josehf34

I'm running a carter AFB #9638S on my Fury's 360 and since I have the carb the idle quality hasn't been great and vacuum signal at idle is something between 14" and 16".

I recently did a valve job, inspected engine, change ignition from aftermarket ICM and distributor to a mopar ICM and distributor but the idle problem hasn't change.

When I bought the carb it came with the stock 120-398 (.98) jet and 16-695 meetering rod and I've tried with differents combinations without success.

Today replaced the main jets with 120-377 (.77) and 120-383 (.83) with differents meetering rods but the idle quality doesn't improve, but, If I start the car without meetering rods in carb the idle changes and is a lot better, smoother and I got 19" of vacuum! (never had so much vacuum with this carb), I suspect my problem is due to rich mixture at idling because If I create a vacuum leak with the meetering rods in carb the idle is great again (not much better but better than without the leak).

I don't know what else should I try, the smallest jet I have in my strip kit is a 120-371 (.71) and even with the 120-377 if I hit the throttle the engine stalls i think due to lean condition

RacerHog

OK... Will Cont. here...
The statement was made.... (For all Yall Catching up).. The newly installed carb might be lean....

Jose.... Question would be in this case.... If the 500 CFM was fine before...
What would lead us to think that the 625 would now be running lean, and why.

RacerHog

Try gassing the system with some propane and see if it shows to really be lean.....

josehf34

The original Holley 2245 wasn't right, I replaced it because was always running rich, idling through primaries and a lot of problems so I took the decision to go with 4 barrel

I think the Carter is running rich instead of lean, before start trying to get a better vacuum signal at idle if I step on throttle I'll see smoke black smoke coming from the exhaust, now I don't have the black smoke problem but the idle problem continues.

My conclusion about carb idling rich is due to the fact that the idle quality improves If I create a vacuum leak for example unplugging the vacuum line of brake booster

RacerHog

OK... But you do know that is a period correct OEM carb for like a 1977'ish 360 used in cars and trucks..... Now with that said... Was it a new carb or a used carb?

josehf34

I bought it used from ebay but I rebuilt it before install on the car.


yeah is like 156.3 CFM per barrel, 313 CFM in primaries, but if the carb is too small for this engine, wouldn't the idle go worse with a vacuum leak instead improve?

According to my calculations a mostly stock 360 like mine will require 550 CFM assuming 90% volumetric efficiency

RacerHog

Oups...I was trying to edit my post and deleted it... Rats.... Sorry...

Ok... So with the heads freshened up... How is the compression now?
And with that I need to get out of here till tomorrow and will continue...
Will find the problem...

josehf34

These were the numbers after the valve job:



When heads were pulled I didn't find any visible problem, just A LOT of carbon in valves, pistons, combustion chamber, wherever but regardless of this I request the shop to clean heads, replace seals, check guides (were ok), check valves (were ok) and do valve seat job

RacerHog

That looks good enough...
After a little thought last night..
I am not so sure you have a jetting problem at this point in time.....
I would recommend reinstalling the Proper setting Jet, Rod, spring, at this point.
Once you have that Squared back up.... I feel there is a problem in the Idling Circuit of the carb. Being the Carb is used, I think you need to pay some close attention in the Low Speed Circuit of the carb.
The info and instructions are a little long to list: But you can find them in the Federal Mogul Carters Tech Instructions on Pages 6-7 under Low Speed Circuit.

Lets see if you find the problem in this area....

RacerHog

I Did find a link to the Document....

http://www.crankshaftcoalition.com/w...rafbtuning.pdf

TVLynn

Chec to see what the setup is on the 9636 I had one on my modified 360 Built to duplicate the factory 360/360 Never had any problems. A chevy carb will never work out of the box with a Mopar

josehf34

I never did other job in the carb prior rebuild and install, what else should be done to have a chevy carb working on a mopar engine ?

red67

with AFB s and AVS s. you can NOT know what the change is if you change both jet and rod at the same time. the basic rule is change ONLY one at a time. i have long paragraph on this on the "A" body only site. i ll try to find it for you.

RacerHog

Sorry I post the wrong link.... This is the correct link..I Did correct the original post also.. Sorry for the confusion.

TVLynn

For one there is a difference in the linkage for the Kick down. I know Holley makes a special throttle lever adapter so that you get the alignment & the correct throw for the linkage The Edelbrock carb also makes an adapter Should work on the carter

Drag Pak

josehf34

Where do you have the timing advance set at? Initial, at 2000 rpm, and total?

What "Mopar" ignition are you using?(part #)

red67

this paragraph should help in tuning jets and rods. DO note to will NOT tell what to run. it will only tell you what % of change you are looking at.

