T500 hopup details

[Suzukidave]

http://www.ozebook.com/compendium/t500_ ... /grant.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[Vintageman]

This is an interesting article, but confusing to me as well. Maybe it has errors?

Also I have a general question when raising exhaust port: should you shave head for example to maintain original compression.

My article review notes:

First advice uses stock carbs “ it took Ron 5 days to tune those carbs” Fussy buggers.
It does not say, but I assume the T500 is a 71.
What gets confusing is the jetting recommended for improvements.
"Main jet was raised to a 260." Are we still talking round mains? 150 round main was stock. Wow 173% larger. really?

“Standard T5 Needle Jet and Jet Needle was used” T5? I think it supposed to be P5 not T5?
Pilot changed to 35 (OEM is 30). OK I found that helps too

“2.5 cutaway in place of 2mm standard slide” OEM states 2.5 is standard. Is this a typo in article and they changed to 2mm?

They also raised and exhaust port 1.0mm. Doesn’t say if they remove same from head or top of cylinder to hold OEM compression.

Emphasize stock exhaust only

Is the above is what the article claims gives the 1.5 sec improvement in 1/4 mile time and additional 10 mph. Wow if so that is huge!

Would love for my T500 to have that type of gain, but I like Chambers too.

Next is radical and they state specific chambers and raising exhaust port 4mm. Never say to shave head to hold compression. Don't need to?

if you do Need to and shave head not 4mm if the shave gets into dome area. If so need to reshape to ensure piston clearance at TDC. Maybe don't need too for chambers raise compression top end only

Are they assuming you know do to this (I don’t know) or truly no other change needed?

Anybody have experince with raising exhaust port on T500?

Thanks

[redline]

When they talk of raising the exhaust port, this is done using a die grinder / dremel and the compression stays the same.

Different from adding a spacer under the barrel which raises all the ports and requires machining of the top of the cylinder.

You could do the mild porting and add chambers, but you'd need to figure out the appropriate jetting.

[tz375]

Yes and No.

Yes the static or geometric compression ratio remains the same. The so called "corrected" CR drops as the port is raised.

Th effective compression will probably rise at higher RPMs because the exhaust is generating stronger pulses, but will be lower at low revs.

[Vintageman]

TZ375 (all);


I was thinking when they raised the port 1 mm (0.040") they just put up with a little compression loss bottom/mid.

"Stronger Pulses” you mean stock exhaust pipes reflected pulses pushing back a bit more charge during compression stroke? They also retarded the timing a bit which goes along with that if I understand.

So we are thinking maybe a 1mm exhaust raise is worth considering as a mild top end hop up as is.
I think you could shave 1/2mm (0.020?) to get some of that back with no worries about clearance

Back to article critique

I think the T5 and move to 2.5 slide cut from 2.0 are typo's. The T5, typo, trivial for they said they did not change and the Needle Jet and 1971 had P5. They lose your confidence ( my typing English sucks too, nor so I like to proof read)

Does anyone know if 2.0 slides can still be bought new for the T500 32mm carbs?

Now 260 mains versus 150 mains… Come on. Is this a typo too? Did they mean 160 mains?

If 260 did it have pods. I think they would have said so

Anybody running pods and dare state their main jet size?

If they truly got 1.5 sec and another 10 mph in 1/4 mile drag time that is impressive and a noticeable change for rider. They did not say, but maybe this gain did not require more top end, just better tune of existing range. Maybe they did geta bit more top????

I was wondering if more experience people with T500 out there tried this stuff or similar to achive mild hop up goal

From here on I no more article question, Just why I keep asking questions on this board about T500

I am looking for a proven mild hop up that places peak power to be at 7000-7500 RPM still have good/better midrange, but don't every care about riding in city traffic as main goal (Ok to loose a little bottom)

If the T500 was popular for Mild to Wild hop ups back when, not too much info made it over to web.

The only mild mods I have seen are

1) The alleged performance drop between early and late T500 peak power dropped from 7000 - 6000 RPM
Some chatter says it was not all true and a bit exaggerated “paper change" to make GT550 more attractive.
But, there is one period magazine article where they tested both at different times and said later T500 performance loss was significant and they condemned such a change.

2) This article that claim a 1.5 sec gain and 10 MPH

I am working on correcting an 0.20” over bore error done on my GT250A (the cutting bar must have jumped loose on guy for a moment for I have deep 360 degree groove just below intake port that has been acting as cheese grader on my piston skirt as the piston moves to BDC.

