Hi,
I may have a good chance to purchase a honda forman with 7k kms(approx. 4000 miles) on it, not sure if its a 400 or 450(450 i figure) Started up and ran kinda rough, tommorow I'd like to go test the compression with the tester I have for my snowmobile. 1.What is the compression of this machine stock from dealer? 2.What would be decent compression for a used one like this, what would be way too low? sounded like a little bit of rattle in it... i thought if the motor has good compression it could just be the valves, 3. Could it just be the valves. 4. If it is the motor how much would a motor job cost to have done(not at a dealer obviously) --- I may be able to get the machine for between 1 and 2000 dollars Cdn funds .... thanks in advance for all the help, any input or comments are appreciated.....

 

Why do you think its a compression problem? does it smoke?

 

i only got a hcance to look at it for a second, but there seemed to be a bit of a rattle or just running a little rough... i dont know if its compression at all, but i wanna test it anyways to see where it is....

 

I would check the spark plug and airfilters. A wet black oily plug means blow by. A black dry plug or brown is okay. Wet with gas is okay too its just alittle rich.
look for pinched or torn vacuum hoses
check the gas it may be old. get some fresh gas and drain the old out the carb bow if their is trash in it or it is gummy clean the jets and carb.l


that rattle is normal even on a new one. 4 thousand miles is really just getting broken in. The compression should be fine.

 

i'd like to check the compression anyways, anybody know where it should be with an 01 foreman?

 

On a new motor, itll be 178 plus ,psi, with the throttle wide open, for the cranking. It needs to spin at least 450 rpm, to get there, so use the starter, and not the rope. If its under 120, id be concerned.
Most likely the spark plug needs changing, and probably the carb needs cleaning.
As long as its not smoking blue...it probably is just fine, and wont need a rebuild. The valves are easy to adjust, and it isnt a biggie..being too loose is better than too tight.