Carb help

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zigs

zigs

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I have a 470 with Hughes cam .540/547
Edelbrock EStreet heads 373 gears soon to be 323 , Edelbrock TM6 intake with Edelbrok 750 carb. I don't have all the specs in front of me but to give you an idea . The engine idles fine but around 30-40 mph starts to cavitate . I'm thinking not enough carb. I know this has been a problem in other 470 builds . I can provide more info when I get home. What's your thoughts for now.
 
By "Cavitate", are you talking about pinging. What is your compression and timing? What are you running for fuel. Kind of sounds like too much timing and you are getting pre-detonation.
 
Frnknsteen said:
By "Cavitate", are you talking about pinging. What is your , compression and timing? What are you running for fuel. Kind of sounds like too much timing and you are getting pre-detonation.
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Its hard to explain kinda like forceing it to go
Compression is 10/1 , I believe timing is at 34* no pinging and 91 octane
 
What does it do when you get on it, or are running above 30-40? Does it just do it when you are cruising or when you try to accelerate without stomping it or getting the transmission to kick down? Does it do it at low rpm's? High rpms? steady rpm's?

I don't claim to be an expert on anything, so please take anything I say as just a point of reference, and something to look into. That being said,... I have been doing a ton of reading as I get ready to build the motor for my Charger. I have heard of others having issues running 10:1 on today's crappy gas. I was talking with the guy who is building the 440 for my Charger, and he recommended not going over 9.25:1 or 9.5:1 if I am planning to run on pump gas.

It if it is an issue of not having enough carb, I would expect to be running lean. Have you pulled your plugs to see if it looks like you are running lean?

Is it possible that it just doesn't like the 91 octane with the 10:1 compression you are running? Have you tried running 93 octane premium, or adding some octane boost to see if it gets better?
 
My opinion of the "cavitate feeling". I believe the engine is running lean, as Frnknsteen noted. Another possibility is too much timing, either attributable to the vacuum advance and mechanical advance. If the carb is just open slightly, it is possible that the carbs transition circuit is to blame. As said previously, look at the spark plugs to get an idea how the engine is running. Paper white center electrode insulator indicates a lean condition. If so, try increasing the primary one step richer. Or increase the carb's fuel kevel slightly, giving the effect of increasing (richening) the fuel mixture. Disconnect the vacuum advance and see the effect. Another possibility is there is too much cam overlap allowing exhaust gas dilution of the incoming fuel charge making it harder to ignite promoting a miss fire condition and a stumbling feeling....especially in the range noted. I'm sure others will have their own opinions and advice.
Bob Renton
 
RJRENTON said:
My opinion of the "cavitate feeling". I believe the engine is running lean, as Frnknsteen noted. Another possibility is too much timing, either attributable to the vacuum advance and mechanical advance. If the carb is just open slightly, it is possible that the carbs transition circuit is to blame. As said previously, look at the spark plugs to get an idea how the engine is running. Paper white center electrode insulator indicates a lean condition. If so, try increasing the primary one step richer. Or increase the carb's fuel kevel slightly, giving the effect of increasing (richening) the fuel mixture. Disconnect the vacuum advance and see the effect. Another possibility is there is too much cam overlap allowing exhaust gas dilution of the incoming fuel charge making it harder to ignite promoting a miss fire condition and a stumbling feeling....especially in the range noted. I'm sure others will have their own opinions and advice.
Bob Renton
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I take everything with a grain of salt but
all imput is fuel for thought. I will be taking it out this after noon when I get home. I will try
a video. Also I will be retiming it.
 
zigs said:
I take everything with a grain of salt but
all imput is fuel for thought. I will be taking it out this after noon when I get home. I will try
a video. Also I will be retiming it.
Click to expand...
To answer the other question everything's fine through 1-2nd get to about 30 or so is when it starts. I can nail it and it doesn't do it
but when I do punch it , its sluggish 500+ HP I should be going sideways.
 
I think your (cavitation) Sound's like a lean surge, Is it a DP or vacuum secondary's?
 
The secondary's are opening to soon, needs a different spring, it's to lean, go up a couple jet sizes, and check the squirter nozzle, go with a larger number, and a pink cam.

also cruise down the road with a vacuum gauge tapped to the windshield and see what the vacuum is.
 
Get back to basics. Did you check fuel filter, fuel pump and fuel tank. Any of these been checked? Could be running out of fuel. I had trouble with junk in the tank clogging fuel filter and had to replace tank to remedy that problem. I thought it was fuel pump at first, but when I saw junk in filter knew it was the tank.
 
tonysrt said:
Get back to basics. Did you check fuel filter, fuel pump and fuel tank. Any of these been checked? Could be running out of fuel. I had trouble with junk in the tank clogging fuel filter and had to replace tank to remedy that problem. I thought it was fuel pump at first, but when I saw junk in filter knew it was the tank.
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New tank , electric fuel pump see through filter. Doesn't hurt to check
 
zigs said:
New tank , electric fuel pump see through filter. Doesn't hurt to check
Click to expand...

