New bike with a few issues

[boogiedude]

The carbs are mikuni VM30 which is a 30mm roundslide, non power jet. The motor had a good plug color before the build Running a 30 pilot and 250 main. So I'll bring the pilot back down to a 35 from the 40 it has now and bump the main to a 300 from the 280 it is at now. I don't think the number scale is the same between the factory carbs and these , when referencing a 380 main recommendation that would be a 13 step increase which sound ridiculous

[boogiedude]

You beat me to the reply seahorse, I'll check with my local moped shop and see if they have the 27.5 pilots and a few sizes bigger on the main to have on hand

[boogiedude]

OKAY update time again. Swapped in the 300 mains which are the biggest I have and the moped shop closed at 4 so I couldn't get any others. Did a plug chop and there is a color ring there. it's faint, and narrow, but that could be in part because there really is no stretch of road here that you can hold WOT in top gear for 10 seconds, so I did as long as I could. I did notice that it kind of fell on it a face and had zero pull about halfway through the WOT pull when my rpms were getting pretty high. Any ideas on that?

[pushstartrearset]

Try 3rd or 4th gear next time (whatever you have room for WFO), don't need to do it in a higher gear until you are close on the mains.a higher gear and too lean can lead to tears early on! ( put new plugs in, ride around using full range of throttle for about 10 minutes (puts some color on the plugs), then do the plug chop and pull them and set aside (install spares to ride home).. Yes , still lean. pop in a 340..that should get a nice ring!!...hardly any ring there if that indeed is WFO!

FLAT dangerous lean. wait until you get a 340. I still remember that last guy saying 320~380 mains like i mentioned before (2SW forum). I'd be willing to bet it is in that range. <--the guy has done numerous times w/ VM28s so VM30s can't be that far off.

good luck and keep cutting shi* up and posting.

NOTE: you may think you are spending a lot on main jets, but it's more expensive to pay an expert, especially w/ aftermarket non-stock carbs (i've heard claims of 400~500 just for the labor!!).

[boogiedude]

That 380 sounded crazy but I'm quickly becoming a believer! You were right about it needing to go way bigger!

And that diagram is a great break down. I'm definitely saving that one

[pushstartrearset]

I would think the 380 would be to rich , so i tried to cut some experimention down for you (NOTE: hold harmless if it seizes...i'm wouldn't thing so, but...i'm taking a shortcut here!!, use at your own discretion!!). Remember: do the chop in 3rd or 4th gear. obvisouly, 3rd will give you a little room to hold the throttle for a little longer on your short runway. The thinking less load on the motor, less chance of a spectacular seizure and what my machinist recommends initially to find a ballpark main jet. I would think 5 seconds is plenty of time...the longer you hold it the more chance for a problem initially...lets find a ballpark main first...so 5 seconds max held throttle to avoid a heartbreak.

Spec II (Gary Schumake) had a trick for the midrange:

"The only way to determine the proper needle position is to try it. At about 60mph and 7,000rpm, hold the rear brake and roll the throttle from 1/2 to 3/4 to full throttle and back and forth. When the needle is too rich, it will pick up when you go from 3/4 to 1/2. It feels like the throttle is wired backwards." <--- what i would do w/ clip position is keep going rich until i had this symptom or it "burbles" 4 strokes = misses combustion cycles...like a deck of cards sound in the bicycle spokes, then move back a clip. <---another sign of rich running is "uneven" acceleration.bike will sort of accelerate off and on, make not of throttle position it happens at. lots of smoke out the tail pipe, drippy pipe, drippy exhaust flanges (bbq sauce), burns the eyes, engine sounds dull.


I ended up going to a richer P4 needle jet because i was at full rich on the needles (ok, so how much fuel does the midrange want!)...i soon found that i had to go back to a P2 needle jet because the P4 was slightly too rich. I found the that P2 full rich needles was it...been good for over 50k miles so i didn't screw that up!

I found on the 76 RD400 that if you get a "hiccup/lean/flat" @ exactly around 1/4 throttle...the needle jet was too small...that bike is ALL stock, so the needle jet needed to be bumped UP to a P4 from P2....Chuck Supertune Quenzler was right on that one...did his stock airbox mods on our 76 RD400.

I had to find "too rich" because on the other bike i had 1 clip leaner ended in seizure right after i pulled off the freeway. went from 4th clip to 3rd, when the bike ran better (later ) on full rich or 5th!!! so the lesson here is run the needle clip as rich as possible w/o burbling or 4 stroking or deck of cards sounds in the bicycle spokes.

