Hard start - Missing at mid-rpms.. Blown Fork Seal.

My Brothers 2003 WR450F with only 2000 miles on it is starting to miss at midrange and its really difficult to start..

I don't know much about yamaha thumpers, and hoping someone can point me in the right direction...

He's got an owners manual, and I suggested we do a valve check and clean the carb to start...

The fork seal is different than my DRZ400 because its inverted - maybe someone can explain the difference - should be simple...

Do these bikes have valve problems or could it be simply that its jetted for the desert and just ran funny at the beaches in Baja??

I assume the fuel screw is accessable, or does the plug need to be drilled out?

Thanks.

Put a new plug in her. Rejet for cutting out (rich condition most likely on main jet). Download the full service manual from this web site. Check your valve clearances it is time to adjust them. Hard starting put in a 72 starter jet for the choke circuit. :)

Put a new plug in her. Rejet for cutting out (rich condition most likely on main jet). Download the full service manual from this web site. Check your valve clearances it is time to adjust them. Hard starting put in a 72 starter jet for the choke circuit. :)

Thanks - I'm going to have my Brother come over so we can do all of that - is there a jetting database for the WR450F?

What is recommended for all the jets?

I appreciate the help! :)

Here is what works for me and you guys can use it as a starting point to jet your bikes:

This recommendation requires air box flow mods and an open stock or aftermarket pipe and ACV circuit intact.

Elevation 0 to 4,000. feet

30 to 45 degrees: 172 main, JD Blue #5, 48 Pilot, 2.0 turns, 75 starter jet, #0 leak jet

45 to 60 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

60 to 75 degrees: 168 main, JD Blue #3 or JD Red #5, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 2.0 turns, 65 starter jet, #60 leak jet

Elevation 4,000 to 8,000 feet:

30 to 45 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

45 to 60 degrees: 168 main, JD Blue #3, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

60 to 75 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 45 Pilot, 2.0 turns, 65 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 1.75 turns, 65 starter jet, #60 leak jet

Elevation 8,000 to 11,000 feet: ( Note you will loose a lot of power due to altitude but your bike will idle and not foul plugs!)

45 to 60 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 70 starter jet, #40 leak jet

60 to 75 degrees: 160 main, JD Red #4 , 45 Pilot, 1.75 turns, 68 starter jet, #50 leak jet

75 to 90 degrees: 158 main, JD Red #3, 45 Pilot, 1.5 turns, 65 starter jet, #60 leak jet

What are the "Flow Mods" you mention - On my DRZ - I cut a 3x3 hole in the top - are you recommending a similar thing on the WR???

As for the Modded stock can - do you mean removing the little restrictor? Thats done.

Thanks for all the specs - I'll look and see where it is at soon, and see what "Fun Bike Center" jetted it with...

You don't happen to have the Valve specs too do ya?

There have been NO MODS to this bike...

As for the fork seal - it is a difficult thing? I replaced my springs and fork oil on my DRZ, but his forks are inverted - does that make it more difficult or easier?

If you've never checked the valve clearance....it's WAAAYYY past due!! :)

What are the "Flow Mods" you mention - On my DRZ - I cut a 3x3 hole in the top - are you recommending a similar thing on the WR???

You don't happen to have the Valve specs too do ya?

Cut holes in the rear of the air box where the snorkel was to allow air to flow into the box from the are above the fender. Uncork the plug as you already have done. now you can jet the bike.

Your intake clearances need to be on the loose side of: .004" - .006"

Your exhaust clearances need to be on the loose side of: .008" - .010"

Valve clearances are very important on these engines! :)

Indy

I have looked a couple of times for the manual to download. is it in the tech forums? I can't find it. probably right in front of me.

and has anyone posted a step by step guide on valve clearances.? or this is in the manual?

Indy

I have looked a couple of times for the manual to download. is it in the tech forums? I can't find it. probably right in front of me.

and has anyone posted a step by step guide on valve clearances.? or this is in the manual?

This will work for you it is for a 250 but same thing just be patient and watch what you are doing very easy

http://www.thumperfaq.com/valves.htm

Link won't open.

I'll keep searching old posts and if anyone can direct me to them, much appreciated.

The site is down or it has been closed due to too many hits. :)

Where can I get a feeler guage for measuring valve clearances and about how much?

Here is what works for me and you guys can use it as a starting point to jet your bikes:

This recommendation requires air box flow mods and an open stock or aftermarket pipe and ACV circuit intact.

Elevation 0 to 4,000. feet

30 to 45 degrees: 172 main, JD Blue #5, 48 Pilot, 2.0 turns, 75 starter jet, #0 leak jet

45 to 60 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

60 to 75 degrees: 168 main, JD Blue #3 or JD Red #5, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 2.0 turns, 65 starter jet, #60 leak jet

Elevation 4,000 to 8,000 feet:

30 to 45 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

45 to 60 degrees: 168 main, JD Blue #3, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

60 to 75 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 45 Pilot, 2.0 turns, 65 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 1.75 turns, 65 starter jet, #60 leak jet

Elevation 8,000 to 11,000 feet: ( Note you will loose a lot of power due to altitude but your bike will idle and not foul plugs!)

45 to 60 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 70 starter jet, #40 leak jet

60 to 75 degrees: 160 main, JD Red #4 , 45 Pilot, 1.75 turns, 68 starter jet, #50 leak jet

75 to 90 degrees: 158 main, JD Red #3, 45 Pilot, 1.5 turns, 65 starter jet, #60 leak jet

You da man! I've been waiting for this to copy for the changing of the seasons. :):):p:D:D:o

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