Pinging - distributor problem?

[tomfreo]

Since I got the bug (1600sp, 28PICT, ZV/PAU 4R5) out of storage where it sat for over a year, and after protracted faffing about it now runs OK. It starts and idles great. It appears to have good power (tho I never take it above c. 45-50mph). After running for 8+ miles, however, there's a persistent pinging accelerating in 3rd and 4th and going up hills. I've never had this problem before to such an extent. It used to ping lightly when I was living up in the hills returning home after a 25 mile drive. But otherwise no problem.

I started putting 95RON petrol into the tank and the problem went away. But it bothers me that it used to run fine on 91RON - something must be off.

The tappets, points and timing are spot on. That is, the vacuum-only advance distributor is statically timed fractionally to the left of the 10*BTDC mark. And the dwell is set statically with a mark 80* left of TDC. The tappets, I have to admit, are gapped at 0.008" in/out because for some reason the PO gapped them this way; he used to drive a lot outback, and the engine has quite a few miles on it now. I didn't think to second-guess his reasoning (and it was in the original manual albeit for a 40HP engine) tho I do read that "all engines are gapped at 0.006""??

The engine seems to be **slightly** hotter than usual after a prolonged run (the dipstick is pretty hot immediately after shutdown, but I can hang onto it no problem).

I suspect the distributor. Prolly only because I had a persistent pinging problem with my other car, a '77 bus, that was fixed by rebuilding the dizzie.

Last time I checked the distributor with an analog (no power source) dwell meter it was giving me wierd readings - like 65-70* odd. Since it was running ok I tried not to worry about it. Someone showed me the base plate was moving about.

I started the bug an hour ago, let it warm up a bit, and checked the timing with a timing light. With the vacuum port detached the light showed idle at specified 10*BTDC, and no change (unsurprisingly) increasing RPM. Plugged the vacuum line back, and the timing jumped about 7mm left of 10* mark, which by my reckoning is about 4*+10*=14* advanced. Revving the engine, the 10* mark moved about 2.5cm left of the crankcase crack - about 17*+10*=27.5* advance. I realise the advance revving a stationery bug is probably meaningless. But I was wondering if anyone might interpret these figures? The timing is otherwise very steady.

My manual suggests timing at the leftmost notch in the crank (7.5*) if the engine starts pinging. Maybe I should just time it there and see if there's any difference?

Maybe petrol here is, really, "just crap" says a local mechanic suggesting I run premium fuel (95+RON) in my bug? Maybe it's something else? Would a large valve gap induce pinging? Would low fuel pressure induce pinging? Should I start checking for vacuum leaks?

Any help?
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'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

[glutamodo]

Well, the .008" valve adjustment was for original "long stud" 1200s. You have a 1600 with should have "short studs" - VW's original specification for such engines was actually .004" - around the start of model year 1972 they "retconned" that spec to .006" for those.

This should have nothing to do with pre-detonation (pinging) though. Pinging comes down down to compression ratio, timing and fuel.. both the type of fuel used and the mixture.

With a vacuum-only distributor like that, you can get a fairly good read on total advance "at the curb", so to speak. Yes it will vary under load some but as for total advance you should able to read and yours seems fine. Are you just guessing those numbers or do you have a timing light with an advance wheel on it? Or did you make some full-advance marks on your pulley for a standard timing light?

Low fuel pressure - if it was too low you'd probably be starving for fuel and having the engine cut out and die. If you suspected such a thing, the final test is to kill the engine immediately when this happens, declutch and coast to a stop, get out and remove the air cleaner and carburetor top and check the fuel level in the carb bowl.

If you have a vacuum leak you're usually going to know it because it won't idle very well. But it doesn't hurt to do the "spray carb cleaner at the intake flanges" at idle test.

Excessive carbon buildup in the combustion chamber and top of the piston can effectively raise the compression ratio, of course...

I used to get pinging from a big-bore 40HP I had in my 62, and had to use mid-grade or premium fuel, especially in the summertime, to eliminate it. But that was due to the compression ratio being fairly high from the non-stock pistons/cylinders. If everything else seems good here I would likely do the same in this instance.

-Andy

[andk5591]

Something I had with a 28PICT1 on my 65 bug sounded similar. The vacuum advance circuit has 2 passages into the carb throat and you have to bear with me, its been quite a few years since I fixed this and Andy will have a better handle on this.

BUT the vac port I think went straight into the carb throat with an internal T going down to a hole below butterfly. When I hooked up the vacuum port at idle, the timing jumped. What had happened is the port straight into the carb throat was plugged, so it was pulling vacuum all the time. I ran a small piece of wire straight in the vacuum port and kept working it until I cleaned out the crud and them blasted it with carb cleaned. Problem fixed.

I am not sure that this is your problem, but it will take you maybe 5 minutes to do and might fix your problem.
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[67rustavenger]

[Dr OnHolliday]

"And the dwell is set statically with a mark 80* left of TDC."

