Anyone else running a 175 main jet in a WR450?

I have read with much interest the posts on jetting and looked closely at the jetting information contained in the signatures of riders posting here. There are quite a few variances going on among riders at the same altitude and in the same temperature regions.

It is still rather brisk up here in Alaska, with highest temps only in the low 50's for a couple of hours before it begins to drop again. I am at sea level. I completed all the free mods the 2nd day I had the bike. I had changed the main jet from a 150 to a 155(the largest one that came along with the bike). I was still getting alot of popping on decel. The bike was running fairly strong off the bottom and came on hard in the mid-range but would not keep pulling hard on top. Unfortunately, the only area I have been able to ride is on the beach. The sand there is very deep and just not well suited for jetting tuning.

After finally getting my back-ordered jets, I installed a 175 main along with a larger 48 pilot. I also went 3 turns out from fully closed on the pilot air screw. I left the needle alone. I was only able to take a short blast through the gears afterwards but felt a tremendous difference in power throughout the rev-range. There was also no popping on decel. Have yet to do a plug reading to see if I went too rich but will get to that when time allows. Seat of the pants feel was very much an improvement :D. It was very chilly yesterday, wind was blowing damp 38 degree air. Has anyone else went this far up on their main? Any suggestions from the experts would be greatly appreciated? :)

I have gone up as high as 172. You are going to need to come back down to 160 if it gets back in the high 50's. I am running a 155 for temps above 55 degrees. You will see the bike hesitate and cough when running rich. A little poping (soft sounding ones are ideal) on decel means you are probably jetted pretty good and need to richen your pilot cicuit to eliminate it. Every bike is slightly different but I run 165 main in 40 degree weather. :)

175 main is way too much gas. Pull the plug and read it. At what ft. level are you running? Popping can be misleading, a loose exhaust will make a pop as well. I cured that by reducing fuel on the bottom, i.e. fuel screw in by half turn, 1 1/4 out now is what the bike whats at 4000ft. Have noticed less red pipe at that setting. :) 162 main, stock needle, 2000 WR400


Oasis_flame, Not trying to be a jerk here but your signature says you ride a 400 not a 450, displacement does make a difference. YOU are at 4,000 feet with desert temps, I am at sea level a few degrees above freezing(I said that in my original post). If a large segment of 450F riders are using 170-172 mains, how is it that a 175 main at much colder temperatures is "WAY TOO MUCH GAS"????????? I am looking for expert, straight-forward advice not careless opinions.

For anyone else reading this thread, no, my pipe is not loose. The bike was popping incessantly with stock jetting and showing signs of fuel starvation. With the new settings I listed(175 main, 48 pilot, 3 turns out on the pilot air screw), the bike ran like a scalded A$$ ape in those very cool temps. Has anyone else encountered these types of temperatures and experimented with larger main jets?

Indy, I really appreciate your post. I will keep what you said in mind as temps rise. We are above 14 hours of daylight right now, with 60-70 degree temps and non-stop daylight on the way.

Hey Nomadak,

You may want to try and run the needle in a one clip richer position with a smaller main when it gets above 60 degrees. That seems to work with my mods. You will know when the hesitation shows up that you are rich. I find it harder to recognize the main jet being the culprit since you have to go way rich to get it to hesitate at full throttle. Good luck with the jetting! By next year we will all have our 450's figured out and it will be so much easier to rejet a few times per year. I have rejetted to the point of dreaming of a fuel injected WR500. I am sure that feeling will go away by next year. :)

A 175 sounds a little fat. I used a 160 in 40 degrees at sea level. At 60 degrees it was too rich.

A main jet takes 30 seconds to replace it's easy to experiment.

What ever dude. Too much gas will wash away the lube on your walls and your bore will last maybe one year. But I guess you have all the answers so run the fat jet and be ready for and engine rebuild. And that little WR400 has been convereted to a 426 with 13.5 to 1 comp. piston, polished intake and YZ exhaust. Last dyno at 4000ft. was 56.3 hp. I'd say my jetting is dead on, not bad for a non-expert with careless opinions! I'll be the guy passing you in 4th. with my front tire in the air. Keep up rookie, see ya at the track, alfa-mike-foxtrot. :)

Didn't mean to offend anyone. It gets tiring trying to wade through post after post of misinformation, even when it is unintentional.

Oasis_flame, sounds like you have a healthy running engine. Understand that your enviroment is completely different than mine. I appreciate the contribution you did make concerning too much gas washing away the oil film on the cylinder wall. You see, that is good information to give.

BTW, if 28 years of riding/racing makes me a rookie, I'll gladly eat some roost. Also, you initially stated you had a 400, how is a person supposed to gather that you had modified it so heavily from your first post? Even still, a 450 is certain to have small incremental differences from a 426 where jetting is concerned.

I found this information today .

It pretty much explains that your jetting is almost spot-on for your altitude/temps and that what I was running that day(175main) was very close to being in the ballpark for the conditions present here in Alaska that day.

I drove over 450 miles round-trip yesterday to one of the few MX tracks here in Alaska to get some more seat time. Temps were much warmer(low 50's) and the track was too tight to get out of 2nd for very long. The 175 main was too rich for those conditions.


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