Tecumseh 3.5 power loss at full throttle

[Redgrinde]

So I picked up a tec H35 (45710W) engine a while back with a handful of other engines and an old basic Kart. I'll start with sorry no pics... yet... I'll see what I can do when I get home later.

The Engine runs well and I've sorted the idle so its fairly consistent though it does speed up as the engine warms up. It generally starts with 1 or 2 pulls. But at full throttle it will fluctuate in power quite a bit. It does this both sitting on jack stands in the garage and while driving.

So far I've replaced/cleaned most of the linkage to make sure the cable isn't causing the issue. I've replaced the spark plug, and cleaned the Carb, then rebuilt the carb when just cleaning it didn't work. It has a simple one piece screw in the bottom of the Carb... I cleaned but did not replace it. Replaced air filter, and tried it in the garage without the filter in place, no change.

The gas tank was removed from the engine as it interfere's with the seat so I remounted it off the side using an engine mount for spacing, I bolted it to the engine... Since it was mounted directly to the engine before I assume this isn't an issue, but it did move two of the three bolts out a bit more than they were.

So did I miss anything? I'm considering picking up a new carb on the Bay but if its the engine (or the guy doing the work) and not the carb then I'd rather not waste the cash... Any thoughts?

Had a thought... Could the gas tank be causing any issues? Its plastic and leaks gas while driving around, leaks out around the cap, I thought it might be due to the terrain as its quite bumpy... I did check the hose but it looks new so I left it.

Thanks
Jeremy

 

[jace]

it's the governor linkage, at full throttle it fluctuates the throttle according to load, it's perfectly normal...

 

[Redgrinde]

Thanks, could it be fluctuating to much? It does it so often that its nearly impossible to use the engine. I have a Subaru 4hp on another Kart that is far more consistent.

 

[anderkart]

Try spraying a little aerosol carb cleaner (with the straw on) around the carb to intake gasket area, with the engine idling. If you detect any rpm change, that's telling you the gasket isnt making a good seal, and this could be the cause of your symtoms.

 

[Bluethunder3320]

ive seen on some tecumseh's that the gas cap vent was blocked. run it with no cap and maybe 1/3 gas so it doesnt spill just to test it out. maybe you can drill a hole through the cap (small one.) if this is the problem. or put a nipple on the cap and attach a tube that goes straight up about a foot.

 

[Redgrinde]

Try spraying a little aerosol carb cleaner (with the straw on) around the carb to intake gasket area, with the engine idling. If you detect any rpm change, that's telling you the gasket isnt making a good seal, and this could be the cause of your symtoms.

Interesting. I'll give this a shot tonight and see what happens.

ive seen on some tecumseh's that the gas cap vent was blocked. run it with no cap and maybe 1/3 gas so it doesnt spill just to test it out. maybe you can drill a hole through the cap (small one.) if this is the problem. or put a nipple on the cap and attach a tube that goes straight up about a foot.

I'll check this as well, I have another tank off a different motor that I could hook up as well... might be a dumb question but would a one way air/water valve like those used for airlines in fishtanks work to allow air in and keep the gas from escaping? Or does it need to vent both ways?

Thanks for your input guys.

 

[Doc Sprocket]

Gotta vent both ways- IN to allow fuel to be drawn towards carb, and OUT to relieve heat-related expansion pressure.

 

[Redgrinde]

So I spent a bit of time messing with the gas cap, didn't really come to any solid conclusions though... I tried it cold, then went to drive it around and warm things up, got to the bottom of the hill and discovered the field on the neighboring hill was on fire...

Called the wife and fire dept. (yes in that order) and put my stuff away... Then it rained hard for 15 minutes or so and put out all three little grass fires... Gotta love the hot dry Colorado plains...

Hopefully I'll get a bit of time tomorrow to go through it a bit more thoroughly...

Thanks for the help so far...

 

[Redgrinde]

Spent a bit of time working on this over the weekend, cleaned the carb again replaced all the gaskets and checked the tank and carb. as described above.

It still idles stable, and I can open the throttle up and it will hold steady if its not moving.

But it still dumps and on occasion shuts off on rough terrain, so I'm guessing there must be some sort of sensor, checked the oil sensor thread and looked over the engine didn't find anything similar so I'm at a loss...

But I think I'm done with this engine gunna pull it put something else on there and see if I have better luck.