to jet or not rejet lets hear your opinions

[bdtoady22]

this is the question for the day what are your opinons on this subject me 78ta were disscuccing this and deciced to post this to get your opinions any way we have 2 400 exs and both are stock jeted with slip ons only mine is 99 with hmf his is 03 with cobra slip on mine started out this spring with 152 main as of yesterday it went to 148 main and ran way beter thanit had for a while any how lets here your opinions is it really nessacary to re jet with a slip on only?

[MtnEX]

Well, considering my own experience here, and reading several other similar ones... here is the armchair opinion I have gathered...

I think when making changes, the tendancy I'm seeing is to just set it richer... which is resulting in overly rich conditions.

Of course you don't want to run lean and overheat, etc. But there's plenty to be said for and had by a proper air/fuel ratio.

I think the pilot circuit should be jetted for good starts and good idle without loading up. I think the needle setting is very important and should be set by plug reading or better... and I think the main jet needs to be selected based on plug reading also to be safe for those times you're actually in the main.

I'd say that your needle adjustments and so forth did more for improvement than changing your main did... unless you spend a whole lot of time with the thing just pinned WFO.


Now, in exchange for my armchair opinion, would you mind giving me a little guidance on adjusting my own needle and so forth?

Do I go in the top of the carb for that?... Take out the throttle valve?... Get the needle out and just move a clip into another slot?

[drew416ex]

Originally posted by MtnEX
Well, considering my own experience here, and reading several other similar ones... here is the armchair opinion I have gathered...

I think when making changes, the tendancy I'm seeing is to just set it richer... which is resulting in overly rich conditions.

Of course you don't want to run lean and overheat, etc. But there's plenty to be said for and had by a proper air/fuel ratio.

I think the pilot circuit should be jetted for good starts and good idle without loading up. I think the needle setting is very important and should be set by plug reading or better... and I think the main jet needs to be selected based on plug reading also to be safe for those times you're actually in the main.

I'd say that your needle adjustments and so forth did more for improvement than changing your main did... unless you spend a whole lot of time with the thing just pinned WFO.


Now, in exchange for my armchair opinion, would you mind giving me a little guidance on adjusting my own needle and so forth?

Do I go in the top of the carb for that?... Take out the throttle valve?... Get the needle out and just move a clip into another slot?

Yeah, the 148 is there from the factory. In some parts of the country that may be lean, but in others it may be rich. Without knowing the A/F ratio you dont know exactly where you stand. Your ratio should be close to 13:1. If you are say 14 - 15:1, It its a little lean, but it will run better and shouldnt hurt anything. Also remember, when you change your main, it affects the needle since that runs through the main.

You pop the plate off the top of the carb and you should beable to get the needle out with some needle nose pliars. Then just move the clip to the spot you need it.

[bdtoady22]

to adjust the needle it is kind of a pain in the arse there may be a better way to do it but this is how i do first you have to remove the gas tank take the top of the carb off should be 3 screws then remove the throttle linkage cover back to the top remove the screw in the arm that goes to the throttle valve, slide the shaft out and then you can remove the slide. with the slide in your hand there is 2 phillips screws in the bottom of the slide remove them and then you can pull out the needle and move to what position u want

[leasureryan]

I want to know why everyone trys to make jetting so hard on themselves....it's really not hard at all, once you understand the basic functions of your carburator

[MtnEX]

Thanks, I just wanted to be sure I was making the right assumptions before I started taking things apart.

[bdtoady22]

leasureryan you are correct to say that people make it harder than it is i am one to cry about it because it is a bit-h on a ex to get to the carb the results are well worth the effort i have found that it is trial and error more than any exact formula and i beleive that most people want to be told you need a 155 or 170 etc but there really isnt a formula for exact you look more for a starting point and go on am i wrong in saying this ive rode 4 ex s all diferent years different configs and they are all unique in sounds, throttle response, style of ride and to say that 2 are alike i beleive is a lie so just cause your buddy is runnin this doesnt mean that yours will be exactly the same

[78ta]

Toady, I was just pondering if the "mixture ring" on the plug we tune 2-strokes main jets with applys to four strokes?

I have read bits and pieces on drag car forums about it. But have found no hard core proof yet.

We should try it on one of these 400's, I think it seems like it should work the same. It was a good easy way to tune with the two strokes mains, then just dial in the needle to seat of the pants and adjust pilot according to air/fuel screw and starting quality.

