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This is not in issue with my GL1100 which is running well at the moment, but with my 93 Yamaha Venture. The bike has only 18,xxx miles on it, so it has sat a lot. It is new to me and I am trying to get it back on the road as I did with the 1100. Anyhow, I am trying to do a carb sync after a rebuild, and the Carbtune does not move at all at idle. The bike will run, although not so well. I have sprayed carb cleaner around the manifold and carb boots, but cannot locate any vacuum leak. I checked the Carbtune on another bike, and it works fine. So, any ideas as to why the bike is pulling so little vacuum that the Carbtune won't register? Thanks.
 

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I know that ignition timing can affect manifold vacuum somewhat, I've seen it on a small-block 350 that I rebuilt once. I forget whether retarded timing, for example, will cause lower or higher vacuum, or vice-versa, however.

I don'tknow whether you can even do anything about the ign. timing on the Venture. :?

I would also expect that things involving the valve train could have an effect on manifold vacuum (clearance, timing, cam chain adjustment, etc.)

Hope you figure it out... :waving:
 

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not familiar with the venture but its possible that the system may use a ported vacuum system,in which vacuum is not available until the throttle plates are open above idle,you might try to find an answer on another forum specific to the venture
 

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If the engine is running and you aren't registering any vacuum then you have the sync hoses hooked up to the wrong place.

I don't know on the yamaha, I've never owned one, but it may be like the Kawaski and just have little tubes on each carb that has a rubber plug fitted over them.

I was working on an R6 the other day and the vacuum ports were actually pluged with hoses that ran between the 1&3 and 2&4 carbs. They went no where else. I pulled the hoses and put the carb tune hoses on where the factory hoses were installed.
 

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Thanks for the replies, I discovered that #4 cylinder is not firing. Possibly that would cause enough of a vacuum drop that I get no reading? I know it is hooked up correctly because I also have a Vmax, and it is basically the same motor. I did put this question on a Venture forum too, but there is so much knowledge on this forum that I thought I would ask here too.
 

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Even if it weren't firing it would still pull some vacuum especially on the other 3. I still maintain that you have it hooked to the wrong place. An engine simply cannot run without some vacuum.
 

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jdvorchak wrote:
Even if it weren't firing it would still pull some vacuum especially on the other 3. I still maintain that you have it hooked to the wrong place. An engine simply cannot run without some vacuum.
This is true. vacuum is the first of the four cycles. suck, squeeze, bang, blow.:ROFL:
 

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four cycles. suck, squeeze, bang, blow


Carl-- love it when things are brought down to basics ! !:claps::claps::claps::claps::claps:

Jim
 

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rideandslidejim wrote:
four cycles. suck, squeeze, bang, blow


Carl-- love it when things are brought down to basics ! !:claps::claps::claps::claps::claps:

Jim
Well I try to KISS (Keep It Simple Stupid).:ssshh:
 

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Goatman, do a compression test on the engine. It could be a valve problem, or piston causing it not to have any vac. Does the carbtune show you any vac on any cylinders?

Or, are you just loosing vac on that one cylinder?



Also, how did you check for the no spark condition?
 

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You're right, I do need to do a compression check, but with only 18700 miles, and it does run on 3 cylinders, I am hoping that will not be the problem. As far as spark, I just pulled the plug wire when running, and I can hear the spark pulsing. When revved up, and on decel, the Carbtune does move some, but nothing at idle. I put my tongue on the Carbtune hoses, and can feel vacuum, just not enough to move the Carbtune rods.
 

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Is it just the one cylinder that doesn't show on the gauge, or all cylinders. If is just the one, do the compression test. If that cylinder show no or real low compression, check the exhaust valve for that cylinder. It could be stuck open. If it was an intake valve stuck, it would be popping back through the carb.
 

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It is all cylinders that show no movement on the Carbtune at idle. I think first off I need to get that #4 cylinder firing and then see what readings I get.
 

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If it's been sitting, you may have frozen rings = no compression or vac. As has been stated, check compression and get it running on all four.

Does the Venture have a vacuum driven advance, vacuum boost or other components that may be messing up?
 

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goatman123 wrote:
It is all cylinders that show no movement on the Carbtune at idle. I think first off I need to get that #4 cylinder firing and then see what readings I get.
Well the simple fact that it does run mean that there is vacuum. You just need to fine the correct port(s) to tap into.
 

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Update. I got the #4 cylinder running, and low and behold the Carbtune showed some action on #3 cylinder. I adjusted the sync screws from there(they were way out of wack) and got the carbs balanced. Thanks for the help.
 
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