300 runs like sh*& when cold

[buddy what not]

hey i have a 1999 honda 300ex it has a fmf power core 4 with head pipe and k&n filter and a dyno jet kit it has a 118 main jet in it but when its cold it runs like crap unless i drive around for about 20 minutes or so then its good when its pinned but as soon as the motor reaches the rpm it cutts out and misses like crazy i have tried the jettin but no luck so far what u all think ?

[300exOH]

Definately sounds like it could be jetting. You could also have a crack in an intake boot or even an exhaust leak. First thing you should do is check your plug to see if it is rich or lean. The 300ex comes with a 122 main jet so your are most likely very lean. Also keep in mind that the 300 is cold blooded by nature even when jetted properly so make sure to give it plenty of time to warm up.

[buddy what not]

ya i will check the plug today to see weather its rich or lean i wil definetly check the intake and exhaust to but my original jet from honda was i 110 i live ontario so i guess thated be the difference the sea level . dopes n e one think it could be the needle ? the dyno jet kit came with one and i put it in should i have left the stock needle in and go bigger on the jetting?

[300exOH]

Sorry I didn't notice you are in Ontario. I wondered why the 118 main. haha

I would try the stock needle. I know I didn't have to mess with mine for my Sparks. Also I don't think the dyno jets sizes are the same as the stock keihin jets which could mean your 118 main is way off. Most people will recommend buying the individual keihin jets instead of the dynojet kit.

Also you may want to go up 1 or 2 sizes on the pilot jet to help with cold startup. Hope this helps some.

[dirtmomma]

I have a Dyno jet kit on my stock carb too, can't remember what size I had in there but I know it was WAY different than stock ;) I'll have to check & see BUT I would check your plug for sure, didn't your kit come w/ #'s??

[buddy what not]

hey i just checked my plug after a good run its almost gray but a light tan which i think is good? and ya i think im gonna ditch the dam dyno jet thing it never ran right since i put it in and i did exactly what the book said i will go to my local dealer and get indvidual jets.
i was wondering if honda would sell a jet kit for it or would that be a good idea? any help would be good

Just about any motor is gonna run like crap until it's warmed up.

Also it sounds like your hitting the rev limiter to me and the motor's doing what it should...:confused:

[300exOH]

As far as I know Honda doesn't offer a jet "kit". If your dealer is anything like the ones near me you might have a hard time getting the jets. My local dealers were telling me it would take 2 weeks for a 42 pilot jet for mine.:eek2: I called the Quadshop and had it in 2 or 3 days.:devil: I did have to pay for the shipping though but it was worth the few extra bucks.

[buddy what not]

nope im not hittin the rev limiter if i am its way to early like about half throttle when its warmed up and a hot day it it runs fine it only does it when its cold out

[buddy what not]

i will try my dealer they r usually pretty good and into the whole racing thing for jets thanks for all ur help

[Tread70]

Im located in South Carolina and I have jetkit, K&N and FMF PC4 full and run a 124mj, needle in the 4th position but need to move it down 1 or 2 Still cutting out toward the top of the rev limit.

[buddy what not]

thanks for all of the replies i am going to order the jets.
does any body think it could be the valves it has a little tick so i planned on setting them up i was wonder what the clearance was for them ?

[dirtmomma]

Originally posted by buddy what not
thanks for all of the replies i am going to order the jets.
does any body think it could be the valves it has a little tick so i planned on setting them up i was wonder what the clearance was for them ?

YEP it could be your vlaves out of adjustment too, I THINK the clearance is .004 intake & exhaust but I will double check for ya ;)

[300exOH]

Yep. .004 intake and exhaust :D

[dirtmomma]

Originally posted by 300exOH
Yep. .004 intake and exhaust :D

;) thanks guess the ol' memory isn't as bad as I thought LOL, OH thats probably cuz we've had mine apart so many times hehehe

[buddy what not]

ha ha thanks dirt momma and 300exoh i will pull it apart this weekend and set them i guess there known to have bad intake valves so thats hopefully it.

[buddy what not]

hey i was out ridin today and i noticed that my throttle had a rough spot in it bout 1/4 or so that it would get hard then id push it more id be easy so i pulled the carb apart and on the right hand side of it behind a black cover there is throttlle linkage i donno what to call it and the cabl pulls a half moon shape thing and pulls another rod up and theres a little plastic roller on it and it has a flat spot do u think this could be why my 300 runs crappy ? i think it runs a fuel pump and the fuel pump isnt being pullde as far up cuz of the flat sopt ?