300ex Not Starting.....

[2K1 300EX]

I just put in a 140 main jet and now it won't start up do I need to get a bigger pilot jet or move the clip on the needle? I have a FMF Megamax II full system, Uni filter, modified airbox lid, i removed the choke. I originally went from the stock 122 main jet to the 135 but it was still running too lean, but when I had th 135 jet in it would crank up and now that I have the 140 it won't start.

[2K1 300EX]

I take it none of you know anything.........

[2K1 300EX]

BUMP

[danney f]

Have you tried cleaning the plug or putting a new one in and then pump the throttle a couple times before trying to start it?
With the choke removed the pilot may be way to small. May want to turn the air screw out a little.
Hope this helps.

[UglyMotha™]

your main jet would have nothing to do with it starting unless you were giving it gas and then you would be flooding it out, can you smell gas real bad when you cranking on it the main jet doesn't kick in until like 1/4 throttle or somthing like that and if your not givin it gas the pilot jet does the feeding but if i was you i would check for a kinked gas line did you turn the gas back on maybe the float is up, check for gas in the bowl cause just goin up a jet size shouldn't kill your ex just make it run like crap most cases

[Scott]

OK, you've got things a little out of whack, let's see if I can help you out at all.

First, it looks like your engine is stock with a pipe and filter/airbox mods. Right? You are WAY too big on the main jet. I have a similar setup and I've run a 125 main for almost a year now. Another 300 ran a 128, but he didn't run an airbox lid at all, and he was a little too rich. If the plug didn't look the right color with the 135, odds are it was because of the fuel additives from the Refinery.

Second, 300EXs are cold blooded beasts. If your pilot jet is stock and you removed the choke, it will be a b!tch to start, and just wait until it gets colder this fall! Go up one size from the factory pilot and that should help the cold starting.

Third, like was already said, the main jet size has NOTHING to do with the idle circuit of the carb, so it won't affect the starting unless you're pumping the gas to it when you're trying to start it.

Last, I would spend the $2 on a new plug because you very well may have fouled yours with the 135 main and the continuous flooding with the 140.

Hope you get it straightened out.

[spliffy]

......Well Said Scott

[phatswinn]

exactly what i was gunna say, and one more thing, were u listning to the 400 guys cuz i think thats the size for the 400, go to the dealer and get a 125 and the next size up from that, then try them both for perforance

[2K1 300EX]

I should have said this in my first post....

I also thought it was a big size main jet, but the guy at the cycle shop said he has put even bigger main jets on 300's. I was doing the plug test and it read it was running lean with the 135, I even put tape over the hole in the airbox lid and wrapped tape arounf my filter and it still read it was running lean; so i put the 140 in and it wouldn't crank. I was pretty sur eit was the pilot jet because according to the FMF site it said I needed to go up to a 40. I was going to get it but I had to leave to go out of town the next day and didn't get time. I was just researching some so when I get back home I can get it running the day I come home.

Thanks for all the help guys, if you have anymore thoughts post them.

[Scott]

OK, I broke out the manual for this one. I see that you're at sea level, so I'm at a higher elevation. Honda drops the main jet one size (from a 122 to a 120) for high altitude, which they did NOT due to my bike, so I guess the elevation shouldn't be that big a deal between us.

Did your bike blubber, cut out, or hesitate with the 135 Main in it when you went to WOT? (I don't mean hitting the rev limiter, I mean going from idle or slightly above to WOT (that will also identify a faulty accelerator pump). If so, you were too rich with the 135, the 140 will be worse. You may not be able to read the plug because every gas that I'm aware of on the market has some kind of additives in it, which will cause the plug reading to be off. You may be rich and the plug might be a light color.

Back to the won't start thing, I'd say you're on the right track with your pilot jet. The factory pilot is a 38, so without a choke, the 40 is an excellent move. I'm considering it for mine even with the choke.

My best friend raced hare scrambles on a 300ex, stock engine, pipe, filter, airbox mods. He's the one that ran a 128 main, and he never finished out of the top 6 for 2 seasons, and that was running against 400s. So he was at the rev limiter the entire time, at every race. The engine ran fine, no smoke, no glowing pipes, and still runs fine today, so there's no way it was jetted lean. That's what makes me thing the 140 (and 135) are too big for your stock 300. But hey, I could be wrong!

[2K1 300EX]

It was running like a bat out of ****, but I could tell it was getting too hot(rode about 50 yrds. to go check my mail and seems like I had been riding it for hours). Even though it was running good, it was backfiring real bad. Doesn't this mean it was lean? Thanks.