Throttle cable adjustment.

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Buckster
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Throttle cable adjustment.

Post by Buckster »

I am adjusting the cables for the fast idle lever and the throttle. The Clymers states 1mm of freeplay at the hand controls and 2mm at the throttle body. My question is when I pull up the cable sheath at the throttle body, it just keeps coming up until you hit the end of the cable. (WFO)
This is the first time I have done this and my first time to do a throttle body sync. I have finally made my homemade manometer and ready to dive in.
I almost feel I should wait to adjust at the throttle body at the time I sync at 3k-3,5k RPM's.
I also read that when doing the higher RPM adjustment to just adjust up or down from the right side only. In other words, adjust the right side to the left leaving the left alone.
Any help would be appreciated!!!
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Re: Throttle cable adjustment.

Post by riceburner »

When you're balancing the throttle cables remember that you're just trying to get the two cables working in the same way. So yes, it makes sense to leave one as it is (normally the left) and adjust the other to match it (the right side). The right side is normally used as it's a little easier to get to!

The throttle cables works by a single cable running from the twistgrip down to a pulley wheel hidden under the airbox - that pulley wheel also has 2 more cables that go down to the TBs. Pull on the twistgrip cable and you rotate the pulley wheel - which then pulls on the 2 secondary cables to rotate the butterflies in the throttle bodies. The Left side cable also rotates the Throttle Position Sensor (the square box on the left TB) which feeds back to the Motronic computer.

So - the upper free-play adjustment controls the free play between the twist-grip and the central pulley - the lower free play adjusters (on the TBs) control the free play on the secondary cables (between the central pulley wheel and the TB).

When you're adjusting the TB's you adjust the BigBrassAirScrew to change the amount of air/fuel ratio at idle (ie with no tension on the throttle cables), and you then adjust the cable free play to ensure that both secondary throttlw cables are rotating the butterflies the same amount - that's why you check the balance at 3-4K revs - ie when the throttle cables are 'in play' and having an appreciable effect on the fueling. DO NOT adjust the BBASs to control the balance at high revs!

hope that's helped!
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Re: Throttle cable adjustment.

Post by racurley »

Dragging this thread up for a clarification. I did a TBS adjustment with the homemade manometer. Probably need to adjust the throttle body cable since it does not stay in sync when I raise the throttle rpms. I imagine it will be obvious when I try this but I'm not quite understanding the cable adjustment procedure. So, you loosen the lock nut on the cable a couple of turns, then hold the cable sleeve to keep it from possibly twisting, and then rotate the knurled knob based on the adjustment. Kind of confused because it's not clear what the knurled knob is actually turning. Sorry if this is a stupid question.
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Re: Throttle cable adjustment.

Post by CycleRob »

racurley,

Here are few very important corrections for you to follow:

1--Be VERY careful you do NOT OVERTIGTHEN the TB cable locknut !! The knurled adjuster is a brass powder metal product, manufactured with high heat and mechanical compression and it is not that strong or hard as a more expensive cast part. If you snap the knurled adjuster's threads by overtightening the locknut, you will need to replace that individual cable . . . an involved/expensive process. Tighten it just enough so it will not come loose from engine vibration, and no more. Maybe coming loose at some future date is OK, breaking the adjuster threads with your wrench is NOT!!

2--You only need to losen the knurled adjuster's 10mm locknut a tiny amount like one hex flat, just enough so you can turn the knurled adjuster with a pair of needle nose pliers (or your fingers if it is initially WAY off).

3--To adjust the "on throttle" 3,500 RPM synch, adjust the cylinder with the tallest water manometer column as it will be the one with excessive freeplay. Because the differential water manometer is so sensitive and easily 5X more accurate than a TwinMax, do not go crazy trying to get it perfect. At my May 2009 tech session:
Image Image

We performed a perfect TB synch with a TwinMax, then immediately changed over to a water Manometer which showed nearly a 2 inch synch error. It is THAT sensitive! Within a half inch (13mm) water column height difference for the "on throttle" setting is OK. For the BBAS (BigBrassAirScrew) adjustment, you can easily get it perfect! Try different higher RPMs and note that the columns may take turns at being the highest as the RPMs increase . . . which is normal with TB shaft wear. The final adjustment you chose must be weighted toward the lower 3,000 RPM reading as the 4,500+ RPM intake manifold vacuum generated EXAGGERATES the actual throttle opening differences.

4--Turn the handlebars lock-2-lock with the engine running to confirm there is adequate freeplay and the idle speed does NOT increase.

5--The engine should be warm or hot for the adjustment and a large fan or 2 should be directed at the hot jugs. If you can think fast and make all the right adjustments quickly a fan is not needed.

6--In all adjustments the highest water column has the smallest throttle applied. That means you loosen the BBAS for idle speed or loosen to raise the knurled adjuster for the "on throttle" 3,500 RPM synch.

