idle problems 1964 Carter AFB 3506 S

[Devildog]

Need guidance, this R1 was setting for 20 years, but have it running and road worthy. Probably have driven it 800 miles highway and suburban, runs go and static idle is OK.

Problem when put in gear (auto) can not get smooth idle..then it gets worse and RPM drop while sitting at stop light. Then dies and often hard to start.

The workshop manual discusses Hot Idle Compensator and refers to a THERMOSTATIC VALVE ASSEMBLY in the carburetor. Not familiar with this compensator, worked with WCFBs which do not have this thermo-valve.   It is in Houston with currently 90+ temps

Before I dig into this, I thought some of you may have some suggestions.

Where would I find a new  THERMOSTATIC VALVE ASSEMBLY ?           Thanks for good support you all give.

Joe

[Peddler]

I can't help you inside the carburetor but I would tell you to check for a vacuum leak which can cause idle trouble and be lass noticeable at speed.  The most likely contender for this trouble is the power brake booster.  Try pinching off the vacuum line and see if it smooths out.  Obviously look for any other vacuum hoses that may be deteriorated. 

[silverstude]

 

One thing to note.....Ethanol gas has a different specific gravity that the older gas formulations.  Try setting the floats lower by  1/16 or 1/32 .

[mfg]

Rough idle problems in Avantis run in high temperatures are not uncommon!......The first thing I'd do is make sure everything is to 'spec' (a good tune up)

Then I'd buy a kit and go through the carb to make sure its absolutely clean inside and all adjustments are 'on the money'.

Definitely use a thick base gasket under carb  (help insulate from heat)

I'd also run a 160' thermostat, and either eliminate or wire the exhaust heat riser valve OPEN.

The carb thermostatic valve is a simple bi-metal bar that does not usually fail....although it can become stuck.

Remember, Stude Avanti engines have 'bigger' cams and will never idle a smooth as a standard Stude 259 or 289 engine.

[Devildog]

Thanks to all for your good suggestions. Done most all those things.

MFG, that thick gasket to insulate the carb base from hot intake is a life saver, in fact on my old Corvettes with WCFBs, I make gasket from 3/16 oak plywood. These old WCFBs start when hot in 95° weather like they were FI.

That bi-mettalic bar, as I read the manual, should be closed or seated down when the engine is cooler...DO I READ THIS CORRECTLY? Then raise-> open if the engine is high heat. This one is slightly open when cold, I can push the button down slightly. As I see this extra circuit, it should be down/closed when cold then up/open if very warm ????

Attached a pic of the bi-metallic bar Hot Temp Compensator  (red marker zig-zag)

Again thanks all

Joe

[Stan Gundry]

Everything written above is good advice. But given the nature of today's gasoline, and given the age of the Carter carb, I think is is likely you will not solve the problem of the engine dying at a stop light when the weather is very hot. In my experience, the sure cure for this problem is to replace the Carter carb, with the Edelbrock knock-off (I useed the 1406 [600 cfm and electric choke]) and then removed the heat riser valve, replacing it with a spacer. Then last of all, totally block off the ports that allow exhaust to go under the carb to heat it up. About two years ago there was are article in Avanti Magazine that showed exactly how that should be done. This approach has worked for me.

[Devildog]

Thanks to all again. A short report for future readers:

I did not completely tear down the carb; however, removed idle screws, etc. put carb cleaner through the all small holes I could access. Then blew 40 PSI air through, repeated twice with cleaner and air.  Pulled metering rods and blew carb cleaner through as well. Some of the circuits did seems to flow better with air after carb cleaner. 

Then adjusted all the external linkages per the workshop manual. Rather than 650 RPM, I set idle to 850 which gives me about 750-800 when in gear, 750-800 with A/C engaged.  No run on when switched off.

I set idle screws with a vacuum gage to peak at about 15 inches.  Very smooth in gear with A/C engaged...no hesitation.

I will do some suburban driving with stop/go driving.  Make a report after a few days evaluation.

Joe

Edited July 5, 2018 by Devildog

[brad]

The bi-metal hot idle compensator valve often gets bent, and remains open. If you look at it out of the carburetor, it should have an offset bend so the valve is closed when cold.  If it is flattened, it will open too soon and will act like a vacuum leak. It's purpose is only to function when the carb is so hot that it puts off enough fumes to prevent an over rich mixture. Gas fumes do cause the mixture to change.

Edited July 9, 2018 by brad

[Devildog]

OK, I think I have the high temp idle problems solved or at least manageable. Rather than the 650 RPMs, I adjusted to 900 RPMs which gives about 750 when in drive. Add in the A/C and drops down to 600. 

Made sure the temp compensation tap was closed (pushed down closed) while adjusting idle screws.

I played with adjusting the tab...think I have tab set so it does not open until surface temp on bimetallic is about 160-180°F. 

I have driven a total of 3 hours in urban-suburban driving in 95 degree with no stalling with A/C running. 

Thanks for advice from all.

Joe

[Gunslinger]

The tachs and speedometers installed by Studebaker were notoriously inaccurate which was pointed out by some car magazine writers after testing the cars back in the day.  When setting idle don't rely on the car's tach...use a test tach if you have one.  The car's tach and speedometer error tends to get worse as rpm's and speed increases.

[GlennW]

If you haven't already done so, check for free movement of the manifold heater valve (on right side), or better yet, remove it entirely (Jon Myer has a "filler" spacer to take it's place) since in Houston you probably won't ever miss a shot of hot manifold air while the engine warms up.

The blocking procedure for the "stove" under the carb is in the Issue #175 (Summer/Fall 2016) as part of an excellent article by Bill Henderson titled "Intake Modification Stops Stalling in Summer's Heat".

 

Edit:, missed Stan Gundry's comment above, somehow, sorry for repeating much of it.

Edited July 14, 2018 by GlennW

[Kennie B.]

Nothing has been mentioned about the "throttle kicker".  If that isn't there, adjusted right and working, the idle will be need to be artificially high in neutral.  

Ken