Carb Tuning - T500

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Vintageman
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Re: Carb Tuning - T500

Post by Vintageman »

ConnerVT.

Correct me if I am wrong. You have a 100% complete late model engine set up cylinder through to airbox (and good OEM filter foam lightly oiled!) and now using the P4 Jet Needle and the 5FP17 spec for that set up later years. You also have stock exhaust with cleen baffles.

But, you are at the moment running 145 round jet main versus 97.5 and 27.5 pilot versus 30?

If it truly a jetting issue it is really not an RPM thing as its is a throttle position issue. I mean, if you hold say at 1/8 throttle the engine should pull from low RPM to High RPM . And, if jetted correctly no issues anywhere in RPM climb for a given and fixed throttle position (Chambers can complicate this some due to compress increase at certain RPMs... One tends to richen mixture to avoid its affect but makes it too rich else where in RPM band... you don't have this complication if stock exhaust).

So when you say not smooth above 3500 RPM, I am not sure what throttle opening you are at. I think you are saying small throttle is OK (Is it? will it rev up at small position?), but larger opening is not OK.

That makes since to me for 145 round mains is way too much IMO. Your pilot choice is a bit small too IMO. The air screw difference could be just a couple 0.010" inch diff in true float height between the two carbs for example.

I have your same bike setup (75 T500), but run Jemco chambers now.

As I adjust jetting for chambers I find the main does have an affect as early as 5/8 to full throttle of course. If the main is a bit too larger 5/8 to 3/4 throttle becomes too rich first (blubbering/struggling to climb RPMS), Full throttle may be OK if just slight too rich.

Adding chambers I run a very large Pilot to avoid raised compression ping when chamber boost at around 5000 rpm and at very small throttle or when I back off throttle from higher RPM. Even though rich pilot I think the Suz Homo(sp?) carb design due to vacuum feedback keeps it lean at low RPMS. It idles fine and runs well slow. Not over rich. This is opposite of my 73 GT550 with chambers for example. A bit too rich small throttle when chamber are not boost (low RPM,). Not a vacuum feedback carb. Point of this? I think you can run a little more pilot than less on the T500 given its carb design

Even when I had stock exhaust I found 32.5 pilot were better for it would not climb and pop corned or crackled.

It seams odd to me why factory jetting isn't close for you. All your parts are from the late model T500?

Maybe I am missing something here?

Does ever go “Bang or Pop out of the exhaust?

Isn't jetting fun?
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ConnerVT
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Re: Carb Tuning - T500

Post by ConnerVT »

Vintageman wrote:ConnerVT

Correct me if I am wrong. You have a 100% complete late model engine set up cylinder through to airbox (and good OEM filter foam lightly oiled!) and now using the P4 Jet Needle and the 5FP17 spec for that set up later years. You also have stock exhaust with cleen baffles.
No, not exactly correct. Cut from my original post, with the latest configuration added and highlighted:
ConnerVT wrote:
  • '73 cylinders (smaller/more restrictive porting)
    Early (short) intakes
    Early Air Box and Boot, with NOS filter installed
    145 Main Jet (now 137.5)
    P-5 Needle Jet (now P-4)
    5FP8 Jet Needle, in 3rd slot (tested with 5FP17, but now back to 5FP8)
    2.5 Throttle Slide (cutout towards rear)
    30 Pilot Jet (now 27.5)
    New genuine Float Needle/Seat, 27.0 mm Float height
What you missed is that this is nearly an early model configuration intake system, except with a 1973 motor. Not the ideal way to go, but there are roadblocks in setting up as late model, on an early frame (Intakes and Air Boxes - Questions).

Not knowing just what component was the major reason for the significant jetting changes between early vs late model, I started with the most rich configuration possible.

The Pilot definitely needs to be 27.5. To get it to idle reasonably, not only were the mixture screws 2.5+ out, the idle speed screws needed to be very far in, to allow some air in from the slides. The bike would foul the plugs just sitting at idle. With 27.5, the mixture screws are about 1.0 turn, the idle speed screws are about midway, and she idles nice at just over 1000 RPM, with minimal smoke.

