Fuel System: R2 Avanti hesitation

[cosmo556]

I need some ideas. I get a pop through the carb and a bad hesitation off of idle. When the automatic trans is put in gear it's nearly impossible to get the car to move without popping and stalling. I am missing something here so maybe one of you can help. Here's the history. I am at the completion of a 5 year restoration. It didn't run when I acquired it. I completely rebuilt the engine. .030 oversize, new pistons, bearings and all the rest. The heads are R1 with the bigger valves. It had them on when I got it so I used them. They have been rebuilt with all new valves, guides and hardened seats. I used thick head gaskets. Ignition is a Myers conversion to the Chrysler type electronic ignition, timed at 24* at full advance. Coil, wires and plugs are new. I rebuilt the correct R2 carb with a SI kit. It has an electric fuel pump and a new mechanical pump. When I finished and first started it and noticed this problem I suspected I missed something in the carb so I shipped it off the Holley Custom Shop. It came back looking really good but the problem was still there. I decided to go back in myself and found that the accelerator pump and its shaft seal had not been replaced. I got new ones and put it together thinking I had found the problem. Not so. Looking in the top I can see gas being pumped through the nozzle when opening the throttle. I have tried the pump rod in all 3 holes. I also began to suspect the rebuilt torque convertor as there was no way to get it up to stall speed. I sent it back to the rebuilder, Dacco, and they found it to be fine. Just to be sure they rebuilt a different unit and certified the stall speed at 2100. No change. It is the same with or without the supercharger connected. I am really still suspect of the carburetor but these pressurized units are too hard to find to give up on it. I am an experienced retired professional mechanic but this is my 1st Stude project.
Help!
Dennis

[PackardV8]

1. A pop and hesitation is usually a lean condition, but you say the accelerator pump is working.

2. What initial advance do you see at idle?

3. Since it's an new build, have you checked carefully for vacuum leaks around the intake? They can cause the carb curb idle to be so out-of-adjustment it won't transition smoothly to main.

FWIW, I now always install an O2 sensor when tuning a carb. It does away with in-the-dark guesswork.

jack vines

[tluz]

I am no expert here, but isn't the compression of R1 heads too high for an R2 setup? Please forgive if this is a stupid question.

[57pack]

Sounds like a timing issue. Recheck distributer position. Had this problem myself years ago, distributer was a tooth off.
Wasn't a Studebaker V8 was a brand X.

[studebaker-R2-4-me]

I am no expert here, but isn't the compression of R1 heads too high for an R2 setup? Please forgive if this is a stupid question.

Not a stupid question, it all depends on how much work has been done to the heads and how the engine was built, ie. eyebrowing, R3 valves, thickness of the head gasket, total cc's, type of piston used dished, semi-dished, or flat-top.

Allen

[cosmo556]

Thanks for pointing me to the timing. It was set at 4* initial and 24* full mechanical advance with the vacuum advance unit disconnected. I hooked up the vacuum line and checked it again and there was no change at idle or at speed. Further investigation uncovered a jammed vacuum advance unit. Hard to believe as it is new. I'll need to source another one and install it to confirm this is the problem. Anyone have a NAPA or Echlin part # for it?
Thanks to all for the help.
Dennis

[studebaker-R2-4-me]

Thanks for pointing me to the timing. It was set at 4* initial and 24* full mechanical advance with the vacuum advance unit disconnected. I hooked up the vacuum line and checked it again and there was no change at idle or at speed. Further investigation uncovered a jammed vacuum advance unit. Hard to believe as it is new. I'll need to source another one and install it to confirm this is the problem. Anyone have a NAPA or Echlin part # for it?
Thanks to all for the help.
Dennis

NLA. Dave T-bow has them rebuilt 10 at a time and will probably ask you for your old one. DO NOT discard this vacuum advance they are getting harder and harder to find for R Series engines.

BTW I'm running full in at 34 degrees with about 3 lb of boost and premium gas with no detonation. Even have had it up to 39 degrees running 112 octane while at the Pure Stocks.

