Club 80-90 Forums

I'm hoping someone can suggest the cause of a non-firing cylinder on a Beetle engine running a pair of Solex H40/44EIS carbs. Three out of the four are firing fine, but cylinder 2 evidently isn't. The exhaust gasses from the right hand bank are nowhere near as hot as those from the left, and the new spark plug in cylinder 2 (all 4 have been replaced) looks the same as it did when it came out of the box. There's a bit of a whiff of unburnt petrol, apparently from the right hand exhaust.

What we've tried so far:
- New plugs (correctly gapped) and leads all round. The distributor cap and rotor arm look quite new. Points are correctly gapped.
- There's definitely a spark in cylinder 2 - we've had it lying on the engine case with the plug on the end of the lead, and can see the spark.
- Timing has been checked and adjusted.
- Carbs have been dismantled and cleaned - there's clearly fuel flowing through the right hand carb since cylinder 1 is firing fine. They are a single venturi type, sitting on top of an inlet manifold that splits into two a couple of inches below the (new) carb gasket. The inlet manifold for cylinder 2 is clear.
- There's a vacuum hose linking the two inlet manifolds - the bosses are on the cylinder 2 and cylinder 4 sides of the inlet manifolds. The hose seems fine.
- Compression seems fine - only measured cold so far, but the range is from 110 to 125 across the four cylinders.

If there was an air leak, or a fuelling problem, affecting the right hand carb I would have thought it would affect both the right hand cylinders. The only thing I can think of is that the mixture on the right hand carb is not right - it's close enough for cylinder 1 to fire, but not cylinder 2.

I'm expecting it might need a trip to a tuning place, with a manometer to balance the carbs and a gas analyser to check the mixtures. But are there any simple adjustments we can try to get cylinder 2 running? Can anyone suggest some other cause that we've overlooked?

Deffo a good spark? Swap lead on #2 for a known good one and see what happens?

Is this a single or twin port engine? Twin port usually because the manifold if not is sealing often from being over tightened and bowed.

ELVIS wrote:Deffo a good spark? Swap lead on #2 for a known good one and see what happens?

Worth a try, thanks.

bigherb wrote:Is this a single or twin port engine? Twin port usually because the manifold if not is sealing often from being over tightened and bowed.

Not sure I know the correct definition. The carbs have a single venturi. The inlet manifold is an approx. 6" pedestal, that has a single circular hole at the top, but it divides into two distinct pipes before it reaches the head. So worth checking the manifold-to-head gasket and the flatness of the manifold mating face then? An air leak around one side of that gasket could certainly account for the symptoms.

CJH wrote:
but it divides into two distinct pipes before it reaches the head.

That is a twin port head then.

bigherb wrote: That is a twin port head then.

Thank you - right then, we'll remove the manifold to check that mating face. We can make a new gasket from some thickish gasket paper. Any harm in using something like Dirko for some extra leak protection?

CJH wrote: Any harm in using something like Dirko for some extra leak protection?

You can do but as they are non setting they are not a good sealer in those applications as the suction force makes them creep and fail if there is a too bigger gap and just relying on the sealer. Best to get the mating surfaces flat.

bigherb wrote:Best to get the mating surfaces flat.

Good advice I think. Thank you.

It was the manifold gasket, as suggested. We took the manifold off, cleaned up the faces, and put in a new home made paper gasket, using the thickest gasket paper I had, about 1mm. Fired it up, and we could tell immediately that it was firing on all four cylinders now. And I've got to say, it sounds awesome! It's a 1641cc engine, with two biggish carbs, and two cherry bomb exhaust pipes (? I think that's what they're called ?) with minimal silencers, and when it's running sweetly it sounds wonderful.

We also managed to repolarise the dynamo so that's working too. This morning, if someone had told me that dynamos sometimes need repolarising I'd have filed that along with realigning the gangle pins, but it's actually a 'thing'. It's stood for so long that the dynamo had lost it's mojo, and was actually outputting a small negative voltage. Just need a new regulator now.

A very satisfying evening's work.

One more question: to remove the inlet manifold on the right hand side we had to remove a chrome shroud that covered the head and the top of the cylinders, and was a push fit over the fan housing. We're pretty sure it's just bling, and since it's not very shiny anymore we decided to leave it off altogether, as it gets in the way of the spark plugs. But my question is, does it serve any purpose for an engine that's hanging out the back of an open body? It seems like the airflow will be better without it, but are we missing something crucial about these air cooled engines?

