I suspect he did Chris, sometimes as I suspect sometimes you need to bite the bullet and take something more apart than you’d really like to. Like my lads SX50…..
Ta, Is the vent just a hole under the cap? I didn't see anything in the workshop manual about it. The bike took 12 liters and there was no issue/wooshing when opening the cap this morning, so I don't believe it's blocked but will check when I find it. I've ordered a fuel pump rebuild kit as it was fairly cheap. If it's still crap after that. I can only imagine the carbs will have to come apart again, though it would be a bit weird for both of them to have the same issue and neither being solved with a smack? Fingers crossed it's the fuel pump, as that's much easier to get at.
I’m still so hurt I’ll forward you the bill from my therapist- she’s very expensive - she charges by the hour. Fun fact - when googling for a suitable image I discovered that there are a number of actual therapists with the surname Hooker
I have a lawnmower that has an oil leak that I have ignored because I’m not 100% certain where it’s coming from - I know the solution would be to completely strip it down and give it a proper rebuild - but kitchen towel and regular oil top-ups are so much easier! Alan may have inspired me! Although looking today it would seem that grass now keeps growing over the winter (thank you global warming!) so extended downtime for the mower isn’t an option. Edit - I have just learned that Canon make an SX50 camera, Cambridge Audio make SX50 speakers, Aprilia make an SX50 motocross bike - and so do KTM. I going to assume it’s one of the last 2!
Aprilia sx50 supermoto, @finm had one to that he methodically rebuilt every weekend. Reminds me Mrs lawnmower needs a service.
Things have only changed a little bit in the last 35 years then I had my own version at 16! I’m glad it never had any mechanical issues because my Dad isn’t very handy!
Ahh the 80’s - a time before the internet when it was possible to live in complete ignorance of things unless you fell over them! I never even knew there was an MB50! I had mates with AR50, MT5, DT50, TS50, RG50 - so basically they were the only bikes in existence as far as my 16 year old brain was concerned - I had other interests that took up most of my attention at the time……. I really need to stop hijacking this thread! Sorry @Cammmy
What none had the AE50, SS50, FS1E, AP50. MB50 was just a road orientated Honda. Lad lives nearby has an AR50 in good nick.
I turned 16 in 1990 so it was the era of the 35 mph 80’d bikes so some of the above would have been ‘old’ in our young eyes. Of course at the time we were all pretty ignorant of how much faster the 60’s and 70’s 50’s were! Now you have jogged my memory I do remember being introduced to the FS1E ‘Fizzie’ though - I felt rather put out that I was restricted to 35mph when this funny looking ‘old’ bike could do 60!
Okay, so still an issue after fuel pump rebuild and two new OEM plugs but it seems to be able to hang on to one cylinder for a while (barely). While the pump was off, I blew through the line to the carbs and it seemed fine. I went out a second time with the fuel filler open and nothing changed. Guess I'm removing the carbs and at the very least taking the bowls off. I still can't fathom why this has started. I fixed an airleak on the manifold that the fuel pump gets it's signal from and I didn't disconnect anything from the carbs. Just took them off the manifolds and propped them up. Not even at much of an angle. The carbs don't leak from the overflow when it sits, so the floats can't be totally stuck. Just seems like they can't open enough.
Having just reread the thread from the beginning it looks like you had 3 issues. 1. it didn’t like iridium plugs - this sent you down the path of ‘it must be an electrical issue’. Now resolved. 2. there was an air leak in the manifold the fuel pump gets it vacuum from leading to the fuel pump not being able to keep up with fuel demand. Now resolved. 3. It won’t idle on the horizontal cylinder. Despite having disassembled and cleaned the carbs once, as others above have suggested, I’d be stripping that carb down again and checking the slow circuit isn’t blocked or partially obstructed. I hate carbs . I like taking them apart, cleaning, servicing and rebuilding them, but I hate the fact it’s so much work/time to actually get them on/off a bike and test them.
Cheers for the reply. The symptoms as it currently stands. The bike ran fine with it's vacuum leak under throttle, it would drop a cylinder at cruise (not the one that was leaking though). After fixing leak, it starts easily from cold on both cylinders. It will ride on both cylinders for a couple of miles. After a couple of miles, it loses power, backfires and can only be limped on what feels to be a single cylinder at about 20. Before fuel pump rebuild, it would often completely lose power. Shutting the bike off and letting it sit for a few minutes will return it to normal for a brief period. I'm going to measure the float level and try get the bowls off and floats out without removing the carbs. Otherwise, out they come again. I don't think it's heat related as while I was setting the carbs, the bike ran for an extended period with no issue on the stand.
If you have ruled out the tank breather circuit being blocked, then going at best from your feedback, it now sounds like "exciter" units both need to be swapped for new ones/different ones. They can fail in different ways, it's usually very obvious but sometimes the failure is intermittent. There is a page on Brad Black's website that shows you the simplest way to check float level without dismantling.
Thanks Chris, I'll keep that in mind. I'll at least get into the floats first as I did move the carbs around to fix the air leak, so seems plausible something may have happened. I found that page. I expect float level to be okay when I measure it as it will have had time to fill. It just seems they can't keep up under load.
Getting radical for a min... Inlet or exhaust cam a tooth out on the belt? (assuming it's an engine that could get away with that) maybe it runs at revs, but you aren't getting valve sealing at idle revs, or on that theme, what's the compression figure for each cylinder? easy to check and would let you know the health of the cylinders themselves.
Compression was good, 150 and 155 from memory. One cam being out could explain difficulty in completely synching carbs even after airleak fixed but even with the airleak, the mechanic noted how well it pulled. Only difference between then and now is new manifold gasket. It still pulls hard when it's had a few minutes to sit. It will just fade out, lose power and start popping until you let it sit again. Prior to that, you could ride it at will. It just didn't like low load Cruise.
