Small Engine Troubleshooting Problems? Ask a Mechanic Now.
I'd agree that this could be a air leak
The best way to locate a leak is to have the engine running and warm and then spray lighter gas/propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
in that case then I'd replace the spark plug with a new part
You can also try spraying some water on the coil pack with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.
in that case how have you set the idle mixture ? as if its too lean this too will tend to make an engine hunt as you describe
there's usually a screw for idle that should be provisonally set 2 turns open from fully closed
I'll opt out and get someone else invovled
Hello, is that an MTD Chinese engine 265 SUA?
Does it look like this?
Sometimes a governor adjustment will fix that especially if the carb was removed. Pulling on the linkage to remove it from the carb can knock it out of whack. I think I have a shop manual.
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If there were an air leak it would be hard to start and not run at the higher rpm's
Did you remove gas tank and try adjusting the governor?
OK, I gave you my input and will opt out. Good luck.
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I was reading through the prior conversation and I would suggest that you have a partially blocked main fuel jet or nozzle. I know that you have indicated that you replaced the carburetor with a new one but it is possible that the jet may not have been cleaned thoroughly during manufacture.
What happens if you hold the governor linkage steady while the engine is running?
I do agree with prior comments that if it were an air leak the engine would be hard to start and if you sprayed around the sealing surfaces while the engine was running you should have noticed a change in the way the engine was running.
This carburetor has a small fixed jet in the top of the carburetor just under the idle adjustment screw that can be removed and cleaned as well however it normally only affects the idle performance of the engine and not the high speed performance.
That really doesn't matter, I have been in the repair business for 28 years and it can happen. I have seen anything from a small shaving left behind to items deliberately left in the carburetors by upset employees that can cause issues. Yes, I understand that it is a new carburetor and one would think that you could rule it out but that is not always the case.
Since you are saying that you can choke it and it seems to run better, it really makes me believe that there is something in the jetting of the carburetor.