Do the carbs not have a heating line? - the 97 900ss has a oil line that heats (only a little bit!) the carbs to try to eradicate the common icing problem.
Nope, I believe that was either for specific markets or an option. Took the bike out. I think it may be running rich. I'm going to drop the float level again, that was a mistake.
Finally getting somewhere. Dropped the float level back down and rode last night. Better but not great. Started at 3 turns on idle screws and went up to 4 but still wasn't good. Felt rich and it's also hammering through fuel. Today, I turned it down to between 1.5 and 2 and it's much happier but still not perfect, any lower and it start to get worse. Still very lumpy at very low throttle cruise and hesitant to pickup if you wind the throttle open. Once it gets up, it hauls arse. Idle is also erratic. If the bikes is switched off for even a minute or two, it idles good but when hot, coming to a stop it will idle low and die. Setting the idle higher means it idles too high at other times. Will check for air leaks again but I didn't find any after replacing the gasket, though I still wasn't able to get the carbs perfectly synced. Maybe it's just the cold and I shouldn't read too much into it until it warms up? Where to from here? If anything, it seems it's getting too much fuel, rather than too little.
Is it worth fitting one of these? https://www.ebay.co.uk/itm/22287953...kQNleNGTy2&var=&widget_ver=artemis&media=COPY Bike has an SC Project exhaust and stock filter. There's also stage two but would something like a K&N panel filter be enough to justify another step up? I've also seen people cut holes in the airbox lid. Does that actually improve anything? https://www.ebay.co.uk/itm/22287953...kQNleNGTy2&var=&widget_ver=artemis&media=COPY Edit: Thinking about it. Pretty confident I still have an air leak somewhere. Where else should I be looking on the carbs? The idle mixture needles were replaced and got new seals but maybe I made a mistake there? Does the float need draining to remove them? Also, that Silkolene FST stuff seems to just be isopropyl alcohol? Already had a bottle of that...
FUUUUUUUUUUUUUUUUUUUUUUUUUUUU!!!!!!!!!!!!! Read something about Mikunis leaking air past the idle jet. Pulled them and sure enough, one oring had a nick in it even though they are new. Lubed them and put back (don't have new ones that small) but also capped the screws off to seal them. Fired it up and it idles way better, was also able to get the balance closer. Go for a ride and hot damn! Feels almost fixed! Ride a bit further and it starts to get worse. Figured I need to pull some fuel as it's possibly too rich when hot. Stop to see fuel absolutely pissing out one of the overflows. Ride it home as inefficiently as possible to try slow the leak. Got it upright and smacked it with a soft blow. Seems to have sorted it but still the odd drip. Still going to have to pull the float and clean everything. Maybe give the needle the lightest smidgeon of PTFE grease? I don't know how this bike does it. Literally every time I fix something,. Another problem arises at the exact same time. I'm gonna believe that maybe I kicked someone's dog in a past life or something as I don't see any other reason.
Gotta salute you for your calmness, patience and persistence. I would have been tempted to have kicked or thrown something by now.
I hate carbs . Thank goodness fuel injection came along. I had a similar issue on a bank of 4, couldn't get the bike to idle cleanly it was always a little lumpy. Also the fact the revs didn't drop quickly enough when the throttle was closed indicated there was an air leak and it was running lean on the slow/idle circuit. I must have stripped those carbs down 3 times and rebuilt them but I never noticed the very slight damage to the o-rings until the final strip down. Lesson learned. I since bought a magnifying glass and made myself a promise that the next person who wants the carbs on their 25+ year old bike being balanced or some carburation issue sorted is going to be told I'm not doing it unless I can completely and utterly strip the carbs, including separating them, and fit new o-rings, gaskets, jets, needles etc etc throughout. Yes, it will add expense (time and parts) to the job but otherwise I've learned I could be chasing my tail. Those o-rings do go brittle with age IME.
Yeah, I sprayed the rest of the carbs I could get to to see if there were any other leaks but had the airbox on, so will take it off and also spray all the bits in the middle. I'm also going to keep those screws capped. So, issues thus far: Plugs Manifold air leak Idle mixture airleak (though that may be my fault) I have a bag of 10 o-rings on the way.
