RZ/RD 350 & Misc. 2-Stroke Tech BBS

I started out with big main jets and have reduced successively. I am now down to 250 and still get the impression that they are too large. The bike still runs better when I back off from full throttle. Same behavior as when I was running larger jets but less. Next logical step is to test 230. I am just a bit hesitant since it seems small?

Full throttle works ok up to about 8000. Then I need to back off to get more revs. I was also wondering if there could be timing issues but I run the curve on the "mule".

1987 F2
Ported but with stock port timing.
Reduced squish same CR.
Kenny pipes
K&N
Zeeltronic
1000 18
1500 20
3000 24
4000 25
7000 25
8000 22
9000 17
10000 16
11000 15
Powervalve
4300 0
8100 100

To me it looks like you are rich. What does your plugs say? Also I feel you can dial in more advance between 4000-7000. I run as high as 29 but 27-28 should be safe. Will let other chime in.

No 2 motors are the same but I will chime in cause I ran them 32mm Mikuni TMs before. I looked up my old specs. I was running 230M, 40P, 6F9 Needle, clip in #2 position. Motor had stock reeds, ignition, no porting, with DG pipes & k&N filters. A little boggy til I hit 6k after that it was a rocket... You're in the ballpark, take your time, check your plugs.

Thank you for your reply's. Now I feel more comfortable to test with smaller jets tomorrow.

Part throttle works fine by the way
I am using same as Leeroy
5FP17 needle
389-Q0 needle jet lowest position.
25 idle jet
air screws 3/4 (not fine tuned yet)

I tried 240 and then 210. Big improvements but still not perfect. I will try 195 next. I find it strange that I can use these small jets but perhaps the carbs work well and suck fuel as they should. Still some misfiring if I try the last 1/8 throttle above 8000 rpm. I wonder if there could be some ignition induced problem, but since there are improvements as I reduce jetting it seems unlikely. I will do some proper plug reading next.
I have ordered P8 needle jets (next smaller) so that I can raise the needle and get it into the adjustable span. I also believe that lowering the needle not just reduce fuel but also alter the timing for when the needle switches ratio. I hope I can learn something from that exercise.

The 25 pilot jets requires small airscrew opening to run and I believe that maybe a 27.5 and a bit more air could work better.

I have some colortune sparks which I haven't found use for yet. I hope they could help me adjust idle mixture. I don't know if they are applicable on twostroke though.

When tuning fuel you should begin with the pilot/screw circuit and work your way up to the mains.

Well, that depends.

OK.

To be safe I have also ordered a new coil from Yambits. Mine has been opened and resealed, which isn't a good sign. New spark plugs and plug caps are also on their way. 27.5 PJ's too.
I am set up for next weekend.
Cheers!

I use this thread to keep record of my progress. I hope it could be useful to others as well.

Yes, the coil was faulty and the new one eliminated the misfiring.

Yes the 27.5 pilots worked better than 25. I have just tested once with airscrew at 1 turn but it picks up nicely and runs well on idle.

The P8 needle jet (one step smaller than Q0) was a big improvement. I ran the clip in middle position (highest before). Next time I will reduce fuel one notch further.

I am now down to 185 mains. Next will be to test 175.

I find it scary that I can use such small jets but the consistent behavior and the consistent improvements give confidence. If I continue to get better results at this pace and do not melt anything, I am soon there. These carbs react very consistently to changes and jets of all sizes are readily available. Then I don't know if they provide any hp gains, but as long as they give great drivability I am happy.

You might find something in this post to help...check all the replies. IN particular, the last post by 5150 for the LC350 ported he has.

LINK: ---->http://www.usa2strokers.com/forum/forum ... ing#344806



For comparison Dave Freist (his RD) was running:
210 main jets
PO needle jets
stock 5FP17 needles on the richer 4th clip
27.5 pilot jets

Dave mentioned that for his RD, he had to change everything but the needles. So DAve runs a PO on his aircooled RD350 and Mark runs a leaner still! 02 on his ported LC, but w/ a 320 main jet (sounds close as a guy that puts VM28s on his RZ, is around a 320 main..somewhere in that neighborhood).

PITA. I know. Why i hate jetting sometimes.

I'm not sure but i would think it is the stock needle (your needle 5FP17) or 6DH7 needles. <--so there is another option if the 5FP17 isn't working.

What I have found in my errors w/ lean jetting/REALLY advanced timing. In my case it FORCED me to go to a huge 55 pilot, 2 sizes larger needle jets...I tried a 170 main jet as a recommendation (mistake...220~230 was more betta). You can sort of compensate (under 3/4 throttle) w/ a rich needle jet, but then when you hit that WFO in the upper gears w/ a severely lean main jet/bad timing, you could end up seizing or holing or both (my case lean main and advanced timing)..spectacular 4 corner seize and holed piston. So rich needle jet, lean main. as you work toward optimum, the main jet size would go up. I went from a P5 and 170 main with advanced timing (only way i could run a filthy rich P5!!) to a (correctly timed) P2 and 220-230 main on my RD400. <---try stock timing curve...advanced isn't always a good thing. seen others that have made the error i made. (although not quite as bad). When my timing was far advanced I noticed 2 things...i could go quite rich on the needle jet size and my pilot size REally jumped on the aircooled bike....ran a 55 pilot when timing was whacked!!! Now i'm back down to a 30 pilot. Don't even think about hitting WFO for long w/ a lean main jet and advanced timing though....that end's pretty fast right around 5th 6th gear..

So be VERY careful...sounds like you might have a needle jet masking the true problem of a lean main jet.

Curious to see what you end up w/.

Thank you Pushstart...

I think my P8 needle jet is very close to correct. I might be wrong but a P0 or an O2!! is very much smaller. I don't think I could go below P6. I actually believe one notch lower and keep the P8 would do. 1/4-3/4 throttle works very well. Full throttle do not work as well but better than with bigger jets.

If you are right about the needle jet masking a lean main jet, I could test that with a richer MJ on these smaller NJ. probably a smart thing to do to avoid surprises.

I attach a table for clarity. TM32 uses 389 series Needle jets.

My ignition is not that radical, is it? I maintain 15 degrees up to redline but that is due to that I have a rev limiter and I believe the retarded ignition at high revs in the stock CDI is designed to act as a rev limiter and is not optimised for power.

Wow, 175Ms & 27.5Ps! They always run best just before they seize. Be careful & do some plug chops....

Bngt wrote:Thank you Pushstart...

I attach a table for clarity. TM32 uses 389 series Needle jets.

My ignition is not that radical, is it? I maintain 15 degrees up to redline but that is due to that I have a rev limiter and I believe the retarded ignition at high revs in the stock CDI is designed to act as a rev limiter and is not optimised for power.

I see what is happening here. Well spotted BNGT. Dave Freist did the the same "series" needle jet mod that he originally did w/ the VM28 carbs w/ the 169 series I believe. So if I am guessing correctly, he put a 169-P0 and Mark used a 169-02? <---that sounds like the only way to explain it.

You might want to go to the 2StrokeWorld board and ask for Mark in SC / 5150 and have him verify what series needle jets AND needles to be absolutely sure. Could save you some jetting time. I'm pretty sure Dave Freist used the 169 series...it looks like you can install that in a Flat slide 28, not so sure aout the 32, but dave had 32s AFAIK, so...verify w/ Mark and see what he says.

Have no clue on an alternate curve ...i have seen people lunch motors when they play w/ the curve though.

I'm not really surprised, my stroked and ported motor with TM32s was fat with 230s last race day, but still the fastest RZ on the grid, so we left it there. I'll need to stock up on smaller mains for next season.