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Discussion Starter #1
74 2000, shankle hi compression, cams, marrelliplex, Weber 40 dcoe32,

36 degrees advance

130, 200, F9, 50F8

it's the transition area, it will sputter & pop until you get through it. My gut feeling is it should be leaner; less fuel more air.

My question is what or which do you change?

What combinations work for you guys?

thanks geneo
 

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The transition is the top of the progression range and is controlled by the idle jet. In my experience it is often the leanest condition. If the rest of the low rpm is good then I would try 55F11 idle jets. They will give a similar mixture strength as the 55F8's but they will be able to provide more of it.
 

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With Webers, a good band-aid is to go fat on ther idle. No harm there, and it may mask the transition. Good suggestion.
 

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Discussion Starter #4
installed the 55F8's and transition is better, nice in fact. But low speed, coming off the line, parking lot first and second gear is very lopie, hesitant, stumble.

Are we into idle adjustment here or going the wrong way on idle jets?

I sure am open to trying some other suggestions.

thanks for the help so far.

geneo
 

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If you change the idle jets you usually have to adjust the idle mixture screws.
 

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Is this at idle, or whilst driving.
At idle but it will affect the pickup from closed throttle.
 

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Discussion Starter #8
I've been driving on the 55F8's now for a few days and I've adjusted the idle screws. they are out about 2/3 to 3/4 of a turn. where they used to be in the old days of good gas. I failed to mention that I only have 10% ethanol gas available to me in this area. according to redline that effects weber tuning.

all of the above said, the drivability is worse with the 55F8 over the 50F8. Heavy bucking, choking when asked for torque down low, wants to live up higher.

now where do I go? what is the next jet size in the other direction from 50F8? I'd like to try it, and maybe I have it.

thanks all, keep throwing suggestions this way,

geneo
 

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But Mad North-Northwest
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Well, both 50F11 and 45F8 would be leaner. My experience going from 50F8 to both of those was that 50F11 was too lean and wouldn't even idle, 45F8 would.

Geneo, might definitely be worth finding somebody with an exhaust gas monitor to see what's going on before buying more jets. From your description it *sounds* like you may be going lean on the transition with the 50F8 and too rich at the low end with 55F8, so not clear that leaner idle jets are the way to go. But without the car in front of me I'm just guessing.

I gotta go check my tuning notes, but IIRC I had a better transition with the F16 emulsion tubes vs F9. From all the stuff I read online F16 and F9 are supposed to be pretty equivalent and e-tube changes are supposed to have very subtle effects, but it made a noticeable difference for me.

But let me check my notes and get back to you: I may be getting that backwards.
 

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F-16 E tubes are a bit easier to work with in many "unknown" set-up's. Eventually others might be better, but the 16's are preferred by many as a starting point.
 

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Discussion Starter #12
thanks everyone for being on top of this. I have in-house some jets from years of messing around and rejetting when I take the car to 7000' for summer.

I have 50f8,55f17,55f8,45f8
200,220,180
F4,f9,f16
122,130,135,140

so based on the input so far; I'll go F9&45F8, then F16&50F8, then F16&55F8 and report back!

any other comments before the games begin?

thanks again geneo
 

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But Mad North-Northwest
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any other comments before the games begin?
Yeah, best advice I ever got on Webers: get 'em to 90% good, then stop messing with them! :D

You'll drive yourself nuts trying to get the extra 10%, and they'll never, ever be perfect in all conditions anyway.
 

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Yeah, best advice I ever got on Webers: get 'em to 90% good, then stop messing with them!
I thought that I had my Webers set up well before I went to the dyno last year - I hade been tuning them for a couple of years. Then minor changes resulted in a 7 HP gain. I now know from extensive experimentation with jets and a wideband AFR that one size of main jet can change the 30mph to 70mph time by 0.5 second. I only stop messing with them when I know that they are as good as I can get them. Maybe I am a perfectionist?
 

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I thought that I had my Webers set up well before I went to the dyno last year - I hade been tuning them for a couple of years. Then minor changes resulted in a 7 HP gain. I now know from extensive experimentation with jets and a wideband AFR that one size of main jet can change the 30mph to 70mph time by 0.5 second. I only stop messing with them when I know that they are as good as I can get them. Maybe I am a perfectionist?
You are an engineer after all ?
 

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But Mad North-Northwest
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Hey, on a race car, go for it. On a street car your d-mn AFR is going to vary enough with day, temp, pressure, altitude, moon phase, etc. that at some point you're just playing in the noise.

The second best Weber advice I got was that once you have them tuned, take the AFR meter off the car or you'll drive yourself nuts. That's straight from Wes Ingram and Tom Sahines, and by God they were right.
 

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any other comments before the games begin?
Yes.
Change only ONE item at a time. If two or more items are changed at the same time, nothing will be learned as to which item(s) effected a change (if there even is a change; multiple changes may offset each other).
 

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The second best Weber advice I got was that once you have them tuned, take the AFR meter off the car or you'll drive yourself nuts. That's straight from Wes Ingram and Tom Sahines, and by God they were right.
Until you change the exhaust, the air intake, the cam timing, all of which change the AFR and will probably require jet changes to get the most from them. I have documented that pretty well in another thread.
 

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Discussion Starter #20
it's been over a week now, with some short grocery store runs as well as a couple hour+ runs since I installed the 44F8 jets. Very driveable, pulls well from down low in 2nd & 3rd. No need for anymore changes; unless, like me, you aren't convinced you've yet reached the limit/ultimate!

my next test will be F16&50F8.

need to order 50F11
 
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