340

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dennis morton

high winder 340
Joined
Jul 11, 2021
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Location
Kingston,ny
Hello everyone, I have a 1966 plymouth barracuda that came with a 273 automatic two barrel. I did a recent build on a 340 and rebuilt my 18 spline automatic as well. I need to go into detail about everthing i did so you can help me with my question so you know what i got. I built this motor to be as close as possible to 1968 . 340 block bored 30 over, keith black kb243 pistons eagle rods, comp cams magnum muscle 20-309-4 or 268ah-10, early j heads with big valves updated seats and seals and springs from comp cams. I have brand new carter avs 4636 with choke as well. I installed a true 21/2" manifolds down to the back exchaust from tti. also running bone stock intake manifold. also running my stock 273 manifolds with a thick copper gasket along with gaskets in my rebuild kit , no leaks fits well. running a stock distributor with pertronix points conversion along with a high voltage coil no ballast. My compression is just back of 10 to 1. I had my 273 crank turned and balanced to match my transmission. i have drove this car some maybe around 150 miles or so off and on. heres my question four of my plugs are black four are kinda getting there tan, two plugs on each side is black lol. I haven't taken the carb apart yet. I also have moved the timing up and down to see how much before rattles and how much it can take for easy starts. no difference on plugs either way. I always found a 340 love some advanced plenty of it, it doesn't seem to waqnt quite as much. Is my carb delivering more fuel on one side?
 
Are you sure your rings are broken in ?
Also you aren't running the 273 crank in a 340 are you ?
273 anything on a 340 is no bueno.
 
trapster said:
Are you sure your rings are broken in ?
Also you aren't running the 273 crank in a 340 are you ?
273 anything on a 340 is no bueno.
Click to expand...
Anything? Uh, no. There is nothing inherently wrong with running a 273 crank in a 340, and people run 273 rods all the time- they make for a much lighter rotating assembly. DC offered prepped versions in their catalog and recommended them in their build guides. And name one builder that hasn't used some form of 273 rocker arm on their builds.
I'm sure the OP's use of the 273 crank was due to the smaller crank pocket needed to run the early 904.

OP, I think your plug situation is a combination of things, including carb tuning (I'll assume for now you've got the carb set up right- choke working correctly and not stuck closed- and at least ballpark idle mixture and jetting, and your J heads don't have worn out valve guides), but not the least of which may be your ignition system. My admittedly somewhat limited experience with Pertronix conversions has been, well, not at all good. Despite claims, they just don't seem to deliver a consistent, hot spark. Too many issues ranging from quality of components to just being somewhat of a compromised design, only marginally better than the infamous "Skip White" all-in-ones. MSDs are a step up, especially if you can find one of the older units new or used. My favorite is the old reliable Chrysler distributor with an older Chrome box- in nearly 50 years I can count on 2 fingers the number of ballast failures I've had, and one of them was my own fault. The HEI converted Chrysler distributor is a real close second. Neither has ever let me down, design wise (just don't use cheap Chinesium parts here).
 
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dennis morton said:
Hello everyone, I have a 1966 plymouth barracuda that came with a 273 automatic two barrel. I did a recent build on a 340 and rebuilt my 18 spline automatic as well. I need to go into detail about everthing i did so you can help me with my question so you know what i got. I built this motor to be as close as possible to 1968 . 340 block bored 30 over, keith black kb243 pistons eagle rods, comp cams magnum muscle 20-309-4 or 268ah-10, early j heads with big valves updated seats and seals and springs from comp cams. I have brand new carter avs 4636 with choke as well. I installed a true 21/2" manifolds down to the back exchaust from tti. also running bone stock intake manifold. also running my stock 273 manifolds with a thick copper gasket along with gaskets in my rebuild kit , no leaks fits well. running a stock distributor with pertronix points conversion along with a high voltage coil no ballast. My compression is just back of 10 to 1. I had my 273 crank turned and balanced to match my transmission. i have drove this car some maybe around 150 miles or so off and on. heres my question four of my plugs are black four are kinda getting there tan, two plugs on each side is black lol. I haven't taken the carb apart yet. I also have moved the timing up and down to see how much before rattles and how much it can take for easy starts. no difference on plugs either way. I always found a 340 love some advanced plenty of it, it doesn't seem to waqnt quite as much. Is my carb delivering more fuel on one side?
Click to expand...
Although it does sound like it's running rich, I wouldn't do any tuning until the engine is completely broken in and 150 miles ain't it. Give it a little more time and then tune it.
 
I'm far from a tuning expert but I'm surprised no one is commenting on the use of 273 exhaust manifolds on the J heads. That has to be a major tuning problem.
 
the carb primary " barrels" feeds 2 cyls on one side 2 on the other in a Y pattern if it is dual plane. Quite possible one primary barrel of the carb is running rich to 4 cylinders.
 
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Bodyperson said:
I'm far from a tuning expert but I'm surprised no one is commenting on the use of 273 exhaust manifolds on the J heads. That has to be a major tuning problem.
Click to expand...

I ran them on my 273 with 72 340 J heads, may not be optimum, but it sure ran good with no problems. You might want to check the float settings after checking post #5.
 
