Bike dropping cylinders?

[STEPHASAUR]

Hey all.
So I'm just going to put this out there. No i am not selling it. Its not worth shit not running so I might as well just fix the damn thing.
+ despite the exponentially growing levels of frustration and self doubt, I am learning a tonne.

Help me debug my bike - 1988 MC17 CBR250R

At random intervals mid ride, the bike feels like it's drops a cyl or two and eventually stalls. It will turn over but only for 1-3 seconds before stalling again. It makes a really low rumbling noise, and when throttle is applied it cuts out and dies. Should also point out that when this happens, power is almost not there and it will not continue to run unless revs stay over 6k.
The initial thought was spark plugs. So those were replaced, along with a faulty coilpack - which stopped the misfire under idle - another past issue

Stuff that I have done to the vehicle so far:

- New sparkplugs
- New coilpack to replace faulty one
- Carbs have been cleaned
- Fuel filter / tank/ tap cleaned
- New fuel hose (old one was pinching)
- New air filter
- New regulator rectifier
- New battery (which is still showing the correct voltage)
- Fuses/ ECU connections all been checked - all OK

I haven't done a compression test, and I have yet to check the plugs are sparking. But I assume they are for it to be able to fire and run the initial 10-30 mins.
The other weird thing is that if i leave the bike to sit for a little while, it will fire up again. It acts like it's not getting fuel, but I've checked and there is fuel getting into the carbs...

I must be missing something. Someone please offer assistance!

[bogan]

Do a compression test. Also couldn't hurt to check tank breather is not blocked up (open cap next time it cuts out and listen for 'whoosh' of air), though I wouldn't have expected it to run at high revs if this were the only problem...

[Akzle]

at 1988. i'm picking your looking at head/rings. but those carbs are going to want some sex too.

[kiwi-on-wheels]

Check the head breather line, mine had an issue with it getting hot and all the blow by collecting In the carbs. Pulled the hose off the airbox that comes from the head, let it vent to air, problem solved. Free to check

[STEPHASAUR]

UPDATE:
So towed the bike via van to my mates workshop for a full breakdown

Compression tested - all fine
Tested spark - very good
Double checked carbs - adjusters were set high, bike was over fueling but otherwise ok (these were adjusted to fix)
Breather was clean

fired up and still same issue

at which point his fathers mate walked in, who's been working on/ racing bikes for a good 30 years. after explaining how it was behaving he told me, no question that my CDI is faulty.

anyone got a running mc17 i can test this theory with?
or would any cbr running the mc14e engine be compatible with the same cdi? in which case mc17-mc22 i could use?

thanks!

[kiwi-on-wheels]

If all else fails I have seen cdi's on flebay for a reasonable price.

Iirc the mc19 cdi will work, some repinning may be required

[OddDuck]

I've been having CDI trouble with the 900ss lately so maybe this is useful... Difficulty starting and running, especially in cold / humid conditions. It got to the point where it very nearly wouldn't start at all. Ran OK after it had been out for a good spin though.

I tried cleaning the spade connectors and making sure they were tight (12V doesn't take much to interrupt; dirt, oxide and oil can do that), some improvement but nothing major. I did the same to the main relay and found the push in connectors were oxidised quite badly, some CRC2.26 and several insertion / removal cycles (to clean the connectors) did wonders for the bike.

Problem resumed earlier this month, following parking up in the shade at work.

I took the CDIs off, wiped the dirt off and had a look at the potting. Most potting is epoxy resin or silicone rubber (flexible). In my bike they used silicone rubber. It's good for the electronics because it cushions as well as seals. Close examination showed what looked like hairline cracks on the surface of the potting. Not too surprising on a 1995 bike.

Now for the good bit... I fired up the fan bake oven and cooked them for 6 hours at about 65 - 70 C.

The reason for doing that was water ingression. CDI's have high internal voltages and if water is getting in then that voltage will start dissipating via insulation leakage. We use this technique at work a lot to dry out electronics that test low for insulation values; it's surprising how quickly it comes back up. You don't have to take it to boiling, just hot enough for long enough in a dry environment to get the water out.

After cooling and reinstallation of CDI's, the bike fired up immediately and ran better than it's run in years.

