T500 carb puzzled!

General discussion about Street two-stroke Suzuki motorcycles.

Moderators: oldjapanesebikes, H2RICK, diamondj, Suzsmokeyallan

ro55o
On the street
Posts: 28
Joined: Sun Feb 26, 2017 7:52 am
Country: yu
Suzuki 2-Strokes: t500, kz400,bsa b175

T500 carb puzzled!

Post by ro55o »

I have a 71 T500 that has 32mm carbs jetted as original except 152.5 mains.
Running pods. Needle clip 2.

Its all good except has a rich bog at half throttle.
Its super rich with the air box and wont pull after half throttle, pods are a lot better.

Tried needle clip 1 and 1/2 with a shim which is better at half but worse below that.

I bought some 159 series p4 and p5 needle jets as I thought maybe the old ones could be worn.
Ive tried the original round jet as it fit with no problem, and a hex 280, but its even worse either way and wont tick over or pull away...again over rich.

Any carb experts have any ideas why the 159s would be so different as they supposed to be the same essentially...got me really puzzled that.

Put it back is it was now as it is rideable, just not dead right.

Thanks
User avatar
tz375
Moto GP
Posts: 6204
Joined: Mon Nov 03, 2008 10:47 am
Location: Illinois

Re: T500 carb puzzled!

Post by tz375 »

Don't the 71 carbs come with 97.5 Large Round main jets in 188 series needle jets? So maybe 100 or 102.5 with pods and stock exhaust.

97.5 round equates to roughly 110 in a large hex according to the charts online. Symptoms also suggest that the mains are way too large.

188 series and 159 series are identical except the threads at the base for main jets are different. Better to use round jets #100/604 in 188 series, and N4/402 large hex in 159 series needle jets.
User avatar
ConnerVT
Novice racer
Posts: 963
Joined: Wed Jan 18, 2012 8:01 pm
Country: USA
Suzuki 2-Strokes: T500R (now), T500M (40 yrs ago)
Location: North of Albany, NY

Re: T500 carb puzzled!

Post by ConnerVT »

My head started hurting reading these posts.

The 1971 carb, is a homopressure carb, so no external vent/overflow.

The 1971 Main Jet is a 150 Large Round. The later (externally vented) carbs use the smaller 97.5 Main Jet.
Tried needle clip 1 and 1/2 with a shim which is better at half but worse below that.
This puzzles me? The correct (stock) clip position in 3 - the middle slot.
User avatar
tz375
Moto GP
Posts: 6204
Joined: Mon Nov 03, 2008 10:47 am
Location: Illinois

Re: T500 carb puzzled!

Post by tz375 »

ConnerVT, glad you jumped in.

The supposed 71 carb I cleaned for a client was not homo pressure, and It had a 188 P-4 needle jet and 97.5 main jet. Now I think about it some more, that suggests he had later carbs or misidentified the year of his bike. The stamping was not clear but looks like 15313 which would make it a T500J-K-L-M. I did not check the year at the time, but clearly the carb I had was not from a 71 model. Good catch.

His other carb was a 34mm round side marked 15010 - so it's an early 68 and it was homo-pressure and had 159 NJ and 410 main jet and brass floats.

Back to this bike. Do we know for sure what carbs are on this particular bike?
Can you please post a picture of the carbs from the side or rear and tell us what they are stamped on the choke plunger housing front face. That would be helpful. If it's a 15601, it's for a 1971 T500R and should indeed come with a 150 round main jet in a #188 P-4 needle jet.

According to the Suzuki Carb manual , Homo-pressure carbs were fitted to 68-71 models.

Back to the symptoms, it sounds excessively rich and if the 280 hex jets in the 159 series needle jets fitted were new, that suggests it's a later carb or the float level is way too high, exhausts are clogged or air passages in the carb are partially or fully blocked.
ro55o
On the street
Posts: 28
Joined: Sun Feb 26, 2017 7:52 am
Country: yu
Suzuki 2-Strokes: t500, kz400,bsa b175

Re: T500 carb puzzled!

Post by ro55o »

Hi, thanks for the replys and help.

This bike came to me in a box so there could well be mismatched parts.
Engine number is 71-72.

Carbs came with 150 round mains, 30 pilot, 5fp8 needles, 188-p4 left and 188-p5 right, 2.5 slides.

It wouldnt pull with clip positon 3 so I went to clip position 2 which improved things.
Air screw is 1 3/4 out.
Float height is set to 27.3.
I changed to 152.5 main and I started richer as I added the pods and wanted to be on the safe side initially.
Exhaust has been cleaned out and timing is good.

Bike runs excellently up to half throttle.
It has a rich bog at half throttle (marked positions on throttle grip to be sure).
Once past that it clears and pulls so its just rich around the half throttle.

