[ClearDark]

Hello all,

I have a 1997 Honda Foreman 400. I just got it a few days ago, and noticed it backfires an awful lot, and it's very loud. It appears to be coming out the muffler.

I looked at the manual and it stated how to adjust the pilot screw. I went ahead and adjusted the screw, but it did not help much. I took the plug out and re gapped it, and still backfires a lot.

Where can I look next?

 

[tomgodd]

I have a 400ex and when I cute out the original spark arrestor out of the exhaust mine started back fireing more. Could be something lke that.

 

[Saber6]

What color is the plug electrode when removed?

 

[ClearDark]

Brownish white.

 

[Redracer]

You are running lean. It is your jetting. That also explains Tomgodd's problem. You cut out your spark arrestor/baffle which is causing less back pressure in your exhaust resulting in a lean condition. Get it jetted correctly for your altitude and you will feel a difference in how your machine runs and you will have the sense of security to know that you are not hurting your motor. A lean condition will cause the machine to run hot, there is to much air and not enough fuel to cool the cylinder.

 

[ClearDark]

I have adjusted the screw to richen the fuel, with no result. My jets are stock. Should I be looking at buying new jets?

 

[Redracer]

Yeah, the screw will only do minor adjustments. Stock jetting is set to run at sea level. What are you running at? For every 1000ft above sea level you want to drop 1 size on the main jet.

 

[tomgodd]

Good advice! I did get mine rejetted. I also put in a K&N filter and the Honda shop told me not to rejet. I went to a buddy of mine that runs a small shop and we rejetted it. The only time it does it now is if I blast down the road a mile and let out and it may do it, not every time. I forgot to tell all that. OpppS!

 

[Redracer]

A backfire on a hard decel every now and again is normal. If it sounds like a shooting range then you got issues.

 

[ClearDark]

I am living at sea level, as in the sea is right next to my house.

I took the carb apart and cleaned it. The jets are not plugged.

What jets should I be running? Can anyone help me find what jets I need?

 

[Redracer]

HMMM... The spark plug says you're running a bit lean. Is there anything aftermarket done to it?

 

[ClearDark]

Nothing aftermarket done to it. Should I try to richen the mixture? I am going to be checking valve clearances tonight after work, in hopes that maybe they are out of adjustment.

Could it be anything else?

 

[Redracer]

I would start with the valves. I suppose if they are not sealing completely that could be causing it.

 

[Saber6]

I Agree with redracer. Do you have any mods K&N? Exhaust?

 

[jrowe06]

there is a screw on the bottom of the exhaust,try taking it out,and reving it a few times(about 10-15)and put it back in.see if that helps.