Nice 110 Jetting Baseline for Keihin PE20

I had a Mikuni VM22 and I gave up trying to tune it.

I ended up getting a Keihin PE20 carb with a jet assortment designed for a Kawasaki KSR110, what I think makes similar power as the Nice 110.

The carb comes with a 35 pilot and a 86 main. The KSR110 jet kit comes with a 38 pilot and a 85, 90, 95 and 100 main jet.

Anyone able to suggest a starting point? I'm starting at 95 and working down. I figured its to rich as is, but wonder if anyone has any experience with this motor/carb combo.

Thanks
 
Anyone?

I'm assuming that this rare engine combo means the odds of anyone running the same carb and motor (at least in North America) is going to be slim.
 

b52bombardier1

Well-Known Member
I run an 80 main jet on a Big Bore 90 cc motor that is now 104 cc with a 38 idle jet. This is inside a 22 mm Keihin carb meant for a CT110 bike.

Hopefully this will get you close.

Rick

Two CT90 and two ST90 bikes
 

racerx

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The only parameter for which you have anything remotely resembling a guarantee of getting close, from the get-go, is the pilot jet size. And that's only because the pilot circuit operates independently, at idle.

Above idle, there are multiple moving targets and they are all interrelated. What do know about the airbleed sizing, needle jet internal profile, jet needle taper & profile and slide cutaway? When starting out blind, as you're doing, peak hp & displacement are about the only reference points you have; make no mistake, this is still a roll-your-own proposition. True enough, hp is closely tied to fueling requirements. However, it doesn't tell you anything about one engine's breathing curve compared to another. You also don't know if your PE differs from any other, or how.

Unless you wish to venture more deeply into migraine territory, which is highly unlikely to make life any easier, refer back to the basics. Tuning parts for this carb are likely limited to pilot & main jets. Thus, the process is the same as always...find the rich limit under full power/WOT, then drop back 1-2 steps back leaner until you find the best throttle response.

There is always the possibility that the carb will be calibrated optimally, for your specific application, straight out-of-the-box. However, an engine can perform well with a lean mixture, these engines can get very hot at sustained speeds above 40-45mph, until there's 4-digit mileage on the clock, and pump gas is likely to be diluted with ever more oxygenates (with wide variations between tankfuls). Frictional heating plus a significant potential of increasingly lean mixtures is a recipe for burnt parts, imo, especially during break-in.

FWIW, last year I saw better than 30% mpg difference between fill-ups, with dramatic differences in engine performance, including peak oil temp. How much are you willing gamble to shortcut the carb setup?
 
Hi guys. Thanks for the advice (racerx you always are so knowledgeable :)

I'm sure someone must know what the stock Honda Nice jet sizes are (for the OEM 19mm carb). This might give me some idea that I'm in the correct range.

The 38 pilot is perfect. Dead on. Works great. (started with 35)

So now to the main jet and needle I'm working on. I started with a 95. It runs good, wants to be on the 4th clip but smells rich and does not do more than about 80km/h WOT. (short burst). Mid range felt good. Plug was blackish.

Then, I went down to a 90 main. Again, needle liked it best on 4th clip. Felt better. Top end felt a little better. Midrange was good. Plug was brownish with black on the outside.

Then I went down to a 86 main. Needle again on the 4th clip. This time I could bury the 80km/h speedo but it was a bit windy out. On the way back I could only hit 75 (into the wind). Mid range is good. Cruising at 60km/h feels like a weak spot and if I go from 1/2 to full throttle there is a stumble when it goes into WOT. Below 60km/h this is not noticeable. Plug still is brownish.

So, long story between all 95 and 86 jets it all feels about the same with the leaner mixture feeling slightly better on the top end. All 3 jet combo's rev out cleanly.

If I knew what the stock nice jet sizes were (its very similar to the carb I have now) then at least I would not feel bad about running the 86 main (i'm worried she's running lean). Engine temp is about par with all bikes not climbing over 90 degrees...but its not been hot enough yet anyhow.

