modified 351 question

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72mach0ne

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Apr 19, 2011
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Location
Los Angeles-Valencia
My Car
72 mach1
65 convertible
i have a built 351 and most the time i drive it i feel like im getting choked out by the exhaust fumes. the car is bare metal other than the dash a little carpet and front seats. even people driving behind me on the road can wiff it. having it idle in my driveway stinks up my front yard too. i dont have any exhaust leaks(i had it checked). im just wondering if these motors are characteristic of that or is it because i dont have interior panels in? or could it be something entirely different?

 
i have a built 351 and most the time i drive it i feel like im getting choked out by the exhaust fumes. the car is bare metal other than the dash a little carpet and front seats. even people driving behind me on the road can wiff it. having it idle in my driveway stinks up my front yard too. i dont have any exhaust leaks(i had it checked). im just wondering if these motors are characteristic of that or is it because i dont have interior panels in? or could it be something entirely different?
Just sounds like its running rich. Tune the carb. and make it run a little leaner.

 
Our carbureted cars will not idle or run as clean as the EFI engines we currently are used to. They idle and run richer because they are not as efficient. No matter how much we tune the carbs they will have rich smelling exhaust fumes unless it is converted to fuel injection.

 
go over the carb and give it a good tune, tune the air fuel ratio screws, power valve size, etc.. just go over it all and make sure the carb isnt too big for the motor as well

 
Check that you are firing on all 8 cyls before messing around with the carb.

Get a vacuum guage. Hook it to manifold vacuum. If you have a stead needle at idle then you are firing on all 8.

This would be a good time to set your initial timing. Advance it to the best (highest) vacuum reading at idle. Test drive. If it pings, back the timing off. Keep driving and backing off until it no longer pings. If you have to really back it off it might be a good idea to look at a recurve of the distributor.

Okay. Now you can mess with the carb.

 
Adjusting timing and carb are good as mentioned.

You may be over-carbed too with that double-pumper, you didn't say what size it is.

A vacuum secondary just takes what it needs so it is more forgiving of over-carbing. A D-P just throws the gas in wheather it can use it or not.

In addition it could be your PCV system not working or not hooked up letting out bad crankcase fumes. You breather has to be un-clogged for the PCV to work.

 
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Learn to tune your engine and carb. You will need a vacuum gage and timing light. Performance builds won't work on a factory tune so don't go looking up the factory timing or idle settings. When I start to tune a new build I set the timing first. Hopefully you checked that the timing pointer and marks on the balancer were lined up correctly with #1 at TDC. A performance build will need more lead timing and less advance curve. I start with 16*-18* degrees advance at idle and a curve of around 14*-16* degrees advance and all in by 2400-2800. Now this is just to start. You will need to change these setting if the car is hard to start or you have a heavy car and need a slower advance or a light car and a faster advance or an engine that needs more total timing. On a street car I like to run a vacuum advance and I like to run it to a full manifold vacuum port. Full manifold vacuum at idle helps clean up the idle and helps cover any stumble you may have off idle. Now that the timing is close, start tuning the carb. Idle vacuum will tell you what power valve you need. Engines with low manifold vacuum (10, 11, or 12 inches) need a power valve circit that starts to open around 4.0-4.5 inches of vacuum. If your idle vacuum is lower than 10 you do not have a street cam and most of this information will not apply. You want your idle screws set at your highest idle vacuum. If you turn the idle screws and they don't seem to change much you my have the idle speed set screw open too far and you are starting to uncover the transfer slot. If this is the case you my need to drill holes in your throttle blades so you can let more air in but close the idle speed set screw. Last is the accelerator pump. Most Fords like a pretty big shot from the accelerator pump so on a Holley put a bigger squirter on first then if this still leaves a stumble change the pump cam. On a Eddy or Carter change the squirter and pump lever hole. The end product is a clean idle no stumble and it goes like stink when you stomp the gas pedal. There is a lot of information on the web about tuning carb engines so plan on doing some reading.

Another area that may need some work is the ignition. Factory Ford ignitions don't seem to do it for me because I like a real strong spark. Some people like the factory Dura-Spark but I have never had one work like I wanted it to. I perfer MSD ignition boxes like a MSD-6A or MSD-6AL. Because these do not pull power through the factory wiring harness you don't get any break down in power supply. Now again there is a lot of information on the web about how to get a hotter spark ignition. I even have one set up on a friends car that uses a GM style HEI module with a Dura-Spark distributor. So do some reading and have fun tuning carbs and stuff.

Andy

 
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