High RPM issues

[Guest Shoe1932]

Hello all.

Ok i know this is not a Plymouth site but you guys are better at this and also better at responding than the Plymouth group. i have a 39 Plymouth P-8 and she starts and drives well. Unfortunately at high RPMs in each gear it acts like it is starving for gas. In 3rd gear it starts at about 45-48 MPH. I thought it might be the flexible gas line which runs from the metal gas line to the carburator. I have seen where those lines can get clogged in the past. It was not clogged and it has not made a difference. The carburator was rebuilt a few years ago and should be good. What are some other ideas or possibilities? I am thinking about putting some carb cleaner down the carb when it is running in case a jet is having some issues. All ideas are welcome. I do have an in line fuel pump but feel that I am getting a good flow of gas until the higher speeds. I took the fuel filter bowl off and cleaned the screen out. It looked good. Just wondering if you guys have any good ideas. Thanks in advance for your help

[mrspeedyt]

I would check the volume of the fuel pump. maybe it doesn't flow enough at the higher rpm.

[Pete K.]

John, If you can open the hood to look at the fuel filter bowl when you hold the throttle open a bit at high rpm's, do you see any air spaces or large bubbles coming into the filter bowl, you may have a porous suction tube in the tank, sucking some air into the line.Make sure all connections are flared OK and tight. Without seeing this it can be hard to tell if it's actually a fuel problem. Could it be a high speed miss because of a timing or ignition issue? A vacuum gauge would come in handy with this problem.

[Marty Roth]

Sometimes what we believe to be fuel-related, is really electrical in nature.

I would check your ignition points gap, and possibly decrease (close down) the gap.

If the gap is actually set to specs, and the problem persists, check to see if there is slack in the distributor shaft which could create a larger gap.

The distributor can be rebuilt, or re-bushed.

Edited April 21, 2013 by Marty Roth (see edit history)

[ply33]

Sometimes what we believe to be fuel-related, is really electrical in nature.

I would check your ignition points gap, and possibly decrease (close down) the gap.

If the gap is actually set to specs, and the problem persists, check to see if there is slack in the distributor shaft which could create a larger gap.

The distributor can be rebuilt, or re-bushed.

I had a '57 VW Beetle that acted like it was running out of gas. Turns out that it was the coil.

This last week on our 900 mile trip to Tucson the '46 Plymouth P15 what was with us had a bad miss on climbing hills or running at high speeds. Was diagnosed as a bad coil and the people in that car had a problem free return trip with a new coil.

Heard once that 90% of your carburetor problems are electrical. Seems to be some merit in that.

Hello all.

Ok i know this is not a Plymouth site but you guys are better at this and also better at responding than the Plymouth group. i have a 39 Plymouth P-8 and she starts and drives well. Unfortunately at high RPMs in each gear it acts like it is starving for gas. In 3rd gear it starts at about 45-48 MPH. I thought it might be the flexible gas line which runs from the metal gas line to the carburator. I have seen where those lines can get clogged in the past. It was not clogged and it has not made a difference. The carburator was rebuilt a few years ago and should be good. What are some other ideas or possibilities? I am thinking about putting some carb cleaner down the carb when it is running in case a jet is having some issues. All ideas are welcome. I do have an in line fuel pump but feel that I am getting a good flow of gas until the higher speeds. I took the fuel filter bowl off and cleaned the screen out. It looked good. Just wondering if you guys have any good ideas. Thanks in advance for your help

Best spot I know on the web for old Plymouths is the forum at P15-D24.com and Pilot-house.com original focus is on the '46-48 Dodge and Plymouths but the coverage is much wider. Certainly has more traffic than the Plymouth forum here on the AACA site or even the official Plymouth Club forum over at Home page of the Plymouth Owners Club Bulletin

[mrspeedyt]

after reading the later posts i agree check the coil and the points. the coil went bad in my 41 desoto. the original only lasted 70 years.

[Mark Shaw]

Good advice here... You might also try real gasoline if you are currently using "Corn Gas".

[FLYER15015]

Shoe,

While your checking all the distributor components, don't forget to pull the vacuum line at the base of the carb and see if you can make the "points plate" move.