I also need to fix the small stumble and weak spot when cruising at 60km/h, but not sure how to do so.

Any advice would be greatly appreciated!!!
 

theraymondguy

Well-Known Member
Ambient temperatures are still a little low to lock down a tune throughout most of the continent.

1/4 to 3/4 throttle is clip position/main jet territory. If 4th clip is the highest position (nearest to top of the needle), you've got to go down 1 more size on your main.

I'm sure you already have, but be sure that your air filter is in a good state (clean, well oiled), you're getting close to the edge and having a well serviced air filter will help with a tuning base line.
 

racerx

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Methinks TRG has it nailed. You cannot necessarily go by any other carburetor from another application...even OEM; there are more variable parameters than just main jet size, in play. No need to go into another longwinded tech lecture/explanation. You're pretty much limited to working with jet sizing, jet needle height settings and, possibly, float height settings, period.

Your significantly lower-than-expected peak oil temps and contradictory tuning results speak volumes...that you need to wait for higher ambient air temps. 60km/h should be about 5000rpm, if you're geared properly for the tire height. At that rpm, the engine should be breathing deeply enough to make any 22mm, or smaller, carb snap to attention. Your speed results are a little on the anemic side, too...again, assuming optimal gearing and a non-stingy speedometer.

Changing main jet sizes should impact needle height...dramatically. What you're getting, so far, makes no sense...unless something is affecting the functional air:fuel ratio in a big way. Poor atomization, as would result from an overly-chilled intake can do this. It's also the most likely cause.

I'd want to see oil temp around 100C and ambient air temp of 25C, at least. The two are related; it should be easy to get the oil beyond 100C...unless ambient temp is on the chilly side. (At 30C, an engine with this low mileage can be expected to top 110C with relatively little provocation.) Then, go back to basics. Find the rich limit at WOT. From there, you can try going one main jet size smaller, which should necessitate setting the jet needle height a few positions lower (increasing needle height). That's an educated guess, I've not worked with this, particular, Keihin carb.

As for the OEM 18mm Keihin metered air & fuel leak from the Nice...virtually non-applicable to your setup. It was calibrated on the lean side, whilst inhaling through a restrictive airbox, exhaling through a somewhat restrictive exhaust and on straight gasoline, as was widely available 10-15 years ago. Don't know what jets were used, not even the series. And jet needle height was fixed, i.e. non-adjustable.

Lastly, I'm still wondering what you're considering a "weak spot/stumble" in the midrange when transitioning to from 50% to WOT. Since this is neither a pumper nor CV type carburetor, there's always going to be a limit to the rate at which the throttle can be fully opened. Unfortunately, this is a vast gray area and tuning from behind a keyboard has its limits...
 
Thanks guys.

By 4th clip, I mean 1 up from the bottom. theraymondguy, you probably though I mean #2 clip (or 4 up from the bottom lol).

needle.gif

If I'm running the #4 clip, (like below) would this mean that I can still go down a jet size? I'd assume if I'm running the #4 clip (richer) then I would infact have to richen my main jet in order to use the middle clip? Is it best to tune and try to get the middle clip the "one"

9_10_08%20028_1.jpg

Its 20C today. Perhaps I'll do some riding tonight

racerx, thank you for your insight as well. I was just curious if someone knew what the stock jet sizes were only that I could make sure that I go above that, as OEM is always on the lean side. I've heard that the stock Nice carb was extra lean lol. I'll see if I can dig it up only for reference sake. If they did indeed run a 85main, then I know I've got to go up up up! :)
 
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theraymondguy

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Yes, raise the clip to lean out the mix 1/4 to 3/4 throttle. You may note a subtle change in your pilot circuit as well.


I would not think of the Nice carb as 'being lean' on it's own. As RacerX mentioned, it was asthmatic based on "It was calibrated on the lean side, whilst inhaling through a restrictive airbox, exhaling through a somewhat restrictive exhaust and on straight gasoline, as was widely available 10-15 years ago. Don't know what jets were used, not even the series. And jet needle height was fixed, i.e. non-adjustable.".

