Revving like crazy in idle (1993 CR250)

**-df-** · 2nd October 2007, 14:27

Went out to the sandpit on Saturday and had a blat around the place...awesome is the only word I can use.

Now the bike was running fine all day, until it fauled a plug...so I pulled it out and put a new one in and when I went to start it, it was reving like crazy. Tried adjusting the idle as per the manual but nothing worked. If I put the choke on the idle comes back down. Took it for a little run to see if the idle would just come right (wishful thinking) and the bike had so much for power it was crazy.

The throttle is closing fully (can hear I little 'clunk' when the throttle returns).

I'm guessing there is an air leak somewhere, does this sound right?

Where is the best place to start with this? going to have a look this weekend but except for the carb I don't know where to look.

**Danger** · 2nd October 2007, 14:31

Yes it sounds like an air leak. You can try spraying WD40 around the carb, boot etc to see if you can seal the leak and trace it when the revs come back down.

**cheese** · 2nd October 2007, 14:53

Did you try turning the choke as tht is the idle adjust on those carbs.

**-df-** · 2nd October 2007, 15:07

Originally Posted by cheese

Did you try turning the choke as tht is the idle adjust on those carbs.

tried that and the mixture screw as per the manual...manual states to use the mixture screw to bring the idle down.

**B0000M** · 2nd October 2007, 16:38

the leak (assuming it is a leak) is between the carb and the cyinlder, first thing to check would be the flange that goes onto the carb, then the joins around the reed block. also check for cracks in the plastic manifold thing

**F5 Dave** · 3rd October 2007, 16:14

Yeah I'd expect a rip in the manifold.

But just to be sure that the carb is closing, I know you say you hear the klunk, but it does sound like you've pulled the cable when changing the plug & it hasn't seated home in one of the ends of the cable. Can always pull the carb out & see that it is fully home on the idle screw (closed). Otherwise why did it happen so suddenly?

**vr4king** · 3rd October 2007, 16:59

Yeah im waiting for the doh post to pop up

These bikes come with the PJ carb that doesnt have a "idle pin/needle" the choke knob sets the idle by basicaly dripping gas past.............not a good design at all

Have you checked both ends off the throttle cable to see if everything looks like it should

Another thing i have found before is a slight scratch on the slide bore stopping the slide from getting home causing it to idle REAL high

Also what id do is pull the top off the carb the bit where the cable goes into and just have feel around and a looksie make sure it all is where it should be

**-df-** · 4th October 2007, 07:22

Originally Posted by F5 Dave

Otherwise why did it happen so suddenly?

Only idea I have on that is I normally burn thru a plug in a ride...but this one has lasted me 3 rides (the bike actually started rev'ing up a little when I put the plug in that I just replaced...but came right with a little ride)...so maybe the plug was on its way out and not firing 100% properly...and the new plug is???

Dunno...but will post up here when I find the problem...and hopefully its not a "DOH!!!" moment.

**Danger** · 4th October 2007, 08:12

Originally Posted by -df-

Only idea I have on that is I normally burn thru a plug in a ride...but this one has lasted me 3 rides

Dunno...but will post up here when I find the problem...and hopefully its not a "DOH!!!" moment.

Well there is your DOH!!! right there! Have you ever attempted to find out why your bike is burning thru plugs? Bikes are not meant to run like that.

**-df-** · 4th October 2007, 08:16

Originally Posted by Danger

Well there is your DOH!!! right there! Have you ever attempted to find out why your bike is burning thru plugs? Bikes are not meant to run like that.

Always figured it was the low end not being adjusted right (seems to mostly happen when I let the bike just idle lots to warm up...which I like to do).

Talked to a couple of bike shops and they didn't seem to think anything of it...but then I'm buying lots of plugs off them!!

**F5 Dave** · 4th October 2007, 08:29

Oh they come with a PJ? I would have thought a PWK. Surely!

Mind you we have no idea how old it is. The PWKs do wear a groove in them which messes the jetting up, but takes an old bike to do, but this happens from vibration at idle.

Yes warm your bike up, but gentle blipping until there is some temp in the head then you can set off but keep it gentle until fully warmed. Only adjust the jetting when fully warm. Google to find what jetting is std for your year & check what you have. Most bikes come with fat jetting. Some adjustment of the idle mixture should clean up the close throttle area a little, but if you get to more than 3 full turns out then wind it in & go to next smaller pilot.

Obviously after sorting this issue.

**Rmxer** · 10th October 2007, 21:12

sounds like my mates old 94 cr250 it used to eat plugs like mad

and also one time we got it going well it started revving like mad like the throttle was jammed

ENDED UP BEING OUT OF GAS!!!! tell me you have checked this!!

**Rmxer** · 10th October 2007, 21:20

sounds like my mates old 94 cr250 it used to eat plugs like mad

and also one time we got it going well it started revving like mad like the throttle was jammed

ENDED UP BEING OUT OF GAS!!!! tell me you have checked this!!

**-df-** · 24th October 2007, 07:30

Well I finally had some time to look at the bike over the long weekend, turned out the bottom bolt holding the carb -> reed valve plate was missing and the 2 ones on the side not even finger tight (also missing the gasket).

Bikes running mint as now.