I want to stress that this is diagnostic or last resort stuff. Do it only when you've got cash and a source for spares lined up. The fix is temporary at best - I've tried coating the outside of the potting in silicone grease, but the bike's showing signs of having trouble again (it's only been three weeks). Replacing the potting would be ideal but that's a saga in itself, and anyway there'll be electrolytic capacitors in there which should be replaced as well. New CDI's for me when I can afford them.

Apologies for the novel, good luck and let us know how it goes. Now for the jokes to begin...

[STEPHASAUR]

I've been having CDI trouble with the 900ss lately so maybe this is useful... Difficulty starting and running, especially in cold / humid conditions. It got to the point where it very nearly wouldn't start at all. Ran OK after it had been out for a good spin though.

I tried cleaning the spade connectors and making sure they were tight (12V doesn't take much to interrupt; dirt, oxide and oil can do that), some improvement but nothing major. I did the same to the main relay and found the push in connectors were oxidised quite badly, some CRC2.26 and several insertion / removal cycles (to clean the connectors) did wonders for the bike.

Problem resumed earlier this month, following parking up in the shade at work.

I took the CDIs off, wiped the dirt off and had a look at the potting. Most potting is epoxy resin or silicone rubber (flexible). In my bike they used silicone rubber. It's good for the electronics because it cushions as well as seals. Close examination showed what looked like hairline cracks on the surface of the potting. Not too surprising on a 1995 bike.

Now for the good bit... I fired up the fan bake oven and cooked them for 6 hours at about 65 - 70 C.

The reason for doing that was water ingression. CDI's have high internal voltages and if water is getting in then that voltage will start dissipating via insulation leakage. We use this technique at work a lot to dry out electronics that test low for insulation values; it's surprising how quickly it comes back up. You don't have to take it to boiling, just hot enough for long enough in a dry environment to get the water out.

After cooling and reinstallation of CDI's, the bike fired up immediately and ran better than it's run in years.

I want to stress that this is diagnostic or last resort stuff. Do it only when you've got cash and a source for spares lined up. The fix is temporary at best - I've tried coating the outside of the potting in silicone grease, but the bike's showing signs of having trouble again (it's only been three weeks). Replacing the potting would be ideal but that's a saga in itself, and anyway there'll be electrolytic capacitors in there which should be replaced as well. New CDI's for me when I can afford them.

Apologies for the novel, good luck and let us know how it goes. Now for the jokes to begin...

Hey thank you for the message!!

admittedly mine reacts exactly the same in cold/ humid conditions
I'll pull mine off and take a look when i know for sure it is the CDI bugging out.

Thank you so much for the "novel" absolutely useful!! :)
will update!

[OddDuck]

A quick update on the CDI's in the 900ss - just back from a 470-mile trip around the lower North Island, quite a bit of it in light rain. Baked-and-greased CDI's worked just fine.

[STEPHASAUR]

UPDATE:

So since the last post I have sourced a replacement CDI which has been tested against the old with very little success
Tested the voltages coming out of the rectifier (incase it had failed again) to find everything was more or less on point.
Tested voltages being produced by the stator - all of which were also fine (couldnt get a reliable result when the bike was running as it barely ran)
Have also tested the ohms on the pulse generator, as one of the suggestions was a sensor was faulty and going OC at random intervals leading to a loss in cylinders. Yet to pull the cover off and physically inspect the sensors however the readings for the both of them were as followed:
yellow / yellow white: 441 ohm
blue / blue white: 426 ohm
Apparently the OEM readings are meant to be anywhere between 315-380ohm (don't quote me on that as i may be a few off) but that shouldn't make too much difference??

Did pull the carbs off again to find that on the underside of the fuel line from filter-> carb did have a massive split in it which could suggest its hesitation when throttle is applied, and perhaps the issue of it dying full stop.
Will be pulling off each individual carb tonight for a full clean up/ re-adjustment as they were set to 3.5 rotations open as opposed to OEM settings which is apparently 2.5 (fuel adjustment) along with checking the valve clearances and re-balancing the carbs (provided there is time)

I suspect battery #3 has also shit itself (not going for motobatt again) only producing 8v under load after a full charge (and discharging rather quickly).
The choke doesn't seem to engage till at least 3/4 into it's turn, which may also be an issue, but that's probably less to do with the running of the machine and more the initial startup.