The same carb could easily be made 'rich' simply by changing the main jet. It was jetted to provide a lean mixture based on the intended engines' flow characteristics operating with the remaining components in the system.

Carburetors do not determine rich or lean: air speed and volume (adjusted by the throttle valve and engine rpm, limited by airbox and air filter) drawing on the jets trying to pull fuel out of the bowl - metered by the jet diameter, needle thickness / clip position and then fuel quality - will equate to a rich or lean condition.


This Keihin PD17 was a NOS piece for a 1985 CB125s until some clown bolted it onto a TB 108cc kit.

CT70exhuast_zps3bc54220.jpg

The CB125s is a slow revving, heavy flywheel, small valved pushrod, whereas the 108 is a free revving big valved SOHC monster.

Tuning this thing was a beast. Swapping jets and adjusting clip height just did not cut it. I nearly abandoned it until it was suggested to make a radical change on the needle, which immediately dialed the mixture in to the 108's flow characteristics.
 
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racerx

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theraymondguy said:
Carburetors do not determine rich or lean: air speed and volume (adjusted by the throttle valve and engine rpm, limited by airbox and air filter) drawing on the jets trying to pull fuel out of the bowl - metered by the jet diameter, needle thickness / clip position and then fuel quality - will equate to a rich or lean condition.
Some good points but, by definition, a carburetor is a variable airflow restriction & fuel metering device...with total airflow volume potential dependent upon how much an engine can draw. There's also "pullover effect", i.e. the pressure drop (vacuum) that the carburetor "sees" at any given rpm, which trg referenced. Engine + carb is an equation/balancing act. Tech gobbledygook aside, needle jet profile, slide cutaway size and airbleed sizing can have HUGE impacts on the fuel curve & jetting...as much as 6-10 main jet sizes, in some cases...same carb, same engine.

Tuning parts, for anything smaller than 32mm have gotten scarce, virtually non-existent for anything below 26mm, with few exceptions. OEMs were the last holdouts - the only ones with the resources to spec carburetor details for smaller units. Now that carbs are a moribund technology, even that's history.

Case-in-point, the OEM Nice carb came in two versions - one for the semi-automatic another for the 4-speed. The jet needle + needle jet combos are different and they're only listed under Honda PNs. FWIW, the stock combo was #42/#78. Good luck with that as your baseline...smells like burnt upper end pieces, to me.:flame:

Don't know of anyone who was able to get optimal results from one and the jets were, reportedly, a weird series, not widely available in the west...and there were a lot of guys who sourced their engines from complete bikes, while they were current production models. Expecting "plug & play" perfection from the stock carb was logical enough. Parts availability and that fixed-position jet needle spelled "k.o.d."
 
Case-in-point, the OEM Nice carb came in two versions - one for the semi-automatic another for the 4-speed. The jet needle + needle jet combos are different and they're only listed under Honda PNs. FWIW, the stock combo was #42/#78. Good luck with that as your baseline...smells like burnt upper end pieces, to me.:flame:


Thanks. Just good to know as my #38 and #86 combo can't be that far off.


How much does the slow jet relate to the main jet? IE, if I a carb with a #38 slow and one with a #42 slow, both with #80main. At WOT, are both carb's using the same WOT mixture?
 
How much does the slow jet relate to the main jet? IE, if I a carb with a #38 slow and one with a #42 slow, both with #80main. At WOT, are both carb's using the same WOT mixture?

Good day. I'm hoping someone can answer this. I'm very curious how the slow jet relates to the main jet. Perhaps someone can chime in? :)
 

racerx

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Thanks. Just good to know as my #38 and #86 combo can't be that far off.


How much does the slow jet relate to the main jet? IE, if I a carb with a #38 slow and one with a #42 slow, both with #80main. At WOT, are both carb's using the same WOT mixture?

