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Hissing Sound

FM Former Member
Lately I've been using the car to drive around and do errands since the weather here has been sort of favorable for the past few weeks. The car has been running fine all along. Today, though, it was perfect until I started to hear a rhythmic hissing, sucking sort of sound that seemed to come from the left bank of cylinders. I thought it was the fan or fan housing rubbing but it checked out alright. I noticed that the car started to expel black smoke even at idle and that smoke sort of hurt my eyes (makes them sting); so that leads me to believe it's suddenly running richer. I also noticed that it was missing and sputtering slightly while in first and second gears; as it revved up higher (from 3rd gear up) the problem would go away. I checked the CB Performance jet doctors (over the idle jets) I installed some time ago as well as the main jet stacks and verified they were fully seated. I'm somehow suspecting plugged idle jet (s). What I still don't understand is that sucking sound; what could it be? Maybe a broken gasket? (I checked if the manifolds were fully tightened on the heads and I snugged them a little more but they seemed fine).

Now; I'm a firm believer of the "if it ain't broke don't fix it" credo so I haven't touched any adjustments on the car since it's been running fine. What can it be??
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FM Former Member
Lately I've been using the car to drive around and do errands since the weather here has been sort of favorable for the past few weeks. The car has been running fine all along. Today, though, it was perfect until I started to hear a rhythmic hissing, sucking sort of sound that seemed to come from the left bank of cylinders. I thought it was the fan or fan housing rubbing but it checked out alright. I noticed that the car started to expel black smoke even at idle and that smoke sort of hurt my eyes (makes them sting); so that leads me to believe it's suddenly running richer. I also noticed that it was missing and sputtering slightly while in first and second gears; as it revved up higher (from 3rd gear up) the problem would go away. I checked the CB Performance jet doctors (over the idle jets) I installed some time ago as well as the main jet stacks and verified they were fully seated. I'm somehow suspecting plugged idle jet (s). What I still don't understand is that sucking sound; what could it be? Maybe a broken gasket? (I checked if the manifolds were fully tightened on the heads and I snugged them a little more but they seemed fine).

Now; I'm a firm believer of the "if it ain't broke don't fix it" credo so I haven't touched any adjustments on the car since it's been running fine. What can it be??
FM Former Member
As I am very unfamilar with VW engines, Ricardo, I can offer you no valid advice.

But if it were a 911 engine, I would check for vacuum leaks and pray that was the problem. Otherwise, broken/pulled headstuds where the cylinder no longer seals make a ghastly sound that is reminiscent of many $100 bills being ripped out of my pocket...

angela
LeonChuppLeonChupp
Black smoke does indicate a richened condition, normaly.

When I was a kid, 13-14yr. old, I accidently left a rag in a DKW air cleaner, {oil bath clean up}.

It wound up restricting the carb intake and causing a "whistling noise". Black smoke was MAX, MAX, MAX. DKW's were {are} two strokers.

Check your air cleaner{s}, and good luck....

Leon C.
LeonChuppLeonChupp
Further thought....is the side with the noise the one which connects to your crankase breather? Or are you using a different system.
I mention this because a developing crankcase pressure problem might give you these problems.

I don't think you have a torn or leaky gasket, as this would lean out the fuel mixture.....

I hope It's not studs...... cylinders are more easily replaced.

Hope it's simple and cheap to fix....

Leon C.
FM Former Member
It's a Type I; the filters are clean enough as they haven't seen a lot of use and they're oiled with K&N filter oil. In the end we didn't take the car over to Ralph (the builder); this is why. I took the valve cover off the left side cylinder head and everything looked in order. Then I looked underneath and noticed a reddish gas type stain coming from the top and dripping over the side of the head. I immediately thought major intake leak but it could also have been from the carb cleaner experiment at the carb to manifold gasket (quarters are so tight that it's really difficult to spray carb cleaner at the base of the manifold and even more so while the engine is running). Anyhow we decided to take the left carb/manifold off the head and I did it in a jiffy; removed the gasket and took it to Ralph to get a new one (since the head and manifold are match ported it needs to be cut to match). That's all we did last night but he did say to really check the carb over in case it's missing a needle, screw or whatever. I should've brought the carb to him but we were so convinced it was the gasket that we didn't. I'll keep on checking things for possible culprits and will report back. Ralph told me he would try to come over Monday or Tuesday to have a looksee....
FM Former Member
Actually; everything looks in order; now I'm wondering if it really was an intake leak. I just took a couple of photos. One is from the backside of the left carburetor in which I found a missing nut on the shaft right below the air cleaner assemblies; could it be the culprit? I'm also showing a photo of how the left cylinder head looks from under the car; maybe the stain came from the carb cleaner? Will keep on plugging away and will let you know what we find out.

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FM Former Member
Funny but the reddish stains weren't there before and they're not happening on the other side. If you look closely the carb body itself has some reddish staining that comes from within. I'm pretty positive it's gas. Larry; how about the best of both worlds and use a paper intake gasket with a light film of RTV on both sides? Would that work fine?

