Engine: surging under steady speed conditions.

[wagonairedriver]

I've just purchased Avanti 63R1880. It has a surge when cruising at any steady speed. The carb is an Edelbrock 1406. P.O. said the fuel system has an electric pump near the tank, and runs through the mechanical pump also. The line running from the mechanical pump to the carb has a tee in it, the other branch running a return to the tank. Is this as strange as it seems to me? I was told the R-1 has had the compression lowered to run on pump premium. Points and vacuum advance can have been replaced.
Is this enough info to help figure out my problem?
Thanks for any ideas, Kelly

[jclary]

As old as all of our vehicles are becoming, the possibilities are many. If you are still running an old style distributor, it could be worn sloppy bushings/bearings. Could even be an intermittent dragging valve/lifter, vacuum leak, loose plug wire, or old plug wires with breaking down insulation causing them to crossfire, fuel delivery, moisture droplets in the fuel, etc. As we often say...start with the obvious, cheap things first, and work your way through the possibilities. Hopefully, you will find it without messing something up that ain't broke.

[RadioRoy]

Hopefully, you will find it without messing something up that ain't broke.

That's a key issue. Proper troubleshooting is in order, rather than the wild shotgunning many folks like to do.

The return line on the fuel and the electric fuel pump are both methods to eliminate vapor lock, which is such a problem for our old cars running in new fuel blends. Even though it looks weird, try not to focus on that just yet.

If the "surging" can also be thought of as "missing" and the problem occurs on the highway, I would ignore the fuel system and look at the ignition system.

As a general rule of thumb, missing at slow speeds is fuel related and missing at highway speeds is ignition related. Avantis have shielded spark plug wires, and you can experience intermittent breakdown from the plug wire core to the shields, and it will all be invisible to your eye (especially since you cannot see under the hood when you are driving).

If the "surging" happens when you are using some sort of electronic cruise control, I would turn that off and try driving with a steady foot. If it happens when you are indeed driving with a steady foot, then I would look at the ignition system.

Can you feel anything else in the car like strange vibrations, funny noises, strange rattles that seem to be synchronized with the surging?

You might even get it to happen by revving the engine up in the driveway, but personally I hate it when people do that. It's very inconsiderate of the neighbors.

But then we had a post some months ago about "fish-bitin" wherein the car was missing on acceleration and at speed and the problem turned out to be a vacuum leak at the intake manifold.

[Bud]

I had to rejet the Carter 9625 carburetor on my Avanti because of a slight surge. It turned out that the fuel mixture was slightly lean because of the addition of ethanol to California gasoline. I installed slightly smaller metering rods in the primary side and went up one jet size on the secondaries which corrected the problem. I also rejetted the AFB on my 62 Hawk for the same reason. Bud

[SN-60]

Bud may be on to something here. Carbs that are jetted too lean for an engine's requirements will 'surge' the engine when held at steady speed. (Assuming everything else is OK)

[j.byrd]

Kelly, this is just a question, not an answer, but you say the PO said the compression had been lowered to run on pump PREMIUM. This is a bit backwards to normal, if it has been lowered, it would be more likely to run adequately on pump regular. ???? I would get some clarification on this. Good luck, my slight surge/miss in one of our old cars was a tiny fuel port nearly stopped up, and mixture screws badly out of whack trying to fix it.

[skyway]

Yes, lean surge.
In the old days (with real gasoline) I kept 2 sets of metering rods for my AFB; richer for the winter and leaner for the summer.
The lean ones would surge a bit, but delivered swell mileage.
Note: too lean is not good for the valves!

[wagonairedriver]

Kelly, this is just a question, not an answer, but you say the PO said the compression had been lowered to run on pump PREMIUM. This is a bit backwards to normal, if it has been lowered, it would be more likely to run adequately on pump regular. ???? I would get some clarification on this. Good luck, my slight surge/miss in one of our old cars was a tiny fuel port nearly stopped up, and mixture screws badly out of whack trying to fix it.

I'm new to R1 engines, but my book says they were 10:1 C.R. That would never run on the 91 octane premium we get now (that is the highest available here), so I think he meant it was lowered enough to run on the premium we can get.
Kelly

[wagonairedriver]

The carb on the Avanti is an Edelbrock 1406 (600CFM), and does not look more than a few years old. Is this too big a carb? My 63 Wagonaire with a healthy 259 is running an Edelbrock 1403 (500CFM) and will leave this car in the dust... I seem to remember some debate about maximizing venturi size to an engine's ability to breathe...
Kelly

[wagonairedriver]

Radio Roy, the car is not missing. I've spent most of my life cleaning spark plugs on worn out engines to smooth them out. It is running smoothly. It almost feels like you are letting up on the accelerator pedal a bit, then pushing it down again. Only occurs under a steady load, and not on acceleration. I've wondered if the distributor is worn out. When I get the car here, I can tear into it. Mean time, I'm just obsessing over it. ha.
Kelly

[ronhusak]

Kelly..
I have a similar situation with my 63 R2. Surge when at steady speed.. I have had the carburetor and supercharger gone through for altitude. The carb. leaned 2 stages and the supercharger clearances set for my altitude. I live at 9200 feet and most of my driving will take place between 5200 and 7500 feet. The car was born and lived its life in South Bend and I drove it home to the Denver area from there. I strongly suspect worn bushings in the distributor. This would cause timing variation most noticeable when at steady speeds.. When I get mine running again in a couple of days I will check with a timing light and vacuum gauge.
BTW the altitude you live at as well as I LOWERS the octane requirements.. That is why regular is 85 and premium is 91 here and there..
Good luck with it..
Ron Husak

[wagonairedriver]

Interesting about the octane. I thought it might be too rich, as the pipes seem pretty black. With no proof at all, I suspect the distributor is worn too.
Kelly

[Studebakercenteroforegon]

More than once I have chased problems with surging at a steady load, thinking it was a fuel delivery issue. Also, more than once, the real problem was a weak coil.

[bezhawk]

When I first got my Avanti, it ran like crap, and surged too. I rebuilt the carb, and the distributor. Didn't find anything wrong with the carb, plenty with the distributor.

[wagonairedriver]

Wow, you guys have given me lots to think about. At least I have several paths to explore. I'll update this thread...
Thanks, Kelly