Picked up a 1997 foreman 400 that didnt run, had a bad cdi. Bought a used oem one from ebay and I have a nice strong spark now. I can not get it to run for the life of me, carb has been completely rebuilt, both when pull starting and electric start the bike will turn over and backfire extremely loud through the carb. Sometimes its accompanied with a loud metal on metal clank sound. I've tried ether directly in the cylinder as well as gas and nothing will make this thing run. I've adjusted the valves but it just wont run, sometimes it cranks and sounds so close and then boom a gunshot out of the carb. I was thinking possibly the timing was off, unfortunately no easy way to look on this particular motor. Any ideas would be greatly appreciated.

 

It is worth doing a compression test to make sure it isn't a worn bore, or valve trouble, but I have just done the timing chain on a 400 with the same symptoms. As you state, not that easy to check the timing, but I checked the spark and it seemed OK, put another carb on, and still no start. It also seemed to spit more out of carb than is usual (all quads do this a bit). Compression was OK, so "bit the bullet" and removed the clutch cover, to find it was about 5 teeth out. If you are getting clunking, it may have got further out than that, and have a valve hitting the piston. The exhaust has to come off to get at the chain adjuster, and the chain I took off had gone strangely stiff. Your problem could be flywheel come loose and put the ignition timing out, you can check this by looking down the plug hole for the piston getting to TDC and checking the T mark on flywheel agrees, a difficult mark to find on a 400, I discovered.

 

Thank you for your response, I believe the flywheel is okay. I put a zip tie down the plug hole and manually spun the motor and stopped when the piston got the highest and the T was in the inspection window. It sounds to me like I'll be doing the timing chain this winter, any chance it could be the used cdi i bought sparking at an incorrect time like during the intake stroke? I'm not the best with small motors, I will have to do a compression test as well.

 

Update compression test yielded only 85psi. Granted motor is cold since it doesnt run and it's about 40 degrees today.

 

hey i have a 97 honda forman 400 i use it with very low oil it shutdown while drive in it and motor got locked so i took off the pulley starter and used a ratchet to get it unlocked while doing it it sound like the piston head was rubbing the piston cylinder and felt hard afte alittle bit of turning the noise whent away so now it cranks with the helectric start but it won't start of course all this was done after i put motor oil but now it won't start it did before any of this happened if you have any ideas please let me know as im new in the atv deal thanks

 

Most air cooled quads seize on the piston, when they free off, the gudgeon (wrist) pin is still partly seized as a rule, and the bore scored to hell, rings are stuck or broken too, so there is little or no compression. Do a compression test to confirm, then take the head and cylinder off. A rebore and new piston will almost certainly be needed. I have known the piston to break up, if it has, the engine would need to be stripped to remove the shrapnel.

 

Thanks i did a pressure test and nothing so i took it a part and my piston is bad n broken now i have to figure how to clean the broken peaces that got inside the motor

This is the broken piston now i have to figure out how to get those O RINGS off and be able to take the pin but yeah also there are broken peace inside somewhere

 

You have to take the engine out and strip it completely. Teaches you to check the oil level occasionally in future. The Gudgeon pin welds itself into the con rod and you have a hell of a job getting it out. I use a threaded bar through the middle of the pin, but have stripped the threads on a few threaded bars, so great is the pressure required to shift the pin. You then need to clean up the con rod eye. At first I was a bit dubious of using a con rod with a scored eye, but because of the cost of a new assembly I tried leaving it, and had no problems. I since have done over 50 rebuilds after seizures and had no subsequent problems with small ends.

 

Thankyou for the info i gues this will be my first rebuilt. Very true i had to learn the hard way to check oil level every other use i was able to pull the rod off now im using break cleaner and burn motor oil to flush the small broken peaces looks like is working now im just waiting for a wire camera so i can see if there's more small or big peaces