Fuel System: Valve timing, now carb futzing

[Ron Dame]

I decided to start a new link that had a more helpful heading, original link here: https://forum.studebakerdriversclub....hom-this-today

Quick synopsis: after wondering about ignition timing. I was wondering about my valve timing, due to low vacuum and a hot cam. Doofus pointed me to how tho check valve timing in the manual, and thanks! There was some back and forth about cam card clearances vs stock cam clearances, and even that was convoluted, as the stock cam clearances and the clearances for checking valve timing are not the same. So I decided, right or wrong, that I would get #6 up to IN-OP (per manual) and check the clearance on the #1 intake. The result was 0.015", or about halfway between a stock cam clearances, and the cam card. I tried the stock clearance next, then the cam card clearance, and lets just say that I do believe the cam timing is indeed, correct.

Now back to the carb futzing: This whole thing started because the carb runs rich at anything but idle. ( Daytona Carbs remanufactured Carter AS, on a modified OHV6), and the vacuum is always low. Cam was reground to a 3/4 profile, and low idle vacuum is not surprise, but it seems low at speed too.. So we now know that the valve timing is correct, there are no vacuum leaks, ignition timing is correct, multiple vacuum gauges have been tried, so, to my mind, we are lead to the grind of this cam. I do have a stock cam and lifters I can install, but want to see if I can solve this Rubik's cube first.

If I am not mistaken, low vacuum causes a carb's power circuit to kick in, correct? If that is correct, what might I do to the Carter AS to make it less sensitive to low vacuum?

I know, I can always go back to the stock cam and probably, my issues will disappear, but I want to know what I could do to lean the mixture before I go to that effort, mostly for my education.

[doofus]

Read up on that Carter as. once you understand how the power system works you will see how to fiddle the metering or step up rod spring to open later. what is your idle vac.cruise vac? factory stepup spring opens at 6 in vac. if cruise vac is 5 or less it's open. i would find a different carb,simpler to fiddle carb to work with. you might try to disable the stepup system as an experiment to see how it affects things. Luck Doofus

[Ron Dame]

Read up on that Carter as. once you understand how the power system works you will see how to fiddle the metering or step up rod spring to open later. what is your idle vac.cruise vac? factory stepup spring opens at 6 in vac. if cruise vac is 5 or less it's open. i would find a different carb,simpler to fiddle carb to work with. you might try to disable the stepup system as an experiment to see how it affects things. Luck Doofus

Thanks Doofus, I'll google again for info on the AS, a few years ago it was too much noise in with the results to find infoermation.. If you know of good info on it, like the step-up vacuum, that would be great. Cruise vacuum is anywhere from nearly zero to10 or 12 inches. Idle is around 14.

[JoeHall]

Recalling my Harley Shovel and EVO hop up days: Some cam grind profiles, i.e. Sifton, primarily increase overlap, which makes the cam 'come on' strongly at higher RPM, but be doggish at lower RPM, especially if OEM / low compression pistons are retained (runs much better with HC pistons). The extra overlap also results in less manifold vacuum, at lower RPM, but more at upper RPM.

Other cam grinds, i.e. Andrews, primarily increase lift, and tend to come on earlier, at lower RPM, and do well with OEM pistons. I ran both Sifton and Andrews, and much preferred the Andrews. The Sifton style profile, which sounds like what you have, is gonna do better if you have lower gears, which keep the motor in the upper RPM range. It will always be a gas hog though. An Andrews style, actually gets better MPG, at least in Harleys. Yes there are thousands of cam profiles out there, and many claim to have the ultimate combo of lift and duration, but it sure sounds like yours has lotsa overlap, which causes the symptoms you describe.

Ideally, you'd add HC pistons, gear the truck down a LOT, and be happy with less MPG, in order to best enjoy that cam. Playing with the carb power valve (to make it kick in later / at lower vacuum) is only gonna decrease performance, and any MPG increase will be negligible. JMHO

[Ron Dame]

Recalling my Harley Shovel and EVO hop up days: Some cam grind profiles, i.e. Sifton, primarily increase overlap, which makes the cam 'come on' strongly at higher RPM, but be doggish at lower RPM, especially if OEM / low compression pistons are retained (runs much better with HC pistons). The extra overlap also results in less manifold vacuum, at lower RPM, but more at upper RPM.

Other cam grinds, i.e. Andrews, primarily increase lift, and tend to come on earlier, at lower RPM, and do well with OEM pistons. I ran both Sifton and Andrews, and much preferred the Andrews. The Sifton style profile, which sounds like what you have, is gonna do better if you have lower gears, which keep the motor in the upper RPM range. It will always be a gas hog though. An Andrews style, actually gets better MPG, at least in Harleys. Yes there are thousands of cam profiles out there, and many claim to have the ultimate combo of lift and duration, but it sure sounds like yours has lotsa overlap, which causes the symptoms you describe.

