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Discussion Starter #1
Hi everyone.

I came upon a 2004 HO 1100c that has been sitting for a while and I'm trying to get her running. I replaced the battery, spark plugs, and changed the oil/filter, syphoned out most of the gas (until I got the low fuel indication) and refilled it with 93 octane. Before I syphoned the gas, she seemed to at least crank fine. I change the gas out and now she seems to turn over real rough with a start-and-stop jerk, almost as if I was intermittently hitting and releasing the start button. Not exactly sure where to go from here. Any help would be appreciated
 

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You need to talk to Ernest T, he is the goto guy for Yamahas. If he doesn't see your post send him a PM.
 

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If it has been sitting, could be a host of problems. From your description I'd worry about a piston ring corroded into place or some other related problem. Pull the plugs and see if it is still rough turning over. Check to be sure you are getting spark. Be sure the pump is clear and that the impeller is not rubbing the housing. Check the compression on each cylinder while you have the plugs out (164 psi is the recommended minimum with no more than 14 psi difference between cylinders).
 

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Discussion Starter #5
Limited by time/tools available tonight, but I got spark on all the plugs, and I don't seem to get any turnover issues with spark plugs installed but unhooked. As soon as I connect the wires I get it. took the intake grate and the surrounding shaft covering off and there isn't anything lodged, but there is some spots of light rust on the impeller and a score pattern on the impeller housing that to me kind of resembles what a brillo pad or crocus paper might do to a finished copper/bronze surface, my gut is that this isn't my hold up because it is uniform around the housing on 2nd look. Will be doing compression checks tomorrow when I can get the instrument, and I have a feeling I'll learn some real info then.
 

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Will be doing compression checks tomorrow when I can get the instrument, and I have a feeling I'll learn some real info then.
The numbers I gave you for the compression are for a warm engine (164 psi minimum. Ideally 185+ would be good warm). Expect the numbers to be lower with it cold, but they should be resonably close for each cylinder. Now that you know you have spark, you might want to take a look at the fuel injectors. There is a little screen on each injector that can catch debirs. Not a bad idea to disconnect the injectors to keep gas from going to the cylinders while you do the compression test.
 

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Discussion Starter #7
I did compression checks, and while my numbers are higher than what you indicated (210 for the good ones), one cylinder read about 90. Safe to say I've found the culprit. Is there anything else I can do to narrow down my field of problems from this point besides just tearing it down and looking?
 

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My guess is a piston ring is corroded in place. You will need to check the cylinder for potential scoring. Unfortunately, you will have to pull the engine to fix it, so you will have the chance to look around to see if there are any other problems. Don't know of any short cuts at this point. Good Luck!
 

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Discussion Starter #9
Thanks for all of your help Ernest. I guess the silver lining is I've been looking for an engine repair to get my hands wet so to speak. Thanks for stepping through the process.
 
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