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Choke Cable Woes


DrMikey

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Last week I sync'd the fuel injectors ('03 RT). Mid and high speeds are pretty smooth. When starting cold on the other hand, it runs rough. I looked closely at the throttle bodies, and noted that they don't open up the same amount when the choke lever is on. With the choke off, everything is fine- they open equally.

 

Is the place to look for the problem in the "cable box" under the ABS modulator? Will it slide out without disconnecting the choke and left throttle body cables?

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It doesn't make any sense that the throttle grip operates the bike right and the choke lever doesn't because of the way the cables pull the short cables going to the throttle bodies. The short cables get pulled by the same round disc no matter how they are opened.

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Morning DrMikey

 

You really need to go back over your Throttle Body balance (especially IF you moved any adjustments when you last did it)

 

Something is not right with your TB balance IF the choke use opening is off but the twist grip opening WAS OK.

 

Possibly the R/H cable wasn't seated in the TB furrel when you did your TB balance or something wrong with your balance gauges.

 

Start out with choke OFF & by by verifying that BOTH side throttle cams lift of their idle stop screws at the very same time. Then verify that both side TB cams hit their wide open stops at the very same time.

 

Once the above is verified then just a minor adjustment should get the above idle TB balance right.

 

Once the TB balance is set then go back & verify that both side TB cams lift off the idle stop screws at the the same time & that both side TB cams hit the wide open stops at the the very same time. (if they don't then look for a valve issue, or a balance gauge issue, or something in the camshaft timing, or something loose or wrong with the throttle shafts or throttle plates).

 

Where are the BBS screws set (turns out from seated) on each side?

 

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The way I understand it, the injection system has (at least) 7 variables: Left and right Idle stop screws, throttle cable (sync) adjustments, and BBS adjust screws; and the single handgrip free play adjustment. On paper, the free play should affect both injectors the same, so it shouldn’t be a variable here. Yet, when I added some slack at the twist grip, the choke cable effect on the TB's almost equalized.

 

So, if we eliminate the main cable, there are 6 variables. Solving a system with 6 variables requires 6 equations. In this system, we have absolute idle speed (1050-1100 rpm), plus the condition left throttle idle = right throttle idle. Ideally, we should be able to set each to absolute nil, with the butterflies fully closed when the idle screws are backed out to butterfly closure, just touching the pin on the throttle cams. This solves two equations. If the idle stop screws are each turned in the same amount, the equality should still hold.

 

The cable adjustments could be similarly set, using the adjustment at the furrells to get both to “lift off” the stop screws simultaneously. Two more equations are now solved.

 

The remaining two equations, as I see it, are low speed right = low speed left, and high speed right = high speed left. The first can be set with the BBS screws, the second with the adjustment at the right furrell.

 

My method for this would entail backing out the idle stop screws until I knew both thottle butterflies were just closed. The throttle cables would also be checked to ensure there was no tension. If the initial adjustment can be made with the intake manifold disconnected from the airbox, I am assuming the butterflies could be visualized. Then, using a piece of paper, the idle stop screws could be brought back to just close on the throttle cams. Next, each set screw would be turned inward a fixed number of turns to get the idle approximately set. Then, using the paper gauges again, set the throttle cable adjusters to lift the throttle cams off the set screws simultaneously. Warm up the bike, use the BBS screws (which are set initially 1 and ½ turns out from fully CW) to even out the idle. Then, use the right side cable adjuster to get the higher speed sync.

 

Now, everything I have read to date tells me to leave the left side (and both idle stop screws) alone. I am probably overcomplicating this. Any advice?

 

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Morning DrMikey

 

Yes, you are w-a-y overcomplicating this procedure.

 

If you can add some free play at the twist grip & make it better then you either have/had a tight cable, or have something wrong with your TB balance settings (either engine mechanical related, or it's vacuum gauge related).

 

Start by VERIFYING that BOTH side throttle cams hit the wide open stops at the very same time. If they don't then you have adjustment issues.

 

All your math & equations fall off the edge IF there is wear on the throttle plates, or the throttle plates aren't perfectly centered in the TB bores, or have worn throttle shafts/bushings, or have a basic engine air flow problem (like leaking valves or cam timing issues)

 

I presume you backed the twist grip cable adjuster off before doing the lower cable adjustments???? Both side TB cams MUST start off solidly resting on the idle stop screws before any adjustments are made to BBS screws or idle RPM's.

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