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... :no:

[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.

[FJRider]

Back in the day it was called an apprenticeship.

Now everyone wants their qualifications from google.

Back in the day ... "fixing" the bike yourself was the option of choice ... regardless of the issue. The Public Library had most of the workshop manuals (and photo-copiers) so some knowledge was available cheaply. And those rip-off workshop mechanic's charged over $10 an hour to look at them.

With the OP having access to THESE forums ... Not having internet is not the issue. They're just obviously too dam fucking lazy to even Google it.

[OddDuck]

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?

Broken throttle cable: the push pull arrangement is so that the rider can close the throttle in an emergency situation. One cable pulls when opening, the other pulls when closing. Neither cable pushes, they just don't work that way. Older bikes used a pull cable to open the throttle and relied on springs at the other end to close it again - all fine until the cable rusts or gunks up and jams in the open position. I'd take the view that it's there for a reason and I'd replace it, but up to you.

What you call the headers - are you talking about the carburettor slides?

There are two types of carburettor used on motorcycles:

CV - Constant Velocity - these move the slides automatically depending on engine demand - i.e they're opened by airflow. The throttle cables go to a butterfly valve mounting in the carburettor body, immediately downstream of the slides. You're almost certain to have CV's if the bike's stock.

Slide Carbs - no throttle butterfly, instead the slide is directly controlled via cable from the twistgrip.

Both types ideally also have a choke valve, this being either a butterfly valve upstream of the carburettor or an enricher which works on the float valve.

Anyway... last suggestion really, once you've got the cable sorted, try putting a voltmeter onto the battery and see how much the voltage at the terminals drops while cranking the starter motor. It should start at 12V and drop to 8 to 10V; if it's lower than this while cranking then that could be your problem.

If it's an old battery it'll drop storage capacity, even fully charged, and if there's not enough oomph left to run the ignition properly then no amount of cranking will get the motor to catch.

[stuartb]

With the OP having access to THESE forums ... Not having internet is not the issue. They're just obviously too dam fucking lazy to even Google it.

I've been trying to figure out the problem for a few months now. Which has included A LOT of Googling and reading old forum posts. Like I said in the first post, I'm new to bikes so I'm trying my best here and I'm keen to learn. I started this post asking for help as a last resort before re-assembling it and taking it to a mechanic.

You've got to be a bit of a dip shit to come on here just to assume and post I'm "too dam fucking lazy to even Google it".

:tugger:

Anyway...


Broken throttle cable: the push pull arrangement is so that the rider can close the throttle in an emergency situation. One cable pulls when opening, the other pulls when closing. Neither cable pushes, they just don't work that way. Older bikes used a pull cable to open the throttle and relied on springs at the other end to close it again - all fine until the cable rusts or gunks up and jams in the open position. I'd take the view that it's there for a reason and I'd replace it, but up to you.

What you call the headers - are you talking about the carburettor slides?

There are two types of carburettor used on motorcycles:

CV - Constant Velocity - these move the slides automatically depending on engine demand - i.e they're opened by airflow. The throttle cables go to a butterfly valve mounting in the carburettor body, immediately downstream of the slides. You're almost certain to have CV's if the bike's stock.

Slide Carbs - no throttle butterfly, instead the slide is directly controlled via cable from the twistgrip.

Both types ideally also have a choke valve, this being either a butterfly valve upstream of the carburettor or an enricher which works on the float valve.

Anyway... last suggestion really, once you've got the cable sorted, try putting a voltmeter onto the battery and see how much the voltage at the terminals drops while cranking the starter motor. It should start at 12V and drop to 8 to 10V; if it's lower than this while cranking then that could be your problem.

If it's an old battery it'll drop storage capacity, even fully charged, and if there's not enough oomph left to run the ignition properly then no amount of cranking will get the motor to catch.

Thanks for the info OddDuck. I've ordered a new throttle cable so I will replace that. Carburettor slides does sound like the proper name for what I'm talking about.

You must be right about them being CVs, I can see the butterfly values under the carburettor slides.

I'll give the battery another charge and see how much the voltage drops now.

[4AGE]

Fuel pump. Common fault on these.

[stuartb]

Fuel pump. Common fault on these.

Fuel pump is brand new and I've checked it's getting fuel through the pipes.

[husaberg]

does it have a sidestand switch

[WALRUS]

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 `_-

You're not wrong. I've got a pair of 1989 MC19 racebikes and yeah, I'm sure they were thrashed harder by teenagers learning on them as road bikes than they ever were on track.

Both of mine are currently in the same state as OP's where they are complete, fuel pump working fuel getting into carbs, got spark and turning over but not firing. I think my problem is just old and gummed up carbs but I don't have the time or know-how to service/clean/strip/re-build them.

Do you have good compression?

When was the last time StuartB cleaned his carbs?

Don't forget, as others have said, this is a 30yo small capacity bike which has done, I assume, many many thousands of kms at eleventy billion RPM with (often) rather poor maintenance and the odd stack or two.

One of my engines has a tendency of blowing headgaskets and doing weird shit

[FROSTY]

probably way late but the most common issue with those lil bikes was fouled plugs.

[jafagsx250]

probably way late but the most common issue with those lil bikes was fouled plugs.fouled plugs can make it drop cylinders and die right? Cos mine is giving me a ball ache with that shit.

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[jellywrestler]

My current mechanic of choice is a spade is a spade type of person.



The phrase predates the use of the word "spade" as an ethnic slur against African Americans,[9] which was not recorded until 1928; however, in contemporary U.S. society, the idiom is often avoided due to potential confusion with the slur


well he's a bit politically incorrect then isn't he?

[OddDuck]

fouled plugs can make it drop cylinders and die right? Cos mine is giving me a ball ache with that shit.

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Weak spark can do that - check to see how much voltage your coils are getting, if the wiring loom's getting old then the lengths of wire / multiple crimp joints / push connectors etc resistances can start to add up.

[Hugo Nougo]

not on here often, but a month and no one knows if its spark, fuel or compression. we can confirm however that spades have no place in the workshop.

[jellywrestler]

not on here often, but a month and no one knows if its spark, fuel or compression. we can confirm however that spades have no place in the workshop.

on the contrary it might have spade terminals.

[jellywrestler]

perhaps.

Didn't know it was a slur or anything like that, just goes to show how things change over time.

Like the word: Gay

The question is: did you understand what I wrote in context or are you going to twist it around to some other connection

yip exactly, just jumping on the pc bandwagen

[jafagsx250]

Weak spark can do that - check to see how much voltage your coils are getting, if the wiring loom's getting old then the lengths of wire / multiple crimp joints / push connectors etc resistances can start to add up.

They checked that. It was ok.

Turned out it was a swollen/perished fuel diaphragm on the fuel cock that was causing the fuel flow to be irregular.

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[OddDuck]

They checked that. It was ok.

Turned out it was a swollen/perished fuel diaphragm on the fuel cock that was causing the fuel flow to be irregular.

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OK - it's a pretty quick thing to check, hence the suggestion. Glad you found the source of the issue.

[jafagsx250]

OK - it's a pretty quick thing to check, hence the suggestion. Glad you found the source of the issue.hopefully once the brakes are done it has no other issues hahah.

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[actungbaby]

Oh sounds like what us old fellows have to out up with oh cock.

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[stuartb]

I replaced all the spark plugs with new ones today and now it runs better than ever! :woohoo:

Didn't think sparks was the problem because they looked ok when I tested them. I guess they must've been weak?