Motorcycle Repair: Power loss, suzuki gs 650, valve adjustment

Question
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Followup To
Question -
Christopher,

I have a 81 Suzuki GS 650, ive had it about 4 months and as far is i know it was working fine.

Over the past few days, ive notice significant changes in the way it performs.

First off, when i used to start it, i pulled the choke back all the way and id rev at ~3500 rpm,
now, i can barely rev over 1300 with the choke on at any position, even with motor on.

Secondly, there is significant power loss. I dont race the thing, its just a work vehicle, but when i start from zero and go, the bike will chake for a bit till it catches speed, then it feels fine, it does this in all gears. If im driving and pulling back on the throttle i dont get a jump in power, i can barely feel any difference compared to before.

I suspect its a fuel problem, im no mechanic and its my first bike. I checked the fuel line and didnt see a leak. The bike has 4 carbs and i got a receipt when i bought it saying the 2 outside carbs needlevalves were changed. I hope its only dirt or something.

Please send me your opinion,

Thank you so much for you're time.

Jonathan
Answer -
Hi Jonathan.
 There are a few things to check here.

1)  Valve adjustment and timing.

2)  Carb synchronization.

3)  Air filter.  Is it due or overdue for replacement?

4)  Oil and oil filter.  Are they due or overdue for replacement?

5)  Ignition timing.

6)  Spark plugs.  What are their condition?  Are they blackened (bike is running rich), whitened/burned off (running lean) or normal looking?

DO NOT ADJUST THE CARB MIXTURE.  That is set at the factory, so leave it alone.  Besides, adjusting the mixture will not fix the problem.

Check those and let me know what you find.
Good luck.
FALCON


The air filter was cleaned out a month ago and looked fine, its just a foam sleave.

I checked the sparkplugs and 3/4 had whitened tips and 1/4 had a tip that looked fine, but may have been blackened.

What do i do to fix the bike if it running lean, that looks to be at least 1 of the problems i have.

I changed the plugs and the bike ran the same (badly) as b4 i checked them.

Thanks

Answer
Hi Jonanthan.
 It sounds as if the bike has either had the mixture tampered with, the carbs need a very thorough cleaning, the manifolds or connections are leaking air or one of the coils may be having problems.

 Check the intake manifolds for dry-rot (small or large cracks in the rubber), tight and correct fit to each carb as well as a secure fit to the head.  If any have any of these problems they will likely be on the two cylinders that have burned up their plugs, but check them all to be sure.  In the case of dry-rot, replace the manifold.  There is no other fix for that.

 The repair manual has the test specs and proceedures for the coils.  Test them both before you try to replace either of them.

 If the bike has spent any time in long-term or seasonal storage, then pull and properly clean the carbs.

 If the mixture has been tampered with, then it will be obvious as the caps that cover the mixture screws will have been removed.  Best to let a factory certified mechanic adjust them in the shop if this is the case.

 I don't recall any bike that came with foam air filters before '86 or '88.  And all of those were dedicated racebike replicas.  Double check with the manual to see if the filter you have is the recommended one.  They were usually paper filters.

Check those things.
Good luck.
FALCON