CBR250 mc19 1988 issues.

**Newo** · 2nd May 2011, 17:36

I'm not sure entirely what information is needed to help diagnose the problem but here goes.

I've noticed the last month that my bike has been backfiring on startup in the mornings. I figured it probably had something to do with the cold so thought little of it. I've also noticed a huge loss of power compared to when I first got this bike maybe 6 months ago or more.

Today I finished work and went to start my bike and the damn thing wouldn't go. It wouldn't idle unless forced to, sounded like a tractor and was back firing when ever you give it more gas. I was quite worried about doing further damage if I kept it running but unfortunately I had absolutely no other way to get home so while trying to keep it running I was fiddling around with the idle to no avail, also when it backfires I could feel it through the whole bike, quite a big vibration.

I gave up and went back inside trying to figure out what to do, ran out of ideas and went back outside to try again. It finally settled down a bit and stopped backfiring but the idle is still all over the place. Still doesn't sound too healthy either but not as bad as it first was.

Any ideas on the cause of this? or what I can do?

I'm really hoping this isn't going to put a hole in my back pocket because as it is I'm barely scraping by. It's due for a service and I was trying to save up for the big one, valve clearances, carby, etc.

help?

[Edit] I just realised I had a similar incident earlier in the year, did a search on myself and found my previous thread:

http://www.kiwibiker.co.nz/forums/sh...ary-bang-noise

If it's still the same issue and it indeed has something to do with Coils, plugs, fuel filter and vacuum leaks, Is it possible that I will cause any damage by riding while this problem continues? I don't think I'll be able to get the bike to the mechanic until the weekend at the earliest. I have no other alternative transport either.

**bogan** · 2nd May 2011, 17:40

Likely causes imo, compression, fueling, or ignition. Pull a plug or two and see what is going on for starters.

**racefactory** · 2nd May 2011, 18:00

Doubt the motor is damaged. Hard to destroy a cbr250 motor.

Definitely first pull the plugs... you really never know what you'll find. A must do.
Otherwise air leak is very plausible and the bike will run like a sack. Pull the carbs and check the carb rubbers for damage and cracks. Check that they are actually seated properly too.

Got to be one of these 2.

**DrunkenMistake** · 2nd May 2011, 18:06

The plugs are pricks to get in the centre, you have to unbolt the radiator and pull the hose off,

Does it have a different exhaust than stock? could be a lack of back pressure,
Carbs are a price of cake to get out, so maybe take them out and give them a good clean, these bikes have fuel pumps and not vaccume hoses so ignore what any cunt tells you when they suggest anything to do with vacuum leaks.

I would suggest doing the simple checks first, your idle should be around 1,500rpm,
take the seat and tail off and take the tank off, be sure to turn the tap to off not on or RES and once its unbolted tilt it to one side and pull the two hoses off,

looking down you will see a while cylinder looking thing thats the fuel pump have a glance at it and see if you can see anything blocking it up when you hold a light behind it, on the other side of it is the filter, it may need replaced I dont think you can just clean them out, If you change the filter, sit the tank back on and plug in the hoses and give it a fire up, if it runs better, problem solved, if not I would suggest moving onto the carbs,

So tank back off, then unscrew the air box, if your not bike Savvy find someone who is to help you, but its the big black box, and run some compressed air over the air filter, I wouldn't recommend doing the carbs if its your first time and your clueless, find someone else.
If you have cleaned the carbs, blown out any shit in the air filter, replaced the fuel filter, and you still have a problem, put it all back together and take off the l/h and r/h fairings and undo the top bolts holding on the radiator, and unplug the hose on the left side thats going into the radiator, should have a hose clamp on it be warned it will flow out some coolant, but not to worry just top up the radiator reserve tank under the seat with water when your finished, once you have undone all that the radiator should sort of swing out a little bit, or you should be able to force it forward out of the way (there could be a bolt on the bottom of it too I cant remember for sure) then you start taking out the plugs and checking them, check to see if they have alot of oil build up on them and what the points look like, I would recommend just replacing all 4 , be sure not to mix up the order the caps were in.
I need to ask, when was the last time you changed the oil and filter? and did you top it up and check the level with the stand down? or standing level? and what is the oil you are using?.

These are all the solutions I can possibly think of, that and dont run it on 91, the manual says 91 but its Japanese 91, which is probably equivilant to our 95

**Newo** · 2nd May 2011, 18:48

Last oil change was between 5000-6000k's ago, filter too of course. Not sure what oil was put in as I had the mechanic do it all under a general service. Since then It's been topped up when ever needed with silkolene 10w40

http://www.supercheapauto.co.nz/onli...44#Description

It's always been checked while on its side stand. I wasn't aware that much of a difference would be made while upright. I'll stand corrected though if it does.

