Yamaha SR250 (1980) won't start, please help!

[Aaron_grinter]

Hey guys.

So one morning stupidly it was 6am and I had to leave for work and my engine was cold so I resorted to jump starting it, whilst unwittingly reversed the polarities and obviously blew the fuse.

After replacing the ignition unit, starter unit and fuse we finally got the electrics back on and attempted to start it, but to no avail.

It seems to spark and turn over but there seems to be no follow through with the ignition.

We replaced the fuel lines and emptied the carb a number of times but when ever we try to start it, it feels as though there is no fuel going through. This is exhibited after checking the spark plug and noting that it is completely dry.

Is there something else that we should be checking?

Note that the air connection seems to be fine and to my knowledge the carburettor is in quite clean condition so there shouldn't be any blockages.

Please help guys, this bike is my life!

[otter]

Hi mate,

I actually happen to have a SR250 too

How long has your bike been sitting for? Mine really didn't want to start the first time, I ended up dropping a _small_ amount of fuel into the cylinder through the spark plug hole to get it started after not running for over 5 years (I imagine this is actually quite dangerous and I was stupid for doing it). I find that after sitting for over a month it's a bit hard to get started.
Have you cleaned the carb with carb cleaner?

When you say it seems to spark, you've taken the spark plug out of the cylinder and when you run it (side grounded to the engine casing) you can see a visible spark?

[Subike]

If this bike was starting every day without fail before this,
and you reversed the polarity of the electrics
then you have fried the electronic ignition.
Have you checked for spark at the plug?
Fuel system should only be looked at after you have checked out the ignition system,
especially if it has been running ok.
If the bike had been sitting for say 6 - 12 mths, unused, then check the fuel system.


just reread your first posting, durr

[unstuck]

Why would jump starting your bike reverse polaritys.

[otter]

Why would jump starting your bike reverse polaritys.

Shit happens right...

Edit:
Ohh I just realised what you said... I don't even know (too tired).

[Aaron_grinter]

Thanks Subike, it turned out that I fried the ignition unit and starter motor. After changing those and the main fuse the battery needed to be recharged, after which she is now running like a dream again.

Time to start customising, my god these 80's bikes can look daggy.

Thanks guys,
Aaron