View Full Version : ATV will not run wihtout choke on ....help.

08-02-2008, 02:53 PM
OK I have a Yamaha 450 Grizz. with 440 miles and it wont run without the choke on. I would think its a dirty or gummed up carb. What needs to be done to get the carb off and cleaned. Seems like a really tight spot to work. Could someone explain in detail how to take the carb apart and clean it as I have never worked on one......Thanks.

08-02-2008, 03:57 PM
Before you do all that get a can of seafoam and take the air filter off the atv. Run it at about half throttle or a little less and pour the seafoam in the air intake a little at a time until you have poured about half the bottle in it. as soon as you think that you have poured half the bottle in shut it off, let it set 10 minutes and restart it, it will smoke like crazy sinnce it is burning off the carbon and the gunk. pour the rest of the seafoam in the gas tank. May help and may not but worth a shot

08-02-2008, 04:22 PM
I haven't looked at a 450 Grizzly, but if it the same set-up as a Kodiak 450, the easiest way to get to the carb is by removing the airbox. I had a similar problem on a Big Bear, ended up rejetting and putting a hotter burning plug in. For some reason ngk pplugs would go bad after about 5 hours of riding, autozone cross-referenced a champion plug and never had another problem.

I would start by checking the boot between the carb and the air box, if the boot is loose(Yamaha's are bad for this) you will pull to much air and need the choke. If that wasn't the case I would add some sea foam and a new plug. If that didn't work I would pull the carb and clean, possibly rejet. You will need a new plug anyway after running with the choke on.

Read your plug, it will tell you what the carb needs. White, chalky plug not enough air, running lean. Black plug, too much air, running rich. Ideal is tan colored plug, not lean or rich. Lean is harder on your engine, causes hotter running temps. My big bear would run so lean that the header pipe would glow orange/red.

Link to read plugs:

Search Highlifter.com or ask over there for input.
www.highlifter.com (http://www.highlifter.com)

Here's a link to a place you can download service manuals:

Nothing for the 450 Grizz, but the Kodiak should be close.

Here's a link to a place you can look up exploded drawings, helps when putting back together.


08-02-2008, 07:05 PM
some of the yamaha carbs have a pump something like a car,if its been sitting for a while it may be stuck.if your colse i'd be glad to look at it for you.

08-02-2008, 07:43 PM
Seafoam worked on mine, runs like a charm!

08-02-2008, 11:17 PM
I just had the same problem w/ my Honda this what I did.
I pulled it of and took it apart and cleaned it. Found a small bee in the main fuel pick-up in the bottom of the bowl.
The Yamaha has a Mikuni Carb on it. This page should help. As far as getting off. I did not take the choke and throttle cables off just the two hose clamps and got it out so I could get to it. http://www.sbtontheweb.com/pdfs/mikunisbn.pdf
Edit I would look for a screw that when loosened will allow fuel to drain from the bowl out a tube coming from the bottom of the carb take that screw out and let fuel drain for a few seconds.

08-03-2008, 10:00 PM
I changed the gas today and also ran some Sea Foam through it and changed the plug. Didnt help. It didnt change either when I took the air filter off. I dont see any air leaks anywhere. I think it has to be the carb. I drain the bottom and gas came out OK it seemed. I may tinker with it a little more then just take it to the shop and let the tear me a new one.

08-04-2008, 03:49 PM
if it will run with the choke on then it is obviously getting gas. IMO your idle screw under the gas shut off has vibrated out cutting you gas flow off. tighten the screw in and it should up the gas flow allowing it to idle. you should be able to turn it with your hand..

08-04-2008, 03:57 PM
my dad has a 450 kodiak , he had this problem. Ended up being a bug got in his gas cap vent hose and plugged it up.

08-04-2008, 04:38 PM
Well today I took the carb apart and cleaned the jets and also adjusted the idle. After some time getting it started again it seems to be running great again. I think it was trash in it. Oh well, thanks to everyone for the help.

08-04-2008, 04:54 PM
ok now that you got it running take it and trade it for a Honda;):D LOL!

08-04-2008, 08:00 PM
ok now that you got it running take it and trade it for a Honda;):D LOL!

Then I would have to call someone with a Yamaha to come pull me out all the time.....:)