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Hi, I have some background experiance working with motorbikes but this one has me. Basicly the bike had been sitting and when started would have a really big flat spot below 3-4k revs. So I thought the pilot jets might be blocked so stripped them and cleaned them. No success, so tested it for airleaks with carb cleaner, there was a slight leak so used hylomar to seal the metal to the block. No change, then replaced the air filter, improved it slightly but still ran like crap on the bottom end. I've played about with the mixtures and just left them at 2 turns out, it now has a new mental problem. When you try to start it, it won't start unless you have no choke and full throttle! It has to be held at full throttle just to keep it idling, it only runs on no.1 cylinder, when you turn the fuel off after a while when the floats are emptying it suddenly picks up on all four and runs beautifully! It then obviously stops when fuel runs out but if you turn the fuel back on then it only runs on one cylinder, its bloody annoying!! This led me to think it was the float heights, set them to 11mm stuck it backtogether and nope still crap. The strange thing is without the airbox it runs on all four fine, pickup is still a bit crap. Its a L1 model, standard jets and micron end can.
Please help as its got me stumped!!
Dave

sounds like its overfuelling heavily.

is the pump constantly running?

Yes mate, it seems to me like the pump is on constantly, new pump then?

You started with an annoying flat spot....................and after all that messing around and fiddling with things you now have a bike that only runs on one cylinder.................................?

I'd go back to the start....................return everything to where it was before you touched it and double check everything as you go.

That way you'll have an annoying flat spot..........................

Sounds more like fuel shutoff needles or needle housing o ring seals.

Hi,

Best thing to do is to go for a nice long run around town and up and down some A roads to use the full rev range on the bike. Get home and whip the plugs out and check the condition of them.

If you can, PM or email me of a photo of all 4 plugs or even post them on here. I'm pretty toad hot when it comes to carbs.

Regards

Rich

Cheers for the ideas, this is driving me round the bend. Right, so it's definitely not the fuel pump, checked with a pressure gauge and it does switch off. So I took the spark plugs out, and guess what, black as you like so I cleaned them up, several times in fact as they keep getting black everytime I run it to see if what I have done has changed anything. I've checked the float heights several times, the float valves for wear, all the jets for wear, cleaned the air jets, checked the diaphragms and needle jets. The float bowl o-rings are fine, checked the filters underneath the float valves which are fine. None of this seems to make a difference, still runs like a dog and only on full throttle when all back together, but when the airbox is left off it'll rev although it will still die if you let it idle for more than like a second.