carb question....

[titan performance]

I have been pondering hotting up my T500 cafe bike for some time.....the motor is mildly ported already, and fitted with Barton squish heads. I have been using the stock 32's along with a set of chambers similar to those we make.
I have a set of jugs that I got with a load of 500 spares over 30 years ago, which have huge ports by comparison to the ones I am currently running. They have pistons with them, and look to be in very good order, with the porting work being very tidy. I will get some measurements and post shortly. I have also just bought a set of flat slide 34's as fitted to the RGV250.....which I am hoping will go on the 500.
Assuming I can use them, I will probably opt for pods, does anyone have a clue what size jets I should be starting with?

[Alan H]

I should think about an inch bore!

'Gas mileage may be less that manufacturers original spec.' (cough!)

[titan performance]

Alan....shall I not bother with a jet, and just leave an empty hole?
To be honest economy doesn't matter at all.....I do very few miles on the bike. Many years ago I experimented with needle heights, and ended up lifting them a notch or maybe two.....result was, it ran shite, and did 17 to the gallon !

[Craig380]

With that new set-up of heavily ported cylinders, pods, chambers etc, it might not be a bad idea to try running the carbs with the main jets removed, just to see if it would be stupidly rich and drowning in fuel, or if it will actually run halfway decent like that.

I'm sure I've seen an article or two either on here, or on Muzz's site about near-TR500 specs for porting and carbs ... maybe one of those would give you an idea for jetting?

At least the carbs are easy to remove & fiddle with, compared to the triples

[Alan H]

Haha TP, when the Cobra first appeared, everyone reckoned the only thing they couldn't pass was a petrol station!
I always did like them, never managed to get one..........yet.

[titan performance]

Heard that said before Alan....though unless abused, I never found the 500 to be too bad on fuel.

Thanks for the input Craig.....I guess some internet research might get me somewhere.

[Craig380]

Here's some stuff to start with ... might give you a baseline to work with: http://www.ozebook.com/compendium/t5015.htm" onclick="window.open(this.href);return false;

[Vintageman]

craig380.

Nice article. I keep seeing reference to the "old go fast"5mm intake, 5mm Ex, 1.5mm off head. Maybe, i'll go 3/5 of that soon on my spare engine.


Titan performance.

Maybe just try the carbs as they are and see what happens and maybe a little tweeking Being only a 250 at first I would think jet is rich to give a good signal but, thinking again this a TZ250 and revs near twice as much as t500 so probally close to what you need?.

Would look nifty with flat side

[titan performance]

Thanks Vintage....I took a chance buying them really, but they were reasonable. They are designed to create a down draft, ie built on an angle, so if I just bolt them straight on they will be tipping backwards, but I thought I could possibly turn the inlet stubs upside down, which will hopefully put them at the correct-ish angle. If they don't work, they will be back on Ebay, and I will have to spend out for some conventional looking flat slides.
I too have read the 5mm off each port story a number of times, and I'm thinking that may be what has been done to the jugs I intend to try...as the ports look huge compared to stock, or even the ported ones I currently use. I imagine my Barton heads will put compression back where it needs to be.....My 2 stroke guru reckons he can get over 100 bhp from a 500 twin....and I have read claims of 90 many times. Though I'm not dreaming of those figures....as I'm sure that would need a lot of cash. To be honest, I never get off the 500 and think that it feels slow as it is, so a gentle but noticeable increase would be great.......lets see how we go.

[Vintageman]

The official early T500 performance bulletin says those changes make ->
60-65 HP at 7800 RPM. That would be exciting. Also no port widening so rings won't void the 6K mile warranty ( ). I wish it was dyno'd to see if it still has some bottom end. I think the 69 H1 claimed 60 hp at 7500 RPM. The artcle craig380 posted kind of implies its a good boost of power, but you can make more. I would like to get a little less maybe peak down to 7400-7500 RPM 55-60 HP.

It also says to run the TS250 Savage MX carb .and it's a 32mm as well "... and are preferable because they are design for competition" My guess is they are not Homo vented like early T500 (hint use later T500 carbs).

I think you are saying those TZ250 flat side bore is meant to be angle while the bowl remains level. So they point directly into engine no bends in flow path (probably key on a high rev'ing TZ)

How about using the later T500 intake Aluminum manifold and boot and mount that upside down? Low cost test to see how close it is. Maybe what you were saying. If not I agree put on eBay and run 32 VM or maybe 34 VMs.

Barton heads? what are those.

[tz375]

We have to remember that dyno charts and HP claims from back in the day were all done on a Crank HP basis and were heavily "adjusted" as a rule.

For example the 68 or 70 HP that a GT750 supposedly made translates to somewhere between 48 and 58 RWHP depending on the dyno.

RGV250 34mm flat slide carbs are fairly sophisticated and are designed to work at a fairly steep downdraft angle. How well they will work remains to be seen and you will have to jet them the same way we always did - jet by jet. The 270/280 main jet is a good place to start but the air jets are really small and power jet are all over the place, but a 50 PJ with 280 main is more or less the same as 330 main jet in a non PJ carb.

Needle jets should be close P-8 or O-0 but I have no data on the needles. I suspect that the slow jets will be too small though.

[Vintageman]

I use these old crank HP @ RPM as a relative figure of merit not absolute. Also no standard agencies to certify results, but looking and period test and later data they all seem to exaggerate the same amount.

I agree it would be tough to jet and one by one and then a few iteration to get spot on. And if you can find jets.

Also if you don't mix some gas with oil and you are too rich on an oil injected only machine you can end up with fuel wash and thus no oil and make a mess of top end very fast.

It can be very time consuming. If me ( I have no patients/too lazy these days)

curious What angle are the TZ carbs

What are Barton Heads? Squish designed, OEM outer look?

I never tried adding Power Jet to VMs. I did recently see a Youtube on a H1 (recent posting) build where the gent added them to his stock carbs. also ported cyls too. Looks like it was tuned well.
http://www.youtube.com/watch?v=inJwd1g_SC0" onclick="window.open(this.href);return false;

[tz375]

Barton motors was Barry Hart and Graham Dyson (of NOVA transmission fame) and they offered a range of parts and services for Suzuki. In fact they also replated and ported XR11 cylinders for Suzuki UK. I have not seen a Barton 500 head but I would guess that it's a squish band high compression design.

[titan performance]

TZ is right on the heads.....I'm guessing they were cast to look like stock, but have a squish internally. Back in the day, production bikes had to maintain the stock silhouette. I had heard that the pipes got opened and cones inserted, then re-welded.

Vintage....the carbs I picked up are from an RGV, not TZ.....and yes, they are downdraft while keeping the bowl level. My bike is a T500M, so I was referring to turning the manifold stub upside down....not sure if the angle will be right, but will give it a go soon, once my TT bikes are done.

[Vintageman]

You did say RGV ... I am clearly suffering from Dyslexia (Dslyxeai) more and more.

Are you goind to try them? Post a pic if you get them mounted

I like the fact Barton kept OEM look. You know, unlike some of the radial finned aftermarket heads for Yams.