Need help from 200x guys

[Hedberg_Racing]

85 Honda 200x.
66mm 10.25:1 piston
Mild porting on head
Webcams 40b cam
2mm oversize Carb from an xr I believe, using xr intake boot.
supertrapp exhaust, 12 back pressure disks.
Moose Filter, airbox lid INSTALLED, with rubber snorkel on front of airbox removed

Okay, ive been dicking with tuning the carburetor on this thing for a wile now. Cant get it figured out, im starting to wonder if the carb is just too big. It runs amazing wide open, it starts and idles great, no backfire EVER. plug is good color. Jetting is 118 main, stock needle on 4th clip, 42 pilot.
I cant seem to get this bog out of it. You pin it from idle, in neutral, and it just Doesn't fire even once from the second you crack the throttle wide open to the second it completely dies, just like you hit the kill switch! If you choke it halfways? great throttle response, in neutral I remind you. However with the choke half on, when you start getting pretty high in the revs it starts to sputter, which is expected. So what should I try next? Ive had all the way from a 35 pilot in, to a 42. Doesn't really seem to make much difference. The needle doesn't seem to affect it no mater where you put it. Ive tried all sorts of different main jets, but it runs flawlessly wide open high rpm. revs REALLY nice and makes the nice dark tan plug color. You don't seem to notice it when riding because I like to keep it in the higher RPMs, but if I try to a slow wheelie from idle, I struggle a lot. What next?!

[lokisbuddy]

Do a wot plug chop. try puttung needle on 3rd clip might have to drop to a 110 main

[stroberts22]

How many turns out is your fuel screw?

[DohcBikes]

If it is running "flawlessly at wide open high rpm" and makes the plug a "nice dark tan" color, then a smaller main is not the place to look.

Bogging like you "hit the kill switch" is indicitave of a lean condition at any given throttle position, when talking about fuel delivery that is.

Don't rule out electrical issues.

[Hedberg_Racing]

Air screw 2 turns. If the bike runs amazing up top with a 118 why do you suggest I go down on the main? If I choke it,and it runs better, what do you suggest I go down on the main?

I originally had a 35 pilot, 110 main and needle on middle clip and it ran worse than it does now. The larger on the main I go, the less it likes to rev out, doesn't seem to make good power up top. The needle doesn't change anything that I can tell no matter where you put it?
I just don't understand it. I highly doubt its electrical, the spark advance system is clean and properly lubricated, it has had several different plugs in it and no change. If it was electrical, I would think it would not make a difference where the choke is. Its got to be something carb related

[stroberts22]

Air screw? your carb is a 2 stroke carb? I think it's something in the pilot circuit the way you said you can choke it and it revs off of idle good.

[yaegerb]

have you tried the 35 pilot keeping everything else the same?

[DohcBikes]

Air screw 2 turns. If the bike runs amazing up top with a 118 why do you suggest I go down on the main? If I choke it,and it runs better, what do you suggest I go down on the main? I highly doubt its electrical

You wouldnt.

I also highly doubt it is electrical. Still don't rule it out.

Sounds lean on the pilot to me, but its getting a little too abrasive around here these days to just make a suggestion off the bat.

Your engine is modified, and it wasn't us that did it so its hard to diagnose something through a computer.

If it IS carb jetting, follow the simple rule, if it works, do it more. If it doesn't, do it less. There are countless jetting threads on this site.

Change one thing at a time and record the results.

Do you have a stock size carb to try?

[oscarmayer]

is the carb rebuild with new parts? if not that would be the first thing I do.

once there, a 200x moded mine runs 122.5 main but mine is more moded. I would say you need to go to 120main. put the needle at 2nd from bottom and use a 1 sized bigger pilot jet. this should help. then set the air screw to 1+1/2 to 1+3/4 turns out. 2 turns can usually start to cause issues as the system is not sure what to do with the extra fuel. Also use a new plug and gap it to 26 thousandths. this helps with sparking under higher RPM so higher comp does not blow spark out.

hope this helps.

[oldskool83]

I used a moose rebuild kit which is working fine, I did buy a factory one for the preformed carb bowl seal.

I have a 40 slow and a 120 main in my motor, ported head and intake, 10.25:1 piston at 66mm bore. seems to run good.

[rg97]

Try bringing your supertrapp discs down to 6 (more back pressure helping low end), and go up a size on both jets, one at at time and try.
With those mods your carb is just the right size, not too big.

[barnett468]

…its getting a little too abrasive around here these days to just make a suggestion off the bat.

Barnett 23:4

“Yea, though ye post on the pages of thine pages of the 3ww forums, thoust should fear no evil trolls for "Art" is with thee and thy “ignore” feature shall comfort thee…”



“Howdy” Hedberg_Racing;


Dark tan plug is slightly rich but unless plug is new its hard to say for sure.

Starting easy and idling well means the pilot is very close to ideal imo and that it likely has no air leaks.

Improved performance with choke on means lean.

Does your carb have a choke butterfly in the venturi [bore] that opens and closes with the choke lever?

If so, it will never run well if at all above 1/2 throttle with the choke on because it is not getting enough air.

If it does not have a butterfly and runs good up to 1/2 throttle then burbles afterwards, it suggests to me that it is extremely lean on the bottom but jetted fairly closely on top.

A big cam can contribute to what you are experiencing but can’t do anything with that at the moment.

An incorrect float level can also contribute to this type of problem.

Based on your info and without any more, it sounds to me like the pilot jet size is ok and the main jet is slightly rich. This leaves the bulk of the problem at just above idle.

Changing the needle from the top clip to bottom clip position must have some effect although it might be small.

First thing I would do is check the actual gas level in the float bowl. An incorrect gas level can contribute to this type of prob.

1. Get a 10” long piece of clear plastic tubing.

2. Attach it to the float bowl drain.

3. Hold it close to the carb with the open end even with the top of the carb.

4. Open the gas valve on the tank and the screw on the bowl drain.

5. The gas should be from even with the bottom of the main carb body to 3/16” below it. The higher spec might be better than the lower one in your case. If is lower than this spec I would correct it. If it is higher it is not causing your prob.


Install a new plug as suggested.

I would concentrate on throttle performance with needle on the top and on the bottom clip position but not inbetween, and don’t floor the throttle quickly. It might never run doing that it you have a big cam and big carb.

You might need a needle with a different [steeper] taper or a needle jet with a taller choke or a slide with a different smaller cut away.


What happens in neutral if you apply the gas slowly?

At a moderate speed?

quickly?

Does it sputter/burble then increase rpms [rich], or does it simply fail to increase rpms like it is out of gas [lean].

[Dirtcrasher]

Simple test, remove air box lid and if it runs better, you were too rich.

Take it off and it gets worse, you are too lean.

[barnett468]

POST CORRECTION


“Yea, though ye post on the pages of thine pages of the 3ww forums...

Should read;

“Yea, though ye post on the pages of thine 3ww forums...


I have no edit button.

[DohcBikes]

Barnett 23:4

“Yea, though ye post on the pages of the 3ww forums, thoust should fear no evil trolls for "Smart" is with thee and thy “edit” feature shall comfort thee…”.

Above quote edited by myself for my own comedic relief.....

I second the air box test, it will add to the information we have here and its easy to do!