[boogiedude]

So I bumped up the mains to a 340 today and did a couple more pulls on a new plug and the results aren't much darker/better than before. Unless I'm not doin the chops correctly, it looks like I've still got a ways to go on the main. It definitely felt better in terms of the flat spot on top though. I don't think I felt it at all this time.


I also noticed a few drips beneath the bike when I got home from work and noticed this. Can I just synch that but down a little? why it would it leak there?

[pushstartrearset]

Wow. Go straight to a 380 and see what happens. The ring is getting darker. So you held the throttle WFO when you hit the kill switch and grabbed the clutch as you coasted to a stop? I see a ring starting to form...still too lean obviously. Getting better.

The drip is only in that one bolt? Looks light like gas...touch it and smell it if you can tell the difference.

[OldTZracer]

FYI - those marks on the main bearings & cases are from "chatter" & not rotation. The forces generated by the crank turning high RPMs will cause the bearings to vibrate back & forth. A couple of drops of Red Locktite will stop it.

[OldTZracer]

Wow. Go straight to a 380 and see what happens. The ring is getting darker. still too lean obviously. Getting better.

The drip is only in that one bolt? Looks light like gas...touch it and smell it if you can tell the difference.

What did you say it had for needle jets? If they are too small, they will restrict the flow at some point.

Don't tighten the bolt. The fluid collects there because it is a low point. It probably came through the hole in the crankcases below the carbs.

[pushstartrearset]

What did you say it had for needle jets? If they are too small, they will restrict the flow at some point.

I didn't and don't know his internals ...trying to work w/ what he has and not complicate things. I've converted my R5 carbs to work in my daytona and know there is more than one way to skin a cat, so i know what you are saying. He could also stay w/ the same series and work richer, which i gather is waht you are saying. you have a VERY good point as i have noted seizing in the midrange my self through lots of errors...that being said, maybe now is a good time for the next paragraph?!!!

BOOGIEDUDE: I listed a link to scootrs on a previous page that runs the bike w/o the main jet (on center stand) to tell if the needle jet is right/lean or rich. I would think this would work w/ our bikes, but haven't tried it yet. Now would be a good time to click that! ----> http://scootrs.com/tech.cfm?tip=tunecarb see "Jetting: getting the most out of your bike". Specifically: Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET.

As an example: my tuner has some flat slide mikuni TM28s he may want me to try/buy. He wants me to try the stock internals first, which would probalby be around a 340 main jet. My option would be to go primary needles and needle jets, lowering themain and essentially a Dave Freist mod. the trick is buying the correct series needle jets so you don't get a mismatch! Looks like a straight classic D.F. (5DP7 needles / 169 series P0/P2 needle jet) carb swap to me, but I will probably humor him trying the stock configuration. If it works, I'll use it....what I'm trying to do here w/o a complication.

I've also read Clinton Whitehouse the difference between primary and bleed needle jets (175 series-RD carbs) racing Dale Alexander on different tracks. The bleed mods and higher mains won on longer tracks willo springs i think....the primary / Dale Alexander (5J9 needles / 169 series needle jets PO/P2 2mm shroud...most likely an R5 carb <--his preference) mods won out on shorter tracks like Sears Point/Infineon/whatever they call it now. I've run primary for the longest time on my 400F (50k miles but w/ 5DP7 needles <Dave Friest's solution to non available 5J9 needles>...5J9 is strictly Dale and his racing/no longer available) and have had no problems...couple times cruising at high speed for 20 minutes straight (80+)...when i do this I like redline synthetic (felt the smoothest and at that time was mixing 24:1 (yes rejetted again!) , very expensive on the street!!!). so i compromised and went amsoil and 32:1...not a bad oil and i get a couple more thousand miles out of a top end using it over lesser oils.

[boogiedude]

My needle is a 6DH3 which from what I've been able to find online is the needle that gary@specII drops into the carbs he sets up and sells. I don't know what my needle jet is off hand right now, but that's a good point about it potentially limiting flow. I'll check that tonight.

