Suzuki 2 Strokes

tz375 -- What you say about pre-mix vs. injection makes a lot of sense. Hadn't thought of how they would differ before your post. Thanks for the insight. More to mentally chew on.

NY500 -- I've finally am down to a 105 Main Jet, just like you. I can feel the improvement each increment down, and the 105 runs great until the last 1/8th of a turn to WOT. I have a set of 100 Main Jets to try, maybe I'll get one more day of nice weather (when I'm not at work) to try them out before I run out of riding season.

I did take a nice long ride on Friday. Nice to be able to enjoy the ride, and not be focusing on how the engine is behaving.

I wonder if the reason for such a radical main jet number (150 to 97.5) difference is the the early T500 has Hex main not Round like the later model.

That would also mean it uses a 159 series Needle Jet not a 188 series since they are the same accept hex vs round.

Can someone verify?

A 150 Hex is between a 112.5 and 115 round so if I am correct still more air coming into earlier model for proper air fuel ratios

They did this same change on early verus late T350 as well.

Just way too much difference to make any sense to me given given what I know about the bikes

I also think most of the change is in the air box/ Air filter deisgn of the late model as well.

All I every heard is the divider is not as significant in the earlier cylinder (wish I could see a pic), no change in port height or width... So that shouldn't do too much to jetting. It could reduce maximum mass flow into cyclider and why less peak HP if the divider is restrictive

This is the same kind of change you see the Yamaha RDs go through main jet reduction as their airbox /air filter changed over the years only. Same kind stuff on GT250

Wish we knew for sure about Jet type, bites a lot of people on the T series if we are talking Hex versus Round

ConnerVT

Just remembered you were running all early stuff accept cylinder. So my whole statement of air filter ain't nothing in this case if your settling on later Main Jet size. Those later cyclinders must be the big difference verus early style? We'll see where you settle.

Still wonder if the early model was running Hex mains versus round

The carbs on the '71 motor from the bike had a 145 and a 147.5 main jets on a P-4 and P-5 188 series needle jets. I've never seen that motor run, but also have no reason to believe that wasn't the configuration that was in it when it ran last.

I bought a second set of carbs off eBay, which had 97.5 main jets on a P-4 and a P-5 188 series needle jets. This is the set of bodies (and one needle jet) that I'm running now.

The rebuilt '73 motor is running 105 main jets (and probably will like 100 better) on the P-4 needle jets, and 5PF17-3 jet needles, short intakes, and early air box with a NOS paper filter. It is very happy at this config, with a rich flat spot from 7/8 to WOT.

Just data, can't make a 100% conclusion from it.

ConnerVT,

I think your 71 (one bike smaple) carb data is good if it agrees with what the specs should be.

I did the same thing with 1969 T350 carb set but in that case the main was suppose to be 170, It was but Hex and the needle jet was a 159 series. I also have 68 T305 carb set and same thing main. I also see no reason two bikes would have changed.

So I questioned the T500

Since you are running all early parts, but the cylinders are later and heading towards the later style jetting ( infact almost there ) it must be the cylinder that dominates.

ConnerVT,

Did you get a chance to finalize your Jet tuning?

I got damn close, but no, I've probably run out of time (and warm air) to get it set this year.

The main jets in it now are 100, jet needle in the middle clip, P-4 Needle Jet. It runs excellent, except it still is a bit heavy/rich at full throttle. I would like to try a set of 95 jets in it, but that will need to wait until next year.

I did get a couple of nice days of riding in with the 100 jets, the bike ran great at just cruising around the southern Adirondacks. The plugs look great, no fouling, and a very light hint of mocha brown on the ceramic.

ConnerVT,

Thanks.

It looks like you settled right in on the later T500 jetting specs even though all but the cylinders are original early T500 style: very interesting.

I like this idea. Your bike remains original, but has later cylinders (that no one can see inside).

This Spring, I may do the opposite. I have the later T500 and may change just the cylinders to the early. I do have the early T500 air box etc. but, based on your experience I may just keep it looking like a 75 T500. I'll use a jetting as a starting point for a 72 T500 for example and may be close.

ConnerVT

Does your bike have the early Homo Pressure Carbs or the Later ones without?
I think you saw the other recent post From Ivan and Tz375 that there is a difference between them.

If you have the later carbs without H-P maybe this is why you have settled better with later Jets

Currious if you rember which you useds

Thanks

Early, non-vented.

I believe your mean you have the original 69-72 early carbs that are internally vented for they are Home Pressure type with internal vented from Venture to bowl.

Again in summary your bike is all early stuff, but the cylinders which are the later.
And you have worked your jetting to be best when very near later specifications and poor when earlier.

Amazing!
Thanks

Dang, I read the other post again where Tz explains the Homo Vent location... And Ivan’ s eBay pic links’ I understand how to tell finally which is which

I read this again too. ConnerVT you have the early carbs proper for your year bike… It is all proper stuff but later cylinders.

Anybody have thoughts here to questions ?

Maybe they used pods? Can't tell by article or cover pic.

If so a lot of people have asked how to jet T500 with pods

Sir, (ConnerVT)
I just read thru your post concerning carb tuning from 2012. I am trying to
do the same thing, i.e., jet an early bike that has a set of later
cylinders. I do have a set of non vented carbs I would like to use. I think
you ended up with main jets-100, jet needle in the middle clip, P-4 Needle
Jet, 30 pilots, 5fp17 needle and early intakes. I think you concluded the
difference in jetting was due to porting changes to later cylinders.
Eight years later has your jetting changed? Do you still think the jetting
difference between early vs late was due to porting changes? Would you
recommend using the non vented carbs or trying to find a set of later
vented carbs?
Thanks very much for any insight you can offer!

Fuel flow through the jets is driven by the pressure drop between the float bowl & carb venturi.
That pressure drop is different for early internally-vented carbs & later float-boal-vented carbs.

So the jetting needs to be different for early & later carbs when everything else is the same.