On the topic of amazing luck i'm having with this metallic horse, the trusty flatmate kicked my front fairing/headlight housing and broke the brackets attaching the headlight... yay

but yea, any recommendations for stuff to look out for while the bike is more or less in pieces?

Thanks in advance!!

[OddDuck]

Kudos for work done so far!! A bit shit that the CDIs didn't sort it.

Right, stuff to look for:

Rust from the tank clogging the fuel filter.

Rust from the tank clogging the carb jets especially slow jets.

Crappy sealing on the air filter allowing air to bypass, this'll super lean the mixture and make the bike run like a dog. Alternately a clogged air filter will rich the mixture up, fouling plugs and leading to weak spark etc.

Vacuum leaks between carb bodies and intake valves - old rubber is suspect #1, then cracked insulator plates etc. Look for dirt traces. If you can see flats set on any O-ring, chuck it.

Pickup coils going open circuit / intermittent after they get hot - difficult to check with the motor in bits, try warming up after reassembly and see if this resistance increases or changes.

Check coil windings resistances.

Test compression in each cylinder if you haven't already.

Go around and (it can't hurt) unscrew and clean each grounding point. Oxide and dirt can really screw a ground up, you need a decent metal to metal contact. 800 grit wet and dry helps, old crimp joints in the wiring are suss too.

Last thing, possibly the most important: if it's eating batteries then there's a chance that you've got a short somewhere. The wiring loom may have frayed and one of the 12V wires could be shorting to the frame, possibly under vibration while running. PITA to diagnose and find... it might need lifting the entire loom off the bike and visually checking for damage.

Apologies if you've done these before, I've got a bit on and haven't time to go through thread again. Good luck.

[Akzle]

UPDATE:

So since the last post I have sourced a replacement CDI which has been tested against the old with very little success
Tested the voltages coming out of the rectifier (incase it had failed again) to find everything was more or less on point.
Tested voltages being produced by the stator - all of which were also fine (couldnt get a reliable result when the bike was running as it barely ran)
Have also tested the ohms on the pulse generator, as one of the suggestions was a sensor was faulty and going OC at random intervals leading to a loss in cylinders. Yet to pull the cover off and physically inspect the sensors however the readings for the both of them were as followed:
yellow / yellow white: 441 ohm
blue / blue white: 426 ohm
Apparently the OEM readings are meant to be anywhere between 315-380ohm (don't quote me on that as i may be a few off) but that shouldn't make too much difference??

Did pull the carbs off again to find that on the underside of the fuel line from filter-> carb did have a massive split in it which could suggest its hesitation when throttle is applied, and perhaps the issue of it dying full stop.
Will be pulling off each individual carb tonight for a full clean up/ re-adjustment as they were set to 3.5 rotations open as opposed to OEM settings which is apparently 2.5 (fuel adjustment) along with checking the valve clearances and re-balancing the carbs (provided there is time)

I suspect battery #3 has also shit itself (not going for motobatt again) only producing 8v under load after a full charge (and discharging rather quickly).
The choke doesn't seem to engage till at least 3/4 into it's turn, which may also be an issue, but that's probably less to do with the running of the machine and more the initial startup.

On the topic of amazing luck i'm having with this metallic horse, the trusty flatmate kicked my front fairing/headlight housing and broke the brackets attaching the headlight... yay

but yea, any recommendations for stuff to look out for while the bike is more or less in pieces?

Thanks in advance!!

is it wrong that reading this, posted by a chick, gives me a semi?

I would say, young luke, that youllre well on the path of righteousness.

[Akzle]

Kudos for work done so far!! A bit shit that the CDIs didn't sort it.

Right, stuff to look for:

Rust from the tank clogging the fuel filter.

Rust from the tank clogging the carb jets especially slow jets.

Crappy sealing on the air filter allowing air to bypass, this'll super lean the mixture and make the bike run like a dog. Alternately a clogged air filter will rich the mixture up, fouling plugs and leading to weak spark etc.

Vacuum leaks between carb bodies and intake valves - old rubber is suspect #1, then cracked insulator plates etc. Look for dirt traces. If you can see flats set on any O-ring, chuck it.

Pickup coils going open circuit / intermittent after they get hot - difficult to check with the motor in bits, try warming up after reassembly and see if this resistance increases or changes.

