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Matt_W

Doing the BK Now, Need Help !!!

8 posts in this topic

Is it my imagination or does the black cam in the middle of the pump move very little when you twist the throttle ??

My pump timing was not very far off at stock. It seems that if you attempt to adjust the timing too far, it won't spray gas at all. As soon as I moved the pump timing screw from the position where it gave me no gas, to just after it gives me a full squirt, it was just clearing the slide where it should be.

Anyway, when your checking the during of the squirt, do you wick the throttle fast or do you slowly twist through to full throttle ?? To me it seems like the duration of the squirt is shorter (faster) when you wick the throttle, as opposed to a nice even twist.

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Matt W

00 YZ426F

94 YZ 250

http://www.mattwilliard.com

"Don't worry about me, how's my bike ?"

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Your post has me a little confused...

You have to open and hold open the throttle. As soon as you close the throttle the timing adjustment screw contacts the black actuating arm and turns the pump off.

I guess if you run the timing screw in far enough the pump rod would never contact the pump diaphragm and the pump wouldn’t operate.

Since the pump is spring operated apart from the throttle it should not matter how “fast” you open the throttle (within reason).

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My main concern is that when I open the throttle and the timing screw allows the pump cam to roll forward, the pump cam barely moves forward but a few millimeters. This is without the BK mod screw coming in contact with the underside of the cam. Is this normal ? I've heard some people say that the spray length was 3-4 seconds long ??!! Even without the BK mod, my spray lenght is barely 1 second ??

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Matt W

00 YZ426F

94 YZ 250

http://www.mattwilliard.com

"Don't worry about me, how's my bike ?"

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Another observation: If I hold the throttle open and push the pump cam forward with my finger, it will move further. When I just open the throttle the cam pump will only move a few millimeters forward on it's own. It's almost like the spring behind it isn't strong enough to push it all the way forward. Also, if I use the new screw to shorten the timing of the squirt, it also seems to shorten the distance the gas squirts. At stock the gas will shoot clear of the carb by a good 8-10 inches. When I shortent the duration of the squirt to the recommended .3 seconds, the gas barely clears the opposite throat of the carb. Does this sound normal ? Does anyone have ICQ and would be willing to chat in real time ??

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Matt W

00 YZ426F

94 YZ 250

http://www.mattwilliard.com

"Don't worry about me, how's my bike ?"

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Matt, I had the same problem. The passage is partially clogged.

Take the pump apart and spray some carb cleaner through the passages. Then blow them out with air. Do this backwards of the fuel flow. The nozzle in the venturi has a very small opening and can clog easy.

Took me a few tries but it cleared it up.

Oh yea, watch out for the small o-rings that seal the ports in the pump, it's real easy to lose them!

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communities.msn.com/FPilotsPhotos

[This message has been edited by F-Pilot#5 (edited October 05, 2001).]

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O.K. I managed to get the pump cam to move further through it's stroke and I got a better stream of gas. I definetely trimed down the duration of the squirt by about half. I think I'm at just over .5 seconds. As I rode the bike the first time, I didn't notice a huge difference. If I wicked the throttle to wide open I still have a bog. I can manage to get a screw driver at the new screw with the carb on the bike, so I turned the screw in an 1/8 rode then an 1/8 more and rode again. It seemed to get better, there is still a slight bog. I kept turning the new screw in an 1/8 and now I don't notice any performance difference at all. I was probably not more than 2-3 millimeters away from the pump cam with the new screw at the start and now I've turned in a few 1/8's. How will I now when I've stumped the pump cam from moving at all ?? What does the bike feel like when you've disabled the accelerator pump all together ?

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Matt W

00 YZ426F

94 YZ 250

http://www.mattwilliard.com

"Don't worry about me, how's my bike ?"

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Very interesting - and very, very frustrating I imagine.

I am very interested to learn the outcome of your mod.

I have an '00 model, and am intersted in the mod. It has to be good - right? Timmy's bike is modified this way, so it has to be the way to go - right? I'm being a bit skeptical because I have seen recently more varied than consistant results.

Please keep us posted - sorry I couldn't be of help - there are multiple threads on this exact topic.

Good luck,

Boomer

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Matt W: Did you rejet the bike? You need to replace the lost gas by using larger brass, you are jetting now for after the squirt rather than during it. Otherwise it will run lean and the mod will not be very inpressive at all. On my 01YZ426, I went from a 155 to a 162 main, one clip richer on the needle, and from 40 to 42 pilot (but I am 5000ft ASL). The bike had a 2.7 sec long squirt. My advice is to use a videocam and get it right. 9 frames will be 0.3 sec, and getting the timing right is easy this way too.

My Wr250F had a good improvement in throttle response by advancing the timing (turning the timing screw out 1/2 turn). It was already at 0.3 seconds so I did not bother putting in the screw.

[This message has been edited by mikeolichney (edited October 13, 2001).]

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