94 suzuki 250 quad - decompression valve

bandit86 · May 17, 2010

my quad had wierd compression problems since I got it, getting worse lately. Did several compression test with and without oil today to see it's only 60psi. once i touched the decompression valve lever it fired right up.

Is there a known problem with these? do the valves maybe carbon up and stick? Once it fired up I took it for a 10 miunute spin down the street and did 45 mph for an italian tuneup. Once I shut it off the plug was black so I adjusted it a bit, ran great, then never started again... The pullcord is super easy to pull. My 300 feels like it'll rip my arm off if I dont get it the first try

I dont know how it works but I think it may have a broken spring that would keep it closed for normal operation.

JRJ · May 18, 2010

Re: 94 suzuki 250 quad - decompression valve

I had an 87 suzi 250 quad. It needed a valve adjustment occasionally. I kept the battery up and didn't use the hand valve. Good luck.

dolluper · May 18, 2010

Re: 94 suzuki 250 quad - decompression valve

The decom valve holds the exhaust valve open a bit to make easier to pull or kick start...as suggested make sure your exhaust valve is set right before you use the decom valve ....yours is manual or auto??

642mx · May 18, 2010

Re: 94 suzuki 250 quad - decompression valve

It sounds like your intake valve has zero'd out. (no clearance between the tappet and stem). The valve hangs open when its suppose to be shut... this keeps it from building vacuum to suck the air/fuel mixture in the combustion chamber... this is also why it has no compression.

Put the engine on TDC, pull the tappet cover and check the clearance. If its tight, adjust it to about 4 thousands lash. Run a tank of gas thru it and recheck it. If its tight again, you need to replace the valve before it breaks and causes major damage.

bandit86 · May 18, 2010

Re: 94 suzuki 250 quad - decompression valve

i pulled the cover not realising it's also what holds the camshaft in place. Nothing bent or broken. i will adjust the valves and recheck like previous post said. Runs very rich after cleaning carb, adjusted the carb but never fired again to recheck

642mx · May 18, 2010

Re: 94 suzuki 250 quad - decompression valve

bandit86 said:
i pulled the cover not realising it's also what holds the camshaft in place. Nothing bent or broken. i will adjust the valves and recheck like previous post said. Runs very rich after cleaning carb, adjusted the carb but never fired again to recheck

You don't need to pull the whole valve cover, just the tappet cover (it will either be an oval shaped plate with 2 cap screws or a round cover with a 17 or 18mm nut on top)

Its running rich because its still getting plenty of gas when its running, but not enough air which would cause a rich condition. I wouldn't recommend adjusting anything on the carb unless you have a very good understanding of how the carb works... I see this stuff everyday.

bandit86 · May 19, 2010

Re: 94 suzuki 250 quad - decompression valve

the previous owner tightened the caps soo hard I couldnt loosen it. i took it off to see if any damage is underneath.

642mx · May 19, 2010

Re: 94 suzuki 250 quad - decompression valve

bandit86 said:
the previous owner tightened the caps soo hard I couldnt loosen it. i took it off to see if any damage is underneath.

You can't adjust the valves without having the tappet covers off. The rockers are on pins in the valve cover.

Don't tear up the cover! Its line bored with the cylinder head and they have to be replaced as a set. (about $400 just for the head and cover)

bandit86 · May 20, 2010

Re: 94 suzuki 250 quad - decompression valve

god to know it's pricey. I will try to loosen it but I already rounded the hexagon part designed for remopving and tightening it so it's on. Maybe the pipe wrench and a wrench will do it

642mx · May 20, 2010

Re: 94 suzuki 250 quad - decompression valve

A hammer and small chisle might break it loose too....

bandit86 · May 20, 2010

Re: 94 suzuki 250 quad - decompression valve

haha you wouldnt believe it till you saw it: had the wrong nuts on the head. Let me correct myself, there are 2 different types, 4 altogether. 2 were mixed up. when I went to tighten I noticed that as soon as my torquewrench clicked and i let off the nuts moved. somehow it didnt lock up properly so i moved the nuts around and tightened up. I've never seen torqued nuts loosen. Once the correct nut was on the correct stud it all worked out. I think the one with the cap on the end bottomed out, no idea. Then adjusting the valves was a super pain, no wonder the manual says take the fairings and tank out. The exhaust was set good but the intake had 1/2 turn extra on top of making contact with the valve. Bloody wonder it ever ran. once it was adjusted, instant compression, started first pull on a dead battery.

642mx · May 20, 2010

Re: 94 suzuki 250 quad - decompression valve

Good to hear. Be sure to keep an eye on that valve. If it gets tight again in a short period of time, you need to replace it and have the valve seat refinished.

And keep the air filter well oiled to help prevent this from happening again. When they suck dust into them, the valve face gets worn causing it to suck itself into the head.... which zero's out the valve clearance. I'd recommend Maxima's Fab 1 or Maxima's FFT filter oil.

bandit86 · May 21, 2010

Re: 94 suzuki 250 quad - decompression valve

actually it's soaking wet with oil, been since I got it. I never heard of valves being sucked into heads though...maybe valveseats should be harder?

642mx · May 23, 2010

Re: 94 suzuki 250 quad - decompression valve

bandit86 said:
actually it's soaking wet with oil, been since I got it. I never heard of valves being sucked into heads though...maybe valveseats should be harder?

Usually the valve seats look good... even when the valve face is shot. Sucking the valves into the head is kind of a Suzuki thing... they have a pretty aggressive cam profile and the valve shuts really hard. Over time they wear, when air filters pass dirt thru, it speeds up the wear.

94 suzuki 250 quad - decompression valve

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