I tried needle clip 1 with a shim underneath which is half way between position 1 and 2.
This cleared the half throttle bog but made the running up to half throttle worse.

The 159 p4 and p5 are new. The round jet and the hex jet both screw in easily with no cross threading or resistance.
Ive tied both 150 round and hex 280 and its super rich and wont even pull without stalling.


Ive assumed these are the homo pressure carbs but if they are not that would explain things.
Ive just pulled the carbs and the numbers are 156 02 on both, I dont know which year/style of carb that is though??

Ive added some pics.
Ill check the air passages too as you suggest.

Again thanks for help, much appreciated! :up:
You do not have the required permissions to view the files attached to this post.
User avatar
jabcb
Moto GP
Posts: 4240
Joined: Mon Dec 13, 2010 4:32 pm
Country: USA
Suzuki 2-Strokes: 69 T350 thru 75 GT750
Location: southwestern Pennsylvania

Re: T500 carb puzzled!

Post by jabcb »

The stamped # is the second half of the part number. So the part number for the right carb is 13201-15602.
Per my printed parts manual, carbs for 1971 T500R & 1972 T500J were stamped 15602, 15603, 15604 & 15606.
https://www.partzilla.com/catalog/suzuk ... carburetor

Carbs specs are in service bulletin Specification-6: http://www.ozebook.com/compendium/techb ... %206-9.pdf

Also per my printed parts manual, T500 K/L/M carbs are stamped 15310 & 15303.
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 & 75
GT380 72
T500 69 project & 73 project
T350 69 & 71
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE
ro55o
On the street
Posts: 28
Joined: Sun Feb 26, 2017 7:52 am
Country: yu
Suzuki 2-Strokes: t500, kz400,bsa b175

Re: T500 carb puzzled!

Post by ro55o »

Thanks for that jabcb, useful info and it appears I do have the correct carbs.

I have cleaned the carbs and checked float height again etc put it back together and seems a bit better, but I only took it up a long road and back.
Im going to give it a better ride out tomorrow and see how it is.

I checked and cleaned the air passages.
The one in the attached pic outlined in red does ....is that blocked off or does it open somewhere... I couldnt see/feel any outlet for it.
You do not have the required permissions to view the files attached to this post.
Vintageman
Expert racer
Posts: 1483
Joined: Tue May 18, 2010 5:38 pm
Country: USA
Suzuki 2-Strokes: Suz, Yam, Honda, Kaw.
Location: New Hampshire

Re: T500 carb puzzled!

Post by Vintageman »

It does sound like you are jetted ok for stock air box. If you have new 159 jets, 150 ish rounds, float height set, right needle jet and no wear... Can you try the/a stock air box just to prove to yourself all is well? If you never have this would sure let you clue you in what is the issue. That year stock air box works well on that bike and doesn't hold power back - and maybe those little pods are phooey?
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
sportston
Expert racer
Posts: 1119
Joined: Wed Jul 10, 2013 12:04 pm
Country: England, UK
Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S

Re: T500 carb puzzled!

Post by sportston »

Vintageman wrote:maybe those little pods are phooey?
+1 on that. Pod filters generally don't work well with 2-strokes without a lot of re-jetting. Normally you'll get more power, or at least a better spread of torque, with a proper airbox.
ro55o
On the street
Posts: 28
Joined: Sun Feb 26, 2017 7:52 am
Country: yu
Suzuki 2-Strokes: t500, kz400,bsa b175

Re: T500 carb puzzled!

Post by ro55o »

Yeah, I have tried the air box .... with the 159 needle jets, and with 188 needle jets.
It wont run at all with the air box and the 159s ..........and its time to drain the cases....and with the 188s its ok until half throttle then wont pull at all.

With the 159s and pods it wont run either, thats the strange thing.
why? If the 159s are the same as 188s its only a different thread... they should work better if theyre new.
The only thing I can think of is that theres something not right with the 159s, and they are genuine mikunis.
I have had those carbs on and off with different combinations....a lot..

It is running "Ok" with the current set up, but Ill know tomorrow after a better run if anythings changed.
Thanks
Vintageman
Expert racer
Posts: 1483
Joined: Tue May 18, 2010 5:38 pm
Country: USA
Suzuki 2-Strokes: Suz, Yam, Honda, Kaw.
Location: New Hampshire

Re: T500 carb puzzled!

Post by Vintageman »

ro55o

I did the 159 swap too on my T500 and work fines in my bike. Those 188 were pitted cuasing crappy mileage and midrange running. So, that can't be your problem. I have done this swap on other bikes too. I also jump straight to the Mikuni round in the 159 series if stock bike. As you noticed it works just fine. If you are making something custom then hex is OK more linear in step size increases if I recall

OH what I do recall once you are too rich on the main jet on the T500 is runs like poop. I remember I was increasing round main jet size and went that 2.5 round next size over and day and night just ran terrible after 1/2 throttle. I would try stock jetting just to see if you are too rich. Sounds like you may be. Just don't drive wide open like a mad man for a long time until you are sure jetted correctly

The other thing with T500 it is known to spin key way (crankshaft has a lot of inertia). If you time ignition with rotor marks you may be way off.

