Jetting issue again.....

[stevengates45]

Guys, once again I need your help. My bike still doesnt seem to be jetted right. Ever since I put a Wiseco 11:1 piston in I cant get it jetted right. My mods are a smoothbored carb thats been bored to about a 34mm carb, supertrapp header & silencer, K&N filter without a lid & a 135 main jet. I know my main jet size is right because after riding a long time its the sortof light brown choclate color. But my main problem is cranking it up. It is a big pain. I punch the throttle once before I do anything, then I hit the start button. It cranks for about 1/2 a second & dies so I repeat this step about 3 or 4 more times to get it to crank, then when it finally does crank & i give it gas to really hear it roar, blue smoke comes out & it backfires & bogs. uhhh this is really getting on my nerves. I tried playing with my air/fuel screw & that didnt work so i put it back where it was. ALL SUGGESTIONS ARE APPRECIATED

[400exredrider]

i dont know if this is right but i think 135 main jet is Way to low......i guess it depends but also things are always gonna start harder and smoke after you have all the pipe **** and especially the 11:1 piston.........i dont know if im right

I am assuming that this is a 400ex?????? If it isnt a 400ex then all the same principles apply just not the actual numbers.

I know that the stock main jet is a 148 so 138 is DEFFINATELY WAY TO LOW! When ever you do any kind of modification to the motor it makes the mixture leaner( less gas, more air) because you are letting the motor breathe a little more with each modification. Ok lets straighten this out. Are you talking about a keihin jet here(the 135)??. Your info sounds a little weird because you say that it is really hard to start(usually too lean on the pilot) but when you start it that it emits blue smoke from the exhaust which is always oil and unburned gas. The reason it emits blue smoke is because you are flooding it when you give it gas before you try to start it so that when it finally fires, all of that fuel that you put into your motor gets blown out of the exhaust. You also say that it backfires and bogs when you start it (also means that the mixture is too lean). But then you also say that the spark plug is a perfect brown color after you ride it which would mean that everything is fine which it obviously isn't!!!!! So maybe if you could clarify the info a little more because quite frankly i don't see how it could do all those things at once. Also what is you altitude above sea level? I only have an fmf pipe, k&n filter and i run a 155 main jet 40 pilot jet and one notch down on the needle clip position. You're motor deffinately needs some more fuel man!!! Depending on your altitude you should deffinately be running a 158,160 or 156 main jet with a 40 or 42 pilot!!!!! Anyone have any comments or corrections? Hope this helps.

P.S. If all else fails, take it to your local honda dealer and just say my motor runs like crap can you fix it? and more often then not they will get it all straightened out for you.

[stevengates45]

300EX, theres no way I would take my bike to our Honda shop. I like to do the work myself, but if it did come to that, I would take it to our Yamaha shop. By the way, if you dont give mine gas before you hit the start it wont start. Not trying to prove you wrong or anything, but you can site there & push the start button till the battery goes dead & if you dont give it a little gas it wont start up. Im sick of all this jetting.

[Winged Warrior]

Before you hit the starter button ,just crack the throttle and hold it there.then hit the button. RRRRRRRUUUMMM RRRRRRRUUUUMMMMM If i thought my jetting was off i would get a set of jets 5 sizes bigger put in the biggest ,then back off till it quits falling on its face at 3/4 throttle.There it a good/simple article on jetting in the last DW issue. also #40 slow jet is a+

[stevengates45]

Yea, but like i said, whenever i ride it for a long time & check the plug, its the brown color its supposed to be. Think i need to lower my needle maybe?

[SGA]

I'm assuming you have a 400EX. When I start my 400 (cold) I pump the gas 2-3 times, full choke on and hit the starter. Slow revs. Then I drop the choke to 2nd notch after 10-15 seconds. Slow revs about 40-60 seconds, choke off and ready to go. If I try to rev it to fast, it balks, plus its BAD to high-rev a cold engine. the oil needs time to circulate. Then I ride easy for 4-5 minutes to let the engine and me warm up. I've never seen a 400 that could take alot of gas when cold, they will stumble and backfire. The 40 pilot was a big help with starting also on mine. I doubt you have a 135 main or you would have burnt something up by now. With the K&N and open air box and pipe you probably need to move the needle clip down 1 notch from stock position, 160-ish(KEIHIN) main, and a 40 pilot. Idle mixture screw should be close to stock position or a 1/2 turn more out. Hope this helps.

[stevengates45]

nope, have a 300ex. My carb I have on it has been smoothebored & the choke was takin off for better air flow.

[Leo]

if you don't have a choke on your machine you really need to have the pilot circuit dialed right in for it to start w/ out the choke..

if you've tried maxing out the pilot screw and it didn't help, try the next size larger pilot jet...

Leo

[Scott]

I also have a 300. Every 300 I've even seen has been cold natured, mine included.

Did you bore it when you put the 11:1 piston in it?

Without chainging the bore or compression ratio, the stock bore 300s I've been around ran a 125 or 128 main with a pipe and filter and modded airbox. But none of us had the modded carb like you. If you increased the bore and the C.R., as well as the carb dia., then you may be able to handle the fuel from a 134 main. Since you didn't mention the bore, I'm assuming it's stock, just higher compression.

If you haven't increased the pilot, that would be the first thing I'd do, especially since you removed the choke. That's a must.

Next, check the plug to see if the main is properly sized.

The way to check the main is to get it up on the top end of the rpm range and kill the engine, then check the plug. That will show you what the mixture is from the main jet.

I run a stock engine and airbox, K&N filter, and a 4" supertrapp on a DG head pipe, with a 125 main, stock needle setting and stock pilot.

Hope something in here helps.

[SGA]

Without the choke its going to take longer to warm up. Just keep feathering the gas lightly till it warms up. If you try to give it to much to soon, its going to bog and backfire. Sounds like the main is fine per the plug color.

[stevengates45]

alright, thanks

[MichaelS693]

should we put this in the FAQ????

[400exJOE]

just a rndom question for stevengates, I was thinking about putting on my lectron carb but i dont know how to adjust the jetting mixture. I know that you have some experience with the carbs. Thanks

[MichaelS693]

he aint on me and him just got back from town i went and got another low glow light and some odd and end screws and nuts and stuff

[stevengates45]

well i havent been around a lectron carb being adjusted in a while because the seasons ended so I really wouldnt know what to tell you. I'll see a friend tonight that use to have one on a Warrior & ill ask him about it.