Opinions on preliminary tune welcome----

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As said, AFB jets will be nowhere near to the Holley jets. If you have 89's in the front, it will be way rich on the primaries. What is your Holley list number?

I would not be running this engine at idle a whole lot. It sounds like you cannot really drive it properly; the ring seating will not be complete until you can 'load' the engine some and put some real compression pressure on the rings. Time to stop playing with the motor and work on getting it on the road. As said, you can't really know where the carb is tuned by just idling.

And as for your vacuum levels, I agree that you could have significantly higher vacuum levels. At some point, you are going to have to start adjusting the secondary stop screw, and then work on the PCV operation. Both of these effect the 'excess air' that is let into the intake at idle.
 
nm9stheham said:
As said, AFB jets will be nowhere near to the Holley jets. If you have 89's in the front, it will be way rich on the primaries. What is your Holley list number? Looks like a starting point on my jetting would be about 62 X 66 and tune from there. It is on the back burner now-moving on.
I would not be running this engine at idle a whole lot. It sounds like you cannot really drive it properly; the ring seating will not be complete until you can 'load' the engine some and put some real compression pressure on the rings. Time to stop playing with the motor and work on getting it on the road. As said, you can't really know where the carb is tuned by just idling. I agree, I put the engine together myself in January and I have been trying to get it running somewhere in my comfort zone so I can finish up the engine bay and put the rest of the car together.
And as for your vacuum levels, I agree that you could have significantly higher vacuum levels. At some point, you are going to have to start adjusting the secondary stop screw, and then work on the PCV operation. Both of these effect the 'excess air' that is let into the intake at idle.
Click to expand...
I have had the PCV valve installed and operating during all of the above tuning. A vacuum gauge connected to manifold vacuum and everything else vacuum-wise plugged off. As I understand it, I have to remove the carburetor and adjust the secondary stop screw from the bottom of the base plate.
I am glad I have done the tuning that I have, I am now in my comfort zone with the engine. I learned that I cannot move forward without installing a fan shroud. That will be next as I am building my own. I was able to verify the drivetrain, checking speedometer operation after my GV install and my new transmission has 3 forward gears and one reverse gear. My new 8 1/4 SB rear end operates properly and quietly and most importantly!!!!-I have verified the total rewire if the dash with MAD conversion and engine bay updates. That was one of the reasons for running the engine and getting it to idle hot in gear properly, all this being documented on my build thread. None of this may have been the "right" way to do it but aside from advice and help from this board I am working alone. Also, this is not my first rodeo, just my first Mopar.
Thanks to all who have contributed up to this point. I plan on an update to my build thread, maybe Sunday evening.
TGIF---------DR--------:)
 
DesertRat said:
I have had the PCV valve installed and operating during all of the above tuning. A vacuum gauge connected to manifold vacuum and everything else vacuum-wise plugged off. As I understand it, I have to remove the carburetor and adjust the secondary stop screw from the bottom of the base plate.
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The thinking behind the PCV comment is that different PCV's will act in very different ways at idle. When the PCV sees higher idle vacuum, it should shut down partially to avoid having too much air injected under the carb at idle via the PCV. The old standard Mopar metal PCV's don't shut down the flow at the lower idle vacuum levels produced by a cam like yours. So you may have excess idle air flow via the PCV, depending on what PCV you have. We moved away from the standard 60's metal Mopar PCV for this reason.

And yes, the secondary stop screw can have a pretty significant effect on idle and off-idle performance. You seem to know the drill!
 
Today I pulled the front bowl off my carburetor. I installed a new 6.5 power valve and in checking my jet size, I see they are stamped 512. I think I am running way rich and don't understand the number. My research says I need around a 40 for the primary jets. The plugs are black except the tip of the electrode which is white.Need some advice!!
DR--------
 
DesertRat said:
My research says I need around a 40 for the primary jets.
DR--------
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The 512 is a 51 jet.

Unfortunately your research is incredibly wrong. You should need around 58's.

You also need to make sure your gas level is just below the inspection holes at idle or immediately after you turn your engine off . If it has a sight glass it sould be around 1/4 way up the glass.
 
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Running NGK BP6ES plugs which according to NAPA cross with the stock commando plugs. That is close to how my engine is built. Trying to decipher what you are saying RRR.
 
Seems counter intuitive to increase jet size if it appears to be running rich. I guess it could have been the power valve blown out but didn't seem to be??????
 
DesertRat said:
Running NGK BP6ES plugs which according to NAPA cross with the stock commando plugs. That is close to how my engine is built. Trying to decipher what you are saying RRR.
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I am sayin that "just cause" the pistons are rated at 10.5, doesn't mean that's what your compression is. Compression ratio must be MEASURED, not GUESSED.
 
I get that, no question my CR is lower. I have been through all that previously during my motor build. Just wondering how that affects jetting?
 
DesertRat said:
Running NGK BP6ES plugs which according to NAPA cross with the stock commando plugs. That is close to how my engine is built. Trying to decipher what you are saying RRR.
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Too cold. Screw in a set of RN12YC Champions and see how it acts. I did the same with my 273 buikld but tried Autolites. Too cold for the less than 10.5 compression the Egge pistons give you. I chased a rough/rich idle condition for a year until I switched plugs and it has been perfect since.
 
DesertRat said:
I get that, no question my CR is lower. I have been through all that previously during my motor build. Just wondering how that affects jetting?
Click to expand...

A low compression engine is less volumetricaly efficient than a high compression one and will therefore need to be jetted differently if all else is the same.
 
DesertRat said:
I get that, no question my CR is lower. I have been through all that previously during my motor build. Just wondering how that affects jetting?
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"Not very much"
 
It's interesting how your story mirror's mine. My 273 burned so inefficiently that it burned your eyes to stand behind it. You could smell the unburned gas. After trying 2 different carbs, distributors, and timing combinations all over the place a simple plug change did the trick.
 
Thanks for the input Mike, I have hot ignition with my pertronix ignition coil, wires and distributor conversation.I will put the plugs you recommended and some 58 jets and see where things go. I have to activate my wideband to check my numbers.
 
Heres plug charts

Spark Plug Heat_Range_Chart.jpg
 

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I have to say this thread makes me want to go to the bathroom and take a massive dump.
 
Change one thing at a time . I would do the plugs first . My comment about the jets is that they "should" be around 58's but I would look at other things first.

One of the things I would do is get it warm, then with the distributor vacuum hose disconnected, advance the timing 3 to 4 degrees . If the rpm increases and it still tuns smoothly, this is a better setting for idle and your vacuum will go up . You should have more than 8 hg at idle with that wimpy cam.
 
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