Problemoes

[roy mawbey]

It doesn't have a vacuum advance system ( but you are right if it did it can give all sorts of problems when the piping fails )

A check I often make it to take off the distributor cap, then by hand rotate the rotor to the stop and let go and under correct spring pressure it should return to the same position. This at least gives you an idea the springs or spring has not broken.

Roy (hope you located the problem since your last mail !)

[mycar]

And.... we`re back.

The red cross package arrived from PRS this afternoon and I`ve just spent an hour or so messing around. Working on the 356 requires a bit of car jiggling, I had to pull it out of the garage, then drive it back in. Now, I haven`t touched the car since last week but she turned over straight away with the minimum of accelerator pumping and dropped to a steady idle at 800 revs. No spitting from the carb (Lhs)

Mysteriouser and more mysterious.

In the package Paul sent me were new points a dizzy and a new coil... which would you have tried first ?

Well, I supposed that the car seemed now to run fine cold... coils go wrong when they`re hot.... swap the coil.

Swapped the coil and things were good. I`m there with my finger on the throttle link, reving the engine and it`s falling back to idle without any hesitation and I`m thinking `Phil is like this ignition genius` and the coil is the root of all my problemoes.... job done.

But.

As the engine warms, things are changing, I`m reving the engine and it`s falling back down to idle readily but it wants to stall and does stall at idle all the time. So to retain an idle, I adjust the idle screws (screw them in) and the engine idles fine... but then when I rev the now warm engine the revs will not fall back and they stay at 2 1/2 -3 k.

This, I think, is not a sticky dizzy thing... it`s a sticky carb thing..
I think when the engine warms up, the carbs change. When warm, they refuse to idle and when the idle stops are screwed in sufficiently to hold an idle, a couple of revs of the engine and the engine won`t fall back to idle... because the idle stops are now screwed in too far.

Confusing, but I think it`s the carbs.

Mike.

[pmjt]

Condenser???

P

[Dakota]

Hi failing condensers tend to cause a fair bit of crackling and popping, I would suggest you stop prodding at it and go back to the start, it sounds like you either had a set of sticking bob weight in the dizzy or a weird air leak under a carb, but really what you should be doing is checking the valve clearances, fuel supply and pressure, compressions, etc and ensuring as far as is possible that everything else is doing its job with timing and carb adjustments coming last.

[roy mawbey]

Mike,

Hope you found the problem. I think if your car was running fine before that long run, its either the distributor or the carbs. Did you try penetrating
oil through the holes of the plate the points are attached to? Did the oil reach the sliding plate I wonder? Maybe a squirt or two of WD40 might get there if you attach the plastic tube to the nozzle.( none should reach the points!)

Then you have now altered the idle adjusting screws. Have you been using a synchronizer to make sure both carbs are equal? Were the jet holes in the idle jets okay?

If you managed to get an idle speed holding firm did you remove both throttle levers from the carbs to see there was no change of speed when you removed them and pushed them back on?

The 2 off idle mixture regulating screws on each carb I presume have not been touched? The synchro tester will be required if they have. Actually any adjustment has to be checked really with this to be sure they are in balance.

Is the nut securing the wire from the coil to the points tight and is the carbon pick up in the distributor cap operating okay on the spring pressure. Is the brass rotor pick up okay and condenser ?

Did you try the PRS coil? How are the plug and coil leads and in fact the plugs themselves?

Dakota is right in the end you have to start by knowing the basics are all working okay.

Do hope you have had some luck

Roy

[mycar]

Evening all and thanks for following my lack of progress, I`ve spent a fair bit of the weekend prodding... all to no avail and now I`m ready to have some one who knows what they`re doing have a look at it.

When I first bought the 911, I made a solemn promise with a serious face to Hayley my good lady wife, that should the car need any work, I would take it immediately to a proffesional outfit and and let them sort it out and damn the expense.

The only thing is with a bit of guidance (always readily available on DDk) I started to enjoy the prodding and started to think that part of owning one of these cars was a least having a bit of a go... ignitions fine... carburetors, prehaps not.

So the state of play, at close of business today is...

