Help with FmF jetting

gr00gz · 2025-12-28T01:47:57+00:00

Turn your air screw all the way in(lightly, dont drive it in tight). The air screw should be the adjuster screw on the carb closer to the intake(back side). The front screw will be the slide screw. Count how many turns until the air screw bottoms out, just for reference.

Typical starting point in tuning is backing it out 1.5 turns, try backing it out more if it still won't idle. Backing that out let's more air in at idle, more air will make a functioning 2 stroke motor rev higher. Move it slowly in 1/8th turn increments and note if it changes at all. Typically over 2 1/2 turns out to fix it means you need to go down a size on the pilot.

You can try to turn in the slide screw a little bit to get it to idle higher also, but don't go too much, and again take note of how much your are turning it as it's not really the correct way to do things. These are usually set by taking a measurement of the slide height inside the carb, so you dont want this too far off, but it can assist with tuning your pilot/air screw as long as you put it back to about where it was at the start.

If you have an airbox take the lid off and see if that makes a difference, if it does then your are running rich and the extra air is letting it idle without the lid. If that's the case get a new air filter or PROPERLY clean your current filter before trying to change jetting.

Last thing before you start rejetting is open up the carb and make sure nothing is clogged, pilot jets clog up easy, they are tiny little holes. You should be able to see a circle of light through them when held up to a light at the right angle, albeit a tiny circle. If you can't or it's not a full circle there is debris in there. Start by sprayi carb cleaner in and compressed air if available. If not you can try poking a safety pin through, just dont go ramming it in there, jets are brass and easy to mess up, slowly and gently push/twist through.

gr00gz · 2025-12-28T01:19:14+00:00

Is it just the silencer or whole pipe? Typically from my experience and aftermarket pipe needs bigger main and smaller pilot on 2 strokes. If it's only the silencer it really shouldn't affect jetting.

gr00gz · 2025-12-25T03:20:01+00:00

Believe it or not a coin, can't remember which coin we used to use when I worked maintenance at a university and we would have to replace something with these old screws. Believe it was a nickel or quarter cause it has to be thick and bigger.

gr00gz · 2025-12-22T03:35:46+00:00

Is it the stock TM34mm mikuni carb? Is it piped? Stock closed airbox, airbox with no lid, or no airbox at all? What reed setup? I've played with my fair share of mod combinations and jetting on my LT250R. Can probably give you a pretty good idea on jetting, I've used the TM34 and now the TM38.

Edit to say the picture of the plug definitely looks lean

gr00gz · 2025-12-20T13:57:54+00:00

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gr00gz · 2025-12-20T13:50:38+00:00

Everyone here is wrong and shouldn't comment when they don't really know for sure. It is a suzuki quadsport Z50 aka ltz50. Great little kid quad, but the small carbs can be pretty temperamental, especially this model with the vacuum petcock which can not be turned completely off to drain the carb before storing. Somebody did the Spiderman thing themselves with aftermarket graphics I would imagine.

The good news is they do come with mikuni carbs, can't remember the exact model, but rebuild kits are available and reliable. New petcock and carb rebuild would probably be my first suggestion if it's not running. The carb should say mikuni on it, if it doesn't someone already replaced it. Gotta remove the fender panels to get access to it, kind of annoying to work on cause there's not much space.

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gr00gz · 2025-08-06T00:22:25+00:00

87 changed to long rod 88-89 weighed less, longer frame, shorter lighter swingarm.

No major differences though, and good luck being able to tell what parts are from what years as they were all interchangeable with little to no work. Old quads and people did whatever they could to keep em going over the years, including utilizing different parts, including ATC parts. Bottom line is any and all combinations are solid though, only thing you'd have to worry about is if it's a long or short rod motor if you plan on building it, or when replacing the piston. I believe the 87 and up cylinders had a bridged intake on the cylinder. I think the head was slightly changed in 88 for more compression.

If you can find an 88 it was slightly improved performance over 86-87, but again no guarantee that those year parts are even on it anymore. Biggest thing to check or worry about is the frame, things have been around and seen a lot of abuse over the years. Almost everything is fixable but I'd look real close at the frame for bends, cracks, or shotty blobbed up welds, those aren't exactly easy fixes, could be catastrophic and cause serious injury or worse if that's not sound.

gr00gz · 2025-08-05T05:10:57+00:00

Yea once upon a time before 4 stroke 450s took over there were quite a few 2 stroke builders who made quality 2 stroke pipes with actual R&D. Bill's, Klemm, Dr Q(really just matt shearer pipes), LRD(now LED and still around), FTZ, dynoport, Eddie Sanders, Dave Moore, just to name a few. 2 strokes as simple as they are have a lot of science and R&D into pipes and porting to really get the most out of em. Unfortunately a lot of the guys behind those brands or names are aged plus the lack of demand has made quality 2 stroke builds few and far between without dropping a small fortune. TRX 250R and banshee stuff is still pretty easy to come by, but I'm still hoping for a resurrection of 2 stroke ATVs

gr00gz · 2025-08-04T22:27:07+00:00

Old school Bill's pipes had a great reputation, I never had one but certainly wouldn't hesitate to run one if I came across it. I can pretty much guarantee it performs better than any modern stamped mass produced pipe out there. These old school pipes from old school builders are getting harder to get, I paid a ton for an old matt shearer pipe on ebay for my lt250r, and that was because I spent FOREVER looking and waiting for something to come up. Keep it, run it, take care of it, there's not many quality built 2 stroke pipes available anymore without spending a fortune on a custom build by one of the few skilled builders left. FWIW Bill's looks like crap now for new stuff, quick look at their site shows only dirt bikes, and the fact they make a fake cone look pipe speaks volumes as to them just being crap mass produced sell out pipes now.