CJH wrote:It was the manifold gasket, as suggested. We took the manifold off, cleaned up the faces, and put in a new home made paper gasket, using the thickest gasket paper I had, about 1mm. Fired it up, and we could tell immediately that it was firing on all four cylinders now. And I've got to say, it sounds awesome! It's a 1641cc engine, with two biggish carbs, and two cherry bomb exhaust pipes (? I think that's what they're called ?) with minimal silencers, and when it's running sweetly it sounds wonderful.

We also managed to repolarise the dynamo so that's working too. This morning, if someone had told me that dynamos sometimes need repolarising I'd have filed that along with realigning the gangle pins, but it's actually a 'thing'. It's stood for so long that the dynamo had lost it's mojo, and was actually outputting a small negative voltage. Just need a new regulator now.

A very satisfying evening's work.

One more question: to remove the inlet manifold on the right hand side we had to remove a chrome shroud that covered the head and the top of the cylinders, and was a push fit over the fan housing. We're pretty sure it's just bling, and since it's not very shiny anymore we decided to leave it off altogether, as it gets in the way of the spark plugs. But my question is, does it serve any purpose for an engine that's hanging out the back of an open body? It seems like the airflow will be better without it, but are we missing something crucial about these air cooled engines?

Reading through this thread I realised that its 43 years since I first started playing with air-cooled VW boxers - frightening thought I have learnt a bit though and my first guess to your original problem would have been an inlet manifold leak. Best solution is proper laminated inlet manifold gaskets sealed with blue Hylomar or similar.

On your last question - two points:
1) Air cooled VWs are heavily dependent on the flow of air over heads and barrels (as well as oil cooling) for keeping cool. If you take off such a significant piece of tinware then it will soon overheat and weld things up - costing you a new engine.

2) There is a very good reason why VW always used matt black for the cooling tinware - that's the best for dissipating heat. The chrome stuff will be cr&p from the far east and is best replaced PDQ. It also should be more than a push fit and should be held in place by screws.

Lets see some pics of your buggy then! What sort is it?

Yes you need all the tinware around the engine, it is designed to direct the cooling air all around the cylinders and heads to stop hot spots warping things.

Well you're both saying the same thing, so it must be true, but I must admit I'm a bit surprised that the tinware is as important in a buggy as it is in a Beetle. The engine in the buggy is hanging out the back, so plenty of ventilation, and it certainly seems like the air flow will be better without it. But of course, the blown air from the fan will be better distributed with the tinware in place.

PetenAli wrote:...my first guess to your original problem would have been an inlet manifold leak. Best solution is proper laminated inlet manifold gaskets sealed with blue Hylomar or similar.

Do you mean one of the metal crush type gaskets? That's what was there already, but it didn't seem like it could be re-used. The dry paper gasket seems to have done a good job for now, and when I looked at buying replacements there seemed to be a choice of metal or fibre, so we figured a thick paper gasket would be OK.

PetenAli wrote: Lets see some pics of your buggy then! What sort is it?

It's not mine unfortunately. It's a mate's GP2, bought as an almost finished project at the end of last year, from a friend of a forum user on here. We've been gradually finishing it off these last few months. The biggest jobs have been making a dash (which my mate has done) and wiring it up (one-eyed man, land of the blind etc). But we're nearly there now, and it should be going for an MOT soon.

CJH wrote:Well you're both saying the same thing, so it must be true, but I must admit I'm a bit surprised that the tinware is as important in a buggy as it is in a Beetle. The engine in the buggy is hanging out the back, so plenty of ventilation, and it certainly seems like the air flow will be better without it. But of course, the blown air from the fan will be better distributed with the tinware in place.

But you are not going to get 32-35 cu ltr min over the engine stationary. When you are moving only the front faces will be cooled the rear cylinders will be shielded by the front cylinders, that's why the cooling air is directed from the top over the cylinders and head via and deflectors flows the air all around the cylinders.

Point taken. We'll put it back. Tsk.

Sorry to hijack post, but would hate to deprive 'Petenali' of buggy pics]weimarbus/media/002_zps6didssbg.jpg.html][IMG]
buggy on silly summer wheels