How much RPM drop from park to drive with stock type 340 convertor

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Bear in mind that some old carbs actually adjusted idle speed with an air leak. The old AFBs some models (I don't think Mopar?) had a great big screw in the middle between the two idle mixture screws. This set idle speed. EFI works the same way. The IAC (Idle Air Control) sets idle by leaking more or less air into the intake. The EFI corrects the mixture and ...........it........idles

Here's one now.........GM application Notice there IS NO mechanical idle speed screw on the throttle lever

carter.jpg
 
MoPar has a similar carb with the third screw up top in the center. It was an air bleed IIRC.
 
Mix of terminology...
I knew what the Transfer Slot is but how does the word 'sync' apply ?
Isn't the transfer slot part of the 'off idle' circuit and feed air from the 'air bleeds' ?

I also know with a '4 speed cam' you don't need to drill the primary butterfly... but .. when do you need to drill that 'bleed hole'?
Can only assume it is needed with long duration 'full race' cams.

I'm running a 340, loose convertor, with 484 Hyd Purple (3/4 race ..lol) and a Holley 750 DP 2 port idle adjust ... and don't have or seem to need the drilled butterflies.

So when do you need to drill the butterflies ?
Can't the original poster also use a vacuum gauge to see if it drops off too much when dropping it in gear which then disrupts the idle fuel/air mixture. ?
 
Buy a 3500 no less then 3000. and you be happier then a pig in ****. End of story. Don't listen to any other bullshit.

Just had a motor here built and dynoed by a member on this sight. What a disaster. And after all the comments and advise on this site by many praising his work. I actually thought he knew what he was talking about. Then I find out that he was Ryan's partner. Or is it Ryan in hiding.

This motor he built is not that impressive . I feel sorry for my friend. Shouldn't have sent it out there. Like Ryan, The pictures are not who he really is. Couple more motors like this one and he'll cut off his own head. I never heard more noises from a motor in my life..

This motor definitely has a RPM maximum before it explodes. You can here its begging to come apart.

All I can say is some people only know what books tell them. I learned from seat of the pants trial and error. Lots of errors in 50 years but at only costs to myself. Race motors do not have a Guarantee . Many shops take that to their own advantage and install their junk in place of parts you are charged or paid for. Ryan did it to me.

Remember I told you 3500 tight... Get in a good stock 340 car that you know has the factory converter and do a brake stall test. Don't listen to the people who heard it from a friend who heard it from someone who heard it from their friend that knows a guy who knows someone that knows.

 
Lots of good info, and some things for me to check, thanks to all! I'll answer some questions and provide more info. Stock 1970 AVS carb with 2 idle mixture screws and the idle screw on the shaft. Timing is at 14 in park, I'll ck it in gear as mentioned. Transfer slot is currently set at square. I'll open it up a bit and back timing down to set idle rpm and see what happens as mentioned. Mixture screws are open quite a bit, its what it wanted. I actually feel the stock jetting is lean, If I had a old strip kit I'd probably fatten it up a bit. Float level has been checked. Vacuum is 14 in park, Ill ck in gear. Idle speed in park is 975, drops to about 650 in D. I'll do some work and report back.
 
Oldmanmopar said:
Buy a 3500 no less then 3000. and you be happier then a pig in ****. End of story. Don't listen to any other bullshit.

Just had a motor here built and dynoed by a member on this sight. What a disaster. And after all the comments and advise on this site by many praising his work. I actually thought he knew what he was talking about. Then I find out that he was Ryan's partner. Or is it Ryan in hiding.

This motor he built is not that impressive . I feel sorry for my friend. Shouldn't have sent it out there. Like Ryan, The pictures are not who he really is. Couple more motors like this one and he'll cut off his own head. I never heard more noises from a motor in my life..

This motor definitely has a RPM maximum before it explodes. You can here its begging to come apart.

All I can say is some people only know what books tell them. I learned from seat of the pants trial and error. Lots of errors in 50 years but at only costs to myself. Race motors do not have a Guarantee . Many shops take that to their own advantage and install their junk in place of parts you are charged or paid for. Ryan did it to me.

Remember I told you 3500 tight... Get in a good stock 340 car that you know has the factory converter and do a brake stall test. Don't listen to the people who heard it from a friend who heard it from someone who heard it from their friend that knows a guy who knows someone that knows.

[/QUOTE
I'm going to try maximize my tune as suggested, any improvements will be a plus either way. I do feel the car will wake up with a 3500 though.
Click to expand...
 
