bad fuel mileage after rebuild

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Horace Reynolds

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Hey, people, I recently had a long block rebuild done for my 225/6 in a 66 valiant. Ive put about 600 miles on it, changed out the break-in oil, installed pertronix , replaced the vacuum advance can, had the Holley 1920 rebuilt by a good local carb guy. It idles rough when cold, even with the auto choke engaged. When it gets up to temp it smooths out, but the rough idle returns intermittently when warm. Fuel mileage is terrible--9-10 mpg. When I give it the beans, I can see smoke in my rear view. Power seems up to snuff and timing is set properly. Exhaust has a gassy smell, like incomplete combustion? Suggestions? Thanks, Horace. I forgot to mention it is an automatic.
 
Pull your plugs will probably affirm what all are saying, it's running rich.
 
I would first and foremost check choke operation. Make sure it's not binding or sticking since the carb has been reassembled. But good call on the manifold heat stove, too.
 
Horace Reynolds said:
Is there a way to measure manifold vacuum on a slant? thanks
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Buy a vacuum gauge from an autoparts store, tool section. It should pull plenty, like 19" or better I would think.
Hook it to a vac port, non timed vac port.
The one for the distributor vacuum advance is timed, it is above the throttle blade 'if my my brain is working, still early here in ca.' and only when the throttle blade is opened enough will it see a good vac signal.
Could go off the manifold if you have to.
Take a pic of your carb if you can and show us which 1920 you have
 
Horace Reynolds said:
Hey, people, I recently had a long block rebuild done for my 225/6 in a 66 valiant. When it gets up to temp it smooths out, but the rough idle returns intermittently when warm. Fuel mileage is terrible--9-10 mpg. When I give it the beans, I can see smoke in my rear view. Power seems up to snuff and timing is set properly. Exhaust has a gassy smell, like incomplete combustion? Suggestions? Thanks, Horace. I forgot to mention it is an automatic.
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My 64 is a little cold blooded for the first half mile or so, then it runs perfectly. (I am so glad I have a Carter BBS.)
Seems a lot of people struggle with the 1920.

As mentioned already, choke operation and heat stove need to be right. Do not bypass the heat stove!
If your choke operation is bad, @slantsixdan swears by the electric choke conversion. That will solve that problem.

"Timing set properly" Try 8 to 10 degrees initial timing with vac advance hose plugged.

Use the extended NGK ZFR5N #3459 plugs without washers. That puts the spark deeper into the chamber and will help burn your rich mixture.

Long block rebuild only? A good solid bottom end will only emphasize shortcomings on the top end. Is the head in good shape? Do a compression check to verify all six holes are close to equal. You can rent a compression gauge from a big chain store for free. If the head needs to be pulled for a valve job, have it milled .080 or .100. You lose compression using a modern composite head gasket. As Charlie says, there is no downside to milling the head. (Unless you don't want better performance and gas mileage)

Edit: OOPS, had a Biden moment. Long block DOES include the head.
Now that I think of it, it did take some time for my rebuilt 225 to break in. Right away it seemed to run hot but all is good now.
 
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KosmicKuda said:
My 64 is a little cold blooded for the first half mile or so, then it runs perfectly. (I am so glad I have a Carter BBS.)
Seems a lot of people struggle with the 1920.

As mentioned already, choke operation and heat stove need to be right. Do not bypass the heat stove!
If your choke operation is bad, @slantsixdan swears by the electric choke conversion. That will solve that problem.

"Timing set properly" Try 8 to 10 degrees initial timing with vac advance hose plugged.

Use the extended NGK ZFR5N #3459 plugs without washers. That puts the spark deeper into the chamber and will help burn your rich mixture.

Long block rebuild only? A good solid bottom end will only emphasize shortcomings on the top end. Is the head in good shape? Do a compression check to verify all six holes are close to equal. You can rent a compression gauge from a big chain store for free. If the head needs to be pulled for a valve job, have it milled .080 or .100. You lose compression using a modern composite head gasket. As Charlie says, there is no downside to milling the head. (Unless you don't want better performance and gas mileage)
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Thanks for your reply! Top end also done. I used S & J in Spokane. New exhaust manifold. I did the carb cleaner test at the intake manifold and found no leaks. Choke operation is perfect. I really think the problem is in the carb. Im going to take it back to the guy who worked on it and have him check the economizer valve. Any other ideas about carb related , running rich issues? Thanks!
 
Juz sayin. I would not be driving that much if it smokes black. Look at the plugs. You may well "wash down" those nice new cylinders, so to say
 
MOPAROFFICIAL said:
That would be one shity hone job or chrome rings on the wrong finish.
my favorite is when the heat stove butterfly thing sticks half closed or more...

Slants ,as good as they are, had some gremlins that stumped a lot of people.
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Maybe. I know on my 08 Jeep Wrangler it took a while for break in. Right at 2000 miles, it felt like it added 50 LB FT of torque. .......that said, it started knocking at 18K miles and had to have a new short block.
 
RustyRatRod said:
Maybe. I know on my 08 Jeep Wrangler it took a while for break in. Right at 2000 miles, it felt like it added 50 LB FT of torque. .......that said, it started knocking at 18K miles and had to have a new short block.
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Friend of a friend got a block back from machining, assembled it...he was green, anyhow it was only bored and not honed...it ate itself in ..I think it was 500 or so miles?
Things happen.
 
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