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| | | | Joined: Oct 2010 Posts: 5 New Guy | | New Guy Joined: Oct 2010 Posts: 5 | i have a 283 with rochester 2 brl it idles great but hesitates and backfires through carb and exhast on acceleration new carb new hei ignition new plugs tried different timing and different settings noticed advance has constant vac is this normal? any suggestions | | | | | Joined: Jun 2009 Posts: 2,201 Shop Shark | | Shop Shark Joined: Jun 2009 Posts: 2,201 | I bet squeeze or somebody will check in with the vacuum routing plan soon.
The symptoms sound like retarded timing. Any chance somebody put a cam in the motor? | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | Full vacuum advance at idle is OK but must be unhooked when setting the timing. If the timing & all is ok your carb probably is not right. "New" carb usually means a reman & about 3/4 of them are not right. Make sure the accelerater pump has got a good shot. Or the float level may be to low. Are you sure the plug wires are on the correct cyl.?
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: Jul 2001 Posts: 3,887 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Jul 2001 Posts: 3,887 | someone call?  you did remember to have the vacuum disconnected and plugged when you set the timing? assuming you've got the line to the right port on the carb, yes there should basically be vacuum there alla time, not necessarily "constant", but the symptoms may indicate that the advance can on the distributor is frapped so the vacuum isn't moving the dist as designed .... pop the cap and make sure the base plate in there can move freely - if not maybe the springs are shot - if yes get a vacuum pump and see if the advance is responding Bill | | | | | Joined: Oct 2010 Posts: 5 New Guy | | New Guy Joined: Oct 2010 Posts: 5 | there is only one port on carb for advance and it has strong vaccume the advance on dist works great but it is new | | | | | Joined: Sep 2010 Posts: 695 Shop Shark | | Shop Shark Joined: Sep 2010 Posts: 695 | I always use a country rule of thumb... if it pops flame out the carb the timing's fast, if it bogs and pops out the backside, it's slow.
Granted I'm not a guru, but it usually is the case from my experiences.
Jerry | | | | | Joined: Oct 2002 Posts: 4,066 Bolter | | Bolter Joined: Oct 2002 Posts: 4,066 | how did it run before you started messing with it...
sounds like something electronic to me rather then fuel but..
Redryder pixMy HotrodA veteran - whether active duty, retired, national guard, or reserve - is someone who, at one point in his or her life, wrote a blank check made payable to The 'United States of America', for an amount of "up to and including my life."I am fighting cancer and I am winning the fight | Pain is part of life; misery is an option. | | | | | Joined: Nov 2002 Posts: 2,763 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,763 | A backfire through the carburetor can occur when there is fire in a cylinder and an intake valve open. Pretty difficult to get the backfire through a closed intake valve.
If the timing is right then the valve shouldn't be open (maybe the valve is damaged).
If the valve is closed when it should be, then the ignition shouldn't have fired.
Solution:
Compression test, followed by full ignition test using an oscilloscope.
Jon.
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Apr 2005 Posts: 1,971 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 1,971 | My guess is that the Accelerator pump is not working creating a lean condition when giving it the gas. It's gasping for air. | | |
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