Do you guys think this is too lean or what?

I pulled apart my carb to find that the guy I bought it from put a 145 main and a 38 piolet jet in it after he put on a full WB R4 silencer and S-bend race pipe also a K&N. I have had it for about 7 months and never thought about the jetting, now that the weather is warming up it started to cut out in 5th gear. I still have my air box lid on, I am sure it is lean so their is no point in taking it off to see. What is stock jetting? I think I might try a 165 main and a 42 piolet. Where do you guys think I should start? Do you think this is lean? The plug looks ok not too black but some white tint. What do other guys with R4 have for jetting thanks in advance.

[VegasEx'r]

What do you mean by cut out in 5th gear. Does it bog? Does it backfire when you let off the throttle? You might be a little lean, but only a little. The 38 pilot is probably okay, I would start by just going up on the main, but a 165 might be too big. BTW, what is your needle set at?

[optikid123]

u sure that ur not hitting the rev limiter cause you have had the bike for a while and ride it faster now

Based on what I have read on this site. 145 main jet seems to lean for a full race exhaust. The neddle is on the stock setting. Do you guys think I should try and adjust the fuel\air mixture screw before I put in a bigger jet. It wouldn't bog down it would just cut out. I wasn't hitting the rev limiter I know what that feels like. I think it might be the weather.

[MichaelS693]

i just put a curtis spraks complete on mine and a k&n and i think its a lil to rich with a 128 i got in there im gonna go for a 125 tomorrow and stock hjettin is only 122 my friend blew hiws bike up and he just got it outta the shop:eek: i took oput his jet and guess what it was a 110 talk about lean....i should of pulled the plug....... anyway i am gettin parts off his bike.... hes got blck maier plastic with green flames painted and i am gonna get that sooner or later and he also has green tire hubs i will have pics up soon haha sory for goin off topic

[crashinmatt]

i am guessin that u r runnin a 400, am i correct? if so i have a r-4 exhaust, but it is only a slip-on. i also have a k&n filter. i am currently running a 165 main and a 42 pilot. but i am also running it without the airbox lid. if u still want to run your lid and not modify it in any way i would say maybe a 150 to 160 main. but it sounds like your right on by the way u say ur plug looks, maybe a tad lean

[Wheelie]

FYI--Warmer weather will cause an engine to run richer, cooler weather will cause an engine to run leaner.

Leave the pilot at a 38. Try a 148 or a 150 main jet.

Good Luck!!

[stevengates45]

Yea, michael is right. That bike had biggest curtis sparks cam, 350x valves, ported & polished, bored .80 over, rocker arms, & valve springs, curtis sparks exhaust, high comp piston, timing key, k&n with the lid off & the jet size he was using was a 110. Stock is 122. Think somebody here was a little coo-coo when they put the jet in!

I went and got a 155 main jet and put it in. I started it and everything was fine. I then took it where I could open it up all the way and it ran ok seemed like it wasn't getting enough air so I took the whole lid off and just ran a K&N with a pre-filter. IT ran better it seems to like the lid off but I am worried about water what do you guys think? Should I mess with the fuel screw or should I try a 160-165 main jet? Or should I put in the 42 piolt? I am going to put a fresh plug in and run it then look at my plug. I am just worried about over heating now that the weather is warmer. What do you guys think? Thanks for all your help

[Wheelie]

Unless you constantly ride in mud and water, leave the lid off.

A #40 or #42 pilot with a #158 main will work well with your setup. Also, lowering the clip on the needle one notch helps overall performance.

Good Luck!!

When I had the carb out, changing the jets was easy no problem there. I couldn't figure out how to disconnect the throttle cable from the carb so I unhooked it from the handle bars. I also couldn't figure out how to change the needle clip, I had no clue on how to get that out. If I go to a 158 main an a 40 or 42 poilt do I have to change the needle clip? Also one more question about the main jet. How does that lock nut on the main jet come into play? When I took out the 145 main their was only 2 visable threads on the jet boby the lock nut was screwed all they way down except for 2 threads so I put it back like it was when I put the 155 main in. Any help here? Thanks

[Stunz]

Do yourself a favor and leave the needle alone. You have no reason to change it.


I run my 400 with a big square hole cut out of the lid. I have no problems with water crossings. I rode thru a steam that was 2-1/2 feet deep last weekend and was very surprised to see that only a little water got into the box. It wasn't the smartest thing I ever did, but a Banshee with no air box cover went thru before me. So if he could make it.....

[generalg]

Here is what worked for me. When I bought my 400 it had a 170 MJ with stock pilot, stock needle but with the dyno jet mj. First time I took it to Little Sahara it ran like crap. It would cut out on 3/4 to full throttle, ran a bit hotter than I thought it should as well. Back at home I got DynoJet on the phone, this is what they told me to do. First put the correct needle that came with the dynojet kit, it has a couple more notches where as the stock does not. Put the clip on the needle in the middle position. Warmed the bike up by riding it for 10 minutes or so. Take off the air cleaner and run it a bit. MMMM it now ran much better meaning the 170 was letting to much gas by. Put a 165 and repeated the above process, still craps out at 3/4-full throttle, finally came down to a 155, needle clip in 3rd position, stock pilot with air screw turned out 3/4 turn. My 400 was a total different bike now.

[330EXman]

OK THAT IS WAY TO LEAN JETTING. DID THE GUY YOU BOGHT IT FROM RUN IT IN REAL COLD WEATHER. THAT WOULD SOUND BETTER


UM IF YOU ARE UNLOADING IN 5TH THEN MOVE YOU NEEDLE WASHER DOWN ONE OR TWO SLOTS. THIS SHOULD FIX THE PROBLEM.

ALSO GO UP ON YOUR MAIN JET AND PILOT A COUPLE OF SIZES SAY MAIN=165
PILOT= 42

THAT MIGHT WORK BUT JUST GO FROM THERE

[twisted threads]

Originally posted by Wheelie
FYI--Warmer weather will cause an engine to run richer, cooler weather will cause an engine to run leaner.

Leave the pilot at a 38. Try a 148 or a 150 main jet.

Good Luck!!


I Agree!! I would try this set up. Just my $.02 :)

what about the fuel screw on the underside of the carb? What do you recommend I do with this? Thanks for all your help it is greatly appreciated

[Wheelie]

Set the screw out 2- 2 1/2 turns.