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Discussion Starter #1
I have a 1991 Honda EM5000SX generator with a GX340 engine with no more than 10 hours run time.
It's been well cared for: run periodically, oil changes, fuel stabilizer, etc. It starts on the first pull every time. The problem is that at normal operating RPM it misses (pops) badly when first started and improves somewhat after warm up.
If I run it at a lower RPM via the Auto Throttle system, it runs smoothly. I've gapped the plug, adjusted the valves, added fuel octane enhancers and I've tried various carb settings.

I've run out of inexpensive ideas...any help would be greatly appreciated!
 

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Model Murdering
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Here's a couple more cheap ones. Verify proper oil level and temporarily bypass the low oil cut out switch if it has one. Check for vacuum leaks at the spacer biscuit and gaskets behind the carb. Check the choke mechanism carefully, adjusting a carb with a wacked out choke is futile. Does this carb have both an idle air correcter and fuel mixture screw? Check the flywheel magnets and pick up coil for corrosion and ensure the air gap is correct. Honda's will also exibit behavioral problems if the head gasket is just starting to let go. Like a minor vacuum leak, this condition will appear to improve as the unit warms up and the offending culprit swells a bit under heat. Until of course it finally blows out. Good Luck
 

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Discussion Starter #3
Thanks, Bill.

Thanks for the very helpful reply, Bill, and sorry it's taken me so long to post a response. I found that the choke butterfly valve didn't move freely and fixed that. However, it appears that my main problem is some type of vacuum leak and I'll try to troubleshoot that in the next few weeks.
 

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Model Murdering
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Dont mention it. I use carb spray for checking vacuum leaks which is a nono cuz it's flammable. I use it cuz I dont have to clean it up later like soap and water. Just be sure you dont have ignition sparks/leaks. You dont have to get all crazy and dowse it. It doesnt take much more than a few little puffs from the can. :p A propane torch works good for the less experienced. They wont back blow on ya. Just open the valve and play it around the suspected area and listen for the change. If it falters, speeds up or weirds out you've found your leak. Remember that there could potentially be more than one, so dont get fooled. Did you readjust your carb after you fixed the choke. Better do that first!
 
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