Please help.. 2005 yz450f jetting and exhaust repacking question

12 replies to this topic
  • 2012grizzly700se

Posted June 08, 2013 - 07:24 PM


I know there's a ton of jetting info on here, so much that I'm getting even more confused. I'm helping a friend with his bike, it has hesitation if you go hard into the throttle and pops like crazy when you let off. It's got a Twin air filter and stock exhaust.
I have read several threads and checked the hot start plunger and cleaned it up and I also cleaned the jets out, the pilot was a little dirty. He rides at about 800 ft above sea level. My question is, I ordered a #48 and #50 pilot jet and #168 and #170 main jet and should I change the needle out with a replacement Yamaha needle and how would it need to be set? I've already ordered him a adjustable fuel mixture screw. Also the bike is extremely loud so im guessing the exhaust could use a repacking, so what would you suggest for the type of repacking and what would i need?Any help or tips would be greatly appreciated. Like I said im sorry to be this topic to death, but my head is killing me from reading so many. Thanks much

  • Thommo_400f

Posted June 09, 2013 - 01:40 PM


Just be methodical.
Clean AP and check for a good stream of fuel.
Pilot first. There is a sticky about pilot jet.
Basically, warm up bike then turn fuel screw in/out slowly until bike idles highest if it is highest at 1/2 turn from bottom. Then smaller pilot needed. If it idles highest at 3 turns out then bigger pilot needed. Otherwise find the highest idle with current one.
Next set needle. Start with stock needle #3 clip and do some tests.
Low throttle cruise steady throttle.
Slow acceleration through all range.
Full throttle rev out.
Snap wheelies.
Main jet last. Test with full throttle runs and see if it revs out easy or it sounds like Brrrooooowwwww and is sluggish.
post results and you will get lots of help.
Some light popping on decel is good and normal with open exhaust.

  • 2012grizzly700se

Posted June 09, 2013 - 03:19 PM


Thanks a lot. I will do that tomorrow if possible.
I took the silencer of to check the packing, I know nothing about how it should look. In you opinion, does it need repacking?ImageUploadedByThumper Talk1370819901.763205.jpg ImageUploadedByThumper Talk1370819940.274902.jpg ImageUploadedByThumper Talk1370819975.565380.jpg

  • Thommo_400f

Posted June 09, 2013 - 03:50 PM


As soon as packing starts to break down its time to change it. If it has good integrity then it should be ok.
Since yours is already out why not do it anyway.

  • 2012grizzly700se

Posted June 09, 2013 - 07:09 PM


Good point. Thanks for all your help

  • 2012grizzly700se

Posted June 09, 2013 - 08:37 PM


I know this a stupid question but I saw FMF has silencer packing and muffler packing what do I need to get? Thanks a lot man for all your help.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Thommo_400f

Posted June 10, 2013 - 02:12 AM


If you choose the option 4-stroke muffler packing from the drop down list you can't go wrong.

  • 2012grizzly700se

Posted June 18, 2013 - 03:34 PM


I went ahead and got him a FMF Q4 pipe. Changed the jets to 168 and 48 and put a after market "tusk" fuel screw in, and backed out 2 turns. Put it all back together and now this ImageUploadedByThumper Talk1371598250.463869.jpg
Fuel leaks out the top where the plunger connects. Also if the bike sits for a few with the fuel on it comes out of the overflow but is fine while riding. ImageUploadedByThumper Talk1371598419.798744.jpg
Cleaned this but is still doing it. Any ideas?

  • Thommo_400f

Posted June 18, 2013 - 03:51 PM


If the fuel screw leaks it means that the o-ring isn't seated properly.
remove it and try re-installing it making sure the o-ring on top of the spring seats evenly.

The little nipple on the top of the float valve has a spring under it (inside the valve). Eventually the springs corrode and bind up and then the valve won't seal any more.
Get a new float valve. Temporarily try pushing the nipple up and down to free it up.

  • Thommo_400f

Posted June 18, 2013 - 03:54 PM


Is the fuel leaking out from the Accelerator pump housing ?
If it is, you must have a hole in the AP diaphram or you have installed it wrong, allowing fuel to squirt back up the shaft.

  • 2012grizzly700se

Posted June 18, 2013 - 04:00 PM


Not having an issue with the fuel screw. It's fuel coming up at the top of the rod"wet spot in the pic"ImageUploadedByThumper Talk1371599898.364809.jpg
I had done what you suggested about the nipple on the valve and it was sticking sometimes during working with it. I will replace it. Do you think the other issue with the wet spot could be a busted diaphragm in the plunger at the bottom of the carb?

  • 2012grizzly700se

Posted June 18, 2013 - 04:07 PM


Sorry , I didn't see your last post. I never took it out"acc pump" but I did blow compressed air thru. Maybe that punctured it. Thanks for your help man.

  • grayracer513

Posted June 18, 2013 - 08:18 PM


The '05 doesn't have a removable float needle seat, so it doesn't have an O-ring at the seat that can leak. If the bike floods while it sits, replace the float needle.

Related Content


First Hare scramble tips by dhend8

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies

100 hrs on 2014 yz450f, shim valves or replace them? by ttr230rider6

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  79 replies

YZ450F 03 Sparks driving me crazy by SirAttard

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

Is the 2016 GYTR Yamaha YZ450F too fast? by Fryboy

Dirt Bike   Special Interest Forums   Pro Racing
  • * - - - -
  • Hot  241 replies

yz400f throttle bog by yz400fmaniac

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • * * * * *
  • Hot  28 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.