Reply To: MOT Day and running issues
No worries about things not making sense thank you for replying so late. I used to work in IT and you’ve given me heaps to go off, making sense of ramblings I got quite good at :).
- Fuel Pump wanning (happens, carb cleaner sorts it when you take it apart CAREFULLY) or as pre-caution, replace with a new one if you want us to get it.
- Fuel Filter Clogging or not flowing fast enough (if its OEM)
- Fuel Float Level low (repeated in service manual too) (check floats are on a good height, as fuel goes low, then the jets won’t reach , due to pump & tap not replacing the fuel fast enough = high revs . high speed , more demand)
- Carb Slides wanning.
- Carb Slide needle may be on the lean setting (sent 1x needle for free, just incase one of yours is bent too)
- TANK TAP , wanning = Common.
I am suspect of the fuel pump, there was green thick petrol residue inside it (which i noticed when i did the fuel hoses before I ran the bike) and I have already had it apart to clean it. I didn’t exactly think the pump was bad but the rubber did seem fairly firm. The fuel lines and filter were the ones you supplied so I can comfortably rule those out. I am questioning the vacumm hoses, that is the next job on my list though, they are the original ones and if there’s a restriction or leak in those hoses that could stop the pump working at high demand too i’d imagine.
I will check floats and slides carefully when I have the carbs off, I keep reading 7mm for the floats on here so that’s well in my head now. Thank you for the needle 🙂
I am wondering about the fuel tap flow rate, I fitted a new one on my tank that was a cheap chinese one and it may be more restrictive than OEM. though it does flow freely when opened and it’s the same design as on the yamaha i have (which is a 650). I’ll drain the fuel and see if the tap is giving a bit more of a restriction than it was when I fitted it. No big loss needing another tap if so though, it was a fun gamble.
One thing that comes to my mind, how does the vent in the tank work? is there a check valve or so? I’ve seen fuel issues before (in my car) where a restriction in the venting of the tank will stop fuel flow as there is a vaccum being built in the tank stopping the pump working.
I will go for a little ride tomorrow and read plugs and head temps when i get back.
Normally , when a hyosung that is all OEM and negelected (either by garage or last keeper) , the carby 125 ones at least , they usually spend their lives in the city with a max of 40mph runs , then owners use crap service parts on them to keep em going, but never touch the carbs , or do engine clearances (valve clearances do eventually get too tight , being a hot engine doesnt help) , never changing air filter….
Clearances are next on my list too, i know when things get too hot/tight it can bump a valve open slightly and cause a loss in compression/power. I don’t think I have the skill to do them myself though so i’ll have to book in somewhere.
I’ll send a reply tomorrow with photos of the plugs after a 2 or 3 mile run 🙂
Thanks again Marcel.