Jetting non ram aired Thundercat

1753 Views 10 Replies 4 Participants Last post by 02337, Jun 2, 2013

02337

Discussion Starter · May 23, 2013

Been making some good progress with my 98 YZF600, replumbed the float bowl equalizer hose to the air box and bike runs OK. Seems to not pull very hard at full throttle as it does at 3/4 throttle, The set of carbs I picked up came with a jet kit. No clue as to what jet kit it is, adjustable needles and 152 main jets installed.

So I'm hoping to get some jetting information from what others have used from stock to ram air delete.

I've heard so many different opinions on ram air deletes from the open holes in the frame creating a vacuum on passing by air, to using fzr air box and 118ish jets.

I've been digging around to try and find if anyone out some filters on the air box that extend out of the frame, or maybe like ram air scoops connected to the holes in the frame?

Bike otherwise runs great but from 7-9k rpms it takes its time but from 10-13 it feels better but still a little sluggish. It doesn't pop or break up any higher rpms so I'm thinking g the 152's are too rich correct?

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Jackstand Johnny

· #2 · May 26, 2013

What else has been done to the intake/exhaust.fuel delivery on the bike? Sometimes when you jet or change out other parts you're gonna hit flat spots that can't be remedied without virtuous patience and scientist like knowledge. If you're wondering if your bike is running rich then pull your spark plugs and examine them. That's gonna be your biggest indicator of the fuel condition. Also with bike specific questions this technical you're probably better off asking them on a bike specific forum. Have you asked on any Thundercat forums?

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RaZed1

· #3 · May 28, 2013

I'd tend to agree, the mains are too fat. While it's still "on the needles" it's OK (probably still a little fat), but once they're fully lifted and you're all on the main it starts loading up. I'd try going down 5 on the mains and seeing if there's an improvement. You might also try dropping the needles one clip. If this pushes the bog higher into the rev range, then you're too rich on the main.

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02337

Discussion Starter · #4 · May 29, 2013

I've removed the ram air and plumbed the float equalizer tube into the air box, exhaust is a SSR2 Vance and Hines shortened and that's about it as far as intake exhaust rest of it is stock. I've tried creating a thread on the Yzf forums but not much help, was hoping to maybe grab the attention of someone who had jetted a non ram aired model.

I ordered some 144's and 146 main jets to try from there I'll play with the needle, I made the post to just verifying that since bike seems to pull harder at 3/4 throttle and pull less at WOT it would mean its rich.

Thanks

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Rob_0t

· #5 · May 29, 2013

I run 430/440 mains on all 3 cyls in winter temps. 390/400 for summer.. with 38mm mik roundslides ......keep an eye on piston wash

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02337

Discussion Starter · #6 · May 30, 2013

Rob_0t said:
I run 430/440 mains on all 3 cyls in winter temps. 390/400 for summer.. with 38mm mik roundslides ......keep an eye on piston wash.

So confused by all of that.

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RaZed1

· #7 · May 31, 2013

02337 said:
So confused by all of that.

Don't be, it's not that complicated.

Jet numbers are a rating for the # of cc's of gasoline that flow through the jet in one minute, from a height of 50 centimeters (for Mikuni). Dyno-jets are measured in millimeters (so a DJ150 is 1.5mm).

Winter air is colder and thus more dense, so you need more fuel to maintain an ideal ratio than you do in summer when it's less dense, so winter jets are fatter.

38mm refers to the bore diameter of a carb, roundslides are a type of carburetor with, well, a round slide throttle (as opposed to flat-slides)

Piston wash refers to what the face of the piston looks like, and reading the "washed" i.e non-charred areas. Too much charring means too lean, too much "wash" means too rich. It's more of a 2 stroke thing since most of the char is deposits from the oil being burned. It's something snowmobilers use as an excuse for losing races, blowing up engines, or spending time in the garage away from a nagging wife.

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Rob_0t

· #8 · May 31, 2013

RaZed1 said:
Don't be, it's not that complicated.

Jet numbers are a rating for the # of cc's of gasoline that flow through the jet in one minute, from a height of 50 centimeters (for Mikuni). Dyno-jets are measured in millimeters (so a DJ150 is 1.5mm).

truth

Winter air is colder and thus more dense, so you need more fuel to maintain an ideal ratio than you do in summer when it's less dense, so winter jets are fatter.

truth

38mm refers to the bore diameter of a carb, roundslides are a type of carburetor with, well, a round slide throttle (as opposed to flat-slides)

truth

Piston wash refers to what the face of the piston looks like, and reading the "washed" i.e non-charred areas. Too much charring means too lean, too much "wash" means too rich. It's more of a 2 stroke thing since most of the char is deposits from the oil being burned.

truth

It's something snowmobilers use as an excuse for losing races, blowing up engines,

2s engine failure has few causes. All but 1 come back to user interface..lean wash is an after failure diag. Not possible to be an " excuse " as its a direct result or "effect" of lean jetting. Jetting can be an excuse.

or spending time in the garage away from a nagging wife.

lmao amen to that

Good onya for gettin the 2 stroke bit. I was just funnin. But i did post my true jetting for my non ram air thundercat

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02337

Discussion Starter · #9 · Jun 2, 2013

We are still talking about the yzf600 aka thunder cat, not the snowmobile correct?
Maybe I should of specified?

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Rob_0t

· #10 · Jun 2, 2013

You didnt need to specify... i KNEW what you meant...

I was adding a humorous ( to me ) bit of tuning info to make people stop reading my post halfway in and say heyyyyy... wait a ... damn you rob ...

.

Carry on ..

And have you found any good info on jettin ur bike.. ??

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02337

Discussion Starter · #11 · Jun 2, 2013

I shortened the exhaust to my liking and was hoping the exhaust flowing a little more would help in the upper rpms,
It didn't do much that's noticeable. So I ordered some 144 main jets down from the 152s in there now so I'll go from there.

Today I fiddled some more with the idle AF and resynced the carbs and noticed there was some gas in 2 of the vacuum lines, not a lot but definitely there. I assume its from the rich main jets.

Kinda hard to dual in rpms when my trail tech is a little jumpy, still working on that. I'll report back when new jets go in.

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