my new strobo gun, how to set timing ? please help

[deQuincey]

hi

trying to fine tune the ignition, i just bought a strobo lamp gun, it is an analogic one, that uses a galvanometer to give you rpms, advance and dwell angle

so i am trying to understand how to use it following the blue manuals

i have gone through the specifications, discovering that for my engine the dwell angle can be, between 35 to 42

first of all i dont understand what is the dwell angle, anyway checking it with the gun it gives me 35 at iddle, and it does not change significantly when rpms are raised up to 1700, this seems to be good (a low dwell angle seems to be good) but i do not understand why, and normally i like to undestrand things

my second problem is with the advance itself, the blue manual says that for tunign the distributor you should raise rpms up to 1700, disconnect advance hose, and check with the strobo-gun to see the ball in front of the arrowed opening while the advance angle is set to zero,

well i can do that, i can see the ball in the mentioned conditions, but now i have a question

is that ball the 22degree BTDC advance that is mentioned in the books, i mean i have seen in other cars that there is even a scale painted there, but in this case the only mark i can see before TDC is the ball, see the following pic

i made a check, and more or less it is located at 22degrees

so, is this the mark for the famous mentioned 22degress before top dead center ?

 

[Stefan]

been there done that got the t-shirt...

and like deQuincey a lot of questions afterwards when following the blue book.

Since my engine runs great I had no desire to hunt answers. But I take a hook on this issue in order to calm my subconscious

Cheers!

 

[Sven]

deQ - The dwell is basically the time (measured in degrees rotation of the distributor cam) that the points are closed and hence the primary current is flowing to the coil prior to each spark event.

Yes, you are correct, the ball is the 22 degree mark (which you confirmed - apparently some fly wheels have the ball at different locations). This should line up with the reference point in the opening of the bell housing with the vacuum advance and retard disconnected and running at 1,700 rpm. Twist the distributor until the ball lines up with the reference. Do not loosen the distributor too much as it may turn by itself or pop up.

 

[deQuincey]

deQ - The dwell is basically the time (measured in degrees rotation of the distributor cam) that the points are closed and hence the primary current is flowing to the coil prior to each spark event.

Yes, you are correct, the ball is the 22 degree mark (which you confirmed - apparently some fly wheels have the ball at different locations). This should line up with the reference point in the opening of the bell housing with the vacuum advance and retard disconnected and running at 1,700 rpm. Twist the distributor until the ball lines up with the reference. Do not loosen the distributor too much as it may turn by itself or pop up.

thank you sven

so as to the first issue, the dwell angle, now i understand, it is like a check of the correct performance of the distributor itself

lets go to the timing, so i lined up the ball with the mark at 1700 rpm, yes, i twisted the distributor until this was done (i had to set the angle equal to zero in the scale using the small wheel in the gun)

but then they say, that when i slow down to 1000rpm (iddle), i must see the OT mark lined with the mark in the small window, and this is not happening

for seeing the OT mark aligned with the reference i must turn the small wheel of the strobo-gun until the angle in the scale reads 42

and i can not tell what this means

incidentally, the blue manuals speak about another angle, the advance timing angle, how cani check this ? they say that i must find the maximum advance, equal to the point in which the vaccuum is maximum, i checked it with a gauge, and i think it is around 3500 to 3700 rpms, can this be correct?

thanks again

 

[Sven]

The last part of these instructions did't make sense to me either. However, this does not affect the position of the distributor - that is determined only by the 22 degree mark. Now you are done with any distributor adjustment. It seems that the last part is to check that your retard vacuum is working correctly. It is odd because OT = TDC and the spark would never occur that late at idle, or any other condition.

 

[61porsche]

1. At idle- you should just barely see the mark "in the window". It won't line up. What this really means to you is a rough check of your distributer weights returning and a corresponding drop in idle rpm. AKA- check your distributer springs or lube it up.

2. 3500 rpm- there abouts your spark or timing should be all in depending upon your distributer. So yes, it's possible and predictible. 38 - 42 degrees sounds right but check the book and your distributer number. Advance plus vacuum or all in.

3. I set dwell to 38 degrees. Right in the middle.

4. You should always check TDC on the damper vs. the flywheel. If it's off a little, adjust at the flywheel wiith the light. Or count 11 teeth.

5. Now with all that, there are a lot of variables- gas, altitude, etc. Find the tune that you and the car/ engine like, runs good, keeps cool, etc.

 

[deQuincey]

thanks for the explanations

here is a nice vintage video that explains pretty well this,


http://www.youtube.com/watch?v=cIrA4iWkhbE&feature=youtube_gdata_player

 

[deQuincey]

answers and questions jerry

1. At idle- you should just barely see the mark "in the window". It won't line up. What this really means to you is a rough check of your distributer weights returning and a corresponding drop in idle rpm. AKA- check your distributer springs or lube it up.

i will need to check this with more detail

2. 3500 rpm- there abouts your spark or timing should be all in depending upon your distributer. So yes, it's possible and predictible. 38 - 42 degrees sounds right but check the book and your distributer number. Advance plus vacuum or all in.

i checked this rpm figure using a vacuum meter hooked up in the corresponding advance hose, and the reading was stopped at that point, so maximum vacuum seemed to be around 3600rpm, the book is not giving you the rpm figure, but it gives you the angle range that must correspond
it is good to know that the 3600rpm sounds good to you

3. I set dwell to 38 degrees. Right in the middle.

as far as i can tell from the vintage vw video, the dwell angle is the same as the points gap set( which in my case is 0.40mm), the good thing of the dwell, is that you can measure without removing the disrtib cap, am I right ?

a question, why in the middle ?, the book says that the lower (within the given range) the better

4. You should always check TDC on the damper vs. the flywheel. If it's off a little, adjust at the flywheel wiith the light. Or count 11 teeth.

5. Now with all that, there are a lot of variables- gas, altitude, etc. Find the tune that you and the car/ engine like, runs good, keeps cool,

yeah, you are right, it is very funny, but before having the gun, i set the distributor advance at iddle just using my ear, and now with the strobo-gun i discover that it was very close ! (i needed only a little extra advace more)

etc.

.

 

[61porsche]

3.a1 I know when the dwell changes from the middle. That's what my car likes. Everyone's different.

3.a2- Yep. No cap off and a lot more accurate than feeler guages. That means you can run the points longer but you still need to check them visually for pitting, burning, running off center etc. Quality control is not what it once was if it ever was. It seems like I go through a couple sets and then it stays that way a long time. But I tune more often trying to get that purrfect idle with a/c is not easy.

Oh well, the temps are nice here now- summer is almost over and the heat is gone ( mostly).