high Speed not so good

SLPreston53

SLPreston53

Senior Member
Here is the situation: I have rebuilt the side bowl carb (it is a late 31 pu) with Renner's jets and kit. The timing is dead on (had the head off and verified TDC). The points and cond are new, as well as the cap, rotor and cam (all also from Renner's). New plugs and contact strips.

The truck runs well at "easy throttle" as per around town here in LA. But, push the throttle like you would getting on the freeway and the truck surges with little power. I do pull the spark to full advance as I accelerate. It helps if I pull a little on the choke lever (in fact that makes the truck run well), but opening the GAV alone makes no difference from 1/4 to 1 full turn.

Any ideas?
 
I took the carb completely apart, soaked it (carb cleaner) and then blew out all the passages with a can of carb cleaner and it's straw.
 
Sounds like possiblity of too small main jet. Did the carb / car run good at first? Were the jets flow tested?? Sometimes a little burr will make them flow slow.
 
i was always told it you think its fuel its probably ignition
if you think its ignition its probably fuel
you checked the fuel already, move on to the ignition
sounds like a condencer or coil to mee
tk
 
If it runs better when you pull on the choke, then it is lacking for fuel.

By pulling the choke a little, you restrict the air a little, allowing it to run richer.

You have a fuel blockage. Either in the fuel system or within the carb.
 
You cannot rely on carb cleaner to clean out the passages in the carb. We runs a tiny light thru those passages to verify they are clean.
 
Try to borrow a known good carb and run a test with it. Try to rule out ignition with another carb.

Messing around with the fuel lines and all, it is easy to dislodge something that will move into a jet. Try taking the carb apart and reverse flushing each jet with a carb cleaner spray. Look for back spray in the bowl or well.

Make sure your gas cap vent is open. You laugh. Seen it so many times.
 
I had a similar problem about 5 or 6 years ago with a rebuilt carburetor and I had a local "A" carburetor rebuiilder, since deceased, look at it. He found the small opening near the threads in the secondary well was smaller than it should be. Opening it slightly cured the problem. Your situation may be different but that was the problem and its solution with my Zenith.
 

Hey SL



It's the carb,,,not enough gas at high speed,,Hence the surging,, Coking the carb made it run better by richening the mixture..



Might have rust inside a passage,


Greg out west
 
I loaned a friend my Tillotson to rule out a carb problem, 2 years later, I called & he's still running MY carb!! What's a guy to do?? Maybe I should only be friends with guys in the STUDEBAKER CLUB!! Bill W.
 
I agree with Steve B. Do a quick test to pull the choke slightly and see if it increases speed. If so you have a blocked jet/passage. I would disassemble the carb, and the best way is to bead blast the carb with all jets removed of course and run a wire through all passages. Check all jets and flow test them to ensure proper fuel metering and stream. Also.... and maybe I should have said this first... make sure you're getting full throttle. have someone press down on the accelerator all the way and the throttle should bottom out on the stop. if it doesn't, you have a linkage issue. If need be you can bend the forged arm linkage ( part of the assembly bolted to the back of the engine. They are forgings so they will bend a little. The repro links are also always suspect as they come built in with the incorrect length ( in otherwords made wrong),

Check that first, if getting full throttle, pull carb and service properly. If you can't flow test jets find someone in your area who can. it is a necessity to ensuring good carb operation. FYI... the newer kits from Bratton seem to be very good as the jets flow test well.. at least the ones I've done. You can't get the inside of the carb clean enough.. so be sure all is blown clean prior to assembly. Steve Pargeters book or Paul Mollers books are excellent.

Good luck!
Larry Shepard
 
I agree with Jim...borrow a friends carb (known to be good) for a test to see if it improves before you do much more.

I suspect you need a larger main jet.
 
Just a long shot, but did you happen to put in a modern points plate in your distributor? When I did, my motor ran well lightly loaded, but was anemic when it tried to develop power....A new "old" plate fixed it right up.
 
Have you checked out the float valve and float height adjustment? At high speeds some float valves don't let enough fuel in quick enough and the Grose Jet ones with the ball bearings have a bad reputation for this. Setting the float higher by removing a gasket from under the float valve or swapping it for a thinner one. Also by carefully bending the float to make it ride higher allowing more gas in the bowl maybe helpful here.
 
It could be any of the above. I especiallylike post 15 and 16. It could be something as simple a an over restrictive fuel filter or too many fuel filters. I've seen cases where people got happy with fuel filters and caused fuel starvation under strain. Most over the counter fuel filters are designed for systems that use a fuel pump instead of gravity flow.
 
Message #8 & #14 above, i.e., borrowing someone's carburetor are good quick troubleshooting methods to narrow your problem search.

Then, from message #11 above:

Why not Email or PM Bill W. to question whether or not he has another spare carburetor to loan & try on your Model A before he runs out to join the Studebaker Club. Don't think Buster-T bites borrowers -- be careful -- could be wrong!
 
:cool:
H. L. Chauvin said:
Message #8 & #14 above, i.e., borrowing someone's carburetor are good quick troubleshooting methods to narrow your problem search.

Then, from message #11 above:

Why not Email or PM Bill W. to question whether or not he has another spare carburetor to loan & try on your Model A before he runs out to join the Studebaker Club. Don't think Buster-T bites borrowers -- be careful -- could be wrong!
Click to expand...
Jist woke up & NO COFFEE yet, but I "think" all I have left is a spare generator, a BIG bag uf lite bulbs, OH! & a '30 choke rod! Iffin' yall need these, jist bring Coors Lite & Doggie:cool: treats! Bill Sucker.
 
Purdy Swoft said:
The Studebaker people may be just as bad.
Click to expand...
But MY parts won't fit them WEIRD old Studes. Dudley Mordigian's mother, Betty, lived by me & her '26 Stude, "ASTHMA's", oil pump ran off the rear of the generator, even! (REALLY!) And the car was this l_______________________________________l LONG & only had 2 wheel brakes & SQUARE tires from sittin' SO LONG!! Bill W.
 
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