Cleaned carbs - how to perform the idle drop procedure

WillemVanKatwijk

WillemVanKatwijk

Joined
Nov 11, 2024
Messages
21
Age
64
Location
The Netherlands
Bike
ST1100S
Now, finally I cleaned the carbs, replaced most (rubber) gaskets and I put the carbs back on the bike. Pilot jet screws were on 2,25 turns from fully closed (loosely tightened).
It starts so I'm quite happy. However it runs on 2,5 to 3 cylinders and I need to keep the throttle by hand otherwise it drops off.
I thought I need some more cleaning so I removed the carbs again and made sure the pilot holes are all clean and tested it by spraying carb cleaner into the pilot jet screw holes and watch carb cleaner comes out all holes. All 4 carbs are checked that way.
The pilot jets screws are all at 1,75 turns from fully closed (loosely tightened) now and (again) the bike won't start.
This leaves me to think that the pilot jet screws are not enough opened. So the idle drop procedure kicks in I'm afraid.
Therefore I have some questions to this knowledge base and hope to receive some answers. :cool:

1. How to perform the idle drop procedure with all carbs on the bike and have it run until it is warm?
2. Do I need 4 of the special tools to turn the pilot jet screws? It's awful difficult to do the procedure with only one tool as there's no place on the bike to move the tool from one carb to another.

I'm starting to get the screws back to 2,25 turns from loosely tightened and then let the bike run for 5 minutes and check the (new) spark plugs for signs of lean or rich mixture and do the procedure over and over again until it satisfies me ;)

The problem I have with this approach that I need to remove the carbs all the time to change the pilot jet screws. Is there a better way to perform the idle drop procedure?

Thanks to all you knowledgeable people who want to help me with this endeavor!

Best regards and thanks,
Willem.
 
It is some years since I had my 1100, but I did work on the carbs A LOT because it had been stood for 10 years. I considered idle drop but as you point out, getting the tool to reach the screws is really difficult, so I left my rebuilt carbs at the standard screw position.

I think the difference in pilot screw opening between the rest of the world and the US is that the US uses leaner low speed jets so the pilot screw needs to be opened more to offset that.

If your bike runs on 2-3 cylinders unless you open the throttle, I would suggest you still have some partial blockage of either the low speed jets or the internal passageways in the carb. The low speed jets have awfully small bores and are difficult to properly clean.
 
Just as a comment based on what I have read;
Martin, from Martin's ST1100 website, states that most people set the pilot screws to between 2 and 2 1/2 turns out and never bother with the idle drop procedure.

Adam (@afrymoyer) seems to have a lot of ST1100 carburetor knowledge and experience. Maybe, if you are lucky, he will chime in.
 
Al st1100 said:
need to sync them first, if they are out of sync it doesn't help playing with the mixture screws.
Click to expand...
Yup... and since one interferes with the other quite a patience game... like when you tweak #2, #1 & #3 are off, and vice versa, etc, etc...
I normally need about 3, sometimes 4 runs till I find it running to my satisfaction...
Plus I place two large office fans in front of the bike providing cooling/airflow, cause otherwise the mixture "enriches" and the engine starts to run like crap...
Andrew Shadow said:
Martin, from Martin's ST1100 website, states that most people set the pilot screws to between 2 and 2 1/2 turns out and never bother with the idle drop procedure.
Click to expand...
Ditto, (2 1/4 on mine) and to even notice the +/-50rpm drop mentioned one would need a digital tachometer to begin with...
 
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