SIV diagnostic advice ??

[SIVAllan]

I'm having an engine problem - maybe someone with knowledge could help with a diagnosis ??

Engine is 1725 with twin zeniths. It was running strong then began to stumble, stutter, loose power, and die. If I pump the gas during the death throe sometimes it will backfire.

This occurs after first drive of the day for 10 or 20 miles. After the engine cools down over night it will become good for another 10 or 20 miles, then the same problem.

Broke down beside the road, after 5 or 10 minutes the engine will fire up and run for about 1 or 2 miles, then same problem.

Things I've done:

--Replaced coil with new coil.
--replaced points.
--replaced dist. cap
--replaced plug wires
--replaced condensor

I don't know a lot about carbs, but finally noticed that, during the predictable breakdown, the back carb appeared starved for fuel.

My rebuilt zeniths have been so troublesome that a pair of running zeniths sitting on their own manifold, linkage and all, was installed.

Same problem occurs only today, instead of 10 to 20 miles on the first drive, only got as far as 2 or 3 miles, then same problem.

I now suspect the fuel pump, which is NOS with a couple thousand miles on it by now but does that make sense for a mechanical AC factory-style pump.

If not the pump maybe the distributor is about shot somehow ??

When cold, sitting in the driveway idleing, all seems well. Cranks fine, idles fine but on the road it is certain to fail...

Thank you in advance...

Allan

 

[RootesRacer]

Fuel pump, or gas line clogged (crud in the tank).

Install a pressure guage on downstream side of pump and see what happens.

 

[Bill Blue]

Jeeezzz Allan, that sounds so much like an electrical problem. I hate to see that changing all that stuff made no difference. A bad rotor can cause the same symptoms, they form mini cracks, allowing the spark to ground through the distributor shaft, but I've never heard of one being heat sensitive.

If the fuel pressure gauge reveals nothing wrong, I'd say the problem is electrical. Try a different rotor, but the symptom of refusing to run under load when warm is classic for bad coil or capacitor. Perhaps you swapped in a bad (even if new) part. I have had that to happen with capacitors.

Bill

 

[Nickodell]

If you get backfiring when pumping the pedal, it's giving the engine enough juice at that moment to provide a weak mixture just able to fire, but this occurs while the inlet valve is still open. Since you replaced all the usual ign. suspects (especially the condenser), everything points to a fuel problem.

You need to check the entire fuel system, from the tank to the carb. jets. It appears that the engine gets enough fuel to function until some dirt gets sucked into a restriction like a jet. I'd replace the float chamber needle valves, and check that the fuel level is correct. Also, clean or replace the carb. jets.

(Or replace the whole gubbins with a Weber! )

 

[Andrew]

What about timing.
Do you have a timing light?
I would also check and make sure your carbs are ballanced.

Can you provide some photos of your carb setup?

You would have to question why she runs good when cold and then not well when warmed up. Sound like carbs or a fuel problem to me.

Andrew

 

[tony perrett]

Is the fuel-line running too close to a heat source thus causing the fuel to vaporise?

 

[SIVAllan]

Spent all afternoon acquiring/installing a fuel pressure gauge that fits inline between the fuel pump and the carbs.

By the time I finished the engine was pretty cold if not stone cold.

Cranked up fine, and the gauge read ~ 1/2 psi at idle, and went to zero if I raced the engine.

At one point it sorta aimed almost to 1 psi, but wanted to live at 1/2 psi.

The carb setup is stock for a Series I, II or III running twin WIP-3 Zeniths.

The fuel line follows the factory route over the thermostat housing then to a T and then to the carbs.

The fuel tanks have been split/boiled out/red coated. Same for the crossover tubes. A new rubber fuel line connects the tanks to the fuel pump.

The fuel pump is a NOS pump with a couple thousand miles on it by now.

The carbs are replacements.

To be more clear, the problem predates the carbs. At first I thought this was due to my zeniths screwing up again, and they now have been replaced with a pair of "running zeniths" only to discover the problem continues.

I have an inline glass filter between the pump and the carbs and watched it for a while.

Every 6 or 7 seconds a big bubble went through the inline glass filter, and the fuel pressure gauge would drop to zero, then after the bubble passed, fuel pressure would rise back to ~ 1/2 psi.

Then I noticed that a bubble rose up in the fuel pump on the fuel inlet side just prior to the bubble going through the fuel filter.

I took a 4 or 5 second video of those bubbles but have no way to post it. Anybody who wants to see a bubble just pm me your email address .

So having done this work, and feeling good I let the car idle in the driveway for almost half an hour, no problem, and went for a spin.

I got about a mile away in heavy traffic - same problem returned.

I checked the fuel pressure off to the road side but it was zero and stayed at zero, even after I waited an hour for things to cool down, traffic to go away,and I could get back home.

Maybe the gauge broke ??

Somewhere I think I read that the AC fuel pumps on our sunbeams produce 2 to 3 pounds of pressure .. ??

I'm at a loss on this, no clue, but will swap out the fuel pump tonight unless someone has a better suggestion... ??

Allan

 

[RootesRacer]

Couple of things to consider now.

1) Your pump could be no good (1.5 to 1.75psi is correct pressure).

2) Your cam eccentric is worn to nothing.

3) The lever on the pump is not right and is limiting full pump stroke. Might want to pull the pump and inspect the wear pattern on the lever shoe.

4) Your gas tank is not vented and you are running a vacuum in the tank as the gas is pumped (pull the filler cap and see if the pressure cames back).

 

[puff4]

...or there's a leak on the intake side of your fuel pump, allowing air to get into the line. I'm betting on this one.

