OzVMX Forum
Clubroom => Tech Talk => Topic started by: PCMAX on April 25, 2012, 07:49:59 pm
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My '81 RM started playing up last weekend it runs great into the start of the power band but then as you hit peak power its like it is running out of fuel or spark particularly if I jam it full open.
I have done the following but the problem persists:
*Replaced the spark plug
*Replaced the plug cap
*Replaced the stator coil assembly
*Cleaned the carby & jets & needle valve & set the float level
*Tried a bigger (270) and smaller (250)main jet
*Pulled the barrel off and checked the piston, rings & reeds
Has anyone had any similar problems or does anyone have any suggestions???
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Have you completed a few plug chops when the problem is occuring?
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My '81 RM started playing up last weekend
so it was running ok before then?
and now it's just started to play up?
and you've replaced the stator/coil assembly with no change?
a blown main seal perhaps.
does it blow smoke when its playing up?
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hi max
sounds like ignition coil.
runs ok down hill and revs ceanly
uphill is a bag of poop coughing and spluttering.
ignition coil will breakdown under heavy load.
being high revs and uphill
Thanks
DOK
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Blocked exhaust?
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Blocked exhaust?
Took the words right out of my mouth, er, keyboard. Check the muffler first, and then the rest of the pipe.
Tex
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How about a partially blocked feul tap/filter. Cheers
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wasp love to build nest in exhaust pipes at this time of year and their good at fully or partly blocking bike exhaust,get a piece on wire with a small hook and go fishing for worms/spiders
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Thanks for all the replies, I will try swapping out the ignition coil today and checking the internals of the expansion chamber and muffler. Will let you know how it goes after that.
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Checked the ignition coil today and found that I have 50,000 ohms resistance from the coil (black/white wire) to the plug cap. The book says I should have 10,000--11,000 ohms so I guess ths could be the problem. Unfortunately I don't have a similar coil to troubleshoot with, all the spare ones i have only have one wire and a plug lead.
Does anyone know what the other wire (white/blue) that runs from the ign coil does??
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One wire is the supply to the coil the other is earth back to the engine at the stator end.
You can use the later z d e f g coils. They all have near enough spec but they are internally earthed so earth to the frame where the bolt on.
Just try the one wire coils you have as a test and only connect the supply wire in the plug, leave the other connector in the plug empty
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on the h/t side of the coil did that test/specs include the resistor plug cap?
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Well another day of blasting up & down the street anoying the neighbours..... Cleaned the pipe (internals) and muffler, checked the crank case breather was clear, tried a mates ignition coil, same problem. Put another 32mm Mikuni on, same problem. Tried another CDI, same problem put another old stator on, same problem. Will pull the barrell off again tomorrow and check the reeds again just in case they are any different from last time I checked.
It runs fine until just before peak power then coughs & dies, if I hold the throttle wide open and keep rolling it eventually fires back into life and then dies again, if I then close the throttle and coast it will become responsive again at low reves and then the whole scenario repeats as I get to peak power.
If I cant fix it tomorrow I'm probably going to do the unthinkable, something I have never done since I started playing with bikes in 1973.....Take it to the bike shop (probably Gunters in Woollongong) and ask/pay them to fix it. A sad day indeed !!
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Pete check your fuel delivery, sounds like its starving
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crank case seal????
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fill the tank and see just how much comes out of the hose going to carb coz its sounds likes it running out of fuel,had a 185 do that till i drilled the passage ways and fitted a bigger needle and seat.fuel filters on taps block up as well maybe try removing it or at least cleaning it,do a test of how many secs to fill a stubbie with filter fitted then another without full tank both times.the hose from tap to carb isnt to long and vibrates too much as had a briggs stationary motor do that and it stopped fuel getting to the carb,no dout its something simple like too small of a needle/seat off of a less powerfull motor maybe
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pc max i think they mean the breather on your fuel cap see if that is blocked.
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Pete sounds like fuel issue to me. But I had an 83 Husky years ago that would die or break down at high revs. Local Husky bike shop said to check that a piece of quartz crystal was not stuck in the main jet as it had happened before and when put to light it was see through. bugga. That was not it. I farted about till late one arvo till I started it in the dark and found a big fat blue spark jumin from the plug cap to the expansion chamber. Simple fix was chuck out the black rubber cap and install a NGK red silicone sucka. $5 fix..............
Pete # 100%
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Thanks for all the suggestions guys.
*Bazza, i'm really hoping its not a crank case seal, is there any other way I can check this without splitting the motor?
