Throttle action

C

chrissoz

Senior member
Location
Sydney, Australia
On one of my carbs 750 SF1 (i.e. 36mm Del O'rto) the throttle action is smooth until about half way open and then gets really stiff for a bit and then OK again. It was so bad that it caused the nipple to pull of the end of the cable (it was only the screw on type). To me it look like it is related to the pumper mechanism where it is forces up the little ramp. The other carb does not exhibit this issue.

Anybody seen this before/got any clues how to fix?

Thanks

Chris
 
Nipple was at the throttle end so did not go anywhere.

The little actuator buttons for the accelerator pump seem to take about the same amount of force to push on both carbs (so I don't think the accelerator pump mechanism is the culprit).

Everything else looks OK - I have put a dab of grease on the ramp for the pump actuator which has made no difference.

At the handlebar it just feels like you have hit the stop but the carb is only half open - to get it fully open need a bit of force.
 
Have a look at where the carby spring meets the carby top,is it seated into the recess.Maybe try the slide without it on the cable,push it up with a finger via the air filter end and see if its still restricted.
Same with the slide connected to the cable but not in the carby.At least you can then see if the carb body is the issue or the cable and twist grip.I am betting you have a twist or misss alignment where the cable connects to the slide. Doest take must to have it out of aline.BTW twin full length cables or is there a splitter
 
Have you tried taking both of the sliders out of the carbies an seeing how free everything is?

If still tight, it eliminates any slider to carbie interface issues.
 
My SF2 with split one into 2 cables had identical symptom. Happened when it got to operating temp and only when riding. I have pump arms removed and shortened springs. After going the new slide and greasing aligning route new nylon lined cables fixed it.
 
Think this is ok now - I was testing it by just pulling the cable end without assembling it into twist grip and could feel a step in resistance - but when assembled into the twist grip the extra leverage makes it much less noticeable. It must have been really nasty before to have felt so bad at the twist grip (and to the extent that it pulled the nipple off).

Waiting for correct length throttle cables and then it will get put back together and tested - seems like a bit of grease and polishing up the little piston thing on the accelerator pumps did the trick.

Thanks for the help.

Chris
 
I think the previous owner had not been able to get cables so they all had screw on nipples (except the brake cable!).

All being replaced.

Screw on nipples are OK for roadside repair until you drop the grub screw into the gravel!
 
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