? What does this mean in 'merican?
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1965 Type 1 sunroof Baja / about 70k miles on self-rebuilt '74 1600 and counting / SP heads and aftermarket valve keepers / non-doghouse shroud with external cooler and filter / 1.5 qt extended sump / Weber 32/36 DFAV progressive carb / 009 dist with Pertronix / 1.25 ratio rockers and ball adjusters / 1.5" stainless steel J-pipes and carbon steel baja exhaust

[tomfreo]

Thanks for the replies.

[andk5591]

Read my post - you should NOT have vac at idle unless you have something like a DVDA which has 2 hoses going to the vacuum canister on the distributor. Of course if you choose to ignore the advice, keep plugging away. Its an easy test and possible fix.

The studs for the heads can be dependent on the heads you are using....

And no reason to set valves to .008. I use .006" on all of ours with stock pushrods. The cars with chromoly pishrodsget set to loose 0.
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[Cusser]

[glutamodo]

[tomfreo]

[andk5591]

[tomfreo]

[andk5591]

The point I am making is to get it to run half decent is that you may have the initial advance set too high, which may result in pinging. Just be careful because detonation can break things....

Something else that I dont think was mentioned was checking for vacuum leaks. Just a good general practice. Lean conditions can cause pinging. What I do is use starter fluid with a straw and with the car idling, give it little blasts at any junctions (carb/manifold, manifiold/cylinder head, carb itself). You will always get a little leakage around the throttle shaft and if you are too close to the air cleaner. And not a bad idea to spray along the intake itself. I have a beautiful, freshly painted intake that I got at a swap meet that is now wall art because of a crack in the tubing.
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[Slow 1200]

vacuum only distributors are notorious for developing slop and/or weak springs that let the advance kick in at idle (i.e when it shouldn't)

advance should not change at idle when the vacuum canister is connected and disconnected from the carb

of course as has recommended above make sure that the carb passages are clear, as that can provoje unexpected vacuum signals that will mess up your advance curve

[tomfreo]

I regapped the valve tappets to 0.006", reset dwell/timing and went for a drive. A little quieter I guess, though not markedly so. No appreciable increase in power.

As for the pinging, I have to admit that between starting the post and today, I was getting low on fuel and filled up with premium 95RON. The pinging has not reappeared. Stupid of me if I was hoping to get to the bottom of the pinging.

There's still a very slight vacuum from the port on the carbie. I'm not entirely sure where I should be setting the idle speed. A 40HP manual I have says to set the speed 550-600RPM. The Idiot book says 850RPM or enough to make the generator light go out.

550-600RPM seems pretty low, and at 850RPM the generator light is on bright. I set the idle at 900RPM. I've heard it also helps cooling in stop-go traffic (?).

Any advice on idle speed?

BTW, the RHS cylinder head has the number 040 101 373 2 stamped on it under the rocker cover. A quick google says this is a 1600sp VW head made in Brazil 35.5mm intake 32mm exhaust.

Does this in any way confirm that I should be gapping the tappets at 0.006" given I doubt I've chromalloy valves?

Sorry for being so persistent about this - I just find it hard to believe the PO would've been gapping them at 0.008" unless told to do so by the people who put the engine in or for other reasons only known to himself. I do know he took the beetle across the Gibson Desert 20-30 years ago - and if you want to have a look at an atlas that's about as remote as you can get in the world - and wonder if he wasn't gapping the valves for the conditions he often drove the beetle? Not that I'm likely to do such driving.
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_________________
'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

[Bruce]

[tomfreo]

ok ok I guess I'm the kind of person who has to hear something more than several times before he's willing to admit something contrary to what otherwise previously believed. Excess serotonin or something.

Re-reading your post, are you saying I should set my valves at 0.004"?
_________________
_________________
'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp

[andk5591]

Set them at .006.....wanting to hear things a couple times is one thing, but what is it now? 5 or 6? Using the PO as a reference doesnt mean squat. I have worked on a shitload of cars that the owner or their mechanic was doing things wrong.

I am pulling out of this thread at this point....You can lead a man to water.......
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[glutamodo]

[tomfreo]

Still occasional pinging going up hills after a long run. I'm running 98RON (highest octane fuel here in Oz) and have retarded the timing to 7.5* from 10*BTDC.

I can't find vacuum leaks. The idle mix has been adjusted following instructions (would this even affect conditions pulling up a hill?)

I checked timing advance with a strobe: max advance is 3cm to the right of the 10* mark. I measured my crank at 17cm which would give 3.37*/0.5cm - so 3cm to the right of the 10* mark would give a total advance of 30.44*. Too much?

But ... there's vacuum at the port going to the (single vacuum-only) distributor at idle (650-850RPM). The timing jumps from 7.5* to about 12.5* at 850RPM (less at 650RPM) when I connect the vacuum line to the distributor.

I tried broddling a wire into the port, spraying with carb cleaner, etc but no change. There doesn't seem to be any block from the vacuum port straight into the carb body.

I don't know about the lower pipe from the vacuum port into the bottom of the carb, where it tee's off. Don't know whether it's blocked or whether this would cause problems?

If what others have said is any guide, I shouldn't see any vacuum at idle. Does anyone have any advice or recommendations?
_________________
_________________
'77 Kombi 2L dual carbs
'61 Bug 6V 1600sp