*TT5 Matt, I will give you flow check theory a go today have put a new filter in & tried 2 different carbs but did not check if the have the same needle/seat.
*Micks, I ran the bike with the fuel cap off, same problem, so its not the breather there.
*Pete Ringo, tried a couple of alternate plug caps but not a silicone one. Might buy one tomorrow
Thanks again to all for your suggestions, will let you know how it goes.
Peter
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This is going to sound really really silly but are the engine mounts tight. Lose engine mount - vibration high rpm - bad earth -bad spark - bad miss - head scratching. A 125 may not be easy to detect a lose engine mount unlike a open class bike.
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Thanks for all the suggestions guys.
*Bazza, i'm really hoping its not a crank case seal, is there any other way I can check this without splitting the motor?
*TT5 Matt, I will give you flow check theory a go today have put a new filter in & tried 2 different carbs but did not check if the have the same needle/seat.
*Micks, I ran the bike with the fuel cap off, same problem, so its not the breather there.
*Pete Ringo, tried a couple of alternate plug caps but not a silicone one. Might buy one tomorrow
Thanks again to all for your suggestions, will let you know how it goes.
Peter
Check the air gap the spark will jump. Also check your float level, set that so it's just before fuel runs out the overflow.
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Hi PCMAX
can you try a down hill run at peak revs.
To me it still sounds like ignition coil.
Fine one day shit the next.
David
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Update #5 checked the fuel flow per TT5 Matt's suggestion. 16 sec to fill 200ml with filter in line, 8 sec without so I just ran a new hose without filter. No improvement. Also removed the fuel cock and opened it up a bit with a 5/32 drill.
*Montynut--check tightened all of the engine mounts and have cleaned all the elec connectors and earths.
*DOK my street has a bit of a downhill but at peak revs she just dies. Tried a mates ignition coil from his 1978 RM125 same part number but it didn't make any difference.
After another disapointing run up/down the street I took the oil filler cap of and shone my torch in to see if I could see any evidence of gasses from a bad crank seal per Bazza's suggestion.
No wisps of fuel fumes but I had a eureka moment when i spied a garter spring on the R/H crank seal. I presumed that the idiot (me) that had put it in last time the crank was out (just before it started playing up) had installed the seal back to front and that was going to be the answer to all my problems. I convinced myself that at peak RPM/crank case pressure the gas was dumping past the seal and into the clutch casing causing it to die.
I removed the clutch cover, clutch and primary drive/water pump gears and popped the seal out only to find that it had a garter spring on both sides and was installed correctly (manufacturers numbers to the outside). However in carrying out this procedure I must have damaged the seal during the remove/install process as she now blows blue smoke like a Singapore mosquito fogger. That really impressed the neighbours......
So I will order another seal tomorrow and look forward to replacing that (NOT!!!) the weekend after next as I am up at Coffs at a mates 50th next weekend. Dissapointed about missing HEAVEN round 3 at Canberra but he's only 50 once i guess, and has booked and paid for my accom.
Anyhow i'm now kicking back now with a very fine Barrossa Valley shiraz wondering where my weekend went.
To be continued...............
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Howdy pcmax,
my '79 rm125 developed a "bog, rev, bog, rev,bog, rev" symptom after 1/2 throttle. Even in neutral.
Turns out, the boost bottle hose spigot which was drilled ( by previous owner ) into the right side crankcase at the transfer port wall was not air tight.
The clue was oil residue around the pipe/crankcase interface.
Anyway, sealed the leak and engine runs sweet.
Check for leaks around and about.
Cheers, kitakitsune.
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PGMAX it might not be soon BUT YOU WILL LAUGH ABOUT THIS ONE DAY !!! I like the way your keeping at it
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My Dad a small motor mechanic for years once showed me this trick , you remove the exhaust, carb air box etc , you then tip raw fuel into the inlet and start if the bike hits full revs as it SHOULD then you replace one at a time till it doesn't.
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ok you know theres plenty of fuel TO THE CARB but is it getting into the carb fast enough?has someone put a little needle and seat in there?is there a partial blockage the the fuel inlet passaages going to the n/seat like abit of fuel hose,try some fuse wire through them and of course compressed air.as a final check fire it up again and get it to do whats its been doing and turn the fuel tap off at that moment its cutting out and remove carb off bike and remove carb bowl and see how much fuel is in there.