So if your motor is OK, :ssh: Battery strong, Ignition parts good and timed correctly and carbs are as you described, air filter clean it should run well.


The only thing I noted about the 159 series versus the 188 is the air inlet for the needle seems like the 159 was smaller a tad due to less chamfer or more round versus oval opening. This would affect the needle pos only. But just think those 188 were manufactured in circa 1974 and the 159s o I bought were in 201x so bound to be small machine differences. but again I have done the Hex Needle jet swap on a couple series now and all work just fine.
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
70 T350,
74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
User avatar
dorT500
To the on ramp
Posts: 253
Joined: Mon Jun 12, 2017 12:01 pm
Country: USA
Suzuki 2-Strokes: '75 T500M since '93 Ridden it over 100,000 mi
Location: Galveston County, Tx.

Re: T500 carb puzzled!

Post by dorT500 »

Vintageman wrote:.......So if your motor is OK, :ssh: Battery strong, Ignition parts good and timed correctly and carbs are as you described, air filter clean it should run well.
Well, I must say, battery condition and bad points gap/gaps did cross my mind.

Also, ro550, did you ever get these issues sorted out? :arrow: viewtopic.php?f=9&t=13067" onclick="window.open(this.href);return false;"

Here is hoping you get her up and running like you want soon.
_____________
______________________
_______________________________
GONE.......WITH A PUFF OF SMOKE AND A BLUR OF SPOKE
ro55o
On the street
Posts: 28
Joined: Sun Feb 26, 2017 7:52 am
Country: yu
Suzuki 2-Strokes: t500, kz400,bsa b175

Re: T500 carb puzzled!

Post by ro55o »

Hi Dort500, yes I did get my crank sorted.

Needed to replace the outer bearings as Jimroid predicted. Luckily my local engineer had 2 nos bearings on the shelf, been there 20 years! Centre bearings are good. Also replaced inner and outer seals. I got the primary gear spacer machined to accept an o ring to eliminate leaks from the key groove etc.
Pressure tested and its all OK.

Just checked my battery and its fine.
I did set points gaps, and timing (with a dial gauge) but Im going to recheck those again to eliminate that.

In fact Ive got a list of things to recheck so will be doing that over the next week as I get time.
Im going to clean my carbs again in the ultra sonic cleaner too.

Thanks Vintageman, its useful to hear that you have done those jets swaps with success.
Also if the 159s are possibly passing a little less air it might explain why the 159s make my rich situation worse.

Ive got a few things to try before moving on..

Ive been cautious up to now as I assumed the stock set up would work. Time to jet it for how it is, just thinking is it worth it with these old carbs, might get some new vm32s and jet as needed from there....Ill have to get some cash together though first!
ro55o
On the street
Posts: 28
Joined: Sun Feb 26, 2017 7:52 am
Country: yu
Suzuki 2-Strokes: t500, kz400,bsa b175

Re: T500 carb puzzled!

Post by ro55o »

Just checked my timing and the left side was out.
Must have slipped as the right is good. The bike has been getting gradually worse so must have been slipping out.
This is good news as at least I have found something I know is wrong!
Ill make sure everything else is spot on then Ill get it back together this week and see if it has any effect on the carbs...trouble is Ive had the carb problem after I have correctly set the timing before........anyway ....I dont care if it sorts it!!

Heres hoping :up:
User avatar
dorT500
To the on ramp
Posts: 253
Joined: Mon Jun 12, 2017 12:01 pm
Country: USA
Suzuki 2-Strokes: '75 T500M since '93 Ridden it over 100,000 mi
Location: Galveston County, Tx.

Re: T500 carb puzzled!

Post by dorT500 »

ro55o wrote:Just checked my timing and the left side was out.
Must have slipped as the right is good.
It's the points gap(or almost lack there of) that I was thinking was the problem.

This would be nice to hear :wink: .....

'The points gap is correct on both sets of clean, flat, squared up non pitted ignition points and the timing is good. I have a healthy blue spark at each brand new NGK spark plug'. 8)

Like you alluded to.....troubleshooting by an orderly process of elimination can be rewarding. Good Luck

Oh, BTW, what was the exact reading you got when you checked the battery and had it happen to be sitting at rest for several hours?
_____________
______________________
_______________________________
GONE.......WITH A PUFF OF SMOKE AND A BLUR OF SPOKE
Post Reply