Jetting Advice 28MM FS Mikuni, 200X race motor - DUMB AGAIN!!

[Dirtcrasher]

My god, everything I have read, everything I "thought" I understood is making no sense to me.

Telling you what I have for mods means nothing, it's all about how it runs and what it's telling you.....

I am running great on top, 3/4 to WOT so I'm very close on the main which of course has a trickle down effect.

So here is where I AM COMPLETELY LOST!!

I am running a 28 Mikuni that had a 20 pilot to start.

I am up to a 50 Pilot now.

The choke is nearly useless which says RICH and I'm watching my front half of my Suertrapp pipe turn cherry red

YOU TELL ME!! that means lean!! but the choke being useless means rich!! and those are all 0-1/4 throttle of the circuit!

There are no air leaks, no worn carb, no float problems and I have the conflicting issues......

Does it make any sense to PEOPLE THAT HAVE TUNED AND BUILT MOTORS?? Because it does not make sense to me...

If your choke does nothing, your too rich on the pilot. If your pipe glows red at idle you are too lean!! WTF is going on here??

I would up my pilot to a 55 (from50) which is the LARGEST one they offered at a given site, but then I wouldn't even have to choke it at that point which is wrong in 15 degree weather. It seems to be COMPLETELY asssbackwards??

The ONLY variable is the "air jet" which of course I can't find one piece of literature to say " the air jet is responsible for..............................BLAH BLAH BLAH!!!

I "THINK" it allows more air into the choke circuit when the choke is on. So, if I drop it down the choke may work again. BUT! even then, why at idle with a 50 pilot. 1 turn out is my pipe turning red - LEAN LEAN LEAN!! A 50 pilot jet in a MIKUNI IS LEAN!!!!!!!!!!!!!!!!!!!!?????????????????????????? ??????????????????? NO AIR LEAKS!!!!

I'm so pissed off that I can fix anything mechanical yet this thing makes me feel like a complete IDIOT/NEWBIE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Air jet?? Anyone?? Please!!

I'm not satisfied with "good enough" I want to get this close to dead nuts!!

[Mosh]

What was it doing with the 20 pilot?

[Saul]

Is this a 2 or 4 stroke?

[Dirtcrasher]

Hey Mosh,

Wit a 20 pilot, the pipe turned cherry red immediately and cooked off all of the PC on the headpipe........

If it's glowing at a 50 pilot you wouldn't start dropping down would you??

IDK if that Mikuni "air jet" is doing this but the choke circuit and 0-1/4 throttle do not seem right.

SAUL- 4 stroke 200X, full porting, 12:1, race gas, no AB lid, aggresive cam, lightened flywheel and a 28MM Mikuni flatslide carb.

It is LOVING the top end whi9ch is roughly a 280 main jet.

[Mosh]

What is your compression at?

This is the built to the hilt 200x right?

Have you ruled out timing?

[Dirtcrasher]

What is your compression at?

This is the built to the hilt 200x right?

Have you ruled out timing?

I'll check it again in the next few, but it was at about 190PSI.....

Timing on a 86 200X is supposedly FIXED, but, I'd be more than willing to oblong some holes and either advance or retard it.

In the Service manual, when timing is off, they suggest ohms tests of various components (I've got many repeats of parts that could be swapped, but I never liked being a "parts changer" )

What are your thoughts on the ignition timing? The thing is awesome from 3/4 to WOT.......

Hey, I can run it. But... I've ALWAYS had a problem when "things" don't make sense to me and thats whats going on right now.

Thank you all for any input and or advice!

[edog]

Could the problem be in the exhaust valve and port?

[Billy Golightly]

Hey Dirt, didn't you have one of those Chinese Mikuni copy carbs or is this one of the actual Mikunis?

[edog]

You NEED to advance your timing.

[Mosh]

I am not going to try to pretend I know everything about jetting.
Honestly, I have seen 2 identical engines run different jetting before,so everyone is unique.
I would think that rich of a pilot would be more than enough.
So all I can do is throw out some theories..
A) 110 gas doesn't combust properly in cold temps..
B) Maybe your cam duration is letting unburnt fuel out of the head.Therefore I would at least try to look at cam timing more closely.

Even all the new 450s glow at the pipe.
I believe this to be becuase they are so heavy in exhast cam duration,some of the combustion takes place in the pipe.

Edit.......You said you just "picked out" a cdi that looked good.
It wouldnt be the first time a CDI was the wrong unit.All the timing advance is built into them,and vary from bike to bike,even though they may "bolt on"

[Jason Hall]

Dirtcrasher, I would think that If the choke makes no difference, then you are still lean. If the choke being on doesn't change anything, and the pipe Is glowing your not getting enough fuel. If the timing was retarded, like Mosh suggested that could cause excess heat In the pipe. What kind of carb Is on It? I know It's a Mikuni, but is the air/fuel screw In front of the slide? or behind It?

[Dirtcrasher]

Hey Dirt, didn't you have one of those Chinese Mikuni copy carbs or is this one of the actual Mikunis?

Hi Billy, At TF08 I had a 30MM roundslide (copy) thats why no one had any jets for it and I ended up drilling the pilot way to fat, running the main way to lean and not having race gas. Then the rain/mud hit and I couldn't tune any more.......

I've got a 28MM Mikuni flatslide now and the slide was worn so I tossed in a new slide and I had new floats so I put them in also.

It is running SUPER on the top but the choke not doing crap and the pipe glowing bothers me... BUT, Mosh has seen headpipes glow before?? I mean. it is a very thin Cobra headpipe - is there enough heat to create this condition and COULD I go leaner on the pilot??

EDOG - Maybe so, but wouldn't I also have problems up top?? I do appreciate anyone's thoughts and arguements. Thats how we learn!!


ANYONE on the "airjet" and it's function?? I assume it's simply in the choke circuit and then done?? anyone??

[edog]

You could always try a dial a jet.

[edog]

You probably look into Jet hot coating the header or wrapping it with header wrap.

[Mosh]

Some consider a 450 glowing to be normal...
I dont think I would be comfortable with it.
You are definatley not the type to assemble the engine wrong, so I am gonna rule that out right away.

If it were me, I would start from square one.
A completely different carb.
I have a carb for a 250R I and others spent over 10 hours on and never got the thing right.
I now use that carb to throw at stray dogs getting into the thrash.
Sometimes it is best just to start over...
But I still wouldnt rule out timing if a different carb doesnt help.
I dont care for Mikuni's, but I never had problems with them either, on a stock machine with little mods.