Jjr came by yesterday with his pails full of hardware and we found an appropriate replacement locknut for the venturi set screws; we installed it immediately. I'm still waiting for Ralph to take a look; then I'll just re-install and cross my fingers.
FM Former Member
Ricardo, I'm a big fan of K&N filters but paper will work fine provided you make sure they are clean and replace them as needed.

Rather than silicone to seal the filters, I use a thin layer of grease along the rubber seals. The grease stays relatively fluid and also acts to trap fine particles of dust and sand that may seep past the seals.
K&N makes a grease in a tube specifically for this application, you can use it or just any good grease. Apply a very light amount of grease, wipe off the residue with Brake Clean or other solvent once you've tightened the air cleaner tops.

Depending on the type of gasoline and its formulation, it could be gas but just based on photo's it's hard to tell... I've seen this type of red stain on carbs that have had too much oil applied to the K&N's. If you're running leaded gasoline, that could also account for the stains.
LeonChuppLeonChupp
Ricardo.....A passing thought from under the shade tree......

If the hissing noise is audible while the engine is running, you might be able to find the source with a 3 foot long piece of garden hose or heater hose used as a stethoscope......

I've found cracked exhaust flanges and leaky cylinders using this "stone age" technique....

Keep at it and give us the "cure"....

Leon C.
I Inter911
Be sure and use the rubber hose method mentioned above....

I once read (in a Brit mag I think) of a shade tree mechanic using a homemade stethoscope made from a can with a welding rod or metal rod attached to one end of the can and the other end of the can was opened. You held the tip of the metal rod onto different parts/sections of the engine and listened for knocks. (wait a minute....this was for knocks and rattles and not hissing but still a good story...)

Problem was the guy got a bit too close to one of the ignition wires and got the full voltage right into his ear. Ouch! to say the least. Of course, a rubber hose wouldn't conduct electricity so you're okay....
LeonChuppLeonChupp
Martin {speedster66} has a good point......

My carbs have no choke assemblies{IDF44's}. If you have choke plates or the Weber starter jet system....it might be worth while to disable it and lock its movement in the open position...As I'm not sure of your carb type this is a blind guess....If you disable the chokes,
you will wind up pumping the carb for initial crank up with spits and carb farts until the engine warms to running temp.

Keep the air cleaners on when cranking and running.....

Leon C.

FM Former Member
Jim, put the OTHER end to your ear LOL!!! I just use the wooden handle. The wood transmitts the vibrations but does not readily conduct electricity. That part is REAL important to me because I decided years ago that I was NOT going to get "bit" by the ignition system anymore.

Hurts. Especially the HEI systems...
angela

FM Former Member
A little bit of an update. Took off the left rocker shaft and retorqued the lower 4 head nuts (they needed a little more torque). I re-installed the rocker shaft and re-adjusted the valves on that side of the engine (found two that were a little tighter than recommended). I'm still waiting on Ralph to get him to inspect the carb before I re-install it with a new gasket; I hope for no more intake leaks and/or problems because at this point I don't know what else could be checked.
FM Former Member
That's funny, guys & gals! Final update: checked out the carb with Ralph yesterday and apart from a few loose bolts and a little debris in the carb everything checked out OK. I re-installed it today with a new intake gasket (put a little wheel bearing grease on it) and got the car started; the hissing is gone and although I haven't been able to take it out and drive it it seems to be idling and working fine. Tomorrow, God willing, I'll take it out for a spin and report back. I'm betting it was an intake leak because nothing else, apart from the auxiliary venturi set screw locknut, was missing. It's really weird how these machines work; they're really mysterious, don't you think?
FM Former Member
Yes, Ricardo, they are.
I get the idle jets, and I understand the set screws. Everything else is like the bumble bee. It just shouldn't fly.

Gordon -- how's the mirror stalk projekt coming? Maybe I should call Chris? I know he's got Big Things going on in his domestic world. ... Hope all is still very well for him?

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FM Former Member
Well Cory; took it out today to do some errands and it's back to its former self so thankfully the problem's solved. Now you guys know what to do if you ever encounter the same symptoms; always keep an extra set of intake gaskets just in case. Mine looked alright when I took it out but it looks like it was leaking.
FM Former Member
Update; this past week I managed to adjust valves, change the oil back to Rotella 40W and lubricate the front beam. Last night I went to Jjr's home to fine tune the car because it had been operating a little erratic at times; it felt like the carb butterflies were sticking sometimes so I had to keep kicking the accelerator pedal to keep it from doing that. After checking the dwell angle and timing (had to advance it a little) we started fiddling with the linkage adjustments and it turns out that the problem was simple. The main shaft nuts holding the throttle arms were not fully tightened so this led to them to sort of stick. After tightening them up a little throttle response became crisp. We then just fiddled with all mixture screws to lean it out a little (exhaust was smelling too gassy) and it turned out beautiful with a textbook idle of around 800 something rpms; totally different feeling car now.
FM Former Member
That's what I'm doing today, my brother! It's an excellent day out there today! I'm living it up because the car is going into hibernation for at least 1 month. I'm flying to New Orleans tomorrow to work over there on an extended assignment. If there's any SOC members in the area interested in a couple of extra hands to work on their Speedsters let me know.
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