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  1. #1

    Broken Reed?? Engine techs please look

    04 GP800R... Could a broken reed cause only one cylinder to starve for fuel, or would it typically effect both cylinders? (saying for instance the rear cylinder is running lean, and a possible broken reed near that carb) Both carbs were just cleaned and rebuilt so I know it isn't that.

    Here's what happend. You all may have remember my post two weeks ago about my ski starving for fuel and me almost torching my motor. Well today I was out running it pretty hard and it ran great for about 15 minutes then all of a sudden it bogged and died. Restarted it and it ran like crap. Towed it in, no compression on rear cylinder. Rear cylinder torched. I will be opening everything up tomorrow. Normally I would just chuck it up to damage from the original fuel starvation/seizing, and go ahead and throw a new piston in there and get the cylinder replated. However, when I was taking the ski apart originally to rebuild the carbs and put the waveeater clips in, I noticed that the rear cylinder wasn't painted black like the rest of the motor. Definitely was replaced at some point, I'm wondering if I stumbled upon a reoccurring issue with this motor that possibly wasn't fixed the first time around before I got it.

    The first time 2 weeks ago I had fuel starvation, it started acting up 15 minutes into hard riding in the inlet, jumping waves, etc, exactly like today. When I rebuilt the carbs the rear cylinder carb had a broken check valve disk, so I thought that was probably the problem. I didn't check the reeds, however obviously this was a big oversight since I was right there and should have. Also, when I pulled the plugs today the rear cylinder plug was dry, front one looked normal (however I don't know if this is a symptom of running for a handful of seconds with no compression or something). I have put probably 3 hours on the ski between the original problem, and today but it was all more or less trolling and short throttle hits. Also it did kind of seem like it was heat seized a bit after it quit the first time today, but I thought then that maybe some of the pieces of the rings or something got lodged between the cylinder and piston or something, but the more I'm thinking about all of this I'm wondering if it could have been fuel starved again.

    Also, it could have just ran lean because of the low compression and incorrect fuel mixture due cylinder/piston ring damage and blowby correct? If you look at my original post that cylinder was down 5 psi from the day before after the original issue, and the ski was idling very low, (it wouldn't idle actually, I have been trying to turn the idle adjustment screw but its really tough to get to) I did a search and found a post that said low compression can cause poor idle because of the compression blowby on the rings.

    I really don't want to rebuilt the top on this thing and have it grenade again because of some sort of other issue. Opinions and advice much welcomed.


  2. #2
    Banned User
    Join Date
    May 2006
    5 psi is nothing as long as it 90 or better it will run fine on that cylinder. Broken reed petels make an einge run rich as the carb gets a signal coming and going. If it bad it wont run right at all. they all leak some. I would pressure test the motor and look for a bad real seal. carbs are the last thing to seize a motor in most cases and the first thing everybody rebuild,unless someone let fuel sit along time. U can mahe your own kit I use old oil juges to make seals for pipe and carbs. Any major leak will cause this problem, looks to be at the rear.

  3. #3
    Thats Rocketman. The 5 PSI drop was after my original problem last weekend. Now its like 20 psi so its definitely gone. Do you have any pics of your pressure testing setup?

  4. #4
    Also are there any good threads for the pressure testing procedure or is it in the service manual or?

    Rocket, your saying it could be one of the rear oil seals? Or perhaps the guy reused the base gasket on the original rebuilt or something and its leaking at the bottom of the cylinder? I didn't see any other crankcase gaskets/seals.

    Edit- After looking at the service manual I see the crankcase splits so it could be leaking from the seam... that sucks if it is.


  5. #5
    mudslanger's Avatar
    Join Date
    Jul 2010
    Huntsville Al
    It sounds like it lean seized and if it happened like that before you may have a cracked cylinder. even if you sent it to be renicked they could have missed it from previous build. before you send it off again you should pressure test the water jacket.

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