Interesting you say not to run it on 91 as I've always run it on 91, and the previous owner before me also. I didn't think it was lacking any power because of it either. When I first got this bike, man it could go. Was even better when I had the clutch serviced with new parts.

[edit]

standard exhaust. no modifications to the bike that I'm aware of other than some fool removing the radiator overflow beneath my seat >.<

**bogan** · 2nd May 2011, 19:03

yeh, always check the oil level when stood upright, makes quite a difference. Think it's going to take a decent amount of teardown and know-how to sort it, so get someone experienced to help would be my advice.

**Newo** · 2nd May 2011, 19:07

I just spoke to the mechanic I use and he suggested much of the things we're discussing on here. If only I had the tools required and I'd definately attempt most of this stuff myself. Seeing as my bike needed the big service anyway he quoted me roughly $470 including parts to do everything including valve clearnances and clean up the carb's, plugs, oils, filters, etc etc.

Earliest he could do the work is friday though, more likely by monday he said.

I havn't given the go ahead just yet as I like to keep my options open and do some research before commiting large sums of money.

Opinions?

**Icemaestro** · 2nd May 2011, 19:13

I would also check the fuel tap - is the mc19 vacuum operated? I had an mc22 that had the same problem, it would backfire when there wasn't quite enough fuel getting in as the diaphragm in the fuel tap had buggered up and wasnt opening out properly to let fuel through

**Newo** · 2nd May 2011, 19:27

Not from my own personal knowledge or experience, but mentioned earlier in the thread was a fuel pump and the lack-there-of any sort of vacuum.

**Icemaestro** · 2nd May 2011, 19:33

Originally Posted by Newo

Not from my own personal knowledge or experience, but mentioned earlier in the thread was a fuel pump and the lack-there-of any sort of vacuum.

Oh yup! Damn eyesight! My bad :-)

**DrunkenMistake** · 2nd May 2011, 20:39

Originally Posted by Icemaestro

Oh yup! Damn eyesight! My bad :-)

Its ok, I wouldnt read my replies either :[
Haha,

The tools are basic man, you need a phillips screw driver, a set of hex keys, a basic socket set (including plug extensions) and maybe a 10 mm and a 12mm spanner.

**Icemaestro** · 2nd May 2011, 21:02

Where abouts in Auckland are you? If no one else with more experience offers, I have every thing but the sparkplug sockets - I have a handy garage across the road I've been borrowing one from. Have done carbs, fuel tap, air filter, oil changes on the cbr, and plugs on my Vfr so have a basic mechanical knowledge, again if no one else more experienced offers :-).

Just out of interest dm, does the fuel pump have a solenoid like the ones on the Honda bros 400/650? Cause possibly it could just be the fuel pump going then?

Regardless, be a good idea to pull the plugs and see what colour they are..sounded like it was running on 2/3 cylinders or something

**DrunkenMistake** · 2nd May 2011, 21:18

Originally Posted by Icemaestro

Where abouts in Auckland are you? If no one else with more experience offers, I have every thing but the sparkplug sockets - I have a handy garage across the road I've been borrowing one from. Have done carbs, fuel tap, air filter, oil changes on the cbr, and plugs on my Vfr so have a basic mechanical knowledge, again if no one else more experienced offers :-).

Just out of interest dm, does the fuel pump have a solenoid like the ones on the Honda bros 400/650? Cause possibly it could just be the fuel pump going then?

Regardless, be a good idea to pull the plugs and see what colour they are..sounded like it was running on 2/3 cylinders or something

Couldnt tell you sorry man, all thats based on the work I done on my own CBR when I got bored on my days off work I used to pull it apart and tweek with everything and what not. and yah sounds like its not running on all cylinders but it could possibly be too much/ lack of air too, And or no fuel/not enough fuel so a blocked Jet

**Newo** · 2nd May 2011, 21:48

Well my plans so far are this.

Seeing as the mechanic can't do anything until friday at the earliest but more likely over the weekend and I really need to get to work somehow (I'd really like to avoid taking the train as I have to walk for ages in the rain) I'm going to see how she runs tomorrow morning. I've been back in the garage again tonight and she seems to still start up and idle now. Hopefully I'll make it to work, and back home again.

If she don't go in the morning, I'm fortunate enough to be able to borrow my flatmates bike, he said he's using the car so thats lucky for me. After work tomorrow I'll check back and go from there.

I live out west auckland, sunnyvale. Maybe if I can get off work early enough tomorrow I'll give some of that stuff a go. I've got your basic screw drivers, sockets and a couple spanners so I'll see how far I can get maybe.