Idle problem on C15 261 CU IN

[Bob Carriere]

Hi Terry

How steady is the reading at 18 inches........?

If she is steady but looses vacuum slowly as you lower the idling speed..... you may have a small air leak that is easily overcomed by more rpm..... now a small leak may be hard to find but an un-ignited propane torch or a spray can of ether should work.......

You say that moving the distributor by hand did not affect the vacuum reading?? It should make it stumble in either direction and you aim for a middle point..... then drive it ... if it pings or stumble it needs to be either retarded or advanced slightly...... I now use the vacuum gauge to set the timing.

Now the idle mixture screw ...... have you played with that yet......

How are you controlling the engine speed right now.... do you have a manual throttle cable installed yet????

Try setting the rpm at around 800 then go in and out no more than a full turn on the mixture screw and watch the vacuum gauge.... aim for the highest reading..... slow the rpm down a notch to 700 rpm using the idle screw on the bell crank and repeat the process.....

You may have to find and cure the leak before the final adjustments.

Don't quit now you are so close.....

.... at worst stay up late Xmas night and ask Santa for advice.

We did our home Xmas yesterday as we are travelling to the inlaws on Xmas eve on the far side of Toronto.... so already all turkeyed out.

All the Best for the NEW YEAR and a very Merry Xmas to finish 2016.

Bob C

[Lynn Eades]

The Pertronix requires resistance leads and the correct coil. If your leads are copper wire then your resistance plugs are probably important.
Have you checked for an air leak at the inlet manifold (at the head)?

[Bob Carriere]

Solid copper wire are mentioned in the Pertronix instruction as being potentially deadly to the module.

Some how, on looking at Terry's modern ignition wires, I suspect that they are the modern 8mm carbon fiber of today.

I was using a set of carbon wire from the 50s when I installed my Pertronix and had to upgrade to a 7mm modern black set up as I was getting shocks whenever I handled the old NOS wires......that Pertronix high voltage 40 thou coil sure puts out a hot spark. Once I regapped the plugs it ran noticeably better.

I lucked out years ago, when plugs were still cheap on Ebay, and acquired a lifetime supply of various NOS AC plugs in assorted heat range.... now they advertise the same plugs as fitting early Corvettes and increased the price accordingly.

[TCLARK]

Hi Bob
The vacuum reading was about 6 at 500 rpm. It went up to 18 at 1000 rpm.
The vacuum held steady at both rpms so that is good. I took it out for a run
and it ran so nice I m almost afraid to touch it. I set the idle jet to 1 3/4 turns
as per factory spec (Chiltons). I will go out and play with the idle screww at 800 and then at 700 and see if I can fine tune. This morn I barely touched the starter and she fired up instantly; never done that before. This is the pertronix and the big spark plug gap doing its thing. I may also get the ether out, some guys use acetylene as a final leak check

Hi Lynn
I did check the manifold and all looks good, I am using noncopper leads
from a hot rod shop they were expensive but leakproof as the wires are so close to the firewall . My coil is a Baster II 8802 I have it powered through the 12-8 volt resistor. I was wondering with pertronix if I need that resister
or maybe its a coil spec?

Thanks everybody for the help and excellent advice . Merry Christmas to all!!
Cheers Terry

[TCLARK]

Thaqt is a Blaster 8202 not 8802

[Bob Carriere]

I don't think you need that resistor.....check the instruction or visit their web site.

The idle vacuum has to come up. Are your windshield wipers connected...? any chance of a small leak in that system??? The only time my vaccum gets that low 6 ......is if I floor the gas in 3rd or 4th gear.

Steady vacuum reading is encouraging...... whatever is leaking must be very small and easily overcomed by the higher rpm.
You are going to have to get very close to the intake manifold, carb base, wiper output pipe, dizzy vacuum advance......check the PCV system as well........ may be stuck open...... take it apart and clean it in carb solution......

Cheers

[TCLARK]

I checked the website and answer is a bit obscure, I think I will stay with
the resistor for now.
I have set the idle at 480-500 rpm the vacuum is still only5.
I have only the carb vacuum port to check, I have no wiper tubing
or port for the wipers. I may need a base with a nipple on it for
wipers. There is no pvc system on this set up so that isn't a worry
This has me thinking I should check the bakelite carb base. It
is orginal to the 1959 2 ton truck this motor came from
Cheers
Terry

[motto (RIP)]

Originally Posted by TCLARK

I have it powered through the 12-8 volt resistor. I was wondering with pertronix if I need that resister
or maybe its a coil spec?

Cheers Terry

The rationale behind the 8 volt coil as I understand it is that it only has 12 volts applied whilst the engine is cranking on the starter. They are normally used with a key ignition that has OFF, RUN & START positions. In the start position the resistor is bypassed, in the run position the coil only gets 8 volts. Applying 12 volts full time may do it no good at all.

David

[TCLARK]

David ,you are correct, however with the pertronix eliminating the points
the only thing to worry about would be damagin g the coil
I know some blaster coils have a resistor built in,but this one does not. The answer would be to ask the Blaster coil guys on their website
Terry

[Lynn Eades]

The wrong coil will kill your Pertronix. There are Pertronix, Pertronix II, and Pertronix III. All require different coils.

[cletrac (RIP)]

I put a Petronix on an IHC Lodestar with the stock coil and haven't had any issues with it in about 15 years.