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My '81 gs1100e carb slides won't open

  • Thread starter Thread starter RipRoaringFun
  • Start date Start date
R

RipRoaringFun

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I took the bank of carbs off to check jetting etc. and discovered that maybe the slides on CV carbs work 'automatically' or something?

The throttle cable connects up to a pulley that opens the 4 butterfly valves (one per carb). But I see no mechanical connection that opens the slides.

I can easily push the slides up and I can hear the rubber diaphragm in the crown of each CV carb moving around.

So yep, this is the 1st time in my life I've had CV carbs to work with (I'm 100% used to 'VM'-style carbs that are common on 70s bikes).

So I apologize for the newbie-ness of this question, but what exactly makes the slides move upward when I give the bike gas? The only *mechanical* connection I see between the throttle grip and the carbs is the butterfly valve in the intake-side mouth of the CV carb.
 
They are CV carbs. They rely on vacuum from the engine to open. Vacuum ports travel to the top of the carb, above the diaphragm. That vacuum lifts the pistons.
 
blowerbike said:
uhuh:lol::lol::lol:
Click to expand...


Sorry :/

The pressure differences between the bottom (atmospheric pressure) and top (vacuum from the low pressure area of the carb chamber(which travels there from the low-pressure venturi through a channel)) of the diaphragm cause the piston to rise.

Same thing, only said more complicatedly.
 
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mlinder said:
Sorry :/

The pressure differences between the bottom (atmospheric pressure) and top (vacuum from the low pressure area of the carb chamber(which travels there from the low-pressure venturi through a channel)) of the diaphragm cause the piston to rise.

Same thing, only said more complicatedly.
Click to expand...
Well, I liked your first explanation better!
 
i liked your 1st response also.
i was just scratching my head about the question posted is all.;)
 
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Okay thanks dudes, makes sense. I'm just not used to working the throttle pully and seeing the slides just sit there as I manually work the pully that the throttle cable connects to. I think its a cool design except rubber exposed to gasoline vapor or simply age is less reliable than a cable or a rod that mechanically lifts the slides. I guess if they were as reliable a design as a cable pull or a pulley-activated rod that mechanically forces the slides to move up or down, racing bikes would use them.

Then again this is a 1981 bike, 30 years old, for all I know the original diaphragms are in there still, and it still works. Still the racing bikes don't use CV carbs as far as I know.

Thanks again.
 
RipRoaringFun said:
Okay thanks dudes, makes sense. I'm just not used to working the throttle pully and seeing the slides just sit there as I manually work the pully that the throttle cable connects to. I think its a cool design except rubber exposed to gasoline vapor or simply age is less reliable than a cable or a rod that mechanically lifts the slides. I guess if they were as reliable a design as a cable pull or a pulley-activated rod that mechanically forces the slides to move up or down, racing bikes would use them.

Then again this is a 1981 bike, 30 years old, for all I know the original diaphragms are in there still, and it still works. Still the racing bikes don't use CV carbs as far as I know.

Thanks again.
Click to expand...

They don't I'd be putting mechanical slide carbs on my 550/650 build if I could. The cv carbs do not give as crisp, or quick, response if you are somewhat skilled at using a mechanical throttle.

Thats one of the reasons they are used on race bikes.
 
mlinder said:
They don't I'd be putting mechanical slide carbs on my 550/650 build if I could. The cv carbs do not give as crisp, or quick, response if you are somewhat skilled at using a mechanical throttle.

Thats one of the reasons they are used on race bikes.
Click to expand...
But they ARE better on a street based bike. Because MOST people arent skilled at smallish throttle openings. Wacking on a set of mechanical slide carbs will cause the bike to dump vaccum and fall on its face for a second at lower RPMs, while the same action doesnt effect vaccum carbs as badly.

I prefer mechanical carbs from a tuning standpoint. Much easier to dial in. And, on a track, I bet they're the cats ass. But for zipping around in traffic, or pushing corners on the street where the margin for error is much smaller, mechanical carbs become even a bit dangerous. Toss your weight the wrong way, or not have a good grasp on maintanence throttle while heeled over hard in a corner, and you might end up wrapped around a telephone pole. Theyre a bit "twitchy", some worse than others with an almost ON or OFF character..
 
TheCafeKid said:
Theyre a bit "twitchy", some worse than others with an almost ON or OFF character..
Click to expand...

What a crock of BS.
They work fine. Sure if you whack them wide open from an idle it will bog for a second, but it's not like you're going to do that accidentally. They are every bit as smooth in operation otherwise, if not they are mistuned terribly.
 
tkent02 said:
What a crock of BS.
They work fine. Sure if you whack them wide open from an idle it will bog for a second, but it's not like you're going to do that accidentally. They are every bit as smooth in operation otherwise, if not they are mistuned terribly.
Click to expand...
I dunno, I found smoothbores and RS series a bit twitchy, but thats just my opinion. The early VMs not so much. There's definately a "feel" difference between the VM carbs and the CV carbs, IMO.
 
TheCafeKid said:
I dunno, I found smoothbores and RS series a bit twitchy, but thats just my opinion. The early VMs not so much. There's definately a "feel" difference between the VM carbs and the CV carbs, IMO.
Click to expand...

Yep, it feels like the throttles are connected to your hand, and the fuel is instantly correct without the carburetors having to think about it for a 1/2 second or so.
Now if I could only get them to work at more than one elevation I would be a big fan of them.
 
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