Explsions back through the Carb on start & stop

[chillihotrodders]

Thanks all for the help yesterday on the Alternator issue - think I got there, however will need to buy a more substantial unit.

 

Moving on to next challenge....

 

On my 1600cc cortina inboard I have recently upgraded the points to an electric ignition. All went well and engine runnung smoothly. However when I start the engine on the first couple of rotations, I get an explosion (sort of a squeeky hiss bang) and a puff of exhaust gas coming back through the carb. The engine then fails but starts Ok shortly afterwards and runs fine with a smooth rev curve. Again when I stop the engine I get the same explosion.

Something can't be right, as it didn't do this on the mechanical points. I have checked the valve tappits and shoved plenty of redex down the carb to ensure I have no sticking. I think it could be timing issues but a bit lost.

These explosions can't be doing the valves & pistons any good....

 

 

Any help from the pro's ?

[Denis R]

It could be a timing issue. I had this problem on a vehicle engine some years ago and a check with the strobe showed that I had to back off the distributor several degrees with the electronic ignition fitted..... On another engine I fitted a Lumenition system and the timing was spot on out the box.

[larkshall]

Definitely timing, if its spitting back thru the carb, the timing is retarded to far.

 

U will need a timing light to confirm this and to re-time.

 

method is paint tippex on crankcase timing mark and on the mark on crankshaft pulley. There maybe more than one mark on crankcase (tdc and say 5 degrees before tdc). slacken off distributor bolt SLIGHTLY> using timing light start engine and monitor the marks light on marks. They sgould coincide with 5 degress before tdC< if not adjust disb slightly till they do< tighten and try engine normally.

 

You don't say but has distributor being serviced?, I would think advance and retard springs would be tired, and/or distributor bearings shot. Oh do check vac advance and retard pipe is fitted first, and is not blocked. worth doing first.....

[chillihotrodders]

It could be a timing issue. I had this problem on a vehicle engine some years ago and a check with the strobe showed that I had to back off the distributor several degrees with the electronic ignition fitted..... On another engine I fitted a Lumenition system and the timing was spot on out the box.

Thanks - just to qualify the jargon backoff means retard the timing? would that be correct

[RobinJ]

Definitely timing, if its spitting back thru the carb, the timing is retarded to far.

Urh! Retard means move to past TDC, advance means move prior to TDC ?

If its spitting back and stopping the engine that would mean to far advanced?

[chillihotrodders]

Now confused, different people saying different things, Am I too far advanced or too far retarded?????????????????

[Yoda]

The engine is too far advanced.

 

The spark plug is firing when the inlet valve is open.

[GSer]

Now confused, different people saying different things, Am I too far advanced or too far retarded?????????????????

 

 

Either way, its seems that the ingnition timing is incorrect and needs setting. But do also check that the advance and retard unit is operating correctly, both are reasonably easy to check using a strobe light, if you are unsure then get a mechanic in who knows what he is doing!

 

Paul

[John Orentas]

Hi Chilli.

 

There is no reason why you can't at least initially adjust the timing by trial and error.. Work out which way the moving bit turns by inching the starter. Then loosen the main body of the distributer after marking it's position.. Rotate the main body of the distributer in the SAME direction, say 10mm every time you make an adjustment, mark the starting position so you ca always get back to where you where.

[larkshall]

Whoops to correct earlier post I said retarded, of coz it should be advanced

[Hairy-Neil]

The run on after you've turned it off can only be caused by self ignition...

 

I can understand it being the ignition advanced causing the problem on starting, but once you turned it off there are no more sparks to cause the fuel to ignite......

[chillihotrodders]

Thanks all for the advice, am taking it out for a spin tomorrow so will do some testing with the retarding. Ill let you know how I get on.

Chillihot

 

Boats coming out for an anti foul - whats the best product on the market?

Edited April 25, 2008 by chillihotrodders

[John Orentas]

The run on after you've turned it off can only be caused by self ignition...

 

I can understand it being the ignition advanced causing the problem on starting, but once you turned it off there are no more sparks to cause the fuel to ignite......

 

 

That 'running on' phenomenon was very common with that engine, people would say that it was red hot particles of carbon igniting the incoming charge.. I had several brand new Cortina's that would do it so there must have been another explanation..

 

I do remember a few heated debates on the matter in the motor trade, like so many of those weird mysteries it just went away.. I don't suppose we will ever know now.

[larkshall]

Which engine?, pinto or Kent?

 

On the pinto they cured run on by fitting a solenoid at carb end, if memory serves, it either shut off fuel, or shut the butterfly valve, in effect strangling the engine.

[Hairy-Neil]

Which engine?, pinto or Kent?

 

On the pinto they cured run on by fitting a solenoid at carb end, if memory serves, it either shut off fuel, or shut the butterfly valve, in effect strangling the engine.

 

All those anti dieseling valves I came across worked by weakening the mixture or venting the inlet manifold with the same end result.