Sudden partial loss of power

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Malc

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Hoping for some help from those wiser and with more experience of VW aircooled engines. I serviced my stock 71 bay about a month ago - oil change, re-set the valve clearances, new points, re-set the timing to about 7 degrees BTDC using John Muir method, new spark plugs, everything checked over generally (it's a new bus purchase, only had it about 6 weeks). After servicing it's been running great, accelerating fine and cruising well on motorways at 60.

Yesterday we went out and after running apparently fine to begin with, when we got on the motorway and met the first gentle uphill gradient, my wife (driving) realized she had her foot to the floor and we were slowing. I'd also noticed the unnerving vibration, like the timing was out and it was fighting itself. We pulled off at the next exit and I took a look, hoping to find something obvious, but no. Weirdly, it was now idling noticeably faster than it had been, and smoothly on all 4 cylinders. I drove it slowly home, not on motorways, and found that it struggled badly on any uphill gradient, but seemed to run smoothly downhill or on a light throttle. Another strange thing was that when I cut the ignition, the engine seemed to take longer to slow down to a stop, but I guess this could just be because it was idling so fast.

Today I've checked over the inlet manifold looking for a vacuum leak (i've got some perished rubber boots that aren't looking too clever, so potential causes I guess). I've also been checking the contact breakers and timing but they look reasonable, certainly not far enough out to cause that kind of chronic problem. Other thoughts - carb problems, maybe? But if so why the fast idle..? Really quite puzzled, but hoping that some kind soul on this forum can point me in the right direction.

For background, I owned a 1303 beetle for about 30 years, and I've previously had a '71 early bay for about 6 years, and I'm used to looking after them myself, so I don't think of myself as a complete mechanical numpty. Maybe a partial one :)

Thanks a lot folks, any help appreciated :)

Malc
 

ozziedog

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This does sound a little weird, do you have a servo and if so have you checked it for air leaks at the servo and the pipe ends.

Ozziedog,,,,,,,anything lost from carb?
 

Malc

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I don't *think* I've got a servo... but maybe I'll double check that. There's a vac connection on the inlet manifold that's been blanked off, I was checking that today but nothing obviously amiss. Also spent quite some time staring at the carb, looks ok, at least, externally...

Thanks a lot for your reply @Ozziedog, really appreciated.
 

ozziedog

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I’ve pondered this and I’m now thinking that perhaps the choke is coming back on, is it an electronic choke, do you have a choke . That might explain less power but also the fast idling.

Ozziedog,,,,,,come on experts where are you? :mrgreen: :lol: :mrgreen:
 

Moseley

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Check the timing with a strobe gun on full advance. Whilst you have set the base advance, there’s no guarantee that the timing is correct at full advance - and you will certainly be at full advance when going uphill with foot to the floor. You may find that you’re quite far from the optimum (28-32 degrees With vac plugged, assuming a standard distributor).

I’ve certainly had experience with aftermarket distributors that don’t drop to the standard base advance figures when setting max advance and there are no obvious symptoms at idle that the advance is out of spec.
 

Bluesnailman

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Moseley said:
Check the timing with a strobe gun on full advance. Whilst you have set the base advance, there’s no guarantee that the timing is correct at full advance - and you will certainly be at full advance when going uphill with foot to the floor. You may find that you’re quite far from the optimum (28-32 degrees With vac plugged, assuming a standard distributor).

I’ve certainly had experience with aftermarket distributors that don’t drop to the standard base advance figures when setting max advance and there are no obvious symptoms at idle that the advance is out of spec.
Yip. Advance timing is the thing to check. If it hasn't been used much then a dose of premium in the tank often makes mine run better, I think the petrol goes off. Also, avoid any petrol with ethanol if you can, but you probably know that. I'm pretty reconciled to stripping and rebuilding my carb every year or so, might be worth a try (and resetting choke at same time)

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kjb01

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I had a similar problem and my points had closed up at bit. Only a little but it was enough for it to be a pain


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Malc

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Thanks @Ozziedog, @Moseley and @Bluesnailman

Pretty sure the electric choke is coming off as normal, but maybe I'll double check that again just to be sure.

Yes it's a standard distributor with vac advance, and I think what you suggest @Moseley is well worth checking. However, I re-set the points again this morning and re-checked the static timing, and if anything it was a little retarded, maybe around 2 or 3 degrees BTDC. With that being the case, I can't see how that fits with the fast idle (we're talking around 1800 to 2000 rpm I'm guessing). Certainly if the advance mechanisms had failed in the distributor, that could explain the drop in power, but the symptoms all started suddenly at the same time.