.
Last edited by CycleRob on Fri Jul 26, 2019 2:39 am, edited 1 time in total.
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Re: Throttle cable adjustment.

Post by racurley »

Awesome. Will give it a go soon.

I am using 2-stroke oil for my fluid in the manometer. I didn't intend to fill it quite so full but I got almost a meter on both sides. I suspect perhaps this is not as sensitive as yours?
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Re: Throttle cable adjustment.

Post by riceburner »

racurley wrote:Awesome. Will give it a go soon.

I am using 2-stroke oil for my fluid in the manometer. I didn't intend to fill it quite so full but I got almost a meter on both sides. I suspect perhaps this is not as sensitive as yours?

The lighter the fluid, the more sensitive it'll be.
I use 3-in-1 oil in mine, which is accurate 'enough'. (I can get the levels within about 1/4 of an inch or smaller).

cant remember what 'weight' 2-stroke oil is now... :(
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Re: Throttle cable adjustment.

Post by racurley »

I first tried to use some old 2-stroke oil for a chainsaw that had been sitting around in my garage unopened. It was literally sludge. I dumped it into a funnel I was using with the tube and it wouldn't even flow into it. I ended up disposing of that tube and had to go purchase another along with new oil. The new oil flowed much better but was probably still a bit too dense. Took quite a long time for adjustments to register in the tubes. Probably need something quicker. No chance that stuff was going to get sucked into the engine.
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Re: Throttle cable adjustment.

Post by CycleRob »

I started out using ATF (AutomatisTransmissionFluid) but is was waaaay too sluggish to be useful. Next was WD-40 oil and it was a little better, but it got nasty and contaminated over time. Finally the change-over to water+Isopropyl made it work the best, with IMMEDIATE response.

Image Image Image Image

I use green food color tinted water with about 10 percent Isopropyl Alchol (the retail product called "rubbing Alcohol" that is 70 percent Alcohol) mixed in to prevent algae and stagnant water decomposion. It gives a very fast response and if there is a large synch error it will get sucked into one combustion chamber, maybe stalling the engine only if it is idling. The water vaporizing itself will not damage the engine if it is still running or started up again.

After Edit: Finally finalized the construction of the very simple, twin screw top wine bottle "LargeSynchErrorTool" (LSET). It is necessary if there is a TB synch error that is "a little too far out" and if you are not ready to quickly pinch-fold one span of synch hose on start-up, the water in the manometer gets quickly sucked into the cylinder with the smaller throttle or smaller BigBrassAirScrew (BBAS) opening.

Image

.
Last edited by CycleRob on Thu Jul 25, 2019 9:31 pm, edited 1 time in total.
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Re: Throttle cable adjustment.

Post by fpgirard »

CycleRob - I'm curious - you mentioned that there was a 2" difference on the manometer even after syncing with the TwinMax. Do you have a sense of what this means in terms of sensitivity measured in PSI or kPA differences? Iow, is it possible to equate a linear measurement on the manometer to a PSI value? I was thinking that the TwinMax might be more sensitive than that....
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Re: Throttle cable adjustment.

Post by CycleRob »

Let me see if I get this right. Our barometers measure atmospheric pressure from a vacuum to 29.92 inches of Mercury (Hg Specific Gravity=13.633) a pressure that would be equal to 407.9 inches of water (SG=1.0). That also means that a differential water manometer is 13.633 times more accurate than the ancient and now deemed dangerous Mercury Carb Styx, of which I still own two :shock: . The TwinMax people specify that it is "Accurate within 1mm of mercury (+/-1.0mm)" which, since 1"=25.4mm, then the difference in accuracy would be (1/25.4) x (13.633"ofH2O/1"ofHg) = TwinMax accuracy of +/-0.5367 inches of water. The differential water manometer has an accuracy of +/-zero (explained later on). I have had opportunities to participate in many sessions with both of these tools and arranged to use one-right-after-the-other, as in using the TwinMax first. At my last Bash attendance we checked 4(?) OilHeads where 3 were close to OK, needing no or tiny adjustments and the fourth had a less than a 2" error. I believe this was before supper, so the entire group was a little grouchy:
Image

Comparing the 2 devices:
1) The TwinMax, $90 at https://adventuremotogear.com/products/twinmax looks really professional, is really portable and can be very accurate if:
--The zero is precisely set.
--The sensitivity is properly maximized.
--The 9V battery is not age-tapering down the output voltage.

2) The Differential Water Manometer, because it is based on physical constants of water and the Earth's gravity is ALWAYS Perfectly Zeroed and Precisely Calibrated. Oh yes, It costs less than $10 to make, less than $5 if you have surplus wood. Its also kinda fun to watch the green liquid on a white background "working" as the pulsing vacuum driven fluid levels are quickly adjusted to a match. :roll: It may require a 1- - 2 year top-off to mid scale "zero" liquid level to combat evaporation and it would require careful re-engineering to make it fold-able for 2 wheel transport.

Number 2 is a real easy choice for me.
.
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