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1986 gsxr750 low compression & smoking


johnnyboy

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Posted

Hi, just got a project bike running and it's smoking a little. I thought I'd wait until it's ridden to see if the smoke clears to indicate stem seals or valves.

In the meantime I’ve checked my compression and it’s reading 105-110 across all 4, the manual says it should be 142-199 and that 114 requires attention (*crap). The apparent test to see if the issue is rings or valve related is to put a teaspoon of oil in, which I did in number 1 and the figure went up a little to 120.

Does this sounds like rings or valves or maybe both? I guess I can refurb the head but then idea if all that work and reassembly to find out it’s still low sounds 
like a pain…

Thoughts?

 
 
Posted
41 minutes ago, johnnyboy said:

Hmm, thanks. It’s only done 15km (apparently), is that typical or pointing to heavy thrashing or poor maintenance..? 

has it been sat unused for a long time ? 

  • Like 1
Posted
1 hour ago, johnnyboy said:

Possible, it’s a jap import so could have been sitting for a year or more… thinking you’re going to say gummed up rings? If so I like the idea… 

yeah go for the easy/cheap option first you might just get lucky !!!!  ive seen people put oil in the tank to help keep the inside from rusting when laid up for a long time, if it was mine i would wash the tank out and fill it with fresh fuel ( plus an oil change might help), then run it till the tank is empty and see if the burning oil has stopped.  if thats the real mileage then you might get lucky ??? if not it'll be a top end strip :(

Posted

Could be gummed up rings or it could be glazed bores from never been ridden hard enough! I bought a 7,000 mile old bike that was 20 years old and it always smoked for a good 5 - 10 minutes on start up - never got any better in 25k miles - eventually got so fed up with it, I replaced all the rings and completed an Italian tune up - never smoked ever again!

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