I've been through a number of configurations since the first post (I can now pull the carbs, rejet, and be on a test ride in 45 minutes). Up through ~1/2 throttle, the bike is well behaves, and the plugs no longer foul, and are a very light chocolate color. Give it more than 1/2 throttle, and she bogs down, and doesn't want to give any more.

Other than an old pair of 97.5 Main Jets, the 137.5 set is the smallest I currently have. It seems the 137.5 is still too rich, and I plan to test with 125 and 110 to see how they work. I know I may end up reinstalling the P-5 Needle Jets, as leaning the Main jet this much may push the low/mid-range too lean after doing this.
Vintageman wrote:Does ever go “Bang or Pop out of the exhaust?

Isn't jetting fun?
No bad noises from the exhaust. Getting to/from my testing grounds (large, empty roads with both flats and moderate hills, in a nearly empty development park) the bike sounds and rides awesome. the process of getting it jetted correctly has been fun, but in this case, time consuming, as there really isn't a factory spec to use as a starting point.
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Re: Carb Tuning - T500

Post by Vintageman »

I do remember you length challenge with getting later intakes and air box to fit in early frame. I also learned that even though the OEM Parts list said frame same on line it actually did change but was backwards compatible with early style

But looking at the picture on that post if I remember I thought you were extending/fabricating the bracket on the frame so you could get all late stuff to fit. Then you have the OEM jetting specs as the definitive starting point.

Maybe too difficult? But, may come a point where that may take less time. Of course the other thing is to find early cylinders which I sure puts a lump in your throat if you can find and $$$$$. I wanted to do the early stuff just to get that 3 hp or so if true. Given chambers I don’t care so much anymore ( I just need cylinders and I could have the early)

I think if I were you I would start with trying to make all later stuff fit (what’s stopping you please?). Even Suz was fiddling with jetting as you noted with different Needle Jet sizes. I can say having a T500 and adding chambers it is fussy and still have a spot I need to fix (I may hijack this post yet a bit). I may need a different need a different needle profile to make everywhere perfect.

Even though we set float heights by eye what the level actually is may vary due to mechanical tolerances. I can say that just changing level by 0.020”: makes a difference and used this technique to help. But this is not your issue (sorry I ramble). As you said you have a unique set up and you are trying to solve it with using one or the other setup parts Jet needle/Needle jet? Well you sound to o rich add larger throttle


Curious. Do you have early and late cylinders and can quantify the intake differences for us? I have not seen this done ever by anyone on this site. I only have the late myself. Again just curious

The 5FP8 versus 5FP17. Do you have both right now so you could take a side by side close up pic. I did see where Tz375 said the taper slop same just start at different point. Is tru? You can get the 5Fp17 still I have Keyster version of the 5Fp8 if you trust (were there specs somewhere on 5Fp8 … I think I saw a hand plot drawing somewhere )

Now I am Hijacking. MY 75 set up with chambers I run 37.5 pilot, P4 (159 series though not 188), 5FP17-2, and was 150 main (hex so what’s that round if forget?). My run before I had 125 Hex main. Very good everywhere, but above 7/8 to WOT it pings. So I went 150 Hex main. Fixed WOT ping but ~ ¾ throttle just a wee bit too rich (sometimes it gurgles and sometimes it don’t). Of course I will now splitt difference and run 140 main maybe that does it. Else I need the needle to slope faster as one option and thus curious 5FP8 versus 5FP17.


So you can do this in 45 minutes. Yeah I might be at about 1 ½ hour. I need new bowl screws getting stripped!
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Re: Carb Tuning - T500

Post by Vintageman »

ConnerVT,

Forgot something (why I asked you if exhaust was popping) so read this and my previous reply please.

I recently did a GT250, added chambers and fiddled with jetting to tune spot on to my liking. I also tried to use a 169 needle jet in place of the OEM 172. Well it doesn’t cross well and makes it too rich (separate topic). But even after getting 172 it was still too rich? It would wet foul plugs Idling or running too at times when if I got after it. I found reducing pilot jet , needle clip and main helped, but still gurgled once and while and fouled plug. Too rich still?#@! Then after riding it some I heard the exhaust go pop/bang a bit. Hey, that sounds like ignition problem. Can’t be! All new stuff. Long story short (if Possible from me) I had changed to new aftermarket condensers: OEM points. One point was pitting and eventually enough to skip several cycles before it would fire plug (pop band). Put OEM condenser and another OEM point set. Could go back to all OEM jet specs. It runs perfect.

