Carb rebuild kits?

[akazoroe]

Looking for a rebuild kit for my T20 carbs.
Ive seen Keyster has their kit but have heard some stories about some of their kits.

Any input on that would be great and any other kits out there.


Thanks

[Ivan]

All you need is bowl gaskets (available from Suzuki)
and needle and seat assy's (I have to look into this to see the best place to get them)
The rest of the aftermarket "rebuild kits" for the old 2 strokes are unnecessary parts that are not the same quality as Genuine Mikuni...

I have a Carb tuning kit for this bike that I am about to release just after the 1st of the year..

Watch this page for details and availability:
http://www.ivansperformanceproducts.com/T20.htm" onclick="window.open(this.href);return false;

The kit contains new needles (my own design) mirror finished stainless steel.
New needle jets - replicas of the originals (nobody is offering these)
Float bowl screws - stainless allens
Pilot jets (2 sizes)
Main jets (3 sizes)
A setup sheet with all my tuning tips for this bike.

Here's a photo of my Kawasaki H2 750 kit (which the X6 kit will contain the same basic parts):
http://www.ivansperformanceproducts.com/h2kit.htm" onclick="window.open(this.href);return false;

This kit is a major improvement in driveability and power for this bike... it'll actually climb a hill in top gear.


Ivan

[akazoroe]

Wow Ivan...I love it.

Gonna wait for your kit I think.

[rbond]

Think you will do carb kits for T500's and GT500's? Would be a huge step up from Keyster stuff....

[Ivan]

I am doing the T500...

I'm almost ready with my 34mm kit for the Cobra... this was a bit difficult because they really screwed up these carbs bad.

Then I just need to get my hands on some 32mm carbs for the rest of them.

Maybe someone wants to lend me a pair?
I'll also need a late model airbox, and intake runners.

Ivan

[lil red s-10]

il let u use mine from my gt750 if u end up making them for the 750

[Ivan]

I would need a GT750 too..
Those carbs from the 750 although they are the same size, the internal orifices are different as are the needle jets too.

To design a needle takes several months for all the prototyping, dyno testing, trial and error, road testing.... more prototyping. Then there's the needle jets... more testing...

I already have a T500.... so to make stuff for the later models, all I need are the carbs, intake setups and airboxes.... the minor porting changes over the years are insignificant to fuel requierments.

It's the later silenced airbox that caused the reduction in main jet size and needle changes.


Ivan

[ConnerVT]

It's the later silenced airbox that caused the reduction in main jet size and needle changes.

This is not correct. Been there, and currently living that.

The main factor in the difference between pre-1973 and 1973+ T500 jetting is the porting of the cylinders.

I have a 1971 T500, which I replaced the motor with 1973. The bike, when I bought it, had a late model air box on it (the front mounting arm was shortened to allow the shorter carb intakes to be used). The carbs on it were jetted with a 145 and a 147.5 Main Jet.

I started jetting the new motor with new 150 Jets. All else the same (short intakes, late model air box). Terrible! Installed an early air box, and (NOS) paper filter. No perceivable difference. Spent a month moving downward in size of Main Jets. Now running decent with 100 mains in both carbs, part throttle good, but in the spring will go even smaller (expecting 95 Mains, and needing a slight tweak richer on the Jet Needle).

I have a thread that I started that follows my tuning, with input from several forum members: viewtopic.php?f=5&t=6870" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[Ivan]

In all my years of experience designing carb tuning kits, intake restriction dictates needle design... When I get to that bridge, I'll cross it.... there is no point in arguing something that I haven't experienced yet.

I've read your tuning troubles... sorry to see anyone that has problems in this area.

Just a thought, the intake boot (carb to airbox) may have some bearing here.


Ivan

[ConnerVT]

In all my years of experience designing carb tuning kits, intake restriction dictates needle design...

Is that applicable to both 2-stroke and 4-stroke? From what I've read here, changing from an air box to less restrictive pods may require jets that are 1 or 2 steps different. The change here is nearly 33% smaller.

Just a thought, the intake boot (carb to air box) may have some bearing here.

Have both early and late carb to air box boots. There is almost no difference between the two dimensionally.