Ideally, you'd add HC pistons, gear the truck down a LOT, and be happy with less MPG, in order to best enjoy that cam. Playing with the carb power valve (to make it kick in later / at lower vacuum) is only gonna decrease performance, and any MPG increase will be negligible. JMHO

I couldn't tell you the specs off of the top of my head, but it is one that Ted Harbit spec'd and ground for me. I can get the cam card later today and post it. As far as compression with the 185 crank and the 170 head I'm already running a guesstimated 10:1 CR. I've got a 4:27 rear and overdrive. Sure, mileage would be nice, but teh sooty bumper and carboned spark plugs, plus the smell, is my frustration.

Worse case ( and I am considering it) is putting in a NOS cam that I have in. It might be better for low end torque anyway.

[PackardV8]

I couldn't tell you the specs off of the top of my head, but it is one that Ted Harbit spec'd and ground for me. I can get the cam card later today and post it. As far as compression with the 185 crank and the 170 head I'm already running a guesstimated 10:1 CR. I've got a 4:27 rear and overdrive. Sure, mileage would be nice, but teh sooty bumper and carboned spark plugs, plus the smell, is my frustration.

Worse case ( and I am considering it) is putting in a NOS cam that I have in. It might be better for low end torque anyway.

In for a penny, in for a pound, Ron.

Yes, one should be able to make a single barrel carburetor run without fouling plugs. You like the challenge, so beg, borrow or buy an O2 sensor and direct readout. I use the Innovate system and once you have that, you will be able to see where you need to change jet, power valve, et al. Some claim the Holley single barrel used on '60s Ford six-cylinders is the way to go. They came in small on the 144"/170"/200" and medium sizes on the 240"/250"/300".

Yes, the OEM cam will be better for low end torque anyway, but as you mention, your dynamic compression would then likely be too high for the combination.

Don't give up on the hot cam just yet.

jack vines

[bensherb]

Joe is right about the cam's overlap dropping vacuum.

I'm not familiar with the carb you mention, but if it's like the other Carters I've dealt with it sounds like you need to put a lighter spring in the needle assembly. Generally the spring lifts the needle as vacuum drops, but educate yourself on how your carb's intermediate circuit works to be sure. If it runs too rich with your "foot in it" you may need a smaller main jet.

The O2 sensor/AFR meter is a good reference if you don't want to run wide open for a few miles and cut the igniton at speed then pull the plugs to check them at the side of the road. Most of the time it's easiest to start with WOT and get the main jet correct first, then deal with the needle/power valve which controls the midrange, since they work in concert with one another. Don't expect to be able to get a perfect AFR throughout the operational range with a carburator though, it's not gonna happen.

I do like the Holley 1904 single, it's simple and easy. They came on more than Fords, I know AMC an IHC used them too. As far as I know the 250 and 300 never used them, they were too new and usually had Carters and the 240 usually an Autolite and somtimes Carters. I believe they were used from 1952 thru 1964.

[doofus]

Ron the full power vacuum spec is 6 in vac. the AS has 2 metering rods and a strange vacuum/mechanical metering rod control system. if it were mine to play with, i would take another intake manifold,and build a 2 barrel manifold and fit a carb that i understood better. maybe a holley since you can get pieces to change power valve vac settings and such. eons ago i ran a turbo 170 with a single 175 CD volvo side draft carb feeding the turbo. worked great to 85 mph then topped out 3 spd no OD. maybe start with a different 1 bbl like a holley or rochester and see what you can do. if you need a spare manifold holler! Luck Doofus

[Ron Dame]

BRB on this thread, I checked my fuel pressure ( like I thought I had years ago, but must have been a different car) and have 7 PSI fuel pressure. I'm gonna get that back to 3.5- 5 and see if my rich running is cured.

[Ron Dame]

Well, great. Louis DeJoy's ( perfect name) changes to the USPS has lost my new fuel pressure regulator. I miss our old USPS service.

[tsenecal]

You said that it runs fine at idle, and rich everywhere after that. It seems like too much fuel pressure would affect idle more than higher rpm. Hope you are able to figure it out.

[Ron Dame]

You said that it runs fine at idle, and rich everywhere after that. It seems like too much fuel pressure would affect idle more than higher rpm. Hope you are able to figure it out.

Good point. Still, it ought to be addressed

[Ron Dame]

The new fuel pressure regulator is in, and it made a huge difference, even at idle. I suppose idle was was as good as I could get it, but now it's not very lumpy at all. It still runs about the same, but does not spew black smoke or (so far) blacken the bumper.

So there you go, make sure that what you did on one car, isn't what you THOUGHT you did on another.

[Ron Dame]

Follow up: After a few weeks, I think the issue has been solved with the fuel pressure regulator. The idle is smoother, the bumper is staying clean, and the exhaust does not smell rich like it did.
Vacuum is still low at idle, but considering the cam and the way it runs, who cares?

[firestoper 25]

Well Ron, my nickles worth.....when I single - handedly destroyed a very expensive Weber 2 bbl (on my 1986 Jeep CJ-7) I replaced it with a brand new EVEN more expensive Weber 2 bbl so I added a pressure regulator AND a very nice liquid filled pressure gage. Now I am darn well sure what my FP is at all times!