The b*gger WILL not idle.

I have fitted a new coil, the dizzy from PRS with its new points and condenser, a new dizzy cap and rotor arm. The leads are new, the points gap is fine and I`ve had no trouble static and dynamic timing the whole lot.

I`m working on the assumption now that this is not an electrical ignition problem.

The car does run, we went to York in it on Saturday, a round trip of 45 miles and as long as I kept the engine from stalling with a bit of heel and toe, the car runs fine on the main circuit.... it just will not hold an idle. The left hand carb spits and farts and on occasion the car backfires like a 50 cal rifle going off. The right hand carb is perfectly well behaved.

Thinking about all this, I feel these symptoms have come on gradually over the last few months rather than being the result of the trip up to the lakes. I`ve done a great deal of reading over on the Registry on the likely causes and I`ve just had a reply from a Richard Shilling who suggest it may be an intake manifold leak and to check it out with some water from a squeezy bottle. (you can here the water being sucked into the engine.) I`ll have a go at that tomorrow and then I`m done.

Roy, Bill, I appreciate your input, I think it`s time to hand things over to one versed in the dark arts.

Mike.

[Dakota]

Hi
don't use water, use something like wd40 or brake cleaner and spray it around the base of the manifold and carb, by the way I'm assuming the carbs are Zenith's not the earlier Solex's, Just listen for a change in the idle although if its not idling at all... It may be worth having a look to see if someone has tapped the offending manifold for a brake servo vacuum take off I have seen this on a few RHD A's and if it has that whatever fitting in in there is vacuum tight, if you need pointers on adjusting the carbs please call me on 07828006570 I was going to try to write it on here but it would be like trying to write down how to tie a shoe lace!
good luck Bill

[Rustbucket]

Id put money on it being the carb/ throttle/ butterfly intakes....
A poorly butterly could stick open- or just be stiff at a certain point, esp off the choke/cold start positions, (when it runs fine), weakening the fuel mix which makes the engine hunt and then die as it looses revs coming off the acceleration.
If you have a dodgy left carb Id start there.If its spitting and popping the fuel mix is untidy. Use some carb cleaner and rev it through


( I know nothing compared to most, but every now and then I remember when the same things have happened to me- in this case a poorly 3L Essex V6!)

[Barry]

I would give it one more shot Mike: you must getting very close now.

I'd either double check the tightness of the inlet manifold nuts, or loosen them off and if they will, lift the inlet manifold on each side a little. Have a look around the join for odd smudge marks: you might well see a clean 'streak' where air had been getting in. You could try the same thing between the carbs and the inlet manifolds. Also look for damaged gaskets, cracks, chips etc. Anything that might let a small stream of air in somewhere between the bottom of the carbs and the tops of the heads. With my 914, I found that someone had fitted aftermarket manifolds, and one of their bases was overlapping the cooling shroud. As you can imagine, loads of air was getting through, and it was astonishing that it hadn't burned out a piston on that side.

Traditionally, the way to check for inlet leaks was to spray a little inflammable 'stuff' (Easy Start, WD40 etc) around the suspected leaky area: if the revs change, you've found the leak. Trouble is, there is the slight risk of torching the car, although I've never heard of this.

TBH, I would simply back off the inlet manifold to head nuts, and give the inlet manifolds a wiggle. If they are not stuck fast to the heads, you've got nothing to lose by lifting them a little, just to see if anything looks out of place. You might even find that one of the manifolds is loose anyway, which could be the problem.

Anyway, I'd stick with it for another session or two if you can: you have already gone a very long way down this path, and to get to the bottom of it yourself would be great: be a shame to hand it over to someone else to take the glory .

The other thing that wouldn't take long is to take the air filter(s) off, open the throttles wide open, grab a butterfly (flap) and wiggle it up and down. There shouldn't be any play there, and a tiny bit won't give your problem. On the other hand, if the thing virtually falls off in your hand, you may have a major leak around the throttle spindle / shaft and the carb body. Most unlikely to fail quickly though, and would have to be something like a previous repair bush falling out to give a fairly sudden failure. Otherwise I'd expect a gradual fall off of refinement over years rather than weeks / months.

