Oil and black deposits inside rear carb

[tbsmith]

My 72 Sprint was only running on the two front cylinders. I removed the rear carb and there is oil inside the venturi and black deposits in the float bowl. There was enough black stuff built up (not like oil sludge, but the consistency of wet sand, only smaller particles) to completely block the main jet. Will clean it out, but where could this be coming from?

I also noticed tar-like oil trails in the manifold running down from the top of the carb where the balance tube opening is and coating the bottom of the manifold as far in as I can see.

The damper oil is full on the suspect (rear) carb, but the damper oil on the other carb is empty.

* Could the rear carb be sucking oil from the front carb, if the front carb damper seals are bad?
* Could it be that since the rear carb is closest to the crankcase vent tube it is sucking oil in from the engine?
* Could oil be leaking directly from the rear carb damper into the bowl? Why would it turn to a mushy black mess as it doesn't seem hot enough.

I'm wondering if there may be two unrelated problems that are causing the float bowl deposits and the oil tracks in the manifold.

The emissions control equipment has been removed, and I do have a fuel filter installed.

Thanks for any thoughts,
Tom

[USA64]

My own car is not running and it has been a while since I did any carb work but as no one else has answered I will offer my thoughts. Sounds like Strombergs? You mention running on front and front carbs have no damper oil? By balance tube do you mean the piece that the cross-over tubes come and go from? I would be looking at the crankcase breather and the sealing of the air filter as it sounds like a dust/oil mix.

[alan.barker]

Sounds like it's the time to overhaul both carbs, diaphragms, needles and a good clean
Get the colourtune out.
Alan

[LaikaTheDog]

Hello
The deposits sound like gunk from your tank. So first step is to replace your fuel filter.
Then clean both carbs thoroughly. Ideally off the car with proper carb cleaner.

The oil is from your crank breather to the rear carb.
You probably had a gummed up carb while running so the rear cylinders never ran properly,

I would fix the fuel system first and worry about oil later

Do a cylinder pressure test while you are in the engine bay. Excessive oil in the crank can be due to worn piston rings which will show as low pressure in one cylinder... then add a squirt of oil and retest... if pressure goes up it is your rings....

but probably just dirty fuel messed up your carb...

[tbsmith]

Thanks for the suggestions. I should have mentioned the carbs are Zenith Stromberg. Not sure if I used the right term, but by "balance tube", I mean the tube that connects the front half of the manifold to the rear half. The previous owner removed the emissions tubes (the ones that cross over the valve cover).

I actually have two fuel filters, one at the tank that is less than a year old and another at the carbs which is clear and no signs of dirt/debris. Also the needle/float valve is clean and works perfectly, so I think I can rule out bad/dirty fuel.

The crankcase breather is a possibility, at least regarding the oil in the manifold. I will remove it and see if there is much pressure in the crankcase from blow-by and or oil coming out with the engine running. Will also do a compression test. And I'll try to look inside the air clearer housing near the crankcase tube inlet to see if there is a buildup of oil.

But I don't think the deposits in the float bowl could be from the crankcase breather tube since the bowl is at a higher pressure (atmospheric) than the venturi.

Iff the seals in the dash-pot are bad, could oil leak down the main jet needle and directly into the float bowl, at least when the car is sitting for extended periods of time? The black crud was thickest inside the bowl drain plug, which I believe is directly below the main jet needle. It was also inside the main jet air tube which I am convinced was blocking fuel flow. One problem with this theory is that I wouldn't expect oil sitting at the bottom of a bowl filled with gasoline to cause crud like this. OTOH, our gasoline can have up to 10% ethanol.

Thanks again!
Tom

[RogerFrench]

Tom, I really doubt if there was ever enough oil in your dampers to be an issue. Even if some does dribble down, it's soluble in fuel and will quickly disappear.
I suspect your crankcase breather may be the source of oil, and the crud maybe from fuel interacting within the carbs or delivery. The ethanol doesn't play nicely with older cars.
What do you have as fuel pipe? You obviously have some mods, because of the filters. Maybe some rubber bits the ethanol is destroying? I agree 100% with the suggestion to clean and rebuild the carbs, by the way.
I've seen your car but don't remember - do you still have the Federal intake manifold with the crossover pipes removed?

[prezoom]

If you have any old rubber in your fuel delivery lines, ethanol will cause them to break down. For Webers, bite the bullet and buy the "Y" line that has a non-rubber fuel line from the mechanical pump to the carbs. If you have a rubber line from the fuel tank, replace it as well.

[billwill]

Check that you still have a wire gauze filter in the breather pipe from head to airbox. Without it you may well get excess oil transferred to the air box.

With it, the oil vapour should condense in the breather chamber (part of the head) and then dribble back through the conical rubber tube to the crankcase.

[saildrive2001]

When was the wire gauze filter fitted to the breather pipe, mine never has had one from new?

[RichardHawkins]

I believe the gauze is also a flame trap to prevent a backfire igniting oil vapour in the crank case.

Richard Hawkins

[tbsmith]

Making progress! I looked inside the breather tube and the carb intake housing and there is no liquid oil in either. They are both black, but I think that is normal. The screen inside the tube is intact and is not blocked by any debris.

I then removed the needle float valve and saw some black residue on the inlet side of the brass housing. So I think many of you are right in that the contamination is from the ethanol attacking the hoses. I'm surprised though that that much junk could get past the needle valve and into the float bowl, while not clogging up the valve.

There are only 2 inches of fuel line between the filter and carb, so I suspect the filter may be bad. I will replace the filter and the short sections of hose.

I reinstalled the carb and engine runs great. But I'm going to remove it again to see if I can disassemble the needle valve to see how it looks inside.

Roger, my car has a fuel cell and electric fuel pump with a filter before the pump and another just below the carbs. I don't know which manifold I have so I attached a picture.

[pharriso]

Tom, Pleased to see you on here & glad you have solved your issue.

As a BTW... you have an early style solenoid on your car, yours should look like this:

[Craven]

I?ve been looking at available solenoids, the one shown here is generally offered as a correct replacement for our cars BUT by observation only, of various published pictures, the original period fitment has the battery connection on the bulkhead side terminal and started connection toward the front of the car. Electrically no problem but it does require repositioning of and slightly longer heavy battery lead.
Anyone found a source of correct terminal layout solenoids.

Tom, Pleased to see you on here & glad you have solved your issue.

As a BTW... you have an early style solenoid on your car, yours should look like this:

StarterSolenoid.jpg

[JonB]

I?ve been looking at available solenoids, the one shown here is generally offered as a correct replacement for our cars BUT by observation only, of various published pictures, the original period fitment has the battery connection on the bulkhead side terminal and started connection toward the front of the car. Electrically no problem but it does require repositioning of and slightly longer heavy battery lead.
Anyone found a source of correct terminal layout solenoids.

I'm guessing you are concerned about the placement of the spade connectors on the battery terminal. Well, the solenoid is a plain old switch, so why not get the one pictured above and move the spade connectors to the other terminal (which then becomes the battery connection)? They are just bolted on by the look of it.

[tbsmith]

Thanks Phil. Does the replacement solenoid have the manual button on it? Comes in handing during compression checks, etc?

Follow up question on the black stuff in the manifold:
Does this look normal? There was also a layer on the engine side of the throttle plate. Kind of gooey and easy to remove with rag or scraper. If not normal, what could cause it? The engine runs fine. The small holes in the top of the manifold are where the (balance?) tube connects the two manifolds.

Tom