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**KEITH KRAUSE** · 07-11-2005, 01:11 AM

I suppose it's always possible to have a problem part, but your synch scenario reminds me of what happenened to me when I first learned to bench/vacuum synch these carbs. You simply did the bench synch wrong. This is a precision adjustment and correct adjustments must be made AND the procedure strictly followed.
The bench synch must be made with a clearance between the idle adjuster tip and the pulley. No interference can be allowed while adjusting for the "fully closed position". Then you also must adjust for the "fully open position" to avoid top end problems. And once vacuum synching, you always bring down the higher level(s) to match the lower ones, or the infamous "high idle without idle adjuster contact" can happen.
The cure is to start over with the bench synch.
I give a detailed procedure about the bench synch at another topic here.
To save me from re-typing it, check out Hoomgars thread "'78 GS1K carb re-jet, bad fuel economy, KK". In the tech section about 4 pages back. Sorry I'm too computer dumb to just post the link for you.
PS: Don't forget to adjust the air screws for highest idle before the vacuum synch. Warm up the motor first, adjust them, then hook up the vacum tool. After the vacuum synch, you can double check the air screws.

**Anonymous** · 07-11-2005, 09:56 AM

Hi Keith,

Thanks for getting back to me. I'm pretty darn sure I did the bench synch properly. I turned the idle screw out all the way, then adjusted the slides. Even then I noticed a problem with the #4 carb slider being lower than the others. When I got the carbs on the bike and hooked up my mercury sticks, all 4 carbs were pretty close. As I tried to adjust #4 (being the highest one) down to the other three, the adjuster screw came away from the slide with no effect on the vacuum. In other words, I could have ttaken the adjuster screw right out of the arm and it would have made no difference at all.

Then I tried to adjust the other three up to meet the #4 carb and ended up with thew high idle off the screw. My air screws are adjusted for the best idle.

After fiddling with this for about an hour, I switched out the arm with another one from a different set of carbs - no difference at all. I am no wondering if the hole is drilled incorrectly in the shaft that actuates the four slides.

I think I will replace the lifter arm, then the slide, then the shaft and see if any of these things help my current situation. Of course, I am open to comments, criticism and advice. Any help is more than welcome.

These are the same carbs that I posted a picture of the other day with the extra vent tube....could that have something to do with it?

Thanks,
Jay

**Hoomgar** · 07-11-2005, 12:18 PM

At the bottom of the carb on the inside where the slide seats when fully closed... you'll see there is a grove cut so the slide can sit down into it. Check to see if there are any foreign particles or dirt in there. Also check the bottom edges of the slide. See if maybe it is messed up. It should sit down in there almost identicle to the other 3. Also check to make sure someone hasn't previously turned the height adjustment screw out the whole way. Does it move the slide at all?

Here is the entry Keith was talking about in the other thread on the bench sync:

The GSResources Forums

http://www.thegsresources.com/_forum/viewtopic.php?p=332826&highlight=#332826

**KEITH KRAUSE** · 07-11-2005, 07:10 PM

Jay, without seeing the carbs myself, I can't really say what's up.
I can only say it's VERY easy to bench synch the VM carbs wrong and have no idea what you did wrong. I've had similar problems as you describe, especially one slide not being uniform with the others after re-assembly. If the difference is beyond .5mm, then adjusting the throttle valve adjuster screw will not work for all conditions. For example, if you adjust that slide down to equal the others, then your fully open position will be off at that carb. It can be a pain.
I doubt it's a problem with a throttle arm or the shaft damaged, but anything's possible.
If I have this problem, I always start over and try to "re-align" everything.
I don't know if I can explain it well, but I would start over. First, back off the idle adjuster knob so it can't interfere. Then remove the throttle shaft and rotate it 180 degrees, so the throttle arm bolts enter from the "other side". You may have replaced it 180 degrees from where it was originally. This doesn't always help, but can sometimes. Insert the shaft stopper plate and torque its bolt. Insert and seat the 4 arm bolts and the shaft to pulley bolt, but don't tighten them yet.
Next, I loosen all 4 throttle valve adjuster holder nuts. If you notice the exposed parts of the adjuster screws aren't reasonably equal, then I would set them at least similar to each other. Then just lightly finger tighten the holder nuts while keeping the screws still. Next, center the pulley and torque the shaft to pulley bolt to 3.5 ft/lb. Don't over-tighten. Next, exercise the pulley a few times to its fully open and closed positions. Now, holding the pulley up a bit so the valves can't "seat", torque the 4 arm bolts to 3.5 ft/lb. Don't over-tighten, it causes binding.
Re-install the throttle pulley spring and do your bench synch again, starting with the fully closed position first. Hopefully, things will be much better this time.