So to me just one step change on pilot jet makes such a fouling plugs for you is odd even given your unique setup. So make sure something else like pitted points hasn’t snuck in to your situation.
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ConnerVT
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Re: Carb Tuning - T500

Post by ConnerVT »

I know many more things now than I did when I started this project. The easiest(?) part of all of this would be to fabricate a frame bracket to move the air box rearward, to the late model location. Or to have the '71 cylinders I have bored 1.0 over, and used those instead. But my knowledge came incrementally, arriving to the configuration I have. Next time, I'll know better. :P

5PF8 vs. 5PF17 -- My super inaccurate measurement (digital caliper and old eyeballs) show that the 2nd taper starts ~3mm lower (towards tip) on the 5FP8, making it slightly leaner for a bit deeper into the throttle. The final change I did last night was to swap back in the 5PF8 for the 5FP17 I had installed. I'll be riding it in about an hour, to see how it changes things.

'71 Cylinders vs. '73 -- I do have a set of each. The '71 are pretty sorry, one is already 0.5 over, the second stock, and both in need of a rebore. The '73 was in great shape, I had them vapor blasted, and used them in my rebuild of the '73 motor. Knowing now what I wasn't aware then, I would of used the '71 jugs. No longer cost/time effective to do anything now about it. As far as measuring the difference in the porting, that is beyond my current abilities, and the '73 jugs are installed on the bike now.

Hex vs. Round -- We always need to be careful comparing numbers when Hex and Round versions are both involved. My carbs are 100% Large Round Main Jets.

Ignition -- I've been through the ignition a few times, and all seems in good condition, and set up properly. I did set the timing using the rotor L/R marks, and not with a dial indicator. The symptoms at revs could be retarded timing, but given the need to resolve the jetting, I would be surprised if it was truly a factor.
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Re: Carb Tuning - T500

Post by Vintageman »

ConnerVt,


Come on, I did clearly state "Hex".

Odd, I have been able to go from 30 Pilots to 37.5 on my T500 and it always idled fine even for a couple minutes at a time. I just could not get full RPM range with small throttle and why I increased.

If you are sure that 30 pilot versus 27.5 prevents plug fouling be suspicious. The only time I have seen that behavior on engines is from week ignition (points, coil etc.). Well, check your points for pits if things don't make sense... bad condensor can ruin points in minutes.

OK, you will continue to try an jet your unique setup. I am sure you will get it. Try one thing at a time .... You are just more confident in your direction when you.

I just changed my main from 150 Hex to 140 Hex. I think I’ve got it after about 6 or 7 tries everywhere :up:

For a 75 T500 all stock but, with Jemco’s chambers here is my setup (not sure if thereis aplce to post such peoples setups)

Brand new shinny 159-P4
140 Hex main (=110 Round supposedly)
37.5 Pilots 1 turn out on air screw
5PF17 - 2
Factory float Height, new floats OEM Float needles
Run 93 octane gas and it can have ethanol
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ConnerVT
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Re: Carb Tuning - T500

Post by ConnerVT »

I know you were working in "hex". Just wished to make sure others who may read this thread also knew. Makes me think of the mars Climate Orbiter where some of the team worked in metric, and others were working in English units. :wink:
Vintageman wrote:Brand new shinny 159-P4
140 Hex main (=110 Round supposedly)
37.5 Pilots 1 turn out on air screw
5PF17 - 2
Factory float Height, new floats OEM Float needles
Run 93 octane gas and it can have ethanol
Other than your 37.5 Pilot jets (+3 steps up from the stock 30 spec), your setup isn't far from where mine is headed, and where NY500 has his (105 Main Jets).

I put back in the 5PF8 needles, which look as they taper a few mm closer to the tip than the 5FP17. Or basically, 5FP8-3 == 5FP17-2 for practical comparison.

