Compression test?

[dickie65]

Hi Steve,
Pull the spark plugs out and put a teaspoon of petrol into the cylinders put the plugs back in and have a go at starting.
If it runs then stops you have no fuel getting in, you might find it will start and pull fuel through and keep running.

[stevenm]

Thanks Bob

Tappets are good and valves are closing  / opening ok from a visual inspection, new springs. I've sprayed cold start into her and have achieved a fairly mighty backfire.
I dont want to try to much advance initially till I know where things are, but if I advance her I get a push back in the cranking.

Ill bench test the valves as has sat a while.

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Hi Steve,
Pull the spark plugs out and put a teaspoon of petrol into the cylinders put the plugs back in and have a go at starting.
If it runs then stops you have no fuel getting in, you might find it will start and pull fuel through and keep running.

Thanks Dickie,

Will try this but will un mixed liquid petrol combust ? and wont the fuel be exhausted after first crank revolution?

Worth a try to eliminate issue i guess.

Steven

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PS Still interested in what the expected reading would be for a cold compression test ?

[Chris KC]

Steve,

There are just so many unknowns with an engine which was not previously running (?) it's difficult to know where to start.
You might find the attached check list helpful, it covers most of the possible candidates (though it was written with an SU carb in mind, so you may have to think about your Zenith a bit too).

  A7 Doesn't Start.xlsx (Size: 18.4 KB / Downloads: 34)

["Slack Alice" Simon]

Fuel down the plug holes is my standard fix for an engine not wanting to go.

You have compression so if the timing and firing sequence is right it should give you a couple of revs which means it has the potential to run.

If you are getting any kickback on the handle it is over advanced for an engine you are having problems with.

[stevenm]

Fuel down the plug holes is my standard fix for an engine not wanting to go.

You have compression so if the timing and firing sequence is right it should give you a couple of revs which means it has the potential to run.

If you are getting any kickback on the handle it is over advanced for an engine you are having problems with.

Thanks Simon , good feedback.

I'm trying this this afternoon as soon as can get to garage.

I had assumed that over advance was reason for kickback, and over retardation the reason for the earlier backfire , will continue to "fiddle".

[Nick Turley]

This may seem like a silly question but have you got the leads in the correct order ?

[Bob Culver]

Hi Stevenm

You dont say what has been doen to the engine. Is the valve timing seriously wrong (valves "rock"" just after tdc.) Are the ign leads in correct order and firng on compr stroke?

[John Mason]

Hi Steven, How old is your petrol. Cars always start better with new petrol. Try some new fresh petrol if you have any and take off your carb fuel chamber throw the old away and fill with new. If it starts and runs for a few minutes then you have proved your problem is old petrol if is doesn’t you have not lost much time or effort checking it. In my experience petrol does not last longer then about 6 weeks unless kept in an airtight container.
As to your advance and retard position. You are correct you will get a heavy kick back if to far advanced. You are probably correct in backfires caused by to far retarded. Now you know where these two points are set the position some where between the two.

John Mason

[stevenm]

Hi Stevenm

You dont say what has been doen to the engine. Is the valve timing seriously wrong (valves "rock"" just after tdc.) Are the ign leads in correct order and firng on compr stroke?

Thanks Bob, visually I have no idea if the timmings are out on the valves however they look about right , also to achive any compression at all they valvues must be in sudo sync with the pistion ? Surely ?

Bob & Nick

Thanks yes I'm 100% the leads are in right order and firing sequence is correct, and rotation is in the right direction , also checked gap, spark etc and that its timmed to TDC on the compression stroke, as discussed im getting puffs of exhaust so were close. 

John - petrol im using is a week old and in a plastic petrol can with lid.

I've no condensor on the spark system, the coil is a RED Accuspark and im using 123 petronics spark not points, ill take a video / pics to provide better info on my configuration and a small update to folllow .

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Fuel down the plug holes is my standard fix for an engine not wanting to go.

You have compression so if the timing and firing sequence is right it should give you a couple of revs which means it has the potential to run.

If you are getting any kickback on the handle it is over advanced for an engine you are having problems with.

Hi Simon et all

Thanks everyone for the support and suggestions,

I put petrol down the 4 cylinders, and cranked got a sort of a run on. so adjusted timing a little , re filled the cylinders with drop petrol AND  burnt out my starter !!!!, looks like just the 2 brushes are gone hopefully so have a new set on order from A7c - so will clean out and rebuild starter over next day or so and hope David is handy to the post office.

Meantime ill tinker with the other 100 issues and get back to you once have a functioning starter.....

[Bob Culver]

The low compression raises suspicion about valve timing. If the valves can be seen thru the plug hole or the tappets observed the valves rock (ie one just closing as other just opens)  about 5/8 inch atdc on flywheel.