Rough tuning...Am I getting anywhere

[JimTMich]

I'm tuning my freestyle 750 sx. Mods include
big pin ported cases,
750sx freestyle ported cylinder
ADA head 26cc domes 190 PSI
Vforce reeds, dominator split manifold (I love this, thanks crammit442!)
dual 44 Mikuni super bn's with short tau ceti's
FPP dry pipe, microtouch ecwi hitting at 1500
ported pump with c-75 8/16 impeller
Total loss

Plus all the usual lifters, pole, bars,......

Bottom end is pretty decent. 115 ls jets, 20psi popoff


Top end won't clear it's throat, As I apply throttle slowly the revs climb, but then it starts studdering when I get to 3/4 throttle and above and rpm's fall.
I was runnign 135's, then 130's, then 125's, then 120's It seems to be getting better. I can now open it up for quick tricks and get nice rpm's befoe it gets congested. That's better than before. There isn't much data on a setup like this. It seems like I'm headding in hte right direction. I don't want to melt anything, that why I have the compression so low and am running 110 torco race gas. I'm goign to try 115's and possibly 110's tomorrow. I've been told anywhere between 110 and 135 depending on who I talk to.

This thing is climbing out of the watter pretty nice now.

I'm trying to take it really slow and not hold it wide open for more than a few seconds.

Any words for me?

 

[Matt_E]

I had something similar going on and found that my main jets were way too lean. I was at 110 main jets with those symptoms you described, and after some thinking, I installed 122.5 mains - problem solved.

 

[ski4]

i'm lean and having very similar issues
just upped from 137.5 to 140 tonight on the big end and 80 from 75 on the pilot

i hope i am close, puling these carbs is a biatch

 

[ski4]

well my studdering was not from being lean, i kept going withthe main jets and adjusters and eventually the studdering got worse and after a full throttle rev it would die
back down to 137.5 main for me and we'll see what happens:Banane01:

 

[JimTMich]

Well, I've tried mains at 135, 130, 125, 120, 115 and I ran out of jets to try. Bottom is pretty nice with 115's 2.3n/s and 22 psi popoff.

With 115 mains it will run WOT for about 1 or 2 seconds and then start missing. with the 130's, it wouldnt' even let me go past 3/4 throttle without missing.

So I'm getting closer. I need to order some more jets. I'm doing a pretty good job of staying patinent. I've been riding my stock sxi pro. better than nothing, but not much fun for the flatwater freestyle tricks.

 

[ski4]

i thik i have mine nailed or damn close

good luck man

 

[Scorn800]

What's your timing curve on the TL?

 

[JimTMich]

no curve, 18 degrees all the time. My system is not programable. I simply set the static timing and that is what I have. That's the other reason I'm running Torco 110.

 

[crammit442]

no curve, 18 degrees all the time. My system is not programable. I simply set the static timing and that is what I have. That's the other reason I'm running Torco 110.

I hate to say it, but you're missing MOST of the advantage of TL if you're timing is fixed at 18 deg.:frown: You'd actually probably make better power with an enhancer and a light flywheel. On a happier note, that manifold rocks, huh?:biggthumpup:

Charles

 

[JimTMich]

I hate to say it, but you're missing MOST of the advantage of TL if you're timing is fixed at 18 deg.:frown: You'd actually probably make better power with an enhancer and a light flywheel. On a happier note, that manifold rocks, huh?:biggthumpup:

Charles

That R&D Dominator split manifold ROCKS bigtime. I can change jets in 15 minutes taking my time. Used to take over 1 hour! Thanks for selling it to me!:Banane36:

It's what I have, it's better than some, worse than others. It would could cost major $ to change, so I'm sticking with what I have while I'm running kawis. My flywheel is 1 lbs 8 oz if I remember right though .

 

[waxhead]

if your ski is shuddring its a sure sign it is rich
if its clean but slow to rev out then its normally lean
use a tacho
ride it read the rpm
lean it off 1/4 turn
read revs again
if they went up then keep going in until you find that there is no more to be gained
then open it up 1/8th of a turn
it will acclerate best like that
as you go in you may find that your adjusteris all the way in
you hen need to go down jet sizes
as a rule of thumb 1/4 turn =5 points on a jet size
ok its rough but its close

 

[ski4]

if your ski is shuddring its a sure sign it is rich
if its clean but slow to rev out then its normally lean
use a tacho
ride it read the rpm
lean it off 1/4 turn
read revs again
if they went up then keep going in until you find that there is no more to be gained
then open it up 1/8th of a turn
it will acclerate best like that
as you go in you may find that your adjusteris all the way in
you hen need to go down jet sizes
as a rule of thumb 1/4 turn =5 points on a jet size
ok its rough but its close

arghhhhhh:banghead:
wax where was this info a week ago. thanks though i feel better about what i have been doing
does a tiny tach register high rpms in a memory?

 

[w-nut]

hi jim im nut sure id this is any help to you but ive just put on a pair off 44sbns on my 750 sx . my set up is 115 low and high speed jetinetics flame arrestors pjs inlet manafold 160psi comresion and a factory limited pipe . other than that my ski is standard includeing the prop . it had a nice hit down low and top end was pretty good now real loading up that i noticed plugs were showing a wee bit rich tho but not far off . Its the middle off winter here so i have done much in the way off playing i dont even know wot the screws are set at on the carbs . i got the carbs real cheap second hand and thats how they were set up let me know how you go with yours that would be real helpfull :biggthumpup:

 

[JimTMich]

as a rule of thumb 1/4 turn =5 points on a jet size
ok its rough but its close

Are you sure on that one? I was under hte impression that 2 turns was 5 points........ That would really change things wouldn't it. Your saying that the full range of 2 turns on the main adjuster is = to going from 100 through 140 high speed jets. I have not experienced that when tuning before.

Thanks for the help guys!

 

[waxhead]

yes i am sure

i said its a rough guide
but it works for me
This is on the high speed circuit

 

[ski4]

wow, that is a huge swing with each turn but makes sense on the demand for fuel on this end of the spectrum i guess

 

[douglee25]

Are you sure on that one? I was under hte impression that 2 turns was 5 points........ That would really change things wouldn't it. Your saying that the full range of 2 turns on the main adjuster is = to going from 100 through 140 high speed jets. I have not experienced that when tuning before.

Thanks for the help guys!

I believe this is correct. There is no way 1/4 turn is 5 pts. If you have a 160 jet installed and the screw is turned all the way in, you're at 160. If you turn the screw out 1 turn you're at 162.5 (roughly speaking). Two turns out and you're out 165. Since they advise against being out too far on the high or low screws, they say go up one jet size and start over with the screw turned in. In this case, you'd go up to a 165, not a 200.

Doug

 

[waxhead]

everybody to there own
i am just speaking from my experience

what ever works for you is great

 

[Mile9c1]

I agree with Wax. However, remember that the screws and jets affect different throttle positions.

 

[JimTMich]

Help!

It still won't run without missing at high RPM/Wide open Throttle.

Low speed is pretty clean 115 ls jets

High speed jets I have tried 135, 130, 125, 120, 115, 110, 105. Plugs have gone from sooted up to quite clean/light tan/white during this process. I tried each jet with the HS adjuster at 2.0, 1.0, 0.5.

So what did I miss? I have the ECWI unplugged. I was starting to think ignition even though it worked fine last year. I put a tiny tach on it to check to see if the ignition was firing and I get a clean rpm reading everywhere. nice and smooth at 8500 for 5 seconds out of the water. So it seems like it is firing. If it wasn't I would expect the indication to fall even if the engine was spinning that fast.

So what else do I need to check? I'm at a loss.