Check coil windings resistances.

Test compression in each cylinder if you haven't already.

Go around and (it can't hurt) unscrew and clean each grounding point. Oxide and dirt can really screw a ground up, you need a decent metal to metal contact. 800 grit wet and dry helps, old crimp joints in the wiring are suss too.

Last thing, possibly the most important: if it's eating batteries then there's a chance that you've got a short somewhere. The wiring loom may have frayed and one of the 12V wires could be shorting to the frame, possibly under vibration while running. PITA to diagnose and find... it might need lifting the entire loom off the bike and visually checking for damage.

Apologies if you've done these before, I've got a bit on and haven't time to go through thread again. Good luck.

https://cdn.meme.am/instances/60465496.jpg

[OddDuck]

https://cdn.meme.am/instances/60465496.jpg

It's just how I am.

Bike's sick.

Must help.

[Madness]

So... not going for motobatt again

There was once this epic battery thread. I'd post a link but some of the technology discussed in this thread was of such a commercially sensitive nature that it had to be deleted. Before it's removal, the thread clearly established that Yuasa motorcycle batteries are in fact the best motorcycle battery that money can buy.

You're welcome :niceone:

[Akzle]

There was once this epic battery thread. I'd post a link but some of the technology discussed in this thread was of such a commercially sensitive nature that it had to be deleted. Before it's removal, the thread clearly established that Yuasa motorcycle batteries are in fact the best motorcycle battery that money can buy.

You're welcome :niceone:

i dunno bro, i've heard that those shorais are pretty trick...

[OddDuck]

+1 on the Yuasa's, I have had nothing but good service from them.

If you don't have the coin then there's the Katana battery line, they're basically Yuasas, but made with recycled materials. Running one in the Ducati now, have beaten the hell out of it over winter (repeated discharges due to CDI issues, standing for a week or two, etc etc), still going strong.

My post earlier... yeah it went on a bit, but if you've found a split fuel hose I'd say it's worth going over as much as possible. Check everything, be sure.

[STEPHASAUR]

UPDATE:

So managed to check the valves, and was rather surprised with the results. OEM settings are meant to be .13-.19 for intake, and .20-.26 for exhaust.

INTAKE:
1 - .152/ .152
2 - .127/ .127
3 - .127/ .102
4 - .102/ .102

EXHAUST:
1 - .203/ .279
2 - .203/ .203
3 - .203/ .203
Biiiiit out of whack to say the least (assuming they should all be identical)

@OddDuck: Thank you for all the suggestions. Will start cracking away at those
@Madness: thanks! I'll take a look now. absolutely over Motobatt haha.
@Akzle: Glad to have been of service :P

Thankfully the boys at the workshop she's now stored at have given permission to completely strip the thing, so i'll be able to check absolutely everything and hopefully get a running bike out of it!

[Paul in NZ]

I would also suggest that you fit an earth rail bonded to the chassis and run and extra earth to the CDI mount and the engine cases. Also Instruments if there is a place to ground them. As they age, using the chassis is not so reliable.

Any battery providing 8V is rooted. Nothing will work properly until you have sorted that out.

Interesting project btw…

[STEPHASAUR]

UPDATE: Still no real success.
re-assembled the engine after a check up/ fix/ replace of a few small things, threw tank on and tried to turn over.

during this attempt i noticed a lot of fluid gushing out of the carb bowls... crap.
well. Time to order some new carb- bowl gaskets LOL. shame they're so damn expensive in nz (cheapest I was quoted was $35 a piece)

So no idea if the bike will run, as it's not getting fuel. If after the gaskets are replaced she still wont start up I'll be throwing a new pulse generator in, if that fails then will take a good hard look at that damn loom. Not going to deny it's been hacked up to a point beyond recognition by its previous owner/s... So wouldn't surprise me in the slightest if that ends up being the cause.
If even after that I cannot get the old girl to run... well then... suppose It'd be time to look for a professional.

In other news. flatmate had another domestic. destroyed my fairings. looks like I'm ordering some from china! Just what I needed!!

[Akzle]

In other news. flatmate had another domestic. destroyed my fairings. looks like I'm ordering some from china! Just what I needed!!

you mean THEY are ordering, right.