70 Buster 340 said:
Mix of terminology...
I knew what the Transfer Slot is but how does the word 'sync' apply ?
Isn't the transfer slot part of the 'off idle' circuit and feed air from the 'air bleeds' ?

I also know with a '4 speed cam' you don't need to drill the primary butterfly... but .. when do you need to drill that 'bleed hole'?
Can only assume it is needed with long duration 'full race' cams.

I'm running a 340, loose convertor, with 484 Hyd Purple (3/4 race ..lol) and a Holley 750 DP 2 port idle adjust ... and don't have or seem to need the drilled butterflies.

So when do you need to drill the butterflies ?
Click to expand...
AFAIK 'sync' is AJ's term.
Yes the transfer slot provides most of the fuel in 'off-idle' but also low speed cruise.
As far as being a part of the 'off-idle' circuit yes and no; it's an intergral part of the idle circuit. It shares the fuel in ht eidle down well with the idle port.

Drilling butterflies is what was done when the throttle position at idle is too far open. Drilling allows the throttles to be closed further with the same amount of air as if htey were further open. Holley even supplied some carbs from the factory with holes in throttle plates.
On an old school Holley 4150/60, greater than .040" of transfer slot exposure at slow idle would generally cause problems as the throttle was opened.
The sidebar Urich and Fisher's Holley Carburetors and Manifolds covers proper throttle to transition slot relationship. (pp. 121-2 in the 1987 edition [Holley Part No. 36-73, HP Books])
The section is called Special Procedures for Wild Camshafts
I've linked it above but the links to copyright material are often temporary.

Chrysler also explained the carburation circuits in several Master technician's reference booklets. Although the general ones are more oriented toward Carters, there's a lot of overlap with Holleys.
Master Technician Service Conference - Chrysler's Training for Mechanics
Go to the pre-emissions Carburetor Fundementals from 1966 to start with.
The one from 1970 covers a few of the differences on the Holleys along with some of the emissions related changes (such as leaner idle mixture and controls).

Can't the original poster also use a vacuum gauge to see if it drops off too much when dropping it in gear which then disrupts the idle fuel/air mixture. ?
Click to expand...
Yes. especially if using a tach thats hard to read rpm drops finer than 250 or 200.
 
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340doc said:
Lots of good info, and some things for me to check, thanks to all! I'll answer some questions and provide more info. Stock 1970 AVS carb with 2 idle mixture screws and the idle screw on the shaft. Timing is at 14 in park, I'll ck it in gear as mentioned. Transfer slot is currently set at square. I'll open it up a bit and back timing down to set idle rpm and see what happens as mentioned. Mixture screws are open quite a bit, its what it wanted. I actually feel the stock jetting is lean, If I had a old strip kit I'd probably fatten it up a bit. Float level has been checked. Vacuum is 14 in park, Ill ck in gear. Idle speed in park is 975, drops to about 650 in D. I'll do some work and report back.
Click to expand...
Sounds like a good plan!
If you can do it safely, check timing at 650 rpm. IMO 14 at 650 rpm would be close, and Rob suggested 15* would be good.
You may find a huge diffence in timing from 975 to 650. Only way to know will be to measure.

And don't worry about the jetting/rod for now. As long as the rod/jet combo is significantly larger than the idle restrictions, it will have no effect on the idle and off-idle.
Carter idle system is a little different than the typical Holley in that it uses a second air bleed and restrictor. So general rules of thumb for a Holley about 'square' or 20-40 thous. slot exposure don't apply. However the concept is still valid: More t-slot will provide richer idle. Too much or too little will cause flat spot or delay.
 
Mattax said:
Sounds like a good plan!
If you can do it safely, check timing at 650 rpm. IMO 14 at 650 rpm would be close, and Rob suggested 15* would be good.
You may find a huge diffence in timing from 975 to 650. Only way to know will be to measure.

And don't worry about the jetting/rod for now. As long as the rod/jet combo is significantly larger than the idle restrictions, it will have no effect on the idle and off-idle.
Carter idle system is a little different than the typical Holley in that it uses a second air bleed and restrictor. So general rules of thumb for a Holley about 'square' or 20-40 thous. slot exposure don't apply. However the concept is still valid: More t-slot will provide richer idle. Too much or too little will cause flat spot or delay.
Click to expand...
Very good. I will admit my knowledge of Holleys is far better than Carters!
 
Tune the carburetor for highest vacuum in gear. The timing should be set accordingly at best determined idle rpm in gear, 14deg ?
 
I do not know why everyone insists on tuning an auto trans car in park. :lol:
 
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