This is now sounding like symptoms of an air leak, which can nullify all attempts to readjust. Have we eliminated choke slides not sealing? Is it 'racing' at any time? Have we eliminated flooding? Inlet stubs to cyl heads gaskets are good and tight?
Inlet stubs to cyl heads gaskets are good and tight?
They are now but I’m beginning to suspect that there may have been an air leak when I initially set them up and I’ve compensated for it in the adjustment then when I’ve done a periodic tighten up I’ve sealed the leak and thrown the whole lot out of kilter.
Quite possible!
Just a thought as I had a similar problem on my 750 Targa and was eventually traced to a sloppy two into one throttle cable junction box thingy. Only discovered it when I took the tank off to retune the carbs with a vacuum gauge and could see the cable outers weren’t always seating correctly when twisting the throttle. After much re-routing and plenty of cable ties, I managed to get a reasonable and consistent reading. Not totally cured but a vast improvement.
I spoke too soon.
We went out for a ride today and it was still playing up at low revs.
I stopped for petrol and as I dismounted I noticed petrol pouring from the mouth of the N/S carb.
I dropped the float chamber and checked the needle valve. It seals fine if you hold the floats up manually but won’t seal with the float chamber in place.
It looks like I’ve got a porous or leaking float after all so well done to those of you who suggested that possibility.
Always nice when you find the culprit.
I had to shave a few thou off my floats, plastic ones, as they were tight on the pivot points, and causing the type of flooding you experienced. I put it down to ethanol causing them to swell slightly as the carbs had been ok since 1991, certainly for the 10 years or so that I’ve had the bike. When I read about plastic tanks swelling on V7s or whatever they are it thought it even more likely. Of course I could be wrong.
I had to do what guzzi4cats done, my L/H carb. float was sticking between it’s pivot points.
Ditto. But just to mention floats could leak or stick BEFORE we had ethanol too.
Mine certainly did, and within a year of purchase too. Nothing whatever to do with ethanol.
I will report back when I’ve received and fitted the new floats.
While we’re on the subject, I have needed to replace various fuel hoses on a fairly regular basis too ever since me first bike the Bantam, also since well before ethanol.
But it’s always nice to have something new to put the blame on.
This is very true…
OK.
New floats in and float height set (18mm).
No more fuel leaks but the misfire at low revs is worse than ever.
It runs on one cylinder (the right) till it gets to about 2500 revs when accelerating out of junctions, corners or roundabouts.
I’m beginning to suspect an ignition fault here.
I have just fitted two new coils and the bike is absolutely perfect. I don’t ever remember it being this fast.
My coils are mounted under the tank so for 4 years I have been using the compact Japanese type coils. One had obviously started to break down.
The new coils are HT12 type from Electrex World. I hope they fare a little better.
I hope that this is an end to this rather lengthy saga. It has been very frustrating to troubleshoot as it can be difficult to accept that two completely independent problems can occur at the same time. There is always a tendency to look for a single cure.
Thanks to all those who offered ideas and help.
A-ha! Congratulations.