During the summer the old Darmah had an occasional habit of spitting back on the front pot. It was never too much to be that worried about and as he was running like a train I put it down to 'character' and they all do that sir. Now the colder weather is here he's doing it a lot more, especially when starting and taking a number times to turn over before it does start. This sort of does make sense as spitting back is often indicative of weak mixture but still doing it when the carbs are tickled enough to flood? I've given it a quick once over to check for any leaks around the carb/inlet manifold and nothing is immediately apparent. It's running fine once it does start and a plug check shows a nice biscuit colour so the main jet is ok. So I'm now thinking pilot jet or can the same symptoms be apparent if the closing valve clearances are too loose, especially the inlet? Any thoughts on a postcard are most welcome.
its usually sign of an air leak , check your manifold rubber, maybe spray a little carb cleaner round it with the engine running and see if the revs increase
one other thought thats cheap to try, it may be running weak on the front. Std mixture screw set is 1.5 turn out but try taking it out to 2.5 or 3 turns out which is the equivalent of going from say a 60 pilot to about a 65.
Thanks guys!! Charged the battery & then took a run out to get some carb cleaner. When starting from cold I usually flood him, turn him over & when he catches, give it a little throttle and he's off and running. Now, any throttle will cause it to bang, pop & die so it took quite a few turns & faffing about before it fired. It even took a few spins & a pop or two when it was left for 5 mins or so when I was in Halfords. Once started it still runs lovely and will settle to a regular idle when warm. Spraying with the carb cleaner made no notable increase in revs and at the same time I balanced the carbs, which included setting the mixture screws, but nothing was untoward. The 40 mm bad boys fitted to the bike don't come with a choke circuit - hence the ticklers for flooding. But any leaks in any of the other circuits have hopefully been checked with the above carb cleaner check. This is going to be my next line of attack as the motor has new valves, guides with the seats lapped/ground and I haven't checked the clearances since I first shimmed it up two summers ago. The front pot was close to the limit of bore/piston wear but I can't believe that (or more wear) would cause these symptoms - or could it?
I get that you balanced the carbs but did you wind the mixture screw out to 3 turns to see if that cured the problem ? If it does its not a permanent fix but it says your pilot jet is too small.
I'm not sure that I did... just the usual moving of the mixture screw to find the highest idle. Which landed at the 1 & 1/2 turns of spec. But as you say it is a check that costs nothing so next time I fire him up I'll give it a go.
Hmmm.... progress. What had bugged me is the hard starting/spitting came on sort of suddenly and I supposed it might have been the colder weather. But what about a blocked jet or some such? so I removed and cleaned out the carb and there was plenty of gravel in the inlet filter plus plenty of finer stuff in the bowl but no obvious pilot jet blockage. So in a non scientific experiment I tried again this morning, without adjusting the mixture, & he fired up pretty much on the first spin. There was still an occasional spit so I adjusted the mixture as per Paddy's recommendation and all was good. I reckon the idle jet is just on the limit of leanness. Looking at my scrabbled notes from the rebuild it looks like it originally had 65s but I changed them for 60s when adjusting the carbs because of richness. Now I never throw anything away but can I find them amongst all the other stuff I never throw away...
With that sort of debris in the filter i would check the tank filters on the taps as well, looks like you have some rust going on in the tank.
Will do... a job to add to the list of winter maintenance. I did get the inside of the tank coated (by someone else) during its refurb so if there is any rust I'd like to think it's only in small patches.
