Any chance that either the vacuum or fuel hoses to either the pump or the vacuum fuel tap could be being squished between the tank and frame? Potentially you could have a situation whereby enough fuel is being delivered to the carbs for idle/low load but not enough for high load so it goes lean. Not sure how letting it sit switched off would rectify the problem though.
Yeah, checked that and couldn't see any kinks or places it's being crushed. Have also checked every line and component is clear as well as replacing the vacuum petcock with a manual one previously. The only thing that changed between it running okay-ish and what it's doing now was moving the carbs to get the manifolds off, plus replacing the torn gasket.
Long shot maybe, but these bikes are prone to carb icing. In cold weather the carbs can ice up, blocking internal fuel/air ways and the bike runs like shit with no power at lower throttle openings. If you stop the bike and wait a few minutes it will start up and run fine for a few more minutes. It never happens when the bike is stationary because the heat from the engine keeps the carbs warm enough. There was a carb heater kit available for the carbed Monster and SS bikes.
you definately have a heat related issue in the fuel system side, sounds obv but that would be my focus.. fuel pump overheating? just a good old fashioned pump on the blink?
The first cutting out issue happened on Sunday, temps were well above freezing but granted, my test rides now have all been below freezing. Progress! But not out of the woods. Unfortunately, I broke the golden rule and made more than one change. I found that there was a hose that looked kinked but was difficult to see because of the airbox. It looks to be some kind of breather. It attaches above the fuel inlet on a pipe that runs to both carbs but goes to open air. It was badly routed, so I re-arranged it and swapped to a more kink resistant silicone hose. Other changes were in the carbs. I got the floats out with them in-situ. I could see that when the float drops, the needle sticks a little and doesn't move until the floats pull it down. I bent the hooks slightly on the float needle so that the float pulls it sooner. Probably a non-issue as even a small amount of fuel pressure probably pushes it open, but I figured it wouldn't hurt. Last thing I did was raise the float level a couple mm but I think this was a mistake, so will probably drop the bowls again on the weekend and put it back. It rode now without cutting out but I think it may have been rich. Still didn't like part throttle and opening it up didn't always have the pick-up I was expecting. Adding choke made it noticably lose power. Still, I'll take it for now! How much difference does as exhaust make to the tuning? Previous owner put on some fairly obnoxious race cans.
It can make a big difference. When fitting a ‘race’ exhaust or anything that is more open and freer flowing the carbs will invariably need to have an increase in jet size on both the slow circuit and the main jet. The freer flowing, louder, race (whatever you want to call it) exhaust typically pulls more air through so more fuel has to be added to maintain the optimum AF ratio. Did you check the jet sizes when you had the carbs apart? How do they compare to what they’re supposed to be?
I didn't check but there are extra slots on the needle, so I could raise a bit of needed. It seems to be low throttle cruise and winding open to full throttle that see issues. Wide open higher RPM seems decent.
Reading your recent problems, carb icing does seem to be a probability , my experience with icing is that any temperature of 7 degrees or less can give you icing problems depending on the humidity of the air, if it’s damp or misty it will spoil you ride especially coming off a trailing throttle. The lovely new fuels seem to be more prone to this, don’t know if it’s still available but PRO FST fuel stabiliser used to solve it, adding IPA (isopropanol) does a similar job Next time you’re out on stuttering ride, from a trailing or closed throttle downhill run, pull over and check your carb body’s for condensation on outside, if it’s there you’ll probably find they are going to very cold and the jet internals are icing My personal way of avoiding this is to leave it in the garage until summer !!!!!
Nice one, thanks for that. I finished my direct access course in November. So trying to get out as much as possible to commit everything. I actually have a 2001 Triumph Sprint RS on the way to use for commuting. Hopefully fuel injection will handle the cold a bit better until spring. In the meantime, I'll wait until it's at least over 10 degrees before I make any calls on where to go next with tuning
That’s good that you’ve got an alternative ride, I’ve had my 900ss for the last 20 years and winter icing has ALWAYS been a problem, but as both me and the bike have got older and wiser we have come to agree on a winter hibernation for us both !!!!
Yeah, I'll see how I get on when it's both cold and raining but work says two days a week in the office and the train is £35 a day. Absolutely ridiculous. Got the required certificate to get the Triumph ULEZ exempt and there underground bike parking at the office
You can get an additive to put in for carb icing, so worth looking into that as it's cheap to do and will rule it out
I have an article on overhauling the Mikuni carbs but it is too big to post on here. It relates to the Suzuki GS1000 but the carbs are the same, albeit 4 of them. If you would like a copy PM me with your email and I'll send you a link.
