At my wits end with a 300ex

[RIDE-RED 250r]

Wonder if you guys can help me spitball this thing. I'm helping my brother in law get a 300ex to run right.

Mods are as follows:
-White Bros full exhaust
-K&N filter with airbox lid removed

Problem is, it seems to run fine unless you stab the throttle too quickly. If you roll into it more slowly it will build RPM's.

What I have done:
-Carb is clean clean clean.
-Slide and butterfly are synched spot on
-Accelerator pump adjustment is spot on and have visually verified it works while engine running
-Jetting stepped up 2 sizes richer than stock on both main and pilot jet circuits
-Tried different positions with slide needle from stock to raised 2 notches
-Sparkplug gap tried between 0.020 and 0.030

This thing has not responded positively to any efforts to do with fuel delivery.

We are starting to wonder if it is time to toss the CDI into the trash can... Possibly not advancing being the cause of the bad stumble that can lead to stalling.

Any other input??

Thanks,
Joe

[yaegerb]

If its bogging when you stab and you have to slowly roll to get it to go its either electrical or carb. A quick test is to drop the main down one size and see if that helps. How does it idle? If it idles fine, leave the pilot alone. If it still bogs when you step down the main step it down again. If stepping down the main helps and it runs right then start adjusting the clip for rich. If none of that works I would rule out the carb and focus my efforts on electrical issues.

[RIDE-RED 250r]

Thanks Yaegerb.

It ran like this with stock jetting as well. I never gave it a thought to go leaner with the main with the intake and exhaust mods. The changes we have made had no effect. And when we did the jetting changes, we went up 1 size at a time on each and here we are 2 sizes richer on both and still no change.

A cannot think of any other thing to check or change that is fuel related.

I think he is going to get a know working CDI and give it a try....

Thanks for the input.

[yaegerb]

No problem. If it is electrical, I would go snoop on a 300ex forum to see if you can find the same type of problem with an answer. I will also snoop to see if I can find anything.

[bkm]

Put the airbox lid back on and see if that changes anything.

[Furno]

If you have a CV carb, you may want to pop the lid off and be sure the diaphragm is not cracked and that it has a perfect, air tight seal with the housing, if it leaks air itll cause issues.

[RIDE-RED 250r]

Quad was missing the airbox lid when he bought it.

Furno: are you referring to a vacuum actuated slide like alot of streetbikes have? If so, this one is mechanical.

[MTS]

You should be able to stick a timing light on your marks and rev it up see if its advancing, if it stays stationary throughtout the rpm range cdi or pickup is fubar.

[yaegerb]

Hey joe,
Are you able to run it around and check to color of the spark plug or is it so bad its unridable? I have searched all over quad forums and they all come up with carb troubles and changing jets. Maybe if you could do a plug read you could at least know if your carb is to lean/rich. I will continue my searching.

[RIDE-RED 250r]

Yaeger, don't feel like you have to search around on my behalf. Yes, we can ride it around and as long as we don't stab the throttle too quickly it will pick up speed OK. But now I am home and the quad is 90 miles away at my in-laws. My brother in law is going to be buying a CDI for it.

MTS: thanks for the suggestion of the timing light. There was one in the garage there and I never even thought to try that!! (forehead slap) But I will relay that to my brother in law to try. AT this point I would be willing to bet that it isn't advancing.

See, we started out thinking it was jetting because the previous owner removed the airbox lid, installed a K&N and a full White Bros exhaust and didn't jet it up. So he finally got arounf to picking up the next 2 sizes richer than stock for main and pilot jets at my recommendation thinking that would surely straighten this thing out.

Just from running it in the garage, the plug has gotten more black since jetting it up. Funny thing is, having the choke half on seems to help it. I can say with 100% certainty the carb is clean and fully operational, so thats why I was thinking jetting.....

I'll have Eric try a timing light on it. Probably going to be a couple weeks since we both drive truck for a living and he won't be back home for 2 weeks this go round due to a mandatory drivers meeting he has to go to in Boston....

Will let you guys know how it pans out though. And thanks again for the input and ideas!

[rttuck21]

Have you checked the valve adjustment? Not sure if you have it fixed yet since its now november

[LT80]

Valves eh....we may have a winner!! LOL
Might as well do a compression test too.

[RIDE-RED 250r]

Thanks for the additional replies fellas...

He ended up trading the quad for a Tri-Z

[Jeepermc]

Reading this I was going to suggest checking the valve adjustment too.....or even checking for a burnt valve if it was run hard and lean for awhile with stock jetting and more air.