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Suzuki FSM for my '81 gs1100ex -- wrong on compression test?

  • Thread starter Thread starter RipRoaringFun
  • Start date Start date
R

RipRoaringFun

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The compression test in the Suzuki fsm as described on pg. 7-9 (the file is down-loadable from this site, filename is "80-83_GS1100T-LT-EX-1000SZ-EZ-SD-ED-ESD.pdf") -- the compression check procedure there says nothing about yanking the carbs.

Yet when I follow that procedure ("motor warmed up, all plugs removed, open throttle fully wide open") I get 90psi in each bore.

That's 10psi below Suzuki's 'service limit' of 100psi. But there's just no way that 90psi is correct, I have tons of power, and no oil burning.

Is the manual wrong? I'm thinking to pull the carbs and check it, I think the fsm procedure leaves that step out. The stock CV carbs are probably not opening fully.
 
The problem is that opening the throttle on a CV carb when the engine is not running opens the butterfly valves, but does not raise the slides. Those are opened by vacuum, and you don't have any with the engine off.
That procedure would be correct for the older VM slide carbs.
 
I get 150 psi+ with just the butterflies open, on a warm engine:cool:
maybe your valves neeed adjusting
 
Cam overlap, elevation, cranking RPM, gauge calibration, and a lot of other factors effect the readings. If they are even and it runs correctly, be happy. Gearhead is right, tight valves is one of the factors, and so are burnt valves caused by running them too tight...
 
I did the compression test before doing a valve adjustment. I just finished the valve adjustment today and capped her off with a new valve cover gasket.

The reason I wanted to do a valve adjustment was -- hard to start. Once it was warmed up, no problem. But I read in the forum that hard-starting can be a sign of valves needing adjustment.

So every single valve was way out. Out of all the tappets, on only one of them could I slip my thinnest feeler gauge leaf, which is .0035mm, between the tappet and the valve pusher (whatever they call that). The others did not even have enough clearance at the 'T' marks for that thinnest leaf, .0035mm.

I had to adjust every valve tappet, they were all WAY out of spec. So based on what you folks have said about the valves affecting the compression test, and it makes sense too, if the tappets had too-small clearance that means the valves were staying open too long -- I'm now looking forward to re-doing my compression test.

I guess this can also explain why the compression can be so low yet not burning oil -- the source of low compression isn't the piston/rings/bore so no blow-by.

Thanks, I'm looking forward to easier starting and re-running my compression test.
 
Adjusting the valves is one of the most important maintenance tasks on the bike and neglecting them will result in both valve and seat damage - burning. Hope your engine is okay.
 
Nessism said:
Adjusting the valves is one of the most important maintenance tasks on the bike and neglecting them will result in both valve and seat damage - burning. Hope your engine is okay.
Click to expand...

I bought this bike 4 weeks back or so and one of the reasons the previous owner was selling was -- 'it's really hard to start.' That led to me checking the valve adjustment.

I may have gotten lucky despite the guy's lack of attention to required maintenance as the bike is quite strong. However, I'm pretty freaked out how out-of-adjustment they were.
 
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