178 main?

5 replies to this topic
  • KAS

Posted October 08, 2007 - 05:43 PM


The dealer I purchased my '07 450 from said they switched out the too-lean stock jetting for a better set up before I picked the bike up and took it home.

I never bothered to check what they did, since they deal with these bikes a lot I figured they probably had a pretty good idea of what makes them run good. And I'm pretty sure mine does run good. I'm not real familiar to how these 450's usually behave, but mine seems to run great and pulls hard.

Tonight I checked what main they put in the bike, its a 178. I didn't check the pilot because I don't have a screw driver short enough to do so, and I didn't feel like pulling the carb off to look (I was bored, but not that bored).

So I check the jetting thread at the top of the page, lo and behold I don't see where anybody is running anything close to that size. Mostly 165/168, somewhere in there.

We are right on the dunes, so I figure maybe they really richen them up so some yay-hoo doesn't melt one down on the sand on the first ride.

The bike did come with some different jets, so I might play around with it sometime. Right now it runs good so I might not mess with it.

Just thought it was weird. :confused:

  • grayracer513

Posted October 08, 2007 - 08:01 PM


... I figure maybe they really richen them up so some yay-hoo doesn't melt one down on the sand on the first ride.

Doesn't work like that in a 4-stroke. 178 is the biggest jet I've ever heard of bring run on pump gas; way too big, IMO.

  • Kasjok

Posted October 09, 2007 - 06:35 AM


I used to have 178 winter time and in summer I am having a 175 main jet. I am about 100 ft above sea level also. What`s wrong with riding so large main jet? My bike runs fine with those numbers and people around here use like 165-175 jets usually.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted October 09, 2007 - 07:32 AM


What`s wrong with riding so large main jet?

There is a point at which the balance of fuel and air in the combustion chamber is such that nearly all the fuel will be burned (you can never quite get all of it), and burned with the maximum amount of energy release. When the main jet is increased beyond this point, the first thing that happens is a loss of power. If you go bigger, you start having other problems, like a faster carbon build up, fuel in the oil, and oil consumption (to say nothing of fouling plugs). The trouble is that 4-strokes tolerate being way over rich, and some people think that because the engine "runs OK" with a bigger jet, it should be used.

That said, a 175-178 may not be far off the mark for an Estonian winter. But I doubt you need more than a 170 in the summer.

  • KAS

Posted October 09, 2007 - 07:38 AM


Thanks for the insight, I have a 165 I might toss in next time I'm riding. It only takes a second so I think I'll try it.

  • Kasjok

Posted October 09, 2007 - 09:09 AM


Thanks Grayracer, I will keep that in mind.

Related Content


Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.