Suzuki 2 Strokes

tz375,

Currently the 6F4 needle is in the bike and it is definitely not correct or close. It's coming out.

So far the #6DH4 needle that came with the VM 34's works the closest. I ran it on the first and second slots, (it came on the 2nd from "bike buzzard" on ebay). With good low/midrange operation on the #1 and so so midrange but pulled great on WOT clipped on # 2. I did not back it down to the 3rd assuming that it would be too rich all together. But I may be wrong.

My initial thoughts are that the Q2 N/Jet is just too large in the ID (rich) and as been verified in using a Q0 n/jet as evidenced by "desmocat" in this thread. These carbs are initially setup for single cyl big bore 2 strokes. The shop that sells these has one on a 490 Maico.

I have downloaded the mikuni needle and n/jet tables to try and get a grip on lengths, diameters, and tapers.

Is it safe to assume that going to a P series from a Q series n/jet will alter up the main jetting and that also will require resizing?

Thanks for joining the thread!

All jet circuits overlap somewhat, but in general, A size or two down on the needle jet won't make much of a difference to the WOT main jet setting.

If you check out the MIKNUI carb manual it shows the effect of changes to each jet over the throttle range.

If the bike runs fine with the needle in the top slot it could be that the main jet is too large, but I suspect it's the needle that is too small at the tip. That 6F4 needle is 2.442 at 20mm and only 1.939 at 50mm.

By comparison a 6DP5 used on the TR750 is 2.518 at 20mm and 1.834 at 50mm. It is leaner at small throttle openings and richer from about mid throttle up.

I would be tempted to go down to a P-8 with the needle that works and see how it responds. That may require larger pilot jets to avoid the small throttle stumble. If that works better at mid range, adjust the needle up and down from mid (#3) and see what that does. If it's closer, try to the the main jet sized right with a WOT plug chop and see where that takes you.

Good luck.

Unless the needle and needle jet combination is too small, it will not have an effect on the main, as from 3/4 to full throttle it's just the main and pilot jet.

Thanks for all the input. I will get some new n/jets and try that out! Might be a week or 2 though.

Well I'm getting ready to get the new needle jets this week finally!

All,

The new Q0 jets are in and the bike fired well in the sub freezing temps. Going ahead and getting a pair of Mikuni 34mm-200 intake boots to get a perfect fit to the new carbs. I should be set with a bit of needle clip tweaking on the #6DH4 needle.

Smoke Em if You Got Em!

Marion

Update:

Got in the new Mikuni 34 mm carb boots in. So as we know it's not a Suzuki item and something will come up

The spacing for the 2 studs was too close and the boots are shallower! So the carb is an inch or so closer to the motor than stock.

So I had to slot the mounting holes and easy fix.

Due to the closeness of the carb to the motor there is a clearance issue. The new Mikuni Carbs have the choke levers facing outboard (left) not inboard (right). So the choke lever won't clear the cyl head when all the way up by a qtr of an inch.(off). Not to fear! I re-purposed the stock choke levers which now faces towards the emulsion tube of the carb and all is well!

I re-synched and balanced the slides, set the pilot to 1.5 turns, and voila, 2 kicks and she fires great in 10 degree temps and the throttle response is very good...on the center stand .

So I'm very encouraged, I set the needle to the center slot to begin with.

Waiting on a decent day to run it around the block!

FYI,

Marion

All,

With the warming temps in the low 50's I went ahead and tuned in the idle/pilot jets. These carbs came with 35 pilot jets. I wound up with 1 1/16 and 7/8ths turns on the air screw. Took the bike around the residential neighborhood and did a few 3rd gear pulls. The bike runs very well and I took it up to about 6500 rpm and it was pulling very nicely @ WOT, the mid range was very good also running through the gears. At a low rpm in 2nd gear making a turn into my street the throttle was a bit boggy, so that will require a tweak. The idle when the engine was hot was very smooth with a nice crackle, no smoke at idle or WOT. I'm currently using Yamalube R as I use this in my IT490 premix bike, but may look for an oil that is specifically for oil injection engines.

I loved to hear the bike scream and couple walking 50 yards ahead turn and look back to see what was coming up the street, as the Jemco's were wailing!

I will dial the bike in farther and will post a video maybe.

FYI,

Marion

All,

Well with the good warm weather I made a final adjustment to the bike. I moved the needle clip down one slot and that eliminated the slight bog off throttle and she runs very well. At about 4500 she really lights up and wants to really pull very hard to 7k plus! Took the bike out on the 4 lane highway at about 65 and the bike purred but the buzzing/vibes are crazy . I will go through the synching and pilot idle tuning to get it closer but it is really there. After moving the needle to remove the bog I will redial the idle to be exacting.

FYI,

Marion

Hello Mario,
I am currently installing aftermarket VM34‘s on my GT750. Mildly ported, increased compression, JEMCO pipes. I started with the stock setup, i.e. 260 mains, which is waaaaaay too rich, it hesitates to rev even in neutral. Due to weather conditions, I cant ride it within the next few weeks. What main jet did you end up with ( the hex style jets). I guess it must be below 200, but I have read comments from other GT750 / T500 users with up to # 280 mains in these aftermarket VM34 carbs. I would like to get into the ballpark for the first street tests

See video from test run

https://youtu.be/q8Jwtv3nyec

Hi, after an afternoon at my friends dyno and taking carbs off and on like 10x, we managed to get the aftermarket VM34s on my BIMOTA GT750 dialled in almost perfect. The bike pulls now smoothly off idle, and gets on the pipe around 4500 to lift its front wheel in 1st.
We ended up with pilot jets +2sizes, needle jet -3 sizes and main jet - 2 sizes compared to what I had before. This carb setup is visibly leaner compared to what most other people have posted here. Engine is mildly tuned, skimmed heads, JEMCO pipes, VM34 with foam pods.
Runs like a dream now!

Nice to see progress there. Well done.