I Don't Believe It! (Actually I Do)

[Guest winmoz]

OK, having suffered a misfire and occasional two cylinder running which was fixed thanks to some good, logical advice from this forum (thanks guys), I took the Thing for a bit of a blat today.

On start up it was running very lumpily and sounded like it had dropped two cylinders again and it wouldn't idle. A quick feel of the exhaust manifolds showed that all four branches were hot, but the carb for cylinders 3 and 4 were pi$$ing fuel from the inlet trumpet (not enough clearance to the frame to allow me to run an air filter).

 

Killed the fuel pump and deflooded the carb. Started and ran fine. Drove it maybe 5 miles and then it started to mis-fire (serious bangs, pops and and carb dets) and went back to that, now so familiar) 2 stroke boat impression. Limped back to pits, running on two pots, but where I could open it up beyond 4000rpm the other 2 kicked in and the unit came on strong. As soon as I dropped below 3000rpm it ran rough again.

 

Blocked jets? Need a good balance? A tune? Someone competent to do the tinker (gets my vote)?

 

Any thoughts as to most likely causes (am running twin Dellortos).

 

Cheers

[Guest peter2b2002]

floats?

peter2b

[megadodo]

Does sound the floats need adjusting to me as well! Maybe the valve to seat interface is dirty possibly?

[cb750]

Sounds like float valves to me, had exactly the same problem on my Honda cb750 carbs after complete bike rebuild. Changed the faulty float needles and seats - cured. Don't know if Dellortos have renewable valves though.

[Guest winmoz]

thanks guys. Will have a look and see what the floats look like. Was going to get it rolling roaded in Slough, but will wait until I have got it running a little better - off to find an online manual for dellortos......

[theduck]

Message me your email address and I will email you a PDF. Also check out the section on dave Andrews site about dellortos

[kevin the chicken]

Check that the float heights are all the same, if they are then that rules out float heights as the other carb is ok. Change the float valves if the floats are ok. They can look ok but a tiny amount of scoring or dirt can cause them to stick. I had exactly the same problem with my webers as somebody had decided that the car would perform much better with the floats set higher. Wrong