mark one @ low revs

cat head · Post by **cat head** » 22 Apr 2003, 22:15

Hi all

have recently acquired a Mk 1 crm and today it decided to act up,
since I've had it it has run erratic at low revs, sometimes when I crack the throttle it'll lift the front otherwise it just bogs itself down, and today I blipped the throttle at standstill in neutral and it stuck itself at the redline

even with the kill switch to kill and the key to off
is this a sign off a dodgy kill switch (I'm taking that apart in th morning.

Also it was bored out by the previous owner (size unknown) should it be rejetted any body had any experience of this?

Apart from that it loves beng ridden hard and is the most fun I've had on two wheels for ten year.

Bargos · Post by **Bargos** » 23 Apr 2003, 09:16

Cat,

Sounds like you have three things to address here:

(1) Erratic low running.
Have you managed to give the bike a full service since you purchased it? I would be inclined to replace the spark plug, strip and clean the carb together with the air filter and see how it runs then.

(2) Killswitch/ignition switch.
It sound as if both the ignition and kill switches are being bypassed. How do you normally stop the engine from running?

(3) Oversize piston/jetting.
You need to try and find out exactly how much oversize the barrel is. To the best of my knowledge a small increment in CC doesnt require rejetting.

Thats all I can think of for the moment and thats the way I see it. I would be interested to see what other CRMers think...

mark · Post by **mark** » 23 Apr 2003, 14:31

I blipped the throttle at standstill in neutral and it stuck itself at the redline even with the kill switch to kill and the key to off
is this a sign off a dodgy kill switch

I have seen this 3 times before on 2 strokes,
the kill switch and ignition were not to blame for the engine not shutting down at full revs.

when an engine runs lean ( too much air to fuel ) it also runs hotter than normal, although i have not proven this theory but i guess it is one of those freek conditions where the spark plug bridge gets so hot that it is hot enough to ignite the gasses in the cylinder.

on one of the bikes i see this happen on we got a big screw driver and popped the plug cap off the plug and it contined running at full revs, in the end we ripped off the K & N air filter and covered the air intake with my hand and it then shut off, so it was definately not being ignited by HT voltage and seeing as petrol isnt compression combustable i put it down to the plug being hot enough to ignite the gasses.

the thing that would worry me is why your bike went on to full revs if you only blipped the throttle, i would cetainly strip the carb and check everything over and set it up by the book and then do a plug chop and see how the mixture looks

Russell · Post by **Russell** » 23 Apr 2003, 17:28

Most likely cause of ignition is carbon build up, may be running to rich or just built up over time, this can glow like embers and sometimes ignite the fuel.

Karl Nicholson · Post by **Karl Nicholson** » 25 Apr 2003, 16:26

mine did something similar and i solved it by turning the pilot mixture screw to about half a turn out instead of the standard one and a bit, run /starts fine ever since

Robb · Post by **Robb** » 25 Apr 2003, 19:10

Hi Cat,

Gotta agree with Russell about the running-on. Lean mixture and carbon build up don't mix and could cause the problem you have described.
This may also cause poor idle.
Lean mixture could also cause the bogging down as you lift the carb slide quickly and weaken the mixture to the point where it wont burn.

As for the reving out, might be something as simple as a sticking carb slide.

Hope this helps

Robb

cat head · Post by **cat head** » 28 Apr 2003, 15:03

Since I've had the crm It's had a really good service, the carb has been stripped and cleaned, spark plug is now a new EGV, air filter has been cleaned and oiled, the exhaust leak solved with a new gasket and the power valve adjusted back to the right setting.

all that and it still bogged down off the throttle.
Ive backed the mixture screw out 1/2 a turn and its a lot better.

thanks for all the help.