Missfire - a lot - intermittent

3.5 on carbs, running on what sounds like four cylinders, then switch off and start a few minutes later and she goes on 8 for a bit then back to four.
If it was plugs then she would do it all the time I think, I've had a look at the dizzy cap and it's pretty new, rotor is new, so I'm thinking maybe a carb is causing the trouble but a quick whiff of easy start dosen't see it going on eight again so maybe not petrol.
Started it on gas (I'm on fumes) and it went on eight, switched over to petrol and it went on eight for a bit then back to four.
Cant make my mind up as it's been stood over a year (fresh petrol as it ran out) with the occaisional start up for a few minutes.
Plug leads are not very old and I gave the carbs new oil and a good dose of carb cleaner.
Writing this now it seems to be that a carb is causing the trouble, fuel pump or maybe sticking float valve not letting petrol in but open to suggestions. Thanks......MOT next week so will put some gas in when I get insurance sorted and try that.

my recently purchased lightweight was running rough for a while, its been laid up for 12-18months prior to me buying it. it wouldnt idle right and cut out and all sorted, but the more i started it and run it, the better it got. It now starts turn of the key, doesnt need so much choke. Eventually I used up the remaining (presume stale) petrol (about 10L)and put fresh in, didnt like it at 1st, but its sorted now. Not fiddled with anything (dont know what im doing) so i wonder if your is just sooty to. Run it on fresh petrol for a bit, leave it warm up and idle, see how you get on.

Just my (limited) experience

Griffdowg said:

my recently purchased lightweight was running rough for a while, its been laid up for 12-18months prior to me buying it. it wouldnt idle right and cut out and all sorted, but the more i started it and run it, the better it got. It now starts turn of the key, doesnt need so much choke. Eventually I used up the remaining (presume stale) petrol (about 10L)and put fresh in, didnt like it at 1st, but its sorted now. Not fiddled with anything (dont know what im doing) so i wonder if your is just sooty to. Run it on fresh petrol for a bit, leave it warm up and idle, see how you get on.

Just my (limited) experience

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I'm thinkin that may be the case, new petrol in now as it ran out but still the same so I'll clean the plugs and scrape the contacts on the dizzy cap see if it improves, if not the carbs may have to come off.
I'll see how it runs on gas when I get the MOT booked.

just had the same prob on mine put a new dizzy on £7 from motor factors then under neath there is a lil nob which i brushed my hand against it was loose so turned it a few times and it runs perfect

Soooooort ed

Started her up today on choke and she fired instantly as usual, after a few seconds she dropped onto a few cylinders. PETROL I thought so switched over to the gas I dont have (empty tank on fumes) and she went on to eight cylinders sweet as anything.
Ran it at tickover for a bit then blipped the throttle and switched over to petrol. Back to a few cylinders again.

So , I thought, there must be a problem with the carbs or the fuel pump.
Next thought was the K+N type filters I put on whilst the 110 was laid up may be weakening the mixture by supplying too much air so I gave the carbs half a turn rich each and fired her up.
She started on eight and ran like a dream, tickover was high but soon sorted that, now she ticks over smooth and even at 800rpm and is responsive to every blip of the throttle.
Drove round the field ok so I'll leave it as is until after the test tomorow and then tune the carbs after a good run.
I recon the needles are fooked by running dry on gas and the previous owner has weakened them off to compensate, thats ok but at low revs it has been very weak and rich higher up. recon its time for new needles and jets as soon as.
I'll get through the MOT tomorrow on gas and if nessesary weaken the carbs off a bit.

weak mixture then:doh: