Classic over carburetion problem?

-
so if engine was pinging do you run high test fuel /put some octane booster in and reset engine timing and try it again /your compression could be to high/ take a compression test as others have said.
I use the pump gas 91. I haven't got a timing light or comp tester but I will. I'll look into the booster too.
 
Carb CFM in question? Put a vacuum gauge on the intake run the hose so you can see while driving at Wide Open Throttle reading should be almost Zero.
 
My suggestion is to find a mentor that is a seasoned gear head, then watch and learn.

What are "ground and drilled rods"? I've owned and fooled Mopars for 44 years and have never heard that phrase. I'm guessing the machine shop resized them.
 
My suggestion is to find a mentor that is a seasoned gear head, then watch and learn.

What are "ground and drilled rods"? I've owned and fooled Mopars for 44 years and have never heard that phrase. I'm guessing the machine shop resized them.
Not to clear..crappy camera but you can see the hole if you look up into the top of the con rod on the right. Don't get mad at me or call me an idiot this is all the shops doing for more oil and strength

 
Last edited:
Richie, not enough converter may be part of your problem, but listen to the advice on here about timing.

Before you do anything you need to find out what the amount of mechanical advance and what your total timing is. You need a nice short advance curve which will allow more initial timing, and total timing should be 34 to 36 degrees.

Once this is dialed in you can start to look at other things.

If you want some help give me a call.
 
Richie, not enough converter may be part of your problem, but listen to the advice on here about timing.

Before you do anything you need to find out what the amount of mechanical advance and what your total timing is. You need a nice short advance curve which will allow more initial timing, and total timing should be 34 to 36 degrees.

Once this is dialed in you can start to look at other things.

If you want some help give me a call.
Thanks Dave I'll think about it. The transmission still works great.
 
Thanks Dave I'll think about it. The transmission still works great.
Most stock and aftermarket distributors have waaaayyy too long of an advance curve, which means you dont have near enough initial timing resulting in a lazy low powered engine at low rpms.
 
Last edited:
Not to clear..crappy camera but you can see the hole if you look up into the top of the con rod on the right. Don't get mad at me or call me an idiot this is all the shops doing for more oil and strength



Not mad or calling anyone an idiot, just never heard the phrase. Maybe it's a regional thing?
 
Alright. I'll have to get some things and do some reading.

I SO wish you were local. I'd have you over and show you how to tune on it and you could learn somethin and I'd make a new friend.
 
Richie, not enough converter may be part of your problem, but listen to the advice on here about timing.

Before you do anything you need to find out what the amount of mechanical advance and what your total timing is. You need a nice short advance curve which will allow more initial timing, and total timing should be 34 to 36 degrees.

Once this is dialed in you can start to look at other things.

If you want some help give me a call.

THIS ^^^^^ No way in HELL would I let the FIRST thing I do be replace the converter. IMO it's well worth your time to maximize what you HAVE first and go from there. That's much less costly and a LOT less labor intensive. Once you get that sorted out, then if you think it's sluggish still, look at the converter. Even though "it might" be mismatched, you can make it run surprisingly well once you get it in proper tune.
 
Not to clear..crappy camera but you can see the hole if you look up into the top of the con rod on the right. Don't get mad at me or call me an idiot this is all the shops doing for more oil and strength



Yeah, that's the oiling hole for the wristpin. A good (necessary) idea IMO if you're using floating pins.
 
Wow!

A HP340 should eat up a Holly 750 DP. Likely lots of other issues in the tune!
 
Hi everybody:

Now that I have over 300 miles on this 340 I'm getting to feel that there might be a problem like I thought. I got my friend to drive it also and he thinks the same thing. It should go WAY better than it does especially in the burn out awards. It hardly breaks the wheels lose :(


1970 340
Ground and drilled rods
Speed pro forged pistons
ported 2.02 J heads
Comp Cam 488/491
750 Holley vacuum secondaries
Edelbrock Airgap intake
Doug’s Ceramic Headers
Super 44 Flow Masters
Exhaust 2 1/2"
727 with 2200 –2400 converter
8 3/4 Dif with 3.55 Eaton trutrac
HP haven't a clue

I read this whole thread. I was gonna say something as soon as I saw 488/491, and 2200/2400.
But I forced myself to read to the end.
No one asked what your cylinder pressure is ,
nor at what altitude you are at.
These are key pieces of information, along with the Ica of your cam.
I'll bet you are at 1000 ft or more.
I'll bet your cylinder pressure is less than 130 psi
I'll be your Ica is greater than 64*
And I'll bet that thing is a dog below 3000 rpm.
Now, cough up the numbers so we can develop a cure and not just bandaid the crap out of it.
If you don't know the Ica of your cam, cough up what you do know.
And cough up the part number of your pistons or give us the measured deck height and whether or not it has eyebrows. And finally, have the heasd been milled and if yes, cough up the measured head-volume.
lol
 
Last edited:
I read this whole thread. I was gonna say something as soon as I saw 488/491, and 2200/2400.
But I forced myself to read to the end.
No one asked what your cylinder pressure is ,
nor at what altitude you are at.
These are key pieces of information, along with the Ica of your cam.
I'll bet you are at 1000 ft or more.
I'll bet your cylinder pressure is less than 130 psi
I'll be your Ica is greater than 64*
And I'll bet that thing is a dog below 3000 rpm.
Now, cough up the numbers so we can develop a cure and not just bandaid the crap out of it.
If you don't know the Ica of your cam, cough up what you do know.
And cough up the part number of your pistons or give us the measured deck height and whether or not it has eyebrows. And finally, have the heasd been milled and if yes, cough up the measured head-volume.
lol

uhhh....yeah. I did.
 