Today I replaced my inlet manifold boots with EMPI ones that you can fit without taking the manifolds apart - they seem like good quality. It turned out one of the old boots had properly split, so I was hopeful that this was the problem. Took it for a test drive... no, still sounding rough and not accelerating like it normally would. So then I pulled the carb off and took a look inside. Absolutely filthy, a depth of swirling muck in the bottom of the float chamber, together with evidence that someone's been in there before (someone not very skilled with a screwdriver at taking out the brass jets).

So now I'm wondering whether the loss in power could be a partially or completely blocked jet or drilling in the carb. But then, that still doesn't explain the crazy-fast idle. Does it? I'm certainly not a carb expert. In my past, I tried to unblock jets and drillings, and my failure rate was two out of two!!

Any further advice, comments and thoughts very much appreciated!

Cheers

Malc
 

Coda

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If you’ve got points and not an electronic module it means you’ve still got a condenser. Have you checked/replaced that?
 

Bluesnailman

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The fast idle is a funny one..... Could be that someone adjusted the carb while it was blocked..... Then it (partly?) cleared while you were driving. Then you now have better flow through the carb and possible the throttle held open on the choke adjustment (screw or coil). That would give you a fast idle. Normally I get a blockage which is tempting to overcome by adjusting the choke to compensate (I dont, I find a nice spot to stop, strip and rebuild - takes less than an hour)

If the carb is full of gunk it needs tackling for sure.

However, most running problems are down to electrics.... But I think idle speed can only be the carb

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Moseley

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As it’s running currently, I would leave the carb and the idle issue. Confirm your timing is good, see if that helps, and then look to strip and clean your carb and reset the idle etc if required. As soon as you start pulling parts off, you might introduce new problems, or find it harder to get to the bottom of the existing ones, so start with trial on error with things that can be checked / adjusted without removing, and then look at the parts individually.

It would be a different story if it wasn’t running, so at least you can test it after!


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Malc

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Thanks to Moseley, Bluesnailman, Coda and all for your replies and suggestions.

Latest update to the ongoing saga...

Decided to just buy a new standard 34 PICT carb equivalent from VW Heritage, since I trust them. That's arrived and fitted, together with a new fuel filter fitted immediately in front of the carb to prevent it getting sludged up again. Test driven... no, still has the problem. Not such a fast idle now though, after basic adjustment of the throttle stop and the electric choke cam.

So then thinking maybe my distributor advance isn't working properly (thanks for the suggestion Moseley). Borrowed a strobe gun off a kind friend and checked that... it's a Mexican Bosch SVDA distributor, and seems to give just over 30 degrees of total advance once you reach 3500 rpm. So I guess that's working fine.

In checking up on timing issues, I now realize I'd made a mistake on my timing. I thought my pulley wheel only had a single notch, and that must be TDC. Looking a lots of photos, and then looking really carefully at my pulley I find that it has the 'dimple' mark on the rear flange of the pulley (well disguised by flaking old paint and rust). So it seems the notch on the front flange of the pulley was 7.5 degrees BTDC, and I'd timed it 7.5 degrees too advanced :( Obviously I corrected this and test drove it - nope, still feeling rough.

So now feeling pretty fed up. Worried that I might have caused a valve to partially stick because of the over-advanced timing, or a valve seat burned. But if so, would it idle smoothly and calmly on all 4 cylinders, as it seems to? (Now at about 900 rpm.) That's not a rhetorical question, I'm genuinely asking what you think.

A kind neighbour who's quite a skilled mechanic suggested I should check the fuel pump (I haven't yet) and also that the fuel tank breather isn't blocked. I don't know where the fuel tank breather is routed - does it have a filter, is it likely to be blocked?

Other thoughts - could the coil, HT leads, distributor cap or rotor arm cause anything like this?

One other symptom: it's a reluctant starter, always has been a bit, but worse now.

Very grateful again for any thoughts, suggestions,mickey-taking, moral support etc.

Thanks

Malc
 

ozziedog

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If you’re thinking fuel supply issues ,then there’s an easy test. Get an empty 1.5 - 2L water bottle laying on its side in the noisey cupboard. Pop your fuel pipe off the carb and shove it into the bottle an inch or so. Disable your motor from starting by removing a rotor arm or similar probably not the coil leads because of sparks. Have your glamorous assistant or handsome helper crank it over for two or three seconds and your fuel should be spurting down around the bottom of the bottle. If it is then you have adequate fuel supply, if it don’t, then you have an issue prior to this point, possibly fuel pump, possibly fuel pipe blockage, possibly filter blockage or possibly tank crude up or even fuel shut off valve sticking. If you’re down on pressure, I’d go straight to the tank and see how well it flows straight out the tank, but if it’s fuel supply then this’ll help you track it. :mrgreen:

Ozziedog,,,,,,,, careful with fuel and sparks :shock: :shock: :shock: :mrgreen:
 

Malc

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Thanks Ozziedog, might try that tomorrow if I'm feeling brave. I don't think there's a fuel tank blockage because 1) when I changed the flexible fuel hose from the tank outlet a few weeks ago, it had no problems in soaking me in the second or two while I got the new connection on :) and 2) when I put the new carb and filter on the other day, the outlet from the fuel pump was flowing fuel at quite a rate before I blocked it off. Actually, should it do that? Obviously the engine wasn't running...

