My new to me Plymouth has a vacuum issue, I think. At idle it has low vacuum, like 7 in/hg. When I rev it up, the vacuum goes up, not down as normal. Any ideas? Is it a big problem? The car runs just fine out on the road. Here is a video of what it does: Thanks fellas
Sounds like it has a vacuum leak with the "Sucking" sound it's making coming from the carb. I notice the choke is partially closed. Does it open all the way when it's hot??? After it's hot & the choke is fully open cup your hand & put it over the top of the carb. partially blocking air flow. Does the engine speed up or wants to slow down???
I will check that and report back. The carb is old and was pretty grody (technical term) and I had to clean it a lot to get it to run as well as it does. It was only partially warmed up so the choke position was normal...I had run it a few times. I changed vacuum gauges to rule that out, so maybe 5 minutes running today. It does not have power brakes and it does not have a vacuum connection to the transmission. All the ports are plugged or in use. It does smell as if it is running very rich; it can almost sting your eyes. Thanks Tom
That's weird for sure. Could it be a timed vacuum port? Even then, I doubt it would be pulling that much vacuum at idle. Have you taken out the idle needles and blown then out with some carb cleaner and compressed air? Maybe it runs fine once it gets into the transfer slots on the carb, but not so much on the curb idle ports. Have you pulled the carb to check the base and gasket?
I did blow clean and blow out the idle circuits; it wouldn't idle when I got it. I have not taken the carb off yet. I have checked it with both ports...it's an AFB carb I think, but it's just like an Edelbrock.
Took the car to the store tonight. When I got it home, I observed that the choke is open all the way and when I put my hand over the carb, the car tries to die (and will die) if I restrict the airflow. The vacuum reading is a very steady 8 in/hg at idle going up as the revs increase. Weird
AFBs are super easy to rebuild. I'd at least pull it off and check the base gasket, and maybe even pull it apart for a good cleaning. Have you sprayed around the base looking for a vacuum leak? Is there a transmission modulator on a Torqueflite? There aren't a lot of vacuum lines on these, but that might be one of them.
It's fubared. Easy enough to get a new one. Matching the trans linkage is another situation entirely.
It's hard to tell, but it appears you have the vacuum gage connected to "ported vacuum", which is not true manifold vacuum. The ported vacuum line would actually increase in vacuum as you rev the engine. See if you can make a connection where the brake booster vacuum hose connects to the manifold or carb (can't tell if you have a brake booster) or a port that connects directly to the manifold or carb base flange. Ported vacuum is above the carb base flange, like what appears where your vacuum gage is located.
I could remove the plug in the back of the carb (3/8) and bush down the hose so I could attach a gauge, I guess. I don't think it would make a difference. It really runs good, just has funny readings.
I must agree. Going back & looking at the video of the vacuum gauge it IS hooked up to ported vacuum (above throttle blades) & NOT manifold vacuum. Would account for the readings your getting. If you have power brakes you could pull off the hose from the booster/check valve & hook your vacuum gauge to the hose. Just slip your vacuum gauge hose into the booster hose, it should fit without any adapters. Mopars DO NOT have a vacuum modulator.
Thanks guys. I said all that in this thread. I tried it both ways; same result. Again, I don't have power brakes. However, I do have a port for them on the manifold. Maybe I'll adapt to that and see what readings I get. This problem exists more than you think, and it baffles people everywhere, including me.