I can take photos of plugs running the 30 Pilots vs. the 27.5 Pilots, and you would see the difference. I can also feel it in take off from a stop, the transition is so much better for this bike. Also starts cold with nearly no need for the choke, which it wouldn't do if it was excessively lean. Going 1 step leaner makes more sense than needing to go 3 steps richer.

The runs I took yesterday (took it to work on my off day, for show and tell) went well, great from closed to 3/4 throttle. Main Jet is still too rich, ordered some more from Dennis Kirk ($6/pair) that I'll have on Tuesday. But I'm getting close. :up:

A jetting configuration thread would be useful. Part of why I started this running commentary -- I was sifting through old threads looking for info. Figured the next person along in the same situation may benefit from what we discuss here. Once I get this bike figured out, I'll start a thread, with a template people can use to capture their setup info.
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Re: Carb Tuning - T500

Post by Vintageman »

Yes I have thought too rich on pilots and went leaner too. In cases a bike is all stock (again accept chambers which I have seen want more pilot then less) I question why.

Your case is tougher for no real stating point, but, I think both setups were torun 30 pilots?
I showed you how much I could change my pilot richer just how forgiving it is to idling not that this works for you. Mine always Idled the same. Never even changed Idle screws setting.

I run Iridium plugs and bought new OEM coils and plug caps no resistors.
stock timing ( I did dial gauge my timing an dmy rotor mark mere spot on which is nice to know)

Maybe your setup is that different. I don’t think plugs would prove that point for me for if week ignition look the same. If you can start without choke it may be rich still.
However, confident you are, in fact you for sure can be correct, do you ever in general check your points to see if they appear to be getting pitted or look even at the surfaces?

The case to be concerned is when you see one small spot/dot, but it is deep.

I moved my clip leaner because I have so much pilot contribution early on and mains later. Since I am usually cruising on needle circuit, I want to preserve MPG and -3 works and so does -2 ( I got 42 mph and world say I my driving style was spirited that time)

I think part of our jetting results is our preference or method to tune. I pick 1/8, ¼, ½. ¾, and full. Start low RPM right up to Full RPM and try to get that whole range to work well for each throttle position. I test on flat straight road. I am a novice at best

Looks like you getting closer. I am curuios to see what you settle on
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ConnerVT
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Re: Carb Tuning - T500

Post by ConnerVT »

The ignition points are good. It was only just a month ago I was reinstalling that part of the engine -- the motor was a complete tear down - crank rebuilt by Bill Bune; new pistons, rings, small bearings & pins, oil dam modification, and other misc stuff. I have the stator/ignition point assy from the '71 motor installed, as the '73 had the connector cut off of the cable. I have a third stator (with the newer stator coils - hopefully a little more output) that I will rebuilding this winter, with a new wires as well as points and condenser. But the points on the bike now are in really good shape.

The current carb setup is pretty good, except for the main being much too large. The P-4 needle jets are the correct choice - the P-5 is too rich for the late model cylinders. I have the leaner 5PF8 needle in it now to make it ride-able, but once the main jet gets smaller, I suspect that I may go back to the 5PF17.

Last evening, I re-tuned the idle mixture screws, since I've been fiddling with everything else. Set at the rich side of the high idle peak, they are both at 7/8 turn out. Everything but the bowl gaskets are genuine Mikuni, so I'll assume they're drilled correctly. The small throttle is running great, so I'm pretty set on keeping the 27.5 Pilot Jets.

A few more Main Jets will arrive Tuesday. If the weather cooperates, I'll have a few more puzzle pieces to figure out what works best.
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ConnerVT
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Re: Carb Tuning - T500

Post by ConnerVT »

It has been a week and a half (and a number of jets) since I added to this thread. I'm close. Real close. 8)

My latest config:

110 Main Jet
P-4 Needle Jet
5PF17 Jet Needle in the 3rd clip
27.5 Pilot Jet

My Gawd, I forgot what a fun, rider friendly motor the T500 can be! Came back from test riding the latest configuration, and needed to take two more rides around the neighborhood before putting the bike away. I didn't want to get off it! :up:

Fear of melting down the recently rebuilt motor, combined with no known factory starting point for my hybrid '71-'73 configuration, had me starting *way* too rich. With the Main Jet close to 150, I needed to keep the jet needle lean just to make it rideable. The last config was with a 117.5 Main Jet, and needed the Jet Needle down one notch. it ran OK, but the engine would load up and clear itself, all depending on conditions. Not a bunch of fun.

