New to 4 stroke tuning

YZcarver

YZcarver

I just bought this 05 WR450f to go dual sporting on and am looking at the jetting as it has a boilover problem and a hard starting problem. Once it's running, it runs amazing, but the starting is bothersome as it won't start with the electric starter. I have to kick it. It also boils over after less than 5 minutes idling in my garage from cold.

I'm familiar enough with tuning 2 strokes. I understand the pilot, needle, main, airscrew, slide and choke functions on my Keihin PWK and PJ carbs.
The Keihin FCR that's on it has a few new features that I'm unfamiliar with. It has an accelerator pump. Yeah, I get that. The airscrew is in a different spot and requires removing the bowl. Goofy, but yeah, I get that too.

I'm cool up to there, but it also has a "starter" jet and a "leak" jet?

I assume the leak jet is associated with the accelerator pump. No?

Can anyone explain to me how these come into play?
 
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SRAD97750

SRAD97750

Moderator
Staff member
The only differences is the leak jet and fuel screw.

The fuel screw is just an idle mixture screw that adjusts FUEL flow. (On 2Ts it controls airflow.)

And the leak jet is an orifice that fuel is allowed to bypass the accelerator pump's diaphragm. If you want the accelerator pump to produce more fuel, you install a smaller leak jet. If you desire less accelerator pump fuel delivery, you install a larger leak jet. -BIG DAN:thumb:
 
cleonard

cleonard

5 minutes is rather fast, but the bike will boil over 100% idling and not moving.

Hard starting is often a signal that the valves need attention. Check the valve clearance before messing with the carb.

If it is the carb, it may have been jetted for high altitude or something. Unless there have been a lot of mads you might want to start with the stock settings first and then go from there.

For info put

fcr carb tuning

into google and start reading.
 
YZcarver

YZcarver

Interesting thought. The guy I bought it from claimed to have the valve tolerances really tight. I guess I'm getting the full initiation for working on a 4 stroke. <sigh> Ah well. Learning new things is good.
 
Mojavekid18

Mojavekid18

Trying to resolve a few carbs issues on my 03 wr450 right now. One of them being hard starting. I'll let you know if i figure anything out
 
O

ossagp

For boil over on anything I usually pressure test the system including the cap.

Did you actually locate the fuel screw? I do believe it is at the front of the float bowl, on it's exterior. Hard to reach and most guys get a longer version that acts like a thumbscrew.

When someone says the valve clearances are set up tight I start thinking they need reshimming. On a shim under bucket valve train, going tight means the valves and or seats are deforming or eroding, usually.
 
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YZcarver

YZcarver

Looking for a reasonably priced service manual now. Dealer wants $80. Never done any valve adjustments or checks. (Never had a thumper) Need a little guidance there, so that's where I am with this now, looking for a manual. Found one for an 06 online, but it doesn't give a worthy explanation of how to do this.

Yes, I found the fuel screw. It is on the front of the bowl, but inside stock. As you said, most drill through the spot covering access to it and replace it with the t-handle one from the GYTR kit or one from ZipTy. This one has been drilled. Access is through the bottom much like the jets. I'm satisfied lean jetting is not the major issue.

Another thought did cross my mind though. Possibly leaking head gasket pressurizing the water jacket and displacing water that would normally be doing it's job cooling. Not sure how to test that thought though.
 
O

ossagp

YZcarver:
Looking for a reasonably priced service manual now. Dealer wants $80. Never done any valve adjustments or checks. (Never had a thumper) Need a little guidance there, so that's where I am with this now, looking for a manual. Found one for an 06 online, but it doesn't give a worthy explanation of how to do this.

Yes, I found the fuel screw. It is on the front of the bowl, but inside stock. As you said, most drill through the spot covering access to it and replace it with the t-handle one from the GYTR kit or one from ZipTy. This one has been drilled. Access is through the bottom much like the jets. I'm satisfied lean jetting is not the major issue.

Another thought did cross my mind though. Possibly leaking head gasket pressurizing the water jacket and displacing water that would normally be doing it's job cooling. Not sure how to test that thought though.
Click to expand...


Did you notice my suggestion about pressure testing. In addition a compression test may show you whether you have a head gasket leak. Getting an air fitting to put in place of the spark plug and hooking up to an air source is one way. Just take the cap off the radiator and look for air.
 
YZcarver

YZcarver

I noticed, but I'm a little slow to digest things.
"Not sure how to test that thought though."
Now that you've answered that, I think I can acquire fittings to get that done.
How much pressure you think I could safely apply?
 
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ossagp

Oh. Your engine under ignition is going about 8 times its own cranking pressure. So you aren't going to hurt anything with a compressor. The sell fittings for holding the valves in place via air pressure in snout every size. 8 bucks at sears

The adaptors for compression testers can work.
 
2strokesteve89

2strokesteve89

ossagp:
Oh. Your engine under ignition is going about 8 times its own cranking pressure. So you aren't going to hurt anything with a compressor. The sell fittings for holding the valves in place via air pressure in snout every size. 8 bucks at sears

The adaptors for compression testers can work.
Click to expand...
Your right about not hurting anything with shop air, just for clarification though cranking compression on a 4 stroke is usually about double of running compression on a sound motor
 
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ossagp

What I was talking about was the pressure that combustion produces. Typically max about 8-12 times what you get without ignition. I am confused by what you are saying.
 
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