Idle problem on C15 261 CU IN

[Bob Carriere]

Hi Terry

The "R" plugs should not be a problem.... what is the heat range?? 42 being the coldest and 47 the hot ones for used for heavy trucks/firetrucks.... delivery trucks doing a lot of stop and go.

Make sure you have a proper connection for the vacuum gauge as once you use it you will be reconnecting again. Vacuum gauge can be used to set the timing without being double jointed with a timing light. and set the carburator idle screw. The aim is always to adjust until you get the highest steady vacuum reading.

My carb came form the Oaks Brothers in the West end of Toronto....... sons have taken over from Dad..... they do a lot of carbs for expensive restoration and calibrate hot rodder carbs using an old fashion flow bench with kerosene......huge contraption that actually flow/sucks air through the carb and allows them to adjust jets for engine cfm requirements. When you get your carb back they are ready to be isntalled and engine will start right away with just minor adjustments to the idle screw. Cost was just shy of $200.

I actually dealt with the Dad who only deals with the older stuff. He has a huge inventory of carb core all cleaned up, but not assembled until required.
He also made me a Zenith 22-228, which was used on the 270 GMC engine and has an external adjustment for the main jetting. Haven't tried it yet.
Another good source would be CarbKing on Stovebolt forum. There is a multitude of YF carbs out there some for Ford and some for Jeeps and AMC... you need to have the right carb number and jetted for the 261..... the Zenith is unique in having a removable inner throat passage that allows to tailor to various CFM requirements...... they were still being manufactured up to a few years ago in California for over $500 US.

I noticed that you have a steel cap fuel pump..... I love the original upside down model where you can see if fuel is moving...... but they are prone to drying up the cork gasket under the bowl and leaking badly...... last time that occurred Grant ordered a dozen gaskets for spare on Ebay.

Phil may be on to something with the fuel supply...... worn plunger running on a worn camshaft.... dirty fuel valves inside...... worn pressure spring.... air leaks...... I think a fuel issue is more likely to cause a cycling of RPM than a steady vacuum leak.... air leaks tend to be air leaks and steady.

What rpm idling speed are you aiming for???? and are you using a tachometer to get an accurate reading...... you might be trying to set it too low.

With the vaccum gauge connected you can adjust the timing by hand to get the highest reading....... than move to the idle screw mixture on the carb and repeat the process to get the highest vacuum reading..... then adjust the mechanical idle screw on the bell crank...... and repeat the last two process until it runs good.

Its always the piddly little stuff that takes the longest.

Cheers

[Bob Carriere]

The Oaks Brothers..... now seem to be operating from the same location under the name....

Carburetor Rebuilders Company Limited
60 Eugene St
North York, ON M6B 3Z4, Canada

The Dad was in is 80 when I last saw him a few years ago.....

They now seem to be offering machine shop services for milling heads, manifolds, ect.

cheers

[TCLARK]

So far the fuel pump tests at 4 psi and holds so its good. The plugs are
AC R43S They all look nice and orange so there is not one misfiring.
Next I will warm up beast and test vacuum numbers 18 psi ??

[TCLARK]

So i set the plugs to 40 and reinstalled. I then hooked up a vac gauge
and got 18 inches at 1000 rpm but only 6 at idle. The minute I hooked up the vac gauge to the carb the idle seemed to smooth out. I put a different brASS
fitting into the carb for the vac line and hooked it up to the distributor..seems to idle nice. It had a slight bog when doing a gentle rev up from 500rpm to 1000rpm, so I retarded the timing and that got better.
The engine runs very nice now not really sure why as I still only have poor vac at idle. The vacuum did not change by adusting the timing??

[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