[Barry]

Sorry, above post was nealry two hours in the making (just started it, and got some calls) so apologies if it overlaps the other replies .

[roy mawbey]

Mike,

Sorry you did all the work and it has not solved the problem. Sure as mentioned above manifold gaskets etc can cause problems but as you say it seems to be affecting one carb more than the other with spits and bangs it still could be a dirty idle circuit. As its only a short job did you recheck the idle jets on the carb that spits? Did you check the air correction jets that are linked to the idle circuit? ( There is chance the carb needs an ultra sonic clean if the problem is in the passages).

It might be worth an hour trying to make sure the carb is tight on the gaskets and the idle jets and air correction jets are for sure clean.

Still, you must know more about the car than you did before and that is useful.

Roy

[john fletcher]

Just to re-iterate what Roy and Barry have said I wouldn't give up now because I think you have eliminated ignition/pump/filter problems which leaves the carbs as suspect. You've cleaned the jets but have you removed the actual mixture adj. needles to see what they are like? With a bit of ingenuity you can also use an airline and blow into the idle holes from the side and from above without taking the carb off. Another method is to put on a glove and stick your hand over the carb whilst revving hard to create a vacuum - you have to remove it quickly before it stalls. This can help dislodge loose particles - might work, might not but it certainly won't affect a good clean carb. Whatever you do don't look down into the carbs with the engine running because they have been known to set cars and hair alight.
The spitting and popping is a sure sign of weak mixture. Now that you have eliminated other problems just try and set the carbs up from scratch. Also with the engine stopped you can operate the throttles and see if the pump jets spray fuel OK, but this won't affect idle.
As Roy mentioned previously ideally you need an air flow meter. This is one I made 20+ years ago - it looks crap but is extremely accurate:-
However you can get pretty close to the throttle settings by listening to the carbs sucking via a tube and if you can get a response to each mixture screw then the idle circuit should be working OK. Just search for peak revs using each screw in turn. If there is no response to a particular mixture screw then there is definitely something wrong and perhaps then is the time to take the carbs to a specialist for ultrasonic ceaning and re-build.
John

[mycar]

Drastic times call for drastic measures.

Spurred on by all your encouragement and support I decided that yes, the problem must lie with the carburetors. Best thing to do... take them to bits and have a look inside them.

This is what they look like inside...



I`ve always been good at taking things apart, It can be fascinating. Look at this beautiful gasket, they don`t make them like that anymore.



Obviously the trick with taking things apart, is being able to put them back together with as few pieces left over as possible.... and there are loads of bit sand pieces in a pair of Zeniths. Fortunately, James your friendly forum moderator and master engine builder was on hand so it all ended happily ever after. Thankyou James.

With the carbs back in place, all rebuilt and gasketed, I spent a good deal of time trying to decide what is exactly wrong with my engine and have come to the conclusion I mis-diagnosed the fault. What actually happens is this...

I can start the car and when she`s warm, adjust the idle stops and get a steady idle at 900. Adjusting the air screws in and out smooths things out and then unclipping the rods I can get each carburetor to suck the same side to side. Clip every thing back together but then... and this is the crux of the problem...I rev the engine up to 2500 and it stays there and won`t come back down to idle unless I unscrew the stops. Then it stalls.

I suppose, in a nutshell, I`m having to screw the idle stops in to far to develope that initial idle.

I still haven`t looked at the valves, I was going to have a go and see if they need adjusting this morning. But didn`t. Can it be the valves ?

All opinions gladly and greatfully accepted.

Regards, Mike.

[Barry]

Mike: a silly question (don't hit me): your throttle linkage isn't getting hung up anywhere I suppose? Try disconnecting the throttle off of the carbs and rev it directly (doesn't matter if you open the throttle a tiny bit differently to each other).

Anyway, assuming it's not the above, a quick review:

You've tested the ignition, and swapped much of it out, and watching the timing and dwell has shown that no drastic changes occur in these as the revs suddenly fall away. Therefore we are concluding that it's no longer ignition?