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Before you can get a good read on the plugs, you need at least 300-500 miles on it to make sure the rings are seated well. This driving needs to be varied from idle to 40 - 50 MPH and don't go hammering on it yet. LOL
 
I have read somewhere that the intake delivers every other cylinder, if that is the case then could my carb be delivering more on one side? also haven't taken carb apart yet to check jetting size also read on a carb site that some had a different jet size on one side than the other
 
Demonracer said:
Before you can get a good read on the plugs, you need at least 300-500 miles on it to make sure the rings are seated well. This driving needs to be varied from idle to 40 - 50 MPH and don't go hammering on it yet. LOL
Click to expand...
I took the carburetor off today, took the top off i have a bent metering rod passenger side. I didn't take the rods out first before removing top it came apart just so easy i lifted the top off not sure how it got bent, there is corrosion green looking close to the top. this is a brand new 4636s avs 1968 carb been setting for years gonna have to rebuild. I have a question on this, so the metering rods regulate primary front of carb? there in the back of the carb, and front jets operate the secondary? also since i had four good plugs and four black plugs this bent metering rod is my problem most likley.
 
I B eleive they are yes they meter the main jets secondaries kick in later and add fuel at higher rpm.
 
Can you straighten the m/rod? A bent/jammed rod can cause your problem. They feed the primaries.
If met rod is beyond repair try our host Woodruff carbs. Rod # is 16-176.
Congrats on using a great carb.
 
dennis morton said:
I took the carburetor off today, took the top off i have a bent metering rod passenger side. I didn't take the rods out first before removing top it came apart just so easy i lifted the top off not sure how it got bent, there is corrosion green looking close to the top. this is a brand new 4636s avs 1968 carb been setting for years gonna have to rebuild. I have a question on this, so the metering rods regulate primary front of carb? there in the back of the carb, and front jets operate the secondary? also since i had four good plugs and four black plugs this bent metering rod is my problem most likley.
Click to expand...

You should be able to straighten the rod carefully in a vice. The rods go into the front primary jets and regulate mixture by vacuum. The secondary jets are in the rear. Don't change anything until you get that carb rebuilt and try it. Do you have the correct choke?
 
66fs said:
You should be able to straighten the rod carefully in a vice. The rods go into the front primary jets and regulate mixture by vacuum. The secondary jets are in the rear. Don't change anything until you get that carb rebuilt and try it. Do you have the correct choke?
Click to expand...
thank you for your reply, i did straighten it, the bend was mostly upper i think it will work fine mainly if it doesn't bind should work. your correct i should wait after i install newrebuild kit filter, and try it before any jet rod changes. four plugs look like there getting there little tan. that bent rod has green corrrosion on the upper part. since four plugs are looking right tells me jetting is right in the park its a brand new 4636s setting for years, 489 16-176 rods 067-065-053 120-689 this carburetor was set up for the 340 engine
 
Bewy said:
Can you straighten the m/rod? A bent/jammed rod can cause your problem. They feed the primaries.
If met rod is beyond repair try our host Woodruff carbs. Rod # is 16-176.
Congrats on using a great carb.
Click to expand...
thank you for your reply, your correct 16-176 rods 067-065-053 489 jets 120-689 on the back
 
dennis morton said:
Hello everyone, I have a 1966 plymouth barracuda that came with a 273 automatic two barrel. I did a recent build on a 340 and rebuilt my 18 spline automatic as well. I need to go into detail about everthing i did so you can help me with my question so you know what i got. I built this motor to be as close as possible to 1968 . 340 block bored 30 over, keith black kb243 pistons eagle rods, comp cams magnum muscle 20-309-4 or 268ah-10, early j heads with big valves updated seats and seals and springs from comp cams. I have brand new carter avs 4636 with choke as well. I installed a true 21/2" manifolds down to the back exchaust from tti. also running bone stock intake manifold. also running my stock 273 manifolds with a thick copper gasket along with gaskets in my rebuild kit , no leaks fits well. running a stock distributor with pertronix points conversion along with a high voltage coil no ballast. My compression is just back of 10 to 1. I had my 273 crank turned and balanced to match my transmission. i have drove this car some maybe around 150 miles or so off and on. heres my question four of my plugs are black four are kinda getting there tan, two plugs on each side is black lol. I haven't taken the carb apart yet. I also have moved the timing up and down to see how much before rattles and how much it can take for easy starts. no difference on plugs either way. I always found a 340 love some advanced plenty of it, it doesn't seem to waqnt quite as much. Is my carb delivering more fuel on one side?
Click to expand...
Just a thought. I also run a "HOT" coil and must use another Ballast along with the stock one.
 
dennis morton said:
thank you for your reply, i did straighten it, the bend was mostly upper i think it will work fine mainly if it doesn't bind should work. your correct i should wait after i install newrebuild kit filter, and try it before any jet rod changes. four plugs look like there getting there little tan. that bent rod has green corrrosion on the upper part. since four plugs are looking right tells me jetting is right in the park its a brand new 4636s setting for years, 489 16-176 rods 067-065-053 120-689 this carburetor was set up for the 340 engine
Click to expand...
Hi good news i installed the repair kit all my plugs have some grey tan there even looking
 
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