Fuel System: AFB Springs for Avanti R2

[avantibngrant]

I am looking to change my springs which open the step rods as they seem to be opening too early. I bought the 5 differnt combinations from 2 in of hg to 8 inches I believe. I was wondering what the original ones should be in terms of in of hg as mine may well have been changed. Also, what whould the jet and needle diameters be stock? Mine may well have been changed over the years and I am wondering which springs and rod/jet diameters it came with originally as a good starting point.

Regards

Neil

[Gunslinger]

The parts manual doesn't give the specs of the stock needles and jets...only the part numbers. You might give Jon Myer a call for advice on that since he rebuilds these carburetors routinely. If Jon doesn't have the parts you might want, give Edelbrock a call with the specs as their carburetor is an updated clone of the AFB and many parts interchange.

[bezhawk]

I use the orange springs....I believe they are listed as 5 in of HG. .095 jets. , and Edelbrock 1456 metering rods- .073 x .047 @ appprox sea level.

[KOOL R2]

Factory main jets were .101.5 and secondaries were .089 Metering rods were .076 X .055 with "orange" springs. With today's fuel containing so much ethanol I am using .071 X .047 metering rods. Also for track use I have my secondaries set at .095

Neil, do not attempt to try to lean out a supercharged engine. Bad things happen.!

Peter Sant

[WCP]

Neil, it is good to start by identifying what you have. The carb should be a 3507S, 3588S or 3725. Mine is a 3588S and would have been supplied with 16-263 rods, 120-162 primaries and 120-159 secondaries. These numbers should be stamped on the individual parts. Carter listed the 16-263 rods at .076x.049, 120-162 at .1015 and 120-159 at .089. Later replacements for these jets would have been numbered 120-401 and 120-389 respectively. My 3588S has 16-263 rods, 120-162 primaries and 120-392 secondaries (.092). As Peter says, you don't want to go lean with the secondaries open.

[avantibngrant]

Thanks folks for the feedback. I took the springs and step up rods out today when I came back from a car show at a local fair on "Drive Your Studebaker Day".
The findings are as follows
Step up rods measured .045 and .079 with my vernier
Springs were the silver ones - the 8 in hg per my measurements.
I did not take the cover off the carburetor to take out the jets. I put the orange springs in an put it together. I took it for a test drive. It is a little better, but still not the power I would expect. It will not squeal the tires with a hard first gear take off - R2 - 3.73 rear end and 205/75 tires with power shift.
I checked the timing and found it was a little advanced per R1 specs which I am supposed to set it to per Dave T whom I bought the distributer from. I set it back to the 4 degrees from the 6 or 7 it was at with the vacuum advance disconnected and taped at idle. Net result is it is even a little less responsive.
To be clear, it is about as fast on the take off as my 63 GT was with the 2 barrel and 3.54 rear axle - still respectful, but I don't think up to its full potential. My next move is the get my son to hold the gas pedal to about 1600 rpm and see what the timing says.
When I think about it more, I am not getting full vacuum at the vacuum advance at idle. It does go up a little when I rev it up off idle, but I would think it should be full vaccum at idle? It is routed to the front of the caruretor via a rubber hose to a steel line. At no load, how should vacuum at this port vange with rpm?
I think the step rods are in the ball park for size, but I will need to take the top off the carburetor to get at the jets. Before I do, I will get new ones to have on hand. I have a lung disease and I don't relish messing with the stinky gas any more than I have too.
What do you experts think about the step rods and the timing?
Regards
Neil

[KOOL R2]

Neil, I think that your Carburetor is OK with the metering rods that you have provided that the main and secondary jets are at factory sizes.
They say that timing is everything!! I am running at 30 degrees at 1600 rpm with vacuum line disconnected. At the track I bump this up a bit more. The vacuum advance should show zero inches of vacuum at idle and increase to about 15-20 degrees at cruise speed. If you set the timing as I describe you will end up with "basic timing at around 15-17 degrees advance at idle. My Avanti seems to like this setting and the power is adequate.


Peter Sant

[WCP]

Neil, just a thought - do you have the proper higher rpm stall torque converter in that car? You can check that out by putting in "drive", holding the brake on, and flooring the accel pedal. You should get 2100-2200 rpm as I recall. Don't hold it at full throttle for more than a few seconds and have an open foreground. If that checks out, drop it into 1st, put into stall and release the brake pedal. I'm sure you will light up the tires. You need to have the blower speed up to achieve the power you're after.

