396

[Ken1960]

Just bought a 68 chevelle, when push on it , don't have power it should I ck time it's ok I think could be carb it has a street avenger on it and a air gap intake motor sounds good on idle. I just bought it machine shop in Boston built motor.

[firebird77clone]

Air gaps work best @WOT after warmed up thoroughly.
At least, that's my experience.

[34_40]

Just bought a 68 chevelle, machine shop in Boston built motor.

Which machine shop? Bostons about 60 miles from me, maybe I know them?
Did they give you a build sheet? Do you have any specs on the internal parts? what pistons, camshaft, springs?

Could be they only built a driver with a "small" cam.. but without any specs, you'll have to do some digging to find out what is there.

[firebird77clone]

Does it get great gas mileage?
If it does, then that's your answer: it wasn't built for power

[techinspector1]

Air gaps work best @WOT after warmed up thoroughly.
At least, that's my experience.

See, here's another example of marketing hype sucking money out of your wallet. If the motor you're building or buying is intended to be used 100% at the drag strip, great, use an intake manifold you want to and experiment with it. But if the motor is to be used on the street, DO NOT USE AN AIR GAP INTAKE. A street driver needs the heat of the motor up into the manifold to heat the fuel charge so that is will begin to separate into a fog of mixture that the motor can burn. When the mixture is cold, it goes into the motor as big clumps of fuel separated by equally big clumps of air and big clumps of fuel will not burn.

Since you didn't spec out the parts or build the motor, you have no idea of the relationship between the static compression ratio and the cam timing or anything else about the motor, so unless you are willing to tear the motor down and measure everything, get used to continuing problems like this.

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[Ken1960]

I know it got me puzzled I think the carb is a 770 dual line. I think I need to get the air gap off there and put a performer intake on it. He said spent 2 k on transmission but it needs a stall converter on it. I think carb is vacuum secondary's, needs to be manual I think

[jerry clayton]

Ken-----------look up Holley site for pics/discreptions of carbs--vacume seconaries are easy to tell from mechanical sec. look in the carb and work the linkage to wide open-if sec throlle plates open its manual------

should be a "list" number across front of chole housing---------the 770 is a vacume sec carb and was a very good unit

[34_40]

For what it's worth, if you're running this on the street daily and use an auto trans.
Stick with a vacuum secondary carb.
Again, for what it's worth - my point oh two.. etc. etc. etc. yada yada yada.

[Ken1960]

I took the valve cover off today it does have roller rockers on it , an is very clean in there don't believe it's been run none since he built it . The back sight glass on carb fuel level is to high will that make her run wrong the front is ok right at bottom back is at top

[jerry clayton]

usually the back float level is set a little higher than front so fuel won't slosh to the rear ucovering the main jets--------

How about checking the list number on the front of the choke tower??????and did you check to see if the sec opened manually????

[Ken1960]

Yea it is a vacuum secondary's. It got a little backfire thru carb when pushing on it can't figure it out, is there anyway of telling if I got a hydrulic cam or a flat tap pet. Cam is a little big I guess when I idle brakes are hard , put a vacuum gauge on her today an at idle got 6 on gauge. It needs a stall convertor just don't have the power it should have. Will a set of aluminum heads bring her around,

[firebird77clone]

The carb backfire was very typical of what I experienced with the air gap intake. A smaller carb helped, but only a performer intake fixed it.

[rspears]

.... It needs a stall convertor just don't have the power it should have. Will a set of aluminum heads bring her around,

Ken, Tech gave you good advice in his post above:

...Since you didn't spec out the parts or build the motor, you have no idea of the relationship between the static compression ratio and the cam timing or anything else about the motor, so unless you are willing to tear the motor down and measure everything, get used to continuing problems like this.

Until you know the facts of your motor, either by going back to the shop that built it for the specs, or tearing it down (pulling the heads) for some precise measuring, you're going to be throwing good money away on pieces & parts in a gamble that might yield a little bit better performance, might make things worse or stay the same. Picking the right parts is a science based on knowns, and once you know your engine you can invest your money wisely in parts and pieces that you can feel confident will give good results.
Good luck to you, and hope you have fun with the new to you Chevelle! Oh, and if it popped back through the carb, even a little, you may have just identified one of your problems.

[Ken1960]

Can I take the timing chain cover off an get the #s off front of cam and that tell me wat cam is in her

[techinspector1]

Can I take the timing chain cover off an get the #s off front of cam and that tell me wat cam is in her

,
Maybe, but cam grinders usually stamp the cam on the rear journal. I suspect that's because when you stamp into the face of a piece, it raises the numbers/letters that you're stamping, causing that material to stand proud from the face of the journal. It might be that when you would then bolt a timing gear onto the face of the cam, she might run a little lolly-gagged due to not sitting on a perfectly flat face. I really have no idea, that's the best I can come up with. I think in recent years, they have begun to etch the number into the front face rather than stamp it, because it does not appreciably raise any of the material.

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