Spitfire Setting Timing on a 1974 Spitfire

[78Z]

Ok so I got the Dwell done spot on. Next using the timing light I get it to 800rpm like book says and timing indicated at 4 BTDC and spec says 2 ATDC but if I set it to that it stalls out. Why? I set to 2 BTDC and it runs ok. Any ideas?

 

[Guest]

Set her where she is happiest. Sounds like you are really running centrifugal advance and not vacumn advance. Has the vacumn been blocked off to your distributor?


Bill

 

[Mark Jones]

2 deg ATDC is with vacuum advance connected. I believe that it should be around 10 BTDC with the vacuum advance blocked off.

 

[78Z]

I do have a vacuum advanced and I tried 2 deg ATDC with it connected. If I try BTDC with the vacuum advance blocked off should it permentently be blocked off or just for setting the timing? Thanks!

 

[Guest]

Set it one way or the other and leave it. If you use the vacumn advance feature on your distributor, you will have to set the timing After Top Dead Center. Without the vacumn curving your distributor, you will set at Before Top Dead Center, and leave it. The vacumn advance is strictly a pollution device and is unnecessary. Some will argue this point and there are other things that happen with the vacumn setting, but running the timing with just centrifugal advance at whatever Mark stated above is perfectly ok. I run my TR6 at 8 degrees BFTDC with no vacumn lines hooked up, 'cept to the brake servo. Set it, and forget it!

Bill

 

[aeronca65t]

78Z:

Generally, if you are seeing a change in timing when you hook up the vacuum advance, your idle speed may be a little high (I know you said 800 RPM. You could drop that just a bit...my manual says 680 for a 1500 Midget).

Typically, the specs tell you to remove and plug the vacuum line to the distributor, but that's just in case your idle is a little high. Be sure the other end of that line goes to a nipple that comes from the carb (or one of the carbs, if you have two). By the way, be sure the vacuum line is not connected to pure manifold vacuum. It should not be connected to a nipple on the manifold (if it is, your timing will be way off).

When you *just* kick the throttle down a bit (say to 1500 RPM), the vacuum advance kicks in a little extra advance for more torque. This can make the car nicer for slow speed driving. The vacuum advance unit really only affect timings from about 1500 RPM to 2500 RPM. During this range, the centrifugal advance starts to kick in and take-over the advance function.

Most racers or performance-oriented drivers do not care about this feature and often disconnect the vacuum line. The vacuum advance unit in my racer has been removed and the moveable advance-plate has been fixed in one postion. A popular "speed-item" for your car is the Mini-Cooper S distributor which is centrifigal-only and has no vacuum unit (yes, it will fit your Triumph). As stated above, you can simply leave the vacuum advance disconnected if you're not concerned about low-speed driveability. Many racers set timing at max RPM and don't worry about idle timing. I set mine around 30 degrees BTDC at 5500RPM.

The 2 degreees ATDC that you quote is the California-only spec for my '78 1500. Sounds wrong to me. I'd try 6 to 8 degrees BTDC at idle and see if the car pings (or "pinks" as the Brits say) when climbing a hill in fourth gear at about 2500 RPM. Reduce timing a bit if you hear any pinging. The Brit-spec cars use 10 degrees BTDC, so you could probably even go that far if you have decent fuel octane in your area.
While you've got the car hooked up, rev the engine with the timing light attached...you should see the timing "move ahead" on the marks, indicating that the advance is really working.

 

[Guest]

See, I told you that someone else would have a better explanation of the mechanics of the whole thing. Thank god for Darth Vader. You ask him the time and he tells you how to make a watch....
One less vacumn line makes for a cleaner engine compartment.

Bill

 

[80spitlizzy]

IIRC around '74 triumph was playing with vacuum retard as well as advance. I'd make sure that all of the ignition and timing advance components are correct for your car. Or just disconnect and plug the vac system. Set a good static advance, make shure the mech advance is moving well and go for it.

I'm running my '80 (slightly tuned) at 12 btdc

 

[78Z]

Well I set to 12 BTDC and plugged the vacumn advance. Runs really well now. I think I will leave it like that. Thanks all !!!