Thread: Lack of vacumn on a 351-W at idle

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I have always had a wimpy third gear shift with a light throttle and was blaming it on the trans but I have the motor in my 55 fairlane with vacumn wipers and I had to rev the motor up to get the wipers to work which is opposite from what it should be,at highway speeds the wipers act as normal but at idle somethings wrong and I have the modulator valve and wiper source at a full vacumn port on the intake. The engine builder put in a 302 cam which I have been hearing could be a problem but I am beginning to think there is a problem with the intake since the motor wants to run rich at idle and lean above idle and there is no leaks between the carb and spacer and spacer and intake,the intake is factory cast iron but was supplied by the builder so I no nothing about it so any ideas on what to look for. Jeff

Have you put a vacuum gauge on it? I prefer the firing order and cam on the 351 over the 302 for power reasons, doubt it would have much effect on the vacuum readings, though. Did somebody maybe angle grind the heads, and possibly the intake could be leaking into the lifter valley?

I wish now that I would of rebuilt the sludged up 76 351 I had since it had never been apart,I think the builder just pieced it togather from whatever he could find. I was thinking that maybe the heads had been milled and the intake is not sealing properly so I am thinking about a head,cam and intake set if the cost is not prohibitive. I am going to put a gauge on it today and see what it reads,its acts like I have the vacumn lines on a port above the carb but I have them on the manifold. Jeff

I put a vacumn gauge on it today and with the choke on its about 20 and when the choke is off its around 15,what is strange is I can take a hose off and create a leak and the motor will smooth out and idle smooth. This has me puzzled and could the problem be in using a aftermarket carb spacer on a factory intake setup to use a EGR valve in the factory spacer. Jeff

Could be a few of the things you mentioned. Do us a favor and tell us what your carb is. Have you found the cam specs yet? Give us everything you can find for parts numbers and specs. It will help a bunch.

I have no cam specs but I told the bulder I wanted a RV style cam and the carb is a holley 650,all I know is the cam is for a 302 since I had to change the firing order. Jeff

Without knowing what the cam specs (overlap/valve timing) is, 15" may be good. A spacer replacing the EGR, assuming all of the possible vacuum holes, leaks and ports are sealed will make no difference for a vacuum reading.

Second - is the vac gage needle steady at 15". If not, you may have other problems?

Next, is the timing correct? It should be in the neighborhood of 9-11degrees initial.

Last, some Holleys had a 'reverse' mixture setting. Depending on the condition of the carb, you could have throttle shaft leaks, body leaks or poor gaskets. Also - a 650CFM Holly is too big for a generally stock 351, especially if it is a '76 motor with the little valves. A 500CFM would be sufficiant.