Hesitation and Timing

[John Moore]

My 70 B has some hesitation when taking up gear. A little history, A friend of mine help me set up the SU's and it ran great, no problems except the idle was high. I thought this might be due to the timing being advanced, so I tried turning the dist, counter clockwise and now, I can't get it running good again. I have since backed off the idle screws to get the idle lower. I have also changed the plugs, points, condensor, cap and rotor (getting new wires tomorrow). Points set to .015. I bought a timing light and I have tried to get it as close to 10 degrees as possible, but still I have hesitation.

A few questions. (I'm trying to elimate all posibilities)

1. I have a hard time getting the car to idle a 600 RPM, to set the timing at 10 degrees. Why does the mark move with higher RPM, even though the vacuum (SP?) is removed? What would happen if I set it at 10 degress at a slightly higher RPM like 8K or 10K?

2. I want to make sure the valves are adjusted. I know the order in which to check the valves from my Haynes manual, but I don't know which valve is 1, which is 8. Does it start close to the rad a count back?

3. Would setting the idle screws back to 1500, effect how the carbs perform.

Sorry for the long post, any help would be appreciated!

-John

 

[aerog]

John:

First, consider borrowing or buying a dwell meter. Setting the point gap is a start, might even be fine, but using dwell meter is a little more accurate - at least that's how I do it.

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Why does the mark move with higher RPM, even though the vacuum (SP?) is removed?<hr></blockquote>

Mechanical advance. I think you'll find your distributor not only has vacuum advance but a mechanical advance using weights and springs. Mechanical advance changes as the rotor (engine) speed changes, vacuum advance changes as intake manifold pressures change (more an indication of engine load I believe). So, to have an accurate timing setting you have to have the engine idle below a certain speed so the mechanical advance isn't a factor.

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>2. I want to make sure the valves are adjusted. I know the order in which to check the valves from my Haynes manual, but I don't know which valve is 1, which is 8. Does it start close to the rad a count back?<hr></blockquote>

Yes - front to back.

 

[aeronca65t]

I agree with Scott.
I will also add that the mechanical advance weights can get worn and loose with time. At lower RPMs, the engine speed may be less steady....this may cause worn springs to allow the upper distrib shaft to rotate "ahead" and "behind", making the timing look unsteady. The mechanical timing advance is normally not a factor until above about 1000 RPM. If you can get the timing pretty steady at about 900 RPM (or so), you should be OK. If you wish, you should be able to drop the RPM to 600-700 after setting.
Obviously, if timing is very unsteady, new springs or a rebuilt distributor is in order.