**earlfor** · 07-11-2005, 09:09 PM

Re: Not your average 78 GS1000 Carb Synch question...honest.

I think thats a relatively common happening if the manual synch is off greatly. Its not uncommon for a manual synch to produce uneven vacuum levels even though slide height is adjusted to be physically the same.

I would say your #4 carb is "pulling" the rpm curve. The solution is to raise the slides on the #1,#2, and #3 carbs. This will lower vacuum on those carbs and you should be able to then turn down the idle adjustment screw to a normal rpm. You may have to lower vacuum levels on 1,2 and 3 a second time, before they together will be able to "control" the spike caused by #4. Once you get back to an idle rpm range, and running off the idle jets, you can vacuum synch normally.

Been there, done that, got the shirt. :-)

Earl

[quote="KnuckleBuster"]
The #4 carb sucks a hell of a lot more mercury than the other three. If I adjust the other three to match it, the idle rises to such a point that the idle screw no longer has an effect. If I try to adjust the #4 carb down to the same level as the other three, it goes down a bit then stops. I can pull the adjuster screw right out of the thing and it still pulls twice as much vacuum as the other three.

**Anonymous** · 07-12-2005, 08:57 AM

PROBLEM SOLVED!!!!

Hey folks,

Thanks for all the tips and info. The good news is that I found the problem through systematic sleuthing and critical thinking!!! I took the slide apart, measured every bit and piece, put it all back together (left the carbs on the bike and just operated on the problem one) and was just about to replace the shaft when low and behold...the problem presented itself!!!

It turns out that there is absolutely NOTHING WRONG with any of the carbs or their parts!

No, my friends the sad part is that yours truly is an utter MORON!!

As I'm putting the carb back together, I noticed a hose hanging around. "Gee, that's odd. Where does that hose go?"

MORON!!

It was the vacuum hose that runs the petcock. I had forgotten to plug it when I removed the tank. Therefore, the #3 carb was sucking all its vacuum through the hose instead of the synchronizer. Once the line was plugged, the synch went perfectly and the bike runs great.

Thanks for trying to help an idiot.

**Hoomgar** · 07-12-2005, 09:23 AM

Man your really stupid buddy. No one else on here has ever done that 8O
You must feel like a total moron!

'cough' 'cough' 'gag' ' cough'

he he he --> http://www.thegsresources.com/_forum...hlight=#343940

**earlfor** · 07-12-2005, 08:25 PM

For sure Mark! Out of many thousands of posts in the tech pages, I have never heard of anythng soooooooooooooo moronic. LMAO. heheheheheheheheheheh :-)

Earl
P.S. We shall not delve into some of my goofs. :-)

Originally posted by Hoomgar

Man your really stupid buddy. No one else on here has ever done that 8O
You must feel like a total moron!

'cough' 'cough' 'gag' ' cough'

he he he --> http://www.thegsresources.com/_forum...hlight=#343940

**KEITH KRAUSE** · 07-13-2005, 04:20 AM

Not another "hoomgar" moment!

Just yankin' yer chain Mark.
Knucklebuster, glad you got it fixed, but I thought the original problem was too much vacuum at carb #4, and the other 3 were all lower?
With an intake leak like that at #3, the vacuum would be almost nothing at 3.

**Anonymous** · 07-13-2005, 07:41 AM

Yeah, that was the problem - I started trying to bring #3 up to the same level as #4 and bottomed the slide out. When I got the #1 and #2 carbs close to the #4 I'd kill the engine or #3 would be REALLY low. Since the other three were so low, I just figured the problem was with #4. All is well now though.

Thanks for the support guys - it's good to know I'm not alone.

Thanks again,
Jay

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Not your average 78 GS1000 Carb Synch question...honest.

Not your average 78 GS1000 Carb Synch question...honest.

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