stock carb jetting

[borednstreched]

my set up is a stock motor with stock carb. no airbox lid, graydon proline pipe with a pc factory sound silencer, stock oil injection. comp/leak tested great.

im having it tuned at creek cycles. he said hes already up to a 310 main and had to order larger jets as he hasnt found the rich spot yet to back it down.

does that sound right at all?

 

[Blaaster]

Does he tune by plug chops or not, some mechanics do noteven know what they are.

 

[EZRider76]

Why would a cycles shop need to order more jets? My local shop has bins upon bins upon bins of them, from low to high....well, from lean to rich.

Anyway, no air box lid means better air flow, not sure about your exhaust, but with the stock injection, it is less oil so I would think you wouldn't need as big of a main. Think about it, pure stock blaster is #220-#230 main. All you've done is change the exhaust and removed the air lid and he's at #310??? Slightly suspect if you ask me. Full FMF exhaust and FMF recommends #270 with stock carb and air box lid.

 

[borednstreched]

the graydon makes way more top end than the fmf's. i have a feeling thats the main reason for the high jet. i cant find anyone else who has one to get jet#s from them, i tried contacting graydon mfg many times with no answer or reply.

hes said it pulls hard, almost rips you off the bike.

i though that sounded real high for a jet# too. i bought the quad and there was a 230 main in it, it still had the lid on and a garbage filter.
that tiny jet could have been the contributing factor to the extensive damage of the piston along with the air leak on the original motor. ring lands and rings blown out of the top of the piston.

i though that sounded real high for a jet# too. im running the same exhaust it was before, no lid and a 2 stage maxima filter now. i thought that was a very large increase.

 

[Blaaster]

#310 is not such a big jet if the pipe is doing a real good breathing job.

I was amazed how big a main and the position of the needle I had to use to get a mundane DMC Alien working well.

#320 main, stock needle in bottom slot, with a stock 26mm carb, running a foam filter directly on the carb mouth with a 25:1 bean oil premix, at sealevel with an air temp of 40deg+

Sounds absolutly ludicrous, and also no air leaks.

 

[borednstreched]

#310 is not such a big jet if the pipe is doing a real good breathing job.

I was amazed how big a main and the position of the needle I had to use to get a mundane DMC Alien working well.

#320 main, stock needle in bottom slot, with a stock 26mm carb, running a foam filter directly on the carb mouth with a 25:1 bean oil premix, at sealevel with an air temp of 40deg+

Sounds absolutly ludicrous, and also no air leaks.

thats true i never thought about it cfm wise. removing the lid and having a pipe that flows lots of top end, results in your cylinder moving much more air at peak rpms.

that makes me feel alot better

 

[EZRider76]

thats true i never thought about it cfm wise. removing the lid and having a pipe that flows lots of top end, results in your cylinder moving much more air at peak rpms.

that makes me feel alot better

I wouldn't say the main caused the piston damage before, considering you mentioned air leaks. Air leaks were the culprit there, the main just couldn't keep up.

 

[borednstreched]

thats what im saying. it would have detonated any way from the air leak, but having that small of a jet still in there made the already lean a/f mixture, an extremely lean condition. causing more damage than being lean from a airleak with the correct jetting.

that stock jet just caused more damage, on top of what was already happening. because the detonation explosion had even more air then fuel in its mix due to the stock jet, the more air you have the larger the explosion, fire/detonation is fueled by air.

 

[borednstreched]

but then again maybe im just thinking in terms of oxidizers/oxygen verus flame/spark. flame or spark ignites the mix using fuel as the combustant, but after that oxygen fuels the fire/explosion.
think along the lines of a camp fire or nitrous. you smother a fire to put it out.
when nitrous oxides it turns to oxygen, filling the cylinder with more air than it could pull in on its own. same idea behind turbo_s/c theroy because your compressing the air being brought into the cylinders.. making a larger explosion on top of the piston by introducing more air, creating more downward thrust resulting in more power/torque.

 

[EZRider76]

LOL...trust me, I get that. You don't know you were definitely lean before though, only a plug chop would tell you for sure. Unless you did one, saw it was lean and road it anyway...shame on you.

 

[borednstreched]

lol i would never do that.