She still is a bit rich at WOT, and I have a couple more jets I can try. My guess is that 105 will probably be where I end up. The weather is getting a bit cooler now, so I know it will run a bit richer next seasons, in the heat of the summer.

Again, it has been 30 years since I rode my last T500 stroker. I knew there was a reason I wanted another one. Just too much fun to ride.
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ConnerVT
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Re: Carb Tuning - T500

Post by ConnerVT »

I have the 105 Main Jet in it now. And it can still go smaller. The throttle opens a little more before it loads up, but still is rich at WOT.

From what I've seen, the air box and longer carb intakes of the later model setups have nearly nothing to do with the change from the 150 to 97.5 Main Jet of the pre '1973 to the 1973 and beyond T500. The cylinder porting must be the vast majority of the need.

I have a pair of 100 Main Jets I hope to put in before I run out of riding days in the Northeast of the US. We had a break in the foggy, wet weather here yesterday, and was able to take a nice ride with the 105 MJ installed. As long as I stayed out of WOT, the bike ran perfect.

I also backed off the adjustment on the oil pump a bit. I had lost the Cable Terminal end (an expensive little bugger on eBay!) as I had the oil pump cable a bit slack, and the pump cover off. So I may of had the oil pump set to pump too much oil for awhile (which would of made it richer). Once warm, she's now smoking much less in high gear cruising with leaner jets and less oil being pumped.
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Re: Carb Tuning - T500

Post by tz375 »

ConnerVT wrote:....................... So I may of had the oil pump set to pump too much oil for awhile (which would have made it richer). Once warm, she's now smoking much less in high gear cruising with leaner jets and less oil being pumped.
"richer" as in too much oil or as in too much fuel? The amount of oil pumped makes no difference to air:fuel mixtures. I'm guessing you are referring to too much oil.
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Re: Carb Tuning - T500

Post by ConnerVT »

tz375 wrote:
ConnerVT wrote:....................... So I may of had the oil pump set to pump too much oil for awhile (which would have made it richer). Once warm, she's now smoking much less in high gear cruising with leaner jets and less oil being pumped.
"richer" as in too much oil or as in too much fuel? The amount of oil pumped makes no difference to air:fuel mixtures. I'm guessing you are referring to too much oil.
Less oil in the fuel mixture actually makes the mixture richer.

Figure in a 2-stroke, there are actually three components: Fuel, air, and oil. Less oil will make the fuel/air mixture a little bit richer.
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Re: Carb Tuning - T500

Post by tz375 »

It is often argued that 2 strokes running on pre-mix will need to be re-jetted if the oil:fuel ratio changes. Arithmetically that is correct but it's not significant.

For example a bike running say 32:1 is changed to run at say 50:1 that's a change from 3% of the fuel/oil load to 2%. On say a #200 main jet that represents a change to #198. Most bikes are not that sensitive to change and probably need to be jetted up to compensate for the ethanol anyway. :shock:

That was pre-mix.

With a pump system, the oil isn't coming through the jets, so it makes no difference to the amount of fuel in the chamber to be burned.. The carb will continue to deliver the same air:fuel ratio if the pump is wide open or turned off.

That brings us to the secondary effect and that relates to the effect of oil in the combustion process. One argument is that oil has a slightly higher BTU level (energy density) than gasoline, so power will increase. Others argue that oil increases or decreases speed of combustion. I have hear it opined that oil changes the way that the mixture burns and causes it to release more or less heat.

Even if any one of those theories were correct, we are still talking a 1% change in oil level in the example I used.

On a bike that is jetted close to the edge of detonation running a high compression and very efficient pipes, it's very important to understand and log every variable including the change from one oil to another, but it's not a real issue IMHO on the street. :)
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Re: Carb Tuning - T500

Post by NY500 »

ConnertVT did you ever get it figured out.I haven't touched my bike in weeks hoping to work on it today.
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