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blocked carbie breather tubes. They are not just overflows but also allow air out of the carbie. If they block it can force the level of fuel in the carbie to be very low and also fill slowly. A bloody wasp taught me that once ::)
;D Not the WASP on here the winged/stinging version ;D
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I agree reg, sounds like a classic case of very low flow of fuel.
Pancho
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It does sound like fuel but sometimes it’s hard to distinguish between fuel and spark problems.
As already mentioned the carby vents are worth a check.
Also wondering if the flywheel has spun upsetting the timing.
Coils and stators can work but break down under heat and demand.
I know this sort of thing can be frustrating but if you give it to a shop they will double check all the same things you have looked at and charge you for it.
You can send the whole ignition away for testing, flywheel, stator, coils etc and they will test it in a running scenario.
There are a few places around that do this for around the $80.00 mark plus postage.
Sometimes it can be worth the 80 odd dollars just to rule out electrical problems
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Black Box ! :-\
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Black Box ! :-\
Great 90's dance music group .. think I have one of their albums somewhere ;D
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Yeah i think it's about track 4 = "Flat spot on top" - not real good to boogie to from memory :D
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Thanks again guys for all the suggestions. Think I have eliminated all of the carby breather/needle & seat problems by installing another 32mm Mikuni but it made no difference at all to the performance.
I originally (about 18 months ago) had problems with the OEM stator coil so I had it tested by Small Coil Rewinds, they found one of the two coils to be faulty and rewound it for $120 a couple of meetings later it started playing up again so I sent the coil to a guy called Andy Wheeler on the central coast, he found that the other of the two coils was faulty and rewound that for me for another $120. Not long after that it started coughing & farting again & rather than spend another $120 I put a spare stator coil from an 82 CR125. That has worked well for over a year and produces a strong spark. During this period I also bought an aftermarket coil from RM Stator in Canada, that lasted just one meeting at Canowindra in 2010. At least the guy refunded my money but i had to pay $36 to send it back to Canada.
When it first started playing up in March this year I immeadiately suspected the stator coil and swapped it with the one I have in a running '82 CR125 but it made absolutely no difference to the problem so I eliminated that as the issue.
Anyhow just "to be sure, to be sure," I have ordered an aftermarket OEM copy from Rick's Stator in the USA and will fit that when it arrives and let you guys know what happens
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I've been following this post with interest to see what the problem works out to be and only now noticed that you have declared you are running CR125 ignition parts. Is that right or do I need to go and lie down? Surely the parts are not going to be compatible? If it's an RM125 then surely youwould use RM125 parts only, even if ignitions from other makes/models fits, they still might not be compatible. Maybe I'm wrong (been wrong more times that I can remember) but I can't see that ignitions systems and particularly component parts are too interchangeable.
I recall using the services of Small Core rewinds (in Geelong) once back in the early 90's when my RS125 developed an ignition problem at around 12,500 rpm that resulted in my exhaust pipe continually splitting. Is the owner still Bert Neville (or a similar name)? I would personally stick with them on ignition matters, or at least stick with the one supplier.
And it also sounds like you've had an ongoing issue with ignitions. Personally I've never heard of such a continuance of problems ... is there something else going on that you haven't mentioned yet?
Sorry just asking to see if some more information comes to light as I believe your problem must be frustrating the hell out of you.
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Simo, all high voltage CDI's work the same way, coil specs are within a few 100 Ohms of each other, the only incompatable bits are the wiring and how the kill switches work.Sounds like the complet ignition was swapped over. Bert Neville might be able to fix and repair coils but unfortunately his ignition knowledge on 2T engines ends there. Your RS would have been over retarding and firing on or after TDC causing fuel to ignite in the pipe(RS's retard off to about 5deg BTDC at that rpm).
Has anyone got a report on the air gap the spark will jump? If not you wasting good money after bad with all the repairs etc etc. That is what determines the health of the ignition. Min is 5mm there is no maximum.
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Simo, all high voltage CDI's work the same way, coil specs are within a few 100 Ohms of each other, the only incompatable bits are the wiring and how the kill switches work.Sounds like the complet ignition was swapped over. Bert Neville might be able to fix and repair coils but unfortunately his ignition knowledge on 2T engines ends there. Your RS would have been over retarding and firing on or after TDC causing fuel to ignite in the pipe(RS's retard off to about 5deg BTDC at that rpm).
Sorry Lozza but I must have misread the OP's post. I though he said he replaced the stator coils with CR items .. isn't that the coil on the stator plate, screwed to the LHS of the motor? Surely they aren't the same for RM and CR? Or are stator coils what I would call the ignition coil (eg under the tank area that the spark plug lead eminates from)?
