took my 74 914 out the other day on an errand, I have the orig Diet system on the car. all of the sudden while driving it sounded like an exhaust leak or flapping as the engine went. Also in between shifts and when I let off the gas the exhaust popped or had a small backfire. Small loss of power and a little rough running.

I'm going to do a compression or leak down on it but I wonder if any knowledgable folks know what this might be ?

If it's a head gasket what's the best way to change it and should i do all the head gaskets for all the cylinders ? thank you, Joe

Would hope just a cracked exhaust pipe close the head.

A visual inspection from underneath might also help to tell if you have leak between cylinder and head.

Fingers crossed.

Blown muffler? Loose spark plug?

Spark plug is a good suggestion.

thanks guys checked the plugs and exhaust is solid also have that backfiring

also if it happens to be an air injection motor... (I think they started in 1975, but sometimes a PO has changed a motor)

I've seen an air port pull out, or unscrews and gets lost.
big leak, and noticeable.

Thank you where is the Air Port ? Thanks

Only on air injection motors

Mine are capped…. Thus the brass top on the air port

And a close up

thanks guys my motor doesn't have the air caps - has anyone done Head gadgets on the 2.0 ? what's the best way to do it ? thank you

Do they exist?

You need to start troubleshooting. Have you listened to it yet?

right on @emerygt350

no head gaskets on a VW engine of any sort.
thermal expansion ultimately seals the motor.
a marvel of calculated differential expansion of different metals between crankcase,
jugs and heads.

why a little bit of warming up before driving off in a VW never does any harm.
but does a lot of good.

The cylinder jugs did have sealing rings on the top and bottom of them. So in a way head gasket.

sort of.
my understanding is the copper rings are there to stop the top of the jugs digging into the softer aluminium heads. but the real seal is done in the fit of the jugs to the heads (around the circumference). same at the block end. and its the thermal expansion that does the full tight fit when the engine is running. copper sealing rings set correct deck ht compression etc for factory standard engines.

i could be wrong. its what my old mechanic told me back when i had the squareback.
that they were not seals in the way we understand a trad head gasket.

but i suppose an overheated engine could distort its heads and get compression blow by out of the top or sides of the head.

in which case original poster with his engine sound troubles won't be fixing that with a "head gasket" job?

i think advice of other responders is correct.

i'd be looking at the exhaust outlet real close with the car up on a hoist and the engine running. advice to be methodical is very good advice.

Push a block of 2x4 against the exhaust pipe. A leaky exhaust at a exhaust port and the noise will get louder. Well sealed on all 4? The engine should load up and stumble at idle.

I’d guess exhaust also
Maybe a stripped stud?

Pull your HE for new copper ring seals and see what you find

With that loss of power it sounds like you lost a cylinder. Have you checked the plugs? The one that isn't firing (if it isn't) will look much different from the rest.

If it is a small loss of power, I don't think you would be losing a whole bank (and therefore probably not trigger points) and more likely a bad injector or bad spark to that cylinder. If I were you, I would (in this order):
1) do the 2x4 bit mentioned above to verify exhaust leak (good to know)
2) pull all the plugs looking for a wet/dark plug
3) while you have all the plugs out, do the compression check (again, good to know)

after that report back and we can go on to the next appropriate step.

Thanks Guys i still haven't found the problem, I'm waiting for parts to make a leak down tester. Compression readings are as follows
#1 - 120
#2 - 110
#3 - 115
#4 - 120

Was that with all plugs out and throttle wide open? Did any plug look suspicious?

Thanks guys Throttle was not wide open when did compression test. Compression test won't tell me if a the head sealing rings.gaskets are blown will it? I tried to do a leak dow but when I applied air while set at TDC the piston/engine moved. Im not sure how to do a leak down and stop the piston/engine from moving.still haven't tried to put wood over the exhaust- want that damage the engine? thanks everyone , Joe

Did you look at the plugs? Cracked/warped heads/burnt valves are what you would be looking for, not head gaskets/seals. Put the car in 5th, block the tires, and emergency brake. Throttle should be wide open for compression check, all plugs out, however, your numbers are not far off of what people get without following the directions so you may be ok. Again. We need to know what the plugs look like.

Thanks Plugs are a bit black with some carbon but that is the way my engine has always ran. Won't putting a block on tailpipe damage the engine? thank guys

Yes, a compression test will let you know if "head sealing rings. gaskets are blown. It's normal for the engine to want to rotate while performing a leak down. You need to restrain the rotating elements from turning when doing the leak down.

Everyone seems to be focused on mechanical issues however backfire when coming off the throttle could also occur in overly rich conditions.

Have you vacuum tested your MPS lately?

Did one plug look different from the others?

And you won't damage anything by pressing the wood. Just don't hit it.

Mps leak down is an easy test to do as well.

Thanks Guys how do I stop the engine from turning while performing a leak down ?

