25 D distributer question

[Acollin]

1966 sunbeam alpine— mostly stock

Hello all

I had a little “dieseling” / pre / post ignition issue( car running on just a bit at shut off.). I set out to do some ignition timing to check to see if that was the cause. I read through the procedures in the wsm and all seemed simple enough.
The wsm says to set the knurled knob at or near a hash mark. I ran the vacuum advance knob in and out and could only clearly see one hash mark with the vacuum advance nob near the end of its travel toward advance.
I can only assume the marks are there and I was wondering if there are any tips you folks might have in helping me find them.

Are they actually engraved— could I feel the marks by dragging a pin horizontally?
— should I apply some paint remover?
— apply some dark paint and wipe excess paint off to reveal the marks?
— should I ask the forum for measurements from a fixed point so I could scratch in a few new indentations?
— feel free to advise, please.
— *** How important are the hash marks on the distributer vacuum advance to timing the car?

The good news is that I turned the knurled knob toward “retard” and was able to stop the dieseling, the running on — when turning off the car. I will check ( no time today ) what I have done with a timing light to see how things line up.
Be well all-
Andrew

 

[Tim R]

Andrew what I have found is that you need to slightly alter the timing to suit the differences in modern petrol (which runs much hotter, vaporises more easily and contains some pretty poor additives to please the environmentalists). The details stated in the WSM are more like a starting point now and it takes a littles adjustment to get the car running perfectly. Once you have it running perfectly I would encourage you to always refill with the same fuel.
Tim R

 

[bernd_st]

Just pulled out an old used S2 Lucas D25 dizzy from my stocks and shot this close up. You can see the notches engraved on the vacuum chamber stem:

 

[Acollin]

I always use non ethanol fuels in my Sunbeam.I am fortunate in that the closest place for me to buy any kind of fuel has a non ethanol option. It costs plenty, but it is well worth it.

Great picture bernd_st. It tells me plenty. Thanks So they are notches and not raised. I see yours just fine- I wonder why mine are so hard to see. The stem looks pretty clean. I guess more “cleaning“ is in order as a first step. I tried a damp rag— maybe a cleaner of some kind.
Ironic- I think I can use your distributer to time my car!!

I will assume the metal is on the soft side so I will not do any scratching at least until I can see something more clearly.

 

[bernd_st]

Welcome. Would recommend you to spray some brake cleaner on the stem notch portion and clean with a soft brush...

 

[husky drvr]

1966 sunbeam alpine— mostly stock

— *** How important are the hash marks on the distributer vacuum advance to timing the car?

The good news is that I turned the knurled knob toward “retard” and was able to stop the dieseling, the running on — when turning off the car. I will check ( no time today ) what I have done with a timing light to see how things line up.
Be well all-
Andrew

Andrew,

The usual cause of "running on" after turning the key off is the idle speed is set too high. It's affected by the interrelationship of several systems. You might try to retune to a lower idle speed (smaller throttle plate opening) and see if you can maintain your original advance setting. Doing so would help maintain power and mileage. You're running the original Z-S 150 carbs, correct?

Since you've read the WSM, then you know that one knob revolution is 3 crankshaft degrees and a verier mark is 4 crankshaft degrees of advance or retard timing.

If you think your issue might be affected by excess carbon buildup, you might run a compression test to see if pressures are up.

Hope this helps,

 

[Acollin]

My idle could be a bit lower, but I never thought it to be too bad— about 900 rpm. I was planning to get it within parameters when I actually set out to time the car.
i suppose a carbon build up could be a problem, but I have not yet moved in that direction. I have recently adjusted the valves and given the points and plugs a cleaning and reset.

My car is actually running pretty well as I have kept it moving all this winter. Starts easily / quickly ( now that I am not depressing the clutch pedal at start up / huge difference) , runs strong and smooth with good acceleration. Carbs are very nice since I topped up the oil reservoirs.
As you well know, there is always something to consider, but many of my running/mechanical bugs appear under control especially since I am pretty sure my “running on” may now be solved by retarding the timing a bit.
I was able to get a lot done in the last few months by keeping the car operational this winter. Still need to have my heater core repaired so the warmer weather cannot come too soon.
Be well and
Thanks for all the information
Andrew

 

[Scotty]

Since we're on this subject, given that the best gas I can get in my area is 92 Octane (which has some ethanol in it...grrr...) , is there a real necessity for running the Vacuum Advance? I've heard two sides of the argument to use/not use and have been told I don't need it, but should I be using it regardless? Mine is turned all the way in and disengaged.

 

[husky drvr]

Since we're on this subject, given that the best gas I can get in my area is 92 Octane (which has some ethanol in it...grrr...) , is there a real necessity for running the Vacuum Advance? I've heard two sides of the argument to use/not use and have been told I don't need it, but should I be using it regardless? Mine is turned all the way in and disengaged.

Scotty,

If you're driving on the street, you should utilize the vacuum advance feature. It improves drivability and mileage.