Possibly...but not necesscelery. It's a logical assumption, yet assumption is still the mother of all :censored:ups. Needle jet profile, airbleed orifice & slide cutaway size can all affect mixture dramatically. If you don't know which of these parts are in both carbs, then your comparison is a guess. Make life easier & less risky...go by what works; start by determining the rich limit.

The pilot jet flows fuel right across the entire operating range, including WOT. The amount of fuel is minuscule. Above roughly 1/4 throttle it has virtually no impact. That's why an engine can perform reasonably well at speed, even with a blocked pilot jet...it just won't idle, it'll die below ~1/8 throttle.
 
Thanks racerx. I'm trying to get a #42 pilot up from my current #38...only the #42's are non-existant.

The bike idles and runs great in the low end. I was just thinking that because the stock carb ran a #42 pilot that perhaps my #38 is not enough.

Just not sure if its worth changing the #38 if its working fine at the bottom end.

You've probably told me a million times...but how do I find the rich limit again? Put a presumably large main jet in (say #100) take it for a quick WOT rip in 1st or second. If it can't rev past 5000-6000rpm, then thats my rich limit. I should then keep dropping main jets until I am able cleanly rev out 1st or 2nd gear then, correct? The question is, do I stop at that exact jet that lets me rev out cleanly or drop it one size down from that?

Thanks!
 
Would I be silly to go to a PD22 keihin...? I'm starting to think I might have to go that way. There was a member on Planetmini's that said he ran a PC20 and a PD22 and the PD22 was much better performance. Anyone have any luck with the PD22?
 

racerx

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The rich limit is, generally speaking, the largest main jet that allows the engine to rev-out cleanly. Above that point, i.e. one size larger, results in rich misfire - because you've gone beyond the rich limit. I'm getting the distinct impression that you're basically lost with carburetion and that's the source of the seemingly insurmountable problems. That's not an insult, it's an honest observation. You're now contemplating going back to a 22mm carburetor...without first getting the 20mm unit dialed-in. If you're going to do that, reinstall the VM22. That, I am familiar with and you have a custom-modded jet needle for it plus the correct pilot jet already installed.

Best advice I can offer is..."patience grasshopper, the road to optimal carburetion has a convoluted learning curve".

The only way to setup an unknown engine/carburetor combination is to "bracket" each operating parameter: pilot circuit (pilot jet & airbleed setting) to get a solid, stable, idle main circuit (main jet sized close to, or to, the rich limit), jet needle setting (to get optimal driveability in the midrange, although it affects WOT mixture with some carbs), then make single increment changes until acceptable results are obtained. Otherwise, with no controls (read: laboratory "control", i.e. working from a known point of reference), you're only flailing around, making blind guesses. That'll only work with a miraculous shot of dumb luck.

FWIW, a 20mm carb has 23% more venturi cross-sectional area than the stock 18mm carb. Upsizing to 22mm, adds yet another 26%...enough to support at least 14-15hp, 40% more than your motor makes in stock tune.
 
Very good post racerx. You are always good with your choice of words not to offend lol :) I'm assuming you've been married for a few years!

Yes, I'm really not sure what I'm doing, but this thread is helping me out. It all started when I was talked into a PC20 by a unnamed Canadian mini bike business, without them having a real experience with the Nice motor. But he assured me it was "the one" as many CRF110's owners upgrade to this (though I've found little forum activity to confirm this...)

The more I read the PC20 is used on 88cc Big bore CT70 jobs as well as Ruckas big bore conversion. Thats its most common application. My fear was the PC20 was under-sized from day one for the Nice 110...but really I may be just at its limit or even a hint below. If you say a 22mm carb is good for 14-15 hp...much more than my bike makes, then I'm probably fine. I'm hoping to make 9 hp on a good day (optimistic?)

That, and a fellow on another forum had also said that he's used both the PC20 and the PD22 of what he found the PD22 to be "much better performing" with the Nice 110 motor. Seeing as how rare it is to find info on this motor and bike and how few people actually know what they are talking about...i was taking any advice I could find and running with it.