Carb reco kit. Smebike.

Insert witticism about mating in your flat.

[Katman]

The bike is a dog and lemon mutation.

Get rid of it.

[STEPHASAUR]

She's going halves on it. better than not at all I suppose.

And nope. I was dumb enough to purchase it, i'll endure a little longer. TBH it hasn't cost much at all so far, just hours of agony, which is still experience I wouldn't have otherwise gotten. Not going to deny I have been scrolling the internet for a replacement however...
On a positive a mate has lent me a little 125 cbr for the last few months, so still getting the daily commute on a bike

[OddDuck]

Sucks about bad flatties doing stupid shit like that.

You'd said earlier that it was sparking OK - is it still sparking?

If you're getting petrol leaking from the carb bowls - surely the bike is getting gas? Try cranking it and then if no start, pull the plugs. If they're wet with petrol then that isn't the problem.

[Drew]

Does the bike only have three sets of exhaust valves? They don't have to be identical at all. Each one just needs to be within spec.

[Askor]

If one of my flatmates even touched any of my bikes....:mad::mad::mad::mad::mad::mad::mad:

Get the cunt to pay for all of it, the damage that SHE did.

[STEPHASAUR]

You'd said earlier that it was sparking OK - is it still sparking?

If you're getting petrol leaking from the carb bowls - surely the bike is getting gas? Try cranking it and then if no start, pull the plugs. If they're wet with petrol then that isn't the problem.

Admittedly I didn't pull the plugs... should probably try that LOL
but yea, they are still sparking. If the plugs are wet then what do you think could be causing it? faulty spark?


Does the bike only have three sets of exhaust valves? They don't have to be identical at all. Each one just needs to be within spec.

Apologies! I must've forgotten to add the additional one.
two were out of spec, so threw some new ones in to rectify that.

[Paul in NZ]

One thing that will kill a motobatt battery real fast is over charging. They don't tolerate a high charge rate like a good lead acid will.

Keep at it - you will get there... maybe ;-)

[OddDuck]

Admittedly I didn't pull the plugs... should probably try that LOL
but yea, they are still sparking. If the plugs are wet then what do you think could be causing it? faulty spark?

No, just a basic check to make sure that fuel is making it to the cylinders. I know you'd said there was fuel coming from the carb bowls due to bad gaskets, that means fuel should be making it up through the jets to the cylinders, but assume nothing.

At this point it's getting puzzling to say the least... hang on. Cold garage? Old fuel? That's a classic with older bikes, there might actually be nothing wrong any more. Unleaded does go off, if you haven't already or recently, try completely draining the tank, chucking in a couple of litres of fresh stuff, and see how you go.

[STEPHASAUR]

At this point it's getting puzzling to say the least... hang on. Cold garage? Old fuel? That's a classic with older bikes, there might actually be nothing wrong any more. Unleaded does go off, if you haven't already or recently, try completely draining the tank, chucking in a couple of litres of fresh stuff, and see how you go.

Bike is currently stored in a workshop, gets rolled outside each day then rolled back in after shop closes up. Fuel was new, had completely drained the system before putting the new stuff in (mobil 98)
I think my bike just hates me... LOL



Keep at it - you will get there... maybe ;-)

hopefully! >.<

[STEPHASAUR]

UPDATE:
Managed to order some gaskets from Taiwan that arrived within a week!
The pricing was great and the kit was for all the seals/ washers in the carbs, which was great as right after the float bowl gaskets are replaced the fuel started gushing out the inlet pipe of all things

Carbs were disassembled to find there wasn't much left of the old seals - a possible answer to the ever going mystery.
Just as I reached the final air fuel mixture jet, Zenki decided to do that she does best... BREAK!
The indents to fit the screwdriver snapped clean off leaving us no choice but to drill the final one out!! Thankfully the carb was undamaged.
Now waiting for a replacement to arrive which will probably be another fortnight but at least there's progress!

[STEPHASAUR]

UPDATE:
YAY! all assembled and ready to go! Except she didnt go

what I think the issue may be is perhaps the fact that the carbs have not been balanced/ tuned/ whatever you call it.
Quite possibly I have it all set up wrong as while trying to turn it over it catches something then just dies. that has to be fuel related, right?
Bike is most definitely sparking, pulse generator could also be an issue but for the moment it does seem to be behaving/
the plugs were dry, idle was set all the way up (along with choke) and the bowls are definitely filled with fuel

is there anyone auckland way who would be best recommended for this type of work?

