VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc '38 line between fuel pump and intake manifold casting

My '38 Master Deluxe has a rebuilt engine, the previous owner had it rebuilt about 20 years ago, and it has not run for the past 10 years at least. When they rebuilt the engine, they stuck a '40s or '50s era Rochester carb on the intake manifold. They disconnected the throttle cable and just let it hang loose and unused. The fuel pump did not work and thanks to the help in this forum, I replaced the fuel pump and now it pumps fine.

The previous fuel pump had a bottom assembly on it that had two brass fittings that connected to rubber tubing. One of the rubber lines went to a fitting in the casting of the intake manifold, directly under the carburetor seat. I looked in my 1938 Chevrolet official parts manual for the '38 manifold, and it does not show the fitting. It looks to me like it was drilled in later, to fit the fuel pump, perhaps in the '40s or '50s? The new fuel pump does not have this bottom assembly on it, so I just let the rubber lines hang loose for now. I put gasoline down the Rochester throat trying to start the car, but quickly gave up; I decided to replace the carb with a Carter W-1, as in the original.

I noticed gasoline came out of the fitting in the intake manifold when I tried to prime the Rochester carb. Can I just put a blind fitting in this hole and shut it off? Also, the other unknown rubber line that came out of the old fuel pump goes toward the back of the engine, and I haven't traced it's path yet. I don't think the hole in the manifold was there originally, but if it is needed for some reason I don't understand it would be helpful. Have any of ya'll run into this issue? Thanks for your help!

Almost sounds like the first fuel pump possibly had a vacuum pump on it. These were added to provide better vacuum for the operation of the windshield wipers. Trace the mystery hoses and see where they go.

Leaving anything open/unplugged near the carb is a bad idea as is any rubber tubing being used for fuel line.

Can you post pictures of the original pump and some of these now unused hoses? Maybe email them to me and I'll post them for you.

I have a 37 Master, so am somewhat familiar with what you are asking. The original windshield wiper vacuum port is on the top of the intake manifold about midway between the carburetor and the # 5 and 6 intake port. It would be a 1/8 inch pipe thread with a fitting onto which the windshield wiper hose would have been attached. I have never seen a port drilled immediately under the carburetor and have no idea why someone would have done that. From what you say, the fuel pump (as Canadiantim suggests above) has been replaced with a vacuum boost model which is not original for a '38, but no reason it couldn't work. The original routing of the windshield vacuum line is from the intake manifold port I mentioned earlier, directly back through a hole in the firewall and then to the wiper motor under the center of the dash. It sounds to me that when whomever added the vacuum boost fuel pump, they made a hole in the manifold, ran a rubber line from there to the pump and then back to the wiper motor. That would be the correct routing for models that had the vacuum boost fuel pumps, except they would have used the original port on the top of the intake manifold back of the carburetor.

By the way, the reason for the vacuum boost fuel pumps is when under load, such as going up hill and the manifold vacuum drops, the wipers stop wiping! The vacuum boost fuel pumps are essentially two pumps in one, with one half pumping gasoline to the carburetor and the other half boosting vacuum to the wiper motor.

To answer you specific question, you can plug the hole in the intake manifold, in fact if you don't the engine won't run properly, especially at idle, if there is any leak in any portion of the vacuum system. I would also check to see if there isn't another port in the intake manifold at described above. I can't think of any reason it isn't there, although sometimes I have seen a plug in the place where it normally would be if the vehicle wasn't equipped with a vacuum operated wiper motor.

Agree, it sounds like a fuel pump with vacuum. Here is a link to one (for reference). My car isn’t driven in the rain, so I don’t need the vacuum pump


https://www.chevsofthe40s.com/detai...h_Vacuum_Pump_Glass_Bowl_Stops_Slow.html

Ron's description is right on target.

The combination fuel/ vacuum pumps are hard to find these days. Lots of places list them but availability is suspect. If you can get a rebuild kit for your old one, do it!

I also agree with Tim that you need to confirm that any "rubber" lines that are part of the fuel supply system need to be proper fuel hoses. Vacuum hoses will not tolerate gasoline.

Another point that might be confusing is that there should also be a vacuum line to the advance diaphragm on the distributor. It normally comes from a fitting at the base of the carburetor.

Thanks for all the help! I have struggled trying to post a picture on this forum and can't figure it out. So I will do my best to describe what I have done. You guys are spot on about the line being a vacuum line from the previous combination fuel / vacuum pump. I traced the line that went into my firewall, and sure enough, it went straight to the windshield wiper system. I took that line and re-routed it into the nipple in the intake manifold, so ideally it should work. If someone can show me how to post a picture I will put one up. Thanks

See photo. Also...your profile says you are a vcca member. Someone on the forum has to tag your profile as a valid member

Thanks Scott. For some reason, I am not getting the "attachment manager" option on my screen when I hit "reply". I am sure I am doing something wrong! I will keep pecking at it and figure it out. And I hope someone tags me as a valid member ... I noticed today the "VCCA member" badge and wanted it to show up on my posts as well. Thanks again

Post in “new member forum” that you don’t think you are vcca member flagged

You have been verified. See PM.

This photo shows where the vacuum line connects to my intake manifold. The tube on the left that is not connected, was the tube that went down to the fuel pump that had the vacuum on the bottom of it. The tube on the right, which is connected to the intake manifold, goes to the windshield wiper motor under the dash. I certainly hope no gasoline is pulled through the tube from the intake manifold toward the windshield wiper. I believe the new Carter W-1 will function in such a way that this will not happen. Thanks again everyone for the advise and help.

That is a factory installed vacuum port for the wipers . Was the same through many years. Same place on my '48.

Thanks for the information! I am glad it is factory installed. That makes me feel a lot better about keeping it connected. Thanks again!