I have about 20 hours or 150 miles on my new Rubicon and it backfires when I decelerate from moderate to high speeds. It usually makes one big bang. I asked the dealer because it says in the manual CONTACT DEALER on backfires. He said back out the screw 1/4 turn to make the mixture more rich. I tried this and it did'nt work. I have changed the $20.00 plug and it did'nt work. I can't imagine a leak in the system. How many turns out should the screw be? what is the normal adjustment? I would appreciate any help I could get.

 

I'm in the same boat as you are. I just had my carb adjusted today and will let you know if it helped at all. The mechanic turned the screw a half turn to make it run richer. Mine is popping and backfiring while going down hills when off the throttle. Probably won't be out on it till the weekend.

 

I had this problem with a machine once..... not a rubicon. chased it for months.... the battery was fine, but one of the cells were weak... replaced it and all was new...... it was cutting the fire back.... the battery is part of the sparking process.

 

1099 and kootenay rider, I set mix screws this way while the machine is running. Get it hot, and turn the idle speed as low as it will stay running smoothly. Slowly turn the mix screw out while listening to the idle speed, you can put a tach on it if you have one. Your screw is set when the rpm is the highest, you may notice that it now idles higher, so finish by resetting your idle speed. The ideal setting may not always be the same, because of different atmosph pressures, slight differences between the same model, etc. But in my experience the mfg setting is always lean on Hondas. If this procedure has no effect, your problem lies elsewhere. High on the list are partially obstructed pilot jets. On the rubicon carb check to make sure that the vacuum lines are attached on the air cut valve, the plastic object on the side of the carb. Also I have seen the plastic nozzle on it break at least once. The symptoms you describe are both a bit different so you may find different causes. As davidpaj points out, sometimes the problem can be somewhere else altogether, like a poor connection or loose battery terminal.

 

I have a good way to find a back firing problem take a rag and wet it down and start the machine and hold the rag up to the muffler so that you are plugging the exhaust if the machine doesn't kill you have a leak if if it stays running look and the head pipe for cracks I have seen this kind of problem on 400 and 450 before if all else false have your dealer call Honda and see if they have had any other dealers a round you have been complaning of this problem the other things that the other have wrote are also good ideas

 

I just have somebody put their foot over the end, while I look for exhaust leaks, they are much more obvious when you do this.

 

My 250X was backfiring REALLY bad and it turned out the head pip was all messed up from the idiot that owned it before me. I had to have a new stud Tigged into the head so I could tighten the exhaust properly. Now the engine purs like a kitten (well maybe a mountain lion [img]i/expressions/face-icon-small-wink.gif[/img]). If it is not exhaust it has to be running too lean.

 

I fixed the problem!!! First I checked the valve adjustments. The exhaust valves were tight and the intake valves were slightly loose. I then adjusted the carb as dzzy suggested. I started it up and it ran like a Honda should. Seems like it gained a little power too! I appreciate all of the helful suggestions.