Another lemon fixed, I think

[F-Type]

Got my hands on an octane today that's been on the shelf for a few years. It worked until it was broken in, did two or three wheelies and then caught the start and stall disease, also known as Octane-16 disease. ? Eventually it was given up on and left on the shelf.

Everything with the engine, cdi, carb etc checked out ok, as so often, even compressions.

Swapped the piston ring for an OS one I had in a drawer. The engine started and stalled two times but the third it kept running on high idle for half a tank without hesitation. Let the engine sit for the remainder of the day and restarted it. Took a few pulls but when it fired up it ran.

So, some tanks of break in coming up and then we'll see if this s*ucker can start pulling wheelies again, for real.

 

[F-Type]

Well, not quite ... but read on

Today started the engine up again. It ran for maybe 10 seconds, and died. Started again, 5 seconds, tried a few more times and realized we're back at the start and stall issue.

Something is fishy. Why would it get into the start stall problem from not being used for a couple of days? And deteriorating quickly into a point where it will not start at all. Fuel is there, ignition is there, compression is there, crank case compression is there.

I have always figured the engine is getting too much fuel (remember I put smaller carb on once...) and I think that's the problem here too. A few things points at that.

So, what I did was to remove the back cover to have a look inside the crank case.
And guess what I found.
Well, have a look at this!



That's a lot of fuel inside the crank case, and that's the "leftover" from running the engine. No wonder it won't run with all that fuel getting tossed around inside the crank case.

This came from running at stock settings, ed.2. The thing is, HPI changed the recommended carb stock settings. This is the updated setting, LS 2 2/3 and HS 1 turn. So I tried the original setting, LS 1 1/4 and HS 1 1/2 turn, so the LS is less than half, so to say. Engine fired up and ran a lot better than before, but stopped after a while. And my time was up. Hopefully will get some time tomorrow to continue.

Held e piece of paper behind the exhaust. It got really wet in just 1-2 seconds on the updated settings, a lot better but still a bit wet at the original settings. With a bit of luck, this engine will be tuned in and up and running again soon

 

[Vmansavage]

Glad to see your finding some things out..my octane runs decent but really loads up at slow speeds get it cleared out and it pulls wheelies tried to dial it in better but all it seems to do is make idle faster would love to find a smaller carb to give that a whirl I also was thinkin of leaning my mix out just a hair but don’t want to fry the engine so for now I will just keep the ol girl cleaned out with blipping the throttle like on my old 2 smoker dirt bikes but any suggestions or thoughts would be greatly appreciated keep us posted on your findings...I would love to pick up another octane like the one you did mine was a similar find person I bought it from found it in the back of a storage unit I don’t even think it was started I have almost 3 gallons through her now and hopefully more to come....I added the Louise wheels n tire combo and wheelie bar....

 

[F-Type]

Yihaaaaa! Seems I found a new issue that made all the difference. Will be back later to tell you more ?

 

[F-Type]

When considering and checking up on the fuel build up in the crank case, I figured what could be the cause, and also noticed the o-ring that seals the back cover slid in a bit too easy and the cover seemed to bottom out without applying pressure, indicating the o-ring doesn't seal properly. Which should mean there'd be fuel on the outside area of the o-ring, on the back cover. And guess what, there was.

So, I made a quick and dirty fix, added some teflon tape behind the o-ring.

And, voila, since then the engine has been running. Started again on the first pull a moment ago, and just ran on a steady RPM.
That was the fourth occasion since I fixed the sealing issue yesterday the engine started without much hassle and run more or less fine.

Though the idle RPM is a bit high in my opinion, and I would like the engine to run more rich now during break in. However, the idle screw is at its minimum, and if I richen the LS, it runs worse and stutters and occasionaly stops. I noticed if I pinched the air filter hose to about half the diameter, I got a good and steady RPM. Once again we see the effects of a too big carb. This is what the T-Shirt in the intake is supposed to handel, to limit air flow at low RPMs. Doesn't work to well it seems. Perhaps I should build an ECU controlled air intake limiter. Wouldn't be that hard actually. But shouldn't be needed

In any case, now the engine is running, from what it seems

 

[F-Type]

Fuel still keeps building up in the crank case, and this is clearly what is causing the start stall issue.
So, question is what is causing fuel to build up in the crank case!?

 

[Kurt2020]

Fuel still keeps building up in the crank case, and this is clearly what is causing the start stall issue.
So, question is what is causing fuel to build up in the crank case!?

i was reading thru what you had been trying and fuel build up is simply to rich on the low needle. you said u tried to lean it and the idle just increases (which is normal) and your idle screw is basically all the way out. so that tells me your engine has an air leak or leaks somewhere. I fly nitro and gas rc planes and when there is air leaks we just use permatex ultra black silicone gasket maker to seal ALL areas that could possibly cause an air suction leak. the engine must be 100% sealed!

I'm looking at the exploded views of the engine now and it looks like the only areas a leak would be is the back plate and where the carb mounts to the engine. could be leaking at that carb spacer. so put a small amount on those areas to ensure they are perfectly sealed. you must make sure it has dried over night before running the engine.

so to directly answer you fuel build up question... the low speed needle is to rich.

go thru the engine with a small amount of silicone to help seal any areas like how you mentioned that teflon in that spot on the back plate and carb

 

[F-Type]

Hi Kurt

Thanks for that info!

I have been looking over those things. New gaskets and no leaks at those two spots I'm pretty sure. When removing the carb the gaskets are all clean and dry.
I did replace the teflon tape with a new o-ring to make a proper seal.

However, there is one more possibility, perhaps. I noted the sleeve is relatively loose when the engine is hot. So, then the question is, what if there is a leak between the sleeve and the crank case, between the crank case inner and the exhaust. On the other hand, I guess that "channel" is open most of the time anyway since there is a gap there between the piston and the sleeve anyway, as it's the piston ring that seals towards the sleeve, and the piston ring is above the exhaust port for most of the time. So the only time that would cause an issue then is when the piston is in the lower part of the stroke.

It seems I do have good crank case compression.