Speedfight 3 - Pop hiss and bogging down

Hi all,

I’m at a loss here. My lad has a speedfight 3 50cc A/C model which was running fine.

Recently when riding it after only a mile or so or when warm it seems to bog down then make a pop from the exhaust almost combined with a hiss. If you back off the throttle quickly and then slowly roll it on it takes off again slowly but seems to be more boggy once the throttle is turned more towards full. Sadly being 16 he only uses the throttle fully open no doubt!!!!

As I was a little sceptical about it I went out and experienced it for myself so I know it’s a “real problem”

Any ideas where to start please?

Thanks in advance.

Dave

 

Hello Dave, speedfight 3 is that 2 stroke or 4 stroke? I can never recall without a reminder....Air cooled so I'm guessing it's a stroker? (2t)

 

Hi, sorry thought I’d miss some vital info. It’s a 2 stroke. Thanks

 

No worries, first things I would do are give the carb and filter a good clean, and check the sparkplug, or have you already done so? My pipe pops terribly but only in the rain strangely enough, which makes me think water was leaking into the fuel tank, and the same thing would happen with the engine as yours....

 

Hello, just ripping carb off now. Filter looks ok and spark plug is relatively new but I can replace them for pennies so its worth doing. I’ll nip to get replacements and post with an update

 

Nice one. Mine was worse, it would bog down and pop and misfire, and the engine would stop. It would always start again though, so I would be limping home in the rain. Problem fixed by making the bike completely watertight. In the dry it's fine.

 

That’s interesting. We’ve had a few lovely days here so might get him to try it again now. Out of interest what did you need to do do make it all watertight?

 

I used this weird sealant spray stuff. Can't remember what it's called as my mrs brought it for me for my birthday. I will find out though cause it works a treat. (Don't use it without a facemask though because it makes you high as a kite)

 

Just a quick reply. Still does exactly the same after full carb clean. New air filter, spark plug, intake, Reed valves and still makes a hiss and a backfire type pop after about 2 mins of riding.

 

Honestly it's the rain. Mine was exactly the same when wet. You need to stop water ingress somehow.

 

It’s been dry garaged for over a week and then rode in the dry though?

 

Ah, sorry I should have asked. That's really strange. I honestly don't know then. Hopefully someone will....

 

The popping is unburnt fuel burning in the pipe, hence the backfiring. Makes me wonder if it's running too rich...

 

It's the mixture. Could be too lean or too rich.
No way to know without riding it