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Runaway at idle

  • Thread starter Thread starter davidsbike
  • Start date Start date
D

davidsbike

Guest
Noob here with a 1978 GS750E project bike. I wanted to get the engine started just to see what I was working with and the bike ran surprisingly well for a machine that has been sitting for a LONG time.

When warmed up, the motor started easily and idled at a constant speed. I'd say it was predictable and reliable.

Fast forward a few days with no changes to the engine. I wanted to ride a few test loops after a master cylinder rebuild and fork seal replacement. Now, the engine wants to runaway. At startup, it's running 4K or more. I confirmed this was not a linkage problem. To see what was going on with the sliders, I removed the pods and started - the sliders are all bottomed out.

Where is the fuel and air coming from to make the engine run like that?
 
Did you have the "choke" engaged? :-k

If so, keep in mind that it does not choke anything, it is an ENRICHENER circuit that is somewhat independent of throttle position. It has its own fuel and air source, they are controlled by your "choke" control.

.
 
After it is warmed up and the choke is off, try setting it back down to ~1000rpm with the idle speed adjuster screw on carbs (near where throttle cables come in). If you cant get a steady low idle speed, the likely culprit is air leak at the o-rings on the carb boots, or at the boots themselves. The orings get flattened and stop sealing over time, the boots dry up and deform and won't seal. Make sure the clamps are tight around carb boots and check for leaks by spraying starting fluid around the boots by the engine. New boots and o-rings is pretty standard maintenance for these bikes.
 
Agree on the intake boots leaking. One of the most common of all GS problems.

Feel free to check the Newbie Mistakes thread linked in my signature to make you aware of some of the more common issues facing new owners. Also check this link for a service manual and whole lot more...http://members.dslextreme.com/users/bikecliff/
 
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