Classic over carburetion problem?

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Richie

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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
 
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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 Eaton trutrac
HP haven't a clue
Would you say you have obsessed on carb tuning (and ignition) and have both set up ideally? Got details of all that tuning you’ve done? Aside from that, (and not knowing rear gear ratio) I’d lose the converter for a quality 3500 tight such as from Turbo Action. That’s my knee jerk response :)
 
As a kid, I had a 69 340 in a Dart, somehow the stock Carter 650 could never be improved upon. Of course, that was in the 70's and the technology changed dramatically.
I did have a Holley 750 on it at one point in time, but the Carter 650 made that engine "light-up".

Too much fuel?

Have you had the car for a while? What was the previous carb and was it better?
Perhaps is not a carb issue and the timing could be advanced.

Chrysler had a pretty good "performance sense" and cars were fast right out of the dealerships.
 
Would you say you have obsessed on carb tuning (and ignition) and have both set up ideally? Got details of all that tuning you’ve done? Aside from that, (and not knowing rear gear ratio) I’d lose the converter for a quality 3500 tight such as from Turbo Action. That’s my knee jerk response :)
Sorry about that I put it in now..3.55s. What about mechanical secondaries?
 
As a kid, I had a 69 340 in a Dart, somehow the stock Carter 650 could never be improved upon. Of course, that was in the 70's and the technology changed dramatically.
I did have a Holley 750 on it at one point in time, but the Carter 650 made that engine "light-up".

Too much fuel?

Have you had the car for a while? What was the previous carb and was it better?
Perhaps is not a carb issue and the timing could be advanced.

Chrysler had a pretty good "performance sense" and cars were fast right out of the dealerships.
Old carb on the 318 was a carter that was rebuilt but still leaks. I think it's too small anyway.
 
I seriously doubt it’s “over carbureted”. Not tuned properly? ... probably. I would verify ignition timing and curve are good and get to tuning the carb. Check the plugs, they’re going to tell a story. Many more folks better versed in this here. Hopefully they chime in.
 
Would you say you have obsessed on carb tuning (and ignition) and have both set up ideally? Got details of all that tuning you’ve done? Aside from that, (and not knowing rear gear ratio) I’d lose the converter for a quality 3500 tight such as from Turbo Action. That’s my knee jerk response :)
This makes sense because the one good burn out that I did do once the revs got up I could have went down the length of the guys driveway...Long driveway
 
What about mechanical secondaries?
What would you expect from swapping to a carb with mechanical secondaries (I assume a Holley double pumper vs other) I’m not much for immediately thinking I need to change parts (aside from the converter you have) I’m obsessive about any tuning I do. You most likely could tune what you have and see much improvement. I’m no tuning pro but I do know it takes time, and trial and error to get things ideal. A Holley tuning book is a lot cheaper than throwing another carb at it. Still need to invest the same effort either way
 
With this Holley it was rebuilt on hand at the shop for only $200 so that's why we put it on the car. Going down the hyw at 60 mph I'm at around 2700 rpm so how high of a stall can you go with that?
 
was the cam dialed in , distributor and timing re set?
 
I don’t think you are overcarbed.Chrysler “under carbed many engines. The std 440had a 575 Holley. The cfm calculator
Shows that a 440 at say 6000
Rpm shows a theoretical need for more carb.
maybe timing issues ??
Enough fuel delivered ?
Look for simple , basic things first.
 
Probably "over pressured". Check your fuel pressure at the carb. AFB/Edelbrock likes no more than 5# and Holley no more than 7#. I have seen stock mechanical pumps put out over 10#.
 
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


Maybe too much cam and carb...

Throw in a set of Rhoades lifters and tune it in right...

Here's Eddie's 340 Dart with a milder cam, LD340 intake, and Holley 600 vacuum secondary carb, Doug's headers, 8 3/4 with 3.55's.... idling from 800 and stomping the gas it will break the tires loose....

 
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


Start with your timing... 17° initial with 34° - 36° total, then tune in the carb from there....
 
Intake vacuum and timing?
I wont pretend that I know a lot because we're getting into things here that I have to learn more about :( I did notice that Eddie's idle is higher than mine so I could turn that up because it is only about 500 rpm
 
The biggest piece of advice I can give is TAKE NOTES! When you try something, try one thing at a time and write down the change and the result of that change. Keeps you on track and you can start to see where one thing can affects another. Saved my butt on many occasions.
 
I wont pretend that I know a lot because we're getting into things here that I have to learn more about :( I did notice that Eddie's idle is higher than mine so I could turn that up because it is only about 500 rpm

I’m running a Holley 770 on a 5.9 Magnum with 3:55 gears and no over carbed issues.
Like mentioned, it’s probably a tuning problem.
 
vacuum 750 is only a 375 2bbl until you allow the velocity of air through the carb to allow the secondaries to open up. That is controlled by a spring in the secondary actuator. Hard to overcarb a VS unless your jets are pig rich and your choking on exhaust fumes at idle and your AF is all out of whack. unhook the secondaries (just pop the actuator rod off the linkage) and run it. See if it acts any differrent. You can get heavier springs that will bring the secondaries on higher in the RPMs. I could light the rears on my 65 with my 340 with a smaller 284/.484 MP purple shaft but I had a 2800 stall and 3.91 gears but still, plenty of power. Heck I could light up 10" meats with a stock 68 340 and manifolds with a 3.55 7.25 SG rear before that. I had a AFB on that one, loved that carb...better response than even the VS holley. Maybe too much cam with that convertor?
 
How does the car feel at 4500 or 5000 RPMs and above does it pull like a freight train because you have a pretty peaky grind cam and it's going to be soft on the bottom end as mentioned in an earlier post you could use a higher stall converter no doubt! I like to advance my cams 4 degrees it really increases the bottom end pull. Also I have never had a carburetor work at low RPMs better than a thermoquad the small primaries will really help throttle response and low RPM torque.
 
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If you want help and I know you do, don't just give us a "yes" when asked about timing. WHERE is initial? WHERE is total? These are specific questions that need specific answers to help you. If your answer is "I don't know", then, you've not done your work on your end. If you don't know, get those numbers for us and report back. Also, if you can get a plug out and run a compression test on that one cylinder, that will help us help you dial the timing in even more.

I saw you answered "yes" to both the camshaft and distributor timing question. If you can tell us "where" the camshaft timing is, that will also help.

As much information as possible will get you the best answers as possible.
 
Not apples for apples, but dad ran a tunnel ram and 660's on my cars original 340. He had a much bigger cam, slight head work in X heads, but stock converter at the time and 4.56's. Smolder tires at will, no hesitation. At the track he would spin the tires 1/2 way thru first gear and run 12.0 at 115mph. That was early 70's. I agree with most, tuning and notes.
 
How does the car feel at 4500 or 5000 RPMs and above does it pull like a freight train because you have a pretty peaky grind cam and it's going to be soft on the bottom end as mentioned in an earlier post you could use a higher stall converter no doubt! I like to advance my cams 4 degrees it really increases the bottom end pull. Also I have never had a carburetor work at low RPMs better than a thermaquad the small primaries will really help throttle response and low RPM torque.
Agreed, thermoquad for street machines great throttle response and tunability. Cheap also I’ve seen them at 20-30 for good cores.
I’ve also quadrajets that rivaled the thermoquad.
 
I ran a Holley DP spreadbore "TQ replacement" on my last 340 for a few months. That carb had thee best idle and best low end of any Holley I ever had including a 625 BG/Demon. And it was a beater, nothing done to it but bolting it on from a $30 swap meet table.
 
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