No Top End

[Aaron]

I have brought this problem up in the past, but I still have not figured out a solution!

48’ B1B – Idles good, operates good until I get up to about 30 mph, then it just sputters and is really doggy.

I have adjusted points, timed it several times, tried a spare carburetor, new fuel pump, new fuel lines, newly restored fuel tank, new rotor, new plugs, new wires.

At this point I am thinking either it is not getting enough gas for some reason, or there is still something wrong with timing???

Is there a manual way of timing instead of using a light?

What do you all think?

[Don Coatney]

Have you done a compression test? What is your sparkplug gap? Have you connected a vacuum gauge to check vacuum levels at all engine speeds? Have you checked around your carburetor base plate and intake manifold for vacuum leaks? What is your valve lash settings? Any one of these things could cause your problems.

[greg g]

You can time it with a vacuum gauge, and attaching the vacuum gauge to the engine will also give you a better idea of the condition of the engine. But before you do that check the wire in the distributor that goes from the coil terminal to the points. These will sometimes fray the insulation and when the breaker plate moves the wire can ground out against the body of the distributor. Also after many years of flexing, it might be down to 1 or 2 strands that are actually conected within the insulation, or can be disconected completly allowing juice to pass until the plate rotates and pull the strands apart.

Also make sure your coil wire is fully seated in the distributor cap, you also may have a bad condensor. You did not mention the condition of your distributor cap, it bears an inspection for cracks, for carbo tracking, and to assure the center contact is contacting the rotor.

On the fuel side, test the pump output by disconecting the line at the carb and directing into a container. Pull the coil wire and have an assistant crank the engine with the starter. Watch the pump out put as the engine cranks, if you watch you will see the flow is in the form of short pulses as the pump works. 12 pulses should give you 8 ounces or more of gas in the container. If you are getting less you have a restriction somewhere in your system. do you have a fuel filter? Have you checked the screen in the fuel pump to assure it is clear of debris?

If you have good flow, then assure your float level is set properly.

To do the timing attach the vacuum gauge to the intake manifold. with the engine at idle, assuming you have a good steady vacuum reading (should be between 17 and 21 inches of mercury) rotate the distributor to achieve the highes steady reading, then tighten the distributor down. then adjust your idle speed as necessary. You may need to retard it a bit if it has a knock or ping under load during a road test. If you do not have a steady gauge, then that indicates other problems that need to be addressed.

There is a good feature on reading a vacuum gauge on the SecondChanceGarage website, you should take a look there. Or just do a web search for reading a vacuum gauge.

And remember the rule, that 90% of fuel problems are electrical, and 90% of all electrical problems are related to the fuel system. hope you find your problem, sounds like it might be a flow problem or float level, but ya never know.

[grey beard]

There are actually TWO fuel pump tests you will want to make - pressure and volume.

Start your engine up and let it idle till it is up to operating temperature. Shut it off and remove the fuel line at the carburetor. Hook your vacuum/pressure gauge to the fuel line and start the engine. You should see a minimum of 5 or 6 pounds of pressure on the gauge at idle.

Hook your fuel line up and let it run for a few minutes at idle, then remove the line again and hold a quart container under it while someone else starts the engine. Let it idle for 30 seconds - it will run that long on the fuel in the carburetor bowl. Like Greg sez, you should get a pint - 8 ozs - of fuel into your container in 30 seconds.

If your pump fails the second test, fix that problem first. Could be a dirty filter, kinked line or dirt in the tank outlet plumbing - there's about 24 inches of line inside Pilotrhouse fuel tanks that can build up with varnish. You may have to drop the tank and work on this opening with choke cleaner. I've even used an old piece of speedometer cable core on a cordless drill, sorta' like a RotoRooter, to clean this line out. It's shaped line an S inside and can get very plugged up. These are not too easy to clean out.

Once you have good fuel flow and fuel volume into your container, running at idle speed, then check your fuel pressure again. If volume is okay and pressure is low, replace the fuel pump.

Once your fuel system passes both the pressure and volume tests, then go to the ignition system. Set your points at about .020" and then set your timing with a light. Don't set the timing much advanced before top dead center. Contrary to local wisdom, if timing is advanced too far, it will ping, but NOT on acceleration, but rather at highway cruising speed - 45-50 mph -when you accelerate.

