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New pump cover and it still cuts out!!!

By dunecj2a,
in YZ400F/426F/450F/450FX

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dunecj2a

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OK I need some help. 04 450 with complete FMF Ti 4 system.

165 main,42 pilot, 2 turns out on fuel screw.(FMF's specs)

I read alot about how great the Boyssen accelerator pump covers were and how they cleaned out the bog. So I went out and bought one.

I cannot tell any difference and my bike was actually cutting out and stalling when I snapped the throttle :D

I messed with the fuel screw and that thing does absolutely nothing. I hardly notice any difference when I mess with that thing :D

Boyseen tech told me to keep jetting at FMF specs and to only turn the fuel screw out 1/4 - 1/2 turn.

It sure as S#$t isn't running the way a 450 with an FMF exhaust system and pump cover should be ??

What do you guys think? Maybe its not in the carb? Valves, foulded plug????

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dunecj2a

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Yeah Boyseen gives you a guage to set it at. Plus they say not to touch it and leave it at stock setting. They give you the guage to reset back to stock in case it was ever messed with?

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Scotty426

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Wow, your fuel screw is giving you no effect? That just ain't right. I'm not doubting you, but if that thing doesn't give effect I'd wonder why. I can tell a big difference in 1/8th turn. I have the boysen cover and she did run a rich bog once in awhile but I tuned her leaner with the fuel screw and it went away. I hate that fix though-shes just slightly soft down low. I am reading up on the accel pump timing mod (BK) on motoman 393 and TT jetting forum. I want to get less accel pump time and set the fuel screw richer than it is now. However, I put the cover on to help prevent stalling and you know what boys? It did. I think Yamaha/keihen plans on a few bubbles in the reservoir when they jet that thing. I have a 426 obviously so mines a different beast. It is possible to have a lean bog and adjust until you have a rich bog. When you relight it, do you have to use the hotstart even if you didn't dump it? If so, I bet your too rich. When you wack the throttle at rest, does it smoke (black) badly? Rich. Carb hoses clogged? Changing the plug doesn't cost much and I would do it just to eliminate it. Boysen will give your money back if you want. You still have situation with that fuel screw though. Good luck. If you solve the mystery, please post.

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smokin529

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I was having what sounds to be a similiar problem with my '04 450, though I just have a Power Bomb Header with the stock muffler. Then I added the Rekluse and the problem got worse. So I went with a 45 pilot and dropped down from a 170 main to a 165(JD Jet kit), turned the idle up a bit..No more stall!!! Before I went to the 45 pilot, my Zip-Ty air screw didn't do much. I picked up the Boyesen cover today and will install it tonight.

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sirthumpalot

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Scotty brings a point that I totally missed. The fuel screw should make a very large difference in the small throttle opening area (1/4 throttle and under). If that makes no difference then I suspect your carb is very dirty. Clean it maticuliously and I'll bet you see a difference. Put carb cleaner and compressed air thorough every hole.

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Chris_from_Oz

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I read alot about how great the Boyssen accelerator pump covers were and how they cleaned out the bog. So I went out and bought one.

I cannot tell any difference and my bike was actually cutting out and stalling when I snapped the throttle ?

I messed with the fuel screw and that thing does absolutely nothing. I hardly notice any difference when I mess with that thing ?

If adjusting your fuel screw has NO effect on the idle of your bike, I would say that your pilot jet is too large? Although, a 42 doesn't seem THAT big for your 450. I would check your AP timing and duration, to ensure they are not causing the bog, and by your description, I suspect that is a big part of your problem. Let us know how you go :D

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dunecj2a

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I'm way ahead of you thumpalot, I completely took my carb apart and cleaned it out. It was spotless before I even did that. I inspected everything and it looked great but I figured since it was apart that I would hose it down in carb cleaner and blow it out with my compressor. Anyways that did nothing. ?

I'm gonna try a richer pilot. If my valves are out of adjustment will that have anything to do with throttle response off the bottom. :D:D

All I can say right now is that I feel absolutely no effect from boyssen's pump cover. I'm sure its not there product, but all my fault for not having the bike tuned right. ?

What about needle height? Anyways I'm gonna check my valves, if there good then I will try a richer pilot. If that does nothin then I will move the needle. :worthy: If no luck there then I will get a YZ250 :D:D

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smokin529

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Hey Smokin let me know what happens :D

Why did you go so rich on the main?

FMF says to go with a 165, did you try that ?

I got the Powerbomb off a closeout rack at a local dealer and it came with no paperwork($110.00 for the titanium one!), so I went with what was recomended in the JD jet kit for sea level.

The bike runs great now

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dunecj2a

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What altitude are you at?

Is there any chance that you put the slide plate in upside down. That's what this really sounds like....I did put my upside down and thats exactly how it acted. :D

Nah I made that mistake a while back :D? I learned the hardway, the plate's in right. I waitin on my suspension to come back and test it at the track. I'm gonna rejet with a 45 pilot and see what happens. I am also gonna check my valves tomorrow night ?

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FlynRyn

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Well if jetting is close and the slide is right and the AC cap did nothing I would think you may have a dirty AC circuit. If it sprays fine maybe not but its worth a check.

There are 2 spring loaded balls in the carb. One is located in the bottom of the float bowl which you can clearly see. Clean that out real well and make sure it flows well.

The second is located on the main carb body float bowl gasket surface. It looks like a hole drilled at an angle. There is a spring loaded ball there that may get dirty as well, as the circuit behind. Clean those out with contact cleaner and blow a little air thru there to make sure they are clean and the balls are moving freely.

Also be sure your idle is right. I believe its around 1900 rpm?

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Scotty426

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I have an '02 426 and run a 175 main-this is down from a 178 for winter. I run a 42 pilot. I ride at 1250ft, DrD 3.5 inch muffler and headpipe, K&N, no air box lid, hotcams exhaust only(for decomp). How I run pretty good to be so awfully rich compared to you guys is a mystery? 5 jets off? Wow. I just did the BK mod, took my AP from 2+ seconds down to approx .8-.9 seconds. This will cure the rich bog I bet. I know she's rich because of the puff of black smoke when I hit it hard. Also, why is my fuel screw so much more effective? she hangs out around 2 turns plus or minus 1/8 turn if I'm playing around. If you go to forums on TT , engine, intake and carb you can get more than you want to know. Also thumperfaq.com. He's a 250f guy but lots of info. Good luck to you

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