1979 gl1000 throttle body shafts


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shark
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1979 gl1000 throttle body shafts

Postby shark » Wed May 11, 2011 10:34 am



seems the bike is getting worse on fuel mileage (16MPG) and runs very poorly after I started riding it regularly. I've synced the carbs, thats ok... I get no adjustment out of the #4 carb air/idle screw adjustment and I have a vaccum leak on the #3 carb where the cable goes on the throttle body shaft. Long story short. I've been looking at kits and I dont see where they offer a seal or is there a seal??? is this like most auto carbs... when they wear out you replace the carbs? very frustrated... I work on cars and trucks for the most part... any help i'm greatful! thanks in advance, jeff.



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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Wed May 11, 2011 11:43 am

Well there is a seal per say.I (as an experiment) removed the carb from the body,removed the screws holding the butterfly valve and pulled the shaft.I found a felt seal in there.Now what?I did find (in one of my 'O' ring kits) a 'O' ring that fit.Did it make a difference?Not that I noticed.If your mileage is 16 mpg,I'd be looking elsewhere.Some vacuum leak around the shaft is expected and tolerable but doesn't explain the low mileage.What does,is stuck slides.If stuck up,it will run badly and the plugs will be sooty black.

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Re: 1979 gl1000 throttle body shafts

Postby shark » Wed May 11, 2011 12:34 pm

even if the sync guage reads the same as the other carbs? sorry for all the questions... i just dont want to pay someone to do it... and i cant afford it ;)

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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Wed May 11, 2011 3:31 pm

Yes,remember that the vacuum is monitored after the throttle valve.The slides are back toward the intake.the vacuum will be about the same whether the slide is up or down.Its purpose in life is to measure air flow (engine demand)through the throat.As air flow increases the slides rise and the tapered needle rises allowing more fuel to get through the main jet.If they are sticking it will allow the engine to draw more fuel than it can burn.Do pull the plugs and look at them,I'll bet they are sooted up.

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Re: 1979 gl1000 throttle body shafts

Postby shark » Wed May 11, 2011 4:03 pm

i will check it out, thanks for your input. ;)

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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Wed May 11, 2011 4:13 pm

There's a lot of info about carb rebuilding.I even posted this..."The slides MUST be absolutely polished clean and move without any drag at all.The slides rise as airflow increases through the carb throat and are spring loaded to return to the bottom.I've found the cap contaminated,the brass slides dirty,etc.Do not use any oil on the slides.The bronze bushings are referred to as "oillite bronze" and do not require and lubricant.After cleaning I have polished with Mothers.The slides will travel(without the spring)down the cap smoothly".

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Re: 1979 gl1000 throttle body shafts

Postby Old Fogey » Thu Jun 02, 2011 8:08 pm

Strictly speaking, the airflow increases as the slides rise, not the other way round. The slides are raised by the increase in the intake manifold vacuum as the throttle valves are opened.
I also believe the 'brass' bush in the cap to be just plain bronze. 'Oylite' bushes are are sintered bronze powder bushes with an open pore structure which is impregnated with oil during manufacture. It would be pointless using these in the cap as the constant vacuum (CV carbs remember) would draw the oil out, leaving a dry bush anyway.
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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Fri Jun 03, 2011 10:33 pm

Sorry to disagree sir,but intake manifold vacuum is not ported to the slides.Also as you throttle up,the manifold vacuum decreases.As air flow increases past the lower part of the slide due to throttle opening,It tries to suck the air out of the upper chamber thus raising it through a vacuum effect.The slide is ported in the bottom.Air flow passes this port,it's like a paint sprayer,the more the air flow the more it will draw a vacuum and lifting the slide higher.
This method is also used in the vacuum advance system.It is ported before the slides,as the air flow increases,it draws a larger vacuum for the advance system.
I may be mistaken(it happens)but I thought "CV carburetor" was short for "constant velocity" not vacuum.
I've added a pix of the basic gl1200 carb , the 1100 and gl1000 are almost the same.
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Re: 1979 gl1000 throttle body shafts

Postby Fred Camper » Fri Jun 03, 2011 10:53 pm

Thank you for the post, appreciate the detailed explanation.

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Re: 1979 gl1000 throttle body shafts

Postby Old Fogey » Sat Jun 04, 2011 1:22 am

Well, after reading your post I went and read up on the operation of Constant VELOCITY carbs.
I'm man enough to say; you have it right and I was wrong, having believed what I wrote was correct for many years.
It was really a case of believing something I had been told, without actually thinking about it.

I still think I am right about the bush in the cap though. I have examined it through a powerful magnifying glass and can see no sign of it being Oylite.
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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Sat Jun 04, 2011 12:01 pm

OK ,I'll give you that one :oops: .It was information I derived from construction theory and maintenance information.It specifically states not to oil the slide bushings.
I guess I also assumed if no oil is used they must use oil impregnated slide bushings.
It's been 35 years sense I dealt with that type of material.Same era,same technology.

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Re: 1979 gl1000 throttle body shafts

Postby 90DAYSURVIVAL » Tue Jun 07, 2011 5:23 pm

I have air sucking in through the throttle cable. The Honda tech said to smear grease around them to stop the leak.

