1500 missing

[Chief1500]

My '78 1500 started missing at high temps, and backfires when shut down. Dwell and timing are right, and I replace points, condenser and rotor. Any ideas? Could this be the coil?

Thanks,

 

[billspit]

I would suspect coil first, then the ignition module.

 

[guzzul]

Dwell and timing are right, and I replace points, condenser and rotor.

Points, condenser and rotor in a '78? Not electronic?

The high-temp miss could be the coil. Also could be plugs, wires or cap. Easy to have a look at them.

The backfire on shutdown does not sound to me like coil, though. More like timing. I would check the distributor advance springs to make sure they're moving freely and the dizzy advances/retards smoothly. Check the vacuum module on the side of the distributor to make sure the diaphragm is working right.

 

[Chief1500]

Your right, the previous owner installed a later model distributor (looks like '74ish) on the '78 motor. Could this be causing the problem?

When I run the motor with timing light, the spark advances well in to ATC range.

Thanks for the pointers.

 

[eejay56]

My 78 also has points. Lucas 45D4 dist. I time it with a static light at 10 btdc and it runs great. Using a strobe light it appears way off.

 

[guzzul]

Your right, the previous owner installed a later model distributor (looks like '74ish) on the '78 motor. Could this be causing the problem?

It's not unusual to run mechanical points instead of electronic, as eejay notes. You just have to tune for them. They have a different advance curve from the electronic models.

The distributor model should be stamped on the side of the dizzy (probably the side facing the engine block). If its a Lucas its probably a 45D4. The week and year of manufacture should be stamped on the side also.

As eejay notes, what many owners seem to do is start with 10-degree BTDC timing, and then experiment with slightly more advance or retard to balance performance and idle.

When I run the motor with timing light, the spark advances well in to ATC range.

ATC? As speed increases you should be seeing additional advance into the BTDC scale if you're measuring with a light.

Check to make sure that the advance increases with engine speed, but then drops again smoothly when you drop engine speed. If your advance mechanisms are binding that might cause the backfire on shutdown.

 

[Chief1500]

I've been setting it at 2ATDC with a timing light, as per the manual, and it advances well into BTDC. I reset at 10BTDC and it is running a much smoother.

The model number on the side of the distributor is V206 862 - 40735A, and the vacuum advance is stamped with DM2. Can anyone tell me which model/year this distributor is from?

 

[guzzul]

The model number on the side of the distributor is V206 862 - 40735A, and the vacuum advance is stamped with DM2. Can anyone tell me which model/year this distributor is from?

Wow. This looks like a Lucas DM2 distributor. I don't have much info on it, but I know the DM2 was used in a variety of LBC's, including Triumph, but not on Spitfires to my knowledge. I have seen it referenced as standard in a TR3-TR4. I think this is a 60's vintage dizzy. The 40735A would be the Lucas part number. Maybe another forum member can add some information.

I've been setting it at 2ATDC with a timing light, as per the manual, and it advances well into BTDC. I reset at 10BTDC and it is running a much smoother.

You have an interesting challenge. The timing spec for '78 is 2ATDC for California cars, but it is 10BTDC for Federal. I would use 10BTDC. You need to check where you are taking vacuum-advance from. Make sure your vacuum hose comes from the top side of the carburetor and not from the bottom.

When setting the timing, I would use a strobe (as you are doing), not static, and I would set it up with the vacuum hose attached, not plugged off. Also, make sure your idle speed is not too high, around 800RPM should be ok, so you don't get advance at idle.

If you check on the side of the vacuum advance unit, you may find 3 numbers stamped on it, possibly close to the tip where the hose attaches. If they're there, these should indicate the vacuum advance curve. I have no idea what the mechanical (centrifugal) advance specs would be for this dizzy.

I reset at 10BTDC and it is running a much smoother.

Does it still backfire at shutoff?

If you can get it to run smoothly, great. If not, you might consider sending the dizzy to Advanced Distributor and get them to check it out. I would want to know the shaft isn't wobbly, and the centrifugal advance is working right. And they can bench-test it to see exactly what the mechanical and vacuum advance characteristics are, how well they're working, and to compare them to 1500-spec to see how you should set it up. Alternately, they might suggest ideas to replace it if needed. No personal interest here, just a suggestion - they seem pretty competant and willing to give you good advice.

 

[Chief1500]

No more backfires with the new setting. I'll have to check the setting with the vacuum attached, as I normally set it with vacuum detached and plugged. I appreciate all the assistance.

 

[Bugeye58]

I'm glad my 1500 is missing. I didn't look very hard for it, either.
Jeff