There were several significant changes made in 1973:

• Cylinder -- Intake porting changes, which a divider added in the intake port.

• Intake runner (carb to cylinder) -- Increased 40mm+ longer.

• Carb jetting -- main jets decreased to 97.5 from 150, as well as a change to a leaner Jet Needle, and (finally) settling on P-4 Needle Jets (early jumped around with P-5 or P-5/P-4 combinations).

• Air box boot -- Very slight change, I believe mostly to remove interference with the tach cable.

• Air box -- Change to foam filters from paper element.

The intake runner length may also play a significant role in the smaller jetting needed. I haven't explored this possibility, as a chose to go the path that kept the bike visually configured as a 1971 model. I bought the early model air box and boot, as the 1971 frame does not have the mounting cross member to accommodate the late model air box (1973 and later frames have 2 mounts for the battery box, as it also needs to move back 40mm+).

My "problems" really haven't been a big deal, all part of resurrecting the old girl, and I've learned a lot in the process. The only real trouble I've had was not having a starting point, and after putting the time and money in rebuilding the motor, I wanted to err on the side of caution, and not run lean and hole a piston.

[Ivan]

I did a little research in my very old carb parts and to answer your question as to why the change in jet size.

You must be running the 5FP17 needles (late model)
These are very thin on the end (WOT) and will require a much smaller main jet.

This is the only thing at this point that would make sense here since you swapped out many of the other intake parts with little effect.

The reason that I thought at first about the intake boot is that the later one with it's internal stacks has 1/2 the intake area of the early boot... and again the later more restrictive airbox would have an effect as well.... apparently not very much.

There's always a pretty simple reason for things in these old bikes.

The difference between P4 and P5 on the needle jets is not significant (appx .0005")



Ivan

[tz375]

Ivan,
Do you happen to know if all T/GT500 crabs were homopressure. The carbs I refurbished recently had homopressure 34s but the 32's vented out of the top of the carb and not down into the bellmouth. What I don't know is if those carbs were typical of one year or all years of 32mm carbs. The set of GT750 crabs I cleaned up were also NOT homopressure and were similar to 500 zinc bodied carbs.

[Ivan]

According to the (1969) T500 II service manual, they are internally vented so I would assume that the early ones (up to 72) are the same.
I'm not sure that all the T500's 32's were internally vented.... this would have no effect on the main jet though.

The 34's and the 32's (on my 305's) and T350 and T200 were internally vented. (Homo-pressure)

H1's are like that too.

These old carbs are very sensitive to needle length and diameter ... change things a few thou in the tip diameter or 3/4 the way down, and it has a pretty large effect.... all the way down to 1/4 throttle operation and cruise.


Ivan

[ConnerVT]

We'll, we are just going to have to agree to disagree.. As most of what you just wrote is contrary to all of my research, both through Mikuni documentation and from a couple of months of experimentation. I have done a number of configurations that I haven't documented in any thread, sometimes 4 changes in a day.

The Main Jet is only a small component of partial throttle operation on the VM carb (unless grossly oversized, as when I started with the 150 MJ). At part throttle, the needle Jet/Jet Needle, the slide cutout, and the Pilot circuit are the major influence.

The difference between a P-4 and P-5 jet is worth moving the clip on a Jet Needle about 2 slots.

The Suzuki needles for the T500 are double taper. The difference between the -8 and -17 needle is where the second taper starts, with the -8 taper starting to make things richer a little sooner.

My 1973 motor is configured as an early model, with short carb-to-intake boots, early air-box, and early air-box boot. Yet is runs terrible with the 150MJ installed (with either -8 or -17 Jet Needle, or P-4/P-5 Needle Jet). However, it runs great with a late model carb setup. Please explain how your thoughts fit this.

[Ivan]

I haven't seen a set of T500 32's in a long time.... so even if the book says they are internally vented, they may not be.... They may be cast with the passage, but it may not be used....

Just like the GSXR750 (1990-1992) power jet carbs that were blocked off.... or the RZ500 power jet carbs that had the passages, but they weren't drilled or tapped to take a jet.

When I get some in my hands to test, I'll document it so there's no question.

Ivan