Carburetor Experteeeze Pleeezzze

[davidathans]

My car stalled on me three times on the way to Cal State Northridge today.
I believe the problem to be carburetor related and i will list the symptoms.
The last time the car was dyno tuned, where the carburetor was looked at was in Jan. of 2005 by Bob Jennings.

Since then, i have noticed a change in the way my motor operates:
1. The idle used to sit still at 1000rpms in Park or Neutral and about 850rpm in gear at idle, once warmed up.
NOW: The idle in Park/Neutral does funny things. I HAVE NOT TAMPERED WITH THE IDLE ADJUSTMENT. I HAVE NOT TOUCHED THE CARBURETOR.
When the car is still cold, the neutral/park idle is where it should be at about 1000rpm, but when the car is hot, once in pull into a parking spot and put the car in park...this is what happens: The rpms will go right to 1000 and then start to rise...sometimes it rises to 1300rpms sometimes as high as 1700rpms. So what tends to happen when i shut the car off, when the idle is high, the engine tries to fire a couple more times with the motor off, so it makes a really nasty sound. What i typically do to avoid this is shut the car off while its still in gear.
ANY IDEAS WHAT IS HAPPENING? IS SOMETHING STICKING OR BROKEN?

HOW OFTEN DO THE GUYS ON THIS WEBSITE PULL THEIR CARBURETOR OFF THE CAR AND CLEAN IT? WHAT IS RECOMMENDED?

2. When the car dies on me, its typically right when i hit the gas at some random point in time, cruizing at like 35 in 1:1 gear. Not giving it a lot of gas, its like instantly right when i touch the pedal. This also happened to me when i was stopped at a red light, right when the light turned green and i took my foot off the brake pedal and touched the gas pedal it just died. And it happened again in a parking lot, rolling along at like 5mph.

3. Once it dies, it doesnt want to start for a while. It took me 5 minutes at an intersection to start the car. I waived people around me and sat through 2 or 3 green lights. EMBARRASING and DANGEROUS. I have tried all sorts of things to make it start:
a)just turn the key, no gas...i hear the starter and ignition trying to get it to fire, but it gets really stubborn.
b)give it a little gas and try to start it shortly after...typically doesnt work, it might have worked on one occation today.
c)Turn the key and tap the gas while its trying to start...this is how it get the car to actually start again, but it will never work the 1st time, 2nd time...after like 6 tries of trying Not giving any gas, and giving some gas, and then giving gas while trying to start...it started. The car actually backfired before it started on 2 occations. When i started it on one occation, it died immediately again when i tried to hit the gas to keep it from dying.

THIS IS MY BEST ATTEMPT TO DESCRIBE THE PROBLEMS IM HAVING. What i need to do is pick up a book on carburetors, specifically the one for the HOLLEY Street Avenger 670cfm Vacuum Secondaries and learn how these things work.

Any immediate reactions from anyone on what could be causing the problem?
I need to know that when i hit the gas to make a quick left turn that the car wont just die and get hit by an oncoming car in the intersection.

Thanks all,
David Athans

 

[davidathans]

Another thing:
A racer once told me that if your Tach needle sits really still when the car is on, even with a big cam, that the car is tuned pretty good. I have been watching my car idle and i must say that the tach needle doesnt sit still. When the car is warm and in gear, the needle will fluctuate between 800rpm and 900rpm and you can just hear the sound of the motor varying ever so slightly. Even in Netural the tachometer needle fluctuates.
Another thing about the idle i forgot to mention:
When the car is behaving...i'll start it without touching the gas pedal and the rpms will be right at 1000...isnt it correct to assume that if something isnt wrong with the tuning, that when you hit the gas and the engine revs and then falls back, that it would fall back down to 1000rpms?? well what happens is the rpms wont fall back to 1000rpms, but to like 1400rpms.
When i put the car in gear and then put it back into neutral, the rpms go to 1000rpms and then slowly rise. There is a noticeable delay in the time it takes for the engine to reach a "stable" idle in neutral.
What could have caused the idle to change from idling at 1000rpm in neutral ALWAYS and 800rpms in gear ...to 1500rpm in neutral and fluctuating without tampering with the idle screw or anything else on the car??????

thanks again for your help and time

 

[davidathans]

Is it true about what the racer told me: Should the rpms of the engine sit still or vary if you dont have a stock cam?

