TOPIC:

Hi,

I have today Mikuni VM24 connected to 1981 z750L engine (Wiensco 810 big bore).

How much more HP and TQ will I get to upgrade to bigger carbs?

What carb option do I have?

You need some porting to really get a noticeable benefit from bigger carbs. The intake ports have a sharp ridge before the turn down to the valve seat. this area needs to be carefully radiused, but not too much or it will hurt velocity. VM26 or VM28 would be nice upgrades and relatively cheap. also a free flowing exhaust will be necessary. This will also change the characteristics of the engine.

Without any porting work on the intake/exhaust head ports/valves you will never get more HP or torque with bigger carbs!!!

Larry Cavanaugh told me 3 to 5 hp on mine going from the 24s to 29mm smooth bores. I would go with 26s or 28s to if I had it to do over again. Like said not a ton of power but every bit helps and porting would for sure add to it.... the 24mm carbs are based on the stock 650 motor and the 750 head along with the 810cc could use more I'm think in.

Scirocco wrote: Without any porting work on the intake/exhaust head ports/valves you will never get more HP or torque with bigger carbs!!!

I have carbs orginal for 650cc engine, it suprise me what you saing, that I will not get more power with the 810cc by increase carbs.

Why was kawa not using the same carbs for 650 and 750 then?


If we talking 3-5 HP increase only, I think I will stay with current setup and then consider porting , cam and carbs in the future.

With the 810 use VM26ss or VM28ss from a z900 or z1000 .
These are the same boot spacing so will drop straight on and are good base for further mods.
You will gain noticeable power but port work, 4-1 exhaust and some better cams will make the most of them.

It will not be any differens between VM26 and VM28, VM26 is large enougf (if I only do the porting and cams + exhaust)?

If I can choice should I take VM26, easier to tune in? Or should I go for 28?

Looks like it’s easier to find a set of vm26 then vm28 on ebay....

I’m thinking install VM26 and then port the top later and then take the cams...

Fun to take in steps then I always have a project

The vm26 was standard on many Kz1000 models. If they work well for a 1015cc motor, that's probably all you need for 810 unless you have big cams and porting. The vm28 probably wouldn't make a difference, and could have worse mid-range power.
It's hard to compare the kz650 and kz750 carbs, since Kawasaki switched from round slide (VM) to constant velocity carbs, and the same bore size doesn't flow the same.

Thank you

Future projects then:
1. Upgrade to VM26
2. Porting top
3. New cam

Is there any issue thaking the upgraded in steps? Must I jetting each time then?

Was thinking first upgrade the carbs and use the bike and then new cam and use the bike and then do the porting....

How many HP will end up on when all these is done?

HP increase:
1. Upgrade to VM26 = HP increase?
2. Upgrade cams = HP increase?
3. Porting = HP increase?

That's the way your supposed to do it, one thing at a time, tune the carbs then add another, tune the carbs and so on. Unless you are installing a proven package.
I have an 810cc KZ650 with ported head, GPZ750 cams and an RC pipe with VM24 carbs. I've used VM24, VM26 and the VM29 smoothbores. I eventually went back to the VM24, they are way easier to tune, give me better midrange and mileage. I give up some at WOT but I don't ride around at WOT much.
I'd say it makes about 65 - 70 HP at the rear wheel, never been on a dyno but feels a lot stronger than a stock 650 or 750.

baldy110 wrote: That's the way your supposed to do it, one thing at a time, tune the carbs then add another, tune the carbs and so on. Unless you are installing a proven package.
I have an 810cc KZ650 with ported head, GPZ750 cams and an RC pipe with VM24 carbs. I've used VM24, VM26 and the VM29 smoothbores. I eventually went back to the VM24, they are way easier to tune, give me better midrange and mileage. I give up some at WOT but I don't ride around at WOT much.
I'd say it makes about 65 - 70 HP at the rear wheel, never been on a dyno but feels a lot stronger than a stock 650 or 750.

The VM26 is orginal setup for 750? So it should not be a issue tunning them in beforr I do the porting and cams?

So you ended up with VM24 and did the rest.,, hem what shall do...,? Hehe

All depends what your looking for. I prefer easy starting nice idle, smooth running and a strong midrange over top end power. I get that with the smaller carbs. I've seen guys put RS34 carbs on 750 bikes then have issues tuning them for all around performance. What they end up with is a bike that runs like shit down low but runs great at the top end. The smaller the carb the better the carburation due the stronger vacuum signals. Most people ride their bikes from idle to midrange and rarely get to full throttle so why tune the bike for full throttle? Also with the VM24 carbs I've had my bike at 125 mph at Willow Springs raceway verified with GPS. That's fast enough for me.
The biggest carb I'd put on an 810, ported, cammed good flowing engine would be a VM29.