After that, a classic sign of dying idle is weak mixture, which is either not enough fuel:

a) Fuel pump, filter and pipes: we know it's not these because the car has power and pulls O.K. I.e. in a state where it uses more fual then idle, it's all fine.

b) Jet blockage, internal drilling blockage in carbs, fuel level in float chamber (have you checked this?)

or too much air:

a) Loose or cracked manifold either at manifold to head join, or manifold to carb join.

b) Worn throttle spindles (wouldn't come on quickly, more over months / years).

Does the problem affect all four cylinders the same: reproduce the problem a few times, and pull the plugs: are they the same, or is one side wetter / darker / lighter /sootier / oilier / colder / hotter than the other? If so you know it's nothing common to both sides, so fuel pre-carbs, points, coil, king-lead, probably dizzy cap. The reverse is true, if all four plugs are the same, one of the above list becomes more likely as a culprit.

Overall though, even now I'd be tempted to throw the strobe and the dwell meter back on the thing, just to make absolutely sure that there's no change when the revs suddenly die. It's a fast and free job, and it gets the ignition off the list (although I'm very aware that you've tried this before, it's just a double check as we're either running out of options, or honing in on the problem, depending on whether you're a half empty, or half full sort of chap).

Anyway, after that it's time for a great airleak hunt: again, a tiny bit of play on the throttle spindles won't cause huge problems: you could always dob some thick grease around the outside of them and try it again just once. If it doesn't change the problem, it's not the spindles. If there seems to be a noticeable change, you're onto something. Don't use thin grease or if the car is steaming hot, as you wouldn't want to suck in huge dollops of grease.

If it's not spindles, I'd get the manifolds off and check: gaskets (replace), cracks in manifolds, fallen out blanking plugs, cracked pipes (if any) that come away from manifold (vacuum gauge in cockpit?, old accessory pipe servo take-off?), uneven / warped head or manifold surface. Often old manifolds get over-tightened if they are not even where people wind then up thinking the gasket will overcome everything. This bends then further and eventually the gasket can't hold in the middle (away from the bolts), and blows. If you find the manifolds / heads aren't dead flat, you can get them near perfect by using a piece of thick glass (I've got an old mirror, about a foot square, 3/8th thick), and use it with a sheet of wet-n-dry with a squirt of WD40.

A bit to ponder there anyway. I wish I was closer, I'd love to have a look myself .

P.S. note that other than manifold gaskets (which you can make yourself if you buy a sheet of gasket material), all above is free, and risk free if taken steadily, so all falls into the 'nothing to lose' camp.

[roy mawbey]

Mike,

I am a little confused about the way you are setting up the carbs. Now you have cleaned them and know the jets are all clear, did you do the following:

1). screw each idle brass headed mixture screw in to the stop then out one and a half turns. Then the 4 idle mixture screws are in a position ready to start adjustment on.

2). If you can get the car started and a little warmed up, remove the throttle drop arms and if the single idle adjustment screws need adjustment to lower the idle speed do so evenly if possible to get something where the engine stays running around 1000rpm.

3). Now by hand screw one of the brass headed mixture screws lightly in and out looking through the rear window to see if the revcounter goes up or down. Turn it by hand till it reaches the max rpm, then very slightly back it off. Proceed to the next screw do the same and then the other carbs 2 screws inn the same fashion. You probably will end up with the screws still very close to the the 1 and 1/2 turns out.

4). This is really where you need to have the syncronizer as you can make final adjustments to make them both even, but, if you follow the above you might no be that far out to at least get an idle.

5). When you push the drop arms on the rpm must not change. If all is okay the idle adjustment screws can be altered evenly to possible bring the idle speed down. ( The mixture screws should be quite near the right position and an idle should be possible.Do not alter these screws )

Hope this makes sense to you, you are doing well, far better to know something about how the carbs work then not.

6). Look onn the registry site and under trouble shooting look for Zenith 32 NDIX and there is a good tune up guide on there.

My check above is to start you in the right direction, the one and a half turn out of the mixture screws is important! first of all.

Roy ( sorry if you were doing the above procedure I just wasn't sure )