My Carb is Driving Me NUTS!!

[mkoloc]

Rebuilt my carb with a fairly good kit with the exception of jets ...She is running way too rich, float level is good, I can pull the floatbowl screw and observe the fuel level,  it's good!! Timing is right on!  Idle screws seem to be pretty much ineffective, they are new.  Pulled some plugs and they have that telltale signs of a too rich fuel mix. I ran her to the gas station to fill my refurbished tanks and to stretch her legs and she struggled to get more than 25 MPH. She seems bogged down.

Can anyone advise me on where I might purchase new metering jets?
Convinced that my issue lies there ... any and all assistance appreciated!! I have a TM9-1826B Ordnance manual for reference.

Thanks,
Mark

[coreyelliott]

Mark,

When you screw both idle screws all of the way in, there is no stalling of any kind?  No change in idle speed?  Do you know how much vacuum your motor is pulling at idle?  What plugs are you running?  You mentioned timing, are you running at zero degrees TDC? 

I have been chasing down the same problem as you.  Not major, but running rich at idle.  We don't have brakes yet, so we haven't been able to drive it so I'm not sure how it will react to that but I might be able to help out.

Corey

[mfrance]

Try running it without the air cleaner on it to see that it's getting proper air and fuel mix .   

[mkoloc]

Cory, I'll check my timing reading .. I am running the recommended plug substitute .. yeah, no significant change in idle with screws all the way in.  I'll get plug number.  Your phone #?

MFrance, I'll check vacume,,, also went thru my fuel pump and vacume was very strong as ties into manifold .. will also check line running to hydrovac.. I'll pull air cleaner hose and check that out ... but am still wanting to replace those jets .. believe they are the original 1943 or 1952 ones and my track sat in a desert environment with lots of sand and dust for 50 years.

Appreciate the advice.  Will get back to you both regards my findings.

[Dinadin]

I am having the similar problems.  It will idle fine, but when I try to drive it bogs down and I have to drive it in low gear.  Some of my friends are saying I may have a vacuum leak.  My friend suggested starting it up and then putting oil on the seals to see if the engine reacts.  Another friend said to do the same thing except spray the sees with starting fluid and see if there is a reaction.

[mkoloc]

Dinadin, so what seals are you spraying... manifold, line from vacuum pump, line from hydrovac to valve on firewall?  Just trying to brainstorm what seals I need to check so I can have some success checking if out.

Markus

[8683jb]

Mark -

You can use starting fluid, brake-kleen, chemtool, etc. Use the straw so you can concentrate the fluid and not spray a cloud that could be drawn into places unknown and be careful it doesn't get drawn into the top of the carburetor. Squirt a little where the base of the carburetor attaches to the manifold, the ends of the throttle shaft, where the intake manifold attaches to the block, vacuum lines/tubes and fittings - anyplace downstream of the throttle plates where there is engine vacuum. If the engine speed increases there is a vacuum leak at that location. Good luck.

Jon

[spillmk1]

How fast is your idle?
Most carbs (I don't have diagram in front of me for half track carb) don't use the jets at idle....
just the idle circuits. They don't "switch" over to jets until RPM/Load increases.
If you are pulling fuel through the jets at idle I'd bet a passage(s) clogged or carb issue other than jets.

Just a thought.

Keith

[R.E.Co.]

I had the same issue guys!  My issue was alittle timing, and really dirty valves.  I took the head off and cleaned under each valve, then they closed and opened properly, allowing me to build compression.  What is the compression you are running?  That will tell if its a carb problem combined with another one.  Otherwise, check the choke, sometimes the choke sticks from when you pull the cable back.  Make sure the choke body is open.  Lastly, run some brake cleaner into the jets with the carb off to make sure no junk got into the jets and air fuel mixture screws.  Beyond this, pray.  Hope you get it working!

Jon

[mkoloc]

Keith, Jon ... great comments .. idle is around 600-700 RPM .. CARB rebuilt last month .. was having this same problem before the rebuild as the CARB was rebuilt by a professional shop in CA but still never ran correctly.. When I cracked open the big brass nuts covering the jet opening and pulled the jets I found dirt and trash in the passageway which indicated to me they had never been cleaned and or pulled.  They were also not replaced during the professional rebuild .. did they need to be replaced ... don't know as they were probably never checked regards tolerances. I tore down that CARB completely with the exception of the metering jets.  I did not want to damage them during removal as I had no replacements.  I do clock and watch repair and have 3 industrial ultrasonic cleaners so everything was thoroughly cleaned via ultrasonic and all passages blown out etc..   