[Drew]

UPDATE:
YAY! all assembled and ready to go! Except she didnt go

what I think the issue may be is perhaps the fact that the carbs have not been balanced/ tuned/ whatever you call it.
Quite possibly I have it all set up wrong as while trying to turn it over it catches something then just dies. that has to be fuel related, right?
Bike is most definitely sparking, pulse generator could also be an issue but for the moment it does seem to be behaving/

is there anyone auckland way who would be best recommended for this type of work?Sounds to me like you've got the plug leads the wrong way round.

[nzspokes]

Sounds to me like you've got the plug leads the wrong way round.

Was thinking the same thing.

[STEPHASAUR]

UPDATE:
Managed to resolve the issue the evening of my last post!

I had the air fuel mixture screws wound in far too much (1 5/8th of a turn) which is just a number I saw on another forum. After winding it to 2.5 turns from fully closed the bike ran!
Now just need to finetune it as the idle was hunting between 4-6k rpm and yes, both the choke and idle adjust were disengaged. Wondering if reducing the turns to just 2 on the screws along with a check that the throttles aren't sticky etc would sort this

Won't be able to check till monday anyway, but will keep posted!
so happy the thing runs though. It's been far too long! :D

[STEPHASAUR]

Seems I am now plagued with this new issue.

the bike now happily idles at 2k rpm, however I find a slight blip of the throttle will bump it up to 4-6k rpm and it'll just hover there for a few seconds before coming back to rest. Both choke and idle adjust are wound all the way out, and the screws are wound back to 2.5 rotations (had wound them down to 2 which only seemed to starve it of fuel)
Adjusted the butterfly valves by eye, so they may not be 100% identical. All valves are sealed

nothing seemed "sticky" but then again I don't really know what to look out for. Perhaps still over fuelling?

[Drew]

Seems I am now plagued with this new issue.

the bike now happily idles at 2k rpm, however I find a slight blip of the throttle will bump it up to 4-6k rpm and it'll just hover there for a few seconds before coming back to rest. Both choke and idle adjust are wound all the way out, and the screws are wound back to 2.5 rotations (had wound them down to 2 which only seemed to starve it of fuel)
Adjusted the butterfly valves by eye, so they may not be 100% identical. All valves are sealed

nothing seemed "sticky" but then again I don't really know what to look out for. Perhaps still over fuelling?

Balance could be out on the butterflies. Could he an air leak. Could be a bung throttle cable.

[aprilia_RS250]

Balance could be out on the butterflies. Could he an air leak. Could be a bung throttle cable.

I reckon it's knob cheese. :msn-wink:

[Drew]

Since you balanced the carbs by eye, I'd bet the issue is there. Balance them by ear with a small plastic hose held over the lip of the velocity stack.

[Askor]

Balancing by eye can get you pretty damn close, I reckon she has an airleak somewhere, or the idle circuit is set far too lean. Check your vacuum hoses/connections.

[Yow Ling]

too lean, wot charlie said

[STEPHASAUR]

Decided this is starting to get a bit beyond me so organised someone to come down on sat and have a look at her. Would rather have it done right the first time then make multiple repeats due to error!
Will run through all that's been suggested when he comes around!

an update will pop up sunday :)

[STEPHASAUR]

UPDATE:
so finally FINALLY these bad boys arrived!

http://i881.photobucket.com/albums/ac20/Iamnothingbutshadow/float%20valves_zpsc8fmv0cv.jpeg (http://s881.photobucket.com/user/Iamnothingbutshadow/media/float%20valves_zpsc8fmv0cv.jpeg.html)

Just noticed I didnt actually post an update to what was wrong, but we discovered that the float valves had rings on the rubber points (dont know the technical terms haha)

so measured up the originals and ordered these from China. Quality looks pretty good. Won't be able to throw them in and set up the carbs correct this weekend as the racecar is going in for some major work so will probably have to just sit tight and wait till the following week after work or something :(

fingers crossed this sorts it (or at least gets us significantly closer to completion!)

[Dannz]

Did that sort it out?