Carbs overhauled......re-assembled, back on bike with clean engine bay (for a change).....everything back together (I didn't forget anything George......the hardest thing to do was get the airbox jubilee clips done up nicely, but no cut hands). Battery charged......switched on ignition and let the pump run, to fill the empty float bowls; put the choke lever on, pressed the start button.... .........Brmmmmm! First time...... But F-me, it is still doing what I took the carbs off for in the first place..... Ticks over at approx 1050 - 1100 rpm. Carbs generally balanced OK and pull together (by ear that is)...... ......but then suddenly at low revs, just above tickover say, 1300rpm, it goes a bit lumpy and will spit in the airbox once or twice.........also had one minor spit in the exhaust. .........a tiny bit more throttle above say, 1500rpm and it suddenly picks up as it always did. Any clues? AL.
Ummm....air leak somewhere into the carbs or inlet...if carbs have accelerator pump, split rubber. You'd probably have seen the latter during the Carb overhaul though. Prob worth renting some carb balancing kit to rule that out.
The symptoms are exactly the same as what they were before I removed the carbs to check them over........ The bike was running perfectly alright and then the problem occurred overnight, so unless the balance screw turned while I was asleep, the balance of the carbs shouldn't have altered. There are no fuel leaks or manifold rubber splits....... ......if it was excess air on the engine side of the carbs, I would expect it backfire in the exhaust (I think)....spitting back in the inlet side of the carbs I thought was excess fuel (but it does remind me of old british bikes spitting from the carb because the advance and retard lever was incorrectly adjusted) ....timing belts are AOK and don't need adjusting..... I have never had a failure with NGK plugs and caps so I discounted them as being the problem; but I am about to change them temporarily....I suppose something could be breaking down at low revs.... The only thing I recall before the problem started, was that I changed plugs and leads about a week beforehand, but it ran OK after that...... And....what an effin awkward place to stick the pilot screws, tickover and synchro screws........can't get at them.... Why? because although I spent a while fabricating a lovely long screwdriver (18" approx); that of course will only work if I am prepared to stick it through my oil cooler..... ....move the cooler? Nah....oil cooler pipes and carb heater pipes don't allow enough movement......I reckon I will have to disconnect the cooler and join the flow and return pipes..... AL
Had trouble with my 750m last week after a rebuild (bought as a basket case)when I first started it sounded flat on one cylinder then started spitting through the carb at low revs then finally popping in the exhaust, checked valve timing ignition timing changed coils and igniters finally traced it to a faulty pickup coil, then a couple o days later would not start a faulty fleabay bought "getridoem" plug pulled out an old set of std plugs from the bin gave them wire brush started first stab o the button. Driving throught the village still a wee bit rought on a whisper of throttle so have sent away for a set of factory pro needle jets. I cleaned the carbs with an ultra sonic cleaner and I had also fitted a stage two dyno jet kit as well. p.s. it had also been running rich, dyno jet suggested setting the mixture screw to 3.5 turns out each time I have taken it out have been gradually screwing the mixture back in now down to 2 3/4 turns out but have not been out again since as the snow has just cleared !
What are you saying was the problem....spark plug or pickup? How did you establish it was the pickup coil if it was that? Just by changing things? Did you notice that the exhaust note at the outlet of the cans started to sound odd on tickover? Sort of like a splashy note? If you are getting Factory Pro Needle jets (I got ordinary ones) do yourself a favour and send your Dynojet needles off to DJ....they do a free exchange service for needles. Have you got the DJ fitting instructions? I have Stage 1 & Stage 2 direct from DJ.....definitely says 3.5 turns out in both. Also, the 750 and 900 SS DJ needles are the same. AL.
I changed the pickup which resolved the popping in the exhaust.I changed the plugs due to it not starting but when I checked if the plug was sparking by earthing it out on the cylinder head it gave a better spark than the set I fetched out of the bin but under compression it would not fire up, I tried them back in after it started using the old plugs but it still would not fire, had a similar problem with my SS using iridium plugs. The exhaust note on tickover was more like 8 stroking firing every other beat. Why would I exchange the needles they are new or are the needles a different taper to suit factory pro jets? Yes I have the instructions but with running rich I was thinking it may have been due to worn needle jets as I have an open air box and a free flow exhaust.:wink:
I had better look at the pickups then after plugs and leads...... Mine runs fine at tickover and much higher revs......it is just above tickover when it intermittently occurs which makes it seem like the carbs are out of synch. I think it is generally the horizontal cylinder that is the culprit and it is hard to tell if the 'backfire' is in the airbox or just in the exhaust just in front of the head (doesn't really backfire in the can)..... I'm actually wondering now if when I blew the carbs out at 100 psi if I have forced a bit of crud into the pilot jet holes, but then if that was the case it would always do it. Apologies......DJ needles seem to wear standard emulsion tubes fairly quickly, but the needles do wear eventually......but yours are new (missed that). Fac Pro emulsion tubes can take the wear better than the standard brass ones. I have no trumpets on the airbox and Laser zorsts, basically straight through......It was all running fine until I changed the HT leads and caps (new) and I made a real good job of them, but maybe I disurbed something in the coils or the igniter box thingy (whatever that does). PS...I forget.....do I have to drain oil to remove the case/cover over the pickups or is it a lean it against the wall job? Thanks Sam..... AL
Mine was popping in the 1/8 throttle position range which is where the needle runs on tickover it did sound if the carbs were out of balance one cylinder stronger than the other. Keep a look out at I think it was Lidle they were selling ultra sonic cleaners for £20/£30 I picked an industrial one up from a guy that had no use for his anymore and was taking up shelve space. I was amazed at the muck that came out of the brass items, jets and emulsifier tubes even after cleaning them in thinners my Pantah carbs came up like new and they had been kicking around in the workshop for 20yrs I was using a seaweed extract solution but have been told fairy liquid works just as good. Don't do as a mate tried by using a metallic container and strapped a sander to it popped his carbs in with some petrol, lets just say it took the hairs off his erse! As for the oil I drained it into a clean container it had only done thirty miles, the jacobs crackers never did taste the same after that.
