Initial engine break-in setup — running rough

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Dec 27, 2011
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Hi folks,

I'm trying to set my engine up to drive it for the first trial drive (page 171 in Tom Wilson's "How to rebuild your Volkswagen Air-Cooled Engine book) however I'm concerned by what sounds like a knock, and also it's developed a regular "miss" (?!) after my initial timing and carb setup. I adjusted the valves prior to this, and both on cylinder 4 were very loose. You can see that when I blip the accelerator it just stutters and eventually dies, I can hear a hissing but all connections feel tight. If I rev it slowly it seems to rev ok though.

I have a handy video recording you may be able to listen to / watch here:

Video of engine running rough

A few specs:
  • Stock 1600 dual-port rebuild—internals assembled by a local company, but that was about 6 years ago. Crank was reground and polished, all new bearings etc. Case has seen much better days.
  • Facet electronic fuel pump to replace standard mechanical pump
  • SVDA distributor (Barely any miles, new replacement prior to rebuild)
  • Blue coil (Barely any miles, new replacement prior to rebuild)
  • New cylinder heads, barrels, pistons
  • 34PICT3 carb (Barely any miles, new EMPI replacement prior to engine rebuild)
  • Static timing set—but the indicator light was always on, I turned the dizzy until it went off, which seems to be the opposite of what I expected (connect to coil negative and grounded on the alternator)
  • Automatic choke was checked and refitted, and doesn't seem to be coming all the way off, there are no visible marks to line up.
  • Carburettor bypass and volume control screws reset to 2.5 turns (also tried 3 turns), fast idle screw set to touching cam and 1/4 turn in.
I have tried to return this back to stock where I can, with the fuel pump being the only update. I'm not concerned that any of the ignition components are worn out, they've all been replaced while the bus was off the road for a decade.

Can anyone give me any advice on what to try next, or what is going on in the video? I want to avoid doing any damage, but I have to admit I expect to rebuild the bottom end next winter once I've finished spending all my money on a wedding...
Video is attached here in case the link above fails to work.


  • PXL_20221128_185838757.mp4
    31.2 MB
I've been out on this again this evening and noted the following:

The distributor is quite stiff and always tries to spring back to a "favourite" position—is this normal?

The timing light I am using is always on, rather than being off and coming on. Also, it only seems to work when I rotate the engine backward (anti-clockwise). During normal (clockwise) rotation, the light doesn't ever go off.

I have reset the automatic choke once again, but the cam seems awfully loose on the spindle, I'm not happy I've got this very accurate.

Still no luck getting it running. If anything it's worse. Doesn't help trying to work on it in the dark and freezing cold!
I’m no expert, but the fact that your revs pretty much don’t react (increase) when opening the carb suggests something is off, but it is running, so I guess that is part of the battle! Do you have a timing gun - I would suggest getting that checked out if you’re unsure of the timing light method. Whilst it would be better to check the max advance, I don’t think you’ll be able to achieve that yet whilst it is running rough, but getting an idle reading might be a good starting point. When checking max advance I believe this needs to be done whilst the vac line is removed from the dizzy and plugged in the engine side.

Have you tried rotating the dizzy whilst the engine is running to see if that makes any difference one way or the other?
Thanks @Moseley all help and advice are appreciated! I think I do have a timing light that I was given but I have never used one—I will try that first, and double-check the ignition components and the valves again.
My two penneth worth ... hopefully it might help.

Make sure you have no leaks on the intake ... at the connections to the heads and as well make sure the carb is bolted down tight enough ... can make set up impossible if not ... check vacuum hose for brakes for leak plus any hose take off for the air filter - otherwise you will have problems with the throttle.

On the carb ... the Bentley start settings are only the start .... you may have to richen the mixture to find the sweet spot (or the reverse) depending on how the carb is working, Final tune and set up will only be possible when the engine is fully warmed through etc etc.

