Engine Problems

Hi guys thanks for all the help i've had on this site ive currently got a 1944 IHC KB-1 its a 3.8 flat 6 GRD 214 i imported 6 months ago. Unfortunatly she keeps cutting out every time under load. it runs a carter yf ive had this replaced with another carter yf but still it seems to be running rich weve tried changing the jets in the new carb from the original carb that came with it but still no go. is this the correct carb or do i need a different one??? if it is the right one what are the jet sizes??? just to let you know i have rebuilt everything else so it is only the carb im having the problem with.

Thanks

Phil Kearsley
England, United Kingdom

Howdy, Phil!
There's a bunch of mechanics on this site so get ready for lots of opinions.
Whenever a customer tells me the carb "has to be" the problem i recall about 40 years of working in repair shops when the problem was anything but.
The carb seems to be the first thing to get blamed. It should be on the bottom of the diagnosis list unless you can see obvious problems like leaking, fuel dribbling from main discharge at idle, etc.
You've tried two carbs so it's time to consider the possibility it's not the carb.
Having said all that many of the old IHCs I encounter no longer have their original carb. One favorite
Replacement carb is the carb from a like year Chevrolet, an old Rochester one bbl. They work fine.
Fuel supply on these old trucks can be a major problem. I just got through fighting 5 gallons of muck in a 1938 IHC D-2.
Have you done a gasoline volume and pressure test at the carb inlet?
Deadhead pressure at the inlet should be around 5 psi. Much more than that the needle and seat can't control fuel. One or two psi and you'll be constantly running out of fuel.
Even more important is the volume test. A fire extinguisher here is a good idea.
Takes two people, really. One to crank the engine and the other to catch the gas in a measured container so it doesn't spill.
Mechanics can tell you after a coulple of spurts whether fuel supply is good or bad. If you can't recognize good flow from the fuel line you need to time how long to get a pint out.
Less than 30 seconds? I don't have the repair manual in front of me.
A tiny pinhole or crack in a fuel line between the pump and tank and the pump will always try to pump air first because it's easier to do. This is a huge problem on old vehicles.
Alternately it only takes a tiny piece of debris to block the whole works.
Gotta love them old trucks!
Once the fuel supply situation is covered it's time to move on to engine performance.
In my shop your truck would be on my oscilloscope in a heartbeat. It quickly identifies all sorts of ignition problems and even does an electronic compression check.
So, what's your compression on all six cylinders warm engine?
I always tell people to get the vacuum gauge out of the toolbox first.
Vacuum on a healhy engine should be about 18"hg or better and STEADY at warm idle. A little hunting of the needle is OK but no flicking. Flicking indicates that one or more valves aren't seating. That's BEST scenario.
Time to adjust valves?
I've heard it said that IHC flathead 6 engines need valve jobs more often than other flathead engines but I don't know if that's true.
Your ignition system has three timing measurements. Initial, mechanical and vacuum advance.
The vacuum advance should be obvious, does your model IHC rotate the entire dist w/ vac advance?
If so, you should see the dist housing rotate slightly on engine rev and then return.
If you don't have a timing light then you can do a mechanical timing advance check by taking dist cap off and trying to rotate and release the dist rotor. This is mech advance. Does it rotate and snap back?
Retarded ignition timing can cause the engine not to want to rev up. What's your initial timing?
Are you still 6v? Is the coil polarity the same as bty polarity? In other words bty pos+ ground then coil pos+ connected to dist?
Have you tried seeing if you have a nice bright blue spark that can jump 1/4 inch or more?
Check some things and let us know. Don

Another thing to check is to see if the pick-up tube in the tank is partially blocked. The tube is only 3/16" inside diameter. It does not take much crud to block it. To check it you turn the shut off valve clockwise till it seats, then remove the fuel line from the valve. With a tub or bucket under the valve, open the valve to see how strong the flow is. If it runs out at a good rate it should be OK, if it just trickles out it is plugged. Some times blowing compressed air back into the valve will unplug it, take off the fuel cap before doing this so you don't pressurize the tank. You can also unscrew the valve from the tank as this will give you access to push a wire through the pick-up tube to clear the obstruction, but first you must drain the tank to do this.
Also you can check to make sure the accelerator pump in the carb is giving a good squirt of fuel in the throat of the carb when the throttle is moved. If the squirt is weak or not squirting it will cause the motor to stall or stumble. Hope this helps.
Bill

I guess Phil fixed his truck??