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carb size vs performance?

Gregory

Gregory

Forum Mentor
Past Site Supporter
This I am sure is a complete newbie question, but couldnt find it in my searches.

Last night I went and picked up a 82 GSX1100E for a friend of mine, and it came with and extra box of parts.

There is a complete set of 34mm carbs, and it got me to wondering whether...
  • A) do larger diameter carbs make a bike faster?
  • B) if so, do the CV34mm carbs fit on a 78 GS1000 that is currently equiped with 26mm?
I am not too seriously considering a change since I have spent quite a few hours and ordred all the parts to rebuild my 26mm stock carbs.

Just one of those thoughts that made me say Hmm?
 
CV carbs have the butterfly valve in the middle of the throat blocking airflow, so you can't compare the size directly with VM carbs. I suspect the CV carbs have more flow capacity regardless, but not enough to justify changing out the parts, particularly if your bike is stock otherwise. BTW, the CV carb heads have larger intake ports where the carb boots attach so you can't easily switch carbs between the two types.
 
Ok thanks for the info. Have any idea what these dirty 34mm should be selling for on ebay?
 
Power comes from capturing the energy released when gasoline burns in the engine. The more gasoline burned, the greater the power. Burning more gasoline requires more air. A bigger carburetor won't increase power unless the stock carburetor doesn't let enough air in. Engine designers and manufacturers work hard to be sure that the carburetors (or fuel injection systems) are big enough to supply all the air that the engine can use.

It gets more complicated, but don't worry about it.
 
Well I guess I will find out. Nasty Jones just shipped a set of CV36mm carbs and I have a set of 36 mm boots coming from Redmond Or. What else is involved, we will see. As for increasing the size of the carb; in general larger carbs improve top end power at the sacrifice of some bottom end response. The CV series carb depend on the "vacuum" to lift the slide. This is very similar to the vacuum secondary's on four barrel automotive carbs. I'm betting that there won't be a problem as they were stock on the GS1100s.
Correct me if I'm wrong.
 
Last edited:
Remington44-77 said:
Well I guess I will find out. Nasty Jones just shipped a set of CV36mm carbs and I have a set of 36 mm boots coming from Redmond Or. What else is involved, we will see. As for increasing the size of the carb; in general larger carbs improve top end power at the sacrifice of some bottom end response. The CV series carb depend on the "vacuum" to lift the slide. This is very similar to the vacuum secondary's on four barrel automotive carbs. I'm betting that there won't be a problem as they were stock on the GS1100s.
Correct me if I'm wrong.
Click to expand...

There was no difference in power between the 1978 GS 1000 with 26 VMs and the 1980 GS1000 with 34 BS carbs

You can't compare the two types of carbs directly

Putting the BSs on the 78 head will likely produce less power due to the huge step down in port size at the head. That will screw up the vacuum needed

Plus, you'll need the 1980 airbox and airbox boots

My advice - sell the BS carbs
 
Big T; My 1000 is now an 1100 and the carbs I'm getting are 36mm off an 1150.
I know about the step and will probably port to match. Also planing on a stage 3 kit for the carbs. As to the air box, Iv'e ran pods since the 80ies.
 
Remington44-77 said:
Big T; My 1000 is now an 1100 and the carbs I'm getting are 36mm off an 1150.
I know about the step and will probably port to match. Also planing on a stage 3 kit for the carbs. As to the air box, Iv'e ran pods since the 80ies.
Click to expand...

As soon as you start chopping that bike up, it loses collector value

Plus, a big bore kit will give you some HP, but not much gain with the 36s BS. You need someone with a flow bench to reshape the intake ports to really get any gains

You'd get more out of a set off 33 smoothbores, provided you put in some cams

Until then, all you're getting is a big flat spot
 
The value was long since lost. The bores were bad, hence the big bore kit. It has been ridden hard and bounced repeatedly. I've kept the paint job up as best as possible. Already the bikes parking at work have dwindles down to two since the weather has cooled. Harley s stay home if it rains.
I would have jumped on some VM33 s. If I can't get the CV36s to run proper the next choice ,I believe , is a set of RS36 carbs. I used to port heads for the drag racers here in Spokane.
 
The fact that it has an 1100 motor should have been mentioned in the beginning.
36mm carbs will work
 
install the big boots...
mark the port where it steps from big to small....
remove boots and shove something in each port to keep the chips out.
funnel the ports to match the marks...
simple shlt not rocket science.
36mm CV flows the same amount of air as a 33mm mechanical carb.

this thread jack is now complete :)
 
i have heard of people putting the 29mm smooth bores on the gs1000's instead of the 26mm....

would there be much of an improvement in performance in that scenario?

I found a set for $50
 
geesh keep it stock



If you want to go faster, buy a different bike.
 
Gregory said:
i have heard of people putting the 29mm smooth bores on the gs1000's instead of the 26mm....

would there be much of an improvement in performance in that scenario?

I found a set for $50
Click to expand...

29mm smoothbores are worth between $600 - $800+ depending on condition.:-\\\ You best grab them regardless...

Oh, and yes, they were a very popular upgrade for the early 1000.
 
barnbiketom said:
geesh keep it stock

If you want to go faster, buy a different bike.
Click to expand...

I probably will keep it stock, I was just curious since i ran across the 29's and had read in an earlier thread about them being worth about $600... (also mentioned again here in this thread)

It just got me to wondering how much extra "umph" you could get out of a bike with them. For me it would have to be significant to pony up that kind of money.
 
On a stock engine, not much improvement. The limiting factor in airflow is the size of the valves, how far and for what time they open, and the shape of the head. Just bolting on a bigger carb won't do much. If you have opened up the head so it can breath with big valves and a cam larger carburetors will make a huge difference.
 
That definitely sounds like wrenchinhg WAY ABOVE my pay grade. Thanks for all the info guys.

The carbs are on ebay right now and I am the high bidder at $50. Someone please out bid me, I have enough money making projects right now and someone here will be able to make a better go of it. (there is another set on for $389)
 
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