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Ignition Or Fuel?


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#1 primrose8

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Posted 21 February 2020 - 01:03 PM

Hi everyone, just working on daughters boyfriends mini bought last week off eBay. It’s going to be a full strip and rebuild, but as it’s not running I thought it would be a good idea to get it running and make sure all is fine.
The old chap we bought it of seemed pretty clued up and had engine out, replaced a gear in the gearbox that had lost a tooth, had cylinder head off relapped valves in ,and refitted it with new hose etc, but had never tried to start it.
I quizzed him about whether he had timed it up and set clearances etc and he said he had . Engine turtfreelyvby hand so I put some fuel in and with plugs out and ignition of wound it over to get fuel to carb.
Then tried to start it, did not even try to fire at all. So back to basics, checked valve clearances which were very tight and miles out! Checked points gap again miles out, then did static timing, lined timing marks at 6 deg btdc, no1 on. Firing strike, no 4 rockers rocking so right there. Adjusted timing using a light on low tension side of coil.
Tried it again and it started, but ran a little rough, moved dizzy while running and got it a little better. But it ticks over but if you try to rev it it just dies, as if it’s choked up, or fuel starvation? The choke is off , I’m sure it’s fuel related but not sure how to proceed, the advance and retard vacuum pipe is missing not sure this would make it this bad? thanks in anticipation of any help,

#2 primrose8

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Posted 21 February 2020 - 01:05 PM

Firing order correct

#3 blacktulip

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Posted 21 February 2020 - 01:12 PM

Check the oil in the carb and that the piston in the carb is clean and free to rise and fall. The the float level is correct. You obviously have spark so sounds fuel related

#4 Alex_B

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Posted 21 February 2020 - 01:18 PM

Since it is running I would say ignition is working well enough, checking you have a good points gap is wise however. 

I would start with a basic check of the carb. Pull the air filter off enough to be able to reach your finger into the inlet  and check the carb piston smoothly rises and falls. I would personally also pull the dash pot off and check the fuel level in the jet at the bottom, now would be a good time to check the needle for wear (if you have a spring loaded needle it will be running along the edge of the jet and wear). Also check the throttle spindle doesn't have excess play in it (will need throttle slightly open so the butterfly isn't giving you a false feel) 

I would also pull off the float lid if you have an external float bowl (HS2 or HS4) it is likely a bit silty in there and if so cleaning it out and the jet tube would be wise (Carb cleaner in a spray would work nicely) check the float valve shuts correctly as well as the float doesn't have any fuel inside. Re-assemble, filling the oil reservoir on top with SU own oil, 3 in 1 or engine oil works as well, and see how it runs, you may need to adjust the settings such as jet height (the nut underneath the carb) or idle settings which is done on the butterfly. Once running you can lift the carb piston (theres a lifter pin on most SU's on the left hand side of the body, this will either make the revs rise, or fall which indicates either a rich or lean mixture, you are looking for the revs to rise up slightly then settle down a bit. 


Edited by Alex_B, 21 February 2020 - 01:19 PM.


#5 mab01uk

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Posted 21 February 2020 - 03:08 PM

Seems to be two threads running on this topic so have posted below again?

Has your petrol gone stale or have you flushed through with new fuel?

http://www.theminifo...ni-just-bought/

 

BP - HOW PETROL CHANGES IN FUEL TANKS

"Loss of light components – impact on mixture The light components in petrol are lost first as the petrol sits in the fuel tanks. These components provide valuable octane benefits during cold start. Because they are volatile they compose most of the air fuel mixture during cold start, if they are absent then the mixture becomes lean resulting in higher temperatures, pre ignition, detonation and piston damage. This is generally the cause of piston damage in high revving engines used in boats and small engines such as chain saws etc. The portion of the petrol that remains has a higher density and higher octane but this is not available during cold start resulting in hard starting. Because the fuel carburetors and injectors operate on a volume metering system the higher density means that more fuel is introduced for a given volume of air and so the air fuel ratio is fuel rich. If all the fuel cannot be burnt then it forms carbon deposits that will foul the spark plug and cause the engine to stop and not start. This is generally the cause of problems in classic cars where the engine stumbles and hesitates or cuts out."

More:-

https://www.bp.com/c...hicle-tanks.pdf


Edited by mab01uk, 21 February 2020 - 03:13 PM.


#6 primrose8

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Posted 21 February 2020 - 05:12 PM

Thanks for all the advice, I’ll be trying when I get back home, it has fresh petrol in the tank though not old stuff

#7 blacktulip

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Posted 22 February 2020 - 03:17 PM

I just read that you are trying to rev it with the choke off? Is that after it's fully warmed up or are you using choke to start then pushing it straight in? If it ticks over without choke immediately from a cold start then the mixture will be too rich at idle. Which indicates a worn jet or wrong/worn needle. Try pulling the choke out to get it started and then seeing if it will rev up with the choke out. If it does then let it warm up before putting the choke back in and see how it is then.

#8 primrose8

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Posted 22 February 2020 - 06:13 PM

Went in garage last night thought I’d have a clear up before I started, I pick up a tin biscuit tin full of nuts bolts screws etc, that came with the muni and I spotted a spring, a quite long spring recognised it at once as the carb piston spring!! , took off housing and fitted the spring and filled the dashpot and it started and runs well! Even had a run up our long drive, thanks for all the replies, I have another mini being delivered tomorrow, that will be no 3 the garage is getting full!

#9 primrose8

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Posted 22 February 2020 - 06:14 PM

Went in garage last night thought I’d have a clear up before I started, I pick up a tin biscuit tin full of nuts bolts screws etc, that came with the muni and I spotted a spring, a quite long spring recognised it at once as the carb piston spring!! , took off housing and fitted the spring and filled the dashpot and it started and runs well! Even had a run up our long drive, thanks for all the replies, I have another mini being delivered tomorrow, that will be no 3 the garage is getting full!

#10 blacktulip

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Posted 22 February 2020 - 09:36 PM

Nice one. Glad it's fixed

#11 Alex_B

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Posted 23 February 2020 - 06:18 PM

Nice one, nice easy fix! 






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