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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Tue Jun 07, 2011 5:58 pm

Sorry,it can't suck air through the cables,their on the outside.It could suck air around a badly worn throttle body shaft.If it's leaking that bad,a bit of grease won't last long(it will suck it in too).
If this carb body is that badly worn out,replace them or try to replace the felt seals with "O" rings.

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Re: 1979 gl1000 throttle body shafts

Postby 90DAYSURVIVAL » Tue Jun 07, 2011 7:48 pm

virgilmobile wrote:Sorry,it can't suck air through the cables,their on the outside.It could suck air around a badly worn throttle body shaft.If it's leaking that bad,a bit of grease won't last long(it will suck it in too).
If this carb body is that badly worn out,replace them or try to replace the felt seals with "O" rings.


Thanks. Any idea what size o ring to use? Where is the best place to find a replacement carb body?

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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Mon Jun 13, 2011 1:56 pm

You would be hard pressed to find NOS for the carb body(new old stock),Probably a classified add here or E-Bay.
If you feel adventurous,I found "O" rings in one of my 2 kits I got from Harbor Freight.
Be aware...removing the screws from the butterfly is very difficult.The brass screws are dinked on the back side to prevent them from coming loose. The felt or "O" ring is installed first and then the shaft.the butterfly valve goes on last.

Are the shafts really that worn?Do they wiggle a bunch?Can you hear(with a tube)air sucking in around the shaft.

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Re: 1979 gl1000 throttle body shafts

Postby Old Fogey » Mon Jun 13, 2011 2:38 pm

Be aware that the butterflies only go in one way. The edges are beveled. If you fit them the wrong way round they won't close properly.
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Re: 1979 gl1000 throttle body shafts

Postby 90DAYSURVIVAL » Tue Jun 14, 2011 7:01 am

virgilmobile wrote:You would be hard pressed to find NOS for the carb body(new old stock),Probably a classified add here or E-Bay.
If you feel adventurous,I found "O" rings in one of my 2 kits I got from Harbor Freight.
Be aware...removing the screws from the butterfly is very difficult.The brass screws are dinked on the back side to prevent them from coming loose. The felt or "O" ring is installed first and then the shaft.the butterfly valve goes on last.

Are the shafts really that worn?Do they wiggle a bunch?Can you hear(with a tube)air sucking in around the shaft.


Only going by what the tech said, Felt is worn.. I haven't had time to look at them myself. It runs great. When it's hot the idle jumps to 1800 rpm and pops like it's running lean.

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Re: 1979 gl1000 throttle body shafts

Postby Old Fogey » Tue Jun 14, 2011 8:16 am

Much more likely is that you have air leaks at the inlet manifolds, either dead O rings where they bolt to the heads, or at the clamps to the carbs. When I was at Randakk's rally in 2009, one of the NGW guys had a similar problem which we cured by re-tightening the clamps with the engine HOT so that the rubber was more flexible.
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Re: 1979 gl1000 throttle body shafts

Postby scotterichmond » Tue Jun 14, 2011 10:47 am

external vacuum leaks can easily be found by applying a small amount of water while it is running. it will smooth out and possibly change RPM's

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Re: 1979 gl1000 throttle body shafts

Postby shark » Tue Jun 14, 2011 2:45 pm

Before I changed out the carbs to some used ones I found on ebay and rebuilt them, I used a very small blast of carb cleaner. That's how I found the leak. Same method I use on automotive trouble shooting. BTW.. I did get the bike running great. It went from 16MPG--- plug fouling----POS--- to smooth running 38MPG now!. Thanks for the Mothers Polish tip on the sliders.... I can't begin to tell you how WELL that worked!!! ;)

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Re: 1979 gl1000 throttle body shafts

Postby virgilmobile » Thu Jun 16, 2011 3:57 pm

So are we to assume that the small leak around the throttle shaft is indeed inconsequential and the great improvement (16mpg to 38mpg) was related to sticking slides?

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Re: 1979 gl1000 throttle body shafts

Postby shark » Thu Jun 16, 2011 5:00 pm

Well Virgil, I did spray some carb cleaner around the shafts on the other set and get no RPM change now. And I get idle speed screw adj. out of all 4 carb screws. The other sliders were a little tarnished and sticky... I might have to say a comb of vaccum leaks dirty sliders was all the difference. Anyway, thanks for great advice. My '79 is running great now. I've put over 800 miles since the carb overhaul! 8-)
here is a pic of the old girl... all original from what i can tell...


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Re: 1979 gl1000 throttle body shafts

Postby Old Fogey » Thu Jun 16, 2011 8:30 pm

Glad you got it sorted!
I think what you found is a good indication that quite often there is no one biggy; just a number of small ones that all add up in the end.
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Re: 1979 gl1000 throttle body shafts

Postby shark » Fri Jun 17, 2011 8:18 am

Fogey, I think that is a good eval... I should have added, I did kit the carbs with "Barracuda" complete carb kits. But, like you said I'm sure it was a comb multi problems. New jets, meter rods, seals, sticky sliders, ect. I have to say I did get some great advice in this forum. Glad I found this site! Thank everyone! Jeff.




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