New Throttle Adjustment - Always Accelerating

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Cyclin

Cyclin

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Jul 4, 2011
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Hi guys!

SO I recently installed the SBP upgraded throttle and now my engine is constantly accelerating. After some searching on the forum I discovered their may not be enough length in the throttle cable. The tips I found were related to installing on RT carbs, but I am unsure if this carb fits that criteria. I bought this build off a local rider and I have not seen this model carb before.

When viewing the carb with the air filter off I see I can achieve WOT, but at resting position it still has some space open at the bottom, allowing fuel to keep pumping in even when the throttle is disengaged. The bike smells as if running too rich now. The engine ran and idled very well before the new throttle+cable.

So my question is, how can I adjust this throttle cable to fix my problem? Thanks for any and all help, and I included pictures of the carb installed on my bike below.

 
crassius

crassius

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Sep 30, 2012
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check the adjustments at the handlebar - the elbow should be threaded up into the mount with just one thread showing below the nut - the other can be set to show no threads

if all else fails, you can remove 1/8 inch or so from the stops of the throttle grip
 
Cyclin

Cyclin

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Jul 4, 2011
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crassius said:
check the adjustments at the handlebar - the elbow should be threaded up into the mount with just one thread showing below the nut - the other can be set to show no threads

if all else fails, you can remove 1/8 inch or so from the stops of the throttle grip
Click to expand...
Perfect! Thanks so much bud. Was able to fix it in under 2 minutes. One thing I noticed was that it wasn't coming down because it was getting stuck on the idler screw pin. I know this is a complete noob question, but when I re-assembled the carb did the side of the cyclinder ( i think its called the throttle valve) with the groove need to be in a certain position? Away from the idler screw perhaps?
 
2door

2door

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Sep 15, 2008
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Your carburetor is the venerable old NT. The best, in many's opinion.

If the cable is too short and not allowing the throttle slide (barrel) to completely return to the idle position maybe there is enough adjustment at the twist grip where the cable enters it. Turning the adjuster inward will give you a little more cable. If you don't have any adjustment left you might be faced with needing to get a new cable. It is doubtful there is enough to resolder the stop on the carb end.
I see you have no adjustment at the carburetor so that option is not there.

How much space is left at the bottom of the slide when you release the twist grip? There will always be a little. It should not close completely. 1/8" to 3/32" is about normal. Also that screw with the little spring under the head is the idle speed screw. It screws in to increase idle speed and out to decrease it. Have you tried that?

Also, a fast idle is a symptom of an air (vacuum) leak somewhere in the intake ciucuit. A poorly sealed carburetor or the gasket between the manifold and the cylinder can cause you fast idle issues.


One unrelated suggestion is to get rid of that spring that is on your clutch cable. It serves no purpose but to make the clutch harder to pull. The bigger spring is a heat shield and should be there. It goes over the cable housing and usually lays against the cylinder cooling fins.

And what is the cable zip-tied to the clutch lever? That shouldn't be there.

Tom
 
Cyclin

Cyclin

New Member
Jul 4, 2011
118
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California
2door said:
Your carburetor is the venerable old NT. The best, in many's opinion.

If the cable is too short and not allowing the throttle slide (barrel) to completely return to the idle position maybe there is enough adjustment at the twist grip where the cable enters it. Turning the adjuster inward will give you a little more cable. If you don't have any adjustment left you might be faced with needing to get a new cable. It is doubtful there is enough to resolder the stop on the carb end.
I see you have no adjustment at the carburetor so that option is not there.

How much space is left at the bottom of the slide when you release the twist grip? There will always be a little. It should not close completely. 1/8" to 3/32" is about normal. Also that screw with the little spring under the head is the idle speed screw. It screws in to increase idle speed and out to decrease it. Have you tried that?

Also, a fast idle is a symptom of an air (vacuum) leak somewhere in the intake ciucuit. A poorly sealed carburetor or the gasket between the manifold and the cylinder can cause you fast idle issues.


One unrelated suggestion is to get rid of that spring that is on your clutch cable. It serves no purpose but to make the clutch harder to pull. The bigger spring is a heat shield and should be there. It goes over the cable housing and usually lays against the cylinder cooling fins.

And what is the cable zip-tied to the clutch lever? That shouldn't be there.

Tom
Click to expand...
Thanks Tom,

Looks like I was able to adjust, but the reason my adjustments weren't changing anything the other day when I was trying to adjust is because the slide was setting down on the idler speed screw. I backed that out and it closes completely now. Should I re-adjust to have the little space at the bottom you mentioned? If so, what is the "optimal" space I should leave there?

The way I understand the idler speed screw is that the pin at the end pushes up the barrel slide to open it up the farther its screwed in. Is is possible that I just set the barrel slide in there incorrectly? On the bottom of the slide I notice there is a 45 degree section opposite the cable groove, should this slanted side be where the pin idler speed screw sits?

I just unclipped the zip-tie and moved that cable you mentioned. I had not even noticed it upon buying the bike but that is the cable running to the rear wheel brake. Thanks for the tip
 
2door

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
Cyclin,
You are absolutely correct about how the idle speed screw works. It simply blocks the slide open a little to provide enough air/fuel for the engine to idle. You can adjust it to set the idle speed that pleases you. I like to get mine as slow as possible. There really is no optimum distance to see it open. Those figures I gave were just ball park measurements.

The slide, or barrel, has a long groove on one side and a short one on the other. The short groove is the ramp that the idle speed screw engages. The longer groove aligns with a guide pin that protrudes into the barrel bore. It is on the right side, looking down at the carb.

Hope we helped. Have fun and ride safe.

Tom
 
Cyclin

Cyclin

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Jul 4, 2011
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California
Thank you both so much. Not only did you help me fix my problem, you helped me understand more how this section of the carb functions.

So not only did you help, you made my day!

Thanks again :) ,

Ben
 
2door

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Cyclin said:
Thank you both so much. Not only did you help me fix my problem, you helped me understand more how this section of the carb functions.

So not only did you help, you made my day!

Thanks again :) ,

Ben
Click to expand...
Thank you, sir. It's why this forum was created.

Tom
 
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