T500 jetting?

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RossB
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T500 jetting?

Post by RossB »

Hey Gents
Just trying to get a better understanding on jetting 74 T500 the motor has all new crank seals Wisco pistons,stock bore and stock air box with UNI foam filter Hiddspeed chambers. The carbs super clean
And have factory jets looking at all the threads it's gets a little confusing bike starts and idles fine
But no mid-range just flat checked needle Jets they look nice the mains are 97.5 don't mind buying jets just need base line I have Mikuni manual and Jetsrus would love some feedback.
Thanks!
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ConnerVT
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Re: T500 jetting?

Post by ConnerVT »

Try moving your jet needle up one notch, and see what the result is. There are shim kits available that allow you to move it 1/2 and even 1/4 notch. It is surprising what a difference a small amount can be. Shim Kit from Exhaust Gas Technologies

Here is one of the better write ups on tuning Mikuni carbs : Klemm Vintage Mukuni tuning
RossB
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Re: T500 jetting?

Post by RossB »

Thanks I will give it a try ordered new Mikuni needle jet and some pilots and mains because I haven't spent enough money on this bike!? Read the Klemm tuning it really helped I have a RD400 and man I got a lot of brass but it runs!
Thanks again!
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Re: T500 jetting?

Post by titan performance »

Hi Ross....I'm not familiar with Higgspeed pipes, but if you were running ours, with pods, I would suggest a 35 pilot, and a 115 main. Leave the needle in the centre notch. You may be able to run a smaller main, but at 115 you'll not melt anything if you cane the motor.
Keeping old 2 strokes alive !
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ConnerVT
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Re: T500 jetting?

Post by ConnerVT »

I know Titan has spent a lot of time tuning for chambers, but #35 seems a bit rich for a basically stock late model T500 with only chambers/pods. Maybe going up 1 step, to #32.5, but only if you can't find a happy place with the idle screw between 1 and 1 1/2 turns out, and the engine coming back down to idle fairly quickly. If the idle doesn't like to drop when you come off the throttle, that's a sign you are too lean.

I would certainly get the Main Jet dialed in first. A pair of Main Jets is usually inexpensive. The shipping typically is a good percentage of the cost, so it makes sense to pick up 115, 112.5, and 110 at the same time. At mid-throttle (~70%) the Main Jet will contribute enough that the Jet Needle probably will stay in the middle notch. If after you are comfortable that the Main Jet is correct, and feel things are lean in the middle, then work on the Jet Needle. Of course, the chambers may be sesigned for power in the upper RPM band, so it may never pull in the middle as you may expect.
RossB
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Re: T500 jetting?

Post by RossB »

Thank you guys for all the information. I have the stock needle jets P-4 and the 32.5 pilots and 100-105 mains coming. Got a little confused with Suzuki service manual one page said 150 mains the other said 97.5 So if you want some 159-Q2 needle jets F6 J6 needles and some 180 mains (round) and some #40 pilots brand new let me know! What's a starter jet? Could it be the choking system?
Thanks again!
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Re: T500 jetting?

Post by Vintageman »

Important! 1973 T500 and up used a uniquely different carb body and different jetting parts Don't be looking at 1972 and earlier jetting spec if your bike has 1973 and up carbs.

Use all Mikuni parts. I know the Needle Jet is obsolete (182 series or 188 ... I always forget which). Some times on eBay. You can cross to a 19x series (I forget the x but can look it up if you need).

If your needle jet inside, the first part where it meters with jet needle, is not perfect in there that will be a big tune problem. You have to look down intothe barrel, where jet needke enters with damn good eye to see condition of that surface. If anything less than pristine performance with suffer 1/8 to 1/2 throttle . It should be smooth if not shiny.

What do you mean by runs flat? No change in pull with no change in sound, or goes quite (lean), stumbles/gurgles (too rich). Or in all cases due to needle jet pitted inside for very poor fuel air atomization or wrong air/fuel ratio. Did I say the needle jet inside, where it meters with jet needle needed to be pristine? Jet needle needs to be the correct one for year too and perfect as well. Once that is solved

Get on road surface with little grade and let RPMs climb (3K - 7K) at these fixed throttle positions (hold throttle fixed when climbing up rpm scale. Will it cllimb up the RPM range? or do any of the above before it gets there. Will it Ping (Lean)

I have 1975 T500, Jemcos, stock air box, OEM filters I run all stock jetting but a couple steps higher on main else it pinged >1/2 throttle and up. All new brass, Mikuni, 19x Needle Jets.

