AFB's: Stutters on acceleration

[Chryco Psycho]

this might be a big help also , no thicker than a carb gasket
http://www.coolcarb.com/

[HP_Cuda]

Very interesting, wonder what the plate is made of.

Btw, Mike what is your vacuum at idle?

Fun (Holley) read which may give you some ideas:
http://www.hotrod.com/how-to/engine/116-0508-carburetor-showdown/

[Topcat]

Btw, Mike what is your vacuum at idle?

I need to re check it. Good idea.
Too damn hot out this week-end.

[Chryco Psycho]

we can work through a lot of the basics & probably get a lot closer , so I would start with bumping up the timing at idle a little & shorten the advance curve this works very well with longer duration cams , then check you vacuum at idle  , , raise the float level 1/16 " & downjet a step or two & see what happens , if this helps we can look at inserting wire into the bleeds & restricting them .

[Topcat]

I feel you could use more initial timing closer to 16* with 34 total as well , so if the plugs are fouling you need either a hotter plug or less fuel to clean it up

What plug gap 40 or 45 and plug brand/p/n do you recommend?

That might be a good start to try out.

[Chryco Psycho]

Plug gap should be no more than .045 , more puts too much load on the plug wires .
 I really have no recommendation on brand , whatever brand you want to have access to various heat ranges , so with Champion you want to have access to 10,12,14,16 etc , Autolite should have similar ranges available , same with NGK which I have always had issues when I use them , Accel & others , whatever brand you can get the different heat ranges in .
 Others may have better recommendations

[Bullitt-]

Read about this in HRM tuning a 6-pack & it might be worth considering in your case... They made block off plates to cover  the outboard carb openings & tuned just the center carb for idle & off idle acceleration, once that was sorted they reinstalled the outbards to deal with the rest of the tune.

[Topcat]

I let Roger at RST automotive go tru my engine and carbs.

Carbs re built.

Exhaust valve clearance from .019 to now at .016.

Primary rear carb: #98 jets #73-60 needles
Black springs

Secondary front carb: #102 jets 70-48 needles
Black springs
Timimg: 36 total And I believe 25 initial.

Plugs replaced RN12YC .040 gap

I took her out today and it's insane power now. Way better.
Added a mix of 101 octane and 94 octane 50/50 mixture.

No more plugs fouling and stutter is gone but she is alot more thirsty now.

[jordan]

I have a FBO distributor.  My settings were not as the spec sheets said.  My spring rates were wrong for my motor and had idle problems because the springs bounced around at idle.  It may not be your problem, but its hard to set up carbs if the timing is off.  My bud made a graft of the rpm and the timing as it advanced with rpm.  It may show that your timing is advancing too fast or too slow.  Im no expert as I have struggled setting up my distributor and my 6bbl set up too.  I keep getting closer with every adjustment.  I have an advance timing light on the way to make more precise changes in timing.  I just keep asking questions and learn as I go.  Keep plugging away at it. 

[Topcat]

It fires right up and holds a steady idle after a 2 minute 2K warm up.
Roger said it's at 12% C02 under load which is pretty good for being carb'd.

https://youtu.be/P4uEkOjisWg

[HP_Cuda]

Mike

You know that the black springs are the heaviest spring you can use? Actually I thought you were talking about Holley carbs but the AFB black springs are rated for 10" of vacuum so you probably will do well with this.

Did you find out how much vacuum you have with your setup? I just found out I have around 13" and I think i can squeak out 14"+ so I don't have to worry about my power brakes.

B

[Topcat]

Mike

You know that the black springs are the heaviest spring you can use? Actually I thought you were talking about Holley carbs but the AFB black springs are rated for 10" of vacuum so you probably will do well with this.

Did you find out how much vacuum you have with your setup? I just found out I have around 13" and I think i can squeak out 14"+ so I don't have to worry about my power brakes.

B

Good question on the springs. I'll have to go ask Roger why he went with the black one's.
Perhaps because it's stroked and pulls more air?

Vacuum seems really good probably 13". You can hardly tell it's a duration cam.

After you get your engine broken in, why don't you join us on a Gilroy run.

[HP_Cuda]

Sounds good, once I get my seats done then I should be able to tear it up.

I don't think I want to sit on a milk crate with this much power...

Good question on the springs. I'll have to go ask Roger why he went with the black one's.
Perhaps because it's stroked and pulls more air?

Vacuum seems really good probably 13". You can hardly tell it's a duration cam.

After you get your engine broken in, why don't you join us on a Gilroy run.

[Topcat]

Roger said today the vacuum is at 17" at idle.
Black springs are used to keep the needles from falling in too quick blocking fuel going in on acceleration.

It's working so I'll leave them in.

[HP_Cuda]

Holy cow 17" at idle!!!

That's pretty impressive.