Running bad lost power

[njmolinelli]

I was driving my 75, and all

of a sudden it started sputtering and running really rough, lost all power, got back to my shop and pulled spark plugs, back 2 were wet had fuel all over them, had really low compression, what would cause this? Blown head? Has this happened to any one? I haven’t torn into the motor yet.

[7502]

Take a good look at your spark at each plug. Did you actually do a compression test? Hope not.

 

Edited November 30, 2022 by 7502
grammar

['76mintgrün'02]

I think the most common head gasket failure is between the #3 and 4 cylinders.  That's my guess.  

['76mintgrün'02]

I just did a search, using [ head gasket 3 4 ] and got these results.  You can just scroll down the results page and read the one-liners to decide which ones might be interesting/helpful.

 

https://www.bmw2002faq.com/search/?q=head gasket 3 4&quick=1&type=forums_topic&nodes=8 

 

I liked this post.

 

 

[TobyB]

Quote

 back 2 were wet had fuel all over them,

 

Fix your fuel delivery problem.  I'll bet your missing compression comes  back

when the cylinders aren't washed down with gas.

 

Float sinking, float valve leaking, fuel pressure too high...

 

things like that.

 

t

 

[ray_]

2 minutes ago, TobyB said:

 

Fix your fuel delivery problem.  I'll bet your missing compression comes  back

when the cylinders aren't washed down with gas.

 

Float sinking, float valve leaking, fuel pressure too high...

 

things like that.

 

t

 

Optimist!

 

[John76]

Tell us more about your '75.

 

Carburation (stock Solex or Weber (model), cleaned jets, float needle and power valve, float (plastic or brass).

Ignition (distributor, plug wires, points, condenser, or electronic).

Fuel system (mech. or electric pump, pressure, filters, fuel return).

Vacuum devices (brake, advance/retard, fuel return valve, dashpot, EGR, air pump).

 

If this happened suddenly as you described, it's most likely something fairly simple e.g., debris in fuel (keeping power valve open), stuck float or a torn accelerator pump diaphragm.

 

John

[E60coyote]

Agree it could be fuel delivery related. I had a similar issue recently. Turned out the secondary Venturi on the primary barrel of my 32/36 Weber moved and twisted out of position. It was loose in the holder so must have just rattled around.  Replaced and rebuilt the carb and has never run better!  Easy to check by just removing your air filter. 

[Dick R]

The symptoms you described sound pretty much the same that I had two years ago.  Damaged head gasket between #3 and #4 was the problem.  Replacing the head gasket was the fix.  

[percy]

On 11/30/2022 at 6:49 PM, John76 said:

Tell us more about your '75.

 

Carburation (stock Solex or Weber (model), cleaned jets, float needle and power valve, float (plastic or brass).

Ignition (distributor, plug wires, points, condenser, or electronic).

Fuel system (mech. or electric pump, pressure, filters, fuel return).

Vacuum devices (brake, advance/retard, fuel return valve, dashpot, EGR, air pump).

 

If this happened suddenly as you described, it's most likely something fairly simple e.g., debris in fuel (keeping power valve open), stuck float or a torn accelerator pump diaphragm.

 

John

 

A compromised head gasket - especially between cylinders might easily account for the symptoms you describe but there are many other possibilities.  That said, a thorough description of the engine condition might prove helpful to any long-distance diagnosis.

 

The above suggestions would ordinarily be encompassed in a standard tune up.  Checking valve lash is always prudent as is a simple compression check.  I recall someone with similar complaint.  The engine was so poorly maintained that the owner failed to notice several severely worn camshaft lobes that clearly affected engine operation.  This does mean your engine suffers from the same malady, but it is a possibility in a poorly maintained high mileage engine.  Lastly, if cylinders 3 and 4 had wet spark plugs, what was the condition of the plugs from cylinders 1 and 2?  If your engine is fitted with a single carburetor, one might expect that a fuel delivery concern would affect all four cylinders assuming that the same carburetor supplies all of them with air/fuel.

 

 

 

 

 

 

Edited December 1, 2022 by percy

['76mintgrün'02]

Paging @njmolinelli 

 

We're all lined up hoping to help you, but more information is needed.

[Son of Marty]

Before you go any further do a compression test, it will confirm or eliminate the head gasket.

[njmolinelli]

Yea 3 and 4 were covered in gas, carb is tight, looks clean nothing is loose, has 32/36 web, all stock, all had low compression, plugs 1-2 were dry, all were replaced a few months ago,

it does have high mileage, but before this it ran good, good compression,

msd ignition

 

 

['76mintgrün'02]

Thank you for the additional information.  I thought your initial post implied that the compression drop was only on cylinders 3 and 4.  Did you do the compression test on a warm engine?  You'll get lower pressure on a cold one.  What were the readings?

 

Are you still getting spark on all four cylinders?  I don't know much about MSD systems, but maybe it crapped out on #3 and 4.  Did you inspect your cap for cracks?

I've had plug wires fail, but having two fail at once seems unlikely.

 

EDIT- A broken engine mount can let the engine rise up and break the distributor cap.

Edited December 1, 2022 by '76mintgrün'02

[ray_]

3 hours ago, Son of Marty said:

Before you go any further do a compression test, it will confirm or eliminate the head gasket.

Oh I dunno...

 

... I'm pretty sure the head gasket is there.

 

 

You're welcome!