My first 2bbl to 4bbl swap.. scratching my head..

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67cudaResto89

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So i recently (last friday) bought a 71 plymouth scamp off of my uncle. It has a mild cam(unknown specs) heddman headers and 3in dual exhaust the whole way back. I helped him put all this stuff in about 5 years ago, now i own the vehicle. the problem i have is its still the stock manifold and 2bblcarb in there.
It hesitates and feels like its not getting enough fuel on take off. Its an everyday back and forth to work driver so i dont want anything crazy. But i feel as tho it needs at least a 600cfm carb(i have an original holley 4bbl rebuilt). I was wondering how hard/easy of a process is it to switch things over to a 4bbl. I'm trying to do this on a budget considerin i just spent the money on the car. any help would be greatly appreciated. Curious about whether or not i need new springs, throttle linkage..etc. pretty new to this stuff so i'm trying not to screw up to badly. thanks in advanced!
 
Buy you a good shop manual or down load one.
Sounds like the 2bbl might just need a good rebuild.
I would rebuild the 2bbl first and see if you can make it run better.

As for the 4bbl.
Find a used aluminum intake in the for sale section.
Remove the 2bbl intake.
If the 2bbl intake is factory there is two small about 3/16 dowel pins that need removed from the block or you will crack the new intake.
Clean everything real good and install the new intake.
If the car is an auto make sure the kickdown linkage is adjusted properly before you drive it or transmission damage can occur.
Most Holleys do not align properly with the mopar kick down or throttle linkage without the proper adapters.
 
Also, check your ingition system, 71's run points unless it has been changed, make sure the ignition is up to proper specifications before you do any carb work.
Alot of stumbling, bad running can be linked to ignition problems.
 
adapter is holley pn 20-7...

the 4 barrel manifold will move the carb...the upper part of the 2 barrel kick down linkage will not fit properly ....

here is a picture of what it should look like...
 

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Ok awesome. I'm gonna go over the whole ignition system tomorrow at work just to double check make sure its up to par. Its still original points I know that. Its been tuned up. I just didn't know whether or not I need a bigger carb due to the cam. I'm gnna try and see if my uncle can find the size.
How do you adjust the kickdown linkage not quite sure on that one.
 
67cudaResto89 said:
Ok awesome. I'm gonna go over the whole ignition system tomorrow at work just to double check make sure its up to par. Its still original points I know that. Its been tuned up. I just didn't know whether or not I need a bigger carb due to the cam. I'm gnna try and see if my uncle can find the size.
How do you adjust the kickdown linkage not quite sure on that one.
Click to expand...

Check the timing, advance curve etc with a good light.

Also a quick check the points with dwell meter and use vacuum gauge.

Do you have a new fuel filter on the engine, you may be getting crap out of the tank if it has sit a while.

Refer to the shop manual on the linkage, if you don't do this correctly you will eventually end up with fried trans.
 
I hope you don't have A/C, because the bracketry can easily drive you insane when you go with an aftermarket intake.

Definitely start out by making sure the ignition is up to speed, and timing is set correctly. Since you have a hotter cam, try a little more advance and see what that does for you.

Down the road, consider an electronic conversion kit to eliminate points. They're $200 from Mancini. It's not "a must", just something to consider.

Assuming you do go with a four barrel... the 318 carb IS pretty tiny...

I don't know what your budget is, but I like Lokar products. It replaces the kickdown rod with a cable, and all of it mounts to the carb, so no brackets on the manifold bolts. Plus, being cables, there are no alignment issues when you change manifolds. You're talking $67 for the trans kickdown, $43 for the throttle cable, and $26 for the bracket. Check this out: http://static.summitracing.com/global/images/instructions/lok-kd-2727htkd-2904htkd-2518htc.pdf

The alternative is to cut and weld something up, or try to find factory or reproduction parts that will fit. Repro parts ain't cheap either!
 
I just got into work and I'm going to check everything out today with timing points etc. Unfortunately I do have a/c and would like to keep it considering this will be an everyday driver. My phone is being stupid so I can't look up those parts but that idea sounds pretty good. Mu budget isn't that small so I should be able to pick them up.
 
some intakes have provisions for the a/c bracket. My LD4B did. I did have to grind the bracket slightly so it fit better but that was no big deal.

