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Rebuild or part out?

  • Thread starter Thread starter DCgs450L
  • Start date Start date
D

DCgs450L

Guest
I have an 86 450L that idles fine, stalls under load (mild load) The right cylinder runs cold for a while and then heats up. Engine also clatters. New plugs, carbs need syncing but should be OK. There seems to be some backpressure on the carb as it pops and sputters through the airbox and I can see the carb push back slightly when it does this. I think I have a sticking intake valve. Can I fix this without pulling apart the top end? I am not a mechanic and am trying to avoid a huge job. She is a commuter (some rust, OK appearance, but not a show bike by any means) Should I part her out or attempt a rebuild? I can get a used, working head for far less than a rebuild, should I try that? Help!
 
You can totally rebuild the head without pulling the barrels off. You can even leave the engine right in the frame and pull the head off no problem. Do a compression test and see what that tells you.
 
I am mechanically inclined enough to be willing to learn, but I was worried about having to pull the engine out to do this. If I can do it in the frame I will try it. I read the workup on compression testing, so i will run the extra test to see if it is valves or rings. I found a head (with valves but minus cams) with only 4500 miles on it. Looks clean as anything, so I was thinking about swapping the heads if I could do it without pulling the whole shebang out of the frame. The bike isn't worth much but I have spent the last year fixing her up and I would hate to scrap it now.
 
Go for it, especially if you already have the "nice" head. The GS450 is a breeze to work on compared to lots of bikes. My CB750 had blown a head gasket. I had to take the engine out of the frame to replace the gasket - you won't need to pull the engine, just the head.
By the way, don't assume the head needs to be removed yet. Check compression (as you mentioned) and all the other obvious stuff (like valve clearances, coils, leaking intake boots, etc.) first.
 
passed compression test

passed compression test

So I did a compression test last night, got 120psi from the left and 135psi from the right. Both held that pressure for 5 minutes. The right cyl is the one running cold. Also the right plug was carbon fouled, but still firing. The left plug was fine. I replaced the right plug, started her, and problem still happens. Obviously I don't have a valve stuck open, could one be stuck closed, or is this most likely an issue of fix the damn carbs and she'll run right?
 
Yup, fix the carbs and you'll likely be fine.

The clattering and rattling is likely because one cylinder is not producing power, so there are some large variations in cranks speed. If the carb problems is corrected and the carbs are synced, this will smooth out.
 
Yeah!

Yeah!

Thanks, everybody! Some simple advice kept me from tearing the engine apart to foul up what wasn't broken.
 
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