You just reminded me of something I meant to purchase ages ago and forgot about! While a friend with some rather useful engineering skills was teaching me how to make a headstock pin for my 959 I couldn’t see well enough to do the job. He handed me an inspector gadget looking headband with a bunch of lenses attached and it was perfect for the job. There’s loads of cheap Chinese ones on the market but I think I’m going to give this one a try - better for keeping both hands free than a traditional magnifying glass! As long as you remember to take them off before answering the door……….
Took, the float apart and couldn't find anything wrong. Cleaned it all and put it back. Went around the corner for fuel and it started pissing out the overflow again. Rode back around the corner home and it had stopped. Went out for about 45 mins and seems to be holding though was back to riding fairly bad. Checked the float level when I got back and it's a few mm high. Will have to take it apart again and re-set it. Guess my bend wasn't enough last night and it's gone back.
Been following your post on this, and if you’re removing the carbs to adjust the float heights it might be worth you checking this filter that’s originally fitted at the fuel to carb inlet, if it’s still there it might be either partially blocked or dragging some debris down the fuel feed if it’s disintegrating, it’s best just to remove it and rely on the main fuel filter Just remember that you don’t have all this fun in the garage with modern bikes, you’d have to sit in and watch the telly with her indoors
Thanks for that. Can't remember if I looked at that or not when I rebuilt them. Might see if I can get it off in place. I replaced all the screws with cap heads when I rebuilt the carbs, so it's pretty easy to get the floats off with just the airbox moved out of the way.
Today's findings. When cold, float levels are where I set them, roughly at the bottom of the bosses on the side of the carbs. When hot, they rise to about half way up. When cold, the choke works as expected and the bike idles pretty well. When hot, even a little choke noticeably... *Ahem*... Chokes the bike and it also stalls at idle. I started riding and it rode really well, no hint of lumpiness... For about 200 yards when it lost all power. Immediately realised I had left the petcock off and set off again. Lumpiness came back into it. I think I'm going to lower the float level a decent bit, so that it's around the bottom of the bosses when hot.
So, dropped the float levels but struggled to get them even this time. The bike ran on one cylinder for about a mile but interestingly, that cylinder was pretty smooth. Second cylinder kicked back in at which point it had lumpy cruise again. Questions are: What's the likely culprit for running too rich? Worn needles or someone putting in oversized jets? I can't imagine the exhaust would cause that? Why does it run well when I forget to turn the petcock on but still doesn't run right with the float lowered? I'm going away for a week, so it will be parked. Should I just order a jet kit for it when I get back? Are there any likely culprits not jet related? Should I go with stage one or stage two dynojet? Appreciate all the help so far. I have another bike I can ride now but I want to get this done. If I park it up, it'll end up sitting while I sort other projects.
I've been following this thread with interest . I admire anyone and everyone who is determined to track down the root of a problem ...... to the bitter end if necessary .... So more power to you mate ..... do not chuck in the towel ! Sadly , I don't have any useful suggestions ..... but I fully agree with you in still being suspicious about possible air leaks . They can cause all manner of weird symptoms which can sometimes be contradictory . @West Cork Paul posted some useful photos of small "O" rings , above , which he politely describes as having " very slight damage ". Personally I'd be thinking totally and utterly ruined ( I was going to use an "F" word there ) My point is that there are often quite a few of those little buggers inside carbs . Are you regularly looking at your plugs ? They can sometimes tell useful tales , but reading them can be a bit of a Dark Art ...... as with tea leaves .
Cheers, I appreciate it. I've replaced the o-rings (again) on the idle mixture needles and also capped them. So I doubt it's coming from there. I'm looking at jets because it's hammering fuel in. I would imagine most air leaks would result in a lean mixture, unless there's a circuit there where a leak causes a stronger signal? I may run it without the airbox and spray in between the carbs. I'm not seeing a leak from the outside or the manifolds now. Also, if I bought new float levels, are they pre-set correctly or generally need adjustment? If I do need new jets, I might replace the levels just to make sure my tinkering doesn't have an effect. Edit: Been cleaning the plugs. They come out pretty black
Not sure if I'm right in saying this, but when you've got the problem sorted it might be worth changing the engine oil? I had an issue with a big V8 in a TVR years ago - rebuilt the Holley carb (wrongly ) and petrol just poured into the engine... Needed a rebuild after that...
