'Amazing Reving CRM' MK11 (I've got one now :-( )

[drillam]

Well to cut a long story shortish I rebuilt my engine due to it having a "revs won't die down problem"
(here's the earlier thread if your bored viewtopic.php?f=6&t=4903 )
It had been running fine when I bought it a few weeks back and went well until I drowned it on Salisbury Plain in a very muddy puddle. Lots of mud in the engine and I eventually came to the conclusion that it had destroyed the crank seals, so time for an engine strip. One of the funny things that happened when trying to diagnose the problem just before I stripped it was that at one stage it revved pretty high on it's own accord and when I hit the kill switch nothing happened and I had to hit the ignition switch. Now I know the kill switch works so I just though it had become intermittant and forgot about it. We'll come back to that in a minute as it's relevant.
So, a new crank pin/big end and conrod, small end, new mains and seals and gaskets came from from LT and I get the engine back together today. I hadn't touched the top end as after a discussion with LT it was advised that it'd be good. It's got a +1.5 PROX piston and the rings were within spec.
I intitially had a problem with the head gasket sealing. It was weeping coolant out of the joint when I filled the rads, this was before I started it, so took the head off again and lapped it on a large piece of granite using course, then med, then fine wet and dry. Back on but still weeping so did it again and this time I used a smear of RED Hermatite. I know a few people have said not to use anything on the head gasket, and others have used it. Don't know if this is relevant but combined with a 24lbs/ft torque to the head bolts instead of the 20lbs/ft advised in the manual it sorted the leak. I've converted the metric torque figures BTW, can't remember what they were, something like 2.7 Newton/thingies I think.
I remember that when I stripped it there was loads of RED gooe all around so the last person to build the engine may have had the same prob, or it may just have been coincidence and he liked using it anyway, who knows?

Started up tonight and it's okish on choke but rough without. Finally after looking on the site I realise I've been a plonker and got the PV cables all bassackwards so redo it and it's feeling much better but - revs are unstable again. Fiddle Fiddle Fiddle and suddenly it starts reving like crazy. I hit the kill switch, no effect. I hit the ignition key, no effect. Finally I whack it in gear and stall it.

So a few relevant points here;
1 It was running fine before I gave it a mud bath, so I know it's capable of it and was
not a problem that came with the bike.
2 It's only on 1.5mm rebore so don't think it has the same problem as the original "amazing revving CRM"
3 The kill switch and ign switch work OK usually, it's only showed a problem at high revs and on both occassions when it has revved of it's own accord.

4 WTF is goin on???? I was supposed to be going for a trail ride tomorrow on Salisbury Plain again, but after being stuck in the shed on the best two days of the year so far getting the wee bugger rebuilt I have another day tomorrow now :-(.
Any clues ?

cheers
Millard

PS
In spite of the thread title it's actually a MK1

[Jonorow]

you will sometimes find that when it starts reving like this, your mixture is way out and the reason your kill switch doesnt work is you;ve heated up the plug and it's glowing, therefore keeping the engine going at these high revs. I've had this happen a few times on my old CR. only real way of stopping it is stick it in gear with the front brake on then dump the clutch!. hopefully it wont jump too far forward and rip your arms off.
Just check all the mixture settings and go from there. another one that happend on my twin Jawa, i got the pistons the wrong way round and bloked the transfer ports up, when it fired, it went straight to WOT, prob down to excess fuel in the crankcase.
try and only use the fuel in the float bowl untill you sort the problem, atleast in will stop after a while then.
Jon

[CR Mmmmm]

I can,t help with you,re problem, but if you get it sorted I,m thinking of going onto the plain tomorrow, it,s a bit boring on my own. Give me a shout. Good luck.

[fallenmikethebike]

There must be some commonality, here somewhere, so expanding Jonerows thoughts, what plug were you running? when the the revs went ballistic, and any others this has happened to, is it as simple as a racing type plugs use?
Mike

[drillam]

"you will sometimes find that when it starts reving like this, your mixture is way out and the reason your kill switch doesnt work is you;ve heated up the plug and it's glowing, therefore keeping the engine going at these high revs. I've had this happen a few times on my old CR. only real way of stopping it is stick it in gear with the front brake on then dump the clutch!. hopefully it wont jump too far forward and rip your arms off.
Just check all the mixture settings and go from there. another one that happend on my twin Jawa, i got the pistons the wrong way round and bloked the transfer ports up, when it fired, it went straight to WOT, prob down to excess fuel in the crankcase.
try and only use the fuel in the float bowl untill you sort the problem, atleast in will stop after a while then.
Jon"

Cheers Jon
I can understand the glowing plug and the kill switch not working, but why did it suddenly rev it's nuts off? I wasn't playing with the twistgrip at the time. I had been fiddling wi the throttle stop screw when suddenly it really took off.
The more I think on it the more I think your right. Gotta be a fuel related prob as the ignition is non adjustable, either it's right or it's not.
The PV seemed to be working ok after I corrected my cabling prob and when I revved it I could see the valve moving to and fro, and it rested on the mark.
Oil pump is adjusted correctly but I ran it on a small amount of premix as I wanted to ensure the oil pump had time to do it's bussiness for the first few minutes of initial fire up.
I used the same mix I used to use for me Beta Techno trials bike and I keep ready for some garden tools.
I'm going to strip the carb again. It had a non standard needle with four positions and it was in the second from top when I first stripped it. I'll take another look to make sure I put it all back together correctly, can't really think of anything else that might be causing the problem right now.