Is the engine in the car, if so put her in gear with the emergency brake on, if out of the car restrain her at the flywheel

Ok guys the motor is still in the car. I tried again to do a leak down, I pulled up the E-brake hard, blocked the wheels, tried it in reverse and 5th and still the engine moves - cylinder #1 to pump to 65 lbs before the engine moved and I lost pressure. Not sure why I can't do a lead down ? Any suggestions ? Thank you

Skip the leak down for a bit. Do a real compression check, plugs out, throttle open. And send us a picture of the four plugs.

OK thank you will do, I'm hesitant to put a block over the tailpipe while the motor is running, seems to me that can't be good for a motor? thanks again, Joe

You don’t block the exhaust indefinitely. Nor is the wood attached. The engine loads up and stumbles quickly if the exhaust is well sealed. Ease off when it does stumble. All you are looking for is to rule out a leak at the head/heat exchanger with sound. A 30 second to 1 minute exercise.

ok thank you so I have a ansa exhaust that has 4 tips 2 on on side and two on the other do I block both sides at the same time ? and what ami I listening for ? perhaps you can describe this procedure in detail? thank you, Joe

you can do bank to bank but what they wanted you to do was just push on it to put pressure on the exhaust flanges. If the sound changes you know it is an exhaust leak. If you put the block on there to cover the four tips and it keeps running, you know you have a pretty bad exhaust leak.

At this point though, I would be more concerned about a burnt valve and the compression test and plug condition will help you there.

thanks guys I will do another compression test and relay the readings asap

Skip the board. Gook luck.

Ok guys compression readings similar to the ones I did without throttle wide open:
#1= 110
#2= 124
#3=120
#4= 125

I was unable to seal the exhaust at the tips while running as I have an Ansa exhaust. all Header note to head are tight.Cdon't see or feel any holes in the muffler. I have been unable to secure the motor from tuning while performing a leak down. I still have been unable to find the cause of this flapping noise. My computer (mac) will not let me add pics of the plugs to this post but they look like they always have - a little black carbon build up. I never had any issues with them like that. there are 3 prongs near the center electrode on the plus care had more power with them after I put them in. I forgot the plug #. I still have been unable to find the cause of this flapping noise. Any other help is greatly appreciated guys I don't want to drop the engine if I may not need to. Thank you all again, Joe

I was unable to seal the exhaust at the tips while running as I have an Ansa exhaust. all Header nuts to the head are tight.I don't see or feel any holes in the muffler. I have been unable to secure the motor from tuning while performing a leak down. . My computer (mac) will not let me add pics of the plugs to this post but they look like they always have - a little black carbon build up. I never had any issues with them like that. there are 3 prongs near the center electrode on the plus. car had more power with them after I put them in. I forgot the plug #. I still have been unable to find the cause of this flapping noise. Any other help is greatly appreciated guys I don't want to drop the engine if I may not need to. Thank you all again, Joe

That first cylinder is a hair low but if the plug doesn't look any different...

My next step would be pulling that plug wire from #1 and seeing if the engine runs any worse.

Ok folks so I pulled all the plug wires one at a time while running. # one cylinder didn't make much difference so I changed out that plug (compression :

#1=110 psi
#2= 124
#3=120 psi
#4=125 psi .

Still sounds like a leak somewhere when I accelerate- kind of flappy like a sheet in the wind. and when i let off the gas in gear it pops a bit. Could this be an vacuum leak? Head Gasket to cylinder gasket? I think Ill put a new cap, Rotor and plugs in and check the timing. Any other Ideas would be appreciated, thanks, Joe

Muffler leaking….be more aggressive holding a board over the tailpipe (s) and force the leak

Or
Smoke test the intake and look for a leak in the plenum or any vacuum lines.

A smoke test (google it) can be done with a cheap Halloween smoke machine….you are filling up the intake with smoke to see if it leaks out anywhere.

With these 50 year old plenums, I have seen rust holes open up in the bottom of the plenum where you cannot see it, and you can’t get your hand down there.

You are looking for unmeasured air here.
There are three places
Intake
Air injection
Exhaust

Rich

These 4s will idle with a plug off no problem. You may want to just try driving it while the plug wire is grounded to the block or something. See if it changes anything. If you notice no difference, you have a dead hole. A new cap and rotor never hurt anyone. If that doesn't cause a change I think you do need to go for the leak down test.

To do the leak down, you need to put it that first cylinder at TDC, put it in 5th gear (5th gear is good for rolling the car into TDC as well). Full on parking brake. Chock the hell out of all the tires, or even push it up against a wall (with a tire as a bumper). Then do your leak down of cylinder one.

The car idles ?
Raise the idle to 2000 RPM and disconnect one fuel injector at a time.
The cylinder that goes quiet has the issue.
Head seal, exhaust leak, tight or leaking exhaust valve