bad surging
#1
Junior Member
JOURNEYMAN
Thread Starter
Join Date: Mar 2004
Location: East Tennessee
Posts: 27
bad surging
In my street car I have a very bad surging problem at all speeds. This started happening after I changed cam and heads a little over a month ago. I know that a bigger solid lift cam will have a little surge to it but I think I have way to much. Even at a cruising speed of 3000 RPM (near 55-60 MPH) the surge is so bad that I am thinking if I do not fix it soon that it will lead to fatigue on the drivetrain. At wide open throttle it runs very strong but it will not level out for cruising at anyspeed. DOes anyone have any ideas what might be causing this? I am out of ideas.
Thanks, Scott
Thanks, Scott
#4
Junior Member
APPRENTICE
Join Date: Jan 2005
Location: Rochester, Minnesota
Posts: 13
My best guess is that your engine is over cammed and not intented for street use/crusing speed. Do you have a mechanical advance in your distributor? If so your weights and springs might not be right for those speeds, might even be broken, also do not use your vacuum advance if so equipped.
Outside of that, look at your power valve and adjust accordingly. Check your vacuum at idle if you have 8 inches of vaccum at idle put in a 6.5-7.0 power valve. Run 1-1.5 point smaller power valve than actual idle vacuum.
Outside of that, look at your power valve and adjust accordingly. Check your vacuum at idle if you have 8 inches of vaccum at idle put in a 6.5-7.0 power valve. Run 1-1.5 point smaller power valve than actual idle vacuum.
#7
Senior Member
RACING JUNKIE
Join Date: Sep 2007
Posts: 4,137
Originally Posted by OneBadGMC
Sounds lean at part throttle to me.
If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
#8
Member
MASTER JOURNEYMAN
Join Date: Apr 2005
Posts: 41
Originally Posted by Tod74
Originally Posted by OneBadGMC
Sounds lean at part throttle to me.
If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
#9
Junior Member
JOURNEYMAN
Thread Starter
Join Date: Mar 2004
Location: East Tennessee
Posts: 27
Thanks to all that have replied. Today I pulled the plugs after driving it for a while and they were tan in color. There are no power valves they were plugged a long time ago. I can not remember what jets are in it but I think I went up about 3 sizes straight from the box. I did not have this issue until I changed cam and heads during the winter so I am guessing the pump to still be good. The float levels haven't changed either. I am using 2- 450 CFM holleys on a Weiand Tunnel Ram Intake (same as before and same dual point distributor as before also. I am just out of ideas.
Thanks again, Scott
Thanks again, Scott
#10
Senior Member
RACING JUNKIE
Join Date: Sep 2007
Location: Belleville, IL
Posts: 658
If you changed heads and cam, and it's making more power, you need more fuel to feed it....
It's lean...
Another thing that can cause crappy performance at part throttle is the lack of an air cleaner, or air rushing over the top of the carb, throwing the air bleeds outa whack.
Did you remove the hood? Did you take off the air cleaners? Change anything on the induction side other than cam/heads?
It's lean...
Another thing that can cause crappy performance at part throttle is the lack of an air cleaner, or air rushing over the top of the carb, throwing the air bleeds outa whack.
Did you remove the hood? Did you take off the air cleaners? Change anything on the induction side other than cam/heads?