Of course I tried your suggestion first. The VM22. Truth is the VM22 and I just did not get along. Don't think I did not spend any time tuning it. I tried for what must have been a good 40 hours trying to get it right. Never happened. Don't think I was shooting for EFI good...I could never get the thing to rev out cleanly past 7000rpm without dropping to a ridiculously low main jet (140!!!). I just did not feel comfortable running it WOT with a 140 or smaller jet from what I heard. Not saying this is not the carb of choice...just not for me and my location. The offer is open, if anyone want to travel to Northern Alberta Canada to help tune my carb, I've got beer in the fridge :red70:

Second truth is the PC20 has been exceptionally easy to tune. Only I've got next to no-one with experience with other for baseline, other than the guy who told me the PD22 was a better carb. So all along I though I'm running the wrong carb, I'm running the wrong carb...this will never work!

I think I'm going to try some more tweaking with the PC20. I just wanted someone to say "Yes, this carb is not under-sized for your motor in stock form (aftermarket exhaust and K&N filter)". I'm thinking your last post your pretty much told me that, so I'm good to go :)

If only someone had a wide-band O2 for motorcycles that I could do a dyno run and really see what its doing.

Thanks for the kind advice. I'll keep you guys posted.
 

racerx

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I'm glad that you didn't misread my previous post. I'm trying to be brutally honest and not offend. Machinery has no social grace whatsoever...and that's what we're dealing with. It either works properly, or it doesn't.

Factory rating for your motor is 9.5hp@8000rpm. Seems a trifle optimistic, imho, but based on what I've observed (i.e. real world speed runs), it's at least plausible. A fully broken-in & optimally setup 110 Nice should pull 100km/h under "normal" (i.e. on the flat, minimal headwind) conditions. A little less when riding into a strong headwind a bit more with a tailwind. With the carb & exhaust you're running, there might be another .5-1.0hp, as compared to the OEM-stock, as-installed, setup. Even that's no bfd...another 4-5km/h, tops, and only under ideal conditions, at that. OTOH, even if you're down 1hp, the top end speed reduction would be small. Seat-of-the-pants dyno results would be virtually the same, up to about 90km/h, as torque would be unaffected.

FWIW, I do use a wideband O2 meter, when in doubt. I understand your reluctance to test a #140 main, I feel the same way. Smallest main I've ever tested successfully with this engine/carb combo has been #145. That said, pump gas formulations have changed significantly in recent years. I've no idea if Mikuni changed anything inside these carbs. Fact is, there's no practical way to verify either. Even when I began the Nice motor odyssey, over a decade ago, there was always a +/- one main jet size range, from one to the next. I just chalked it up to manufacturing tolerances. A minuscule change inside a carburetor can have a huge impact. If you've been following anotherct's thread, his engine ran best with a #150 main...that was verified with an O2 meter, in realtime. Same motor, carb, intake & exhaust...and about the same observed top speed (ran it up to 62mph - 104km/h), briefly since the rebuild was fresh.

Though (ostensibly) unlikely, it's possible that Honda changed the cam profile. Semi-automatics & manuals had different PNs. I'd assume the semi-auto grind would be more conservative, for added low-end torque.

So, consider the potential variables in this equation: fuel, carb & cam changes. A 140 jet is only one size smaller than what has, hitherto, been the lean limit. Below #150, the size increments are -5, instead of -10. If Mikuni is consistent within their own jet size nomenclature, you're only a half-size below the previously accepted threshold.

I'd have tried a VM20 but, that's a little too "I told you so", for now at least and probably unnecessary. Discard the old <school> preconceptions. Go back and verify that your intake outlet is perfectly aligned with the intake port and that the carb end is aligned with the insulator & carb throat...which is really easy to do, just remove the slide and look. Verify that the rubber O-ring that seals the main jet well to the bowl is healthy & intact. If it's nicked, torn or crunchy, replace it. A leak there can richen the mixture beyond control. Next up, source a 140 & 145 main, set the jet needle at max height (C-clip on the lowest groove) and see what it does. If it still goes into rich misfire, raise the C-cilp 2 grooves at a time & restest as needed. Start with fresh gasoline and a new plug. As I've mentioned previously, this carb can be a temperamental sumbitch to get right. At most, you can be on cusp with two main jet sizes and two jet needle settings per jet. When you go just below the rich threshold, you'll know...the motor will rev-out, with enthusiasm, right up to redline.