The T500, with that jet needle is tough to tune all throttle positions (need a better tapered needle IMO, none I ever found). I have two tunes that work all throttle positions over a wide rpm range. If say degrees 70F and up and another if less than 70F
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Re: T500 jetting?

Post by ConnerVT »

74 T500, with original carbs, use the 97.5 Main Jets OEM.

72 and earlier used 150 Main Jet, as the used a different carb body ("Homopressure", which had an internally vented bowl). If your carbs have vents (overflow lines) that are outside the carb body, they are from 1973 and later.

The series of carbs for T500 does not use a Starter Jet.

They also do not have a "Choke", but rather, use an enrichment circuit. Pressing the lever raises the plunger, allowing a second pilot-like circuit to open, making the mixture much richer.
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Re: T500 jetting?

Post by RossB »

Thank you. This is where I'm at put new needle jets in 159-Q-2 102.5 mains and tryed 30 pilots ran ok sluggish,struggling in 1/4-1/2 throddle changed to 32.5 pilots made it worse takes forever to come back to idle and any air screw adjustment made no differents think that tells me pilots are to big? Ran good over 4 grand. Going try some 25 pilots just to see how it acts. Really good at taking carbs on and off.
Take care!
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ConnerVT
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Re: T500 jetting?

Post by ConnerVT »

25 is much to small. 2.5 = 1 step.

Put the stock 30 Pilots back in. Screw should be 1 to 1.5 turns out from gently seated. In is richer, out is leaner.

Also be sure you have the slides in the correct carbs. I could buy NOS fenders if I had a $1 each time someone admitted they got them swapped. Curved cutout at the bottom of the slide faces towards the air box.
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Re: T500 jetting?

Post by Vintageman »

Should be P-4 on needle jet as you noted earlier

with the 159 series Needle Jet at 102.5 main. Is this the large round main? I assume it is due to .5.

If you increased the pilot and middle got worse, too rich is possible. Pilot contribution made it just that much more richer. But its the middle needs to be fixed (too large main will affect here too)

When you get the p4s, run the factory main jet size/type, factory pilot size, factory needle jet(what is the number on needle jet?. factory clip setting on needle, factory float height. factory ignition timing, factory air box, plugs gapped to spec, good battery, Doesn't matter pipes for moment. The bike should run OK mid throttle. Once you get base line working decent, you can tweak for perfection. Isn't it fun taking carbs off-on-off-on-off-on-off-on...

This bike stock should work just fine. If not we'll look elsewhere

Update. When you check ignition timing use dial Gage versus rotor marks for I have see a couple T500 rotors spin that little woodruff key way. That's can be hell to debug and I always check this. Fresh points I assume?
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RossB
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Re: T500 jetting?

Post by RossB »

Thanks! First off I will check Points (new) gap and timing with dail gadge put everything stock thanks for all the help really need good base line. The 32.5 pilots were to big air screw wasn't doing anything
And took forever for idle to settle down. I will sort things out tomorrow night thanks for all the help! The guys at Auto Zone aren't much help!
RossB
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Re: T500 jetting?

Post by RossB »

Checked points like new ,adjusted gap little to opened then timing left side .05 out! Right about .02 out
Put all stock jets in runs great! Checked plugs after small ride left pretty lean nice white porcelain right side nice mocha brown, found out why I was smoking so much pump wasn't adjusted just dumping oil
In to motor.Might try bigger mains down the road cause I spent $150.00 on jets for nothing!
Thanks for all the help!
Really!
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Re: T500 jetting?

Post by sbaugz »

ConnerVT wrote: Also be sure you have the slides in the correct carbs. I could buy NOS fenders if I had a $1 each time someone admitted they got them swapped. Curved cutout at the bottom of the slide faces towards the air box.

Been there, done that myself.
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Re: T500 jetting?

Post by sbaugz »

RossB wrote:Checked points like new ,adjusted gap little to opened then timing left side .05 out! Right about .02 out
I've got pretty much same exact setup as you with one exception- a power dynamo electronic ignition. If you've got money burning a hole in your pocket, I would strongly suggest it. Mine runs great with it without a battery, and it eliminates those points, which I absolutely hate.
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