Could my "383" be running to lean?

[Barry M.]

After 6 years, I am just about finished with the restoration of my '71 small block convertible that I purchased in rather poor condition. I would credit much of my success to info obtained on this forum. Now my question. As part of the engine work, I had my engine builder install a stroker crank and the block was bored .40 over. I now have a 383 in the car. A good friend of mine said that he though the car sounded like it was running lean. He asked if I had rejetted the carburetor that I installed (not the original but one off of a 76 Corvette) to compensate for the larger displacement. I did not change the jetting on the carburetor that I installed. Is this something with which I should be concerned? I do not drive the car hard at all. Thanks for the help, Barry

[Gene M.]

Re: Could my "383" be running to lean?

After 6 years, I am just about finished with the restoration of my '71 small block convertible that I purchased in rather poor condition. I would credit much of my success to info obtained on this forum. Now my question. As part of the engine work, I had my engine builder install a stroker crank and the block was bored .40 over. I now have a 383 in the car. A good friend of mine said that he though the car sounded like it was running lean. He asked if I had rejetted the carburetor that I installed (not the original but one off of a 76 Corvette) to compensate for the larger displacement. I did not change the jetting on the carburetor that I installed. Is this something with which I should be concerned? I do not drive the car hard at all. Thanks for the help, Barry

The mid to late 70's stuff is normally on the lean side......... Why would you not use a performance Carter or a Holley?

[Timothy B.]

Re: Could my "383" be running to lean?

Barry,

I am not sure how a engine sounds when it's running lean but after changing many stock parts in the engine tuning the engine A/F ratio is a good next step. Lots of info on the net about this but not as much here as you would expect.

Best approach is a A/F ratio that provides a clean idle and cruise for the spark plugs and make certain the A/F ratio at WOT falls around 12.5. IMO, for your engine and street driving a 650 vacuum secondary carburetor will probably work fine and be very close with the jets.

[Edward J.]

Re: Could my "383" be running to lean?

Barry, Edelbrock make a direct fit Carburetor for a spread bore inake. and will look like factory. Keep in mind a lean running engine is not a good thing as combustion temps. rise after extended periods. Your engine spec.s were really not posted other the it was stroked. Cam profile, compression Ratio, headers?

As Gene states the mid to late 70's Rochester carbs, were on the leaner side and and Its likely you'll want to change out the carb. I can tell you the guys from summit racing can set up with the correct carb. after you give them some spec.s on the engine.

[Barry M.]

Re: Could my "383" be running to lean?

Gene, I chose to stick with a Rochester as I wanted to keep the engine looking as stock as possible. I appreciate the heads up on the lean mid 70's carbs. Tim, I will check out the A/F ratio. This was also suggested by my friend as he commented on the "lean sound". Ed, I believe that the only other modification of note that I requested of the engine builder was to install a cam that would increase low end torque. He chose a Melling. I will get the specs on it and report back. I would be interested in your opinion. Thanks, Barry

[Gene M.]

Re: Could my "383" be running to lean?

Barry
A 212 degree @ .050" intake and around 110-114 lobe center cam would be a torque off the line monster with the added cubic inches. Going much bigger will need the benefit of headers but for originality is a no. A Rochester calibrated similar to the '68 L79 should run ok and keep you looking like it is supposed to. I'm guessing a jet/metering rod change might be helpful but not a requirement as a starting point.

[Barry M.]

Re: Could my "383" be running to lean?

Gene, It looks like my engine builder installed a Melling MTC1 cam. The specs indicate intake @.05" lift to be 204 deg. exhaust @ .05" to be 214 deg. The LSA is 112 deg. I am considering another carburetor. Do you have an opinion on an Edelbrock vs. a remanufactured Rochester from Autozone or equal. I would like to maintain the look of the original Rochester. I have no clue as to how carefully remanufactured the rebuilt Rochester would be. Either way I probably should have the air/fuel ratio checked to see if the existing jetting is sufficient. Barry

[Craig H.]

Re: Could my "383" be running to lean?

Hi

His have a 383 in my 71 with a Howard cam 214 @ .050 for intake and exhaust running a stock quadrajet.

Seems to run fine but I am waiting to get a bung in the exhaust so I can put an a/f meter on it to check for sure.

carb builder said to possibly change main jets up a couple of sizes if needed.

depends if it is lean at all in wot or cruise.

Once I can get the meter on it we can decide what jet, rod combo may be needed, if at all.

[Gene M.]

Re: Could my "383" be running to lean?

Gene, It looks like my engine builder installed a Melling MTC1 cam. The specs indicate intake @.05" lift to be 204 deg. exhaust @ .05" to be 214 deg. The LSA is 112 deg. I am considering another carburetor. Do you have an opinion on an Edelbrock vs. a remanufactured Rochester from Autozone or equal. I would like to maintain the look of the original Rochester. I have no clue as to how carefully remanufactured the rebuilt Rochester would be. Either way I probably should have the air/fuel ratio checked to see if the existing jetting is sufficient. Barry

Cam selection is excellent. Go ahead and check out the jetting/metering rod and make adjustments as results show. You may find only the primary needs attention. If the secondaries are ok the coolant temperature will verify it too by not running hot at highway speeds. Too lean tends to run hotter. Give it a shot.

The Rochester ('68 L79, I've had good results with) is a good selection. Once you get it dialed in it is good on gas on the small primaries and good throttle response. I don't know what all it would take to get your '76 model up to task. I'm not familiar with the internals of it.

The Holley and Carter AFB (to a lesser degree) have more available tuning pieces to buy. That is why I would push you in that direction. In my area the parts store carry Holley parts on the wall.

[Patrick H.]

Re: Could my "383" be running to lean?

Barry,

Can you open it and see what primary jets and rods are in it now?

Patrick