Tecumseh OHH65 cuts out over bumps

[Gasteffens]

First, I did search and found an older thread that reads identical to my issue , except the kart has not been rolled or wrecked.

Yerf dog 3203, Tecumseh 6.5 OHV, stumbles over itself over bumps.

Engine cuts out over bumpy terrain...

I hope that I am posting this question in the right place. I have a Yerf Dog 3203 that a friend gave to our family. It has a Tecumseh 6.5 hp OHH65 engine. It ran pretty well except when you hit bumpy terrain...then it would briefly stall and then catch and fire back up fine. It was...

www.diygokarts.com

Unfortunately, this doesn’t end with a conclusive fix. Several Google search results from other sites offer the same - no smoking gun. But often it comes up the 6.5 as having this stumbling over bumps issue. What was the difference in the 5.0, 5.5, 6.0 and 6.5 OHV engines?

The carb is CLEAN. It starts easy, idles great, no smoke, no knock, and launches like a banshee until you hit a bump. I have tried three different float settings, perpendicular to the carb, closer to it and farther from it all yielding the same result.

I will likely end up with the almighty 212 when they put them on sale, but with the block being in great shape I have a hard time ditching a whole motor. I could try an Amazon carb, but if it does the same nonsense again it’s wasted time and money, both of which are in short supply.

Edit: Interestingly after we bought it we had 5-6 rides with NO issues like this, almost as if the few tanks of fresh fuel moved something around, but the fact it’s tied to bumps is a mystery.

Thanks!!

 

[JTSpeedDemon]

It's a well known thing with Tecumseh carburetors. It even happens on some Briggs carburetors. It just comes down to the fundamental carb design. One way to avoid this would be an upgraded carburetor like a Mikuni, but other than that, there's nothing you can do.

 

[Gasteffens]

It's a well known thing with Tecumseh carburetors. It even happens on some Briggs carburetors. It just comes down to the fundamental carb design. One way to avoid this would be an upgraded carburetor like a Mikuni, but other than that, there's nothing you can do.

I had a feeling something like this might come up. I guess we'll just live with it in the meantime. It's strange, 15-20 years ago I had a Manco Dingo-Rattler, with a 6.0HP Tecumshe (primer, not choke like my current 6.5). We ran that thing up hills, forded shallow rivers with it, beat the snot out of it in the snow and it never skipped a beat. But this current one tragically does not perform the same.

 

[Crazznewt]

I have the same problem with a Predator. It works well on pavement but sputters while dirt tracking. I though maybe the fuel flow was affected by the extra vibration so I bought a fuel pump which didn't solve the problem. There is a Mikuni coming soon.

 

[Gasteffens]

I have the same problem with a Predator. It works well on pavement but sputters while dirt tracking. I though maybe the fuel flow was affected by the extra vibration so I bought a fuel pump which didn't solve the problem. There is a Mikuni coming soon.

Hmm, so a Predator may not solve my woes. I guess I’ll have to see what I can do, perhaps draining and trying to do a deep clean on the fuel tank may help - perhaps there is some chunk of crud that slows up flow just right at the outlet. It’s just a shame because it does pull hard in between cut outs and even starts up warm easy with no choke and then sits there and idles like a dream.

 

[JTSpeedDemon]

It seems to be more or less a problem with all small engine carburetors aside from performance motorcycle carbs. My solution is to use a Tillotson pumper carb.

 

[NightHawkJ30]

Did you check Float height?

 

[NightHawkJ30]

I had similar problem on My 03 Yamaha Kodiak. It go over bumps and run exactly how you describe. Turns out just needed the float tang readjusted. Installed a new one and adjusted for good measure.

 

[Gasteffens]

I did check the float, and sorry for the messy pictures but I in those I changed the float out for a new plastic one with a damper spring. Currently the float is set to the 11/64 spec. For kicks and grins I tried adjusting it obnoxiously high and low, and same result.

With the bowl off, I have held very light pressure on the float and fuel does NOT pour or trickle out. The needle and seat appear okay from what I can see, and considering when it sits still or drives over smooth terrain it’s fine, I don’t think the needle or seat is an issue. It also starts easy cold in 1 or 2 pulls with the choke, then hot restarts are easy with no choke 1 pull.

I’m starting to think perhaps either the fuel system sucks in this, or I’ve ruled out fuel.

I’m going to investigate something grounding/snorting out on the ignition side. I’m not sure why I haven’t tried this before but next time in the shop I’m going to disconnect the remote kill wire and see if its changes. Next I will inspect the plug wire itself.

I’m just bamboozled because years ago I had a Manco go kart with the 6hp version of this engine which we beat the ever loving snot out of and it never skipped a beat.

 

[NightHawkJ30]

Damper spring? You don’t need that’s probably reason why it running like that. It holding the float. Open so it floods its self out. The plastic float to is updated part then the brass one. When buy the New float the plastic one it comes with instructions on the damper spring. When to it is needed or not.

 

[Gasteffens]

My understanding is the damper helps hold it shut, as it pushes on the back/side of the float ever so slightly, and looks to be the case by how it’s installed. It basically runs identically to how it did before so I don’t think the spring changed much if anything.

 

[NightHawkJ30]

Did it have a spring in there already?

 

[Gasteffens]

Did it have a spring in there already?

No it did not, but I have read elsewhere and talked to some guys locally who have added these when it is indeed a bouncing float problem. It hasn’t changed how it runs so I’m not sure I gained or lost by putting it in there.

 

[NightHawkJ30]

So everything is clean then? Bowl jet and idle jet and Emulsion tube?

 

[NightHawkJ30]

http://www.barrettsmallengine.com/manual/tecumsehcarburetormanual.pdf

 

[Gasteffens]

Yes it is clean clean clean inside.

 

[NightHawkJ30]

When I rebuilt my Tecumseh Series 11 carburetor i read this manual a few times to help understand how these carburetors work.

 

[NightHawkJ30]

So your saying it was running good they after few runs. It starting with the stumbling problem?

 

[NightHawkJ30]

Actually you know what it could be a ground

 

[Gasteffens]

So your saying it was running good they after few runs. It starting with the stumbling problem?

Correct, but I had not ridden it over any rough terrain either and pushed it hard like that. You can take it wide open down a flat street and it’s fine. Hit some bumps and that’s it.