Timing wrong but drives fine CU Aircooled

[melvin]

Hi All,
Got a strange one here that has been baffling me for ages.....

First off it's an Aircooled 2.0 CU, Proper Dual Vacuum/Retard Dizzy.

If I set the timing in accordance to the given spec in the Haynes manual it runs rubbish, lacks power popping through the exhaust on de-acceleration, just not right.
I've set the timing as below:

Idle stabiliser unplugged and joined together, engine warmed up
6-8deg BTDC with vacuum hoses disconnected at idle
Which gives me 20-30deg BTDC at 3500rpm and 6deg ATDC idle with the hoses plugged back in.

Now if I set the timing with the following she runs a treat:

12deg BTDC Hoses connected at idle
With the hoses disconnected, this gives me 30deg BTDC at 3500rpm
Plug the hoses back in and it goes way off the scale, probably around 60deg BTDC.

I would just leave it alone but this makes it hard to start, feels like you have a flat battery and its just not right, surely this amount of advance should give pinging symptoms, but I cannot hear any

Anyone had this before or know why it might be the case?

Cheers
Melvin

[ajsimmo]

Ok, this one certainly sounds weird!
Firstly, how are you setting the timing?
Correct timing scale still fitted around the pulley, or some other method?
Fixed strobe light, or dial back adjustable one? Has the pulley notch been tampered with?
Are your vac pipes on right way round (advance to left carb, retard to idle circuit cross pipe (usually via t-piece at airbox))?
If all the above is correct...vac checks on dizzy can. With timing set correctly, vacs connected, 5° ATDC. Remove retard pipe, should now be 7° BTDC. Slightly open throttle, advance signal kicks in from carb and immediately snaps timing forward some more. Is it behaving like this? Either way, report back and we'll take it from there.
BTW seen your wanted ad and I might have a dizzy, but I'm not convinced that you need one yet...

Sent from my B1-830 using Tapatalk

[melvin]

Thanks for your reply!
Since posting my question I have found that the dizzy I have is from a DG engine, the unit looks the same but it has different codes and I should imagine a different advance curve?
Hence the lookout for a CU dizzy, anyway, I'm timing it using a gunson fixed strobe light, the pull your notch appears to be in the right place as tdc (as best as I can tell) is lining up correctly with the marker. When looking at the engine the left side vac pipe goes to the air box with a tee to a take off behind the box and the right pipe goes to the left carb.
I'm working on the van again tomorrow so I'll check the timing as you have suggested and report back.

Thanks again
Melvin

[melvin]

Ok, this one certainly sounds weird!
Firstly, how are you setting the timing?
Correct timing scale still fitted around the pulley, or some other method?
Fixed strobe light, or dial back adjustable one? Has the pulley notch been tampered with?
Are your vac pipes on right way round (advance to left carb, retard to idle circuit cross pipe (usually via t-piece at airbox))?
If all the above is correct...vac checks on dizzy can. With timing set correctly, vacs connected, 5° ATDC. Remove retard pipe, should now be 7° BTDC. Slightly open throttle, advance signal kicks in from carb and immediately snaps timing forward some more. Is it behaving like this? Either way, report back and we'll take it from there.
BTW seen your wanted ad and I might have a dizzy, but I'm not convinced that you need one yet...

Sent from my B1-830 using Tapatalk

Right, first of all the "pull your notch" in my previous post is meant to be pully notch, but you probably figured out my crummy autocorrect kicked in at the wrong moment, anyways......

Went out this morning and set the timing at 5deg ATDC with the vac connected, removed the retard pipe (the one connected to the underside of the vac can, closest to the dizzy) and the timing went to 7 BTDC, reconnected it and slightly increased the throttle and it advanced the timing, also at high rpm the timing went to about 32deg BTDC....... but it ran rubbish, holding back on acceleration and popping through the exhaust. On the plus side, it starts nice and strong.

Melvin

[ajsimmo]

Sounds like it's working as it should, and your problem may be elsewhere, such as carb balancing and/or blocked jet(s), or an air leak leaning it off...?

[melvin]

I did think carb first, so I took that apart and cleaned out all the jets replacing gaskets as I went, being that it is running fine with the timing out could the fault still lie within the carburation side of things?

M