Yamaha Jog CV50 - More power after sitting for ages

[cods4]

I have a 2012 Jog CV50. Since I have owned it I have upgraded to a bigger front pulley and tried a few different roller weights.

The strange issue I'm having is that after the scooter has been sitting for a while (say 2+ weeks) and I start it up again, it takes a bit longer to start, but once its going it seems to run much better than normal. It has faster acceleration, it's much quicker up hills and hits a higher top speed (70-75kph) on the flat.

Firstly, the gearing seems to be much better, it stays at higher revs for longer when I'm accelerating. But I really think the engine just has more power.

What could be causing this? Since I have had the scooter I have thoroughly cleaned out the carb (slightly easier starting), changed the piston and ring (no change), cleaned and tested the autochoke (not quite sure about it still), cleaned the reed valves, and kept it full of good fuel. The oil that is in it at the moment is cheap generic 2 stroke oil.

I can't really think of what would cause this, the power remains very good for the 15-20 minute trip to work, but then when I ride it home again 10 hours later the power will be back to normal. The gearing seems bad, i.e. the revs drop down far too soon and I go much slower up hills, and my top speed is 10-20kph lower at around 55-60. It's still just as quick as most other 50cc scooters on the road, but I know it has more.

[cods4]

Any ideas?

[pinkscoot]

I'm not a Jog person but its a basic Japanese 2 stroke. I would get a better 2 stroke oil, it won't hurt but might help.

[repherence2]

it's probably running on the lean side when you experience "More power after sitting for ages.

I'm under the impression that you're running the stock oil injection pump. when the bike sits, some oil leaks past the pump, and it ends up in the crankcase. it would happen on my Chinarelli. same issue, if my bike sat for 2 weeks, it took forever to get it to fire up. and when it finally fired up, it would blow massive amounts of smoke for a few minutes.

[cods4]

Thanks guys, I will try running some quality oil and premix it. What ratio would you recommend 40:1?

[repherence2]

May 19, 2019 20:16:11 GMT -5 cods4 said:

Thanks guys, I will try running some quality oil and premix it. What ratio would you recommend 40:1?

probably will have to rejet your carb if you switch to premix. you might want to check what size main jet you have in the carb right now. then you can buy a jet set that has incremental jets above your stock main jet. so for example, if you have a 68 main jet, you might want a jetset that goes from like 70 and up, preferably in increments of 2. that way you can do some fine tuning of the main jet. also if you decide to switch to 32:1ratio, you will already have the jet.

I recommend that you buy a Cylinder Head Temperature gage too so that you don't overheat/seize your bore. I think it makes main jet tuning easier. for me, I tune my carb main jet by temperature at Wide Open Throttle.

[cods4]

May 20, 2019 20:41:08 GMT -5 repherence2 said:

May 19, 2019 20:16:11 GMT -5 cods4 said:

Thanks guys, I will try running some quality oil and premix it. What ratio would you recommend 40:1?

probably will have to rejet your carb if you switch to premix. you might want to check what size main jet you have in the carb right now. then you can buy a jet set that has incremental jets above your stock main jet. so for example, if you have a 68 main jet, you might want a jetset that goes from like 70 and up, preferably in increments of 2. that way you can do some fine tuning of the main jet. also if you decide to switch to 32:1ratio, you will already have the jet.

I recommend that you buy a Cylinder Head Temperature gage too so that you don't overheat/seize your bore. I think it makes main jet tuning easier. for me, I tune my carb main jet by temperature at Wide Open Throttle.

Thanks for the help, I'll look into cylinder heat temp loggers and jet kits. If I'm going to all that trouble is there anything else worth doing such as fancy reed valves?

[repherence2]

May 22, 2019 15:37:29 GMT -5 cods4 said:

May 20, 2019 20:41:08 GMT -5 repherence2 said:

probably will have to rejet your carb if you switch to premix. you might want to check what size main jet you have in the ciarb right now. then you can buy a jet set that has incremental jets above your stock main jet. so for example, if you have a 68 main jet, you might want a jetset that goes from like 70 and up, preferably in increments of 2. that way you can do some fine tuning of the main jet. also if you decide to switch to 32:1ratio, you will already have the jet.

I recommend that you buy a Cylinder Head Temperature gage too so that you don't overheat/seize your bore. I think it makes main jet tuning easier. for me, I tune my carb main jet by temperature at Wide Open Throttle.

Thanks for the help, I'll look into cylinder heat temp loggers and jet kits. If I'm going to all that trouble is there anything else worth doing such as fancy reed valves?

nah, just that for now. you can always change to fancy reeds later. instead of a fancy reed valve for now, look into getting a tachometer. helps with tuning the transmission, like knowing when the clutch engages or if you have to stall the clutch more to get into the power band. a tach can also be helpful in roller weight tuning for the variator.


learn and understand how to tune the carb for now. it's very bad to change a lot of things at once, it makes tuning everything difficult. tune 1 thing at a time. I feel that learning how to tune a carb is important. later on if you decide to change pipes or transmission parts, you may end up having to retune the carb later. I tune for Wide Open Throttle; I change jets incrementally until I find a main jet that keeps me below 350° while holding WOT. others may tune differently, this is just how I prefer to tune.