Lean running condition

[sunroof]

So I bought this '59 beetle last summer:

I spent all winter assembling it back into a car with the intention of selling it:

But due to a problem with the motor, I can't sell it:

It starts and idles very nicely but as soon as you step on the gas it goes extremely lean. What happens is that you can feel the accelerator pump give its little shot and as soon as that fuel is burnt the power drops out and it starts to backfire out the carb. I have tried 2 carbs on the car, both rebuilt as carefully as I know how. I took the intake off and leak tested it as well as made sure the preheat tube was not blocked or leaking. I set the valves up very carefully and checked the timing and advance with a timing light. I checked the throttle shaft play and both carbs were as tight as I have seen an old 28PCI. I am at a loss for what my next step is in troubleshooting this engine. Someone suggested to me that it might be a cracked head but it runs too smoothly for that I think.

A bit about myself: I have been working on '50s beetles since 1979 specializing in 1959 T1, I have had probably a dozen '58s and '59s. This is the first time I have run into a problem like this. I welcome any and all suggestions. I have a fuel pump rebuild kit on the way and will see if this makes any difference.

BTW I made a heavily modified Triumph TR6 engine with Zenith-Strombergs on it purr like a kitten so how hard can this be?

Don

[berliner]

Have a look at the vacuum advance mechanism;they have a tendency to stick/seize after fifty years or so.
_________________
I'm part of the problem.

[sunroof]

So today I rebuilt the fuel pump thinking it might not be putting out enough pressure to keep the float bowl full but it made no difference what ever. Tomorrow I will swap in a known good distributor. I know you all are on the edge of your seats on this one so I won't keep you in suspence.


Don

[58Blue]

[my59]

You have way more under your belt than I do, and I got to start with an unmolested kept by the book ride- did you check the vacum connections to the carb? Mine has to be threaded just so. Does the advance work on the distributor?

Rebuilding the fuel pump, did you replace the interior springs? Rebuild kit with little metal internal 'valves', or hexagonal thicker (what ever they are made from with the cross hatching on them) 'valves'? I've had the metal ones get whacked in the pump because they are too thin and the springs cannot close them right as the springs are near the end of their spring ability. Hole in pump diaphragm?

Hows the gas tank sock filter, and is the fuel tap clear of rotted rubber crap from not being used?
_________________
my59: Well son, my grandfather died before I got to drive it, so does that answer your question?
our79: sunroof bus w/camper interior and 2.0 FI
Other:'12 Jetta, '77 Benz 300D, and a 74 MG Midget.

[ejonn]

Did you actually squirt something around the throttle shaft to check for a leak? I chased a very similar problem and thats what it took to find it.

[sunroof]

Thanks guys. I sqirted brake clean all around the intake and carburetor. I rebuilt the fuel tap and cleaned the fuel line out with gunk carb cleaner. I did not replace the springs in the fuel pump but took it apart and cleaned everything and made sure the check valves were working before installing it.

Tonite I made a tool to check the vacuum advance on the distributor. I took a vacuum pump with a gauge on it and hooked it to the disty. It started pulling the plunger in around 150 mmHg and the plunger was all the way in by 220 mmHg. I then left it for a few minutes and there was no drop in vacuum. So the vacuum advance works and does not leak.

I do not know what to do next.

1. I changed carbs
2. I checked the intake for leaks
3. I checked the heat riser for leaks or blockage
4. I changed the fuel pump
5. I tested the vacuum advance for leaks and function.
6. I rebuilt the fuel tap and cleaned out the fuel line.

Perhaps I will make a gauge to test fuel pump pressure.

Don

[my59]

I've never used a timing light on my 6v system, just done it static with a test lamp. How did you do it with a timing light without a degree pully?

Have you checked the points/cap/rotor?

When you re did the carb, did you take out the brass plug and clean the two ball bearings related to the accelorator pump? Is the float operating right? I've had a couple of rebuild kits come with float valves where the pin did not consistantly open as the float moved.
_________________
my59: Well son, my grandfather died before I got to drive it, so does that answer your question?
our79: sunroof bus w/camper interior and 2.0 FI
Other:'12 Jetta, '77 Benz 300D, and a 74 MG Midget.

[sunroof]

I used a timing light when I first started the motor and it worked nicely. You can see the notch in the pulley advancing as you rev the motor to about 30 degrees.

Everything in the ignition system is new. Plugs, wires, cap, rotor, points and condensor.

When I step on the gas I can feel the shot from the accelerator pump make the car accelerate normally and then once that is burned, the power drops out and it starts backfiring thru the carb.