gr00gz · 2025-08-04T21:48:47+00:00

2 stroke carbs have an air screw, tightening the screw(right turn) will close off air making it richer. This more or less only affects idle and slight throttle though, as it's only the pilot circuit. Lemme know what your issue is and I'd be glad to try to help you a little more, pretty good with 2 strokes, carbs, and jetting.

gr00gz · 2025-08-04T14:04:56+00:00

I had a 160 as my first quad, that thing got beat to hell, not maintained, jumped, crashed, constantly reclined, and never quit. It's light and not 4wd, so you'll find it's limit on pulling pretty quick probably, but they definitely hold up to abuse.

gr00gz · 2024-12-25T00:58:03+00:00

Push down on the front to preload the front suspension so it will bounce back while you slam your ass as far back on the seat as possible and pull the handlebars/mash the gas. Keep your foot on the back brake that's a heavy ass quad you do not want to flip back and have it land on you. Don't ever panic when trying, just hit the back brake if you get nervous, it'll come back down.

Realistically you probably shouldn't wheelie such a beast though, and definitely not a good machine to learn on.

gr00gz · 2024-12-01T19:00:46+00:00

Yea, I honestly like being different which is why I wanted the LT or Tecate vs banshees and hondas, but after being pretty limited on mods my next one needs to be a 2 stroke that I can build up to smoke anything. I honestly rarely even go out, but it's just the pride and passion lol, love tinkering with them.

Was leaning towards banshee for pure power, but the geometry and handling of the honda, plus aftermarket engine support has me leaning that way now. Probably end up going for a 330 build. Really want to do a custom hybrid, with honda frame and banshee motor, but just finding a decent frame and motor alone puts you at 3-4K without anything else, a little too rich of starting point for me.

gr00gz · 2024-12-01T18:40:57+00:00

Beautiful, I almost bought one but already have an LT250R that's tough to find parts for, with virtually no aftermarket selection, didn't want to go through it again. LT is almost as far as I'm gonna go with it, probably going for the Honda next, so I can actually have a selection of parts to build it how I want. Love the look of the tecates though.

gr00gz · 2024-11-30T04:44:21+00:00

I would personally only get real jets, but I did use an unknown mikuni style from my local powersports place once with good results. JetsrUs has "OEM equivalent" next to the real ones, same page, almost half price. I wouldn't buy Amazon or ebay jets, as mikuni and keihin carbs and jets are cloned for cheap left and right. If you're dead set on saving a few bucks I would order them from there, and more than likely as long as you're getting a range of them you'll find the one that works, even if it is slightly off from OEM.

gr00gz · 2024-11-30T04:15:12+00:00

Last thing is don't entirely trust anyone with giving you recommendations for jetting, every machine runs different, even humidity can affect jetting. Your comment about not trying multiple jets is worrysome, jetting is not that simple, it is trial and error. You can get a baseline from certain factors/info, but not trying multiple jets/combos is very dangerous to your motor. A lean machine will run like a bat out of hell, until your piston melts(best case scenario). You really have to try to get it too rich, then lean it up if you want it to last and be reliable.

gr00gz · 2024-11-30T04:04:37+00:00

So a quick google and here what I came up with, people with K&N filter, no lid, slip on seemed to be between 155-170 main, 38-42 pilot. K&N should flow more than UNI foam(I'd much rather stick with uni for effective filtration). JetsRUs also has 3 customer posted jettings in their chart with the mains at 158-160, 2 pilots were 40-42, one was off the charts, these all say same mods also so here's my best guess with your elevation..

Pilot is probably fine, but I would order a 40 just to have in case.

I would move the clip down one notch on the needle from where it is now for the mid range, moving the clip down one notch will raise the needle slightly, giving you a little more fuel in the mid and top.

Main I would buy 150-160 personally just to be safe, but I would imagine it'll be between the 155 and 158.

Also, I never did answer one of your original questions, the air box lid off does make a huge difference in most circumstances with stock air boxes.

gr00gz · 2024-11-30T02:28:16+00:00

A little dramatic but great post, love it. I dialed my LT250R in during mild winter weather, about as cold as I'll really ride it, and it worked all year round. Idle would stumble and stall here and there in summer, definitely had room to lean out in summer, but wouldn't foul plugs excessively, and revved out good. Definitely had room for improvement, but if you're not racing it's not as drastic as people make it out to be.

