Idle problem on C15 261 CU IN

[TCLARK]

Maybe someone has had this problem also. I am having trouble getting the Chevy six to idle nice. It never quits but seems to go up and down about 150 rpm when idling.
I put in a carb kit (Rochester B) and added a pertronix ignition. Still not
idling nice.
The pertronix was quick to put in and the engine starts instantly now. Also the plugs had been black with poor combustion but I took it out for a spin and they
are all light brown. I think that it also has way more power than pre pertronix.

The distributor vacuum seems to work fine but this engine does not want to idle
smoothly.

[cletrac (RIP)]

Check for a vacuum leak.

[TCLARK]

Maybe the vac advance pot is leaking, I will check that. I heard that propane around the leak will increase rpm and can be used for finding leaks.
Thanks

[Bob Carriere]

Hi Terry

With the Pertronix I had to increase the gap from low 30 to 40 thou...

What kind of plugs are you using??.............. I am using AC C43

Have you tried a vacuum gauge yet..... directly to the manifold....... reading should be steady at 18 + or _ at about 500 rpm.

How slow are you trying to idle the engine...... the 150 rpm variation was it seen on a tachometer?

How does the increase come on and off........ regular intervals or odd interval.... at what RPM those the engine smooth down???

Do you have a see through old style glass gas filter just before the carburator???? do the fuel level vary a lot when idling....... bowl should be about 2/3 to 3/4 full......

The rebuilt Rochester B .... was it the original for that engine and does it have the larger throat opening... any sign of leakage around the carb top cover..... did you check against a flat glass to see if it might be warped.

If you were closer I would suggest swapping carb with mine to see if makes a difference...... currently using a YF carter which is a dream.

The increase in rpm as to be either more gas coming in or an air leak but a leak is a leak...... maybe just lack of fuel..... carb float too low...... anemic fuel pump not sending enough juice at low rpm....

Puzzling......

Cheers

[TCLARK]

I'm using AC plugs with an r in front of the number meaning they have built in resistance, that could be a problem.
I haven't yet hooked up a vac guage, my vacuum line is original steel and needs
to be tee'd.
The rpm flutters at idle at odd intervals about 2-5 seconds apart, I do have a new
plastic in line fuel filter, that is not plugged.

The carb is original to the 1959 261 engine,it has no gas leaks, but I didn't
check for warpage. I saw on you tube that warpage can be a problem.
Bob where did your carb come from?? What year an d model of vehicle,
I wouldn't mind finding one.
I will tackle this again tommorrow

[Phil Waterman]

Hi Terry

Everyone is hitting the most likely cause for lopping at idle, so you have a long list of things to work through. To add to the list what do you have for fuel pump? As Bob suggest fuel flow and pressure are also possible causes. Air leak in can be one of the hardest to track down. I had air leak at the fuel selector valve that took forever to find.

Reason for asking what do you have as fuel pump, is mechanical pumps can have problems at low RPM if the pivot points are worn, or valves in the pump are not sealing, fuel pressure gage should help ID those issues. Electric pumps seem to be more bothered by air leaks on the suction side. One quick check I've used is installing a section of clear tubing just before the carb, looking for air bubbles.

Keep us posted on what you find.

Cheers Phil

[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

[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]

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.

[Lynn Eades]

David, my guess is that your coil is about the right resistance to match the Pertronix then.
Have a great Christmas! It's about 28 minutes off for us down around here.(leading the way into the next day)

[TCLARK]

Just read the question and answer portion of my pertronix instructions.
The 6 bangers need 3 or greater ohms resistance on the coil, while an 8 cyl. needs 1.5 ohms or greater. With a high power coil we then need a ballast
resistor....my resistance is 3.5 with resisor in circuit. To get away with
no resistor, the coil on a 6 banger can be only 40,000volts.
Merry Christmas everyone
Terry

[Bob Carriere]

Hi Terry

Survived another Xmas........ came back from TO today...... in freezing rain.... 401 was shut down on the East side and a parking lot for us heading East bound...... in a section that dips and curves near Brighton over 9 or 10 transport we all smashed up.... I mean broken up with cargo spewed all over.... more large and extra large two trucks and cranes trying to unload steel coils off the wrecks onto safe flatbeds.....

Back to reality..... I suspect that that your vacuum connection to the carb port is/may be to blame for such a low reading and the engine still running good. That vaccum port is only intended for the dizzy vacuum pot I beleive.

But you are on to solution when you say you will need a spacer for a proper vaccum and wiper connection. Originally my 1959 Chev 261 had a vaccum port on the square chamber just below the carb phenolic insulator. But when I went to install the engince cover there was not sufficient space for that original fitting so it was removed and plugged.

I had a local metal fabricator cut out a spacer from 7/8 flat stock based on the outline of the phenolic insulator. Had him drill and tap three 3/8 holes for future vacuum connections. I used thin paper gasket between all surfaces and the thick gasket with the groves immediately below the carburator. My centre hole matches the 2 15/16 in. bore of the carburator. One hole is currently used for the wipers..... which work quite well.... and the other for my permanently mounted vaccum gauge.... mounted below the dash left of the steering wheel.... the 3rd hole is used for the PCV.

Are you saying that you do not have a PCV or it is not connected??? or are you using just a open draft tube...?

now for the photos.

I really think that if you were connected to the full vacuum of the manifold you would be getting a different reading.

