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excess vacuum ports

  • Thread starter Thread starter Remington44-77
  • Start date Start date
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Remington44-77

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I have a 1978 GS 1000 C with the following mods; 1100 cc big bore kit, Vance & Hines 4 into 1 tubes, K&N pods, Pingal fuel valve, Dyna 2000 ignition box with crank trigger & 2.2 ohm gray coils. The carbs are VM-26 SB with a Dynojet stage three kit, 128 main jets and the needle on step two.
My question is; is there any reason not to cap the three vacuum ports on the carbs? I've currently got them capped as I don't see any useful function for them.
 
Would capping the vent tubes not allow for pressure equalization... thus allowing flooding to occur? Have you tried priming and/or running the carbs with caps installed? :-k
 
cap the vacuum port between 2 & 3 carbs but Not the 2 other ports, they are vents for the float bowls. the bike will not run right if all 3 are capped
 
Agemax said:
cap the vacuum port between 2 & 3 carbs but Not the 2 other ports, they are vents for the float bowls. the bike will not run right if all 3 are capped
Click to expand...
That port is actually on carb #3, but the rest of that is accurate.

They are not "vacuum" ports, they are VENTS. They are the source of the atmospheric referrence for the float bowls that allows your carbs to work.

.
 
Thanks, I wasn't sure of their true function. Since I only drive a couple of miles to work each day, with lots of stop lights, they haven't made any noticeable objections yet.
 
Number 3 is the vacuum to the petcock...DO NOT EVER cap off the vent nipples. Youll have gas running out the intake sides of the carbs in short order. They must be open so the floats can equalize with the atomospherics pressure as was mentioned earlier.
 
So if I have this right, cap off the second carb from the left, and leave the two right hand carbs open. Or just don't cap anything.?:?:
 
Nice bike, but like the ad says, it's a 1979 GS1000N.

No choke lever, no "skunk" crease in the tank mean 1979

Nice bike, very collectible from what I've read. You need to be riding it farther than a few miles each day, needs a good run occasionally to flush out crud

Pull off those 2 caps and take it for a good run before winter sets in
 
The insurance guy said the serial number made it a 78C. I have ridden it thru the winter before, although I was much younger. Ever break trail in a foot of fresh snow? The winter of 84/85 I rode it to college From Spokane Wa. to Eastern Washington University.Its about a 16 mile ride each way. Snow and Ice make for real tense riding. I don't see me doing that again. :lol:
 
Remington44-77 said:
So if I have this right, cap off the second carb from the left, and leave the two right hand carbs open. Or just don't cap anything.?:?:
Click to expand...

Agemax said:
NO. you cap off number 3 carb and leave 2 and 4 open
Click to expand...
The carbs (and cylinders) are numbered from left to right as you sit on the bike.

That means that #1 is under your clutch hand, #4 is under your throttle hand.

The vacuum port would be on carb #3, which is the inner carb on the right side of the bike.

.
 
If you have a stock petcock, how is it running without vacuum supplied to open the diaphram?? Is this a pingle ON/OFF gravity petcock that doesnt require vacuum? If so, then cap off numer 3 nipple and leave the other 2 open. I ask this question because what type of petcock you have will effect the correctness of the answer.
 
chuck hahn said:
If you have a stock petcock, how is it running without vacuum supplied to open the diaphram?? Is this a pingle ON/OFF gravity petcock that doesnt require vacuum?
Click to expand...
He answered that in the original post, Chuck.
Remington44-77 said:
I have a 1978 GS 1000 C with the following mods; 1100 cc big bore kit, Vance & Hines 4 into 1 tubes, K&N pods, Pingal fuel valve, Dyna 2000 ignition box with crank trigger & 2.2 ohm gray coils. The carbs are VM-26 SB with a Dynojet stage three kit, 128 main jets and the needle on step two.
Click to expand...
 
The carbs are VM-26 SB with a Dynojet stage three kit, 128 main jets and the needle on step two.
Click to expand...
Interesting, my Dynojet stage three kit came with 138 and 142 main jets, I'm using the 138's. I'm assuming you meant to say 138, 128's would be destructively lean.
 
1 138 DJ jet is equivalent to 130 Mik. a 128 Mik jet is a 136 D/J jet,a 128 DJ jet is a 120 Mik.
it depends whether he is using DJ jets or Mikuni jets as to how it will perform
 
To OldVet66: you are correct ,I got the jet size wrong, the off the top of my head input was off. I've got carb #3 plugged. The Pingal valve has no vacuum port but does have a reserve position.
I noticed the bike gets light in the front when accelerating form a rolling start. I haven't cranked on it real hard as the speed limit downtown is 30 MPH. But it feels like the front could easily go up.
I'm an fat old, 63, fart about 285 Lb. It will be fun to get on the road with it again.
 
I have 4 1000s and each has ample power to raise the front wheel if I really wanted to. The front will raise quite a bit as you accelerate as the forks extend..it feels light but thats just the way they are...take alook down at the tubes once as you roll thru a few gears and youll see what i mean.
 
Your right about the front end getting light, especially with your big bore kit. In stop and go traffic several times I got the same light front end changing lanes with a fast roll on in second, until someone asked me how I did that with the front end 4 inches off the pavement. I don't know because I thought both wheels were on the ground.:o
 
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