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Discussion Starter · #1 · (Edited)
from everything that's been said, when running crossovers you jet up

so I'm trying out something different

38's with my crossovers

with 40 pilots it's around 7-8 afr on LM-1 at idle, checked both exhaust pipes....same thing

LM-1....new O2 sensor and calibrated it. I remember something being said about how to check them....propane torch???

Other than appearing rich...... just running it in the garage, it runs and revs out great

when running something like this, both cylinders should be running about the same afr, even say if one carb might be jetted a little different????

:confused:


 

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looks good either way! The Webers were way rich with the big common plenum but it had to be leaking somewhere... it was ridculous. After the next race I am going to play around with the N/A set up again...
 

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Discussion Starter · #3 ·
that was an old mock up picture, basically the same design though:)
 

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Discussion Starter · #4 · (Edited)
I would think now it should be pulling a lot more air through, and being that these carbs do operate on velocity and vacuum that it if anything it would be pulling less fuel through the jets.

Got to be pulling a lot more air through than the (ms) crossover intakes

really has me stumped
 

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The crossover is too big. The intake runners aren't directed into the cylinders. The A/F doesn't know what direction to go. Too much turbulance in that intake.












Just guessin. :D
 

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Discussion Starter · #6 ·
I don't know how much or if that is coming into play

It does sound good, and revs quick, probably quicker than the fcr's. Kinda hard to tell without actually loading it though.

I didn't have a chance to do any rejetting, need to go smaller on the mains. It would hit about 10.5-11 afr, mid throttle on up.

I don't have any smaller pilots, and it just surprised me....I was thinking I was gonna need to put bigger pilots in
 

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That's hard to say, what carbe were you using the 38's??

with the plenum that big it can be flooding it due to no low end velocity. and with the larger cam i/e overlap you could be puddling fuel in the intake.

Use a propane torch. you should see 12.5:1 on the a/f range with the flame touching the sensor

butane straight from a lighter will read 10.0:1

if it's correct, jet accordingly

John
 

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it all depends on the motor and airbox setup. but YES, on a stocker you have to drill the jets or run a 235ish main. modded motors you also run same jets or smaller.

closed airbox like on a prairie or 650 brute you jet WAY down. into the low 130's and still make 45-48 rwhp

but you always have to go up on the pilot

I have some new crossover intakes being made up by a local company. They claim they can get a better/smoother finish than the old UPP's

I thought about making a set for the Teryx as well as there is plenty of room in there to add a set under the cowl. I know they'd work.

John
 

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Discussion Starter · #10 ·
That's hard to say, what carbe were you using the 38's??

with the plenum that big it can be flooding it due to no low end velocity. and with the larger cam i/e overlap you could be puddling fuel in the intake.

Use a propane torch. you should see 12.5:1 on the a/f range with the flame touching the sensor

butane straight from a lighter will read 10.0:1

if it's correct, jet accordingly

John
it wasn't calibrated right

the front is ticking over right around 13, the back is reading around 17....I was really thinking with that intake set up, the front and rear cylinders were going to be real close

yes, Kehein 38's

LTE's

checked for a possible air leak on the rear intake and exhaust system....looked good

would the rear pipe being so much shorter have any effect....I do notice the exhaust pulse is quite a bit different between the front and rear
 

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When you are running larger cams with large duration the rear cylinder will have a weaker pulse at idle compared to the front.

it can be the carbs. they are street bike carbs and can have 20,000 miles on them. so they can get different readings.

the asymmetrical shape of the cams is what makes that happen. if you look at the Front cylinder. the ramp will open gradually and close fast (causing a rise in cyl pressure and providing a better pulse). on the rear, it opens fast and closes gradually causing a cyl pressure loss at low rpm and a weaker idle pulse.

very common with crossovers on built motors and big cams

jet it accordingly. it should work.

John
 

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Discussion Starter · #12 ·
tankQ

not carb related...I flipped em around just to see :D

I'll try some bigger rear pilots,got 40's in now..... got 42's and 45's I can try
 
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