Club 80-90 Forums

Drove 2 hours to Nothallerton to a rolling road to get my newly fitted dellorto 40's tuned only to find out when i got there that the van wouldn't fit in. Pissed off to say the least. The mechanic messed around and balanced carbs etc, to be fare he was a decent enough bloke and I left with it running a bit better than when i got there, £70 + fuel lighter.
lesson learnt for next time - check garage door height before booking.
Anyway rant over, one thing he did find out was that setting timing at 7.5 btdc, vac pipe removed, this gave me an advance to around 50 with around 3500 revs. To me this is way too much and i'm going to end up cooking the engine. I am getting a flat spot when setting off and can't push it past 60mph.
Do i need to just reduce the advance on idle or am i looking at a replacement dizzy, halls sensor kit?
Also what is the advantage of fitting an anti pulse vacuum unit.

i'd rely on good old intuition si and keep retarding it a few degrees till it runs sweet. you're no shop egg,, you know the score and will get it right without paying others

50 degrees advanced at 3500rpm if way too much considering you have set the idle timing correctly. Over advancement is very likely worn mechanical advance mechanism and springs.

Martin

Isn't the idle timing ATDC?

I'm fairly sure it is... fairly..


I kind of remember looking it up and double/tripple checking as i'd never set up at After TDC. If it is atdc then that would knock 15 degrees off your 3500rpm

Seems you MAY need to return to the garage.
Just proves one needs to look before putting one's foot in ones mouth lol. See below. AFTER TOP DEAD CENTRE
CHECK ENGINE LETTERS!!!!!

CU Engine - 2000cc Aircooled Flat Four - Twin Carburettors..

ignition timing 5°±1° ATDC with vacuum see note at bottom of page
Mech'l ignition advance checks 0°-1° @ 1150RPM w/o vacuum and basic timing
9°-13° @1600RPM w/o vacuum and basic timing
21°-25° @3400RPM w/o vacuum and basic timing

Notes.

When setting ignition timing on vehicles with DIS (digital idle stabilisation) the two connectors of the DIS unit must be removed and plugged together.

Disconnect engine crankcase breather and plug on side of air cleaner.

Cool i was right!


So you timings above are without vacuum so with vaccume it should be about 10° more?

31-35° at 3.4k sounds better.

the 50° BTDC your getting at 3500rpm might trim out Ok when the timing is correct

Thanks for all your advice.

Tried the theory tonight, set at 5deg atdc and no power at all on load, which in my head makes sense. With the Dells there is no retard, so i may be wrong but
Retard, manifold vacuum, works on idle and drops off with throttle - retard moves angle from 7.5deg btdc to 5 deg atdc.
On throttle, with all vac pipes attached (if i still had retard), retard would drop off and advance, ported vacuum, would take over at 7.5deg btdc.
So would a static setting of 7.5deg btdc be right without retard, or am i getting confused?
If that is the case then i still believe the problem is the dizzy.

Sorry, you've lost me.

I'm guessing by dell you mean a dellorto carb? Are you saying you have an aftermarket carb?

Set it to 30° full advance.
ie. Rev the nads off it and set the timing once all the advance has happened.
You don't want any more than 30°.
See what it settles to at idle, I would say somewhere around 5° to 7° BTDC
Disconnect and leave disconnected the DIS.
Remove and plug the vac advance.
There is no "correct" timing for it, it will be trial and error till you get it right, starting, no pinking and decent power.
Vac advance is an economy measure to advance timing under light throttle cruising, you can live without it.
The timing is set ATDC due to the DIS, it needs some leaway to be ablbe to dick about with your timing to achieve a smooth idle.
Rolling road is the best bet though.

Oh, and if your really interested in numbers go buy a G-tech or similar, or you can buy an app for your I-phone that does a similar task.

Simon Baxter wrote:Set it to 30° full advance.
ie. Rev the nads off it and set the timing once all the advance has happened.
You don't want any more than 30°.

NOW you're taling Simon - still the way I time type 1's although I tend to aim for around 29 degrees.

thanks Simon

Set at 7btdc to start with, it likes that for starting and idling, revved the nad's off it, as you say, and it advanced to about 40btdc then steadied out at about 35btdc. Adjusted and Dropped it to 30btdc. Still idled fine so took it for a drive. Lacked power on pickup with a flat spot - Had to rev hard to get out of the drive.
Advanced it a tad and pickup improved - still a flat spot but better - popping at high revs. Tried this with and without vac pipes. Idle Stabalising unit has been removed and plugged together
swapped for another dizzy - thanks Rich. No different, so i'm hoping, by this, that my dizzy is ok.
so I think i may have the best I am going to get it and need to find me a rolling road, one that fits a pop top t25, can work on Dellorto's, is preferably familiar with an Aircooled and not too far. Can't be that hard - can it

most likely need jetting to allieviate flat spots.