Allen

[cosmo556]

This is one of Meyers Chrysler conversions. I think the advance unit is Chrysler as well, just don't know which one.

[bezhawk]

Chrysler units used for Studes, are generally big block units. They have the same counterclockwise rotation

[bige]

Doubtful that your lack of vacuum advance is the root of the problem. Vacuum disappears for a moment when the throttle blades are opened so no vacuum advance anyway.

1st we need to make sure that centrifugal advance isn't kicking in at idle. Drop the idle as low as you can and then set the timing. Forgetting the overall setting and driveability for a moment set static timing around 10 degrees not 4. Reset idle, check timing and keep at it until you can move the idle around a few hundred RPM up or down without a change in timing. Check off idle throttle response. Is the response better? If it is you have pretty much eliminated the carb as the main issue.

Move to the carb and linkage. Typical test for accel pump discharge is to blip the throttle open by hand and watch the stream. Thing is that's not how the throttle moves as you are trying to accelerate normally from a dead stop. Watch the action of the linkage from inside the car or with a helper. How far does it move before the carb actually reacts? My R2 had all kinds of slop.
Next grab the linkage at the carb and move it gently and slowly and then watch the stream. Before I started making adjustments between the accel linkage and the carb linkage there was almost an inch of movement at the pedal before any fuel made came out of the nozzles. Get as much play out of the linkage as you can then start working the 's' link at the top of the accel pump itself. Chances are you have a good amount of pump linkage movement before that pump actually moves in the bore.

Of course there has to be fuel in the accel pump chamber so float setting is important.

Back to distributor. I ran static timing on my R2 at 14 degrees. But limited to centrifugal advance to 26 degrees. Total with vacuum advance was kept around 50 degrees. Each engine is different but that higher static timing does not cause pinging as long as total timing is kept close to factory settings. You need to have light springs but a mechanical limit of some kind in the distributor to have the full centrifugal advance limited to only 12-14 degrees movement but come in at the 1600 or so rpm that the R2 was designed to run with.

My R2's new owner is a Forum member and I'm sure he would agree that throttle response on his R2 is almost like driving a fuel injected car.

ErnieR

[avantibngrant]

I struggled for a long time with mine. Changed the metering rod springs, setting the float, timing setting. Biggest improvement came from find the hot idle compensator valve was stuck open. I bent the bimetal bar and experienced the biggest improvement in driveability then from any other changes. it never stalls at a stop sign now and take the gas as it should. A lot of people plug this orifice right up and that would be an option. Take a look and maybe you will get lucky!
Neil

[karterfred88]

Sorry but I'm old school. If it's popping through the carb ignition is happening before the intake valve is fully closed. Pull the valve covers, put #1 at true TDC with spark plug out. Look at your vibration damper and make sure it is at zero. If not make a new TDC mark with a paint pen If it's right check that both valves are closed at TDC and they have proper clearances to be sure both are off the cam ramp. A little bit off at the timing gear can cause the pop back, vibration dampers are known to move between the inner and outer shells(never trust a 50 year old damper to have the correct TDC position marked). Then pull the cap off the distributor, with the engine still at TDC on the crank mark the rotor contact position on the distributor body, then put the cap back on and see how close the mark lines up with #1 plug wire. should be real close. If not rotate it till it is there, and check each plug wire in counter clockwise direction against the firing order. If all these checks show correct and still pops back, put an OEM point distributor in it, if you still have it. If not check the inside of the Chrysler cap for tracking or a crack, or a bad rotor. This should get it running without popping back, then you can advance it a little at a time (turning it clockwise to advance) till it runs well, disregarding the marks.

[CaffeineRacer]

Just to be clear here does the car idle fine and you only get the popping during off-idle operations? Is it a dead spot off idle and if you punch the throttle does the engine then pick up again? Is there a difference when the engine is cold or hot?

I would heed the advice to go back and reverify TDC as your first operation of trouble shooting. Set you initial advance to 10 to start with.

Second make are you are getting spark to all cylinders. What gap are you running the plugs at? Are you sure you're running the correct ones?

Once you do that then start looking at the carb as a potential issue, but to me the backfiring makes me think timing.