300ex starting Q

[leasureryan]

Just traded an 88' trx250x for a 98' 300ex big bore. Runs great....kinda won't start when cold without being hooked to a car with jumper cables. Then it fires right up. Brand new battery, just seems not to have enough cranking amps. Called local honda store, said they don't make batteries with higher cold cranking amps??? The first thing he asked me was if it had a big bore kit. He said it was common for those atv's bored 30 over to have trouble. Is this true? Any way to fix it? My buddy said it is probibly jetted wrong, or valves are sticking. Any of this sound right?

[bwamos]

The starters are a bit wimpy. My 330 has always been a slow turnover when it's cold.

The most important thing is to keep the battery on a Battery Tender to keep it at max charge. If it's at 85% charge it has a hard time starting up. The tenders are fairly cheap and well worth it. I always have mine hooked up when it's being stored.

On the dealer comments.. classic dealer knowledge there. 30 over does not equal a 330. ;) 30 over would equal 0.030" overbore = ~0.75mm Generally pistons come in 20, 40, 60, 80 overbores etc.. 0.5mm increments. Besides a 300ex is 282cc to start with.

A 330 would be a 240 overbore.. 0.240" or +6mm. 80mm bore x 65.5 mm stroke.

Just an FYI. ;)

I don't trust our local dealership mechanics as far as I can throw them. :P Some are great but most shouldn't be allowed to own a wrench, lol.

Also if it is a big bore w/ pipe and filter you may check the pilot jet. You'll probably want a #42 in there. Stock is a #38.

[MY FYN 79]

Originally posted by bwamos


A 330 would be a 120 overbore.. 0.120" or +6mm. 80mm bore x 65.5 mm stroke.

Brandon, I'm not nitpicking here by any means, rather trying to confirm my own sanity with all this big bore stuff.

Wouldnt a 330 be a .240 overbore with a stock 65.5 stroke?

[leasureryan]

like I said, I'm new to all this big bore crap...lol. Guy said it was a 330 big bore. I am the one who assumed it was bored 30 over, thought that is what it meant, only to have just recently found the threads that told me otherwise, and you ofcourse. Thanks.

So battery not it, has brand new carb on it replaced 2 days before he traded it to me. I am assuming it has stock jets??? Hope it's not to far off. I will try the bigger pilot, but will have to see what is in it first.

any other reasons it has trouble starting possibly besides the battery not being powerful enough?

[300exOH]

I would have to 2nd the battery tender. These quads need full battery power or they will not start in this cold ohio weather. I just picked a sears 2amp charger up at kmart for around $30. The 42 pilot will help. I have one in mine and it starts much better but it is still stubborn when it drops below 30 deg. I always set it to full choke and pump the throttle 3-4 times and crank it. If it doesn't start/stay running I repeat until it does. That's the best method I've found when its really cold. I would also go up to at least a 128 or maybe a little higher on the main jet since you have a pipe. Stock main should be 122.

[300exOH]

Forgot to add... if your valves aren't properly adjusted you can have problems starting also.

[bwamos]

Originally posted by MY FYN 79
Brandon, I'm not nitpicking here by any means, rather trying to confirm my own sanity with all this big bore stuff.

Wouldnt a 330 be a .240 overbore with a stock 65.5 stroke?

Yes you are absolutly correct. Brain fart.. lol.

.040" per 1mm. 6mm = .240

Thanks for the correction.

It's a good thing I'm not in engineering... oh wait.... :P

[bwamos]

Hmm.. if your carb has stock jets they are WAAAAAAAAYYYY off. ;)

If you're running a 330 w/ full aftermarket pipe, filter, and vented or removed airbox lid you should be running around 140-145 keihin main jet, 42 pilot jet, and needle raised up 1-2 slots.

Stock is a 118 or 122 depending on what part of the country you are in with 38 pilot jet.