Another problem - C2

[Paul Reynolds]

Seems everytime I fix one thing, I get another problem.

Here's today's mystery.. A beautiful day, low 70's. I replaced the fan clutch yesterday, and let the car idle for an hour in the driveway so I could watch the temperature. Stayed right at 180* the whole time. Verified with an IR gun. Took a one hour leasurely ride on the back roads to see how everything would perform on the road.

When I first started out, the car idled fine at 800 rpm. About 20 minutes into the cruise, the idle started to drop. At steady throttle in 4th gear between 1000 and 1500 rpm the car was starting to "buck" a bit. As I kept cruising, it got steadily worse.

I thought it was loading up, so I did a couple of blasts to 6500 rpm with no breaking up or any other problem, so it seems the ignition system is working correctly. By the time I got home, the car was barely idling at 550 rpm. It seemed to be running really rich. Engine temp never got above 185*, so I know it's not a coolant overheating issue.

Checked the timing, 10* BTDC, Dwell 30. No fuel leakage observed, but that may not mean anything.

Both float levels appeared to be correct when I pulled the sight plugs, but I knocked both front and rear float levels down about 1/2 turn each, but haven't made another run yet. Hoping that will fix it.

Car is a '64 vert, running a "correct as GM built it" '64 327/365 setup with LT-1 cam. M20, 3.36 rear. "New" restored 2818 carb installed last month.

Any other ideas out there? Thanks.

[Joe R.]

Re: Another problem - C2

Paul,

First, chunk that LT-1 cam in the garbage. The only cam worse is the 30-30! If you want solids go to the 097 used in the 63 FI and 340HP.

Then, you will want to adjust that "new" 2818 when the beast is hot. Probably will take some time tinkering with the timing and carb to get it right.

After Duke reads this post, and he comes back down to earth, he can help you with the timing.

Regards,

JR

[Gary S.]

Re: Another problem - C2

To the untrained (me) it sure sounds like your carb is running really rich and loading up. If you can blast up to red line, then you can't possibly have ignition problems. Have you checked float levels.
Gary

[Paul Reynolds]

Re: Another problem - C2

Actually I Love this cam. Pulls well in 4th from 1000 rpm - up. Great Low end torque.
Pretty sure the timing is good. 36* total all in by 2500 rpm. Really feels like a fuel problem, but as it's been said before, 95% of all fuel problems are ignition related. That's why I checked that first. Mechanical advance is not coming in at idle (800 rpm).

[Rob Dame]

Re: Another problem - C2

What heat range / brand of plugs are you using?
Have they been wet before?
Have you checked them to see how they look?
That will tell if it's running rich.

[Duke W.]

Re: Another problem - C2

Did you check the vacuum advance for proper operstion? Is it a correct OE or replacement part? Does it leak? Does it meet spec?

With the vacuum can connected and 10 deg. initial, the total idle timing at about 900 should be in the range of 26-30. At 900 you probably pick up a few of degrees of centrifugal because the 327/365 centrifugal curve starts at about 700.

Duke

[Paul Reynolds]

Re: Another problem - C2

Duke, I'm running a new VC1810 can. Initial timing 10* BTDC, and the timing mark goes up almost under the waterpump when I hook the vacuum back up.

This problem only exhibits itself during a longer cruise (30 minutes or more). I work only 6 miles from home, and I drive the car every day. No problems on the short runs. Smooth as silk.

[Paul Reynolds]

Re: Another problem - C2

Plugs are AC R45's. On short runs, they look good. On a long back road cruise, rpm range 1000-2000 in 4th, they look a little sooty. After a long highway run, they are slightly gray. Only happens during a long leasurely cruise through the country.

[Gerard F.]

Maybe, it's the carb HS vents

Paul,

There has been some recent posts about intentionally blocked or never drilled HS vents on 4160's, and 4150's have basically the same body. The HS vents are the four inner smaller vents in the air horn.

I understand that the purpose of these vents is to emulsify the fuel with air as it it enters the venturi booster, thereby leaning the fuel. The vents also act as a siphon break. Maybe you have blocked HS vents, and that after a long run, fuel is siphoning fuel into the carb. This I think would make you run rich, and rich at idle.

So, check your HS vents, maybe that's the problem, or maybe not. And maybe Clem will get into this with his experience.

Jerry Fuccillo
#42179

[Paul Reynolds]

Re: Maybe, it's the carb HS vents

Thanks Jerry. I'll take a look at those tomorrow. Aside from "expanding" fuel in the bowls due to heat, your suggestion makes sense.

[Paul Reynolds]

Re: Maybe, it's the carb HS vents

I checked on those HS vents I think.

There are 2 holes towards the outsides of each venturi, near where the metering blocks are, on all 4 barrels.

The outermost ones have larger holes, and the inner ones closest to the venturis have "medium" holes for the primary side and real tiny holes for the secondary side.

Are these the holes I should be looking for?

[Gerard F.]

I think so, it's the 4 inner ones

Paul,

Here's a post with a picture of my 3810:

https://www.ncrs.org/forum/archive22.cgi?review=180455

You'll see two of my inner ones (one primary, one secondary) never drilled.

You could also have some dirt or remnants of the restoration in the smaller vents. You need a wire gauge drill set to check them, if they are open and won't blow out. I found a hobbiest #60-#80 set by Exacto at a hardware store (Orchard Supply), which is the size range of the smaller vents.

I'm not an expert on this, and your problem could be something entirely different. I haven't put mine on the 67 yet.

Jerry Fuccillo
#42179

[Paul Reynolds]

Re: I think so, it's the 4 inner ones

Yup, those are the ones. Mine are all drilled. They look very similar to the sizes on your drilled ones. Ran a small wire through mine and they seemed to be clear. When I pull the carb, I'll check to see if they will pass air.

[Paul Reynolds]

Re: Another problem - C2

Here's another "theory":

I'm starting to think that the carb body may be warping as it heats up, and when things cool down it returns to its "correct" shape as the car runs great for the first 30 minutes or so after warmup.

When I first installed the intake, I didn't block the exhaust crossover. Figured I wouldn't need to since I'm running an FI spacer(no heat riser valve). This weekend I'm going to pull the intake again and block those. Maybe with a little less heat buildup under the carb it may run better.