I am going to assemble one of my other motors and put all the top end parts from this motor on it and see if the problem persists. If it does then I know it is a top end thing and if it doesn't then I will know if it is a bottom end thing.

Don

[Hammarlund]

[sunroof]

A lot of trouble to go to when I know from other degreed pulleys what 30 degrees looks like. There is no doubt that the advance is working. It is a feul delivery problem.

Don

[KTPhil]

Have you checked the jetting in the carb? Checked for intake leaks? Tried adjusting the accel pump stroke (I think early carbs let you put the cotter pin in one if several holes to adjust). Did you fit the accel pump cover loosely at first, then hold the throttle fully open, and only then, tighten the screws?

[ejonn]

Does it run at all off idle?
Have you used a known good carb?
There's no mention of your inlet valve (the new ones in the kits are notoriously bad).
What's the bowl fuel level level look like?
Does it run any different with the choke closed a bit?

[sunroof]

Thanks guys.
Please reread the whole thread.
Closing the choke a little does not make a difference since the 28PCI opens the throttle before the choke butterfly makes much difference to the mixture. It still runs lean even with the choke all the way out.

[ejonn]

Ok....I guess your calling the inlet valve a "tap" ?


What Im asking is

Your description of the symptoms strikes me as while driving. Is it the same in neutral not under load.

If you have tried a known working carb.....not one you rebuilt and really don't know if its good or not.

Actually looked at the bowl after it leans out to see if its running low or dry?
If you look into the carb (not running of course) after it runs lean , and actuated the accel pump, how many "shots" will it pump?

[sunroof]

The fuel tap is under the gas tank. The inlet valve is in the lid of the carburetor.

It does not display any symptoms when it is not under load. That is to say it only has a problem when I am driving and accelerating. Although, It does backfire occasionally when driving over 50 Km/h into a wind. The car will not go much faster than 55 Km/h at any time. At first I thought the rings were siezed but it does not smoke at all. I have not taken the compression. I will say again: when the accelerator pump gives its shot the car behaves normally.

The one thing I have not done is lift the lid to look at the level in the float bowl. I will do that today. The reason I have not done this previously is because the blue '59 has a problem with the fuel tap where it gets plugged and does not deliver enough fuel to the pump. The car runs fine until the float bowl empties and then the engine dies. If I put the clutch in and pump the accelerator the car comes back to life. It never exibits the lean running condition that I am experiencing with the red car. How many of you have run your car out of gas? Because mine has no gas gauge, I run it dry regularly. It coughs and sputters and finally dies but never loses power or backfires thru the carb.

Even though I have tested the intake manifold for leaks, I cannot escape the idea that it is the problem.

As for the "known good carburetor". It is a good suggestion BUT: 28 PCI is such a simple device and I have rebuilt so many of them and neither of ones I used made the slightest difference, I can't believe it is a carburetor problem.

Keep the suggestions coming, this is very helpful.


Don

[larryvance66]

Do you have a see through fuel filter on the system? If not get one. Look at the filter and see what it looks like when the car is running. If the filter is full it or something upstream is clogged. If it goes empty it is starved i.e. clogged tank petcock or line. When all is normal the filter should be half gas and half air bubble. This may help narrow it down. Other things I can think of:
-Fuel filters built into carb blocked.
-Fuel line partially clogged. (Had a mud dobber do this to me while a line was off a car for a couple days)
-Coil not putting out.
Sorry I got nothing for sure but maybe.......
_________________
I got a Volkswagen for my wife....Best trade I ever made!

[sunroof]

So I took the car for a drive and made sure it was warmed up nicely. I stepped hard on the throttle making it backfire thru the carb and turned off the ignition and drifted over to the side of the road. I took the lid off the carb and the float bowl was full right to where it is supposed to be.

On to the next idea.

Don

[ejonn]

Darn, I was hoping that it would be something easy after all the work you've done...

Things that make you go hmmmm...(insert head scratcher emoticon here)

[my59]

Is itcompression and a leakdown test time- fuel delivery appears to be answered.
Are you sure the valves are set right?
The timing is not 180 degrees out?
I'm wondering if the vacum advance, while pulling vacum may not be advancing correctly- there is an adjustment on the shaft that can be made
_________________
my59: Well son, my grandfather died before I got to drive it, so does that answer your question?
our79: sunroof bus w/camper interior and 2.0 FI
Other:'12 Jetta, '77 Benz 300D, and a 74 MG Midget.