Suzuki 2 Strokes

Now that the bike is mostly ride-able with a few small things still to go, I've been zipping around the neighborhood trying some things out.

Yesterday noticed that certain throttle positions have essentially no power. Off idle is weak, half throttle is MAX POWER (encouraging) and after that it seems to just lean out and make a gargling sound.

I used some fairly terrible chinese rebuild kits on the carbs. Came with 150 mains, bowl gaskets that don't seal, needles that don't fit, etc etc. I ended up using the new needle/seat combos, main needles, main jets and idle adjusting screws.

I'm thinking that I may need to raise the main needle a notch? currently in middle notch. And maybe a larger main jet? Kit came with 150s, on the bike were smaller, 90 something, not sure which is correct?

I appreciate any feedback. I consider myself pretty good with carbs, but never really had to re-jet anything before.

I'm also considering something crazy like buying a new pair http://www.ebay.com/itm/32mm-Mikuni-Car ... 1438.l2649" onclick="window.open(this.href);return false;

Or maybe upping to vm34s? Anyone done something like that?

Skaal-tel wrote:I used some fairly terrible chinese rebuild kits on the carbs. Came with 150 mains, bowl gaskets that don't seal, needles that don't fit, etc etc. I ended up using the new needle/seat combos, main needles, main jets and idle adjusting screws.

I highly recommend you take all of the brass bits from the kit you bought out of your carb, and either put the (cleaned) original parts back, or replace them with genuine Mikuni parts. The rebuild kits (mostly sourced by Keyster) are trash. Mikuni carbs rely on exact dimensions of orifices and needles, and the kit parts look close, when measured are off by a significant amount.

Another scary thing about Keyster kits, is that they say they are for "'1969-1975 Suzuki T500". (or worse - 68-75). The T500 had 3 completely different carburetors during this time. 1968 was a bigger carb than the rest, 1969-72 had "homopressure" design, with a 150 Main Jet, and 73-76 was externally vented, with a 97.5 Main Jet. One size doesn't fit all.

Skaal-tel wrote:Yesterday noticed that certain throttle positions have essentially no power. Off idle is weak, half throttle is MAX POWER (encouraging) and after that it seems to just lean out and make a gargling sound.

If it is making a gargling sound, it is likely too rich, and not too lean. That gargling sound is typically called "4-stroking", with the engine not firing on every revolution, but on every other (or more). Too lean just generally feels flat, as it has, figuratively and literally, run out of gas, and has more to give, but just can't do it.

From what you have described, I'll make a bet that the Main Jet from the kit is much closer to 150, than the 97.5 that you need.

You're right on the money, it is a 150. AND it's a keyster kit.

This is what I get for trusting a welder to buy the carb kits.

I'll post some pics of the differences for posterity when I get them apart.

Thanks!

Old very dirty jets cleaned up quite nicely.

Needles were very slightly different as well.

All the way back to stock and now it flies. HUGE difference.

Excellent. Glad you are making progress.

You aren't the first person bitten by the Keyster kit. I always recommend getting the genuine Mikuni parts, when available. The Main and Idle Jets are still readily available from a number of sources. The Jet Needles and Needle Jets are NLA, and the Jet Needles were a custom design for Suzuki.

The two Jet Needles (early and late) are slightly different. The late model was slightly richer (if I recall correctly) with the taper beginning a bit sooner. One time I measured both models of Suzuki's needles, and compared it to the Keyster. The Keyster wasn't a match of either one of the correct needles.

Skaal-tel wrote:Now that the bike is mostly ride-able with a few small things still to go, I've been zipping around the neighborhood trying some things out.

Yesterday noticed that certain throttle positions have essentially no power. Off idle is weak, half throttle is MAX POWER (encouraging) and after that it seems to just lean out and make a gargling sound.

I used some fairly terrible chinese rebuild kits on the carbs. Came with 150 mains, bowl gaskets that don't seal, needles that don't fit, etc etc. I ended up using the new needle/seat combos, main needles, main jets and idle adjusting screws.

I'm thinking that I may need to raise the main needle a notch? currently in middle notch. And maybe a larger main jet? Kit came with 150s, on the bike were smaller, 90 something, not sure which is correct?

I appreciate any feedback. I consider myself pretty good with carbs, but never really had to re-jet anything before.

I'm also considering something crazy like buying a new pair http://www.ebay.com/itm/32mm-Mikuni-Car ... 1438.l2649" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Or maybe upping to vm34s? Anyone done something like that?

Its good that You have made the right Changes in your bike. Things looks Great. Thanks for the link by the way.

Well, still testing and tuning at this point. Carbs working with all stock settings and parts.

I've set points at 0.40mm gap (0.16), had them at 0.35mm.

Idle jets at 1.5 turns out, needle at 3rd position, 97.5 main jets.

Having a little less power and very occasional backfire at full throttle. Gets up to 90mph no problem, but has MORE power at 1/2-3/4 throttle than at full open.
Pod filter problem? I'm having a hard time deciding if it's lean or rich at full throttle. Just seems to have less power than mid-range. No gargling sound like with the 150 mains....

The only change I had to make was to UNI filters, as the old toilet bowl style air cleaner just doesn't fit on the carbs anymore.. the rubber has shrunk.
As I see it I can mess with air filters (no filters, uni filters, attempt to fit old filter)
And then try to source new main jets.

