Bike back fires and then cuts out

..... · Quote Me Happy Joined: 15 Jan 2005 Karma :

Right, my XR400 is giving me grief.

I'll start it up ride off and everything will be fine for a few mins.

Then it will start to pop a bit on the over run and cut out occasionally when coming to a stop, usually when stopping quickly.

The bike revs fine through the rev range and pulls well, but seems a bit hesitant on a constant throttle.

My thoughts last week was an air leak into the carb so loosened both boots and checked it was seated correctly. This seemed to work and there was no more popping. However, I only took it on a quick spin round the block so it didn't get a chance to warm up properly.

The bike idles fine - I was thinking if it was an air leak the revs would be shooting up on their own?

The bike was unused for 6 weeks over Christmas/New Year but don't think this could cause the carb to become gummed up so quickly? Combined with the fact that it revs through the rev range fine I'm at a bit of a loss.

The carb isn't the standard Honda carb, it's a Mikuni pumper.

The only other carb thing I can think of is the float level but having no experience of carbs could an incorrect float level/stuck float cause this?

The air filter is clean and oiled, I don't think it's over oiled as I wrung out any excess as much as I could.

Any pointers gratefully received Thumbs Up

Cheers.

Ichy · World Chat Champion Joined: 15 Jul 2005 Karma :

Has it run fine before with that carb fitted? Any idea on how old the carb is?

To check for air leaks spray easystart or WD40 around the manifold.

It may be running rich which is why you notice it once the bike is properly warmed up.

Have you checked the plug to see what it looks like?

Could be down to worn jets or needle, stuck or incorrectly set floats, blocked air filter, choke stuck open, or maybe even a dodgy accelator pump.

I'd start with the easy ones first. Check the choke is opening and closing properly then try a run without the air filter.
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..... · Quote Me Happy Joined: 15 Jan 2005 Karma :

Cheers Ichy.

The carb is only a few months old. I haven't checked the plug yet but the bike has been running fine with the carb as it is now.

I just undid the float bowl to look at the contents and lo and behold there was water in there and quite a bit of dirt.

Thinking back I came off in a huge muddy puddle last time I was out on it Doh!

I guess it's time for a carb strip down and clean.