Hello everyone,
I have some back fire problem
on a Acat 400 4x4 2001 manual engine.
I have had a carb. clean and change the point.
It starts very easily but touching the start button.
When engage in1st gear and gaining some speed
to switch to 2nd gear, it has a laque of power
and some times back fire.
What should I check next?
Thank's for any advice, I really appreciate![img]i/expressions/face-icon-small-blush.gif[/img]

 

It sounds like your running too lean, for some reason. Check to make sure you arent leaking air into the airbox, or carb somewere

 

Last time my machine did that I took the spark plug out and checked it and found it was black and covered in enough gunk to almost bridge the gap.

I put in a new plug and and it did the same thing to that plug before I went through half a tank of fuel. I then checked the jets and found some gunk in the jets, a small air leak in the intake and the mixture screw was out too far.

I am not sure which one fixed it but it ran much better after than ans stopped backfiring when I let off the throttle to shift.

SJ

 

A back-fire occurs when unburned fuel gets into the exhaust pipe and then is ignited.

I would change the spark plug to start with and then make sure the carb and airfilter are clean and the carb is set correctly.
As the gap on a spark plug can change the timing by the size of the gap I would make sure the gap is correct.

Then I would check the timing.

The I would start to look for some air leaks in the manifold.

Two last things you can do is bring it to the shop and have a certified mechanic find the problem and the last thing you can do is get a good set of ear plugs so you don't hear the backfire - lol.

Good luck... but seriously the first thing I would do is change the spark plug and make sure it is gapped correctly. If your system is not firing correctly is the reason why you get raw gas (unburned) in the exhaust pipe that causes the backfire, or fires when an exhaust valve is open.

 

Changing the plug is always a good idea.

Yes, a dirty air filter could cause this.

Unburned fuel in the exhaust is the cause of this problem, butthe fuel problem is almost always causeed by a lean mixture in the cylinder.

Where did you learn that the gap of the plug would change timing? No way, no how and not possible in this universe at least not with the phsyics we now work with.

Doudtful if timing just suddenly changed as this system doesn't work that way. For it to change by itself requires something to break. Beside the idle speed would be affected the most.

Yep, an air leak in the manifold will cause his problem.