I read this whole thread. I was gonna say something as soon as I saw 488/491, and 2200/2400.
But I forced myself to read to the end.
No one asked what your cylinder pressure is ,
nor at what altitude you are at.
These are key pieces of information, along with the Ica of your cam.
I'll bet you are at 1000 ft or more.
I'll bet your cylinder pressure is less than 130 psi
I'll be your Ica is greater than 64*
And I'll bet that thing is a dog below 3000 rpm.
Now, cough up the numbers so we can develop a cure and not just bandaid the crap out of it.
If you don't know the Ica of your cam, cough up what you do know.
And cough up the part number of your pistons or give us the measured deck height and whether or not it has eyebrows. And finally, have the heasd been milled and if yes, cough up the measured head-volume.
lol

Elevation of Kelowna, BC, Canada
Location: Canada > British Columbia > Central Okanagan >
Longitude: -119.49601
Latitude: 49.8879519
Elevation: 342m / 1122feet
Barometric Pressure: 97KPa

Things are looking up. I gave my brother a call. He doesn't drive like I do and back in the day 60s and 70s I can't count how many mopars he had. He jammed his foot to the floor, first the carb hesitated then it caught and sure enough it did a big long burnout. My foot was hitting the rubber mat I guess and I thought that was the steal floor. The carb didn't do that caugh when I tried either. I still don't like vacuum secondaries though they never even seem to open up.

The only thing I can really answer right now is about the rpm 3000 and yes that's when it starts to go good.
Here's all the cam info.

51139672103_ea6ed0abd6_b.jpg

 
Last edited:
Wow!

A HP340 should eat up a Holly 750 DP. Likely lots of other issues in the tune!
Some guy says Holleys with vacuum seconaries aren't really DP they only have one pump. Mine has vacuum secondaries and I don't like :elmer:IT
 
What jets and power valve, what pump shooter #/size, which color pump cam?
What secondary spring color?

Timing should be at LEAST 12btdc, and really more like 18-22 initial with about 32 total/full advance , but no more than about 34.
 
What jets and power valve, what pump shooter #/size, which color pump cam?
What secondary spring color?

Timing should be at LEAST 12btdc, and really more like 18-22 initial with about 32 total/full advance , but no more than about 34.
Because of my lack of experience on getting this kind of information we better give up for now. I don't want to waist your guys time anymore. I don't think things are as bad as I thought for one thing. I won't have to a switch the converter and gear ratios to get a burnout out of it but I do hate that vacuum secondary carb, I think it's going for a 650 or 750 DP mechanical secondary ..end
 
For a 4 speed car with tall gears I’d agree that the double pumper is a better carb choice but for an auto with a low stall and 3:55s you’ll probably like the vacuum sec carb better. Either way the amount of tuning you’ll NEED to do is about the same. A little more with the DP. For a new hot rodder with limited experience you’ll be better off learning on the VS carb. Don’t just throw parts at a problem to fix it. Diagnose, adjust, test. Then if you need parts replace them.
 
I’ll just say this, if you haven’t learned how or attempted to really tune a Holley vacuum secondary carb, and think you can just bolt on a DP ootb and expect great results......you might luck out but it’s doubtful. You will just be wasting your money on another carb that likely will just bog off the line (that’s just one gremlin you can encounter with a DP that isn’t tuned, especially with an automatic and that low stall converter you have) Pay $25 for a Holley tuning book like this:
A4860712-08C1-4688-89C7-620E8BE3CC7E.jpeg
and then read the thing like when you were in school. Then reread it as you work on each circuit step by step as shown in the book.
 
I’ll just say this, if you haven’t learned how or attempted to really tune a Holley vacuum secondary carb, and think you can just bolt on a DP ootb and expect great results......you might luck out but it’s doubtful. You will just be wasting your money on another carb that likely will just bog off the line (that’s just one gremlin you can encounter with a DP that isn’t tuned, especially with an automatic and that low stall converter you have) Pay $25 for a Holley tuning book like this:View attachment 1715738875 and then read the thing like when you were in school. Then reread it as you work on each circuit step by step as shown in the book.
I was thinking of ordering that last night
 
Because of my lack of experience on getting this kind of information we better give up for now. I don't want to waist your guys time anymore. I don't think things are as bad as I thought for one thing. I won't have to a switch the converter and gear ratios to get a burnout out of it but I do hate that vacuum secondary carb, I think it's going for a 650 or 750 DP mechanical secondary ..end

Richie, just get two basic tools and you can answer both important questions and do most of the tuning yourself. A good timing light and a compression gauge. Practice around with them. You have an old car, so you need them and need to learn to use them anyway. We ain't goin anywhere.
 
-
Back
Top