1988 CBR250 turning over but won't start, can't figure it out.

[stuartb]

I've only owned the bike for about 6 months and I'd take it for a couple of rides a week. Then one morning a few months back I couldn't get it to start and it hasn't started since. I haven't been able to figure out the problem.

It just keeps turning over and nothing else apart from the occasional back fire.

Things I've tried:

• Tried starting with full choke/no choke/half choke and with some throttle etc.
• Fuses all look good and all ignition lights are lighting up as usual.
• Fully charged the battery many times while trying to find the problem so dead battery isn't the issue.
• Thought it was a faulty fuel pump initially so I replaced that and have made sure fuel is flowing through the lines.
• Checked the two spark plugs on either side which both appear to be giving a spark. I haven't checked the inner two plugs because they look difficult to get to. Even if one spark plug was completely stuffed wouldn't the bike at least show some signs of starting?
• I've just replaced the ECU box because the old ones plugs looked corroded and covered in what looks like glue.

I'm new to bikes so really keen to hear anyones ideas/suggestions!

Here's a video of me trying to start it just now:
https://www.stuartb.nz/misc/cbr250r-cranking.mov

I know the battery sounds dead again but it does the same thing with a fully charged battery, just louder...

[OddDuck]

Change fuel - unleaded has a nasty habit of going off if sitting for a few weeks

Check kill switch contact resistance and loom wiring - have a look at voltage delivered to the coils while energised - if this is low due to resistances adding up in the wiring then it'll affect the ignition

Check valve tappet clearances

Get to inner spark plugs and check insulators on all plugs for carbon fouling

Check that all spark plugs are tight!

Check compression, all cylinders

Check air filter for holes or bad sealing - any air gap will badly lean out the mixture and make starting a nightmare - on that note also go looking for vacuum leaks through the inlet manifolds. If there's O-rings sealing the manifolds to the cylinder heads then these can flow and set over time and gradually fail to vacuum seal properly.

Good luck and let us know how it goes?

[nzspokes]

Pour a little fuel down each carb and try again. If it fires its carbs, if not most likely a lack of spark.

[Katman]

Pour a little fuel down each carb and try again. If it fires its carbs, if not most likely a lack of spark.

Stick to servicing push bikes.

[nzspokes]

Stick to servicing push bikes.

LOL, I can fix a petcock.

[FJRider]

Change fuel - unleaded has a nasty habit of going off if sitting for a few weeks

Check kill switch contact resistance and loom wiring - have a look at voltage delivered to the coils while energised - if this is low due to resistances adding up in the wiring then it'll affect the ignition

Check valve tappet clearances

Get to inner spark plugs and check insulators on all plugs for carbon fouling

Check that all spark plugs are tight!

Check compression, all cylinders

Check air filter for holes or bad sealing - any air gap will badly lean out the mixture and make starting a nightmare - on that note also go looking for vacuum leaks through the inlet manifolds. If there's O-rings sealing the manifolds to the cylinder heads then these can flow and set over time and gradually fail to vacuum seal properly.

Good luck and let us know how it goes?

If the OP was capable of checking all of that ... it's unlikely he would have asked in these forums.

Probably his best move is to take it to a motorcycle mechanic ...

[FJRider]

LOL, I can fix a petcock.

Yet to be proved ...

[husaberg]

LOL, I can fix a petcock.

Careful hes likely to offer a very small one up to you.

[Scubbo]

need to know a bit to keep those old jap 250s going now that theyve done a million kms at redline for most their life `_-

[OddDuck]

If the OP was capable of checking all of that ... it's unlikely he would have asked in these forums.

Probably his best move is to take it to a motorcycle mechanic ...

Fair enough, but everyone's gotta start somewhere.

[Katman]

Fair enough, but everyone's gotta start somewhere.

Back in the day it was called an apprenticeship.

Now everyone wants their qualifications from google.

[FJRider]

Fair enough, but everyone's gotta start somewhere.

True ... The OP started this thread and hasn't been back ...

[stuartb]

Thanks for the suggestions OddDuck!

• I've emptied the tank and put fresh fuel in.
• I've checked all the sparks now and I'm sure they're ok.
• I can't see any holes or gaps around the air intake/filter.

Before I see if I can do your other suggestions we've found something...

Since posting two days ago a friend of mine came to have a look. He discovered that one of the throttle cables has snapped and is missing so I'm thinking this is mostly likely the problem.

From what I can see the top throttle cable pulls while the bottom cable pushes. The bottom cable is the one that's missing. My question now is are both cables absolutely necessary or is the top cable capable of doing the job on it's own?

Also when I try to start the bike or open the throttle the headers don't open. Could that be what the missing cable is for? Are they supposed to open when you turn the throttle or are they opened by a vacuum?

[nzspokes]

Thanks for the suggestions OddDuck!

• I've emptied the tank and put fresh fuel in.
• I've checked all the sparks now and I'm sure they're ok.
• I can't see any holes or gaps around the air intake/filter.

Before I see if I can do your other suggestions we've found something...

Since posting two days ago a friend of mine came to have a look. He discovered that one of the throttle cables has snapped and is missing so I'm thinking this is mostly likely the problem.

From what I can see the top throttle cable pulls while the bottom cable pushes. The bottom cable is the one that's missing. My question now is are both cables absolutely necessary or is the top cable capable of doing the job on it's own?

Also when I try to start the bike or open the throttle the headers don't open. Could that be what the missing cable is for? Are they supposed to open when you turn the throttle or are they opened by a vacuum?

If by headers you mean carbs then thats your fault.

Nice easy fix.

[FJRider]

Before I see if I can do your other suggestions we've found something...

Since posting two days ago a friend of mine came to have a look. He discovered that one of the throttle cables has snapped and is missing so I'm thinking this is mostly likely the problem.

From what I can see the top throttle cable pulls while the bottom cable pushes. The bottom cable is the one that's missing. My question now is are both cables absolutely necessary or is the top cable capable of doing the job on it's own?

Also when I try to start the bike or open the throttle the headers don't open. Could that be what the missing cable is for? Are they supposed to open when you turn the throttle or are they opened by a vacuum?

In most cases ... one cable pulls the carb slide open and the other pulls the carb slide closed. As the slide is usually spring loaded to a small degree ... one cable may not be a great (the) issue.

Depending on what you have removed ... it is hard to say what you are looking at. With all connected as it should be ... not much internal carb movement will be seen.

Have you tried push starting ... ??? well ridden bikes often start with a bump start cold but not on the electric leg. Thus a more defined set of issues need investigating then.

Also ... you can look in the forums at other threads on this very subject. Trust me (lol) ... you are not the first to have this issue.

But seriously ... if you want to find the issue FAST ... take it to a motorcycle workshop. They will find the issue and advise what needs to be done. A charge for the time spent looking at it (money well spent) will probably be asked for. Then you can either get them to do the work or you acquire a workshop manual and do it yourself.