Just remembered I contacted the guy I bought the bike from he said he had a missfire once and traced that to a loose connection on the igniter box have you tried changing them around to see if the problem jumps to the other pot.
I have just hauled the carbs out again........ Having checked electrics over and found nothing abnormal...... .......apart from a wire to one of the ignitor boxes is showing a tiny area of wire through the insulation which is close proximity to the underside of the tank, but I don't think it has been shorting out....no black carbon tracking anywhere......... Checked compressions....145psi when cold and throttle closed........ 175psi when hot and throttle open (warmed up stationary). I turned my attention to plugs, plug caps and leads.......changed for others rather than swapping around..... .....tried brand new Champion plugs, but the spark isn't anywhere near as blue and fat as the old NGK plugs....no change problem still there.... Horizontal spark plug hardly any carbon on it......Vertical, covered in black soot..........so I reckon it is still carbs. Had another look at the float valves.....almost invisible wear marks on both float needles, roughly only half way round them...... I suppose they could rotate so the wear points in the valve and on the needle allow some excess fuel to pass......and getting the odd drip from the overflows (mainly one side) but I think there is some chance the hot engine causes some expansion in the float bowl and pushes a few drips out...... ....so I am going to change the floats and the valves. Had a real good look at the pilot screws and noticed that one was tighter to turn and the spring was about a 1.5mm shorter than the other......I have a feeling previous owners may have had a fiddle (possibly when the Dynojet kit was fitted) but because one pilot screw was tight maybe it was overtightened, then slackened off by another mechanic some time later.......might have allowed the O ring to drop off it's seat and allow air in......I did notice petrol residue on the spring, screw, washer when I cleaned the carbs up the first time. had another close look at the diaphragms and although I doubt they would affect the low rev running and they whip up nice and fast when I whack the throttle open, one of them appears to be slightly pitted (and porous maybe) around the fold, so I guess they are worth changing too. What a palaver.... And then I noticed a carb heater hose was leaking between the hose and the union crimp....see 'WANTED' If you hear a big thump next week, that's a sledge hammer into the tank....... (I get like that) AL.
You can have my carb heater hoses if they are still lying aroung for the price of the postage I junked my set. Long shot did you re-set or check the float heights I think I re-set mine to 14mm.
Hi Sam......Yep, I did set the float heights....and in the distinct absence of getting a specific dimension from anywhere (sssshhh! it's a Ducati secret) I set them to 14mm as well.....(or they may be nearer 13mm).....but considering it had been running 'properly' with them at 12mm and 9mm, 13mm should be somewhere in the right field. Thanks for the offer; if you really don't want your carb heater hoses, I'm happy to relieve you of them (mine actually work) although I only really need the one short one to the tap.......PM coming......assuming my WANTED request hasn't already got several winging their way to me as we speak. AL
Cheers, Sam.....Many thanks......(Might be a bit ambitious to think Royal Mail from where you are to me is that good).....I might get the d*mn bike back together this weekend..... AL.
I haven't done any work like this on carbs for years and when i did it was mostly on cars. One thing that I found invaluable was a colour tune plug which would let you see the colour of the flame on ignition. Sounds like tht would be useful for you cos you could pinpoint the mixture issue (or misfire). Trouble is I dunno if they ever did them for bikes.
Always used to use a Gunsons Colortune plug on my Guzzi.......in fact I used two at the same time....easy peasy......F-knows where I put them though....and I'll bet the thread size is different...... ....but the problem I have is intermittent, which means it can't really be mixture, otherwise it would be like it all the time.....which is also what I would expect from ignition electrics..... .....this problem literally occurs within 10 seconds of being alright....and then a few seconds later it's alright again.....a bit like something floating around and getting caught in a jet and then freeing itself until it gets caught again..... I'm replacing the floats and valves just in case the float needles are turning in the incoming petrol flow, until they meet a wear point, so they let a bit too much in. AL
Ah, at least you know what I'm talking about then! I feel your pain here - intermittent faults like that are a b@stard to track down!! The thing about Dukes is the vibration is constantly moving things around which makes things worse. Short of replacing everything it does sound you need someone with some diagnostic equipment to pinpoint the problem i.e. Electrical or mixture. Once you've done that you'll be half way there.
Sam has sorted me one Pablo, thanks.......unfortunately we are relying on Rotten Moll to deliver it....not seen it yet........ AL.
