1971 T500 Main Jet

[Vintageman]

Hello,

I see the 1971 T500 is supposed to have a 150 Main Jet. I went to order this from Suzuki and stated Unavailable. Is this a Large Round Mikuni Main Jet? If so it is available from people like JetsRus. My guess is it is not or Suzuki would sell it too? If not what style is it?

I see there are Keyster kits on eBay showing a Main of 150 and correct needle too. Is this correct kit for the 1971? I think it is? Has anyone had experience with this kit?

Funny some post says it covers 69-75 and Paul Millers states up to 77. I thought 73-77 used a different main jet and Jet needle too?

Well I need to know if I can get the correct style 150 mains new for a 1971, else will the Keyster kit work for the 1971, else is it truly an obsolete styled main style


Thanks

[desmocat]

Correct main jet for a 1971 T500 is #150, and it is a large round style (with screw driver slot), not the hex jet. When port runners got longer in 1973-77, jet size and style changed.

[T350guy]

Stay away from those carb kits. The only thing that's usefull is the needle and seat and bowl gaskets. the main ,pilot jets and needles are useless.. Mikuni still makes those jets

[Vintageman]

Are you saying the Jet needle is no good too? I was relying on this to be OK for the 71/72 use a different jet needle than the 73/74/75 on. Has anyome had success with it?

Back to main jet. Is the 71/72 to same type as the 73/74/75. I mean they are all using Large Mikuni round jet just the earlier is a 150 and the latter is 97.5. Does soemone know for sure. Can someone look?. I do not have a 71 or 72 I can look at.

I hope the Keyster jet needle is OK and is like the 71/72 (claims it is). This is not available anymore

[tz375]

According to my records, the early bikes used a 5DP2 needle but I don't know what needle was fitted to a 71 model. How were the original needles from that bike marked?

Do you know that they are worn or is that more of an expectation? The needle jets are as likely to be worn. They are 159 series P4/5 according to my notes, but that could be incorrect.

[jabcb]

Carb specs for 71-75 are in Service Bulletin Specification-6:
http://www.ozebook.com/compendium/techb ... %206-9.pdf

Carbs spec for 65-70 are in Service Bulletin Specification-11:
http://www.ozebook.com/compendium/techb ... 010-14.pdf

[tz375]

Thanks, I forgot to look at those. That says 5DP8 and I have no specs from SUDCO Anyone have one that we can measure and find a close match.

[jabcb]

Looks like the 71 T500 uses 5FP8. Don't what the the difference between "F" & "D" needles are. Sudco lists the 5FP8.

[tz375]

I'll have to get my eyes checked again. I read that as 5D not 5F. That's much better. SUDCO list them and we have those in the old graphs of needle size if that's needed.

That needle is very rich at the top end and relatively lean lower down by the looks of the data on the chart.

[Vintageman]

The 71/72 uses a large round Mikuni 150 (funny Suzuki shows obsolete and still available elsewhere. This concerns me a bit).
The 75 has a 97.5 large round too. I have this Bike so I can see it as well.
So I don't think 70/71/72 versus 73 and on use a different style Main jet as an early reply to one of my posted stated.
The main jet in this early model is just larger. I think initially some thought it was a different hex/amal style and I don't this is the case these years. Correct????
The Jet Needle is different so need the 5fp8 if running the 70/71/72 setup.
I can also tell you the boot between carb and air box is different. The 73 and on use some additional baffle tube (add restriction I am sure)
The air box is different of course and the intake boot are different (shorter as noted by others). The shorter ones have the carbs setting at downhill angle, but don't see any difference really in float height between the years. The 73 and on intake boot is longer and levels the carb. I think they are all the same carb body correct?????. So my 75 carbs should work at the slight angle with shorter intake boots
Also I see on the 72 only that one side uses the next large needle Jet (p-5). I am guessing they had issues with it lean and found it better to go a bit richer. I think these are a 158 series and not available ( I think that is what I read on my 75) . The 159-P5 is available although designed for Hex main jets (only difference). I do believe you can screw a Large round jet in a 159 series part way and it will hold.
I just want to be sure I have the jetting correct. For it is going to cost me some coin the get the full 70/71/72 setup
Yes I want to try the 70/71/72 setup on my 75.
I am confident this is why the horsepower and top end dropped a bit. Yes a lot of money for a few more horse power. I am putting my 75 back together fully stock first and will have something to compare against someday.

[tz375]

I haven't compared early 32mm carbs to later ones, but I did have an opportunity to check out some 34's compared to 32s and to regular VM series and they were very different. 159 should use long hex (5.0 x 1.0 thread) and screwing a large round (5.0 x 0.8mm) in there is not good. It either falls out or damages the threads.

I think the other jet you are seeing is a 188 series and it's the same as a 159 AFAIK but it takes large round jets.

Stock Suzuki carb bodies are drilled very differently to regular VM32 carbs and have an air bleed into the mouth of the carb that changes the fuel slope. I suspect that later carb bodies are drilled differently and would require different brass to make them work.