"There must be some commonality, here somewhere, so expanding Jonerows thoughts, what plug were you running? when the the revs went ballistic, and any others this has happened to, is it as simple as a racing type plugs use?
Mike"

Cheers Mike
Spark plug is the one it came with and it ran fine before I drowned the engine. I'll get the number of it when I get outta me dressing gown and open up the shed.

"I can,t help with you,re problem, but if you get it sorted I,m thinking of going onto the plain tomorrow, it,s a bit boring on my own. Give me a shout. Good luck."

Cheers CR Mmmmm
Will definately take you up on that at a later date, IF I ever get the bugger running!!

thanks for your replies folks, I'm off to the shed now for another day of spannering and cussing.

[drillam]

Well I think I've found the problem, it's me being a plonker again.
Looks like this wee spigot on the side of the carb is not blanked off as I first thought

http://i14.photobucket.com/albums/a340/ ... C01675.jpg

but I've misplaced the hose that comes off it when I first stripped the carb and don't know where it goes.

Any ideas please?

cheers
Millard

[drillam]

Hmmmm, on second thoughts, I think that's just the overflow

[Jonorow]

yes it is and overflow pipe, check your float hight is set at 16mm (when the needle stops and before the extra bit pushes in. This will make a difference)

[fallenmikethebike]

Sorry to ask mate , but you were fastidious with the clean up of the air tract after it's dunking? only a small residue of grit, could , if your unlucky, jam the throttle slide half open , thus, the run away RPM.
Mike

[drillam]

Solved, at last.
Those more familiar with the joys of two strokes will no doubt laugh, shake their heads and think "plonker"
In my worry about the oil pump being primed in the first burst on the new engine's life I had decided to use a small amount of premix, as previously stated. However the mistake I made was to leave the oil pump feed to the carb off so I could see when the oil started to flow through the end of the line, leaving the oil feed spigot on the carb inlet stub open to the elements, thereby sucking in lotsa nice clean fresh air down the inlet tract AFTER carburation, therby weakening the mixture badly - see, I told you you'd laugh!!

It's still very slow to calm down after a blip of the throttle but I think that's because just prior to discovering the above self induced fault with the oil line, I had taken Jonorow's advise and looked at adjusting the float height, but set it probably way too high I think.

One thing that confuses me about the float height adjustment though, I can't figure out from the various threads I've read here on site where the 16mm is measured from as regards to the actual float. I know that on the carb side it's to the joint line of the carb body and the float chamber, but on the float are we talking about the top of the float when the carb is in it's usual upright position? or the top of the float when it's turned up to close the valve? in effect the bottom of the float?
If it's the top of the float then do you measure from the corner of the float furthest away from the pivot pin? as it doesn't obviously travel in a parralel line in it's upwards stroke but in an arc.
If it's from the bottom of the float then do you measure from the pointy bit in the middle? the highest point when it's turned up?
Better still is there a diagram anywher that someone can point me to?

I appreciate you help, guidance, advice and patience guys.
thanks
Millard

[Jonorow]

hold the carb on its side with the pivot at the top. now slowly tip it backwards until the float needle seats. this is the point you need to measure it at. now if you tip the carb further the extra sprung pin goes in, Dont measure it from here as this will set the float too high.

[drillam]

[quote="Jonorow"]hold the carb on its side with the pivot at the top. now slowly tip it backwards until the float needle seats. this is the point you need to measure it at. now if you tip the carb further the extra sprung pin goes in, Dont measure it from here as this will set the float too high.[/quote]

Thanks Jonorow, but which specific point on the actual float do I measure to?

[Jonorow]

the edge of the upperbody and the bottom of the float. Dont worry about the measurement on this pic the carb is cleaned and sprayed for storage, and is not set-up.

[drillam]

Perfect!!!!
Thanks for that Jonorow.

[fallenmikethebike]

I just,re-checked the float height on the MK3 carb, luckily I had a piece of 16mm flat bar, in the garage, that I could use to to scribe the 16mm measurement onto the [ baffle plate, shiny plate in Jonerows photo].
Strange thing, even if i push the float as high/in, [shuts fuel off], there is 15 mm of float showing, as measured in the prescribed manner.
I'm not doubting the information, or the technique described, more, have i got the right floats in my carb?
Mike