Here's a kicker...when you have the choice between two different main jets that will allow full WOT rev-out, the jet needle height can have a larger effect on part-throttle mixture than the jet size & needle height will on WOT air:fuel ratio. Typically, the smaller jet, with the jet needle 3-4 steps higher, will produce part throttle A:F ratios about .5 to one full point richer and about .3-.4 leaner at WOT. I like to see about 12.5-12.6:1 at WOT, running pump gas. That said, 12.8-12.9:1 is still plenty safe. When in doubt, check the plug. Even with shitty 2014 pump gas, it's easy enough to see a black or lily-white plug tip. Burnt VHT on the headpipe is pretty hard to miss, also.

Bottom line, if the VM22 cannot be tamed, it'd be the first & only one...no exaggeration.
 
Thank you kind sir. I will give this all a go.

When in doubt, check the plug. Even with shitty 2014 pump gas, it's easy enough to see a black or lily-white plug tip. Burnt VHT on the headpipe is pretty hard to miss, also.

When you say check the plug, you are talking about doing a good 'ol WOT plug chop, right?

I should get some new spark plugs. What plug and temp are you running just to make sure I'm starting with the correct one.

Let me know
 

racerx

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A plug chop is a good idea. However, I've long-since ceased doing them with this combo. The O2 meter is more accurate...not to mention telling...especially since current pump gas makes plug reading a lot trickier than it used to be. You can easily get by without one. Unless there's something really weird going on with your engine/carb combo, consider most of the R&D done. The motor will go into rich misfire when A:F ratio reaches 12.2-12.6:1, depending upon the fuel mix you happen to get. You're probably safe as long as WOT ratio stays below about 13.4:1. And with this carburetor on this engine, you'll get huge transient lean spots in the midrange long before you can go that lean. Consider this the poor man's A:F meter.

Main jet size changes will alter WOT A:F numbers by about .3 -.4. That's making changes one size at a time + changing the jet needle height to match the new jet. Essentially, you're walking a tightrope between pig-rich (won't rev-out at WOT) and lean spots lower in the throttle range that'll leave the motor falling on its face with normal rates of throttle opening. How's that for specified parameters?

The process is simple enough. Set the idle & WOT mixtures (the only adjustments over which you have complete control) as rich as possible and, hopefully, the vast range between those two extremes will fall into place. The lone exception is low-rpm/light-throttle tip-in; that's where lack of airflow velocity can produce a 1-2 second (it seems like forever, while riding) transient lean spot in the fuel curve, under certain conditions. Re-profiling the jet needle can minimize this but, it's a fiendishly tricky proposition ...best left for another time - like once you have the WOT mixture sorted-out. Besides, you already have a re-profiled jet needle.

As for which plug to run, go by the factory-stocker. It'll either be a u20 or C6hsa (going from memory). I'm not a fan of R&Ring plugs from an aluminum head, while hot. Do yourself a favor...apply a little high-temp anti-seize compound and use just enough torque to compress the gasket. That'll keep the threads healthy.

Having said all of that, I do check the plugs in all of my machines, from time-to-time, especially when there's a change in throttle response...such as what happened when E10 became the standard. These are usually done after a typical ride, before the engine is cold-started or spends any time idling. I'm evaluating the overall carburetor setup. The plug body should be black or at least dark brown, the center electrode & insulator medium-to-light gray or tan. Heavy black deposits on the plug body mean it's running rich; on the center electrode & insulator...you're likely to be getting misfire. A lily-white insulator is a bad sign...overly lean.
 
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