I have a Foreman 400 thats been backfiring alot, espesially in the cold. What could be causing this and whats the best way to stop it?

 

Honda jets their quads really lean from the factory (so does yami). Where I live (subdivision with about 50 houses) there are a lot of honda 4x4s.. In the winter you always hear them having problems getting them started. Even with the choke.

What I would do first thing is to up the pilot jet a size or two. I did this on my Kodiak (for sale! tee hee!) and it cured the problem straight away.

 

Yes lean would do it. I don't think it's necessary to upsize the slow jet though. Try turning your mix screw out to about three and a half turns. On a few of those, if I am remembering correctly, I raised the needle a notch. Also check to make sure you don't have any intake leaks, especially loose carb clamp or carb not installed all the way in the intake boot. Also exhaust leaks will cause the backfire. I am remembering an especially tricky foreman 400 that a coworker was fixing. It would backfire EVERYTIME you deceled from higher rpm. The problem turned out to be a pinhole in the headpipe where the heat shield bracket was welded on. I found it by putting my foot over the muffler while it was idling. If it's got an exhause leak, you will really be able to hear it obviously then.

 

I've tried the pilot screw on a couple neighbor's machines, It's just not enough to make a difference. But of course they don't want me to rip into their carbs, so they live with the hard starting and popping. [img]i/expressions/face-icon-small-smile.gif[/img]

 

Not too familiar with the yami's but it seems all mfg. machines are a bit lean at idle and just off. I have found that the mixture screw adjustment makes a BIG difference on the Hondas. Mainly they idle much smoother, especially in that period of time when they aren't cold anymore, but they're not fully heatsoaked either. I would bet that 1478 is hearing a loud gunshot type backfire, which I don't consider quite like popping. The foreman 400's were prone to that backfiring, much more irritating than a little decel popping like other Honda's might do. As far as hardstarting, bvstone, I have found the Honda's are GREAT cold weather starters if you have good fresh gas in the carb, a good fully charged battery, proper heat range spark plug and oil viscosity, and you know how to do it.

 

My kodiak did the same big backfire thing. Once I upped the pilot 2 sizes, it works great. Now I set it at about 1 turn out for summer, and 3-4 turns out for winter and its perfect. Funny thing is, a loud backfire usually means rich. Go figure, though. It "runs like a honda" now. [img]i/expressions/face-icon-small-smile.gif[/img]

Yes, I'll agree that some owners don't know how to start em when they're really cold. I love the sound of em starting, killing, starting, killing, then starting and they rev it super high and it coughs and spits until it's warm. hehe..

But, I can tell you, up that pilot two sizes and it will start no problem. And you can lean it out in the warmer temps using the pilot screw.

 

Backfiring when you're trying to start the machine would indicate it's flooded, or I guess you could say rich. But it in my experience, if it happens on deceleration, richening the mixture somewhere, or fixing vacuum or pressure leak fixes the problem. As far as hardstarting in cold, I have found it helps alot, or in some cases is necessary to pump the carb mounted primer a few times, especially when it starts to get around 10F or colder. But infrequent use is probably the biggest offender in hardstarting, often all it takes is to drain the carb and allow fresher gas from the fuel tank in. It seems it only takes 2 or 3 weeks for the 70cc or so of gas in the carb to get too "thick" or lose it's volatility. If you try too hard to start your machine with that thick crap in the carb that used to be gas a couple months ago, you are asking for a fouled plug. I can see where the pilot increase would help in the winter. I haven't found it to be necessary though, and I would worry about plug fouling and poor idling issues when it gets warm, especially if the customer idles around a lot. Really, I have found that (and I am talking Honda's here, as I am familiar with them) they run about perfect with just a mixture screw change, with a few exceptions, such as first year recons and some early foreman 400's in which a slide needle height change fixed the lean problem, a richer pilot would have been my next option.

 

Honda1478, have you ever adjusted your valves? Valves set too tight will also cause backfiring.

 

I have never heard that honda usually puts there quads out lean, I have always heard they are rich. I can get my dads 400 foreman to make a backfire noise but I have to down shift it when going fast. I t never has been much of a prob, the rubi has done it a few times to but it's far from lean.

 

Greetings
That seems to be a common problem with the Honda 400 Foreman and I have heard the same complaint for the last 3 or 4 years. Sometimes a Dyna jet kit will help a little. [img]i/expressions/face-icon-small-wink.gif[/img][*]let me loose