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BK accel pump mod post

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This a reprint of my previous post concerning the accel. pump modification.

I work for the Factory Yamaha race team and we use the DSP titanium ex. pipe exclusively.

Unfortunately our jetting is different than yours because we have a slightly different carb. It is a FCR but it has factory mods to the accel pump. I set up Tim Ferry's stock practice bike with the production DSP ti. pipe and ran a 168 main, 45 pilot, lifted the needle 1 clip pos. and limited the accel pump spray length to .3 seconds. To limit the accel pump spray length you must drill and tap the pump cam stop and install a 4mm screw/spring combo. that will contact the pump cam. A hex socket bolt works well, approx 25mm long. Remove the sub frame so you can look down the throat of the carb and with a stopwatch time the length of the pump spray when you stab the throttle. I usually click the stopwatch at exactly the same time I turn the throttle and click it again when I see it stop. It may seem weird but it works! Also you need to adj. the pump timing screw so that the spray doesn't hit the slide when is is raising. The timing is close when the spray just misses the slide. Then set the duration of the spray to .3 seconds with the adj. screw you installed. This probably sounds complicated and it is but is the only way to get rid of that pesky bog off bottom. If you have any more questions email me and I'll try to post some pictures that may help. By the way, Timmys stock bike rips with the pipe and these carb adjustments! Brian (BK)

MXWrench@msn.com

P.S. If you have questions feel free to email me and I will try to answer asap.(sometimes it may take a while though)

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BK,

Thanks for the info. It's great to have people in the know, give real information.

I have a question for you, I'm looking for the name and phone number of the Yamaha Regional Motorsports service manager for the SE Region. I met him and have talked to him a couple of times, but lost his card and moved and would like to contact him.

Thanks

Darryl

derwud@lycos.com

------------------

Derwood,

trapped in IL.

I've escaped! I'm heading back to Cali and beautiful Jawbone and Glamis......

99YZ400

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Thanks for the info BK! This really works! It makes the throttle response much better and is incrediably sensitive. Just turning the screw 1/4 turn makes a huge difference. This is amazing when you consider that the screw reduces the stock pump stroke by at least 5-6 full turns!! I was initially skeptical that Yamaha 's setting could've been that far off, but quickly became a believer. As soon as I started increasing the pump stroke (backing the adj screw "out") fron BK's recommendation the throttle response degraded severely. Plus, as an added benefit this improves starting--because the bike is not so easy to flood if you twist the throttle as you're crashing (or picking the bike up from a crash). Thank's again Brian.

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bk, do you think this mod would work on a '99 yz400 as well? what about the 2000 426? i have both, and the 400 still has a bit o' the bog.

------------------

will pattison

racer, engineer

www.ignitioninc.com

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BK - are you saying that the 2001 FCR on Tim's bike still has the bog? Or is this due to the DSP exhaust & jetting changes? One thing I have noticed on my 2001 is no bog. I have a 2000 that has the bog demon. Also,

Would you suggest the ""FIX" for only DSP pipe owners or any aftermarket pipe owners bike?

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ga426owner,

i got an email from BK last night with the YoT specs for Fonseca's/Ramsey's bike. they suggest the "fix" for the baby as well. the baby has bogitis too. :)

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SUnruh, maybe I am the lucky one. I am wondering:If Factory Yamaha doesn't use the FCR that us mere mortals have, maybe they have the bog issue due to the enhancements they have put into their modified FCR's. My 2001 does not have it nor do any of my local 2001 rider/friends bikes. this is what I noticed first and foremost on the 2001. My 2000 has it, thank goodness it is going to be picked up this weekend - been for sale a long time.

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SUnruh, maybe I am the lucky one. I am wondering:If Factory Yamaha doesn't use the FCR that us mere mortals have, maybe they have the bog issue due to the enhancements they have put into their modified FCR's. My 2001 does not have it nor do any of my local 2001 rider/friends bikes. this is what I noticed first and foremost on the 2001. My 2000 has it, thank goodness it is going to be picked up this weekend - been for sale a long time.

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This adjustable pump stop only can be installed on the '00 and '01 model carbs. The P-38 Lightning is an option for the 98/99 if you want to reduce the stroke, but it is not adjustable.

I made the modification to my bike about a month ago and the carb was designed perfectly for it. This is a good idea for any WR or YZ. The pump stroke was set to about 1mm versus ~3mm stock. I used a screw instead of a bolt. Adjustments can easily be made on the bike with a long screw driver from below on the left side of the bike. The right side is nearly impossible to access because of the pipe and how the screw head faces down.

