I took my Vforce in for the recall after my exhauast install. MBRP suggested 142/137 jetting with no airbox mods I installed 142/138, my dealer said he couldn't order a 137 jet. So I had them take a look at the jetting, he checked my front plug. It was black on the end, but he said since there was no build up around the electrode I was fine. My concern is that there is a little smoke that comes out of that pipe, and none out of the other. It does smell a little like fuel, and at the mid pipe to muffler clamp, black residue will drip out on my motor, only on that side. I told my dealer all of this also, the kid was young working on it. MBRP said they tried several airbox mods with no success. So what should I do, is there a way to get a 137 jet for the front, mod my airbox, or leave it. Thanks for your input guys. [img]i/expressions/face-icon-small-confused.gif[/img]

 

First check and see if the choke is sticking on that cylinder, some 650 Pra's have had choke sticking problem's, and then if it's fine put the 135 jet back in and try it.......

 

There is no 137 jet available. When they say no airbox mods they probably mean nothing too radical like removing the snorkle or lid, but I'm sure you could safely add some 1" univents to the top of the airbox and that should help bring in a little more air.

 

So the jets go from a 135 to 137 increment? So I actually only went from a 140 to a 142 on the rear, going up one size, and a 135 to a 138 on the front , going up one size? When you say univents, is that an actual product, or drilling some one inch holes, and plugging some if I'm too lean? I just came from my first day at the mx track, I am sore. You guys do some seroius work out there. I think I'm addicted! I love the tabletops. It does act a touch rich though, overall very good day.

 

When running a dual exhaust the jets in the carbs need to be one jet size apart. Put the 135 back in and she'll run great. You lose the scavaging effect with duals so the front cylinder tends to run a tad on the rich side with the front and rear cylinder jetting 2 sizes apart. hence the reason for the 1 step jetting difference.

 

I am having the same problem with the rear cylinder. It also doesn't seem to fire correctly when at an idle. Any ideas would be helpfull.

 

I am running the MBRP's with no other mods yet. I just took my plugs out to check them, and they were both chocolatey brown, the front a little lighter than the rear. I'm pretty sure we're at roughly 600ft. elevation here. When I installed the duals, I fired it up, it didn't backfire and the power increase was noticeable so I didn't worry about it.

VFORCEONE, I'm not getting any leakage at any of the joints, I was impresssed at how well they fit together and seated. Is it possible you have the short "joiner pipe" too far forward to seal properly at the muffler?

 

I think my pipe fit is o.k. the taper is all the way slid in. I guess I could have torqued the clamp down more, so I did. I figure the black drip residue, being only on the front cylinder side, was due to running rich, hence the little bit of smoke from that pipe, and none from the other. They did sound good, and idle good at installation, with stock jetting, but there was noticeable white smoke, after burn-off from manufacturing should have been done. Now if I put the 135 back in the front, and leave the 142 in the rear, that doesn't make the too far apart and lean out the front cylinder? I'm not doubting you, and am open to all sugestions, but I am new to this. I also could tell a little congestions at certain points in the power band at the track yesterday, that is what I assume you mean by the scavenging? The 135 sounds good, how will I know if I am too lean, what can I harm? Thanks you guys for all your help with this.

 

If one size difference between the two cylinder's is what you want to try, you need to put the 135 in the front carb and a 138 in the rear, I'm not sure about these dual system's as I only have experience with the 2 into one pipe's, but if the stock jet's are 135 front 140 rear thin one size up on both carb's should be 138 front 142 rear........

 

First check for bindage in the choke cables. Then mess with the jetting. Check your rear plug to to make sure its not running rich also. It may not be coughing black smoke but it may still be rich. From what i have heard from my buddy the mbrp runs best with stock jetting. But that depends on your elevation. With mine i had the rear rich and the front was spot on with the 2 sizes split. Put mine at 140/142 with perfect results. But that was with HMF exhaust.