And the RS ignition was definately faulty and sporadically advancing and then retarding as much as 13 degrees which was the source of all the problems .. I won't go into the full blown story in detail here but it was character building stuff apparently ::)
Anyway, needless to say I learnt how frustrating ignition problems can be so back to the original post and lets see if we can help PCMax before it gets too much for him.
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The earlier 76-78' RM two piece stators were physically the same as the CR's , and even the later model bridged ones fitted -79' thru early/mid eighties :)
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The earlier 76-78' RM two piece stators were physically the same as the CR's , and even the later model bridged ones fitted -79' thru early/mid eighties :)
This is one of the things I love about this site .. something new to learn every day.
Has anyone got a report on the air gap the spark will jump? If not you wasting good money after bad with all the repairs etc etc. That is what determines the health of the ignition. Min is 5mm there is no maximum.
Lozza could you please explain a bit more about this. Are you saying the spark needs to be able to jump at least 5mm to be considered good? Is that just on kick over?
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Simmo, ignition problems should not be frustrating at all. I'm yet to even read where the engine has been strobed with a timing light. That is the most basic check you can perform, I fail to see how you can do without a timing light for setting up or diagnosing an engine.
Overview.
The ignition coil merely amplifies then dumps voltage to the plug. The source and pulse coils are located on the stator, they provide the voltage for the spark and a small trigger pulse, so the CDI can tell the coil to dump to the plug. The position of the magnets in the flywheel say when the trigger pulse is timed.
It does not matter 1 aviating sex act who made the ignition,pulse or source coils what matters is WHEN it sparks in relation to TDC.
The igntion 'curve' is controlled by the CDI it will have a maximum amount of advance, and retard from there according to RPM. The ignition cannot predict the future.
So we come to the air gap. First I'll ask this question under what condition is the spark attempting to jump from the J strap to the centre electrode?
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Thanks for the informative learnings Lozza, ignitions and wiring in general always seems complex to me mainly becasue I have never learnt or understood them. Hence I guess the potential frustration.
So we come to the air gap. First I'll ask this question under what condition is the spark attempting to jump from the J strap to the centre electrode?
I'm not sure what you are asking here. I thought you were saying that the spark needs to be able to jump a minimum of 5mm to be considered a good spark. Did I get that wrong?
Sorry to PCMAX for getting a bit off topic but maybe these questions will help him as well?
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Yes the spark needs to jump a min of 5mm air gap, but what I'm asking is WHY do you think it needs to be able to jump a 5mm air gap to be considered healthy.
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Because the resistance across the plug gap increases in accordance with the increased compression pressure as the volumetric efficiency reaches its max.
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The igntion 'curve' is controlled by the CDI it will have a maximum amount of advance, and retard from there according to RPM. The ignition cannot predict the future.
I use a strobe to set my timing on all my engines and have noticed that there is no advance at any revs on my 2/stroke huskys .
The mark stays exactly where I have set it from idle to flat out.
Do I have a problem ?
Mike
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Because the resistance across the plug gap increases in accordance with the increased compression pressure as the volumetric efficiency reaches its max.
Basicaly, the plug must fire under pressure and turbulence also at higher rpm with less time to recharge the capacitors.
I use a strobe to set my timing on all my engines and have noticed that there is no advance at any revs on my 2/stroke huskys .
The mark stays exactly where I have set it from idle to flat out.
Do I have a problem ?
Mike
Just means you have a fixed advance ignition
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Yes the spark needs to jump a min of 5mm air gap, but what I'm asking is WHY do you think it needs to be able to jump a 5mm air gap to be considered healthy.
Lozza, The air gap test is starting to make sense particularly after Pancho's comments "Because the resistance across the plug gap increases in accordance with the increased compression pressure as the volumetric efficiency reaches its max." This sound exactly like what's happening as I can rev the crap out of it in neutral but when it's pulling hard in 2nd or 3rd is when it breaks down.
How do I set up for this test? Is it just a matter of bending the spark plug tang away from the center elcetrode by 5mm? or do I need to modify a plug somehow?
Ohh almost forgot to ask. If the spark will not jump 5mm gap what is the fix? which component should I replace?
By the way I have checked the timing with a strobe and set TDC with a dial gauge in the plug hole, I rotated the stator the stator to achieve a firing point of about 2mm BTDC at idle.
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2mm static timing sounds like too much, I posted a ebay link to a air gaps tester .