The two advance mechanisms inside your distributor - vacuum and centrifufal - will not peak until nearly 2800 engine rpm. It is at or near this speed that you will encounter pinging or preignition. This can be pretty hard on an engine, and can lead to burning a hole in a piston dome, if left go unattended too long. I would be a little leary of "power timing" our flathead engines. It is at road speed where this problem develops and we all know that there are a lot of other noises present at these speeds which can keep us from hearing preignition sounds, especially if your ear is untrained for picking these out from other sounds.

Finally, if your engine lacks top end power after you've done these tests, try adding a little choke to your warm engine while you are driving at road speeds. If the engine gains power or smooths out when you apply some choke, you may be dealing with carb issues like mebby an incorrect carb for your engine, wrong main metering jet size or float level way too low. If the choke application makes no change, your problem is likely elsewhere.

Let us know what you find.

Good Luck

[Aaron]

Thanks for all the good advice, but I have a few questions that need clarifying.

I need to buy a vacuum/pressure gauge I guess, any suggestions?

Once I have the gauge, specifically, where do I hook it too? Is there more than one place? Pictures are always helpful!

[greg g]

Vacuum gauge is connected to the intake manifold. If your vehicle has vacuum wipers, simply remove the tube that feeds the wiper motor and attach the gauge there. If you have electric wipers, the vacuum port that was used for the wipers on other models should be available and plugged. You might neet to put a fitting in to attach the gauge to. Fuel pressure gauge can either be t ed into the line from the pump to the carb, or just attached to the line with the line removed from the carb. Both the gauges should come with a few optional attachment fittings.

Neither one is expensive, and probably harbor freight or tractor supply might even have them packaged together.

[Don Coatney]

My vacuum gauge is a "compound" gauge meaning it will work both as a fuel

pump pressure tester and a vacuum tester. I bought this gauge sometime in

the early 60's from JC Whitney and it still works well today.

[Aaron]

Couldn't find the vacuum port the windshield wipers use so I used the port located at the bottom of the carburator that runs to the top of the distributer, is that acceptable? The vacuum gauage read zero when I had the truck at idle. When I gave it gas, then it would start reading...

Fuel pressure is good, compression is good. I haven't check fuel volume yet, but that is next on the list. I'm struggling with this whole vacuum thing right now...

[greg g]

Nope using ported vacuum is a measurement of vacuum generated by the carb. You need to hook up to the intake. Look between the carb and the firewall on the intake, you should be able to find a threaded port that has a plug in it if it not being used to feed the wiper motor. You may need to pull the plug and screw in a hose adapter.

If you have vacuum wipers the easiest thing is to unattach the hose at the manifold and plug the vacuum gauge in there.

[Aaron]

The latest...

My fuel pressure measures at 5 pounds

My fuel volume at 12 pulses is 4 ounces

(running engine for 30 seconds gave me a good 25 ounces of gas)

Compression - all 6 cylindars are right around 110 psi

Vacuum from intake manifold is right at 19 inches of mecury

Timed at TDC mark of crankshaft

Tried 2nd carburator

Still the same problem!!!

It cuts out bad at higher speed and rpm. sounds like it is either flooding or lacking gas...

Now what?

Edited August 30, 2009 by aforests
added sentence

[greg g]

12 pulses should give you 8 ounces at least. I suspect you have a blockage somewhere, or you might be sucking air on the tank side of the pump.

[Aaron]

If I'm sucking air on the tank side of the pump where would be a couple places to start looking?

[Jerry Roberts]

If I'm sucking air on the tank side of the pump where would be a couple places to start looking?

Look for any holes worn into your steel gas line , sometimes these show up as a wet spot . Look for any rubber hose connections that are old , these might need to be replaced . Look for any loose connections on the gas line that could suck air . On another note ; there is a small wire in the distributor that moves each time that you use the throttle , if this little wire is grounding out or making a bad connection , you could be having this problem too .

[grey beard]

I had this identical problem with my engine when I first overhauled it, and sorta' pulled my hair out till I found it. It started and ran just fine, but wouldn't go over 2000 rpm.

