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GS 1000 CV carbs hesitation around 2500 rpm

J

John Kat

Forum Sage
I recently added a 4 into 1 exhaust on my GS 1000 ST and since then, the engine will hesitate when accelerating ( slowly) from 2500 rpm.
The problem seems worse when the engine is hot.
The bike will also not take full throttle below 6000 rpm but pulls strongly to red line.
The idle runs perfectly.
The bike is equipped with Dynoman pods, Dynojet stage 3 kit and Jama exhaust.
The hesitation remains with a Kerker 4 into 1 exhaust.
Main jets are 147.5 ( Mikuni size) then 142.5 ( no change) and needles in 3rd position from top.
When needle was in 2nd position hesitation was much worse and stopped only above 6000 rpm.
I suppose, I will have to try the needles in 4th position ( i.e.richer)?
Any suggestion?
 
My only suggestion would be to tell us what the throttle setting is when you are experiencing your problem.

Engine RPM does not have nearly as much to do with problems as the actual throttle opening.

Example: sitting in neutral on the centerstand, it does not even take 1/4 throttle to hit the red line.
Or, you can be in fifth gear at 20 mph (which is less than 1500 RPM), and hit full throttle, trying to go faster.

.
 
Steve said:
My only suggestion would be to tell us what the throttle setting is when you are experiencing your problem.

Engine RPM does not have nearly as much to do with problems as the actual throttle opening.

Example: sitting in neutral on the centerstand, it does not even take 1/4 throttle to hit the red line.
Or, you can be in fifth gear at 20 mph (which is less than 1500 RPM), and hit full throttle, trying to go faster.

.
Click to expand...
Yes, I should have mentionned that:confused:
The hesitation occurs at 1/4 of throttle opening.
 
I've read most of the litterature including of course the Dynojet documentation:cool:
Clearly at 1/4 throttle opening, it should eitheir be the needle or the pilot jet?
The issue is always is it too rich or too lean?
Given that the bike can't take wot until 6000 rpm does this mean too lean?
I've now moved the needle up to the 4th position and I'll try again tomorrow if it doesn't rain?
 
Isn't the 4th position the one that is recommended by DynoJet? :-k

Keep in mind that it's the 4th position from the blunt end of the needle, not the pointy end. :o

.
 
The reason I asked is that Mikuni CVs are tuned from the top down, you must get the main jets perfect first, then the jet needles and all of the others. The fact that you are still swapping mains from 142.5 to 147.5 tells me you haven't done this yet.
 
tkent02 said:
The reason I asked is that Mikuni CVs are tuned from the top down, you must get the main jets perfect first, then the jet needles and all of the others. The fact that you are still swapping mains from 142.5 to 147.5 tells me you haven't done this yet.
Click to expand...
Many thanks, I didn't know about this:o
The reason, I downsized the main jet was because the spark plug electrode (?) has a nice brown color but at the thread's edge there was some black soot.
I felt I wasn't far off on the main jet as the bike pulls very strongly above 6000 rpm ( at wot) but I just wanted to make sure I was spot on.
FYI, there is no smoke coming out of the exhaust at any time.
If it still doesn't work tomorrow, I'll do a roll on test on the dyno and monitor the AFR.
 
Presume your ignition system is ok? Had similar symptoms on a 80 1000G that turned out to be the ignitor box... :)

What is it they say... about 80% of carb problems are ignition related ;) :D
 
salty_monk said:
Presume your ignition system is ok? Had similar symptoms on a 80 1000G that turned out to be the ignitor box... :)

What is it they say... about 80% of carb problems are ignition related ;) :D
Click to expand...
You are right but I didn't have this symptom with the original exhaust:cool:
 
It worked:D
I tested the bike this morning with the needle on the 4th groove and I have:
ZE canyon carver:dancing::dancing::dancing:
As much as I don't totally trust my std GS 1000 S this bike is a delight to ride in the fast twisties.
Here's a picture "as built"
Thanks for the support!
LalandusseetGS1000XP003_zps49c9efb1.jpg
 
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