Bike bogs down at 60

[Kookas]

Just replaced chain and sprockets and after 20 or so okay miles it's now bogging down at 60. I assume it's to do with the things I fitted but perhaps not?

[Watcher]

Unless you changed the gearing, I would say it has nothing to do with the chain and sprockets.  Usually this kind of behavior is related to intake of fuel/air.

Can you give us more information?
If you drop or raise a gear to change RPMs does it behave differently?
If you put on the choke while experiencing the issue does the behavior change?

If it only happens at 60mph +/- and never at lower speeds, it could be as simple as the air box drain line being damaged or routed wrong and it causing an airflow issue as a result.


Try this as well.  If it will bog consistently, let it bog for a bit, clutch in and stop the engine with the cutoff switch, and come to a stop on the side of the road.  Pull a spark plug and see what color it is.  If it's white you're leaning out somehow, if it's dark you're enriching somehow, if it's toasty brown the issue probably isn't related to the intake.

[Kookas]

Actually, did 175 odd miles down to Cornwall today and it was just fine. Don't know what was up yesterday, maybe I mistook wind buffeting for something else.

[Kookas]

So, new update. Since then, did another 300 miles. Problem reappeared three times: first, the engine simply sputtered, slowed down and then caught itself back up again for another 40 miles. Then it sputtered, stalled and I had to pull over, at which point I got it to turn back on and then it ran just fine (no loss of power or anything like that at all) for the next 160 miles or whatever it was I had to do to drop my girlfriend off at the airport (so I couldn't go home or whatever until I had dropped her off, had to keep going at all costs).

Finally, 60 miles into the journey home from the airport - again, no signs of anything wrong for those 60 miles, no issue starting it, no power trouble, nothing - the bike suddenly starts to sputter again, lurching forwards until eventually it stalls out, and I'm forced onto the hard shoulder.

I was just maintaining 70-80mph as I had been doing for the many miles prior to when it happened, not really changing the throttle much aside from hills and the like, when this happened.

Stopped there on the shoulder, it struggled to start for a brief few moments, but then I got it to start again, got it back up to motorway speeds (again, no obvious trouble accelerating or anything like that). This time, it started lurching and then stalled almost straight away after getting to sort of 50ish mph. Did the same thing once or twice more on different petcock settings (RES, ON, PRI) to no avail, called it quits and called in for a rescue.

The bike starts just fine, doesn't sound funny or anything, and I can rev it no problem, it seems like it's just when it starts to get going. Worst thing is, it's hard to test - I live in the middle of a British city (read: traffic, pedestrians and speed limits) and my only hope of getting it to speed is a few miles away. If it fails down there it'll be a long walk back pushing the bike.

Anyone know what that could be?

Oh, I also tried putting the choke on, downshifting (was in top gear when it happened), using more or less throttle, none of those stopped or even really changed the lurching and then stalling.

I'm going to pull the plugs and see what those look like too, but perhaps someone knows what that sounds like.

[sledge]

Does it feel like its missing?.....or like its being starved of fuel?

Those vaccum operated fueltaps can be unreliable and the ignition pickup coils can develop intermittent faults when warm that will give the symptoms you describe. You need to try and identify if the problem is electrical or fuel related and try to narrow things down.

Try this next time it happens, pull over and open the fuel cap. If the issue goes away the vent is blocked. Long shot but its quick and easy to do. Also check the pipe that runs from the back of the valve to the carb. If this can't hold vacuum it will prevent the tap functioning directly.

[Kookas]

Does it feel like its missing?.....or like its being starved of fuel?

Those vaccum operated fueltaps can be unreliable and the ignition pickup coils can develop intermittent faults when warm that will give the symptoms you describe. You need to try and identify if the problem is electrical or fuel related and try to narrow things down.

Try this next time it happens, pull over and open the fuel cap. If the issue goes away the vent is blocked. Long shot but its quick and easy to do. Also check the pipe that runs from the back of the valve to the carb. If this can't hold vacuum it will prevent the tap functioning directly.

I remember I'd googled the problem at some point at the airport and saw the fuel cap thing, and then when it broke down I tried opening it but it hadn't worked. I'll try to check the vacuum hose, should I be able to see if it's damaged just by looking at it under a strong light or would I have to take it off to test it?

Also since running it on prime changes nothing, wouldn't that say it's not a vacuum problem, or could it still be?

[gruntle]

If it's intermittent then that suggests crud in the float bowl to me - stuff wafting about and every now and then clogging things - long journeys at steady speeds then bogging points that way. Check floats not sticking, check fuel filter (if fitted)...
Good luck squire...

[Kookas]

I drained the float bowls earlier today actually. Have yet to test it and see if that solves anything. No fuel filter (did buy an inline one but then I heard the GS500 can struggle to get the fuel it needs through them so never bothered to fit it). The stuff that came out of the bowls looked like just petrol to me, but I dunno, maybe it's hard to actually see even if it's there?

[gruntle]

Meant to suggest draining bowls (had a Guzzi that suffered badly from water intake thru bell mouths!)
If there was crud there you'd likely see tiny brown flecks in the drained stuff, but if you've got the patience (and float bowl gaskets) then a carb clean might sort it - my float valves were seriously iffy last time I pulled my carbs so put it on the list of possibles. My bike has no filter and totally non standard/non vacuum fuel taps 'cos the Suzy one is bollux...
Carb kit's about £12 x 2 on fleebay...

[gruntle]

If you do pull the carbs, try to use a JIS bit (NOT a Phillips) - and it's prolly worth investing in either hex or allen bolts to replace all the the carb bolts if you plan on keeping the bike - summat I'll definitely be doing next roundtuit...

ps: Make sure you get the right Carb kit for your bike - later models are different, and your float bowls WILL leak 'orrible brown gunky stuff if you don't change the gasket...

[Kookas]

I quite enjoy doing stuff like that and I would, but the bike at least would have to stay outside and I'm always paranoid it'll rain and I'll get water in the engine or something. Maybe I could put a bag over the hole the carbs go into or something.