going slower, derbi sends 50cc

[charrington96]

I have a derbi senda 50cc 02 plate
I went out on it today and I could only reach 40mph instead of between 45-55...
I hadn't riden it in a week but it runs fine, once its warmed up after riding for 10-15 minutes I can reach 45
Any ideas?

[SQL]

wind, jacket undone, shoelaces undone, air pressure, air density.

[charrington96]

Lol I was more thinking is the piston on its way out or something?

[SQL]

what is the compression like?>

[charrington96]

How do I find out what the compression is like... I know that its not as powerful as it used to be

[SQL]

Compression tester, what you could do is to rebuild the topend mate will cost not much and can only make the bike better.

[charrington96]

I put an air filter on it and think it ruined it... Do you know how much it would cost roughly?

[nathan k]

Put the stock airbox on, or up jet if you want to mess about with the carb and keep the filter.

Keep riding it and it will seize, get rid of that filter and you might get away with just new rings...£15. Small end bearing and piston are all cheap as chips for that bike and would be your best bet if keeping it.

It's a fragile engine. If you've put a 'performance' exhaust on it then go back to the old air box AND up jet because that will lean it out further.

[charrington96]

Thanks
I've put the stock back on, its a stock, deristricted exhaust and I haven't touched carb or anything... I'm 17 in a month, do I spend money on it? Its a big job too isn't it?

[SQL]

put airbox on it put all mods in a box and sell it with the bike.

[charrington96]

Will it last till I sell it though?

[P.]

[charrington96]

I need to get to school and work still

[P.]

[charrington96]

Its gotta last 300km

[SQL]

Does it still go to 40? if yes then good if no then good it should only do 30 so no one will no the difference.

[charrington96]

As long as it dont get worst... Once its warmed up it'll do an extra 5mph or slightly more, just dont want it to blow up on me haha

[SQL]

Don't ride like a wang then it should last if not knock £100 off selling price for a rebuild.

[charrington96]

I dont... Ive seen so many peds get pulled over by disguised police cars Ive never had any accidents or trouble