need help on a old flat head

Yesterday the head gaskets came in and the flat head finaly got buttoned up. It is a 1946 truck motor with al. heads, a tuhickstun pm-7 intake and 2 fresh 97's on top. We didn't have much problem with it firing up but you have to keep your hands over the top of the carbs to keep it running. If anyone has any sugestions let me know? Also on a 97 carb where is a good starting point for the air fuel mixture screws?

 

is your gas tank fulla crap? Is the pickup line stopped up? Is the gas line clear with no holes? Is the fuel pump working? Is there a stopped fuel filter? Is the float needle stuck? Do you have stopped up passages in the carb? Do you have your shoes on the correct feet?

 

the one thing obvious is that you're running dead lean.
Start experimenting with stock jets and screws maybe 1 1/2-2 turns out.
I think you'd be better off starting the thing with stock manifold and one carb until engine is debugged and running right--you really don't need further complications.
If normal adjustments don't get it to idle, suspect low float level.

 

make sure that both carb. butterfly are completly closed at and idle. You will need acarb synchronizer unless you are very good at multiple carbs. check for vacummn leaks. Do you have a fuel pressure regulator and have you changed the jets? Try about 1-1 1/2 rounds to start. If you can't find a synchronizer, I have one.

 

thanks for the help. the fuel system is clean with 2 psi at the carbs. how does the synchronizer work?

 

No one thought about that he could have a vacuum leak, either at the manafold or at one of the carbs.This will cause you to either choke it all the time or keep the revs up high.To check for this take a can of starting fluid and spray around all of the gasket edges on manafold and carbs. If the engine speeds up as you are spraying,you have a leak at that area, and that is your problem.--TV

 

they work off vacummn, measuring at top of carb. I have one if you want to use it.

 

it helps synchronize the amount of vac. running through your carbs so its equal (by agj.). but that shouldnt make in not idle. it sounds like a vac leak to me, but ya never know until you fix it

 

Sounds almost exactly like the setup I am using on my flatty so I will attempt to help based on what I fingered out.
Obviously first check for vacuum leaks like the others mentioned. That may be your problem and a simple fix.
As far as the 97's are concerned; air/fuel screws set at about 1 to 1-1/2 turns out should be good enough to get the motor running but not running perfect. 3/4 to 1 turn out seems to work better for me. Once the motor is running you can synchronize the carbs using a Uni-Syn or something similar. There are different types available but I use an old Uni-Syn just because it is what I have.
There was a thread a while back about how to use them, I think it is in the tech section, but here is a quick run down on how they work. The Uni-Syn measures air suction into/through the carb. The tool is adjustable and and has a float which measures the amount of vacuum the carb is creating. The float moves through a clear tube and the tube has increments marked off the length of itself. Adjusting the uni-syn is done by increasing/decreasing the available area that air has to flow through it. Adjusting the uni-syn should not make the engine idle change. If it does, the carb idle set screw is needs to be adjusted. After setting the "float" level for one carb you just make the necessary adjustments to the remaining carb until they both match. After getting the first carb's setting, do not mess with the synchronizer. Any changes to the setting on the Uni-Syn will throw the other carb settings off. Getting both carbs utilizing the same amount of vacuum is done by adjustment of the idle set screw on each carb. Once both carbs are "sucking" at the same rate, the mixture screws can be, well, screwed with. The uni-syn should be used with the throttle linkage disconected. Maybe I should post a tech article on how to do this...
Did you rebuild the 97's yourself? The reason I ask is because most rebuild kits will tell you to set the float at a level that is not all that close. I found the best way to set the float in these carbs is by doing it wet but without the car running. Remove the top part of the carb and measure from the gasketing surface farthest from the fuel inlet to the highest point on the float. Use a good gauge, not the crappy paper ones the rebuild kits have you cut out. Those paper one's are about as accurate as throwing a rock at it. I tried many different dimensions for float settings and found that 5/32" seems to be about the best using the above method.
The suggestion of getting the motor running using a stock intake and a single carb is a good idea.
Hope this helps.

 

I'd say TV is right, sounds like you have a vacume leak, could be an intake valve not closing all the way, but it would be backfiring through the car when you rev it up if that's what it is.

 

You hook up that line that comes from the distributor on the front of the motor? Just a thought...

 

Always start with the simple stuff first....Fuel filter, sediment bowl, etc.

Sometimes when I get into these kinds of problems, I tend to make it more complicated than it really is by tearing stuff apart, when it ended up being something simple in the first place.

Flatheads forever!!