Hesitation at speed after engine rebuild

[ianralph]

I've just completed a major overhaul of my 79 GS1000S including having the head rebuilt, a rebore with new pistons and rings. I have given the carbies a good clean and replaced the inlet manifold O rings.

It starts and runs well with lots of power. After it's first long day on the road I was returning home at a sustained 110km/h (about 70mph) and it started to hesitate slightly. As I rode further the hesitation got worse, but at no stage did I have to stop. The oil temp gauge was at about 100 deg C.

When I open the throttle, while it is hesitating, it pulls away cleanly.

It will run at lower speeds without any hesitation.

The plugs are new and the colours indicate a good mixture at this speed.

Any suggestions about what to look for?

Thanks

Ian

[Nessism]

Sounds lean. The plugs may look good overall but you could still have a lean condition in a specific location in the powerband. Did you change the exhaust or intake while rebuilding?

[Steve]

I will tend to agree on the "running lean". Assuming there were no other changes during the rebuild (pipes, pods, etc.), double-check your valve clearances, then your carb float levels. It might be as easy as raising the fuel level (decreasing the measurement while they are open and upside down) about a millimeter.


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[ianralph]

Thanks to both of you for your replies - I'll check the valve clearances and the float levels and let you know how I go.

Ian

[ianralph]

Bingo!

Pulled the carbies off to check the float level and found that the pilot jet was blocked. Cleaned it up and it is running much better now.

I do hope I never have to pull those carbies off again in a hurry - correction, it's the putting them on again that I hate.

Thanks for you help.

Ian

[bwringer]

Pulled the carbies off to check the float level and found that the pilot jet was blocked. Cleaned it up and it is running much better now.

I do hope I never have to pull those carbies off again in a hurry - correction, it's the putting them on again that I hate.

Thanks for you help.

Ian

Cool! I love a happy ending.

If the carbs are hard to remove/replace, you might want to put new carb boots on your wish list pronto.

[Nessism]

Good job on finding the problem. Hopefully it was not due to contamination inside the tank. If so, you may have to do the sealer job.

[SqDancerLynn1]

I usually run some seafoam cleaner thru the carbs every 4-6 months regardless.