I'm running a 160,165 jets at 2 turns at the air screw it was jetted at about 70 degrees it is about 90 outside right now. My V-Force is hesitating at 1/4 throttle am I running rich or lean do I need to change the main jets or adjust the air screws. I really don't want to change the jets myself so I was going to use this as an excuse to have my dial a jets installed on a dyno. But I really did'nt want to do that till I received the diamond G snorkle. What do you guys think I live around 800' above sea level what should I try before I go to a dyno I want to ride this weekend so I want to try and clear it up as good as I can since it would take me about a week to bring it to the dealer with the dyno since it is not close to me at all. Help please.

 

NYVForce,

A properly adjusted carb can idle without a main jet according to the DynoJet docs you get with one of their kits. I've installed four in four different quads and have had to experiment to get good results....

This is my humble understanding of fuel delivery.....
There are basically 4 paths/combinations of fuel delivery when you open the throttle from fully closed to fully open. At a fully closed throttle, the bike runs off of the pilot circuit (idle circuit). No main jet here. The richness/leanness at idle depends largely upon the pilot screw adjustment. At 1/4 - 1/3 throttle, the carbs are transitioning from the idle (pilot) circuit to the needle jet circuit. So there is a little overlap in the path that fuel flows to the engine. The needle jet circuit uses the main jet and needle position in the needle tube to determine how much fuel flows. Fuel flows from the main jet up the needle tube into the carb venturi. So the more open the throttle, the higher the needle is pulled out of the tube and the more fuel flows from the main jet. The needle circuit is the primary circuit from about 1/3 - 2/3 throttle opening. From 2/3 to fully open, the needle is pulled out of the needle tube eliminating any restriction and the primary fuel flow is from the main jet.

I would guess there is a lean condition at the 1/4 throttle transition point.
Based on my understanding of your description, you could try a couple of things, but my disclaimer (as always) is that I don't take any responsiblity if you follow my advice and damage your quad in any way :

1. Turn your idle mixture screws (pilot screw) out 1/4 turn at a time to see if that fixes the problem.
OR
2. Move the e-clip on the needle down one groove. This will move the needle up in the needle jet and allow more fuel to flow. You'd have to remove the top of the carbs to do this to get to the needle. It's more invasive than #1 and more work.

Hope this helps.
Mark

 

You could always try some duct tape on a couple of holes in the airbox to see if you are too lean. If that solves it then problem solved. I run HMF duals with jets drilled at 150/155 with no airbox mods and it runs great from 500ft to 8500ft. At 8500ft I just open the back two clamps on the airbox to allow a little more air, rich running problem solved! I would jet lower and cover the holes in the box lid. The box is capable of breathing enough air to run the duals. My .02.

Good luck
Ken

 

Do you think I'am rich or lean my problem is that when I hit the gas it seems to hesitate at first when excelerating and then it seems ok. It does'nt seem to have the power if should.

 

NYVorce. Markdf is right on .... a masterful job of explaining the throttle/fuel process !

I also think you are lean... at the 1/4 to 1/3 throttle point. . I have the same issue develop when I installed the
160-165 jets. When using jets that large, you have to open the air box, alot. If you don't, it will be too rich on the top end.

Summary, Those jets(with the extra air) are too large for the stock needle settings. You either have to back the jets
down ( and reduce the amount of air ) .... or increase the amount of fuel at the 1/4 to 1/3 throttle.

Just my opinion , based on my experence [img]i/expressions/face-icon-small-smile.gif[/img]

 

My needles are shimmed up with dyno jet washers, so you think I'm lean and not rich so should I close up some air holes in my air box. Or am I rich. Help

 

Well.... if you have changed the needles.... then do an experment. If you close off some air holes.....and the hic-up goes
away.. you are running lean. If you close some off and it gets worse.... you are too rich.

The other dirrection is to un clip one end of the air box,,,, block it open a bit. It is runs better... you are rich and need more air