This is a verson of a program I did for the Commodore computer. That my son did for PCs.
1. this program can not tell what jets to run. It can only tell you % diff of the jet you are looking at to change. When doing jets only enter .000 for all rod enterys.
2. 2. the label jet#1 , or jet#2, means the jet and the two steps on the rod.
3. The top box is for the jet number only like this .065
4. the second box is for the economy step, the largest dia of the rod. .085
5. the power step smallest dia goes in the bottom box. .075
6. test#1: jet#1 .100-----jet#2, .110 = 17.355% arrow will point to the left meaning more fuel.
7. Test#2: jet#1 .100 jet, power step .065 econo step .075 jet#2 .100 jet, power step .067 econo step .077 = 6.948% leaner arrow points to the right.
8. This will NOT say what jet to use, only what % of change. It is up to you to decide what to use.
9. All this means you CAN calculate both jet AND rod changes
10. for Carter AFBs and AVSs.
11. http://clarkehackworth.com/files/JetsAndRods.html

josehf34

My timing light is broken so I'm not sure, I set the initial advance with help of the vacuum gauge

Yesterday I rebuilt the carb (Again ), checked with pressurized air all the holes I saw and any of them are blocked. Put the original jets and rod and the maximun vacuum I got idling was 15", the idling quality wasn't great but this time If I create a vacuum leak the idle doesn't improve, just goes worse until engine stops.

Trying with different meetering rods and jets combinations reached 16" vacuum with 120-395 jets (.095) but the idle quality isn't great.

I'm going to try to borrow other carb from a friend and try with it, maybe my carter is looking for retirement

I don't know if really matters but I got the best idle quality when the mixture screws are only open between 1/2 and 3/4 of turn

RacerHog

You have to get the timing handled before you go any further....
The wrong Timing can cause your vacuum to be low..
So you could just be chasing your tail.. And there might not be anything wrong.

red67

this system has dropped my post 2 times in the last week. i cant do this any more iam gone for good NOW..

Drag Pak

(Quote post #8) When heads were pulled I didn't find any visible problem, just A LOT of carbon in valves, pistons, combustion chamber, wherever but regardless of this I request the shop to clean heads, replace seals, check guides (were ok), check valves (were ok) and do valve seat job(end Quote)


Wouldn't hurt to check the timing chain and gears for wear?

josehf34

I'm going to get a new timing light and see what I got. Should I buy a timing tape too? my damper timing mark only goes from 10 ATDC and 10 BTDC

Could be an option but this engine only has something like 800 miles since rebuild


I'm thinking about the posibility of buy a new carb, went out for a drive and the engine stalled sometimes on hills (I think due to float level), vibrations while idling and no bogging at WOT but I feel like the response could be a lot better, also the engine compartment I think was very hot for a ride of less than 20 minutes so maybe sometimes the carb is running lean

What could be a better option for a daily driver? please take in mind that I'm planning to build this engine with something like 9:1 or 9.5:1 compression ratio and want to have all performance before 6200 RPM

I have these carburetors in mind:

-http://www.summitracing.com/int/part...1901/overview/ (I like the thermoquad similar design)

-http://www.summitracing.com/int/part...555c/overview/

-http://www.summitracing.com/int/part...-650/overview/


Or maybe a Thermoquad or Quadrajet with their respective adaptor plate for being used on a square bore intake

-http://www.ebay.com/itm/1973-Mopar-C...pWbgUt&vxp=mtr

-http://www.ebay.com/itm/ROCHESTER-QU...torefresh=true

RacerHog

Get a inductive dial back timing light.... Works better.....
https://jet.com/product/detail/51c9f...VBkaAr888P8HAQ

No tape needed at this point...

Dont put the cart before the bull.... lest work with what you got at the moment...
I could work with any of those carbs....
I like to use a Holley 750 or Street Avenger 770.. But thats just me...
Or you could step over to one of the EFI systems...

josehf34

EFI would be great but is cheaper to replace the entire engine than spending 4K on an EFI set up (yes I know there are some TBI systems for less than 2K but those are still big numbers)

I'm going to look for the timing light tomorrow

josehf34

Now I'm Back again with some time to continue dealing with this problem

I got a new timing light and i've been trying to find my current engine timing with the cyl#1 but i can't see any timing Mark on damper!

I think it's well mounted because I can't feel any vibration but i don't know why i can't see the timing mark.

EDIT: i just found the timing mark, the timing was too advanced so that was the reason of not seeing it

I set the time at 14BTDC but when i rev the engine up to 1500RPM it moves to 9BTDC and at 2000 it stays bouncing between 13 and 16BTDC and if i let it idle again it doesn't stays in 14BTDC it sometimes bounces between 11BTDC and 14BTDC and also found that vacuum advance in my distributor is broken

I think my timing chain is worn or maybe bad installed, maybe when the engine was rebuilt the mechanic never changed it, am I right?

Does the distributor can cause this kind of problem too? because I'm using the original distributor but when I installed it doesn't noticed any kind of play or damage in the rotor