for me at least, as case of too many choices which just leaves some doubt in the customers mind as to what one to use.
Any comments? Or suggestions?

Gizmo-RCU

My Feedback: (27)

Use the Synthetic, costs a little more but works well for me. A little cleaner, less carbon in my opinion.

Jim.Thompson

Ok. Will do.

Jim.Thompson

I have the engine installed in the plane and running with the original chainsaw inlet manifold.
I am unable to tune it at high speed. It will only run on part throttle opening with the high speed needle fully closed.
What does this indicate? The metering needle assembly needing adjustment?

Gizmo-RCU

My Feedback: (27)

Go back to about 1 1/2 turns on both needles, or a little richer and tune from there. Sounds to me like the High speed is very lean and you are only receiving fuel on the low side? Did you change anything while installing the engine in the plane?

Jim.Thompson

We are unable to start it with those needles settings. The high speed is running rich actually; when I open it out, the engine will cut out.
It is very erratic and inconsistent with both needle settings. Accordingly, the Walbro manual indicates this is most probably damaged needle seats.
We have a different intake manifold on it now. At the moment, it has the standard rubber intake from the original saw.
I will not attempt starting or running it again until I receive the replacement carburettor from my pal Laurie; it might arrive by the end of next week.
Both my buddy and I have sore arms and wrist from our last couple of sessions attempting to start it. On more than one occasion, it kicked back and knocked the chicken stick out of our hands.

Gizmo-RCU

My Feedback: (27)

You were smart to not push it! Any chance of an air leak? Check out the manifold and any gaskets for leaks..........You pay the airfare and I'll personally come and fix it!

Jim.Thompson

There is little chance of the rubber manifold leaking; it is held on the spigot off the head with a hose clamp and the very positive Stihl attachment to the carb. All gaskets have been checked and re-checked. The air leak is a logical question though; given that the needles are shut and almost shut etc. etc.
edit:
Actually, it's just the opposite. If there was an air leak in the manifold, the needles would need to be opened further to compensate for the excess air.
That is no idle boast! I do admire your confidence.
Should I start saving up?

Gizmo-RCU

My Feedback: (27)

Totally!!!!

Jim.Thompson

I have tried the engine with the replacement carburettor. No good at all. I did manage to get it to fire and run for a 2 second burst. Tried a new plug, re-timed the engine using a newly machined converted spark plug as piston position stop similar to the one on Adrian Ciulei's video. Timing set to the recommended 30 deg.
I suspect weak spark, but Adrian assures me it is over 30 kv.
This problem is becoming intactable and I'm just about over it. I will give it one more week; if I don't fix it by then, it will be shelved and I will close this thread.

bogbeagle

Long shot, but here goes.

I was once given a two-stroke engine that "absolutely will not run properly".

The piston had been fitted 180 degrees out of kilter, such that the porting was incorrect. This may not be applicable to your engine, but we are at the "clutching at straws" stage.

Jim.Thompson

We are at that stage, you are right. I dissembled the engine and re-assembled it in the company of a proffessional engine re-builder/mechanic buddy of mine. We suspected something like that, and the exercise was for the reason that you raise.
Unfortunately, it is assembled correctly.

There is a glimmer of hope this afternoon. I found the metering lever low by around 2 mm or more. I adjusted it up and re-assembled it. However, I since found that some of the metering kits have a lever that clips onto the diaphragm pin when I read the limited literature on these carbs on the forums.
I have now corrected that and clipped the lever over the recess in the centre pin as it should be and closed it up again.
I plan to give it another try in the morning. It's dinner time here and I have to try this engine outdoors.
I'll report back if I do any good.

I suspect that the engine is flooded now, so first step is to blow it out with compressed air to make sure the crankcase is dry to start with.

kmeyers

There are no pics with the new carb. post a couple up. Don't give up!

Gizmo-RCU

My Feedback: (27)

Jim,
You had it running well before these problems, something you did may well be


causing this. Yes, if the Diaphragm is not properly installed it may well be pushing the needle down thus reducing gas flow. I have many hours operating Stihl saws and they are some of the best, period. I doubt that it's an Electronic problem if it's firing..................

kmeyers

Pushing the needle down opens the flow of fuel to the metering chamber. On the forked diaphragm without the needle inserted into the fork lever, floods the engine. These forked lever and diaphragm are on the larger series walbro's.

If you didn't have it inserted and you were getting too much fuel you have found your problem.

I've got my fingers crossed.

Jim.Thompson

Yes.
Here is a quote from Wind-drifter.com:

"Important Notes on Carb Re-asembly:
.....................................
2) When re-assembling, make sure the Metering Lever clips into the Metering Diaphragm, or the engine just won't go. This does not apply it you are using the metering kit that does not incorporate the lever & diaphragm clip.
.................................................. .........."

There is little if any specialised information available from Walbro for the WJ57. Not that I have been able to find anyway.

spaceworm

Do I understand that you have had the same problem with both the original and the replacement carbs? Did you rebuild the replacement carb also before you tried it? Are both carbs incorrectly assembled? Good luck.

Jim.Thompson

It appears that there are two types of metering kits. One with the machined slot for the lever to clip over and one just a plain pin. The original carb had the latter, so was assembled correctly.

Some good news!
I just got the engine running. I had it running for some 5 or 10 minutes. It is running poorly and required both needles to be almost closed to run at all. I conclude that the metering lever is now bent far too high. My next step is to adjust it down 1 mm then test. More if found to be necessary.

Jim.Thompson

Better News!
I adjusted the lever down about 1-1.5 mm below the level of the casting, re-assembled the carb and started the engine again with some prime fuel in the carb throat. It now runs with the low speed jet open 3/4 turns. The high is around about the same. Running better than before and is responding to throttle ok. Sounds good at half throttle and more.
I conclude from this that the lever should be bent down a bit lower, is this correct?

edit:
I just phone the local Stihl agent. His opinion is that the lever should be set at the same height as the carb casting.
Also, exf3bguy suggests the same here:

http://www.rcgroups.com/forums/showp...&postcount=544

Which is puzzling, as I could not get it to run on that adjustment without having both needles almost closed and could not lean it out well.

I have this post from Zagnut in mind:
http://www.rcgroups.com/forums/showp...&postcount=548

Accordingly, I will start it up again a few times and maybe leave the metering lever adjustment where it is.

Jim.Thompson

Fuel metering lever adjustments: further thoughts.

I started the engine a couple more times. It will occaisionally cut out when idled down from part or full throttle.
Studying this Walbro chart leads me to conclude that the arm is in fact still set too high.

http://www.wind-drifter.com/technical/walbro_chart.jpg

So, I will measure where it is now and bend it down another .5 mm or so then try the engine again.