780 jetting help

M

Maheu

New member
Joined
Apr 4, 2011
Messages
32
Age
46
Location
Bangor, ME
I took my sled for a ride and checked the plugs seems and feels rich on my pilot circuit. I have cpr pipes, agresive porting, mega head compresion 150 around there cpr pipes. My pilot jet is 55 needle 4th both washers underneth .165 mains 2.5 turns out on feul screw. And its vented. Should I drop the pilot down? Does this seem rich to anybody? Any help would be appreciated. Thanks guys.
 

Before I started changing the pilot jets I would try closing up the fuel screws...2.5 turns open is as many turns open as one would normally run before going to a richer pilot jet...this gives you room to close them up hopefully enough to clean up the richness at off idle throttle. I wouldn't run them less then 1 turn open before going to a smaller pilot.

People with more 780 Viper tuning experience then I may pipe in with more jetting recommendations but I believe most tuners were venting outside of airbox with mod Vipers.

JM.02c

Bob
 
How about getting the specs from whoever built the engine, they should have settings fr you to use as a baseline. Jetting is determined by reading the plugs and adjusting as need for the circuits, so if the plugs are very rich down low then the pilot jet and fuel screw adjustment will be what you want to look at.

then take the sled out for mid throttle runs and adjust the needle settings to where the plugs and pistons are in the safe zone, usually this area of the mid throttle long cruise section is around 600-700rpm on a extended distance like 1000ft, check plug

then onto your wide open runs longer then 750ft wide open youll be able to adjust your main jet settings according to your plugs and piston top readings.
 
I baught the set up a guy on this sight iv been trying to contact him. No luck there. Ill do what u say. But frankly im not sure what to look for. Yea I read all the post on reading plugs. Im running synthetic amsoil. My plugs r black half way threw band then almost a gray color. They r new plugs to. Is this normal don.
 
Maheu said:
I baught the set up a guy on this sight iv been trying to contact him. No luck there. Ill do what u say. But frankly im not sure what to look for. Yea I read all the post on reading plugs. Im running synthetic amsoil. My plugs r black half way threw band then almost a gray color. They r new plugs to. Is this normal don.
Click to expand...

I would suggest going thru the circuits if its unknown any information on engine tune, like i posted and you can tune it in. gray plugs is lean plugs, dont want to spend much time there or its gonna get expensive. :o|
 
Staggs u do any side work. Better yet you no any one in maine that is a good tuner. Im headed out of state for work and it will be good time to get it looked at.
 
Hammer gave me a different air jet I cant read the size. Anyways do u guys usually put in smaller air jets when u run a 780.
 
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