Lucky I found 1.25mm “ART” (may have been piston OEM for Suz) over pistons and should clean that up.

The 75 T500 may be next. Found its top end a bit boring and breathless to be a fun streat bike.

[tz375]

The article is slightly ambiguous in that it includes two stages of tune, mild and wild and a gearing change, so it is not clear which combination achieved that 1.5 second change. The picture of the bike that had the 1.5 second caption clearly has chambers and they mention that chamber work with the Wild combo.

The article also shows small diameter crank wheels and stuffers, so I suspect that the improvement is the 4mm exhaust plus chambers and crank state of tune.

1 to 2mm off the roof of the exhaust should help a little and raising compression is usually a good idea as long as the timing is pulled back a little. The ports lack area for big HP at higher revs and must be wider as well as taller for a big top end.

A set of good pipes and ports could make the bike a lot more fun.

[Vintageman]

Thanks for looking at article and advice

Yes, maybe that is the Wild to shed 1.5 sec/ and gain 10 mph. Given all sated I thought they would have more gain. Maybe 1.5 sec is a lot

Yes, they did say 13 tooth versus 15 up front for that gain in a drag. Also too high rpm for street

260 main for “Mild” must be typo and meant 160. Well this is trivial

My brain tells me they really used 2.0 cut slide not 2.5 during the mild tune… that must have helped midrange. This sounds like nice to have for street. I think bike could be better here too.

How does one figure out what family of Mikuni slide the T500 had and then if 2.0 is available still?

Well I think I’ll use my early cylinders and intake stuff I acquired, Jemco chambers, Wossner 0.5 mm pistons, modify exhaust ports a tad, shave heads a tad (safe piston to head clearance?), retard timing a bit, 14 tooth sprocket, 2.0 cut slide if I can find. Then Jet as needed

$$$$ = Fun I hope

[tz375]

I checked the article again and the pictures and the original carbs were 32mm Homopressure types which were swapped for a pair ofVM3x aftermarket carbs. I can't tell you what size, but that's were the 2.0 slide comment came from. And the exhaust ports look much wider too.

[Suzukidave]

( Some info sent to me for posting to this thread by Cyzygy in Aust. ) The T500 pictured
ran a best of 11.88 in 1976 and I'm reasonably sure /SB had to use standard carburation (I can check). Best times I saw in the day for a stock T 500 here was low 14s so that would mean a drop of 21/4 plus seconds making the claim of 11/5 seconds feasible. I'm reasonably confident this T500 would have been the quickest one in /SB in Australia. /SB in Australia at the time was stock external appearance except for exhaust system turn indicators and rear view mirrors with any internal engine modification allowed. The Honda rider in the near lane is Steve Harker, an Aussie who has competed in Top Alcohol Funny Car in the NHRA in the USA.

[Vintageman]

I checked the article again and the pictures and the original carbs were 32mm Homopressure types which were swapped for a pair ofVM3x aftermarket carbs. I can't tell you what size, but that's were the 2.0 slide comment came from. And the exhaust ports look much wider too.

Tz275

The third page second paragraph says->

"Stock carb proved to be just fine. Changes were as follows. The main jet was raised to No. 260 ..."

That's must be a typo

Later they talk about TS250 carb with 240 jet

[Vintageman]

I checked the article again and the pictures and the original carbs were 32mm Homopressure types which were swapped for a pair ofVM3x aftermarket carbs. I can't tell you what size, but that's were the 2.0 slide comment came from. And the exhaust ports look much wider too.

Tz275

The third page second paragraph says->

"Stock carb proved to be just fine. Changes were as follows. The main jet was raised to No. 260 ..."

That's must be a typo

Later they talk about TS250 carb with 240 jet

They also said the 2mm change with stock carb

[tz375]

The stock car is fine for the mild tune, but they used a different carb for the one with chambers.

[Vintageman]

Tz375

I focused mainly on mild stuff and page 3 paragraph two that talks about stock carb mild mod more I think about it is full of errors IMO. I do believe they changed slide though just other way versus what was stated.

[tz375]

The combination of poor writing, incomplete data and obfuscation all lead to confusion rather than clarity, and that was probably what they were trying to achieve.

[hogpacker]

these are definitely not mildly ported t500 barrels
but thought you might be interested in having a look
Lawton barrels of a Colemans tr500