Note that Brian also lifted the needle 1 clip position. This is an important point. If you shorten the stroke without shifting the needle you're doing half the steps. But, this is a setup for hard racing not a casual trail ride. Maximum snap and minimum bog.

You might foul a plug on downhills with the needle clip set this way if you are less than hard charging. Keep in mind who is riding it and how they're riding, this is not a low maintenance bike. I'm sure Brian has it dialed like a swiss watch. :)

James

[This message has been edited by James Dean (edited 03-29-2001).]

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James, what year is your bike? My 2001 does not have the bog issue. It seems that this "fix" is great if you have the bog. What other advantages does this "fix" give your bike?

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Ga426owner,

This modification was on a 2000WR with YZ pipe.

The pump flows long after it's needed. The extra fuel is not of any benefit and COULD be overkill and hurting performance. Your bike is jetted to perfection until someone shows you how much better it could actually be. For example, try the "perfect" stock jetting on the WR. :)

The '01 YZ's supposedly have a "remapped" pump stroke but nobody has said how much shorter the stroke actually is, if any (2mm?). All YZF's will bog if you whack it hard and low enough, it depends on your expectations. Just turn the idle down and whack it open. The main benefit of having the pump adjustable is dialing in the needle clip and secondly diameter/taper for more power and consistent jetting.

I've tried settings very close to BK's post, and they scream! :D

James

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Hey BK,

I have a 01' YZ426 w/ a WB high boy header and R4 exhaust and have been trying to get the jetting more precise (sometimes it fouls plugs and isnt as responsive as I would like it to be) and this sounds like it will cure my dilema! I cant even imagine how fast Timmy's bike is (the bike sure sounded fast at the Houston SX) it looked cool when he took the outside berm after the triple and "slingshot" out of the berm!

Im sure everyone would appreciate it if you could take some pics...if you email me the pics at motoman393@hotmail.com I will post them on this site so it will be easier to understand! Thanks a bunch,

Garrett

------------------

I get my kicks on a 2001' YZ426!

Friendswood, TX

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I've been fouling plugs since shortly after I purchased my bike and at this time I have yet too figure out why despite a new coil, CDI and constant tinkering with the jetting. I am wondering if the output of the accelerator pump is shooting to much fuel into the intake. My fouling is a result of a black sooty plug not necessarily wet. Does anyone know the duration of the spray on a 2000 WR? Besides timing and duration is there any way of adjusting the orifice that controls how much gas is in the stream? This is my first experince with the pump so be patient with me...Thanks

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Moto-Mike,

It is unlikely the pump is causing your problems. The orifice on the pump may be replaceable but we haven't seen any source for one yet. The duration is about 2-3 seconds, way more than needed but not normally a problem area.

You would be best to turn the pilot screw in until you feel it hesitate or move the needle 1 step leaner if everything else on the carb was checked out and has been cleaned.

James

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Originally posted by BK:

This a reprint of my previous post concerning the accel. pump modification.

I work for the Factory Yamaha race team and we use the DSP titanium ex. pipe exclusively.

Unfortunately our jetting is different than yours because we have a slightly different carb. It is a FCR but it has factory mods to the accel pump. I set up Tim Ferry's stock practice bike with the production DSP ti. pipe and ran a 168 main, 45 pilot, lifted the needle 1 clip pos. and limited the accel pump spray length to .3 seconds. To limit the accel pump spray length you must drill and tap the pump cam stop and install a 4mm screw/spring combo. that will contact the pump cam. A hex socket bolt works well, approx 25mm long. Remove the sub frame so you can look down the throat of the carb and with a stopwatch time the length of the pump spray when you stab the throttle. I usually click the stopwatch at exactly the same time I turn the throttle and click it again when I see it stop. It may seem weird but it works! Also you need to adj. the pump timing screw so that the spray doesn't hit the slide when is is raising. The timing is close when the spray just misses the slide. Then set the duration of the spray to .3 seconds with the adj. screw you installed. This probably sounds complicated and it is but is the only way to get rid of that pesky bog off bottom. If you have any more questions email me and I'll try to post some pictures that may help. By the way, Timmys stock bike rips with the pipe and these carb adjustments! Brian (BK)

MXWrench@msn.com

P.S. If you have questions feel free to email me and I will try to answer asap.(sometimes it may take a while though)

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I have a '01 426 that was one of the foulers and my mech. took care of me by replacing the CDI, Mapping circuit, and a new carb off a bike from the sales floor. I have moved the needle clip up one position to lean it out. This has cleaned up the plug and I don't have the back fires, I am thinking of going to a 168 main jet as you recommended. With all these alteration the bike doesn't bog. The question is do I need to adj. the accel pump? Any info would be appriciated

Thanks

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