Vapor Lock?

[JSinMO]

It is hotter than blazes here today. Upper 90s high humidity. As we were running the 648 around today it started having trouble running. It appears to be a fuel problem as I can choke it and keep it idling. Im thinking it’s vapor locking. I put new gas line in when we got it going and every thing was fine, but it wasn’t hot out. Have you guys had this problem? What kind of gas line are you running? I could have sucked some junk in carb too I guess. I didn’t have time to look at it today. Something else to add to the list to check out!

[propane1]

I can says I ever had a vapor lock in any of my tractors. That I know of. But have heard about it before. We get 85/90F here at times. I’d be guessing dirt in something. Hope you get it figured out. And if it is vapor lock, how did you fix it.

Noel

[thebuildist]

I had a 442 that liked to vapor lock just like that. You may have to look at some shielding or ventilation to keep the fuel lines cool. Specifically you're trying to be sure that the heat from the exhaust can't reach the fuel lines.

Bob

[DavidBarkey]

@JSinMO The Onans are known for intake leaks at the seam where the two halve meet. The higher temps could be bring it out. Also the extra heat could be affecting the coil weakening the spark . A richer mixture is easier to jump the gap . I do you know how to use propane to check for vacumm leaks ? I would do that first .

[JSinMO]

@JSinMO The Onans are known for intake leaks at the seam where the two halve meet. The higher temps could be bring it out. Also the extra heat could be affecting the coil weakening the spark . A richer mixture is easier to jump the gap . I do you know how to use propane to check for vacumm leaks ? I would do that first .

When we got it running I made new intake gaskets and resealed the seam with high temp gasket sealer. I’ve never used propane to check for leaks, but I’ve used carb cleaner to do it. I’ll check it next time we run it. I should probably go over the intake bolts too.
Thanks.

[Eugen]

I don't know if you already checked the gas tank and or fuel line for debris. Most of us also have a little inline fuel filter. Hope you make sense of it soon!

[JSinMO]

I just went up and started it this morning with everything cold. Sure enough it starts right up runs to full throttle and work perfectly. This convinces me I have a heat related problem, and I think it’s fuel delivery.
When we got it running I had the tank off to patch a couple of holes in it. Its been cleaned out. I replaced the gas lines from the tank to the carburetor, and I’m running two filters. This has an electric fuel pump, I put 1 filter before the pump and 1 after.
I don’t think it’s a spark issue because when it happens I can get the tractor to idle with full choke.

I should be able to do a couple of easy tests if it happens again. I can check the intake for leaks, or reroute the gas line. Right now I have it routed through the engine compartment to the carb. I can run it outside of the engine and see it it changes.

If it happens again, I’ll report my findings.

[Eugen]

Oh! So it's clear that clean fuel gets to the carburetor. Seems like the problem really is that the air/fuel ratio gets too lean when the engine is hot. As it runs on the lean side the engine will also overheat, making the problem probably worse. If all the engine shrouds are in place and the engine has good air flow, then what's left is the intake, but you said you already rebuilt that. I'm also assuming the muffler and exhaust pipes are separated by tin from the engine, as that's how it is on my 446 Onan for instance. You have a good puzzle on your hands

[propane1]

As you know, I don’t have any experience with vapor lock. You say it idles with full choke when it takes its fit. If it was vapor locked, doesn't that mean no fuel is getting to the carb ? So how would it idle if that’s the Case.
Just wondering.


Noel

[thebuildist]

That's exactly how my 442 behaved when vapor lock happened. The vapor locking causes a fuel shortage, and by choking it you can increase your fuel "suction" to keep the engine running, albeit poorly. This sounds precisely like vapor lock to me.

Bob