My '40 Buick seemed a bit sluggish a while ago, and low an behold the vacuum advance diaphram had crumbled in the can.

New unit in and much better performance now. Got mine on e-bay at a very reasonable cost.

Mike in Colorado

[Brian_Heil]

All good inputs so far. You can check that the timing advance works be using a timing light and rev'ing the engine and watching the timing mark move and hooking and un-hooking the vacuum line to the advance diaphram too and watching the timing mark move.

My additional comment: I've seen a carb. float set too high do the same thing. It could never fully 'drop' to let the inlet needle open all the way.

My money is on the fuel pump not getting the job done or here's another simple one, the vent on the gas cap is plugged or partially plugged and the fuel pump is pulling like heck but you have negative pressure in the tank because the vent path is plugged. Take the cap off and do a power run.

You made my day with your comment about the Buick Pre War site. Smiling here in Michigan (and I have a really good friend who is a great guy in the WPC too!)

[Brian_Heil]

Actually thinking about it, I think the float was set too low so even when fully down, the float arm at the needle was still not fully down holding the needle up, restricting flow. But I think you get my point.

Another quick check is to look at the choke plate, is it out of the way, straight up and down and not getting sucked shut (loose) and how about that air cleaner? Easily removed also to check for restriction on a power run.

No charge for Plymouths. We just think of you as a future Buick ower. :cool:

[Brian_Heil]

Any kind of heat valve in the exhaust on that Plymouth? I had one of those stick restricting exhaust flow on a 1960s car.

How's the fuel filter look including the sock in the fuel tank? I've had both of those plug on me too.

[jenz38]

I would check the Carb Float too, maybe it slowly switched over to a "Diver" ?

Also i would replace the Ignition Condenser in every case.

Would check the Cable between Coil and Points for damage and Shortcut to Ground. Sometimes it only happen while

The Pointplate move to advance and the damage Cable inside the Distributor then have contact with the Housing or plate.

M2C

Good Luck

[ply33]

. . . No charge for Plymouths. We just think of you as a future Buick ower. :cool:

Don't all the really fine cars have names that start with "P"? Packard, Peerless, Pierce-Arrow, Plymouth, . . .

Any kind of heat valve in the exhaust on that Plymouth? I had one of those stick restricting exhaust flow on a 1960s car.

How's the fuel filter look including the sock in the fuel tank? I've had both of those plug on me too.

There should be a heat riser with thermostatic spring on the exhaust manifold below the carburetor. Parts to fix that are available from Antique Auto Parts Cellar, but a bunch of people find they can lock it in the hot position and not need it. I personally find that cold start drivability, especially on cool (35 to 40F) damp mornings, is greatly improved by having it functional.

[Guest Shoe1932]

You guys all rock. I have quite a few things to get started On. Thanks so much for the imput. It may be electrical or vaccuum related. The fuel pump and carb were rebuilt a few years ago and it ran great until September of last year when I took it to Amarillo (I trailered it for the 9+ hours). It was acting up before I took it. The coil is 3 years old also so I hope to rule that out also. I will get started on these tests and will keep you posted as to my success / progress. I am hoping for more success than progress at this point, but will settle for either.

Brian, I do enjoy the Pre War site. Everyone on this site has been helpful over the last year since I joined the BCA. I am looking forward to meeting some of you at future meets and tours.

Marty, I believe you and I were next to each other at the Canyon TX meet last year. You had your '37 Buick Limo and I had my '39 Plymouth that day in HPOF. Next year I will bring the '32 Buick.

Thanks again for your advice. Be in touch soon with my progress.

[Brian_Heil]

Your trailering comment reminded me of another issue. I trailered my Buick all the way from Michigan to North Carolina 1999ish got there and it would not run for a darn. Issue was the float. Carb was dry so on the trailer that float was just banging around in the bowl. On an old Marvel carb. a little bolt and nut holds the cork float to the float arm. That little bolt and nut had shook loose. The float would drop but the arm would not follow since it was no longer bolted to the float. Sounds like you may have shaken something on that trailer ride too?