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Low vacuum
Recently rebuilt a 351W and installed SEFI. When I initially started the engine, I had to rotate plug wires around the cap one spot in order to get the engine to fire. When I attempted to time the engine, I noticed the timing marks were off significantly - about 30 degrees AFTER TDC - not BTDC. Engine ran fine though. Next, I noticed I was only pulling 8" of vacuum. Before buttoning up the engine, I did ensure cam and crank marks lined up on TDC. Any advice on where to start fixing this problem cause I assume they are both related to one another. Thanks for the help
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Pull distrubitor, find TDC compression stroke and reinstall disrubitor, see if that helps.
The distrubitor may be off a tooth or so. |
Did you check that the damper TDC mark and the pointer lined up with the #1 piston at TDC? If not, check that, the outer ring on the damper might have slipped.
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There are different timing covers with a timing mark at 10 oclock or 11 oclock, the harmonic balancer marks must be matched. Some balancers have several sets of marks. If you couldn't re-index the balancer, you could find TDC and put some timing mark tape on your balancer .
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Hard to believe that motor would "run smooth" at 30 ATDC......
but the low vac reading certainly points to retarded timing. ASSUMING, you have no vac leaks, valves are adjusted correctly and your not running some radical cam. |
Some ideas
Not knowing the WHOLE story on this engine: Stock heads, type of cam, correct push rods fot the type of head, and valve, solid or hyd. lifters, was the engine assembled correctly, or maybe the ring gaps may be incorrect.
If all the above is correct, remove the #1 plug, be sure the #1 piston is at the top (on the compression stroke) pull the dist and re install so the rotor is pointing to the #1 wire. follow the rotation, and check each wire to be sure they are all in the correct firing order. |
I'm with Mike on this, the small block Ford has had the timing pointer in at least three different locations over the years. If you mismatch the damper and timing cover the timing mark will be crazy.
You cannot have 30 degrees AFTER TDC timing and the engine starts and runs. The 8" vacuum could be the result of not enough timing, since you really don't know what it is now, or just a very low idle RPM with a performance cam. Ed |
Most of the 1970's on up smog engines are designed from the factory to run retarded. If you upgraded your cam and and replaced the timing chain and sprockets with a factory or OEM unit, your engine could be out of time.
To fix this you must start over, install the cam timing chain sprockets that are compatable with the cam. Also some sprockets on the crank on after market units have as many as 3 different key way groves for differnent timing applications, so if you put all new stuff in, make sure the sprocket is lined up on the right key way groove. Call the tech line at the cam manufacturer, and find out if your parts work with theirs. Don't waste your time with some guy behind a speed shop counter for the right information. |
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