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Spitfire Spitfire igniotion issue?

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tomkatb

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My 77 Spitfire 1500 was recently rebuilt. It idles and runs well. However it seams to miss badly between 2000-3000 rpm.

Timing is set at 10 degrees and is rock solid. I have noticed that when I put the timing light on the #1 plug the flashing is intermediate at the 2-3000 rpm.

I reversed the #1 & #4 plug wire and plug and there was no change.

Are cap failures common?

Is the 25 year old Allison ignition possibly going south?

Larry
 
Does it have points? If your distributor cap looks dirty on the inside AT ALL its time for a new one. Your points could be set too close. They could be arcing at higher rpm. Faulty condensor?


Adam H.
___________________________________________________________
1973 Triumph Spitfire.
 
Points are a definite possibility, but I would also suspect the coil or condensor. I have seen many coils act this way...where a certain frequency causes them to break down.

Does the timing light flash intermittently on all four plug wires at that rpm?

My 1977 Spit 1500 has a solid-state breaker in the dizzy. I'm not sure if that's stock or not. What do you have?
 
If the problem is above 2000 rpm, and ignition returns to normal when you drop it back, I wouldn't suspect the electronics, at least I wouldn't be looking there first. Normally they crap out with heat, and it should affect ignition at all engine revs.

Distributor caps defintely can cause problems. As noted in an earlier post, check carefully for arcing inside the cap. Also check for any cracks in the cap or in the rotor. Check the contact in the centre of the cap (where it pushes down on the rotor) to make sure it still has some tension and it's not broken. Also have a look at the electronic pickup inside the dizzy, just make sure it doesn't wiggle and that its clean etc. Make sure the flash cover is still fitted under the rotor.

You can check the plug wires by pulling them and checking with a volt meter. Touch one end of the wire to the (-) battery terminal as you measure the voltage at the other end of the wire. Anything above 7 volts is probably good. I would start with the coil-to-cap wire.

Is the distributor advancing properly? If you are 10d BTDC below 900 RPM, you should be advancing to 22-28 degrees at 2500 (i.e. off the scale). If not, could be a sticking centrifugal weight or seized weight spring.

If all that checks I would suspect the coil next. It should measure 1.3 to 1.5 ohms across the primary (with the wiring disconnected, measuring only the coil). It could be breaking down at higher rpm.

The electronics are always a possible, of course. If yours has an external amplifier it should be a little more reliable though. I would initially try and rule out everything from the coil through to the plugs, its a lot cheaper to look at those components first.
 
Timing lights start to stutter as engine rpms increase. The cheaper the light, the more pronounced the problem.

If you get this stuttering on all 4 plug wires, it's most likely your light. Especially if it simply quits reading at even higher rpms.

From your symptoms, I'd most suspect carburetion maladjustment.
 
This was just odd as only the #1 plug wire acted strange.

Oddly enough I changed what appears to be a perfectly good cap and the symptoms went away.

There was no apparent issue with the cap.

This car is a 76 titled as a 77 with the vacuum retard. What Initial timing are you all using?

I am at 10 but, I think it is not the right number.
 
If you hate the way your car runs at 10 BTC try 2 ATC. I think I have a similar year engine to yours and in my case the car runs great at +2.


Adam H.
___________________________________________________________
1973 Triumph Spitfire.
 
Great - if the problem is fixed, you're golden. Caps are cheap. Note if its just the number 1 cylinder, pull and check the plug gap also.

For a '76 motor with dizzy number 41646 your timing should be 2d AfterTDC with the vacuum connected. Sorry, I assumed you had a '77 engine. As you point out, 76's had a vacuum retard, not advance.

There has been lots of discussion about timing values in another Spitfire thread in this forum. I have a '78 Spit with a '76 engine also. At 11" Hg the vacuum retard unit is supposed to provide 12 degrees (crankshaft) ignition retard. These units have quite a bit different centrifugal advance profile than the '77s.