If you want to improve performance, I'd suggest replacing the heavy stock carbs with a set of nice new VM32s or 34s. Messing with proprietary carbs is always a bit of a challenge.

[Vintageman]

tz375.

If knew what carbs to buy and what jets would be needed that's a great idea (more $$). But It can take (me) quite some time to get it jetted correct if ever.

So instead I am not modifying factory carbs, I am just using a previous version of factory specs. Factory airbox too. I am sure this will bring back the 4 hp (~10% gain). I see no other change. If I am wrong oh well, still should run fine or just go back to 75 stuff.

You are probally correct 188s. I did read on Ozebook (some T500 tech data somewhere there ) that the 159 series you can screw in the round jet (guys were doing this was my take). It will hold. Can't go other way around (188 with Hex). I have some 159s and the round jet screwed in a fair distance and was very snug. Not sure I really even need the P5, but I bet the P5 changed was for good reason.

OK good the 150 main is a Round Mikuni too. It is still avaible but not from Suzuki Strange (makes me uncomfartable). I thought maybe suzuki did some custom on this main. If anyone gets a 150 main to look at please reply if not standard large round.

I now need to decide (my other post) if I should change the crank seals. $$$$$$

[tz375]

Hex jets can be cross threaded into 188 as badly as Rounds into 188. i.e. neither is a smart move. There is no reason to use teh wrong jets. Large and small round jets and hex are available from any Mikuni stockist. Suzuki have stopped listing many carb parts either because they see no demand or because they are no longer available. In this case they are available.

I thought that someone more knowledgeable than I on 500 twins suggested that the length of the intake made a difference or was it that it was related to the revs at which the motor peaks.

Mikuni and Suzuki changed those OEM carbs over the years. If you are changing carbs, manifolds and airbox as a complete set, that would work, but you should check the carb bodies too. There were some changes to the design and that can make a huge difference to fuel delivery rates.

having had the opportunity (thanks T Grogan) to compare a few different 500 carbs (not all), I have to say that I wouldn't bother with stock Mazac carb bodies. I'd get a cheap pair of sled carbs off ebay and jet them to match what I was running. But maybe that's just me. Heck with new carbs at a ton or less each, there's not much reason to mess with old ones - except to see what happens.

[Vintageman]

tz375

188-P5 is not available anymore. So why I suppose people use the 159-P5s. I have tried it and look like no worries to me.

As far as the Suz custom carbs on the T500 I think the only difference is what Suzuki did to effect low speed performance. They bragged about it somewhere... they ratio bowl pressure to inlet side to make less rich at low speed or something. So I think OK carbs other than this low speed lean change. I am no expert, just what I have read.

You are correct I need to verify carb bodies are the same on a 75 versus 72 for example. I have only seen some ebay pictures and look the same (gulp).

If anyone knows this to be the case or not let me know.

If someone has done this with standard Mic Carbs let me know what they did for Jetting and air filters. I like the stock airbox for it reduce intake noise some. But if someone has done it right aftermarket ( no issue slow, medium or WOT) let me know.

I did this same kind a change on 74 GT250 with earlier T250, If I remember it resulted in Slide change (shorter on t250), airbox to carbs boot straight through on the 71 versus 74 and air box (larger intake opening). It made a/the difference. The bike was much more free to rev and to me no change in low speed.

IMO Suz did the change on the T500 not so much for the GT550, but to reduce intake noise. I think they had to satisfy stricter noise requirements as years went along. Maybe I am wrong.

So I am still going to do this swap someday. If I get 10% back to me its more then just something to try. It is perfect. (if someone can send me various pics of the 70/71/72 that would help too)

I appreciate everyone’s help for so much knowledge here about Suz 2 stroke.

Road my T350 yesterday about 110 miles. Was about 80F, fall colors everywhere in Vermont where we road. Nothing like riding a 2 stroke! Got 42 MPG!

[debby]

Just to confuse things some more, my 1970 T500 has large round main jets, but it's a 1974 motor fitted with early style short manifolds and Unifilter foam pods. I'm currently running 147.5 mains, but could go down to 145s. This is at 5000 ft. elevation of course.

I have a set of the earlier cylinders and the intake ports look a lot different (larger). It's been said that Suzuki made the porting changes to detune the bike because they didn't want it to be more powerful than the new GT550. One of these days I'll put the 1970 cylinders on and see how they run, but I expect I'll have to spend a lot of time rejetting, so I've been putting that off.

Don't remember what needle jets are in my carbs. I'll have to look the next time I have the carbs off. From what I've read in the Sudco catalog and other places, there are three series of main jets - hex head, large round head, and small round head. Each style has a different thread pitch and which one is correct fitment depends on the needle jet.

I've been buying my main jets from denniskirk.com. They sell them in twin-packs, just right for our twins! Now I see they have another brand, "RD" of jets that are supposed to be compatible. They sell those individually. I haven't tried any so I don't know about the quality.

hope that helps,
Debby