[avantibngrant]

Peter. I think you are right on more advance. My experience with my tractors is advance as far as possible withjout pinging on a hard pull and no startert binding.
Just looking at the centrifugal advance curve int he repair manual for the R2 - 1600 RPM shows an advance of 18+/-2 deg and and the same for the R1 at 1600 rpm. My Malory is to set up per the R1 curve which is a little different as at 2000 RPM, the adavnce peaks out at 20 +/-2 deg. So with the 30 degrees, the idle no vacuum advance basic timing would be 30 - say 16 to 20 which would be 10 to 14 if my math is right? It seemed to run better at 6 degrees than 4 so I would well amagine another 10 degrees or so will help for sure. It is exactly what I would do if I was working on one of my tractor engines. A by product will be it will run cooler also. I am going to try to set it to 14 at idle and try that. It will make it a one person job and more importantly, how would you set it to 30 degrees as the numbers end at 24 degrees btdc?
Thanks again for all your help. BTW I really enjoyed the visit with you in Kingston.
Regards
Neil

[avantibngrant]

WCP, I will try that for sure after I get the timing set a bit better per Peter's good advice. I suspect it is ok as I think it has never been apart.
I am not looking at burning the rubber, but I just am trying to get it to not stumble on take off as it does some times.
Were you one of the folks at the Kingston event?
Regards

Neil

[KOOL R2]

Neil, Use a "dial back" timing light. Set the dial on the light to 30 degrees and run up the engine to 1600rpm with vacuum line disconnected and the timing mark should point to "zero" on the timing plate.

Peter Sant

[avantibngrant]

Update on timingi and AFB springs

Peter and WCP - thanks for the advice.
Peter, I see what you mean about the set back timing light. That is a feature of the $149.00 Candian Tire one. The Scottish blood in me made me buy the $49.00 one instead which does not have this feature. I set the idle timing to 14 degrees with the vacuum advance disconnected. That sure livens it up at the lower end. No binding on the starter and no pinging as of yet. I had a visit from a Scottish collegue from the UK today and was describing the situation and he was saying a couple of pings on acceration is "the sound of fuel economy" I don't hear any yet, but I think I will drive it for a while like this and check the mileage and operating temperature. If it is ok, I may advance it to 16 degrees.
I do find it interesting it runs so much better at 10 degrees over the stock setting. What do you other guys set the timing too?
WCP, I tried the stll speed and it is about 2200 rpm. It will definetly break the tires loose with a rev up in low with the brakes being released. I did not want to do it to much around my house, but it seemed to break the tires loose in low also if I am percieveing it right. I am just glad to get the stumble put to bed which seems to be so far. There still is a little change in engine speed through 1500 rpm as the carbureter changes circuits, but I will live with that to be sorted out later.
Thanks again.

Neil

[ronhusak]

avantibngrant ..
Be very careful with too much advance on a supercharged car.. You won't have the "sound of economy" but will have the "sound of destruction". With all the other noise of full boost loud exhaust and all it can be very difficult to hear the sound of dentonation.. Err on the side of being conservative.. This can damage an engige quite quickly..
Ron Husak

Peter and WCP - thanks for the advice.
Peter, I see what you mean about the set back timing light. That is a feature of the $149.00 Candian Tire one. The Scottish blood in me made me buy the $49.00 one instead which does not have this feature. I set the idle timing to 14 degrees with the vacuum advance disconnected. That sure livens it up at the lower end. No binding on the starter and no pinging as of yet. I had a visit from a Scottish collegue from the UK today and was describing the situation and he was saying a couple of pings on acceration is "the sound of fuel economy" I don't hear any yet, but I think I will drive it for a while like this and check the mileage and operating temperature. If it is ok, I may advance it to 16 degrees.
I do find it interesting it runs so much better at 10 degrees over the stock setting. What do you other guys set the timing too?
WCP, I tried the stll speed and it is about 2200 rpm. It will definetly break the tires loose with a rev up in low with the brakes being released. I did not want to do it to much around my house, but it seemed to break the tires loose in low also if I am percieveing it right. I am just glad to get the stumble put to bed which seems to be so far. There still is a little change in engine speed through 1500 rpm as the carbureter changes circuits, but I will live with that to be sorted out later.
Thanks again.

Neil

[avantibngrant]

Ron, I agree with you as the exhaust is pretty loud. What do you run for timing with the R2? Does the 14 sound out of the ball park? It seems to make sense per the 30 degrees petter is using at 1600 rpm, albeit on the high side of the range. I could put it in the middle at 12 degrees. I do not want to harm the wonderfull piece of history I get to drive to cruise nights.
Regards

Neil

[ronhusak]

avantibngran Neil..
Can't go by what I use as I live at 9000 feet and mine can tolerate and in fact needs more advance..
Check the manual.. Then maybe a touch more..
Ron