Rotate the dizzy left and right when running to see how this effects the running

Read up on the timing light ... it may not aid in fine tuning but it will get you in the ballpark. The fact that it is on shows it is working, the fact that it doesn't go off suggests either you are doing something wrong or something is wrong in the set up. - This is probably grandmothers and eggs but:

Make sure the points gap is correct and they are opening on the cam, that you have TDC for number 1, the firing order as far as the leads to the cap are concerned is correct from where the rota is pointing. Set the advance position using the pulley notch .. then turn the dizzy until the light just goes out and lock down.

good luck.
Thanks @Raggles — with regards to the vacuum hoses, I swapped them all out for this silicon hose in the hope they will last longer:

Amazon link to silicon vacuum hose

These are only 3.0mm ID which is slightly smaller than the official 3.2mm (I think)—would that cause any issues?
Last edited:
Thanks @Moseley all help and advice are appreciated! I think I do have a timing light that I was given but I have never used one—I will try that first, and double-check the ignition components and the valves again.
If you want to borrow a strobe, you’re more than welcome to mine - I’m not too far away in Worcester. It is very useful to have one with an adjustable advance dial on it.
Check valve tappets gap first of all. Check points are clean and gap. Then do the dist rotate thing when running. Check fuel cut off valve is connected good. A bad connection will cause it to intermittently shut. Do a compression test as hissing seems suspect and could be a leaky cylinder.
It sounds like a mis-fire only running on three maybe.. as suggested check tappets are stil good, after all you had once set loose -why was that??

No the dizzy should not 'spring back' - loosen teh calmp and try turning itas suggested. If you cannot solve the issues through ignition/tappet adjustment then I agree that a compression test is needed.
I’ve listened and .listened again, I reckon that’s only running on two cylinders. You’ve got something a bit wrong there. Try taking the leads off at the dizzy one at a time to try and find which cylinders aren’t working. then take it from there. Has the motor been turned at all without the dizzy in ? I’m wondering if the drive has been shagged somehow or the leads are in the wrong order. Why were the gaps so wide ? :unsure:

Ozziedog,,,,,,,,, start with the leads and work from there:)
Gents—thanks for all the advice. I did complete the initial 20-minute run-in at 2000rpm successfully a couple of months back with no concern, but I will check everything thoroughly now before running it again. Think it might be time to book some annual leave!
Sounds like it’s missing, I’d check the obvious first, are the plug leads on snug, and in the right firing order at the distributor (I’ve made that mistake a few times). And that you’re timing it on cylunder 1 compression stroke. I’ve never known the light to go out using the static timing method, only on. Is it running points? Some electronic ignitions can’t be static timed like that. But if you can, check dynamic timing with a strobe-at full advance if possible ( vacuum hose removed and plugged ).
I’m not sure what you mean when you say the distributor springs back, it should turn freely in either direction and stay there once unclamped.
Havent looked at the choke setting procedure lately, but once the motors warm if you slacken the 3 screws holding the choke you can turn it slightly until the choke is just fully upright, that should be close enough.
And dont leave the ignition on too long at a time, you can burn out the coil.
hope you sort it out
Right—just spent my lunch inspecting the engine. The #3 HT lead pulled out of the dizzy cap too easily so that was obviously loose. HT leads all in the correct order, I set about checking the valve clearances again. #1 and #2 were perfect, opened the left-hand side and saw the rocker assembly had lifted and the exhaust valve #4 rocker had slipped off the pushrod. You can clearly see in this image below, along with the positions of the rocker shaft retaining nuts—the shaft has been pushed away from the engine on cylinder #4:


I have now removed the rocker assembly, the pushrod isn't bent, but my concern is the exhaust valve may be bent. It doesn't look like it is, but why would this have happened? Perhaps the rocker retaining nuts weren't tight enough and have worked loose?

What should my next move be? Should I:
  1. Reassemble everything apart from the valve cover
  2. Turn it over by hand and watch for correct valve movement on #4
  3. Refit the valve cover and attempt to start the engine if everything looks ok?
Cheers @67panel —they both look ok, the heads are brand new so I would expect them to be!

Maybe a little more attention to valve clearance procedures perhaps. There’s not really another way that could happen as far as I can thi… if you get a little baffled by the procedures, then do them one at a time. As soon as you see the cam is starting to depress a valve set the gap on the opposite side and you can’t go wrong.

Ozziedog,,,,,,,,easy peasy but time consuming :)
@ozziedog you're bang on here, the trouble I've got is that I'm now getting so excited after waiting so long to drive this thing that I'm starting to rush and squeeze jobs in during my lunch breaks while it's still light. Hopefully, there is no internal damage...

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