Why does my ATV engine pop when I give it throttle? This is the beginning of a very detailed question one of our readers asked the ATV AnswerMan.

Here is exactly what reader Jayson asked the Answerman (it is long and extremely detailed), followed by his answer:

Help,

I have a 2001 arctic cat 400 manual shift. The problem, The machine will start fine and idle like it should, once you get into the throttle it will start to misfire and back pop but will not die even if you hold the throttle, it just pops.

What I’ve done,

Last summer I began to have battery charging issues, my dad, who was the original owner of the bike, came over we started looking into fuses and wiring connectors and YouTubed the symptoms. What we learned was the voltage regulator could be bad so we purchased a “universal” for a certain amount of years arctic cats, mine falling in the category. The battery began charging correctly and everything seemed to run fine, appropriate voltage back and such. A short time later it began to run rough, so I assumed it was a fuel issue which, is what it seemed like and also we had done nothing to the carb other than drain it every year in the 10+ years we’ve had it. The carb was fairly clean a few chunks of stuff were in it but I’ve seen worse that runs better. I then put the carb back on after a thorough cleaning and installing a inline filter and had the same problem. I began searching just about every forum on the web and found a guy that had the wrong or bad voltage regulator that was sending to much power to the battery if he’d turn on the headlights it drew enough power to run fine. I figured quite a long shot but what the hell. I put the meter back on it and I was getting almost seventeen volts back, which was not the case when we first installed it. With the headlights on it drew down to almost perfect voltage, 14-14.6. It seemed to run great with the lights on which led me to believe the “universal” regulator we had bought which was much cheaper than others was the wrong one for my bike, we don’t have the receipt and I can’t get much help from who we bought it through to get it returned so I said screw it and ran the bike doing things around the yard like pull the harrow with the lights on until I could afford a full priced regulator. After three or four times of riding it it has begun to run like garbage again.

Backfiring and popping and dying and it would only start and run with the choke halfway on. I put it aside due to other projects which were two 90 atvs and come to find out I had junk in a gas can that clogged both of them up, so I thought maybe that’s what had happened to the 400. Today I cleaned the carb and once again it was still very clean inside. I put it together checked the voltage at an idle with the lights off and was getting a good reading and ran it around the yard a little and it began to misfire and pop I pulled it in checked the volts again and was back up around seventeen, lights on it dropped to 14.6 but still was backfiring.

I’m not sure what to do and I’m just about out of hair to pull out. >I’ve read a lot about the flywheel magnets and stator issues these bikes commonly have however it seems to me that none of the symptoms are similar to mine, a few here and there but nothing concrete. Hopefully it’s not just me trying not to except the hefty repair. I don’t know much about the internal parts of the bike such as the stator and flywheel, I’m just a dirt worker, and I’m nervous to get into pulling covers and flywheels and such, however I have family that does this for a living whom I trust and I guess I just wanna give him a good starting point.

Have you heard of anything like this? If so what we’re some of the outcomes? Should I just tear into the flywheel and stator and see what I find? Any advice is good advice at this point I’ve had this bike a long time and it’s been great, also been through hell and back. I really want to repair it and put it back to work.

Thanks in advance, Jayson

Quick list of everything I’ve checked so you don’t have to keep going back and forth through the mail.

All electrical plugs and wiring

Spark plug (brand new now)

Fuel delivery and tank

Carb (about twenty times)

Voltage back to battery( 17 w/o lights 14.6 w/ lights) Air filter and carb tuning Spark Choke Good clean gas Fuses (all good)

Thanks again

Holy Moly, Batman, this is the longest question and the most detailed I have ever received. I love it! I’m impressed that you have taken the initiative to dig right in and try to solve the problem and also that you let technology be your friend. That is what forums and the World Wide Web is about. Sharing is caring. Now some information can be misleading, but sifting through the core of it you can find the most common issues pretty quickly. With that said, lets try a few things to see if it helps the problem become better or worse.

My very first thought is that the engine is not getting enough fuel. The popping is most typically a result of a lean running condition. Have you pulled the plug after a good warm up to see what it looks like? While some will argue you need to ride a few minutes and then pull the plug, we know by your comments that the machine will not run without popping or backfiring.  So warm it up and place your hand over the snorkel opening to the air box to temporarily close off the opening. That is the shark fin looking thing on the front of the air box lid. As the engine is running and you have your hand cupped over the opening, press the throttle to see if the popping gets worse, quits or smoothes the engine out. By choking the engine this way you introduce more fuel to the cylinder. The result tells us to either move on or stop and check the fine inlets for the primary fuel meter circuit. Trust me when I say that I know how clean a carburetor looks after going into it 10 times and it still will not smooth out for you. But also understand that one little spec somewhere in that Carburetor is potentially laughing at us both.

Here is another thing to note: This AC Carburetor has a filter screen on the main fuel needle jet seat that can also get clogged easily. You have to pull the needle seat out of the carburetor body to see it, which most never even know is there. Fuel can get in, but maybe not as fast as it needs to in order to supply the primary circuit. It’s not positively the issue, but one to look at.

Moving on from the fuel system, the head pipe on the machine could be leaking and drawing in air somewhere along the exhaust. Check for cracks in the header pipe, or faulty seals where it comes out of the head as well as where it joins up to the silencer about midway back on the quad. These leaks cause popping and backfiring when the engine is warm, but could be severe enough to show up right when the engine is fired up for the first time of the day.

So as an important note about using a voltage regulator that swings the supply voltage that much and relies on demand to control its output; I would toss that dude out and get a factory part that steadies the supply before it cooks something else in the system. It could be the issue with the running of the engine, but I’d say it’s at least going to be a problem at some point. As for the flywheel key etc, if it sheers or stretches or even tilts one direction or the other, the timing would be off enough to keep it from running at all.

Now valve timing and clearance is another totally different issue. When was the last time the valve clearance was checked on this Arctic Cat. This affects the running and function of the engine as well.

Good luck!

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