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low compression

5K views 11 replies 8 participants last post by  Pete236uk 
#1 ·
Good day everyone, I have done a compression test on my bike a f650 gs 2002 and can only get 75 psi with no oil and 90 psi with some oil added ,I think I will remove the head and do a top end job . can someone help with a work shop manual ?

egbert
 
#2 ·
Hi Egbert,
plenty appear on eBay, copyright issues if some one points you to online version ?
suggest check valve clearances first, may save your self some work,
but sounds like rings/bore with oil increasing PSI,
 
#4 ·
The problem doing a compression test on an F650GS is that it is fitted with an auto compressor which reduces the pressure in the cylinder on start up. It's possible your measured pressures are ok. Before going too far, I would take off the valve cover, remove the decompressor and then try the test again. If you then get less than 150-180 psi, a top end overhaul is probably required.
 
#6 · (Edited)
Good day everyone I recently bought a f 650 GS 2000 model which struggles to start in the morning. I have to give it quite some throttle to get it running and have to constantly play with the throttle or to keep it alive or it will die on me I recently did a compression test and it showed about 35 psi ??...Is that even possible on a bike like this ? Considering I can still spin the wheel in second gear if I'm reving it and the bike still pulls really good. I also wanna add that it does have tons of oil in the air tank, about 200ml comes out when i drive about 50 km
 
#11 ·
The pilot screws get damaged when someone uses too big a screwdriver to adjust them. The threads in the carb get damaged and you have found the result.
You may be able to run a metric tap in there to fix the thread enough to get the screw out.
The same carburettors are used on quite a few japanese bikes. Suzuki 500 twin had them. I used to get my parts for the carbs from the suzuki shop as they were much cheaper. As were tappet shims.
I got sick of the twin carbs on my funduro and bought a bombadier Ds650 manifold, shortened it about 25 mm had it re welded and fitted it to the bike.
Then I used a carby off a DR650 ( mikuni BST40) on it and it was much easier to work on.
I also used a Keihin FCR40 carb on it later and it went really well. With a single carburettor the bike had more bottom end torque.
Pete
 
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