Ideas?

CSM (Clauss Studios) makes a T500 air box intake boot. Don't bother with any used or NOS OEM - the rubber is just too hard. Though you can try baking yours (low heat) to see if you can make it pliable enough to install. The down sides are if (when) you pull the cabs again, you have the same problem, and the rubber shrinking when it cools makes it want to pull away from the carbs. A replacement is a better solution. http://www.claussstudios.com/id47.html (Search their site for: N100.604-100 )

For the WOT jetting, my instincts are saying you may be a bit lean (especially since you know what too rich feels like). I would try 100 and 102.5 Main Jets, to see if that helps. I get my Main Jets from Dennis Kirk, but JetsRUs is also an option. They are $6 USD/pair at Dennis Kirk, ~ $8 shipping in the US. Your milage may vary, as you are north of the border.

edit: Let me give you a "Do as I say, not what I do" tip - Keep a written log while you play with the jetting. Write down what you change, the current configuration, and how things behave at different throttle settings (coming off idle, 1/4, 1/2, 3/4, WOT). It helps tremendously to remember where you are, especially after you dial in one setting, only to have it mess with some other one. The Main Jet, mid range Jet Needle, and Idle Jet all overlap each other to a certain extent. Writing it down helps to make sense of it all.

Two years ago, late in the season, I tried an experiment that seemed not to make a difference, so I left it. Last summer, the bike ran hot, and had a few times when I turned back to home early, as I was concerned how it was running. Believe I had changed the Needle Jet from the P-5 that was in it, to a P-4 with a new Jet Needle clip setting. While the mid-throttle was about the same performance, it ended up making the Main Jet too lean. This year, I bumped the Main Jet to 152.5, and I immediately felt the WOT has much more pull. I feel it still has some more to give, so I will be trying 155 next week. If I kept a log (as I did when I first put my bike together) I wouldn't have basically lost the whole riding season last year. Yeah, I'm a dumbass sometimes...

Thanks for the tips. I actually used a dremel and grinding stones to increase the ID of the boot I have.. and got it to fit.. ish, while I wait for jets to show up.

I'm going to keep trying with the pod filters. I like the noise, the style, and I feel it actually runs better in the lower range.

Up here in canuckistan we have a few decent bike parts suppliers. Being in ontario, https://fortnine.ca/en/" onclick="window.open(this.href);return false; is probably the best. All types and styles of mikuni stuff, about 6 bucks a jet. I replaced the needle jets (the tube the needle goes into) while I was at it. 159 series, if anyone is checking, works. Ordered a few jets too.. but still waiting on the ones I actually need.

Note that the 159 series is not a direct replacement for the 158 series.

158 uses large round jets Main Jets
159 uses hex main Jets

The threads on the jets are different. Some have been able to make them fit (brass isn't *that* hard a metal), but I wouldn't make the recommendation without some testing and thought.

So I think you mean 188 needle jets?
I've heard about that as well but being a skeptic by nature, I'm not so sure about that info.
First of all, there are no longer 188 p-4 needle jets available, anywhere, which makes it a moot point.
Secondly, I'm using large round N100.604 mains, and I checked the thread pitch of the jets with the pair which came off the bike - looks like a perfect match. They're tight screwing in, but not what I would consider cross-thread tight. More like new parts interference fit tight.

I found some info saying that 159 series were meant for the hex jets. However, the hex jets are 5.25x0.9 thread and the large round 5.0x0.75 so... the large round should be super-loose if all that were true.

http://3cyl.com/mraxl/partid/carb/jetid/jetid.htm#chart" onclick="window.open(this.href);return false;

I'll take a thread gauge to the bench with me next time and put this to the test but.. Right now? So far so good.

Keep in mind this is the later carb setup. I don't even have a carb parts book for this year.

Having fun theorizing... still waiting for jets..

Yes. 188. Was replying from work, from memory.

There is a good cross reference here (and on the web) that crosses large round and hex jets. They are measured differently, so it isn't a 1:1 replacement. Getting ready for work now, will look later (unless someone here has it handy).

NM - just looked at your link. You're on it.

Skaal-tel wrote:So I think you mean 188 needle jets?

Secondly, I'm using large round N100.604 mains, and I checked the thread pitch of the jets with the pair which came off the bike - looks like a perfect match. They're tight screwing in, but not what I would consider cross-thread tight. More like new parts interference fit tight.

I found some info saying that 159 series were meant for the hex jets. However, the hex jets are 5.25x0.9 thread and the large round 5.0x0.75 so... the large round should be super-loose if all that were true.

You are correct. 159 series are designed to work with Large Hex main jets and that is what the majority of bikes use. the obsolete 188 series used large round.

Some people insist that it's OK to use large round mains in 159 series but large hex jets are too tight in a 188 series. The argument follows that hex jets and round jets are measured differently and there is not always an exact size to match the jet that's being replaced, so keep the rounds.

Others of us prefer to use hex jets and be done with it. There are a couple of charts out there to use as a guide. In reality, the difference in performance between a half jet size is fractions of a percent and the average butt dyno is calibrated to around +/- 10% sensitivity. In other words the difference is imperceptible.

If you feel comfortable using round mains, go ahead. It's your bike. I will keep using hex jets in needle jets threaded for them.