I'm reading through the scootrs site and there's lots of good info there. Good find. Based on my 1/8-1/4 throttle burble, it seems that my taper may be too rich, although it does pull hard and revs very cleanly as soon you're past that point. I can snap it open to 3/4-full from 1/4 throttle in the mid range and it'll shoot off like a rocket so I feel the needle is pretty close. Does anyone know what the nomenclature on the needles translate to? 6DH3 is just a random group of letters and numbers to me

[pushstartrearset]

TaPER: yeah they are referring to the Keihen carbs (primer is for both Keihen and Mikuni). your 1/8th throttle problem could be slide cutaway...i usually try to jet that out 1st, if that doesn't work i change the slide cutaway...for that 1/8th area. see next paragraph. Also 1/4 could be needle jet. do you get a hiccup @ 1/4, like a short flat hiccup? if not , i would concentrate on teh pilot for now.

you'll probably be fine w/ the 6DH3 needle (others have jetted to it). What pilot is in there now? Try messing w/ the airscrews (not idle screws)....the RZ is funny as you can have a useable range from 1/2~2-1/2 (stock VM26carbs) <---unusual considering what the mikuni manual says. Find out where the bike runs best in the airscrew range and tell us how far in our out from full in the airscrews are set at (do both equally). If you have to turn the airscrews all the way out, the pilot is too big. If it runs fine w/ the airscrews turned almost all the way in, it's too small (usually, although an RZ can run @ 1/2 turn). <--try this before running w/o the main jet. I usually jet this by the seat of the pants and try taking off from zero throttle...if you have to use too much throttle or it falls flat, lean...turn the airscrews in. if it won't idle, burbly burbley, most likely rich, turn airscrews out. if you have to turn past 2-1/2, the airscrew will likely fall out from vibration and pilot is too rich. 1/8th if i remember correctly could also be gary ran a cut slide, maybe leaner? can someone confirm this? I think Gary did do a minor cutaway to the stock slide.....if you didn't, then you probably have a stock rich cutaway slide. I'd try to jet the burble out first w/ airscrews turned out or a smaller pilot...if that is a no go, then to make his mod work, you might need to have the slide cut also. <---RB Designs in Portland, OR (website) can do this...he's done it for me before.

I found another post for the RD350/RD400 and for that "coyote" put in 5DP7 needles, either P2 / P4 needle jets w/ 5DP7 needles (my best guess is that the series might have been changed to 169-P2 or 169-P4 or is it 159 series REALLY NOT sure. might call mikuni and see if 159 and 169 can be swapped in the VM30 carb?, since that is what runs in the RD (169 series) and maybe the RZ as well. and made sure the airjet was a 2.0 (should be 6 o'clock positionin bell housing). The slides were also cut leaner to 2.7. http://www.2strokeworld.com/forum/index ... 5#msg56845

Ask Gary if the 6DH3 needles are specific for the RZ and if they 5DP7 is mainly for the RD, also what series needle jets and slide cutaway for the RZ?....be prepared for an angry response <--worth an earful to save time.....(()&(*&*#&!!!!

[pushstartrearset]

might be better to e-mail gary (I'll PM his e-mail and phone).

[pushstartrearset]

Found this from Supertune in an old post i saved (USA2strokers circa Oct. 17 2010):

"
I used a set of 30mm form Gary on a customers '77 RD400, Came with 40 pilots, 2.5 slides cut to I think 3.0, maybe less? 6DH3 needle set in the middle (3) 159-P2 needle jets, 2.0 air jet and 250 mains the the cables, adapters for 'Y' boot and the 'Y' boot with K&N filter.
This engine is one of Garys early ported engines with the welded TZ plate reed conversion.
NO CROSSOVER TUBE OR BOTTLE!
DG pipes are on it for now, which are being replaced as they don't match the powerband very well, as the porting really comes on as the pipes start signing off, but that will be cured with a new set of pipes.
These carb were WAY rich and always fussy on this bike.
Finally got rid of the 'Y' boot and the adapters with Uni Pod all foam filter and started running consistent.
I looked hard at the adapter and decided that they weren't a good choice for this setup as the adapters somewhat blocked the air jet holes and just didn't see the proper flow to me.

So, 6DH3 needles, 159-P2 needle jet (you could possibly run a 159-PO...RD350 runs a PO size), 2.0 airjet, slide cutaway most likely 2.7 cutaway, no adapted Y-boot...use INDIVIDUAL (you will have to find the right size to fit on bell housing) all foam UNI pod filters (no hard end!)

again, try to jet w/ the stock slide first...ifnot doable...THEN the cutaway. I suspect, thought, you may need to cut the slides. I just would hate to have you cut them and find out oopss...you know.


what a hassle jetting is but once you get it right...you can forget about it. This is the joys of jetting w/ a non stock carb.