PDA

View Full Version : Spitfire Ignition Timing for my Spit 1500...



Lionheart
01-14-2007, 10:44 AM
Dynamic (strobe) timing for the 1500.
This is a 1977 motor with emissions removed except for the cat. It has a single ZS carb and electronic points.

I have seen every number under the sun for ignition timing. Anybody got a solid recommendation?

Would anyone recommend using a vacuum gauge to set the timing?

Thanks,
Len

tdskip
01-14-2007, 10:58 AM
In case you don't have a Haynes Spitfire manual handy, it says....

Idle speed of 700 - 900 RPM with vacuum connected.

10 degrees ATDC for 1977 49 State model
2 degrees BTDC for 1977 - 1981 California model

No value add to offer, sorry.

Lionheart
01-14-2007, 11:04 AM
Thanks. I should have mentioned that I have no less than 2 manuals for this car.

Anyone care to ponder the effects of emissions components (or lack thereof) on timing settings?

terriphill
01-14-2007, 11:06 AM
I know this is a real stupid question....I have a 77 midget 1500. (It's a 1500 spitfire engine) The midget 1500 repair manual I have says 10 degrees BTDC. If its the same motor, is the ignition timing that much different? /bcforum/images/%%GRAEMLIN_URL%%/confused.gif

tdskip
01-14-2007, 11:15 AM
The numbers I posted were for DYNAMIC timing, which is what the Haynes manual lists as the only option for 1977+ Spitfires.

It does seem weird that the manuals are so far apart.

Lionheart
01-14-2007, 11:20 AM
Perhaps the numbers for a ~74 spit (pre-emission?) would be more applicable?

CaptDon01
01-14-2007, 12:32 PM
I've got an 80 1500 Spitfire, stock except having been de-smogged, and have the timing set at 12 BTDC with good performance, no knocking ever, and I run 91 octain fuel.

Don

TheAssociate
01-14-2007, 01:20 PM
Well, I've had three Spitfires, and trying to get these cars to run right can be trying at times. I will give you my best advice: Take all three settings in your manual and try each. Go with the one you are most happy with.
There seems to be something else at play here with these settings - such as cam position, or distributor position, something different about the models.
For example, When I tune my '73 to spec for that year it runs with such a lack of power and excitement that it is undriveable. However, when I tune it to a later spec,(2degrees ATC)the engine is very excited, lots of power(for a stock Spit at the moment), idles perfectly, does not overheat etc.
It is also an observation that my car has a later engine installed.
Unfortunatly I've found with my other Spits that these timing figures in the manuals are completly interpretive at times, and really helps if you know the year of the ENGINE and DISTIBUTOR in your car.
Also, try to be precise with your timing - use a timing light on the front pully, use the stock specs and run through each one until something works. One of them will make your car run great. You may have to adjust your idle - and your high idle(see manual) to get perfect results after your timing is set.




Adam H.
__________________________________________________ _________
1973 Triumph Spitfire.

Lionheart
01-14-2007, 03:20 PM
Adam, that is what I'm thinking...trial and error. Thanks for your insightful advice.

guzzul
01-14-2007, 05:59 PM
The 1500's used 4 different distributors, each with somewhat different characteristics. (You may want to check the Lucas part number on the side of the distributor to make sure you have a '77. The part number should be 41697.)

US-model Spits in 75-76 employed distributor vacuum **retard** in addition to the distributor's internal centrifugal advance, whereas the 77-79 employed vacuum **advance**. These all had the same Lucas 45DE4 type-designation, but they had different Lucas part numbers and their timing specs and advance curves (both centrifugal and vacuum) were different.

If you do have a '77 distributor, your 'dynamic' timing spec is 10 degrees BTDC for Federal models (NB: 2 degrees After TDC for California). These are crankshaft degrees, not distributor degrees, and are spec'd for the engine idle speed of 800 rpm and with the vacuum unit connected. At 800 rpm, the centrifugal weights are not supposed to provide any advance, and all the advance should be coming from the vacuum unit. The vacuum advance unit is supposed to be providing 16-24 degrees advance at 10" of mercury. This is quite a lot compared to other distributor advance or retard mechanisms used on the 1500s, and it infers your basic (i.e. 'static') setting is considerably retarded

Emissions removal should not affect this setting much, basically 10d BTDC is a pretty reasonable setting overall. As noted in other posts, you might want to experiment a bit if you feel performance is wanting, but I would not go more than 2 degrees up or down.

I would thoroughly check out how well the distributor advance mechanisms themselves are functioning if you're not satisfied with overall performance. If the centrifugal weights are sticking (or conversely if the springs have gotten weaker over the years) you will not get a very smooth advance curve from them. Similarly, if the vacuum advance unit is sticking or if the mechanical pickup plate inside the dizzy is sticking, you won't get very accurate changes. Sometimes the vacuum diaphragm itself gets damaged and you won't get reliable advance.

heliguy
01-14-2007, 07:32 PM
Timing specs are for just getting in the ball park. Engine wear, octane of fuel you use, altitude car is driven at all come into play. Set it at what ever spec the book says, then go out and drive the thing. Advance it a couple of degrees and see what happens. Find a hill and drive up it in 4th gear, get the car to ping, and retard just a bit from there. That will be your optimum timing for that engine, with those carbs ( carb ) and that grade of gas etc, etc, etc.
If you dont want to do that then figure out just how much total advance you should have ( ie: 34 degrees at 3500 RPM ) and set the timing to that. Either method works well, but the first method is tailored to your particular car.......

Lionheart
01-15-2007, 09:58 AM
I am really glad I posted this. Lots of good info coming in...thanks to everyone.

I'm going to check out the dizzy today. I've got a hand vacuum pump that I hardly use...might as well put it to work.

Tell me if I'm wrong here, but the dizzy spins at crank speed/2 right? Therefore, there should be 720 crank degrees in one dizzy revolution.

On the mech advance, I should be able to see that working with the strobe by reving the engine with the vac advance disconnected.

Thanks Again,
Len

guzzul
01-15-2007, 05:20 PM
Yes, dizzy degrees are 1/2 of crank degrees.

Yes, with mechanical advance, if you know the engine speed you should be able to use it to map to the mechanical advance.

Using the Federal '77 spec, you should get the following (Crankshaft degrees):
800 RPM: no advance
1200 RPM: 0-10 degrees
1500 RPM: 6-14 degrees
2200 RPM: 12-16 degrees
3500 RPM: 16-20 degrees

Vacuum advance specs are (in inches of Hg and crankshaft degrees):
3.5": no advance
5.0": 0-5 degrees
7.0": 5-13 degrees
9.0": 14-20 degrees
10.0": 16-24 degrees

Maybe Jeff from Advanced can answer the question better than I, but it would seem to me these advance mechanisms must 'overlap' somewhat. If you combine both vacuum and mechanical at 3500 RPM you would be looking at a maximum of 44 crankshaft degrees (22 dizzy degrees). I wonder if the plate inside the dizzy will actually move a full 22 degrees. Seems like a lot. In any case, there is obviously a 'range' in the figures above, even in the official specs, so deadly accuracy is going to be tough to find.

Which would suggest you get your initial dynamic setting 'right', and then play with it a bit to find what suits your engine best overall.

But first I would try to ensure that both the vacuum advance and the centrifugal advance mechanisms are working properly. See if applying a measured amount of vacuum does advance by more or less the right amount and also if a measured engine speed results in the right amount of advance. No sense trying to tune something if its broken.