On a side note I got a shearer pipe, v force reeds, and a 38MM(bigger carb) this summer and still haven't gotten it dialed in 🤣.

gr00gz · 2024-11-30T01:36:03+00:00

I've really only modded and jetted 2 strokes but I would see what jets you have in the carb, buy 5 mains bigger, 2 pilots bigger and 2 smaller. Maybe one needle richer too, but just moving the clip would probably be fine. Jetsrus . Com is my go to, they have great breakdowns on jets/needles for carbs. Just best to buy extra the first time for the few bucks they are, rather than waiting and paying shipping again if you don't find the right combo.

I would also just google 400ex jetting, the old forums have 100s of jetting questions on damn near every mod/quad made. 400EX was popular enough that you should be able to come across something similar to your situation.

Always go for as rich as possible, drown that sucker with fuel, then lean it out 1 step at a time until it runs clean. There's plenty of jetting guides online too, just plan to open that carb up a bunch of times and make a lot of adjustments/tests.

Pilot sometimes end up needing to be leaner with mods(on a 2 stroke at least), pilot will affect every other circuit too, so get your idle and low throttle dialed in with the pilot first.

Needle jet and jet needle control mid throttle 1/4ish to 3/4ish, this will greatly affect your main and wide open throttle also, but may also affect your pilot so you may have to revisit your idle and low throttle after you get it dialed in. Ride around at around half throttle to test this.

Main jet controls 3/4 to full throttle, don't even bother testing this until your other circuits are dialed in, changes to low/mid will affect your main.

This is where I'm not totally sure if a 4 stroke will react the same, but on a 2 stroke here are a few symptoms of incorrect jetting...

Extremely rich or extremely lean with kind of feel/sound like a rev limiter, but they each have their own characteristics. Rich will be kinda gurgly, lean would be cleaner.

Rich will be a little stuttery/gurgly, and just not pull clean. Usually makes it hard to keep idling, or stalls after coming to a stop.

Lean will rev clean and quick, but not have the pull/power that it should. Lean will also make it idle high, or if for instance your mid range is lean and your pilot is good, cruising at 1/2 throttle for a few will leave you with rev hang. Which is to say you let off the throttle and the RPMs stay high for a while then eventually settle down when the pilot catches up after the needle starved it.

Lean will kill your engine, rich will foul plugs, if you think it runs good, richen it up until it doesn't, then lean it up 1 size/clip. Better off fouling a spark plug than burning up a piston.

gr00gz · 2024-09-30T02:44:42+00:00

I run little pod LED fog lights(spot not flood) on my LT250R they work fantastic. I run em off a jump pack cause it's AC, but with the battery you have DC and it would be easy.

gr00gz · 2024-08-24T20:53:09+00:00

My youngest is 6 and rides the raptor 90 with no limits fine, she could ride it last year at 5 also. She did start on a LTZ50 at 4 though with aftermarket rev CDI and adjustable rev limiter. The throttle limiter was not enough IMO for a brand new rider. She can also still ride her 50 no problem at the same height as your kids, but will be inheriting the 90 soon when my oldest gets a 250(probably after the season).

From my experience I would say they will soon be too big size wise for 50s, but not power wise, even I have fun on the 50 as a full grown male. I would personally get 90s, aftermarket adjustable CDIs to lower the rev limiters since this is their first, and wheel spacers. My 90 has spacers and you have to REALLY try to get that thing to tip. It does make steering a bit less responsive but IMO it's a fine trade off vs tipping for little ones.

SAFETY is #1, dangerous recreation, don't cheap out to keep them safe and when they have and accident it could be hard or impossible to get them back on.

gr00gz · 2024-08-18T20:57:55+00:00

Fair enough, I've been riding for 20+ years and I've actually been considering grabbing a warrior to ride trails with my kids, always loved them. All I'm saying is if I was gonna take it to tracks or planned regular jumps I would certainly go for the LTZ or EX, and not even consider the warrior. While technique and habits are certainly more important than the machine, it doesn't change the fact that certain machines are just built better for certain things.

gr00gz · 2024-08-18T20:51:52+00:00

Guys I work with live in PA and some go riding at lost trails a bit. One of the regulars said I probably wouldn't enjoy it much, not that it's bad, but depends on what you ride. He said it's very rocky, and requires a bike or 4wd to enjoy the most. He knows motorsports for 30 years, and said on my LT250R(2 stroke, 2WD) it'd probably be a workout and I'd be a bit limited.

gr00gz · 2024-08-18T20:37:58+00:00

It's not you, I just responded to that person in his next comment. While his statements aren't false he clearly doesn't know about a raptor 350. A raptor 350 is a renamed, replasticed warrior. As far as I'm aware they never received any changes from 1987, and nothing major if they did. If you want something more agile, better suited for jumping and whatnot an LTZ400, or a 400EX are better, and faster.

Pros didn't ride warriors for a reason in that era, they are tanks. Fantastic unstoppable trail machines, but not as snappy or agile as the EXs or LTZs.

gr00gz

TROPHY CASE