Carb not sucking in fuel when cold.

Britfrog · Post by **Britfrog** » 09 Jan 2017, 17:25

Hi. I've just bought a Mk1 (I think!) CRM 250 for exploring the many miles of green lanes in SW France. The only way it will start from cold is to squirt neat fuel into the plug hole. When it is warm there is normally no problem. There is a good compression, the throttle response is good and the power throughout the rev range is impressive! It ticks over nicely too. I've stripped and cleaned the carb, the 'choke' or more accurately, fuel enrichment system, seems to be working ok. I connected a fish tank airline to the pick up tube in the float chamber then immersed the carb in a container with petrol. Operating the 'choke' lever redirected the resulting bubbles to front of the carb. Also, when the bike is running - it's obvious that the choke is creating a richer mixture. But when the engine is cold and despite repeated kicking (no throttle, lots of throttle) it never seems to juice up the plug. Squirt some fuel in the plughole and 9 times out of 10 it fires up! Has anyone had a similar experience or any advice please?

Post by **fallenmikethebike** » 09 Jan 2017, 17:49

Some acquaintance with your particular bike might be needed. Assuming that the bike starts and runs without issue you could try the old " rock-a-by-baby " technique. How so ? Key in ignition, but NOT turned on, petrol ON, choke ON, engage 1st or 2 Nd gear, start rocking the bike backwards and forwards enough to get the piston travelling up and down the barrel.
A minute of that should be sufficient, engage neutral, turn on ignition, a smidge of throttle, then several sharp kicks, this works nearly every time. If it fails you might need to check the fuel flow from the tank, is the gauze filter in the tank clean?
Is there an in-line filter that needs cleaning, is the float set to the right height?
Good luck.
Mike

Britfrog · Post by **Britfrog** » 11 Jan 2017, 19:37

Hello Mike, thanks for the reply. Rockabybaby??? Really?? I want the stupid thing to wake up - not stay asleep!!!

I followed your advice yesterday but forgot to restore the kill switch so nowt happened! I only realised after I'd squirted a little fuel in the plug hole, since then it has started about 10 times on the first kick. But I haven't warmed it up enough to take the choke off yet - I suspect when I do then let it cool it will be back to not sucking fuel in again. So I will try your method if that's the case and let you know:)

Post by **fallenmikethebike** » 11 Jan 2017, 19:46

It's normally just a case of getting to know the bike, they all seem to have their own idiosyncrasies.
Pilot jets being blocked/ munged up are a notorious reason for a lack of starting.
Sometimes it's worth replacing the existing pilot jet, even if it looks clean, with either the same size, or going up a size.
Carb specs are in a window off the front screen.
Mike

Britfrog · Post by **Britfrog** » 23 Jan 2017, 10:22

Hi Mike,

Tried rocking it on several occasions but no luck. Thanks, I will try a new pilot jet but I'm not too hopeful. Correct me if I'm wrong (I often am:)) but I thought the choke bypassed the pilot jet? From my airline tests it should suck fuel from the pick up tube in the float chamber and eject it through a hole in the front of the carb next to the inlet manifold so it can be sucked straight into the cylinder? The carb looks almost new, I need to start checking specifications I guess:) Any recommendations where to buy new carb bits please?

Cliff

Post by **fallenmikethebike** » 23 Jan 2017, 10:32

Leasure Trail, would have the carb spares. It is the correct carb I assume?
The float height was correct?
If once started, it ticks over steadily, then the compression and pilot circuit should be fine, I would have thought.
Mike

Post by **pudzie83** » 26 Jan 2017, 16:58

Have you tried cleaning all electric connections?

Britfrog · Post by **Britfrog** » 30 Jan 2017, 17:55

UPDATE...........Thanks for the suggestions, think I've cracked it! My starting technique was wrong! I'm used to booting off big 4 stroke singles - easing it over compression then big kick. Then repeat. Turns out the CRM responds better to 4 or 5 kicks in rapid succession

Post by **gregorious77** » 30 Jan 2017, 19:34

makes sense I suppose as a 2t has to draw the mixture down through the crank, up the transfer ports and into the combustion chamber.

Post by **gregorious77** » 30 Jan 2017, 19:35

makes sense I suppose as a 2t has to draw the mixture down through the crank, up the transfer ports and into the combustion chamber.
I always push the kicker to just before the compression then a nice long full kick.

Carb not sucking in fuel when cold.

Carb not sucking in fuel when cold.

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Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.

Re: Carb not sucking in fuel when cold.