2004 Argo Conquest FD620D backfiring under load

[jjort]

engine starts fine and runs great in neutral...revs up no issues but after it warms up and under load it starts to backfire and lose power.... If I back off the throttle it will run ok but as soon as I try to give it full power, it starts the missing/backfiring (puff of smoke out of the exhaust) and losing power.....

what I have done so far:

changed the fuel to fresh 93 Octane
pulled the carb and ran it through the ultrasonic cleaner
ran some seafoam through the intake.
changed the fuel pump
cut the pin off the carb solenoid



my guess is that the valve backlash is set too close and when it heats up the valves are not closing properly.... going to check that next.... however I am pretty sure I did that already last year

kind of at a loss

Turns out I had a bad spark plug... never would have guessed that.... anyway goes to show you. Next time I have any problems, the first thing I am doing is changing the plug.... Thanks everyone for the suggestions

[reichstall]

you may want to check if valves have a build up on them but the only way to do this is to pull head. The build up comes from the wonderful ethanol .on cleaning the carb and I do not know what yours looks like it is very hard for ultra sound to do its job unless completely torn down this includes welch plugs if yours have any.

[jjort]

you may want to check if valves have a build up on them but the only way to do this is to pull head. The build up comes from the wonderful ethanol .on cleaning the carb and I do not know what yours looks like it is very hard for ultra sound to do its job unless completely torn down this includes welch plugs if yours have any.

Thanks for the suggestions..... I did pull the carb apart and it looked pretty clean inside.... blew out all the jets with compressed air after.

at this point I am thinking about replacing the valves and pushrods..... not that expensive

[reichstall]

really no need to replace just clean. I had thought about this yesterday I had suggested to another to use l leak down tester it will verify where your promblem is . You can get them at harbor freight for about 39.00 us or if you know someone who has it . Might save you a tear down.

[jjort]

really no need to replace just clean. I had thought about this yesterday I had suggested to another to use l leak down tester it will verify where your promblem is . You can get them at harbor freight for about 39.00 us or if you know someone who has it . Might save you a tear down.

Thats a good idea with the leak down tester....will give it a try...... in the mean time, I rechecked the valve gap and it is fine.... I had too much oil in the engine so I thought that might have been the issue...changed the oil and verified the level... still havent resolved the problem....what gets me is....the motor runs fine with lots of power for about 5 mins.... once it is warmed up, thats when the backfiring and loss of power happens

[dirtdobber]

Think about the possibility of a heat related ignition problem. Observe the spark through each plug when cold, and then again when hot and acting up. I don't know if you will see a difference but its worth a try. Or you could also pull one plug wire at a time and notice the change in the engine, both when cold and when hot. The engine should change tune equally with each plug. If it doesn't then you have a place to start. Be aware that pulling a plug wire on a running engine can give you a shock!!

[jjort]

Think about the possibility of a heat related ignition problem. Observe the spark through each plug when cold, and then again when hot and acting up. I don't know if you will see a difference but its worth a try. Or you could also pull one plug wire at a time and notice the change in the engine, both when cold and when hot. The engine should change tune equally with each plug. If it doesn't then you have a place to start. Be aware that pulling a plug wire on a running engine can give you a shock!!

Hmmmmm it could be a bad coil.... they dont look like they are too handy to change

[jjort]

Turns out I had a bad spark plug... never would have guessed that.... anyway goes to show you. Next time I have any problems, the first thing I am doing is changing the plug.... Thanks everyone for the suggestions

[dirtdobber]

I'm glad you got to the bottom of it.