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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Feb 2008 Posts: 23 New Guy | | New Guy Joined: Feb 2008 Posts: 23 | Hi Bolters...need some expert advice. I have a grandson with a 1954 3600 ad. He is a minonite and cannot have a computer. He has trouble with vac. advance and timing. He has a 1973 250 chev. six, 4.1 liter, Rochester single bbl. In it. He says vac. coming from base is too strong and messes up timing. Is this possible?. He put a tiny ball valve in line to reduce vac. in order to run at all decent, I said I would ask the experts. What is the proper way to set timing so it performs thruout the rpm curve..Appreciate input Sepp
Plattelnjpichler
| | | | | Joined: Feb 2004 Posts: 29,792 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,792 | Tell him to get a horse!  Actually, most carburetors have two types of vacuum ports- - - - -Manifold vacuum, which is taken from beneath the throttle plate, and "ported" vacuum which is not present at idle, and comes in gradually as the engine speed increases. If he's putting full manifold vacuum to the advance at idle, that's probably the source of his problem. Try to find a carb port that does not get any vacuum until the engine speeds up above idle RPM. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Feb 2008 Posts: 23 New Guy | | New Guy Joined: Feb 2008 Posts: 23 | Jerry...thank you very much. Makes sense. I wil ask to see where he is picking up Vac. Much appreciated...Sepp.
Plattelnjpichler
| | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | The ball restricter is a bad idea. The vacuum needs to fall off imediatly when you accel. hard. Jerrys sugestion is good. Also he may have too much initial timing.
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Feb 2008 Posts: 23 New Guy | | New Guy Joined: Feb 2008 Posts: 23 | Thanks again. I remember timing my own 53 3100. I always block off vac. hose to time at idle. I have to see for myself when I get out to their farm. 150 mi away. Going there when weather gets better here in Pa. Appreciated....Sepp
Plattelnjpichler
| | | | | Joined: Jul 2006 Posts: 190 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Jul 2006 Posts: 190 | My vac line has a fitting that where it hooks to the vac line the hole is 2x the size of the hole that screws into the carb.(small hole is about 1/8 across vs 2/8 on opposite side.
Last edited by wasat again; 01/28/2011 12:41 AM.
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