 

[RootesRacer]

...or there's a leak on the intake side of your fuel pump, allowing air to get into the line. I'm betting on this one.

Yes, or a torn diaphragm, in which case there will be gas in the oil.

 

[George Coleman]

Sounds like the Black death coming from the fuel tanks or vapor lock!
Are you running the stock fuel pump? Look at the site glass and see if you have some black flakes in the bowl, if not it could still be clogged back at the fuel tanks were the fuel line comes out or some were in between. Good Luck

 

[Bill Blue]

Sounds like the Black death coming from the fuel tanks or vapor lock!
Are you running the stock fuel pump? Look at the site glass and see if you have some black flakes in the bowl, if not it could still be clogged back at the fuel tanks were the fuel line comes out or some were in between. Good Luck

Hope its not black death. Allan had to redo the tanks fuel line to get gasoline to the carbs. The problem is almost certainly somewhere in the fuel pump or loose fuel fitting.

Bill

 

[George Coleman]

It is probable not the problem, the fuel filter that you show has been known to not let fuel through, just something I have had happen to me!

 

[SIVAllan]

Hello everyone,

And many thanks for your advice!

Progress is occurring, but the issue remains...

Last night I managed to swap fuel pumps.

The replacement pump is the same AC pump as before but it has the SIV outlet fittings, not the SV fittings, and does not have the manual lever to prime the carbs manually.

After hooking it all up this morning, I replaced the fuel pressure gauge just to be sure it was reading right.

The replacement gauge doesn't seem to work at all.

Some cryptic comment on the box referenced air pocket issues, that supposedly resolve themselves in time.

SO...cranked the engine, it ran at idle fine, so I let it run and watched the the pump's glass bowl and the glass filter.

After 10 minutes, a few bubbles began to appear noticeably in the glass filter.

Then I spotted them in the fuel pump bowl.

After 15 minutes many bubbles began to appear, visible in both pump and filter.

Since the filter is downstream from the pump, it likely is not the source of the bubbles.

After idling for amost 30 minutes, the engine died with the same symptoms.

I checked the carbs and the front carb was not getting fuel.

Sometimes when this happens, the back carb has no fuel.

But if one or the other goes, the engine stumbles and dies.

After one hour of cooling off time the engine cranked and idled fine with gas to both carbs, but with bubbles in the pump and filter so I shut it down.

If it means anything helpful, vacuum gauge reading stayed constant at 20.

I tried opening the gas tank filler cap but that did not help.

REGARDING the pump that was removed, I inspected its arm for wear.

The arm shows a slight shiny spot right where I'd think it belongs.

The arm shows no wear on its top, so it must have been correctly installed.

I tried to feel the cam lobe with my finger to assess lobe wear, but not enough experience to know what I was doing.

Reading your comments, thinking this through (at a rookie level of course )

I suspect the next step is to:

--clean or replace the fuel line from tanks to fuel pump ??

Regarding the fuel line...

Originally, there was a one piece metal line that ran from crossover pipe to the fuel pump.

Now only about 3 inches remain at the crossover pipe, and about a foot remains at the other end at the fuel pump.

Replacement rubber hose hooks to each piece of metal pipe, running from one end of the car to the other along the factory route.

So a leak could possible occur:

A--where the original metal pipe fits to the fuel pump;
B--where the replacement rubber fuel hose hooks to the metal section running out from the pump;
C--where the replacement rubber fuel hose hooks to the stub of metal pipe at the crossover pipe ...
D--rubber hose could have a pin hole leak

--drain the tanks to remove suspected crud?

How can I be sure any contamination would be removed?

I dumped a can of a product called Sea Foam in the tanks to melt anything organic based, but maybe it did not do anything.

--replace the line AND drain the tanks...???

Wow, this is frustrating, but good thing I love working on a Sunbeam .

The big worry is lack of time before a 400 mile event April 3...

Again, your comments are most welcome!!

Allan

 

[Andrew]

As a test

Hi Allan,

I would try and connect a new line from the fuel pump to a temp gas tank just to see if the same thing happens. Just take care not to cause a fire or get a static build up, and turn off your cell phone! At least by doing this you would then know if it is a problem with your line or exiting tank assembly.

Try and narrow down the problem. You have had a rough go with the old girl, I hope you get things worked out.

All the best and please keep us posted.

Regards,
Andrew

 

[Bill Blue]

Allan, might try running a temporary line from the pump to a can of gas.
Didn't you have the tanks dipped and sealed in the summer/fall of '07?
Bill

 

[RootesRacer]

Did you pull the fuel filler cap like I suggested?

Something is making the pump rather pull in air from the inlet side, rather than suck fuel from the tank.

 

[RootesRacer]

Oh and the rear carb goes dry first because the front carb is closer to the fuel source.

 

[SIVAllan]

Bill, Andrew,

Good idea; doesn't sound too difficult and I'll get on it!

Bill yes I did. The tanks and crossover pipes went to a SIMS radiator shop nearby and were boiled out and red coated.

When I bought the car in March '07, it had the fouled gas tanks problem and the original fuel line was fouled as well.

I kept a short lenght of the original fuel line at either end, in order to have something to use to attach the replacement rubber line.

The stubs of the original line were cleaned, and reamed "real good" with a coat hanger.

So the tanks "should" be AOK but I could not swear to it.

Allan

 

[SIVAllan]

Did you pull the fuel filler cap like I suggested?

Something is making the pump rather pull in air from the inlet side, rather than suck fuel from the tank.

yes, that was done. The SIV cap is a flip open cap, so I just flipped it open and left it open for a while to see if that produced an effect.

I could determine no change with the cap open or closed.

Allan