Got my new points from NAPA - Echlin brand. Unbeknownst to me, they use a separate steel spring inside the contact point set. This steel leaf spring was missing in my box, and the points were actually floating at higher speeds because the only thing closing them was the thin brass contact strip. The real spring was missing. A new set of points made all the difference in the world.

Here's the moral of this story . . . . . .

New parts "out of the box" can sometimes cause problems, too.

[greg g]

check out this posting o another forum regarding air infiltration between the tank and pump. (and I gotta find this guy,he is one of three people I have found that agrees with me tha vapor lock betweent he pump and the carb can't exist without suspension og the laws of physics and or hydrodyamics)

http://en.allexperts.com/q/Classic-Antique-Car-2542/1949-Studebaker.htm

[Charles Furman]

I had the exact problem you are experiencing. Everything worked great until I ran at higher RPMs, especially if I put my foot in it. Then it would act as if were running out of gas.

I changed carburetors and did all the normal stuff, then just before I started kicking things, I was leaning over the fender looking at the fuel pump when I reved the engine and saw air bubbles in the glass fuel bowl at the filter. Upon closer inspection I found that the 6 inch rubber hose that connects the steel fuel line running down the frame to the fuel pump had a split in it. It was not a big enough split to leak fuel out or affect the engines performance when it was drawing fule at a slow pace, but when the pump was trying to draw a lot of fuel it would suck air in through the slit in the rubber hose.

Good luck.

[Frank Elder]

I had the exact problem you are experiencing. Everything worked great until I ran at higher RPMs, especially if I put my foot in it. Then it would act as if were running out of gas.

I changed carburetors and did all the normal stuff, then just before I started kicking things, I was leaning over the fender looking at the fuel pump when I reved the engine and saw air bubbles in the glass fuel bowl at the filter. Upon closer inspection I found that the 6 inch rubber hose that connects the steel fuel line running down the frame to the fuel pump had a split in it. It was not a big enough split to leak fuel out or affect the engines performance when it was drawing fule at a slow pace, but when the pump was trying to draw a lot of fuel it would suck air in through the slit in the rubber hose.

Good luck.

The small rubber line will also rot on the inside and collapse starving your carb thus affecting your speed.

[greg g]

Didja check inside the of the fuel pump yet??? You don;t eed to take it off, yu can take it apart and look while its on the car.

[Aaron]

Greg, what am I looking for when I take the fuel pump apart?

[greg g]

There should be a fine brass screen seperating the inlet chamber from the output side, It may be plugged, and the bolt that holds the bottom cover on is hollow. I had a situation where there was a piece of stuff within the bolt that acted like a flapper valve. It would pass fuel all day at idle or up to about 30 MPH, then the flow would cause it to move, and shut downthe flow, the car slowed back down, adn the flow decreased then it would relax and the car would drive at 30 again. This is the fuel pump that does not have the glass bowl on it. but I believe the ones with the glass have he screen also.

What have you done so far? as noted before the 12 strokes should give you 8 or more ounces of gas.

[Aaron]

since checking everything else, I now need to start checking things from the fuel pump to the tank. Although all lines are new including the rubber line and the fuel pump is new and the tank has been restored I suppose there could still be something out of place...

I'm hoping to get some time one of these nights...

[Aaron]

How does one specifically check to see if the vacuum pot on the distributer is functioning?

[TodFitch]

How does one specifically check to see if the vacuum pot on the distributer is functioning?

One way: Remove distributor cap, attach hand vacuum pump with gauge to "vacuum pot" on distributor. Pull a vacuum. See that the points plate moves. Verify that it does not leak down.

Another way: With engine running, a hand vacuum pump with gauge attached to "vacuum pot" on distributor and a variable advance timing light setup: Pull vacuum to value in book, check for correct amount of advance. Verify that it does not leak down.

[greg g]

The tank has an in place filter (oilite bronze) it could be the tak treatment has gummed it up wioth sealer. Becareful removing the line from the tank, you want to pay special attentune to the ferrul that if you don't watch it will escape and hid in the darkest corner of your shop.

[Merle Coggins]

Nice thoughts Greg, but trucks don't have the filter on the internal pickup tube, nor do they have the little ferrell that tends to go missing on the car tanks. However, it still could be a plugged line in the tank or elsewhere.

Merle