Coil wise I am running a Pertronix 40K coil and no resistor.... runs fine. This is my second Pertronix..... the first one was installed in the original 1959 tall dizzy cap distributor..... which I found did not have sufficient clearance for the darn engine cover panels.... so I used a NOS 216 low cap dizzy with a new PErtronix as the old one from the later tall dizzy did not fit inside the older 216 distributor.

Cheers

PS.... first picture shows the Rochester B second shows the Carter YF.

Also elected to make use of the steam vent line on the head. We originally installed it with a valve in the system. We would run the engine until well hot than open the valve and see all the foam and bubbles vent to the radiator through the clear vinyl line. We concluded that it was worth while to have it connected permanently and replaced it with a repro steel brake line, covered in fabric as per the original, and it has served us well so far.

[TCLARK]

Funny , I today was working on the truck and thought I should replace the
phenolic spacer on my truck,as I mentioned earlier. I have the original vacuum hole on the manifold closed off, so this makes sense. I will pursue this tommorrow, as I need
a vacuum port for the wipers. I may also tap another 2 ports as you have
done,Bob! Can't wait to see if the vac is better! I do have an open draft tube. I may not meet California emissions standard!


Anouther little problem I have is with the heat gauge on the dash . I have tested my original gauge on the bench and it worked. I hooked a new sender
to it and get no response. I do have that 12 to 6v electronic voltage reducer
on my truck and am taking 6 volts off that to power up the heat gauge. Now
I'm wondering if there is a difference between a 6v sender and a 12v sender.
I have a 12v sender on a 6v gauge?? Probably an issue

Your engine looks great Bob, very lucky to have you to do my homework for me,ha ha
Cheers
Terry

[Phil Waterman]

Hi Guys

Wondering what are you using for a manual on the 235 & 261 engines? Are there significant differences between any of the timing or carb specifications? Particulaly are there differences between the US and Canadian versions.

I've had sectons of the 1960 Truck Manual covering the 235 and 261 truck engines http://canadianmilitarypattern.com/1...e%20Manual.htm if there are other sections of that manual that anybody needs let me know.

I remember that some of the vacuum advance systems have a special fitting that looks like a regular fitting but has a very small passage through it, purpose to dampen sudden changes in vacuum. Can not find my notes on which engine or carb I found this.

Cheers Phil

[Bob Carriere]

Hi Terry

................ Hi Phil

My truck has a GMC civilain rectangular dash. Only the gas gauge and the amp meter are connected and working. I used a voltage reducer on the gas guage and the amp meter as is.

I am using an after market mechanical heat guage with the bulb installed on top of the steam outlet on the original 216. I also have a mechanical oil pressure and a vacuum gauge. I later installed a tachometer......all in the interest of better monitoring the performance of the engine..... they may be removed at a later date not sure when as I now depend on them.

Nice to know you are doing 2000 rpm at 30 some mph even though the engine is screaming and the gears whining all is good. Gets close to 2900 at 44 mph flat out..... with me holding on tight. Nicer to drive at 30 - 35 mph just relaxing.

Really curious to see what kind of readings you get when you have a proper manifold connection.

Phil........ any tips or tricks you want to share....?

On a 248 GMC fire truck engine they actually add a 5 to 6 inch adapter/spacer for clearance purposes with other do-dads installed on the engine. I have read somewhere, from hot rod sources, that increasing the length of the air flow and increasing the size of the vaccum plenum is beneficial to engine performance...... so an extra inch spacer certainly will not hurt. Just make sure that you have a good seal on all joints..... paper gasket smeared very lightly with silicone sealer works great for me. Just apply the silicone to index and thumb and smear the paper...... gets tacky and compresses well with no overkill silicone getting inside parts.

Phil are you using a NOS spacer or a homemade one??? they do come up on Ebay once in a while.

Cheers

[TCLARK]

Hi Phil and Bob
Phil you were right just a small hole to suck vaccuum thru for the
distributor. I would guess for dampening also.

Bob I just got the spacer made ,it took about an hour but visiting neighbors
for a piece of 5/8 flat took half the day.
I put it all together and voila about 20 inces at 475 rpm idle. I'm
so happy, this engine purrs like never before.

Now I have to hook up the wipers does anyone know where to get the proper Blades?? I have one new nos wiper arm I got at a swap meet (even orig. OD) and one not
so good but usable. How does the blade attach to the arm?

Cheers and thanks for the great advice!
Terry

[Bob Carriere]

Good show.....

Now how about a picture of the spacer???? and your wiper arms......

.........will Photo some of my wiper arms and wipers... and post later tomorrow....usually available from most Jeep repro sellers.

so glad it worked out for you.

Now that you are getting a better reading...... try getting a higher reading first with the dizzy then with the mixture screw on the carb try for 21 near 22.....

Cheers

[rob love]

The old trico wiper blades were/are still used on the MLVW. I believe they are 11 or 12" long. You can find the same design bladfes as short as 4-1/2" long. Have a look on ebay for M35 wiper blade, or M38A1 wiper blade. If the blades you get are too long, you can cut them down with a dremel tool with cut-off wheel.


http://www.ebay.com/itm/Wiper-Blade-...5R6DvU&vxp=mtr

http://www.ebay.com/itm/Jeep-Willys-...5X0xFj&vxp=mtr