Got me thinking about chopping up plugs from the Red Dragon and messing with it too


On a side note, did you have time to blast and powdercoat my spindles/hubs yet? I cain't wait to get them 450r front brakes on!

[78ta]

I still think that people with the same bike, same mods and different jetting has a lot to do with engine condition. -ie- worn rings and or a little different compression ect. from bike to bike.

And to add to the confusion I don't think half of the people that "jet" their bikes know what they heck they are doing, or are just putting in what some one else told them to do with out any testing at all, and are just proud to tell you that a xxx main jet is perfect on his bike.


my 2 cents

[leasureryan]

Exactly!!!.....you can't just tell someone "oh...you got those mods....use these jets".....it doesn't work like that....at all!

plug checks now days arent the same. Their are additives in the gas to reduce carbo buildup and make the engine run much cleaner especially Shell. I have used Shell because its so cheap and it does some good. I'm in a bit oh a dilema i guess you could say. I had my quad running 155 main, 42 pilot, needle on the 4th positon and the slide would just go past 3/4 and stop. So obviously the main isnt working 100% but it ran as smooth as can be. People would tell me wow that thing runs absolutly perfect awesome job on it. Yeah well then I opened it up and adjusted the quad so it was 100% throttle it was running lean on top and stuff. I threw in a 158 main. It ran great just a slight studder if you revved it quick but it was minimal, I figured I was done jetting and I wouldnt be into my carb for awhile. Wrong I go on vacation and the quad was sitting for maybe 3 weeks without starting it. When I came back from vacation i wanted to hear it rumble again and just to keep it running every so often when i know i'm not going to be riding it start it up for a few minutes. I start it let it warm up idling for 3 minutes or so and shut it off to check the oil before i do some revving and stuff. Oil level is good ready to make some noise. I hit the gas quickly and it just shuts off. I start it up hit i again quickly but let off sooner and it wanted to cut out when I revved it quick. So now something isnt right. I cant imagine it being my main because when I did a top speed run with the 158 the plug looked perfect I dont think it could have been better. So I think maybe its lean I put the needle on the 5th and do the same and it got worse. I put it to the 3rd and it seemed better but still not right. Then to the 2nd slot and it ran without a studder but it didnt feel like it had the same power. I took it for a spin and it wouldnt wheelie in 2nd with me just hitting the gas. Now I dont know what to do. I'm about ready to take it and have it dynoed A/F tested for $35 or so. See how it is and adjust it and have another run. I rather not spend $80 in a day. Anyone have suggestions? I doubt my flywheel slipped so its not 6 degrees advanced and its like 4. It was on there tight ad torqued down

[bdtoady22]

mine run good with the bigger jet but ran awesome with the leaner one maybe try to go back to 155. ive never done anything with timing so i cant give you any advice there when you say past 3/4 what do you mean, like looking in the carb or did u take the throttle linkage cover off and watch the accelerator pump cam?

[bdtoady22]

78ta you wanted the hubs fire engine red and the spindles mirrior black right?

Originally posted by bdtoady22
mine run good with the bigger jet but ran awesome with the leaner one maybe try to go back to 155. ive never done anything with timing so i cant give you any advice there when you say past 3/4 what do you mean, like looking in the carb or did u take the throttle linkage cover off and watch the accelerator pump cam?

looking into the carb the slide was just going up past a 3/4 mark. therefore it wasnt 100% throttle even when you had the thumb throttle pushed all the way. I adjusted my throttle cable so it would be at 100% and it ran like crap it was running lean so i threw in the 158 main and it seemed fine. now something is up where it doesnt have the power it did before. i seems to run good but it wont pick the wheels up like it used to

[5084Jr]

I'm by far no expert, but we run a 42 mm mikuni carb on my racecar. We ran the car out of fuel and even WITH a filter, some bits of dirt got into the carb and clogged 'er up. I'd say check to make sure you don't have dirt in there somewhere. Maybe it would be wise to take out a few jets and clean them?
.. Brake cleaner works wonders to clean 'em.

[78ta]

78ta you wanted the hubs fire engine red and the spindles mirrior black right?

That is correct

[bdtoady22]

i wouldnt use brake cleaner not so good on rubber carb parts imo

[5084Jr]

Don't squirt the whole carb with brake cleaner. It works good to clean out the insides where you might have a piece of dirt.