jetting

[blindsey]

I know this is a question everybody has, but I personally called hmf about jets I should run and everything and I still cant get mine to run right, maybe you guys can help. 03 400ex with hmf full exhaust, open air box and an all around cam made by hot cams. Hmf told me I should run a 180 main 42 pilot and three turns out on my air/fuel screw. I did all of that and the damn thing wont idle and it back fires. I have checked the plug and it looks good. I live in alabama. Maybe the main is to big, I have heard of guys just running a 160 main with 42 pilot? Can someone please help me???

[GPracer2500]

Questions:

What brand jets are you using? Keihin (or Keihin copy-cat)? Dynojet?
Stock piston?
What air temps and elevation do you normally ride in?

As far as the idling, what happens when you turn up the throttle stop screw (idle adjustment screw). This is a different screw that the fuel screw (you probably know that, but just incase). Have you tried tuning your fuel screw in to 2 turns out to see what happens? See HERE (http://www.exriders.com/vbb/showthread.php?s=&threadid=229923) for a guide on setting your fuel screw and determining the proper pilot jet size.

When does it backfire? At what throttle opening?
How does it run at 1/4 throttle, 1/2 throttle, and wide-open throttle?


FWIW, the Internet rumor I've heard is that HMF's jetting sugestions are too rich. I figure they do that on purpose so people don't accidently run their quads lean and damage them [shrug].

[blindsey]

keihin jets, stock piston and I have to be honest and tell that I dont know what my elevation is, but I only ride in southern states, Alabama, Tennessee, Georgia, and Kentucky. I had a dynojet main 170 and it would idle, but it would really bog down if I was running at a low speed and just tried to hammer the throttle.

[blindsey]

something else I forgot to mention that it will do is at about 1/4 throttle it will run and then do this hiccup sound like it is gasping or missing or something, maybe you can help me with that as well.

[boricua]

that hiccup usually means a lean condition. does it sound like its coming from the air box? its kinda like a quick puff or sneeze accompanied by a brief stall or jerk like the motor hesitated....all this could happen very obviously or suddelly. but i do agree throttle position will help point you towards the section that needs attention. I like to start from the pilot jet and work up to the main.

[GPracer2500]

Originally posted by boricua
[snip]...I like to start from the pilot jet and work up to the main.

Agreed. That's the best way.

A DJ170 seems awfully rich. Try a smaller jet and see if it improves.

[blindsey]

Well after spending all day on figuring out what my problem was, I finally ended the day with a 42 pilot 160 main and two turns out on the air screw and the circlip in the third slot from the bottom. It still has just a slight bog in it, so where would you guys think the tweak needs to come from? Thanks for all your help

[boricua]

assuming your air filter is clean...............
i'd start by getting a couple spark plugs, then make a few test runs focusing on each of the throttle positions and where it starts to pop or bog. after you have an idea where its bogging, run it at that throttle position, under a bit of a load......so not just revving it up.....kill the motor immediately and then check the plug.
its a bit of trial and error for sure, not to mention some slighlty burned knuckles :p . bogging usually means rich, but not always.
good luck, check back with us.....

[jsmith2232]

Keep in mind that the dynojet 170 is equivelant to a kehien 190. The 170 DJ was probably way too rich, I run a bit on the rich side with the 170 using the mods i have listed in my sig. when i had just the header, pipe, revbox and k&n I ran a 160 kehien and it was about perfect. do you have the dynojet needle in or the stocker.

[blindsey]

I put the stocker back in. I have now arrived at having 160 main with 42 pilot and two turns out and it still has just a little bit of a bog at first throttle and it still has a little bit of a hiccup and about 1/4 throttle. Need some help on tweaking this out.

[boricua]

take a look at the accelerator pump. it should squirt fuel as soon as you crack the throttle, if its not it will hesitate, hiccup, bog, etc. unitl it gets enough fuel from the other jets. one or all of these things can happen quickly or slowly....keep that in mind. also, if its squirting too much fuel, it can hurt you. it can bog you down by richening the mix early on....after that it will run on the jet settings. its usually noticeable on first take off or slow speeds....but not always. you can check if its squirting...you'll have to take off the air box to look into the carb. you can do this with the motor off-recommended. i had a similar problem on my yzf250, bogging/stalling when i crack the throttle....turned out to be too much fuel from the accelerator pump, choking the motor with gas......good luck!

[blindsey]

well I did a little back tracking today and I put the old pilot jet in which was a 38. The quad would idle with that pilot jet in and a dj170 main. So I put the 38 pilot jet back in and started out with keihin 170 main and it was to rich. I then tried a 165 main and it was to rich. I then tried a 160 main and the plug is a real lite charcoal color and it idles real good and it doesnt have that intial bog like it did. I may try my 152, but I feel as if that put it to lean, I feel like a 155 main might be exactly what I need.

[GPracer2500]

Originally posted by blindsey
well I did a little back tracking today and I put the old pilot jet in which was a 38. The quad would idle with that pilot jet in and a dj170 main. So I put the 38 pilot jet back in and started out with keihin 170 main and it was to rich. I then tried a 165 main and it was to rich. I then tried a 160 main and the plug is a real lite charcoal color and it idles real good and it doesnt have that intial bog like it did. I may try my 152, but I feel as if that put it to lean, I feel like a 155 main might be exactly what I need.

Sounds like you just about got it. There's a lot of trial and error in the jetting process.

[blindsey]

amen to that

[boricua]

your getting really close to stock jetting, hmm. even with all your mods, sounds like you only needed a few minor jetting changes. well thats good anyway. let us know what you end up with.....

[blindsey]

I know that is what I was thinking. I think a 158 might just do the trick.

[boricua]

give it a shot. remember a fresh plug will give the most accurate reading. also, your idling issues should have nothing to do with your main, or even your needle position. each time you change your pilot, you should adjust the mix. screw. both of these should effect idle and just off idle performance. sounds like your on the right track though :macho