Too much degrees BTDC?

paul

paul

XjunkieNL
Hi Guys,

I'm looking for some advice for setting the static timing.
My '78 X picks up and revs best when I set it at 10 BTDC or a little more.
The 'little more' comes from me looking down with a stroboscope and not being able to line up the marks exactly.

I'm using vacuum advance and mechanical on the distributor.
The manual suggest 5 BTDC.
With this setting everything is almost okay.
Except in 1st gear, with little gas, driving away gives a hick up.
Are there any negative effects of a higher BTDC?

The vac and mech advance give according to the manual 28 + 10 degrees.
This with static 10 BTDC gives a total of 48 degrees.
Is there a thing as too much BTDC, even if the X drives good?

Thanks,
Paul.
 
Too much advance.

Depending on the temperature and driving loads too much advance can be harmful to the engine. Ping which occurs when the engine is hot or on a high load situation like climbing a hill will cause the engine to fire before the piston reaches TDC. Sustain firing before TDC will cause the top piston rings to fail. More advance will give more power, it causes more emssions and more heat for the engine to get rid of.

As for marks on the flywheel or crank pully, move the pully to +10 and paint on the marks as the pointer is showing +5 and +10, which will give you now +15 and +20. I normally time by ear, if the engine pings, then I back the dizzy off a bit and use that setting.

Enjoy the power because the car you are driving can always use more of it.

TonyK.
Grimsby Ontario Canada.
 
Yeah Paul... as TK says...

... 38 degrees is probably max.

Do be sure both the centrifical and vacuum systems are indeed working correctly also. When they do... there should be a SMOOTH transition (once warm and even when cold with no transitions, but smooth...) especially when the carb secondary opens. If you still have the 3-way valve installed... controlling advance, gulp and secondary... this is/was the primary cause in vacuum failures.

If it is failing... many times its the water circulation that has been clogged. If smog certification is required and you wish to conform... you can correct or replace the valve or clear the circulation problem. Another method would be to remove the "problem" altogether and just connect the vacuum lines direct... even removing the gulp system.

Let us know what ya find...
 
That is a great tip TonyK!
I will paint some marks before and after the standaard dot.

The smoothness is there from 2000 rpm and up, especially the vacuum advance helps.
It's mainly at low revs (1000 - 1500), when driving off, it hick ups.
First I will put in a smaller jet in the primary jet, and see if it gives a positive or negative effect.

Most of the emission stuff is stripped.
 
I have done some more reading and it seems I have been a bit enthousiastic with the numbers.

First the mechenical advance of the uno ignition is not as much as the original.
Does anyone know how much it advances?
I was not yet succesful in findind that info.
Secondly the vacuum advance is almost gone when the mechanical reaches its max.

This would leave some room for the static advance.
Am I still on the right track?

Thanks,
paul.
 
advance

paul said:
Hi Guys,

I'm looking for some advice for setting the static timing.
My '78 X picks up and revs best when I set it at 10 BTDC or a little more.
The 'little more' comes from me looking down with a stroboscope and not being able to line up the marks exactly.

I'm using vacuum advance and mechanical on the distributor.
The manual suggest 5 BTDC.
With this setting everything is almost okay.
Except in 1st gear, with little gas, driving away gives a hick up.
Are there any negative effects of a higher BTDC?

The vac and mech advance give according to the manual 28 + 10 degrees.
This with static 10 BTDC gives a total of 48 degrees.
Is there a thing as too much BTDC, even if the X drives good?

Thanks,
Paul.
Click to expand...

I don't know about non USA specifications, but in North America a 1300 does not have a vacuum advance.
Specification is:
set idle speed to less than 1000 RPM, you may need to do this again during the operation.
Remove & plug the hose at the vacuum retard on the side of the distributor.
Set ignition timing to 10 degrees before top dead center.
Install hose, it should be at TDC.
Please note that the TVS for the retard on most cars has failed and the car actually runs best at 10 degrees with the hose plugged! If you must pass smog it had better be at TDC when the tech checks the timing!
It never hurts to check full advance, I would need to check notes as that spec is not burned into my skull. I always check ignition response by flipping the throttle a few times, a distributor that allows it to retard before the mechanical advance starts will cause a drivability problem that can only be resolved by rebuilding or replacing the distributor.
 
Thanks for the explanation Chris.
I installed an electric ignition from a Fiat Uno (don't know if they ever sold these in the US, overhere it was a very common little car), which has a vacuum advance.
Still what you say is also valid for this unit.
Thanks,
Paul.
 
Fiat Uno

paul said:
Thanks for the explanation Chris.
I installed an electric ignition from a Fiat Uno (don't know if they ever sold these in the US, overhere it was a very common little car), which has a vacuum advance.
Still what you say is also valid for this unit.
Thanks,
Paul.
Click to expand...

I have driven Unos, as rental cars. I try to open the hood of every rental at least once. We never got them here.
 
You must log in or register to reply here.
Back
Top