 

[PFSlim]

David

Since you race and need the horsepower, I would recommend you have a professional look at your carb. We had a guy build ours and I can adjust on it alittle, but if I was racing like you are, I would go professional. I sure don't have the expertise you need for a fast car!!!

Just my opinion.

Paul

 

[PNewitt]

When I lived in San Diego years ago, I had to learn how to rebuild my own Holley (600).

It seems that under a load that it stalls. At Idle it surges, and takes off.

Since you drag race, something with your accelerator pump, vacuum leak, and/or the throttle linkage must be wrong--or overused. But, before you pull it all apart...

Look for:

1. Is the ignition OK? No fried points, etc?

2. Is there a vacuum leak? I had one in the throttle body at the shaft from years of use. Check all other hoses, etc. It might be a vacuum hose, not the carb. A carb will idle "OK", but under load drop off and "die", if there is a vacuum leak.

3. Bad metering blocks, bad gaskets in the Holley, or at the intake.

4. Bad gas? How is the filter? Is it on the Holley, or in line?

See if any of these might help. Sorry to hear about this. It's happened to me several times over the years...been there, done that!

Paul N.

 

[Mustanger]

Dave,

If you need a professional to look at it, I highly would recommend Performance Associates in San Dimas. They've been around a long time and they are experts in drag racing and in Mustangs (they were started by Les Ritchie, and he raced with, and also built, Gas Ronda's AFX Mustangs back in the '60's). The shop is now being run by Randy Ritchie (Les' son), and he works "magic" with "old" stuff AND the "new" stuff ...

If interested, let me know and I can put you in touch with them... they build some awesome cars!!!

 

[PNewitt]

Did Les race at Pomona in the 60's?

I have a "nodular 9" rear end invented" story to tell....and I think it was a AFX Mustang that was used to do it.

Paul N.

 

[Mustanger]

Did Les race at Pomona in the 60's?

I have a "nodular 9" rear end invented" story to tell....and I think it was a AFX Mustang that was used to do it.

Paul N.

Yes, Les along with Gas, were sponsored by Ford and raced AFX Mustangs (predecessor to Funny Cars) and Galaxies, at Pomona in the '60's. Unfortunately, Les died in a racing accident. But Gas is still around ... in fact, I was at the shop a few weeks ago and he dropped by to see Randy and his crew, unfortunately I wasn't able to stay to see him, but I'm told Gas comes by once in awhile ...

 

[rvrtrash]

David, check all the things Paul N. mentioned but after that you're probably going to need a carb. rebuild. I had the same thing happen to me on with a Motorcraft 735 CFM on my '72 Mach 1 decades ago. Turned out the carb was just worn out and was leaking gas into the intake. If you pulled the air cleaner and looked in the carb after it had sat a little while, you could actually see gas puddled up on the floor of the intake. Extra gas causes the engine to vary speed and sometimes flood. If you're running a high volume pump, you might be forcing the float open and need to install a fuel pressure regulator. Hope this helps. Just some more things to consider.
Steve

 

[davidathans]

Thank you all for your help. Im definitely going to have a professional look at it. That professional is Bob Jennings, he has a shop in north hills with a dynamometer. I think it would be a good idea to toe the car there, that way no accident occurs do to the problem. Im going to learn from him about carburetors while he fixes it. Thanks again!!
Paul:
The ignition is ok im sure of it.
I think the vacuum leak sounds like a suspect, because i had this problem like this before and it turned out that part of the intake manifold gasket had been sucked in so there was a leak.
As far as gas goes...i have only used CA Chevron 91...isnt it supposed to be the best out of the rest?
The fuel filter was replaced less than 3000 miles ago im sure...it is inline after the mechanical fuel pump.

To avoid problems like this: HOW OFTEN DO THE PEOPLE ON THIS WEBSITE PULL OFF THEIR CARB AND INSPECT IT, CLEAN IT, MAINTAIN IT? WHAT IS THE RECOMMENDED FREQUENCY...SOMETHING LIKE EVERY 6 MONTHS OR ONCE A YEAR?? Cuz like i said the carb hasnt been touced in 14 months.

