I got my HMF duals in 2 weeks ago and couldn't wait to try them out. I put on the new pipes and paddle tires and headed for the Little Sahara sand dunes in Central Ut. Pulled the Vforce out of the trailer and tried running it with the stock jets (135/140) and it ran like crap. I put it back in the trailer and put in 145/148's and it still ran poorly on the top end. I decided I didn't want to mess with it anymore so I took it to the shop and told them put it on a Dyno to dial it in perfectly.
$105 dollars latter I picked up the 700 and asked them how high the had to jet it to run right. I dont have any air box mods but I was expecting 155/160 at least. Boy was I shocked when they told me the put in 122/125 and turned the fuel screw out 1.5 turns. They showed me the Dyno chart showing it picked up 5.5 hp with is very respectable for this altitude. I was very suspect of what they had done but when I took it for a trial on Saturday it ran fantastic. I was very impress with the increased torque and power.
The only thing I noticed was a slight backfire when I let off the throttle completely. They told me its nothing to worry about it just the way the duals work. Any second opions out there? Do I need to worry about the slight backfire? If so, how do I make it go away?

PS I love the HMF pipes and what great folks (Kevin, Roy and Hauns) at HMF to talk with. Very customer oriented!!!!!

 

Some pipes you can never completely get rid of the backfire.

If the idle is lean, it increases backfire. Mess with those air screws until you find the sweet spot, see what that does to the backfire.

Also, the more you ride with those pipes, the more you will know if you are jetted right. You may have lean needles. Shim them or maybe wait an see if a jet kit is out for that 700.

 

Im running stock jetting with my duals and it runs great...They say the bike was jetted slightly rich from the factory anyway and it seemed to clear it up..Seems like most people think they have to have huge jets to make any power????

 

Do you have air box mods or have you removed your snorkle and replaced it with radiator hose and cut out the baffle, and live at 800' above see level there are reasons to increase the jet sizes and shim up the needles and it may still be a little lean.

 

P.S. lets not get on each other for being different like the yamaha guys.

 

This is important info for me since I ride at 4600ft too. I wont be getting a pipe until maybe christmas, but I think I'll be trying smaller jets right now. I just wish there were instructions posted seomwhere (hint hint) on how to do that. I'm also a K&N fan so when they make one that should help lean the machine too.

 

I ALWAYS run my bikes on the rich side. It is only to save the motors. An engine will almost always make the most hp when jetted lean to the point of overheating and blowing up. Just my two cents.

 

To all,
MY AIR BOX IS STOCK WITH NO MODS! I have a second kfx700 that the wife rides that is completely stock. I plan on changing the 135/140 stock jets for 130/135. Thanks for the info on stock jetting at Littlle Sahara and also the idle screw adjustment. I will give both those a try before I head out this weekend.
Love the sound and performance of the HMF duals. By the way, If anyone wants to keep the heat away from your left leg you can use the stock heat shield with a few minor modifications.
There is a slight difference in the bends on HMF pipes vs stock and the pipe is slightly larger. All you have to do is cut the heat shield off immediately in front of the 2nd clamp (from the head pipe), get rid of the stock bolts that hold the 2 remaining clamps together, get some smaller longer bolts and some lock nuts. Push the longer small bolts through both sides of the clamp and tighten down the lock nuts and yor done. It would be much easier to do this before you put the pipe on, as I found out the hard way, but it is still possible after the pipe is installed.

 

I am at about the same elevation. I called HMF and they recommended 142 up front and 145 in the rear. Are you still happy with the jetting? I would be willing to try that out rather than waste riding time swapping out jets. Feel free to email or private message me I am going to be ordering the duals this week and would like to get some jets ordered as well.

Are there two fuel screws to adjust and if so are they both 1.5 turns out? HMF made it sound like there were two of these to adjust.

thanks for your help!

 

Do you have a print out you can post? Ive been trying to post mine and this site keeps saying "pending approval"....so I gave up. 5.5hp is alot to gain. Ive tried 2 different pipes and did not gain that much. Were in the curve did you gain 5.5hp? Where is you HP at 60mph? If its not over 30hp, your pipe will kill your overall performance. Some people use different clutch springs to compensate for this loss. The stock pipe was better at the top MPH than the DMC......[img]i/expressions/face-icon-small-disgusted.gif[/img]