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Won't Fire Even Though Have Fuel And Spark

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#1 adman020

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Posted 25 November 2023 - 07:15 PM

I have an issue starting the mini which is getting very annoying. The engine turns over but wont fire.

 

It's a 1980 998c it has been in garaged for 7 years - I had it running last month after adding a replacement original fuel pump. Then took out the fuel tank to do some welding and now can't get the thing to run!

 

First I checked the electrics.

I had disconnected an alarm so was worried that it could be this not giving enough voltage to the coil but the voltage was fine.

I then replaced point's (set correct gap)/condenser/plugs/dizzy cap.

I get a spark from all plugs when next to the block

 

I did a compression test which was not great... I will have to tackle this later on. But that shouldn't stop it from firing.

 

cylinder 4: 8.5

cylinder 3: 1.5

cylinder 2: 8

cylinder 1: 8

 

Next fuel
I refilled the petrol tank with the old fuel but mixed a jerry can with some fresh E5.

The carb is getting decent amount of fuel from the fuel pump 

Also added fresh petrol into the carb float chamber and cleaned the gunk out of the bowl
I wondered if it was the float needle so replace that and gasket. The float hasn't got any holes.

Now the HS4 carb seems to just puddle fuel - I don't seem to hear any spray of air/fuel - not entirely sure what to expect with a SU carb.

I removed the spark plugs and they were wet with fuel 

 

If I spray some easy start spray into the carb - it fires for a second - so must be fuel related right? 

Timing is probably way out now which doesn't help so might just set to static timing for now.

 

Is there anything else I can try?



#2 timmy850

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Posted 25 November 2023 - 08:29 PM

SU carbs don’t spray fuel. Assuming the fuel bowl is set to the right level it’s sucked from the jet at the bottom into the engine.

No compression in one cylinder will definitely make it hard to start

#3 bpirie1000

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Posted 26 November 2023 - 08:01 AM

If you have spark rule the immobiliser out.

Certainly carb related from the sounds of it..

Have you got a good spark? If weak then try changing the plugs? Sometimes assists heating the plugs and giving them a clean up.

Start at the start reset the timming and work from there...

#4 Shaun78

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Posted 26 November 2023 - 08:03 AM

Hi if the engine has not ran for years the bores will be dry I would try putting some oil in the bores to seal the rings,if the engine is good it should bring compression up in the cylinders and give it a chance of starting.

#5 cal844

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Posted 26 November 2023 - 01:18 PM

Pour 50ml of oil into each bore, preferably using an oil can

Then repeat the compression test

Edited by cal844, 26 November 2023 - 01:19 PM.


#6 bpirie1000

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Posted 26 November 2023 - 02:19 PM

Wet and dry compression figure will read differntly..

#7 adman020

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Posted 26 November 2023 - 05:14 PM

Cheers all for comments - i'll try what's mentioned, static timing and oil in the bores. Plugs are new. Is there a decent online resource to follow what step to try? or is it back to the Haynes manual? I just don't understand why spraying in the carb autostart would make the mini love it whereas it doesn't like the carb?!



#8 bpirie1000

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Posted 26 November 2023 - 05:56 PM

Cheers all for comments - i'll try what's mentioned, static timing and oil in the bores. Plugs are new. Is there a decent online resource to follow what step to try? or is it back to the Haynes manual? I just don't understand why spraying in the carb autostart would make the mini love it whereas it doesn't like the carb?!


The easy start is so potent that it composts.

The needle which controls the flow of fuel being sucked into the combustion chamber is controlled by the needle.

Stick to the Haynes manual. Always right. May I suggest resetting the carb settings. The needle needs re centring...

Or wind out the mixture to increase the amount of flow 5hrough the carb.

Would also suggest that since there was some build up in the bottom of the fuel bowl clean out the pipe linking the fuel bowl with the bottom of the carb/jet...(compressed air- but only if dry......)

#9 timmy850

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Posted 26 November 2023 - 10:19 PM

Honesty - figure out why you don’t have compression in one cylinder before trying to get it to start

Check valve clearances are ok
Check valves are moving ok
Then take off the head and check the head gasket

#10 greenwheels

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Posted 27 November 2023 - 06:11 PM

Honesty - figure out why you don’t have compression in one cylinder before trying to get it to start

 
Then take off the head and check the head gasket

And valves are OK - not chipped or not seating properly



#11 Steam

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Posted 28 November 2023 - 01:16 AM

Given that it was running recently and now has no comp on no3 I would suggest the old fuel has gummed the valve stems and stuck them open. A visual check under the rocker cover will verify.
A common fault caused by old fuel.

#12 Cooperman

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Posted 01 December 2023 - 05:25 PM

Go back to basics.

First set the points accurately at 0.015". Then set the static timing at c.6 degrees BTDC.

Check the valve clearances at 0.012" using 'rule of nine'.

Check that the carb dashpot will rise easily and falls smoothly with a slight 'click' as it stops. It's always worth removing the dashpot cover and lightly polishing the inside of the cover. Make sure the needle is centred, will adjust weaker/richer easily and that the choke when pulled out lowers the jet assemble. Use 3-in-1 oil in the carb dashpot.

Make sure there is a good spark at the plugs. Then, so long as the timing is not 180 degrees out, it will start.



#13 adman020

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Posted 16 December 2023 - 12:52 PM


Think I found the issue with compression on cylinder no.3! broken valve. I'm going to clean up.


https://ibb.co/BqVJXmK

Valves - Is it worth cleaning up or just replacing with new?
https://ibb.co/r51Cgpg


This is chipped - circled in green - does this need to be replaced?
https://ibb.co/QjPqRg0

#14 bpirie1000

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Posted 16 December 2023 - 06:01 PM

Certainly think you need to flush your coolant out before your running that anywhere far away....

I would also say and question what is going on between cylinder 3 and 4 on the first picture.....?..clean up the head and check it all over before spending much more time on that.?


Not so bad on the last picture you attached...

Edited by bpirie1000, 16 December 2023 - 06:02 PM.


#15 timmy850

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Posted 16 December 2023 - 07:59 PM

If you are replacing valves it’s ideal to get a full head refurb. If the valves are that worn, it’s likely the valve stems are worn and the seats will be past their best too

IMG-9964.jpg

IMG-9969.jpg

IMG-9968.jpg





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