1970 Lt1 carb. settings

todd micheal · #1 06-13-2010, 02:21 AM

Looking for some feed back... I have a 1970 LT1 M21 4:10 ratio 1970 in a nova. all stock including, air cleaner, exhaust manifolds full exhaust,11 to 1 compression, solid cam with a longer ratio rocker arm, and a smog pump spinning around but not pumping.With a 780 holley carb. My car seems like it could use more fuel. The 202 heads have been ported by machine shop,and bowls have been cleaned up.this is the only wild card. I have the timing set to 8 degrees.Engine has 14 inches of vac. at idle. The primary jets are:78 high flow Power value is 5.0 front and rear. The rear jets are 80 high flow I have a 35 squirter in the primary. Thats whats funny i have been up to 42 and makes no difference, whats going on.... Looking for feed back from z28 guys and deuce owners with similar engine internals to what makes the best torque and horse power. Please help. Thanks todd.

al8apex · #2 06-13-2010, 02:38 AM

What do you mean by you think it needs more fuel?

Is it running out of RPM?

I run a lot more initial timing that that (more than twice) but you need to know what your total advance is and when it is acheived.

I found the FACTORY jets to be WAYYYYYY to rich for my 1970 Z28 M22 with 3.73's for the street. But if you are only going to run it down the drag strip, your cylinder wall washing richness is ok there, but WAY too fat for the street IMHO and experience.

I took my stock primaries (70) and moved them to the secondaries (that WERE 76) and went to 68's for the primaries, lots more response, crisper and only on severe upper acceleration was it any different than the jets that kept on fouling my plugs during everyday street driving

you could take it to a dyno and get it dyno tuned, that's what they did back in the day

todd micheal · #3 06-13-2010, 02:58 AM

Thanks for the input. i had more timing but went back to stock and had to start some where. How do i figure total advance What size squirter do you use. Never have fouled a plug yet in 2000 miles, yes feels like the car could have more off the line. it pulls ok , wont break tires loose unless you drop clutch. car pulls ok and then kinda goes flat, stops pulling but keeps aclerating.

al8apex · #4 06-13-2010, 03:18 AM

sounds like your timing is one of your issues

I have the stock carb, 4555 780 cfm, stock accel pump

al8apex · #5 06-13-2010, 03:30 AM

the power valve should be 8.5:

http://www.mopar1.us/carbs.html

todd micheal · #6 06-13-2010, 03:36 AM

Yes that is the one thing i m going to do is change power value to 8.5 How do i set timing up like you have done with total advance. what is the stock squirter size?? Thanks todd

**markjohnson** · #7 06-13-2010, 06:08 AM

I can't believe it calls for a 8.5 Power valve! On a decent-sized duration camshaft, that PV would be opening early and fouling plugs. I think I'd go with a 6.5 PV. Get Eric's (Vintage Musclecar) advice on this.

todd micheal · #8 06-13-2010, 06:39 PM

Any idea what i could advance timing up to?? And from there i will get a vac. reading and split in half and pic power value.

todd micheal · #9 06-13-2010, 07:23 PM

How do I contact eric (vintage muscle car) any one.

**markjohnson** · #10 06-13-2010, 07:46 PM

I'll do my best to verbally explain this since no one else has stepped up. I'll assume that there's no timing tape on the balancer. Take a measurement on your timing tab from the O-TDC hash mark down to the 12 degree hash mark. Multiply that measurement X 3 to come up with the distance where 36 degrees should be on your balancer. Mark this position with some white paint/chalk on your balancer, while revving the motor up to 3000 RPM, check where your timing mark is on the timing tab. That's the total degrees. I use a very simple Timing Light (without the dial) and make sure the Vacuum Advance is dis-connected. 36 Degrees total is a great starting point and motors are usually very happy righ there.