Has this ever happened to other 300ex owners?

[ExDevil250]

Okay, here's my situation. My father and I recently bought a beatup 1994 Honda 300ex. We've replaced most all the old parts. However, when I recently took it out for a test ride, I noticed that in third gear and up the engine starts to stumble when I give it the throttle. So I figured the previous owner must have fooled around inside the carb and changed the jetting. Therefore I took off the carb and opened it up. Aside from the small amount of dirt and grime, I found that it had a stock main jet (122) and nothing had been messed with. Next I did some research in the forums and thought maybe the fuel mixture screw had been turned out or in, so I looked up how many turns the fuel screw is turned out on a stock machine. I found that it was 2 and half turns on a stock machine. After testing the machine with 2, 2 and half, and 3 turns out, I found there was no change. So what could be the problem? Is it the carb or something else? Has anyone else with an older 300ex had this problem? Please help... I trust one of the many 300ex owners on this site to help me find an answer...

[redrider69]

is tha choke on u would never think thats it but ive done it several times

[ExDevil250]

Thanks for the reply, but I've made sure the choke wasn't on... Any other ideas?

[Aceman]

Have you cleaned the tank out and made sure your getting full fuel flow through the hose on the bottom of the tank? Make sure your float height is set correctly in the carb. Did you blow all the passageways out with air and carb cleaner when you tore the carb apart? It sounds like a either one of the fuel circuits is plugged that you only notice when the quad is under a load or the c.d.i/coil is cutting out after they get warmed up. Make sure you have a clean airfilter also. When it starts to stumble in third gear can you downshift into second and make the stumbling go away?

[toby400ex]

Check all the plugs on the coil, sometimes mine would come loose do the same thing ur talking about.

[ExDevil250]

Thanx for all the ideas everyone... in response to Aceman's question, I can shift down into second and the stumbling stops, but as soon as I shift back into third and give it some throttle, the stumbling comes back. I'll check into everyone's suggestions, but please keep the ideas coming.

[ExDevil250]

Come on someone has to have more suggestions! Please help...

[dirtmomma]

WEll it could be your wiring/electrical. Mine sometimes 'FREAKS" out on me, it'll just go completley dead like there is no battery or anything, so we got a new wiring harness thinking that was it, & sometimes it still does it, the last time it did it I did bump start it then when I would rev it high it was cutting out BADD!!! But we jiggles wires some more & it stopped, I think if I was you I may take the harness apart(unplug) up under the front & maybe see if there is crud in the plug then spray some WD-40 or dielectric(sp) grease & spray in there to displace the water. We have my nephew who has an older 250x that is having the same problems & we think it's electrical also. WEll I hope this makes SOME sense LOL & Good luck!!;)

[EXerHonda400]

i don't have a 300ex, but on my 400ex it was kind of doing the same thing, and it was the electrical, i took an ohm meter to a whole bunch of things and found out that my kill switch was faulty, it kept grounding out periodically, but not enough to completely kill the engine. also you could check into your CDI some times it doesn't take much to screw them up, esspecially if it has ever been flipped or crashed.

[ExDevil250]

Thanx everyone! I'm going to try out all of your suggestions today and see what happens.

[mustang93]

Originally posted by Aceman
Have you cleaned the tank out and made sure your getting full fuel flow through the hose on the bottom of the tank? Make sure your float height is set correctly in the carb. Did you blow all the passageways out with air and carb cleaner when you tore the carb apart? It sounds like a either one of the fuel circuits is plugged that you only notice when the quad is under a load or the c.d.i/coil is cutting out after they get warmed up. Make sure you have a clean airfilter also. When it starts to stumble in third gear can you downshift into second and make the stumbling go away?

This is most likely the cause especialy since you said there was dirt in the carb, I would do a fullblown carb rebuild like aceman sugjested

[RideRedEX]

first take apart your carb and clean it real well. if that don't work check your CDI box. I took my 300 to honda for the same thing and i had to replace the CDI.

[ExDevil250]

Okay thanx for the new suggestions, but I'm only 14, so what do you mean by a carb rebuild? What do I have to do?

[Extremerider]

tHIS HAS NOTHING TO DO WITH UR QUESTION BUT WHAT MODS ARE ON UR 250ex?

[ExDevil250]

Ummm... let's see:

K&N Jet Kit and Air Filter
Holeshot Tires
Acerbis Handgaurds
AC Racing Front Bumper
DG Skid Plates
DG Nerf Bars

and I used to have a Pro Circuit T-4 exhaust, but I took it off because it was extremely loud.

If I remember anything else I'll post it. It's definately a tough machine for its size. I love it.

In regards to my post, my father and I recently took of the spark plug and found that it was completely black. We looked this up in the 300ex Clymer manual and found that it was carbon fouled. It says that the spark plug is either too cool or the fuel is too rich. So I looked up needle adjustments in the carb section. It said that moving the clip up will make the fuel mixture more lean. Right now the clip is stock on the third groove from the bottom. Does anyone know if moving the clip up to make the fuel mixture more lean will fix the engine stumbling?

[RideRedEX]

moving your clip up a notch will help but it is easier to just change the main jet. find out what size your main jet is and go down a size or two

[ExDevil250]

But my main jet is stock. Why should I have to go down to a 120?

[Aceman]

You don't need to go down on your mainjet. Do the carb rebuild like I said before and blow all the passageways out with air and carb cleaner. Also, you might have a bad ground. I would clean your battery terminals at the battery posts. Then I would remove the negative cable from the frame, clean the end of the cable up and scrape the frame off with wirebrush, etc. and reattach the cable. Next, remove your engine mount bolts (there a 4 of them) one at a time and wirebrush them clean, spray with WD-40 and reinsert. Clean the engine mounts off also where the engine mount bolts contact the engine mounts. As soon as you can get this engine running halfway decent, then start fiddling with the jetting. Where your jetted at right now should be close enough to get it running.