Anyone running a TR500 spec engine with VM34 carbs?

Lets talk about those Suzuki Two-Stroke road racers here.
H2R
Posts: 7
Joined: Mon Nov 21, 2016 7:30 pm

Anyone running a TR500 spec engine with VM34 carbs?

Postby H2R » Tue Jun 06, 2017 4:12 pm

Hello,

I've got a Kawasaki 750 with a full H2-R spec engine, but fitted with Mikuni VM34 spigot fit carbs and I'm trying to sort a base spec for them: I thought that a TR500 with the same carbs might come close. The H2-R customer bike came with specially made VM35s and it's not easy to emulate them with a VM34. Mine are as follows, and I'm particularly concerned about the Needle Jet size as the Q8 seems to be the biggest for this size VM34, whereas the 250 jet is about 3 or more sizes smaller than I'd have thought safe:-

Main 250
Pilot 30
Throttle valve 3.0 (35.5mm dia)
Needle 6FJ6 or 6F5 in centre slot
Needle Jet 159-Q8
Air jet 2.0
Needle valve 3.3

All three carbs are from 1974-76 TZ350s.

Anyone with a TR500 spec engine care to share info? PM me if preferred.

Many thanks

Stephen
It's a great life if you don't weaken!

170plus
Posts: 129
Joined: Mon Sep 14, 2015 3:05 am

Re: Anyone running a TR500 spec engine with VM34 carbs?

Postby 170plus » Tue Jun 13, 2017 4:05 am

What was the H2-R stock needle jet size?

Interesting..sorry, no TR500 experience or data, but I'd be surprised if you needed richer needle jet than a Q-8. The 250/350 34''-equipped TZ's ran O-2's for years as stock (and probably too rich) - even the last non-powerjet TZ250F ran an N-8. Since each nozzle size is approximately an increase of 5% in 'richness', I'd be surprised if you needed an extra 70% (or thereabouts) over what a TZ cylinder would need (on a rich day) - or are you using it for cooling?

Here's a link to MikuniOz -it shows the biggest size available for the 159 nozzle as being an R-8, in case that helps. http://www.mikunioz.com/shop/mikuni-159 ... eedle-jet/

As for main jet - the TZ's would be safe in the 280-300 bracket, if that helps. Start at 300?

Personally, I'd get it running on what you have and get to a dyno and see how the exhaust gas works out, with a sniffer.

Let us know!

Dave E
Posts: 3
Joined: Thu Feb 09, 2017 10:11 pm

Re: Anyone running a TR500 spec engine with VM34 carbs?

Postby Dave E » Tue Jun 13, 2017 9:50 pm

Typical TR500 carb settings are:- Main Jet 310
Needle Jet Q-0
Needle 6FJ6 -3rd notch
Pilot 35
Cutaway 2.0

Or Tuned T500 barrels are:- Main Jet 270 - 310
Needle Jet Q-2
Needle 6FJ6 or 6DH3
Pilot 55
Cutaway 2.5

hope that helps Dave

H2R
Posts: 7
Joined: Mon Nov 21, 2016 7:30 pm

Re: Anyone running a TR500 spec engine with VM34 carbs?

Postby H2R » Wed Jun 14, 2017 7:54 am

Hello All,

Thanks for your feedback, this gives me a good base setting from which to start. I was fairly close, guessing a 300 main to begin with, but the needle jet will want playing about with.

I'll let you know how I get on, supposed to be out at Donington Park this weekend!

Many thanks again.

Stephen
It's a great life if you don't weaken!

User avatar
linker48x
Posts: 96
Joined: Wed Sep 16, 2015 12:14 am
Location: Alaska

Re: Anyone running a TR500 spec engine with VM34 carbs?

Postby linker48x » Wed Dec 13, 2017 12:06 am

We never heard back from you. How did you end up on the carburetor jetting?

I have never run a 750 Kawasaki, nor a 500 Suzuki, but I have ridden a bunch of 70 x 64 250 motocross singles, which would differ mainly by having a smaller main jet, and a larger cutaway.

Not that it is a direct comparison, but in 1969 I rode a 250 CZ, a 70 bore x64 stroke engine, with a 34VM carb on it. It used a 240 main, 159 Q8 NJ, 6FJ6 needle middle clip, 3.5 cutaway slide, 40 pilot, and number 2 airjet. It was about a 30-32 hp cylinder, probably a little under what you have.

The stuff you can reject here are the 240 main jet size, which is obviously too small, because the dirt bike exhaust port was low and the engine did not rev very high (maybe 7000), and the slide cutaway, because a big cutaway was a necessity on the open/shut throttle style, the stop and go, typical of a motocrosser. If it is any help, the main jet size is pretty much a function of hp in the cylinder, and rpm.

After I ported this engine, it ended up at a 270 main and 32-34 hp, so I am guessing your 300-310 main is close with higher rpm. That is more or less what I use in a 400 Yamaha twin with 34 VM's, with a 32 hp cylinder--I am guessing that is about where you are with this. The cylinder is smaller, but the hp is about the same. And I use a 2 cutaway slide on the 400 Yamaha, also. So my guess is, your information here was a pretty good starting spot to try to get the jetting dialed in.

H2R
Posts: 7
Joined: Mon Nov 21, 2016 7:30 pm

Re: Anyone running a TR500 spec engine with VM34 carbs?

Postby H2R » Wed Dec 13, 2017 8:31 am

Hello all,
I took a long look at the VM34s and found that there was a lot of wear on the carb body where the float arm spindle slides in, and the throttle slides, so I wanted to have them overhauled, but because this was mid-season all the carb experts had long waiting lists. I needed to move more quickly than 6 weeks so I bought a set of VM36 carbs and had them set up with:-
main jet 300
pilot jet 60
needle jet R-6
needle 6FJ6
throttle valve 2.5
main air jet 2.0
lever choke

It's a bit rich lower down so I'm getting it on a dyno next month to sort it out. It runs well as is though, and went well on the Vintage parade lap of the Classic TT in the Isle of Man. Pulled well throughout the rev range and really sang above 7000 revs. Fuel consumption is an issue, hence the need for a good dyno session. Struggling to get 10mpg (Imperial) at the moment!

I'll post the results of the dyno session, and later when I've finished the results for the spare engine I'm building which will have VM38mm carbs.

Thanks for all the input.

Stephen
It's a great life if you don't weaken!

170plus
Posts: 129
Joined: Mon Sep 14, 2015 3:05 am

Re: Anyone running a TR500 spec engine with VM34 carbs?

Postby 170plus » Wed Dec 13, 2017 5:57 pm

That's pretty rich in the mid-range, but if that's what it likes...! Keen to hear how the dyne runs go - hopefully, you'll have the use of an exhaust gas 'sniffer' to tell the tale, rather than doing things 'longhand' with repetitive runs and plug checks, etc.


Return to “Suzuki”

Who is online

Users browsing this forum: No registered users and 2 guests