Mondo spark knock !
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Joined: Nov 2003
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From: taos
Mondo spark knock !
I'm looking for suggestions to eliminate excesssive spark knock in my 302. I put a used 302 out of a 79 mid sized car in my 78 f 150. I eliminated all the pollution control devices ( most pieces were beyond repair) egr etc., plugged the back of the heads . I took the vacumn for the dist off the port on the left side of the carb and set the timing to factory spec. It's ok at idle and light throttle but under load in mid range it knocks like a diesel. I know I can retard the timing but I don't want to back off to much on it and I also suspect there is a problem or a better soloution. Should I be taking the vacumn off the manifold instead ? Is it possible to richen the fuel mixture on the stock 2 barrel carb to eliminate this ?
I looking for any and all answers '
Thanks.
Ice
I looking for any and all answers '
Thanks.
Ice
Senior User
Joined: Oct 2003
Posts: 480
Likes: 1
From: Elyria, Ohio
knock
Distributer should be attached to port on right side of carb (vacuum zero at idle; increases with speed). Mixture screws at base of carb (2). screw in until bottoms gently (don't gall). Start with each screw at 3 turns out. Using vacuum guage adjust each screw in a liitle at time and equally to achieve maximum vacuum at idle. Vacuum should be 19-21" and steady at idle or you have other problems. EGR valve connects by vacuum to a temperature controlled vacuum switch at back of left intake manifold. It gets vacuum from intake manifold or may get it from ported vacuum as the distributor; depends on calibration number. It should open at delayed higher speed and only when engine is warm. It allows exhaust gases back into cylinders to cool combustion of gas-air mix. Engine was designed for this operation; but many people successful remove it and air pumps and check valves; without problems. Removal requires careful blocking of non-used vacuum sources and removal of EGR base plate or a block off plate. Openings at heads where check valves were attached should be blocked also.
Cargo Master
Joined: Dec 2003
Posts: 2,735
Likes: 38
From: Sunny Florida
Whats the timing set to? Is it hard to start when its warm? If so then you need to retard the timing. This will ease the hot start problem if there is one and it will also reduce or elimnate the spark knock.
It sounds like you have to much advance in your timing. Higher ocatne could helps as well.
It sounds like you have to much advance in your timing. Higher ocatne could helps as well.
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New User
Joined: Nov 2003
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From: taos
The timing is set at 8 degrees btc at idle with no vacumn to the distributor. There is no hot starting problem. It seems as though I'm getting to much advance once I come off Idle . I'll check my vacumn source for the distributor with a gauge back off a degree or two on the timing. and do the carb set up as advised. I'll double check all the vacumn points I sealed off and let you know the results. Thanks one and all!
Elder User
Joined: Apr 2003
Posts: 627
Likes: 1
try adjsuting the tension on the springs in the dist. there is a slot through which you can put a screwdriver and bend the tab out which stretches the spring further and slows the mech. adv. so that your timing is less adv. at speed. in effect changing the curve.
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