. Could be any or all of the compnents faulty if you don t get a good jump across the gap. Look for min 110vac off the stator . All testing should be done at the rpm where the drama is .
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I had a problem on an RM125D where the LHS crank main seal was leaking slightly due to pitting on the seal fitting surface.Common problem on the old water coolers. It was picked up by someone who noticed an oily residue around the stator and flywheel- blowing past the leaky seal.
Another issue was to do with the airspace/gap between the flywheel and the inner metal of the stator assembly. Something about it being uneven from memory.
Is the keyway/key in good shape and is the rotor tightened properly?
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Latest update
I attempted further trouble shooting today. Replaced the stator coils with an after market set from Ricks Stator in the USA....problem persists.
Put the old carby back on (the other VM32 made no difference) and installed a 240 main jet. I was previously running a 260....problem persists.
Replaced the 5,000 ohm resistor NGK plug cap with a 1,000 ohm one.....problem persists.
When I open the throttle fully with the bike in neutral it presents the normal problem (ie missing and spluttering) but I did notice some squirts of fuel from the carby overflow. Why is the bowl over filling? Is this "fuelling"? How does it happen & why?
Lozza/Pancho---I bought a plug gap tester from a guy in Brissy on ebay "partszoos" 14 days later no part, no response to emails. So unable to test if spark will jump a 5mm gap
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It has probably been mentioned before but are you using the same carb manifold every time?
It may be sucking air.
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Yeah using the same carb manifold for each carby. Have had a look at it as installed for splits etc. Might pull it off the bike tomeorrow and have a closer look.
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still thinking seal
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Just start a PayPal dispute and state in 72 hours I'll start a claim. That gets their attention. Have you made a plug chop and posted a pic of the plug and piston crown?
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Bazza, I did think it might have been the seal at one stage but I have replaced the right hand crank seal and there is no evidence of the left hand seal leaking. The flywheel casing is completely dry.
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PCMAX this is real brain teaser,one day you will laugh about it.
Have you sprayed around carb inlet boot to see if it is sucking air from tiny hole/slit?
Has the bike run ok for a few meetings then started to miss one day? or did you buy it and it was lke this?
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Hi there,my KTM had some different looking type of fuel line when i bought it, it looked more like car type fuel line,any way the first few rides on the bike were not too bad but it wass missing a bit before entering powerband,i did'nt ride the bike much but everytime i did the bike got worse, in the end the bike would hardly run and was flooding real bad so the carby was pulled down,the culprit was the fuel hose had started to delaminate on the inside and some black gooey gunk was around the pin that goes holds the float on and the float was sticking open,after cleaning everything out the problem was solved and the bike runs perfectly now,i know your problem sounds more spark related but hey,anythings woth a try at the moment.
cheers Dale.
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don't just spray round inlet for leak do base gasket n crank case gasket had one that was leakn/sukin right below middle of crank
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While it is running spray some aerostart or metho around manifold and gasket areas ....if there is a pick up in revs investigate.
Tmman beat me too it.
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Well well well, Bazza said that one day I would laugh at this.......
After several weekends of replacing components and trouble shooting along with a good deal of head shaking and swearing, today I firstly tried a hotter plug B6ES but that didn't make any difference. Reluctantly I pulled the carby & barrell off AGAIN and checked the reeds AGAIN and had a good look at the rubber inlet boot for cracks etc. Found nothing.
Whilst I had my head jammed inbetween the frame backbone and the now exposed piston and crankcase I happened to look rearward at the hole in the airbox. Some of you may know that the early RM models have a (approx) 10cm round plug in the back of the airbox hard to see as it's just in front of the rear shock spring. I have no idea why it's there as it seems to serve no purpose. Anyhow it had become dislodged and was rattling around inside the airbox.
The bike ran fine when not drawing much air but when I hit high revs/full throttle it was being sucked forward restricting or blocking the airflow to the point where the bike ran like sh*t. So after pulling one side off the airbox and resecuring the plug at the back all my problems seem to have been resolved. She goes like a scolded cat again......Yeee Hawww!!!!
Thanks to all of the contributors to this post for your suggestions I've certainly learnt some stuff. Now where's my glass, no make that BOTTLE, of red.
Until the next major drama.....
Peter
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Well done, more often than not it comes down to it being something simple.
Happy riding.
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good to hear mate
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LOL
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Glad to hear you found the problem, and yes as mentioned usualy end up being something simple.
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I admire your perseverance
I probably would have reached for the bottle of red a few pages ago!