You are too lean at cruise. That is why Chrysler’s had 3 step rods, from 273’s through 440’s. Perfect at idle, off idle and WOT. But lean at cruising speed. You can try and get it with springs or fatten up the idle, but now you are too rich at idle. Or you can get some extra rods and “modify” them with sand paper or very carefully on a grinder. I’ve heard about your problem too many times from people who know what they are talking about, some of whom where using an A/F meter in the car while driving.
 
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I guess I missed the edelbrock part, so not vacuum secondary's
So disregard what I said
 
Is that like a [email protected] on a 110
Aluminum heads?
In Post one; where are the throttle valves when this begins?
Is this at WOT, part-throttle, cruizing, where?
Is it related to a particular rpm, or just to throttle input?
Does it get worse in each successive gear?
Does it go away immediately if you back off the throttle just a bit?
Put a vacuum gauge on it, in the cab, or on the windshield where you can see it while driving, then go for a roadtest, keeping an eye on the gauge. Is the issue related to a particular vacuum level?
Are you running a Vacuum Advance?
 
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AJ/FormS said:
Is that like a [email protected] on a 110
Aluminum heads?
In Post one; where are the throttle valves when this begins?
Is this at WOT, part-throttle, cruizing, where?
Is it related to a particular rpm, or just to throttle input?
Does it get worse in each successive gear?
Does it go away immediately if you back off the throttle just a bit?
Put a vacuum gauge on it, in the cab, or on the windshield where you can see it while driving, then go for a roadtest, keeping an eye on the gauge. Is the issue related to a particular vacuum level?
Are you running a Vacuum Advance?
Click to expand...
AJ/FormS said:
Is that like a [email protected] on a 110
Aluminum heads?
In Post one; where are the throttle valves when this begins?
Is this at WOT, part-throttle, cruizing, where?
Is it related to a particular rpm, or just to throttle input?
Does it get worse in each successive gear?
Does it go away immediately if you back off the throttle just a bit?
Put a vacuum gauge on it, in the cab, or on the windshield where you can see it while driving, then go for a roadtest, keeping an eye on the gauge. Is the issue related to a particular vacuum level?
Are you running a Vacuum Advance?
Click to expand...


I was hoping you'd chime in but think I got it figured out. Took Tonysrt advise and went back to basics . The carb is a rebuilt. the fuel/air sets don't really do anything at least not to feel any fade or rise , so I pulled the filter blew it out ,then the fuel intake port then pulled the mixer screws and blew a little air in the ports put it back together
started it up and took her for a spin. It was like night and day. Dirty carb.
The things on its way out. I took a video but can't seem to transfer it.
 
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What comes after you started it up? Did you fix it or still groping for answers?
 
tonysrt said:
What comes after you started it up? Did you fix it or still groping for answers?
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Sorry was trying to transfer video but not working . Yes started it up made some adjustments took it around my three mile run , it made a big difference.
As I said it was a used rebuilt , must of had some dirt in it. I'm thinking its on its last leg . Thanks for everyones help
 
My Holley 750DP is circa 1970, and it still works great! To be fair, it hasn't been in service for every one of those years, but maybe half? I regasketed it a couple of times, tho.
 
AJ/FormS said:
My Holley 750DP is circa 1970, and it still works great! To be fair, it hasn't been in service for every one of those years, but maybe half? I regasketed it a couple of times, tho.
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You can't beat Holleys love'm or hate them.
Edelbrok are good out of the box but I don't think they rebuild as well as Holley but I've
Always had good luck with them new.
 
I've run all the popular stuff from the 70s, all my stuff is old and well used . Like the old TQ I run on my 318 pick-up. It's probably circa early 70s. I also have AVSs, and AFBs from that era, but most haven't been installed for 20 years.......or more.The point is, I can make almost anything run, if you're not looking for perfect AFRs. And run well by the way. That's not a brag, that's just matter of fact. If you put one of these carbs on a tiny-cam engine, it might run a tad off, but once you get to a 220 cam,in a hi-compression engine she is desperate for air anyway, and a lil leakage here or there is easy to cover up.

BTW, the only combo I ever had that mighta bin able to use a 4-corner idle, was that brutish 292-292-108 Mopar cam, in at 11.3Scr(aluminum heads). But I found a work-around. The other two cams; 223, and 230, @.050s are happy with the secondaries slammed shut but not sticking. Altho, I mighta drilled a couple of very small holes in the primary blades (one in each) for this 230cam I have now; I can't recall exactly. This is usually done to drop the T-valves back into sync with the T-ports. Yeah the more I think about it, I think I mighta done that.IDK, that carb has been off and on dozens of times.......to get it just perfect,lol.
 
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