Any ideas on this carb spitting back would be welcome as I've run out of ideas. It's a 79 Darmah. I've not had this bike long and effectively bought it as a non runner. Rebuilt the carbs and set them up a few times now, the bike runs perfect except for the front cylinder spitting back thru the front carb at 3500 to 4000 rpm on gentle throttle openings like changing up gear or accelerating gently thru this rev range, it will clear with a handful of throttle. Up to 3500 is perfect and pulls like a train with a handful of throttle, Plug is a nice biscuit colour, I've checked for air leaks, valve clearances are spot on, I've checked the valve timing, over 150 psi on each cylinder, I've swapped the plugs over also the coils, leads and igniter boxes trying to eliminate everything but still spits thru the front carb, today I swapped the carbs over and it still spits thru the front one so eliminated the carbs too. The only thing I can't check is the ignition timing but can't see it being that ?? but I'll probably get Tony Brancato to set it just to be sure. Rear cylinder runs perfect all the time. Anybody shed some light?
Hi Dave, the bike runs and rides great, I've done 200 miles on it now, I'd just like to sort this spitting back, I can't see it being ign timing but something else to eliminate. Funny it's only ever the front cylinder. Regards
I found my 1980 Guzzi LeMans 2 would do it, if the carb slides didn't open or shut together at the same moment.........It was like one cylinder was trying to slow or pull the other.........It was only the tiniest of difference..............Basically unbalanced as one was shut and the other still open a bit. Luckily with the Guzzi you could stick a mirror on the frame where the seat fitted, and then turn the throttle while looking in the mirror............I reckon it would be harder on a Darmah.
Uncle Steve will be along to help get yr problem sorted. If he can't find a solution/word of advice no one can.
Thanks for that Arquebus, carb synchronising is something I've already done. I'm going to try one of the original k4 needles in the front carb as previous owner changed them to k5's which are a tad leaner, worth a try.
I also had a lot of trouble with my LeMans from new as it would occassionally misfire on one and then the other cylinder.... ...the dealer and the importers changed leads, plugs and points at least four times but it didn't cure it.......... .....I noticed that it only seemed to be in damp atmosphere but not when raining and soaking wet........... .........eventually I took the coils which had been tested OK several times; to an auto electrical specialist........... .......they wrapped the coils in damp rags and then tested them........the sparking and tracking across the tops and down the outside was really bad.......... So I changed the Magnetti Marelli ones for Bosch and it was perfect after that.....why only damp and not wet, we don't know.
After checking out absolutely everything it turned out the previous owner had replaced the needles in the carbs with the wrong ones, correct needles in and now runs great with no spitting or misfires. The bike has been serviced inside out now so all turned out great..
Being out in the breeze more, I can understand why the front cylinder would run consistently cooler but why would it run consistently weaker?
The k5 needles are slightly leaner at small throttle openings, replaced with k4 and that little bit made a big difference to the front cylinder. The book doesn't quote a needle for the Darmah with 40's , guess it must be different to the ss mhr etc as it has air filters and different heads. As it turned out all the original jetting was spot on.. The front cylinder actually runs hotter than the rear as the front mudguard deflects the airflow from it. I guess that's why the front likes to be slightly richer.
