85 LT250F won't fire after valve job
 

I did a valve job on my old 250 Quadrunner. I have good spark and compression. I put a tank above the carb to gravity feed fuel into the carb. It won't fire at all. I sprayed starter fluid into the air box toward the carb and still nothing. I wonder if I have spark on the exhaust stroke. How would I check to make sure my timing is correct. I used the Clymer manual to step thru assembly. Thanks for your help forum members!

If your not sure on spark,just have the plug in the cap against the cylinder and crank the engine over.Should have a good spark. If not retrace your steps.Could be a simple coil wire loose.

"I have good spark."

Well that's one thing out of the way.. If it wont at least try to bust off with starting fluid then you do need to retrace your steps on cam timing,etc.

I have too good of compression for the cam timing to be off. I double checked that when I assembled it. But I don't know if the ignition timing is 180 degrees out of phase. I didn't mess with any of that directly. I set the piston to TDC and aligned the mark on the flywheel when I set the cam timing.

Not that familiar with the LT,but should have the tdc mark on the flywheel and the cam sprocket should have timing marks on it that usually align with the head. Some have different marks and set differently. Just go by your manual on this. Plus lobes should either be pointed down or away from the rocker arms at tdc and rocker arms should be loose. This is where valve clearance is checked/adjusted.

Yes, all that was done at assembly. I'm just wondering what triggers the spark at the end of the compression stroke instead of at the end of the exhaust stroke. I don't see any sensor on the cam. Because I'm not getting a pop, I wonder if it's sparking after all the fuel has been expelled. I know some four strokes spark at every TDC of the piston. What else can it be besides ignition timing way off? Even if my timing light will light up the timing mark under the plug it's not verifying that it's firing on the correct stroke.

I'm not familiar with the LT250F either, but the last bike I know of to have the ignition tied to the stroke was the 200cc Honda. All later quads have the trigger coil outside the flywheel, and spark at both TDC on the compression and TDC on the Exhaust stroke. This is known as the "dead spark" system.

Have you actually done a compression test? Even with starting fluid, the air/fuel ratio has to be close to being right, if compression is OK, clean the carb out, and check fuel is getting to the float bowl.

It's running! Sort of. But at least my mystery is solved.

The reason it didn't fire is because the carb flooded gas into the cylinder before I could crank it. It's leaking out the float so there must be a needle/seat issue. I'll open up the bowl and see what's going on. But at least it's running now.

Thank you both who contributed to this forum help session. Happy Easter! :D

Parts are bound to be worn out in an old 33 year old carb.Mainly the needle valve and seat if replaceable on this old one. Rebuild it so you don't have to go back into it if setting the float level,etc doesn't work.https://www.ebay.com/itm/Suzuki-Carb...Nac6pj&vxp=mtr