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just installed hmf utility...jetting experience so far...

5162 Views 20 Replies 5 Participants Last post by  chevy2500hd6L
well guys, i just installed the hmf utility, i didnt do a thing besides that, my air intake setup, etc is bone stock. i left the air/fuel screw alone, the main jet... all stock...and infact this is what my honda dealership said to do before i started messing with rejetting. Well at first i didnt have the spark arrestor in and it did a little backfiring when i let off the throttle, but then i went ahead and installed the spark arrestor, and i guess this would restrict some of the airflow or maybe its not even made to be used without it? anyways, now it runs perfect, from idle to full throttle, it runs exactly the same as backfiring or anything, idles smooth and accelerates smooth and i definently notice more power and of course i love the way it sounds, it lifted the fronts off ever so slightly without me even trying when i pinned the throttle, never did this before, and i have 27s by the way...and as far as checking the spark plug..well i checked it with the stock exhaust and it was pretty dark (rich) but i hear this is pretty normal for stock hondas? by the way rich is good, right? well it wont hurt anything at least? lean is what you have to be worried about, correct? which is a whitish color? anyways i cleaned it and ran it around a little, not nearly enough yet, because my neighbors are nearby and its loud as ****, however the little bit i ran it around did give it a color, a nice light to medium brown color which is good from what ive been reading...are there any other checks i can do? i know something with the choke? so what is all your guys opinions on this? im gonna ride it all day sunday as it doesnt seem like its in any condition to do any harm, and i may still then have the shop rejet it just so i get the most performance out of it, or would you even bother? but would you guys say im atleast good to ride it this sunday? the shop couldnt get it rejetted in time for this the way im in nj so you know what altitude im working with..

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This is a great post I would like to hear more from guys with experience. I have heard stock hondas run a little rich also. Actually I just changed out my plug and from the looks of the old one it was running a little rich, i had 100 miles on the quad. Yes rich is better then lean. I want to put a hmf on mine as well and was wondering due to it running a little rich would I need to rejet or would it be ok. Good Luck
I know that you wont get all the gain that you can get if you don't rejet it. Um as for messing it up by riding it Sunday, I can't say if it will or not. But when you say there is a little smoke, is this when you ride it of when you rev it?
smoke? i didnt mention anything about smoke, no smoke i said i think it was so rich from the factory, that now with the exhaust, the jetting is actually better...again like i said the spark plug is now a light brown instead of the stock black...
Well rev it high and see if there is any smoke.
ive done so, no smoke...i messed with the fuel screw a little, but it doesnt seem to do much? i turned it all the way in (bottomed out) and at this point it runs poor, but all i have to do is turn it out a bit and it runs fine and then if i turn it out anymore it doesnt seem to change anything.. i thought it should start to get rough as you turn it out and at this point you turn it back in til its smooth?
Yea well then you did it right. It is going to work becasue you have your air mixture balanced with the amount of fuel that the stock jet will put in. Since you can move more air you can give it a bigger jet if you want and adjust your a/f to compensate for introducing more g as to the mixture.
whats the stock size jet on my rubicon? hmf recommends a 165 keihin, so im gonna just try that out along with adjusting the fuel screw, and the needle jet i think its called where you move the clip, i can just leave alone?
o ya and a 170 keihin jet came with the hmf which is what hmf says to use on a foreman, but mines a rubicon which a 165 is suggested, what if i was to use the 170, to much fuel? i got a uni air filter to, but i doubt that adds to much air, im using the stock box and all...
Well I will say I have heard of people running 170 mains. I personally run a 165 which is what HMF sent me. I installed the jet and adjusted my a/f and it runs like a top. I did have to adjust the a/f a bit whenever I went to TX for Mud Nationals... but Im guessing that slight change in elevation made a difference. I would stick with a 165 it definitely seems to be a good setup. In Low I can't get the wheels about 10 or 12 inches off the ground with my 29.5s on. I haven't had a chance to run my bike yet with the stockers yet.
well after all i did notice a slight backfire with the throttle pinned and then when i let off it, so i got a 165 main, uni filter since i dont like the stocker and i did it! it was actually extremly easy, if you have any common sense and mechanic skills you can easily do the main jet, and the backfire is now gone, and i adjusted my fuel screw, i guess the filter made somewhat of a difference?? because i needed to readjust the fuel screw after installing the new air filter...and it may be just me, but it just seemed overall a lot smoother and better sounding with the new main and airfilter, it runs like a champ! and it definently has more power, i didnt try low yet, because im home and its to loud but i gave it a quick run in drive and it ever so SLIGHTLY pulled the fronts up when i pinned the throttle which it never did before, again i have 27s, so im very pleased! you dont even know how much im looking forward to riding tomorrow, cant wait to test my new power and sound...
Let us know how she does
Sound clips? lol

And it would be interesting to know the top speed difference between stock and the HMF setup...I know you don't want to put the stocker back on to see though; I sure wouldn't. Bet it sounds sweet
i could probably get some clips tonight, it does sound sweet..
That would be great, man. I've been wondering what it would sound like on the Rubicon. All I Have heard the HMF exhaust on is a Rincon.

Oh, and umm...about the new top speed? could you possibly get that information for us?
im going riding this weekend, so ill try to get a speed, but prolly wont beable to, the trails are pretty hardcore and average speed is 15-20, only a few small straights that i can get to 45, plus a few mph probably since my speedo may be off because of the 27s, but then i run out of room...and ill try to get a clip today
A sound clip would be awesome, but don't kill yourself trying to find out what the new top speed is for me haha.

And Chevy2500hd6L, are you having fun keeping gas in that LQ9 with the rising summer gas prices?
Did you get the quiet core with your HMF or just the spark arrestor? If you don't like the noise I think the quiet core helped mine alot and didn't seem to rob any power.
just the spark arrestor, i love the noise, haha...
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