I am a cheap SOB so i just did cutting and welding to get the kickdown linkage and throttle cable to work.

should be a do-able swap over a weekend. make sure you get everything you need. Also your 2 barrel air cleaner wont fit on the 4 barrel so get one of those too.
 
yea im pretty cheap too but i just dont have the time anymore to cut and weld.(new lead tech at work!).. another question all my original vacuum lines i have are they going to have to be plugged? my car is already a vacuum line nightmare considering i have two that go absolutely nowhere.(one is for heater controls so i'm going to have to tee it in to the main vac somehow). the other i have no idea.
 
It sounds like you want it smooth off the line and a well-behaved daily driver. A 2 barrel carb should be fine for that. Most likely the accelerator pump in the carb is bad. If not, it might be running too lean. Cheapest solution would be a new 2 bbl carb, if you can get one like I did 2 yrs ago for $25, but I lucked out on ebay.

If you go to a 4-bbl intake and carb, you do not want "at least 650 cfm" for how you say you want it to drive. The worst mistake is to "over-carb". It can even lessen your performance, but definitely impair driveability. For best mileage and smooth off the line, look at a small carb or at least one with small primary bores. Say the Holley 4360 Economaster, or a small Spreadbore - Carter Thermo-quad or Quadra-jet (preferably Mopar model).

Finally, get a dual-plane manifold. Even better might be the unique Offenhauser Dual Port 360 manifold, which seems an ideal match for a spread-bore. I see them on ebay occasionally and got one to try on my 383.
 
Well i want to have a kinda quick car even tho its a daily driver. i'm kind of on a budget and want to use the stuff i have. im in the process of getting an edelbrock performer intake. and i have a 600cfm holley carb that i rebuilt its a factory one from a 383. i'm gonna go ahead and get the electronic ignition kit from mancini. the car isnt running lean its running extremely rich. i checked timing it was advanced a little bit so i brought it back down to tdc. it ran a little bit better. But it has a terrible hesitation. and bogs out. lower rpm it feels like its dragging but once i get up into the higher rpms and highway driving the car drives beautifully.
 
By around 1972-73 Factory 4160 Holleys were known to have problems and were taken off at the dealerships and replaced while under warranty. I have had three or four laying around since that time that a couple of line mechanics were tossing out and gave me. I vaguely remember someone saying the secondary metering plates were warped, compared the Chrysler plates to aftermarket carb ones, decided they would just be too much trouble, and never did anything with them.
At any rate, they were smog era carburetors calibrated for a big block (383), and even one in good shape would most likely require wholesale changes (pump shooters, main jets, power valve, secondary vacuum pot and spring, etc.), not to mention conversion to 4150 configuration (secondary metering block and jets instead of plate) to get the secondaries dialed in to make one right for a 318.
My plan for any basic 318 would be 302 heads, a dialed in stock mag pulse distributor set up with a GM HEI module (the slant six. org guys have had this one in their bag of tricks for years now), a Thermoquad tweeked for the 318 on a Performer manifold, and decent exhaust.
 
I set the timing to 0 like the factory sticker calls for and it was a mistake.
Sluggish and low powered.
Try kicking your base advance to about 20 BTCD and see how she runs.
Mine is advanced a little more than that, but I live at 5500 feet.
Also, you might consider removing the airhorn in your carb and drilling the metering jet holes to about 30 thousands.
I know you said it runs too rich, but the timing advance may help with that, and it's also possible that the jets in the carb are just too big.
Just a heads up that sparkplugs can cause almost everything you describe too.

Food for thought.


67cudaResto89 said:
i checked timing it was advanced a little bit so i brought it back down to tdc. it ran a little bit better. QUOTE]
Click to expand...
 
The car has had a complete tune up. And it ran worse when the timing was advanced. It wouldn't idle properly at all once I brought it back down to 0 it smoothed out a lot better and I had less hesitation.
 
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