 

[rvrtrash]

Sorry I missed the second part of your question. Keep in mind the weather here is different than what you have-6 months of every year my cars sit in a heated garage under covers. Every fall I fill my tanks and add Stabil, a fuel stabilizer. In the spring, I fire the cars up and check for leaks. About every 4-5 years I pull the carbs apart, clean them and put in new gaskets. It's worked for me so far. Your carb shouldn't have worn out in 14 months. I'll also answer your tach needle question. The tach needle works off inductance so minor variations are dampened but 100 rpm variances will show up. Also, this may sound odd but your tach isn't measuring engine rpm directly. It's measuring the frequency of the pulses of your coil. As the engine changes rpm, the distributor discharges the coil at different rates which the tach reads. What I'm getting at is that a worn out distributor, cracked coil that's discharging to ground, bad tach or wiring, or other factors may cause your tach to fluctuate. Hope I didn't oversimplify, insult or confuse you. Just trying to help out.
Steve

 

[bbeatty]

To avoid problems like this: HOW OFTEN DO THE PEOPLE ON THIS WEBSITE PULL OFF THEIR CARB AND INSPECT IT, CLEAN IT, MAINTAIN IT? WHAT IS THE RECOMMENDED FREQUENCY...SOMETHING LIKE EVERY 6 MONTHS OR ONCE A YEAR?? Cuz like i said the carb hasnt been touced in 14 months.

I have 64.5 convertible I bought in 1979. I still haven't touched the carb and it is still one of the smoothest engines I've ever had. In fact I'm afraid to pull carb because I might mess something up! :scared:

 

[bbeatty]

I forgot to throw in my 2 cent diagnosis on my earlier post.

I’ll go with the general direction of a few of the others, I don’t think this is a carb problem but rather an electrical one. If you’re sure the timing is good, I’d look for loose wiring and then I‘d swap out a few of the electrical components, starting with the coil. Even if some of this stuff is brand new doesn’t mean it’s good. :frust:

 

[admin]

Also, this may sound odd but your tach isn't measuring engine rpm directly. It's measuring the frequency of the pulses of your coil. As the engine changes rpm, the distributor discharges the coil at different rates which the tach reads. What I'm getting at is that a worn out distributor, cracked coil that's discharging to ground, bad tach or wiring, or other factors may cause your tach to fluctuate.

So David, do you actually feel the engine reving higher, or is it just the tach you're reading? That should help narrow that part down at least.

 

[Mosesatm]

David, the carb has a modulator on it that lets it gradually go back down to idle speed. I can't remember if it's spring loaded or run off the vacuum. It can't be causing all of your problems but there might be more than just one thing going on. Anyway you might want to check that. Remember, always fix the simple, cheap stuff first.

 

[davidathans]

Thanks all again for the comments. The electrical is fine, its a full MSD ignition system that i installed myself...i know for sure its the carb. Bob Jennings consideres the Holley Street Avenger a piece of crap. "its only good for a doorstop"...he recommended the model number 4150, part no 0-4779C which is the Holley 750cfm double pumper with mechanical secondaries. so i bought it today at PAW for $436.xx...he's going to modify it and retune the car and the plugs have 10000 miles on them, so we're changin those too they are autolite 3924s. I cant wait to see what a difference mechanical secondaries will make. Hopefully the car will make more power too. Im most likely going to try and sell the street avenger on ebay...someone with a low budget can buy it and rebuild it. I'll let you guys know what kind of difference the 750cfm carb makes in terms of Horsepower, torque, and overall feeling. Im excited!

 

[Mustanger]

Thanks all again for the comments. The electrical is fine, its a full MSD ignition system that i installed myself...i know for sure its the carb. Bob Jennings consideres the Holley Street Avenger a piece of crap. "its only good for a doorstop"...he recommended the model number 4150, part no 0-4779C which is the Holley 750cfm double pumper with mechanical secondaries. so i bought it today at PAW for $436.xx...he's going to modify it and retune the car and the plugs have 10000 miles on them, so we're changin those too they are autolite 3924s. I cant wait to see what a difference mechanical secondaries will make. Hopefully the car will make more power too. Im most likely going to try and sell the street avenger on ebay...someone with a low budget can buy it and rebuild it. I'll let you guys know what kind of difference the 750cfm carb makes in terms of Horsepower, torque, and overall feeling. Im excited!

4150's are good carbs, they look period correct also ... I personally favor regular Holleys that are "dialed-in" myself ... let us know the results!!!