Thanks again!

Malc
 

Bluesnailman

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On your new carb you are adjusting the air mixture and idle speed screw on the side,? I'm sure you are.... Some manuals got the two the wrong way around. The big one on the side is the idle circuit, screw it clockwise very gently to reduce idle speed

It's doubtful that a carb straight from a supplier should work perfectly but an idle speed of 900 only needs a little adjustment.

I suspect your fuel pump is working fine, suggest more fiddling.....
1) warm engine up, then fast advance set with vacum disconnected and covered
2) Lower your idle speed a bit, but don't bother to perfect
3) get the airmixture right via a test drive on quite flat road (get out and adjust with your screwdriver, back in drive a again - repeat),
4). Before you go home, tweek idle speed,
5 when you get home, check idle speed

For me as a novice, took about 90 minutes. Bentley manual gave me the best directions....


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ozziedog

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Try the fuel pump test. (Empty bottle) then you’ve virtually eliminated the fuel side of things and we’re onto lecky stuff. But it does sound from what you’ve said that there’s plenty of fuel. While you’re doing the fuel test, leave an inch or two of fuel in the bottle and put the top on it, leave it overnight somewhere safe and calm but also visible to see if anything separates from the fuel overnight so you can see it without disturbing the bottle.
Next, allow the motor to idle but take off the plug leads one at a time to see which cylinder might not be responding as well as it could, then we’ll know where we’re going with this.
Every time I think of something I keep going back to the fast idle which is throwing me.

Ozziedog,,,,,,,,,,condenser sound likely apart from the fast idle. :mrgreen:
 

Moseley

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Just to confirm with the timing (as you really do want to be sure this is correct before checking other things), you did remove and cap the vac advance when setting the max advance?

A good way to confirm the notches on your crank pulley (and you only have to do this once, or if you ever got a different pulley) is to align to number 1 piston firing with the pulley mark lines up with the split in the case, and then lower a sturdy wooden skewer into the spark plug hole so that it is touching the top of the piston. When you rotate the engine slightly back and forth either side of the mark, the piston should be at the point where it is changing direction, not continuing to go in either up or down.


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Malc

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Thanks again guys.

Decided to start with Ozziedog's fuel pump test, hoping / expecting it would fail. It didn't, the fuel pump was merrily blasting fuel to the end of the bottle. Doh! So decided to check the timing one more time, just for fun. While rotating the engine to no.1 firing position, it occurred to me that this was a rough and ready way to check for even compression in all the cylinders. I found that this definitely wasn't the case, with no.3 showing noticeably less resistance to push past its firing position.

At this point I was resigned to the fact that I'd dropped no.3 exhaust valve, and went into the house for a general sulk and to look up prices and availability for replacement cylinder heads or even a complete engine. After a while, I thought I might as well take off the rocker cover and see the stuck valve, just to be certain.

What I saw when I took the rocker cover off left me completely gobsmacked. There was a gentle plink as a nut fell into the rocker cover, and I realized that the rocker shaft was completely loose, both nuts were off. It turned out that someone in the past had substituted the rocker shaft stud O-ring oil seals, and used a generous helping of blue hylomar (or something similar) instead. This had 'splurged' beneath both rocker shaft pedestals, meaning that they presumably had never been tightened down properly, and had worked loose.

I now need to clean up the mating faces, and find the right o-rings if I can, and then fit and re-adjust valve clearances. But pretty sure I've found the problem :D

The amazing thing is that it would start (reluctantly) and run in that state! The rockers were being pushed against the inside of the rocker cover - there are eight little polished dints in the painted finish - and presumably they were still just operating the valves a tiny bit.

Thanks again for your patience with me and your suggestions. Hopefully I'll have a happy van again in a couple of days (meant to be chucking it down tomorrow and I don't have a garage!).

Cheers

Malc
 

Coda

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Bloomin Nora. Blue hylomar is great stuff WHEN ITS USED PROPERLY! Not shouting at you, but rather the muppet who did this bodge.
Well done finding that, I hope it will go back together properly and there’s no damage.
 

Bluesnailman

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Well, there is something there about starting with the basics, and checking valve clearances is something we perhaps should have suggested. Glad you've found something that will be causing issues, hope the other side is ok.....

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