Running rough.

Hi everybody,

So had head off for skimming, put everything back together and engine will now only run with the choke on. Wont rev freely either. I've checked all the jets in the carb and put new plugs in. Cant find any leaks anywhere .... open to any suggestions.

have you touched the timing? worth starting from scratch, check list style. points and condenser good? static timing set, is there a good spark.. you've had the head off, so are the tappets set properly?

kermit_rr said:

have you touched the timing? worth starting from scratch, check list style. points and condenser good? static timing set, is there a good spark.. you've had the head off, so are the tappets set properly?

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No haven;t touched the timing. Tappets are set and seem good. Engine starts fine just wont idle without at least a little bit of choke.

laurie109 said:

No haven;t touched the timing. Tappets are set and seem good. Engine starts fine just wont idle without at least a little bit of choke.

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i'd check it, doesnt take a moment.
how many turns out is the mixture screw? sounds like it needs another turn

kermit_rr said:

i'd check it, doesnt take a moment.
how many turns out is the mixture screw? sounds like it needs another turn

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So how do I check the timing. Not something i've ever done. Not sure how far out the mix screw is never adjusted it.

laurie109 said:

Hi everybody,

So had head off for skimming, put everything back together and engine will now only run with the choke on. Wont rev freely either. I've checked all the jets in the carb and put new plugs in. Cant find any leaks anywhere .... open to any suggestions.

Click to expand...

Are you sure you used the right plugs? There are several kinds for petrol Series.
And are you sure you put the plug leads back in the right order?

Turboman said:

Are you sure you used the right plugs? There are several kinds for petrol Series.
And are you sure you put the plug leads back in the right order?

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RTC 3751 for the plugs. Pretty sure re the leads.

laurie109 said:

RTC 3751 for the plugs. Pretty sure re the leads.

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The numbers mean not much to me. But I do know that if you use the plugs with 3 electrodes round the centre electrode in a head that should have I electrode above the centre, it won't run properly. And likewise if you use short reach plugs where long reach are intended.

What age is the head? And why did you have it skimmed in the first place?

Pretty sure isn't good enough with the leads. If they are wrong, it may run a bit, but not very well.

Head was skimmed as the head gasket had blown. It runs smoothly within a certain range but take choke off and it dies, press pedal and it will struggle and splutter ....then dies.

laurie109 said:

So how do I check the timing. Not something i've ever done. Not sure how far out the mix screw is never adjusted it.

Click to expand...

surely you've taken the mixture screw out when you cleaned the carb? or perhaps you've moved the screw by mistake. checking that would be my first start. count how many turns it takes to screw all the way in, don't tighten it, just until it stops turning. write that number down so you can go back if you need to. most carbs are set to 1 1/2 turns out, try that and see how it runs, if its still poor, turn out half a turn at a time before you start any fine tuning. if its still not right at 3 turns then something is badly wrong

what carb is it? if it has a diaphragm, that could have perished

laurie109 said:

Head was skimmed as the head gasket had blown. It runs smoothly within a certain range but take choke off and it dies, press pedal and it will struggle and splutter ....then dies.

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It isn't usually necessary to skim the head after a blown gasket, unless it is badly pitted, or has deep burns where gas has been running across it.

I presume you used a quality composite gasket? Not the copper one.

The symptoms you describe could be countless things. Timing, as suggested^^^^^, carb or air intake issue, wrong or faulty plugs, leads in the wrong order. Just a few that spring to mind.

In order to diagnose the issue, it is helpful to know the age of the vehicle, if the head is original to the engine that is in it. If it is a 3 or 5 bearing engine, etc.

kermit_rr said:

what carb is it? if it has a diaphragm, that could have perished

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Or the advance retard unit could have packed up, or the tube may have come off it, or broken.

I do love the endless realms of speculation.

laurie109 said:

Head was skimmed as the head gasket had blown. It runs smoothly within a certain range but take choke off and it dies, press pedal and it will struggle and splutter ....then dies.

Click to expand...

Sounds like it's too rich, pulling the choke also pulls the throttle open a little before it increases the venturi.
Opening the throttle quickly will flood/stall as the needle drops out of the main jet if there is already to much fuel present from the idle jet.

I'll go for a 'close' the mixture screw by 1/2 a turn ... (i'm guessing and not an expert at all BTW).