craftsman rider there is no flow restriction from fuel tank
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engine spits and backfires at full throttle
- Thread starter ACF
- Start date
Backfiring is almost always a sign of a lean fuel mixture. Is the new carb adjustable? If so, richen the high speed mixture (bottom of float bowl) at WOT until it slows down and burbles, then lean it back out until it smooths out. Adjust the low speed mixture such that when dropping to idle from WOT it slows down smoothly without any popping or backfiring.
If the carb is non adjustable, and is a properly matched replacement, I would be looking at the jets to ensure the jets installed are big enough. If the replacement is a cheap knock-off from Amazon or eBay, it will undoubtedly be a funky reproduction with little to no QC. I would clean the original carb with care, and reinstall without any question.
Next, I’d ensure the magnet and coil surfaces are cleaned of any rust and re-gapped. A piece of 80-90# cardstock or a business card are excellent gapping tools for setting coil gap.
If the carb is non adjustable, and is a properly matched replacement, I would be looking at the jets to ensure the jets installed are big enough. If the replacement is a cheap knock-off from Amazon or eBay, it will undoubtedly be a funky reproduction with little to no QC. I would clean the original carb with care, and reinstall without any question.
Next, I’d ensure the magnet and coil surfaces are cleaned of any rust and re-gapped. A piece of 80-90# cardstock or a business card are excellent gapping tools for setting coil gap.
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Lawn Addict
When you relaced the cam, did it also come with the lifters? New cam and old lifters usually will result in another cam failure.
The popping a snorting you described favors a badly worn-down cam lobe or valve clearance needs to be readjusted properly.
The popping a snorting you described favors a badly worn-down cam lobe or valve clearance needs to be readjusted properly.
You say:
Starts and runs good at low speed.
Ran good for 2 months after cam replacement.
Spits and sputters at high speed.
See how it re-acts if you use your hand so as to add some choke by restricting the air intake at the carb or reach behind the carb and slowly give it some choke.
I suspect a lean carb at high rpms and this is quite common with Nikki carbs and their clones.
Also you cannot just take a Nikki or clone apart and clean and put back together and expect a good run if you do not replace the gaskets and o rings.
But install a properly gapped NEW spark plug first.
Starts and runs good at low speed.
Ran good for 2 months after cam replacement.
Spits and sputters at high speed.
See how it re-acts if you use your hand so as to add some choke by restricting the air intake at the carb or reach behind the carb and slowly give it some choke.
I suspect a lean carb at high rpms and this is quite common with Nikki carbs and their clones.
Also you cannot just take a Nikki or clone apart and clean and put back together and expect a good run if you do not replace the gaskets and o rings.
But install a properly gapped NEW spark plug first.
changed spark plug, cleaned carb not a nikki, adjusted valves, only spits out carb, fly wheel key good. upon further looking at valves is there a possible chance that the valve guides have come loose, it looks like the intake valve guide is out more than the exhaust valve, this was done only by looking at difference between the two, the intake you can see good on the second turn of the compression spring was as exhaust none is seen. so if the intake value is not opening completely would this cause the problem of backfire and spitting back thur the carb
thanks
AC
thanks
AC
I think you are on the right track. I think it is either a worn cam lobe, or it has slipped on the shaft. I have seen the lobes slip on the cam shaft. Check the lift on the intake valve and compare it to the exhaust valve lift. If the lift is the same the lobe is not worn but it could have slipped on the shaft. Most of the time if it has slipped it will kick back while trying to start the engine.
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What do the cooling fins look like?upon further looking at valves is there a possible chance that the valve guides have come loose, it looks like the intake valve guide is out more than the exhaust valve,
Sounds like she was or is over heating killing the engine. Valve guides are not supposed to move. Should be the same installed height as the adjacent ones.