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Discussion Starter · #1 ·
We just finished our 2001 720 Vito stroker build and we went with the largest jets in the kit 180/185 (I think) or 175/180 (I built the carbs a few months ago so I don't remember for sure) The fuel screws are 2 1/2L 3R per Vito's starting suggestion, 25 Pilots, and we started with the needles on the lowest setting from the bottom full rich. The question I have is it seems good from 0 to 1/4 and then it starts to sputter and then it cleans up as I get closer to wot. We lowered the needles one clip at a time and it seemed to help a little each time. Last run was at third clip from bottom and it was better but still has some sputter. What carb setup have you guys had the best luck with?

When we start it in the garage I can hold 1/4 throttle and its smooth and I can bump it up to half and it sounds good but under load the sputter begins.

We are running No Lid, K&N, Full Trinity Stage 4 Exhaust and we are in Dayton Ohio.

Does sputter mean Rich or Lean?

Thanks Jason
 

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I am unique
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We just finished our 2001 720 Vito stroker build and we went with the largest jets in the kit 180/185 (I think) or 175/180 (I built the carbs a few months ago so I don't remember for sure) The fuel screws are 2 1/2L 3R per Vito's starting suggestion, 25 Pilots, and we started with the needles on the lowest setting from the bottom full rich. The question I have is it seems good from 0 to 1/4 and then it starts to sputter and then it cleans up as I get closer to wot. We lowered the needles one clip at a time and it seemed to help a little each time. Last run was at third clip from bottom and it was better but still has some sputter. What carb setup have you guys had the best luck with?

When we start it in the garage I can hold 1/4 throttle and its smooth and I can bump it up to half and it sounds good but under load the sputter begins.



We are running No Lid, K&N, Full Trinity Stage 4 Exhaust and we are in Dayton Ohio.

Does sputter mean Rich or Lean?

Thanks Jason
Way to rich, go to about 165 mains and needles half way up if the air box has no lid or is modifed..............
 

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Master of the Electron
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Yes, I agree - try 165L/170R mains, needle (is it a Vito's?) at middle.

Tests in the garage will tell you major issues with jetting, but the only way to get close is by riding.
 

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I'm not the expert around here but I recently had the same problem and I bumped my pilots from 25 to 27.5's and got a new choke plunger or "carb starter kit" and now its a screamer.
 

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I had to run 27.5 pilots with my 720. But your problem isnt from idle to 1/4.

You really need to start the jetting process from the top down. Start by finding the best main jets that preform the best at WOT.

Then dial in the needle clip.

Then the pilots and fuel screws.

That way you dont end up with severly off needle setting to compensate for the wrong main jet. Same goes true for the needle to pilot jet.
 

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I always thought you jetted from the bottom up? This is a new concept to me. Doesn't the idle screws and the pilot jets have a very small affect on the larger circuit too? Basically if you were to put in a main jet that runs good, when you put in a bigger pilot wouldn't that make the main slightly fat?
 

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Master of the Electron
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Contribution of the pilot jet and pilot screw (which is just a valve to turn the pilot jet down) is minimal by above 1/3 throttle.
If your mains are wrong, you'll never get the needles right - so I agree - top down.

Get mains working well from 3/4 to WOT, then set the needles for 1/4 thru 3/4 throttle, then tweak the pilot screws for good idle, good transition onto throttle and minimal hanging idle and popping on decel... then tweak needles again just a bit, if necessary, because of the slight overlap between pilots and needles.
 

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I always thought you jetted from the bottom up? This is a new concept to me. Doesn't the idle screws and the pilot jets have a very small affect on the larger circuit too? Basically if you were to put in a main jet that runs good, when you put in a bigger pilot wouldn't that make the main slightly fat?
No because the needle will have the main jet plugged or almost while your riding on the pilot jet. But the pilot jet will still be functioning when your at WOT with the main jet open.
 

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No because the needle will have the main jet plugged or almost while your riding on the pilot jet. But the pilot jet will still be functioning when your at WOT with the main jet open.
Right on, the pilots do contribute through the whole range but if you see the hole in the pilot jet, which can be as small as .020'', it really doesnt compare to the mains which are much bigger..........:D
 

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Discussion Starter · #11 ·
Yes, I agree - try 165L/170R mains, needle (is it a Vito's?) at middle.

Tests in the garage will tell you major issues with jetting, but the only way to get close is by riding.

Yes they are Vito's needles.
 

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Discussion Starter · #12 ·
Thanks guys Ill let you know how it goes after I get everything switched.
 

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ive been through this exact issue on my 727 big bore. i too ended up with the vitos stuff,and it only had up to 160/165 jets with it. ran good with that and ended up on the 3rd clip on needles to get rid of it. i now have 180/185 in it and it really seems to pick up a lot to me,. i then had to go to 2nd clip due to the mid range richness again. still not sure im not too rich,i may try to lean it out a bit soon
 

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I had the same problem on the Dyno, afr was set good I have 27.5 pilots,185/190 mains but at mid was sputtering. We found the Stator was bad and it fixed the problem. I have a 720 +1 valves stage 2 cam and full port. It Dyno at 62 HP 48 torque at the wheels.
 

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if you did that on the dyno,i must not be far off on my 180/185. everybody on here says im too rich with those jets. sure seems to like it too much to be rich.
 
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