Here's another sled problem for you - Snowmobile Forum: Your #1 Snowmobile Forum

lovethepowder · 03-12-2006, 09:09 PM

Not having good luck with sleds lately....

On the weekend I took our '98 ZL 500 for a ride. I hauled it on the trailer about 20km's out of town with no tarp on. When I went to start it up it wouldnt fire so I figured it mustve gotten frozen up from being on the trailer, so I took a hair dryer and heated up the fuel pump and that got it started. And then while riding, I would be going along good for about 5 minutes then it would bog right down and I couldn't get it to pick up rpms. Tried choking it just to see what would happen and it killed the engine. It took a while to get started, and while pulling on it it would backfire once or twice. It also back fired while driving it too(right when it started to bog). I'm no mechanic so I have no idea what the problem could be, but I decided to change the fuel filter with a spare one I had. After changing that it ran excellent for at least 30 minutes worth of riding. We came back and went in the house for a break and then decided to go for another ride about 1 hour later. Well about 10 minutes into our next trip it started doing the same thing and bogging down, almost like it was running on one cylinder(but i'm not too sure). So when it bogged down I didnt touch the throttle and waited to see what would happen. Well it would struggle for about a minute and then it would jump back up to its normal rpm's and I could take off again and it would run fine....for about 2 minutes then it would do the same thing again...sometimes it would shut off.

When it was bogging the tach was barely even picking up the rpm's(while at a stand still). I had putten gas line antifreeze in it when I feeled up also.

I also noticed a couple times on the second ride of the day that when I would hit a jump/large snow drift, that is when it would bog down too. But it would also bog down while just riding in the field.

I have no idea to as why it was backfiring so much either while I was trying to start and while I was riding it(it would only backfire when it was bogging). The spark plugs were bran new and had good spark whenever I checked them.

Sorry about such a long post but any help would be greatly appreciated. We finally get a dump of over 15'' of snow and our snowmobiles break! At least the 340 is always reliable...doesnt handle the deep powder so well though

**smallengineguy** · 03-12-2006, 09:47 PM

Definite fuel problem. I still think there may be water in the fuel system, or some kind of blockage in the tank.

lovethepowder · 03-12-2006, 09:59 PM

yeah that's kinda what I was thinking too, that there was maybe some crap sitting in the bottom of the tank...whats the best way to get to the screen on the bottom of the tank(i think there is a screen anyways)?

lovethepowder · 03-12-2006, 10:57 PM

I was reading on another site about "throttle bushings".....something about it cutting the engine off?

**smallengineguy** · 03-13-2006, 06:18 AM

I think they meant position sensors. You can also check those to be sure thay are adjusted correctly.

**BC_Dan** · 03-13-2006, 03:52 PM

there is a switch in the throttle block that is notorious for going out on AC sleds. The bushings are top and bottom of the throttle, and sometimes changing them out will help. There is an upgrade part that is supposed to seal better, replacing the top bushing. You can use the stock part for the bottom one. The upgraded part number is 0609-144. If it continues, you may have to replace the throttle block; new bushings gives you a bit of delay in doing that.

The backfiring you are describing would lead me toward the safety switches, and if you get snow dust or ice in them, you will get intermittent problems running and a really bad bog until it opens up past 3500 or so. I had the same thing happen to me on a ride last week, the powder was getting into everything (darn

). I ended up with ice in the throttle block assembly, and I let it idle with the hand/thumb warmer on for a while to help melt it out; the problem went away after that.

lovethepowder · 03-13-2006, 04:22 PM

Thanks for the replies and help. That would almost make sense cause there was over 4ft of powder I was riding in that day. I will get my dad to check it out soon(I'm 2 hours away so I can't). Does anyone have any pictures of what i'm supposed to be looking at...i'm clueless when it comes to fixing these things but I will try to explain it to my dad the best I can.

**smallengineguy** · 03-13-2006, 08:45 PM

www.brownsleisureworld.com

Go to parts microfiche and enter your sled info, then click on carbs for the safety switches.

**BC_Dan** · 03-14-2006, 03:12 PM

The throttle pivots on a pin held in place by a circlip at the bottom. There are two plastic pieces (throttle seals) that keep dirt, snow, and moisture out of the throttle block safety switch. Replacing those plastic pieces can help keep the stuff out of the throttle block. The seals are $1.14 US, the throttle block is about 60 bucks. To replace the throttle block safety switch, you have to replace the throttle block.