Not starting, tried almost everything

[westonpack]

I have a '91 FZR600 that refuses to run again. It sat unused for about a year and now it won't start up. The bike ran fine before I let it sit, and it has been continuously garaged so rain or pests are not a factor. I'm a very experienced motorcycle mechanic by the way and have done complete engine teardowns, so I am confident in my work. I have cleaned, synchronized, and tuned the carburetors completely, and I know that is not the problem. I get strong spark from all 4 spark plugs, valve clearance has been checked, and triple checked, and it is flawless. Initially, I found that I had low compression on the first cylinder so I removed the head and did a leak down test and found small leaks in the intake and exhaust valves. The intake valves were pretty worn so I replaced those, while the exhaust valves look like new. I lapped each valve on the first cylinder and there are no more valve leaks. I put in a new head gasket, fresh fuel, and checked the fuses. Everything cranks over fine like normal, but the engine won't rev up with or without the choke. If I open up the throttle fully, I get an occasional (but rare) backfire and some smoke out the exhaust pipe so I know I have spark since the fuel is being ignited. I am at witts end. My only next thing to check is the compression on each cylinder. If I can't get this fixed within a week or so I'll unfortunately need to sell it fully assembled for cheap. I just want to get it fixed and find out what the problem is. If I can't get it fixed is anyone interested in a parts bike or just interested in working on it? The body work is flawless and the fairings are without any damage whatsoever. I don't have time to part it out. Any thoughts on what to check next to fix it? Thanks,

[reelrazor]

I have a '91 FZR600 that refuses to run again. It sat unused for about a year and now it won't start up. The bike ran fine before I let it sit, and it has been continuously garaged so rain or pests are not a factor. I'm a very experienced motorcycle mechanic by the way and have done complete engine teardowns, so I am confident in my work. I have cleaned, synchronized, and tuned the carburetors completely, and I know that is not the problem. I get strong spark from all 4 spark plugs, valve clearance has been checked, and triple checked, and it is flawless. Initially, I found that I had low compression on the first cylinder so I removed the head and did a leak down test and found small leaks in the intake and exhaust valves. The intake valves were pretty worn so I replaced those, while the exhaust valves look like new. I lapped each valve on the first cylinder and there are no more valve leaks. I put in a new head gasket, fresh fuel, and checked the fuses. Everything cranks over fine like normal, but the engine won't rev up with or without the choke. If I open up the throttle fully, I get an occasional (but rare) backfire and some smoke out the exhaust pipe so I know I have spark since the fuel is being ignited. I am at witts end. My only next thing to check is the compression on each cylinder. If I can't get this fixed within a week or so I'll unfortunately need to sell it fully assembled for cheap. I just want to get it fixed and find out what the problem is. If I can't get it fixed is anyone interested in a parts bike or just interested in working on it? The body work is flawless and the fairings are without any damage whatsoever. I don't have time to part it out. Any thoughts on what to check next to fix it? Thanks,

Wow, I would have done the leakdown test BEFORE pulling the head..you know, the normal way it's done.

Slight leakage at one cylinder's valves? Slight bummer..not enough to keep the engine from running though.

I like the post title "Not starting, tried almost everything"...pretty accurate, but there is something easy being overlooked, or too much confidence is being put on basics.

Compression, fuel, spark.

Dust the carb mouths with ether while cranking, does it fire up? I am betting it will.

How do you "....cleaned, synchronized, and tuned the carburetors completely.." if it doesn't run?

Take the carbs to a pro, or at least re-visit your previous work...be especially noteful of the possibility that you switched the main jets and starter jets

[HybridSport600]

do a full tear down and clean the carbs, gas goes bad as little as a 30 to 60 days, and the longer it sits the faster it will tarnis the jet holes and possibly clog them resulting in no fuel to the cylinders. then check spark, and leave off the air fliter for these tests......let me know