I'm going to do the vacume test suggestions, going to pull the distributor and ensure the advance is working.  Timing checked by induction process and is good ... going to try to source those jets and replace .. and if all else fails going to use a different CARB or slit my wrists :-) ... will most likely go the CARB route.

[Outsider]

Take the vacuum line off for the intake for the brake booster and plug the hole. Then take the air horn off the top of the carb and repeat playing with the idle screws to see if you can adjust the air fuel mixture. You could be pulling either brake fluid that bypassed the seals in the chamber or oil out of the air filter and burning it to make the engine run rich all the time. With the idle screws all the way in the engine should not be getting enough fuel to idle if the choke is not on. For the engine to be running rich with the idle screws all the way in the engine has to be getting another source of fuel and you just have to figure out where that is.

Steve

[mkoloc]

Distributor advance checked out, no vacuum leaks in my system and not a drop of brake fluid in my Generation III hydrovac. 

After a very gratifying phone call with a technician who rebuilds these things for a living in Florida, there is no doubt that my discharge jets need to be pulled.  The special Stromberg tool T-24967 used to pull the discharge jets is still available.  The Stromberg type 97 Carb jets are the same as the AAV jets and are still available.

Option #1:  Source all jets from carb parts suppliers using the Stromberg 97 part numbers and install.

Option #2:  Fill in the existing brass jets (no new parts) with solder and then drill and ream them out to size.  As a Horologist I actually have these types of reamers on hand. Clock parts suppliers sell these types of reamer sets.

Option #3:   Send it in to a competent company for a "complete" rebuild and ensure that all the jets will be pulled and replaced as needed.  I was a bit naive when I sent mine in for a professional rebuild to an outfit in CA.  I never asked those questions (I plead ignorance) .. the jets were never touched.

In my conversation with the tech today in conjunction with TM 9-1826B DTD 1 Apr 1944, we talked thru the idle circuit which has frustrated me no end.  The Stromberg Aerotype has a two stage idle system that behaves quite differently depending.....

During the 1st stage with no load and "AT IDLE SPEED" the idle air bleed, idle tube and the metering orifice work in conjunction with the idle needle screws to control the amount of fuel flowing thru the lower idle discharge holes in the CARB and into the engine.

During the 2nd stage, again no load but "AT FASTER THAN IDLE SPEED" and using these same components fuel is delivered via the lower and upper idle discharge holes and the turning your idle screws in or out will have no effect.

Correct idle speed does make a difference!!!!

During both stages, the emulsion of fuel and air via the discharge and metering jets needs to occur.  If these jets are not correctly sized or are not working properly your in a world of hurt magnified when your in the acceleration or power circuits causing your CARB to run way to rich!!

Am going to pull, repair or replace all of my jets!  Let's see what happens.

[coreyelliott]

When you pulled the plug on the side of the carb to check fuel level, did you do that while the engine was running?  The manual specifically says it must be running, I didn't know that during my first time troubleshooting.

Corey

[mkoloc]

Yes while running .. float level is not the issue .. I believe it's a jet issue ..pulling them today.

[mkoloc]

Okay after pulling the last of my hair out ..broke down and sent my Carb to Tim, at Daytona Auto, FL.    Mentioned Tim in a previous post ... after almost 4 weeks (their busy there) I recieved a call from Tim today that the Carb is done and for the handsome sum of $305.00 which includes shipping I can repatriate my Stromberg! 

On the way!!!  Of course I wanted to know what Tim had found during its rehab,   HIS COMMENTS FOLLOW:

Carb main body hairline crack all the way down to base.  As the Carb heats up, crack expands.  My carb is original to the track, and sometime during its time with the French someone took a hammer(?) To the side of the carb where the Aerolite emblem is stamped into the body.  Perhaps they were trying to free up the float or some Somali POS just decided to vandalize it while it was in the desert.  Anyway that was most likely the cause of the interior crack and a slight bulge into the accelerator pump cavity. 

I had sourced a spare AAV carb from a 47 Cadillac and even though the top and bottom of the Carb was different the bowl portion was the same.  Even the casting numbers were the same so I figured it might be a good donor.  Needless to say, Tim was able to make a couple of parts and it is now the correct replacement for the damaged piece. 

Will shoot some pics when it arrives next week.  Can't wait to get it installed!!!