Can you run without it? Yes, but that scenario works best when you drive off the gas or fully floored - no in between.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi-yOyD6c_9AhXVkokEHcYZDvEQFnoECBAQAw&url=https%3A%2F%2Fhelp.summitracing.com%2Fapp%2Fanswers%2Fdetail%2Fa_id%2F5127%2F~%2Fwhat-is-a-vacuum-advance%253F&usg=AOvVaw0lDgII1giHIWDfvBgdWiOT

 

[Scotty]

Scotty,

If you're driving on the street, you should utilize the vacuum advance feature. It improves drivability and mileage. Can you run without it? Yes, but . . .

Works for me! How do I go about setting it up?

 

[husky drvr]

If nothing has been modified or mechanically disconnected, just hook a vacuum hose between the port on the vacuum can and the ported vacuum port on the carb. Next time you adjust the timing you might set the vernier wheel in the middle of its travel to have A & R adjustment. Some have the adjustment start at full retard and then advance to the fuel's limit.

 

[Gordon Holsinger]

1966 sunbeam alpine— mostly stock

Hello all

I had a little “dieseling” / pre / post ignition issue( car running on just a bit at shut off.). I set out to do some ignition timing to check to see if that was the cause. I read through the procedures in the wsm and all seemed simple enough.
The wsm says to set the knurled knob at or near a hash mark. I ran the vacuum advance knob in and out and could only clearly see one hash mark with the vacuum advance nob near the end of its travel toward advance.
I can only assume the marks are there and I was wondering if there are any tips you folks might have in helping me find them.

Are they actually engraved— could I feel the marks by dragging a pin horizontally?
— should I apply some paint remover?
— apply some dark paint and wipe excess paint off to reveal the marks?
— should I ask the forum for measurements from a fixed point so I could scratch in a few new indentations?
— feel free to advise, please.
— *** How important are the hash marks on the distributer vacuum advance to timing the car?

The good news is that I turned the knurled knob toward “retard” and was able to stop the dieseling, the running on — when turning off the car. I will check ( no time today ) what I have done with a timing light to see how things line up.
Be well all-
Andrew

When I tune my car I set static timing first make sure valves are set properly, and adjust carbs with a vacuum gauge for highest at idle, then I adjust the distributor. New fuels are not like the 1960’s.

 

[Joe-dick]

As stated above, the most common reason for running-on or 'dieseling' is throttles too far open/ high idle speed. I'm surprised that you said retarding the timing stopped the dieseling. Usually retarded timing requires larger throttle openings to maintain idle speed which exacerbates dieseling problems. Perhaps retarding the timing simply brought your idle speed down low enough that the engine was close to stalling already.

Running on is called 'dieseling' because the engine will try to run via compression ignition when the spark is turned off - a relative of 'pre-ignition' as you alluded to in your first post. So to eliminate dieseling you just need to remove at least one of the elements required for combustion: fuel, air, ignition. Some carburetors (and obviously fuel injection) have a facility for shutting off fuel supply when the key is turned off - ours do not so that's out and leaves us with air and ignition. Air, as we now know, if excessive either due to excessive idle speed or too much air related to lean fuel mixture, needs to be at the lowest rate feasible - in other words correct idle speed and mixture. Valve adjustment can be a problem here too. If your valve lash adjustment is far enough out to cause rough idle you'll have to compensate by higher idle speed. Ignition (spark) is normally shut off when the key is turned off, but if there's some other source of ignition such as a hot piece of carbon buildup, overheated engine, or high compression caused by overall carbon buildup in the combustion chamber this can become your source of ignition. With modern gasoline this usually isn't a problem unless you know you've been burning a lot of oil which can leave large carbon deposits inside the engine. This part of the equation can also come from low quality gas - if the octane rating (anti-knock ability) of the gasoline itself is too low the fuel will be more likely to spontaneously ignite at otherwise normal conditions. Maybe you're as old as I am and remember oil company TV commercials touting the ability of their premium gas at avoiding run-on.
So to boil it down the reasons for dieseling in order of frequency (in my experience) are:
>Too much air flow trying to maintain idle in the face of lean fuel mixture, late ignition timing, faulty valve adjustment, or just plain too high idle speed due to sticking throttle or choke fast idle linkage.
>Hot spot, carbon buildup, or overheated engine. This factor can be also caused by retarded ignition timing which increases engine combustion chamber temperature.
>Low fuel quality/octane allowing self-ignition under otherwise normal conditions. Usually you'll notice engine 'pinging' under load if the gas is poor enough to be the problem.

Note that retarded timing shows up twice in my list as it cause increased temp and also requires larger throttle openings, so as in any other tuning, verify the ignition timing first.

Joe

 

[Jay Laifman]

The damn 25D is why I now have full Holbay head, cam, distributor, pistons, etc.

Here's the sad story. I went away to law school and my Alpine sat in front of my folks' home. I then graduated and bought a 911, while the Alpine sat more. I decided to get it running again. Compared to the 911, it just didn't have power. I decided I had to "fix" that and went full Holbay. It was of course a fantastic transformation.

Sadly, during the rebuild, as we turned to the 25D, we discovered that the advance weights had rusted stuck - meaning I was not getting any advance and my car was therefore obviously running well below what it should have! It wasn't just the comparison to the 911.

Had I realized that before I went Holbay, I suspect there is a good change I never would have done it!