The official manuals say to strobe-set the timing with the retard attached, and to set it to 2d ATDC. As a check then, once you have set your timing, if you pull the vacuum line off the dizzy (and plug it) you should see your timing go to about 10d BTDC on the strobe light.

As noted in the other posts, every engine will run slightly differently. In addition, the vacuum retard and/or the mechanical advance are not deadly accurate (particularly after 30 years of use). The general consensus is to start with the official spec setting (2d ATDC) and then to vary it a bit depending on your own engine characteristics. My suggestion is to vary about 2 degrees from spec up or down until you are satisfied with overall driveability and performance.

Having said that, first go through the necessary checks to make sure your centrifugal advance is working reasonably well, and also that your vacuum retard unit is working properly too.
 
The dizzy on my car appears to be a 416978 as best I can read upside down in the dark. Does that make any sense. I know it is the origional..

Larry
 
That's probably a "B" on the end of the number, not an "8". But 41697 is a valid number. If you look to the right of that number you should see "45DE4" (the dizzy type) and then an arrow ( like ---->) and then a number with 4 digits. Those 4 digits should be the week and year of manufacture.

I love how all these numbers are on the engine side of the dizzy where its almost impossible to see....

41697 should be a 1977-79 distributor. And it should have vacuum advance, not retard. If you can confirm the week of manufacture you will know for sure.

If you want to test whether the vacuum is advance or retard, just pull the vacuum line off when the engine is running. A strobe will tell you whether it retards or advances when you pull it.

If you have a 77 distributor, you probably have a 77 engine (although not necessarily I suppose....). The 77 spec is 10d BTDC.
 
Thanks for the help. Yes the dizzy is a 41697B with vacuum advance.

It appears to run well. There is no vacuum at lower rpm’s which I assume is normal.

The centrifugal advance seems to work correctly. As I rev the motor is well beyond 30 degrees at about 3000 rpm.

I just love the brits. The car has a factory sticker on the body that says it is a 76; however the title and VIN number say it is a 77. Got to love it.

Right now it is running well at 10 degrees btdc.

I think I will bump the timing up some and see what happens.

Larry
 
Thanks for the help. Yes the dizzy is a 41697B with vacuum advance.

It appears to run well. There is no vacuum at lower rpm’s which I assume is normal.

The centrifugal advance seems to work correctly. As I rev the motor is well beyond 30 degrees at about 3000 rpm.

I just love the brits. The car has a factory sticker on the body that says it is a 76; however the title and VIN number say it is a 77. Got to love it.

Right now it is running well at 10 degrees btdc.

I think I will bump the timing up some and see what happens.

Larry
 
tomkatb said:
There is no vacuum at lower rpm’s which I assume is normal.
Click to expand...

Hmmm...not sure that's the way it should be. The vacuum tap for the distributor should come off the intake manifold, and at lower rpm you should have vacuum. I'm not sure exactly where it taps off on a '77 engine, but normally it should tap from just inboard of the carburetor.

The idea is that vacuum provides most of the advance at low rpm. As engine rpm increases, the throttle is open wider, and vacuum should drop off at that tap. At higher rpm the centrifugal weights should be providing most of the advance.

So if you have 10 degrees advance at less than 900 rpm, and if you have no vacuum at the distributor at that rpm, then all your advance is coming from the mechanical setting of the dizzy.
 
On my 77 Spit:
The vaccuum line comes from the carb top near the manifold end. It has no vaccuum at idle, but provides vacuum when the engine is revved.
 
I wonder if this is a different setup from the '76. I would have thought they would be the same, but maybe not. On mine (a 76 engine in a 78 Spit...) the distributor vacuum tap is from the bottom of the carb, just where the carb mounts to the intake manifold. It has vacuum at low rpm - actually I've never measured how much, but it does have vacuum.

The vacuum tap you reference on the top of the carb goes to the EGR valve. It has little to no vacuum at idle, which would make sense, since logically it should increase vacuum with engine speed in order to open the exhaust gas recirculation.
 
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