Confusing sparkplug color

[promisc]

This is my current setup:
Stock bore, T4 slip-on, K&N air filter w/ precharger, Dynojet 170 main(:huh), Stock Pilot Jet, No airbox lid (but homemade outterwear) and choke removed.

There is my problem, the sparkplug is white/light-gray(no crap on it) with a big 170 main. But sometimes, like when its cold or when i hit the gas at low rpm, the engine wants to die. Thats mean im too rich i guess ? Also, when i go down a hill, without hitting the gas, the engine is backfiring.. That means im too lean??? Its backfiring when i release the throtle too..

If my sparkplug is already white/gray with a 170, it is dangerous to run with a 160 or 165 ?

Thanks

[Guy400]

Well you've got a couple problems going on here.

#1. The DJ 170 main is too big of a main and that's why you're bogging on the bottom end.

#2. Your spark plug can be white/gray but still have a rich condition given the type of fuel you're running. Most of today's gasolines have additives and detergents in it and this makes spark plug reads confusing.

#3. If you're using a DJ main jet you need to use a DJ needle. The hole in the DJ main is shaped specifically to fit the taper on the DJ needle.

#4. Backfiring on deceleration is a function of the air screw usually. Run the screw in until it bottoms out, turn it 2 turns out and see if that gets any better. From there turn it out in 1/2 increments until it gets better.

No matter what, I'd get a DJ needle before you start messing with carb adjustments or you're just going to give yourself fits.

[promisc]

I actually got the DJ needle at #3 position. The gas in Quebec is only 91. Should i consider to add extra octane in it? Whats the best octane rate for a stock piston? 93?

[MIKE400EX]

The backfiring on deceleration might also be caused by an air leak at the header pipe to cylinder flange. But like GUY said, one way or another it's being caused by a lean condition at closed throttle.
91 octane gas should be fine for a stock piston. Does the gas in Quebec have a high alcohol content?

[promisc]

Originally posted by MIKE400EX
The backfiring on deceleration might also be caused by an air leak at the header pipe to cylinder flange. But like GUY said, one way or another it's being caused by a lean condition at closed throttle.
91 octane gas should be fine for a stock piston. Does the gas in Quebec have a high alcohol content?

I dont know the specifications of the gas in there. I only know that 91 is the higher i can buy at the pump.

What about adding Xylene or Toluene to increase the octane rate ?

[Guy400]

Your octane rating has nothing to do with the problems you're having. You're struggling with a carb that's a little out of tune right now and no fuel is going to fix that for you.

Drop down to the 165 DJ main, leave the needle where it's at and turn the air screw 2 turns out. This should get you a pretty close baseline to start from. Make these changes and tell us how it runs and we can go from there.

[MIKE400EX]

Get the jetting straightened out, 91 is more than sufficient. Xylene and Toluene are quite dangerous if not handled properly. The correct ratio of fuel to additive is critical. Worst of all they can be absorbed through your skin and are lethal, blinding etc....

[zlam27]

hey, i have the exact same mods as you (T-4, no lid, stock bore, K&N, choke removed) and im running a 160 DJ and a 42 pilot. it seems to be doin alright, i could probably use a 40 pilot but ill just turn the screw in for now. im wondering if i need to buy the dynojet needle to use with my DJ main jet.... does it make any difference? mine seems to be running strong right now.

any opinions?

BTW: elevation here is about 750 ft and its about 80 degrees. if its cooler there, you will need a smaller main and if its higher altitude you will need a larger main (is the elevation part correct?)

zach

[speedy400]

Originally posted by zlam27
(is the elevation part correct?)

zach
I always thought the higher you go the smaller the jet(less air pressure)-darren

[hondafox440]

The main jet has little effect on the pilot and needle circuit. The main really only affects 3/4-WFO throttle. Sounds like your pilot is too rich. Lean it out and see. The correct color for a plug after a throttle chop test is a mocha-tan.

Is it time for a jetting guide again?

[promisc]

Thank you guys.

An other litle question; Whats the benefits of getting a 40 or 42 pilot jet vs a stock 38 if my fuel-pilot screw is not completly unturned (like 2 1/2 turns) ?

How many turns it takes to get a 38 completly free? 4 turns?

|.|
\|/ Pilot screw
.v
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| | Pilot jet

[cals400ex]

the pilot on the 400ex may even be a little lean from the factory. a 40 or 42 will make more of a difference than the fuel skrew. the fuel skrew is more or less for fine tuning. i would get a 42. these bigger pilots make starting the bike easier in cold weather too. turning the fuel skrew out richens the air/fuel mixture. also, the colder it is outside, the bigger jets you need. the more humid, the smaller jets you need. the higher altitude you go, the smaller jets you use. i don't think altitude changes much on the jetting until you go 2000 to 3000 feet above sea level. i think once you have the fuel skrew out 3.5 or so, its time for a bigger pilot. i am not positive on that though.