914-6 Popping and Missing

[cdn914]

I have a completely stock 914-6 with a persistent problem - popping from the tailpipe and missing intermittently. I have changed every ignition component including the ignition switch and distributor, and even the carburetors but the
exact same problem persists. I have substituted four CDS units and the problem is exactly the same with all four. However, none of the four CD units is new. All emit a hum with the ignition on and the car does run. How would I know if the problem
is the CD unit? Can they be tested and if so, how? Do they completely fail (car will not run at all), or can an intermittent problem be caused by a bad CD (or in this case four bad CD units)? Is there a better alternative to the CD ignition? Any and all suggestions very welcome.

[rdvnac]

I feel your pain, but think I may be able to save you further grief.

Install an MSD 6 or 6AL and matching coil. YMMV, but this set up *completely eliminated* a similar problem for me.

http://www.msdignition.com/

Good luck and HTH.

[J P Stein]

The possibilities here are many, however......................

Take a look at your headers/heat exchangers.
Exhaust leaks.....as in holes in the header pipes, can cause the poping out the tail pipes.

"Missing" is not a likely result of the above.
Since you've gone thru the ignition pretty well, I would look at the carbs again. Improperly tuned and balanced carbs will cause
all sorts of running problems. This assumes the carbs are spotlessly clean inside and the floats are set at the right height.
Well filtered gas and the right fuel pressure ..............

Have you looked at the plugs for proper mixture. White and black are bad, grey is gud......fouled is common, with the rich idle circuit we are forced to run.

A weak coil, old plug wires, the right plugs .....I like NGKs, they cleared up running problems I had at one point and I've used em' ever since.

edit:
Yup, MSD is good and I have one also. I suspect something other than the ignition system (CD), however.

Long distance tuning is a b!tch. Maybe something in this mess will give you some ideas.

[cdn914]

I have replaced with new parts: the points, the plugs (with NGKs), the cap and rotor, the coil, the ignition wires with OEM Bosch wires, the heat exchangers (new - expensive!), the muffler(another used unit), the ignition switch, the relay board (with a used unit), the complete distributor (with a low mileage unit), the alternator and regulator, the battery, the carbs (with rebuilt identical Weber 40 IDTs), the fuel filter, all fuel lines, the gas tank, the fuel pump (new)(fuel flow and pressure are good), the fuel tank cap, and air filter. I even have removed the screen filters in the Banjo fittings on the carbs. There is nothing left to replace. I have had the carbs adjusted by a local expert twice in the last couple of years. The car will idle perfectly and accelerate but the popping from the tailpipe persists and eventually it starts to miss again. The ignition timing has been set multiple times. The only constant seems to be that no matter what I do or change, the exact same problem persists.

[cdn914]

One more thing - no matter how the carbs are adjusted, I cannot get the car to run rich.

[JWest]

Try replaceing the left headlight (it sounds like you covered everything else!)

Uh, since you seem to have covered all the ancillaries - how about the engine itself. Is it stock inside? Bigger cams or something making your stock jetting incorrect? How about valve adjustment? Maybe buidup on the back of the valves or even a burned valve?

Good luck - I know it can be very frustrating.

James

[J P Stein]

OK.....now we're getting some where.......too much info is better than too little.

The best advice I can give is to become your own "local expert".

That post by T bird is really very good.....tho I have no assistant.
The 911 guys do the "Weber dance" but have fewer steps than the we 914 types.

Your comment on not being able to make it run rich leads me to believe that you need bigger jets on both the idle and main circuits.....idle, for sure. I would try going up to 55s on the idles and 120/130 on the mains and you REALLY need to recheck the float levels. If they are too low, you're not going to get enough fuel into the engine, regardless of jetting.
Also, look to the accellerator pump for the proper amount of fuel delivery......I don't have that amount off the top of my head, sorry.

I run 60s on my idles (2.7L)......1 1/2 turns open does it.

[rdvnac]

As usual, J P has some excellent comments.

I will also second his thoughts about the idle jets. If you do have a truly stock setup, the original idle jets are inadequate for today's fuels, as documented by Bruce Anderson, Jon Lowe and others (see Lowe's comments in the Q & A section of the PCA website for specific info).

I run 55 idle jets (and I think 130 mains, although we tried so many combos my head spins trying to remember w/o looking at my notes) on my "2.5" (stock stroke, 2.7 RS pistons).

When you do solve the problem (and you will) please do us all a favor and post a follow-up; this is a not-uncommon problem on the sixers and the more shared info the better.

[red-beard]

Is it popping in the exhaust or is it popping in the intake?

My problem with my 6 is a popping through the intake...The problem seems to get worse under decelleration (high vacuum), especially foot off gas, clutch still engaged. If I press on the clutch and let the engine drop to idle, the popping stops.

Any clues? Some have said it is an intake manifold leak. If this is the case, what is the mechanism for the popping?

James

[J P Stein]

Sounds like a lean pop, to me.....the F/A ratio is off.
Dunno if that causes the charge to ignite before the intake is closed or it is left over when the intake reopens. The results are the same either way.....try to keep your face out of the way.
It's tough on eyebrows.
Worn throttle shafts will also cause this.

Some time back, I had one cylinder that I couldn't tune out the "lean pop" no matter what I did (#5 hole). Upon removal of the offending carb, I found (to my surprise) that the gasket beneath that runner wasn't even marked.....no impression from the carb. Vacuum leak, anyone? A .005 shim took care of that.
The bottom of the carb wasn't flat......go figure. It was an IDT, BTW.

This identical thing also happened to one Mr. J. Dunkle.

Learning to tune Webers isn't rocket science, but it does take some doing......bout 18 mos for me, but I ain't all that swift......and I didn't have all this gud advice.

[cdn914]

I forgot to mention that I changed the idle jets to 50s in the last few weeks. This made very little if any difference. The car ran very well until about four years ago when the problem started. Since then I have done all I describe(some things many times). I also blew a head gasket last year (cylinder 3). While replacing all the head gaskets, I also replaced both camshafts (old ones were worn) and put rebuild heads on (I am not making this up - really!). The popping/missing problem was exactly the same before and after I did this. The popping is predominantly from the tailpipe.

[J P Stein]

Went out and did some rootin' thru my shi.....er...stuff. I have a spare set of both 55 idle and 130 main jets if anyone wants to try em'. I do need them (or their replacement) back should this become a permanent fix, tho. A guy can NEVER have too many Weber bits:rolleyes

Lean condition ignites wherever it wants to, near as I can figure ....late, early, never....
Slightly rich is more controlable.... that's my latest theory.
I'll hang with that at least till my eyebrows recover.

[red-beard]

I have the gaskets to remove the carbs from the manifolds and from the manifold from the heads. Hmmmmm. Maybe over the years the manifolds warp? I'll put a straight edge on them and see if I can see light under them. Maybe it's time to have these surfaces faced.

What's the best source for webber parts? If I'm running lean during decel, it sounds like I may need to re-jet. Any one local in Southern Cal?

James

[jabb]

One thing to remember is all the tunning and adjusting should be done on a warm engine

[mike95125]

James,
You may want to try Fibertech/Carquest in El Cajon off of Prospect. They have some cool stuff there and may be able to hook you up.
-Mike