I recently rebuilt an H35 Tecumseh for a mini bike I'm restored, of which pics are in another thread elsewhere. I got 'er running and now am seeking help in getting 'er fine tuned.

My issue is this: I can get it started, and if I hold the throttle above idle, steady, it will stay running, but if I close the throttle, she won't idle. Also to note, holding the throttle open it's definitely not running as it should, but I recognize this is because the idle and main circuits aren't "fine tuned yet."

Here's the behavior: when I close the throttle, the engine seems to surge in RPMs before dropping back down to idle level, at which point it stalls out.

The engine isn't flooding out, and it always restarts relatively easily. I just recently noticed that the o-ring on the main jet needle valve on the bottom of the float bowl seems to be distorted and leaking, but I discovered that following my last attempt at tuning yesterday evening (ran out of daylight rapidly).

While rebuilding the carb, I blew out all the passageways, replaced both welch plugs, checked the float level and all that good stuff. Brand new needle valves, so I know they're not damaged.

Any thoughts? I haven't checked my ignition for intermittant spark yet.

Drive chain removed or rear wheel suspended off the ground.

If it starts ok then the initial settings your using are probably ok. First turn in the idle stop screw for a fast idle.

For no load adjustment start the engine, open the the throttle using the throttle control (twist grip) so that the governor is working. If the engine wants to die at top speed open the lower adjustment (load) screw 1/8-1/4 turn at a time until unit runs smooth, if unit sputters and blows black smoke out of exhaust then turn load adjustment screw in 1/8-1/4 turn at a time until unit smooths out.

Once you have the load adjustment set, start backing out idle screw to bring engine to a slow idle, if engine dies when it slows down turn out the low speed adjusment screw (side of carburetor) 1/8-1/4 turn at a time until idle smooths out, check for throttle responce, if it hesitates or wants to die, open the low speed adjustment a little more to increase throttle responce, you may have to open load adjustment a little also if the low speed does not take care of hesitation. Reverse low speed proceedure if engine chokes down at idle or chokes down and runs rich when accelerating engine.

The load adjustement may have to be reset when a load is applied, most of the time if any adjustment is needed, it will have to be opened up a little.

The load adjustement affects the low speed adjustment, so whenever the load adjustment is changed, you may have to adjust the low speed also. Minor adjustment to the low, usually have little or no effect on the load setting.

I hope this explanation makes sense, I have always had a good ear for adjusting carburetors, but for me - explaining it is not near as easy as doing it.

Thanks, I'll give it a whirl!