How much ignition advance will stop a Ferret running?

[sexton]

I came across something interesting working on a Ferret yesterday. She ran like crap, didn't want to idle, missed badly coming off idle, but then ran sort of OK at higher rpm and load.

 

Carb was rebuilt. Points were cleaned and gapped. Condenser meggered OK. Compression test showed 125-130 psi on all cylinders. Plugs fired cleanly in tester up to 140 psi. Lots of fuel being delivered to the carb. Still ran like crap.

 

Then I checked ignition timing with a timing light at a fairly fast idle. It was about 90 deg BTDC. I couldn't believe it. I rotated the distributor to the stop which reduced the advance to 46 deg BTDC. Not surprisingly, the idle improved. I pulled the distributor. At #1 TDC firing, the drive tab down in the block was parallel with the engine centreline as it should be so it wasn't a tooth off. But the drive sleeve on the dizzy had three holes in it as shown below. (Another sleeve I found had only one hole.) The 1/8" drive pin was installed in one of the end holes. I removed the sleeve and reinstalled it with the pin in the middle hole. That allowed me to time the engine properly. It then ran fine.

 

I wonder if anyone has any experience running an engine this far out of time. I mean the plugs were firing when the piston was only halfway up the cylinder, right? How could it have run at all? I can only guess the significant rotating mass of the engine, fluid coupling, and gearbox combined with the low dynamic compression at idle speeds provided enough flywheel effect to push the pistons over TDC.

 

Malcolm

 

Edited July 10, 2015 by sexton

[robin craig]

Dear Malcolm,

 

no words of wisdom on the timing for you, well done on digging deep for the problem. That is called a "POST". Previous Owner Stupid Trick!

 

Just shows how you cant take anything for granted when working on an MV.

 

Keep going mate

 

Robin

[timbo]

Last year I spent ages trying to properly time the J60 in my Sabre (should be 19 degs +/-0 btdc at 2500rpm). It was way off this when I put the timing light on it, but bizarrely seemed to run ok. After a lot of head scratching and faffing about I realised the previous owner (the army!) had refitted the flywheel with the timing mark 5 or 6 degs away from the actual TDC point! Doh! So never take anything for granted when working on old vehicles...though Im sure you all know that anyway.

[sexton]

Very true, guys. It's one of the interesting parts about working on this stuff - you never know what you'll find.

 

I found some more distributors. One had 4 holes drilled in the sleeve! The others had just one. Somebody suggested that the extra holes were drilled to deal with the drive shaft on an engine being installed one tooth out. And then that distributor got installed on the engine I am working on. Makes sense.

 

Malcolm

Edited July 15, 2015 by sexton