Carb Mystery!

adamscm

Well-known member
Ok, I just tried putting a Holley 1909 onto my 144. The engine ran fine, carb working fine. I tinkered for a while to fashion a hot air choke tube, then screwed it on. Then when I restarted the engine, for no apparent reason, vacuum started sucking through the automatic choke! I haven't taken it apart yet, but what the heck is going on when your auto choke housing (with the spring)) is sucking vacuum?!!
 
:shock: yep it's suppose to have vacuum to draw in the hot air that closes the choke! Good luck :nod:
 
Ok, I learned that vacuum does pull through the choke housing to pull up the warm air. Next question--the hole in the exhaust manifold where the tube attaches--does it "dead end" in the manifold or go through it--in other words, does the choke contantly pull air through or is it just a vacuum created at the dead end hole?
 
There should be a tube that runs all the way through the inside of exhaust manafold sometimes these can get rotted out allowing exhaust gas into the choke housing and then would need to be replaced. Yes it constantly needs to pull air into the choke housing. Good luck :nod:
 
Ok, Thanks--it's a new manifold, I just couldn't remember if the hole went through. So I guess there's just that much more air sucking into the manifold that needs to be offset by the idle adjustment. Seems odd to have an unfiltered air source coming in, but I've just never thought about it before.
 
I think you can put some steel wool in the incoming end of the hole for a filter
 
The amount of air coming in the choke riser tube is minimal. Soot from the exhaust is a little more problematic IF the wall between 3 and 4 is burnt through. Chances are it is. It should be closed off by tapping and plugging the top and bottom of the choke riser stove. Then you can run an aluminum or copper tube to one of the the exhaust outlets and wrap it around the exhaust manifold a few times. As the manifold heats up, the tube does too and pulls the choke plate open.

This is what I did. The tube and the little collector on the pipe came from a speed parts store. There was no filter in the original and none in this kit.
 
Thanks, I just got a kit today so I can fashion a tube up to the new carb. The hole in my manifold is good--it's a new manifold. However, my tube-bending skills are precarious! I'll show results when I can........the tube in the kit is aluminum--will it bend easier if heated?
 
it will bend easily period
too easily, so go slo. No big deal, just cosy it up there.
Think of it as a tube of air that rises as it gets hot, the hole in the exh. is just there to hold the end…
 
I've did HVAC for almost 20 years. Use your thumbs. Start wide at a tight bend and go slow and careful but with certainty about the radius, direction and angle. That tubing bends real nice, they use the same tubing for pilot lights. Just don't kink it ;)
If you do I have a trick or two for that, first one involves a crescent wrench
 
:D When bending steel brake line I just use whatever is handy for the right radius.Hammer handle,socket piece of pipe of some sort. Just whatever happens to work for the radius that I need.
Good luck.Have fun.Be safe.
Leo
 
(if U can - go w/ Matt & Vintage. Some of us here R tryin to build him up so as to cater to our needs even more as he grows).
 
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