Speedfight 2 (50cc) won't run - fuel issue (possibly).

[panoalto]

A friend of mine asked me to look at a Speedfight 2 which has been laid up for over a year. After tending to all the obvious things like clean fuel, new plug, etc, we ended up with a non starter. Having now stripped the carb down, cleaned it up and blown the jets through etc, we now have a motor which occasionally runs but not for very long.

We eliminated the fuel tap and everything above the carb by feeding the fuel via a gravity fed auxiliary reservoir (plastic bottle) for a while. The only way to get the motor started is by restricting the air intake (by hand) and then, as it starts to die, restricting the air intake further to keep it running.

I'm a bit stumped with this and obviously the ped can't be ridden in this state. Any ideas would be greatly appreciated.

Regards,
Chris Shepherd

[Matt-]

" keep it simple stupid " is my basic rule of diagnosing a problem.

so you have worked your way down the bike, so fuel is not an issue from the tank and the fuel tap, when you say you have cleaned the Carb do you mean just taken to bit's, drained the bowl so on, did you clean the residue in the bottom of the bowl, this is most likely going to be the problem if you ever get blocked jet's.

Next i would go to the firing side of thing's, replacing the plug may be useless, if it's sat for a very long time, moisture an work it's way into your coil and HT lead which would give you a weak spark, kick it over or on the starter motor, turn it over 5 time's each time turning it over make sure you have a good healthy strong blue spark, Remember Make sure you earth it on something

When you say it will only run with you blocking the air intake, this might indicate it's getting to much Air to Fuel, get your air filter back on ( Once given a good clean )

Let us know how you get on

Matt
____________________
RIP jack (wheelie king), you will never be forgotten.
Current Bike's - Road Legal TZR 125 Pitbike, Aprilia SR50R 2010

[panoalto]

Hi Matt,

Thanks for the advice.

We cleaned the carb as in, took everything except the float assembly out, removed the residue from the bowl, blew air through the jets and poked some nylon fishing line through those just to be sure it was clear.

I'm thinking too much air might also be described as too little fuel. With the airbox and filter in place the motor won't start at all. I suppose that, by blocking the air intake we are creating a choke situation where the motor draws more fuel. This carb has an automatic choke gadget fitted. Could that be the problem?

If we assume the fuel supply to the carb and the carb itself is ok, is there any other reason for not enough fuel entering the combustion chamber? Possibly reed valves or something like that but I'm not sure what else the bike has in this regard.

We have a good spark with either the new plug or the old one. I don't think ignition is a problem as when the motor is running with the aforementioned conditions applied, the motor will rev without any problem.

I don't think the fuel/air mixture screw has been moved as it seems to need some kind of key to adjust. Either that or it's been broken.

Still at a loss and would really appreciate any further input and ideas anyone has.

Regards,
Chris

[Matt-]

next i think you should try and play around with the idle screw if you turn it down ( which i think is Anti clockwise ) you will determine if it's running to lean or not.

Reed valve's shouldn't be an issue.

the only other advice i can really give you from experience is to do some more basic checks, do a compression test if you have or you have a compression tester you can borrow, if you haven't get a piece of rag or tea towel or cloff and stuff it into the spark plug hole

If the bike has good compression it should shoot it out

also to try another thing: when you are doing all these things and it's not firing all your fuel is entering your cylinder and not going no where, only fouling your plug, so i would suggest taking the plug out cleaning it and letting it dry and then without the spark plug in the cylinder, turn the engine over on the starter, should blow fuel out the spark plug hole, then leave to dry for 2 hour's then try again with everything connected.

All the best hope this helps

Matt
____________________
RIP jack (wheelie king), you will never be forgotten.
Current Bike's - Road Legal TZR 125 Pitbike, Aprilia SR50R 2010

[panoalto]

I ran this by a mate of mine and his immediate comment was " the piston rings are knackered". Would anyone agree with this possibility?