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Discussion Starter · #1 ·
I have a question about the Acceleration Duration screw.

From this article : http://www.roadstarmagazine.com/2003/07/how-to-adjust-the-road-star-accelerator-pump/#more-149

and a virtually identical description on another form.

My bike is a 2003 Yamaha Road Star. All stock when I got her.

My basic problem is that I did a carburetor rebuild on my Mikuni BSR 40 and instead of improving matters, things go worse. Hitting the gas did not make the engine take off quickly as it should, and there is now a lot of backfiring through the carb.

According to that article, the bogging problem could be alleviated by adjusting the 'Accelerator Duration Adjustment Screw' outward to increase the amount of fuel squirted. However, upon investigating this screw, it seems to be floating. Not that it's loose, it just never touches the black plastic piece underneath that is supposed to adjust the amount of gas being squirted when the throttle is hit.

Does anyone know approximately where this end of this screw should be touching? According to the article, turning the screw (it is secured by a lock nut) clockwise should decrease the amount of fuel provided. So, just guessing . .. being retracted so that the screw never touches the lever underneath, it should be squirting the maximum amount of fuel.

Does anyone know an approximate starting position that this adjustment screw should be set at? Is the screw too short? There is also one on the back side that sets a quantity. Yes, confusing, they both say quantity, but really one is duration and the other is quantity.

Also, all that I have done, engine wise, besides new plugs, is to put on a high flow K&N filter. Not the small one that replaces the OEM, but the triangular large RK Series that requires a new outside plate to hold it in place. None of these changes should be causing the backfiring, sputtering, and bogging down when the throttle is applied. I've made no changes. I used the needle valve that came with the kit, the Non-adjustable one with a single notch and the main jet replacement was the same original size of 165. Testing is done with the air box off anyway, so air flow availability is at maximum.

I would love to hear any other suggestions on solving the backfiring problem. So far, I have increased the turns outward of the Pilot Jet screw from the original 2 1/2 turns out to 3. I have a replacement Needle Jet on order that has cut slots so that it can increase richness. I don't know yet if I should be changing things into a more lean direction. Advice on that would be greatly appreciated.

Thank you in advance for any advice.


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That black piece moves. The proper method to clean and lube is outside my skill level. But I used lots of carb cleaner and silicone spray. That black piece moves to press on the accelerator pump. That part supposed to move up and down freely. Which squirts out the tube at the opening.

did you ensure all the openings are not clogged with corn residue?

baron’s jet kit is recommended for the needle.
 

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Discussion Starter · #3 ·
did you ensure all the openings are not clogged with corn residue?

baron’s jet kit is recommended for the needle.
Oh, Yes, indeed. I did. When I rebuilt the carb, it was entirely disassembled and cleaned. That is what is so frustrating about the present problem. When testing the accelerator pump, I never saw either screw hitting that black plastic piece, so I was never sure where the screws should be set. It has been advised that one of the reasons for the backfire through the carb was the pump. But, I still haven't isolated the problem yet. Thank you for replying.
 

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I saw your post on the other site. Get that black piece to rotate. When you crank on the throttle, the screw comes off the black piece. The black piece rotates and presses on the accelerator pump. Does that pump move easily if you press on and squirt fuel out?

The black piece could work the other way around. It’s been about two years since I got mine working. Memory kind of faded some. But it should make sense when you look at it.

pilot and main jet changes if you have after market exhaust with a less restrictive air intake. Don’t remember what was posted on other site
 

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Discussion Starter · #5 ·
I saw your post on the other site. Get that black piece to rotate. When you crank on the throttle, the screw comes off the black piece. The black piece rotates and presses on the accelerator pump. Does that pump move easily if you press on and squirt fuel out?

The black piece could work the other way around. It’s been about two years since I got mine working. Memory kind of faded some. But it should make sense when you look at it.

pilot and main jet changes if you have after market exhaust with a less restrictive air intake. Don’t remember what was posted on other site
Thank you. I will be checking on that black piece soon. I've ordered some parts, as per some advice on the 1600. I have the stock sizes in there now from the rebuild kit, but I'm going to bump up to 172.5 main and 37.5 pilot. I'll be checking for leaks on the manifold side too, but they were OK after I did the rebuild. Hopefully the parts will be here soon, they've been processed.
 

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Should probably go 170 or 167.5 main with the baron needle and the stock exhaust. I got an aftermarket carb rebuild kit from the dealer and was not impressed with the components. The kit pilot jet didn’t look the same size as original pilot or the mikuni 37.5 or 40. Same for the main. If you got the baron jet kit, it will come with actual mikuni main jets.

the recommendation for the pms from the other site is spot on. Make sure the pieces are in the correct order. Did you remove it and clean the opening?

petcock cleaned out?
 

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Discussion Starter · #7 ·
Should probably go 170 or 167.5 main with the baron needle and the stock exhaust. I got an aftermarket carb rebuild kit from the dealer and was not impressed with the components. The kit pilot jet didn’t look the same size as original pilot or the mikuni 37.5 or 40. Same for the main. If you got the baron jet kit, it will come with actual mikuni main jets.

the recommendation for the pms from the other site is spot on. Make sure the pieces are in the correct order. Did you remove it and clean the opening?

petcock cleaned out?
The kit that I ordered to rebuild my carb was the All Balls from Fort Nine. Some of the parts in there were different than the stock. The needle valve had a screen over the end of it where the stock did not.

I have some parts on order and I'm hoping the changes will work. I have ordered a 37.5 for the pilot and 170 and 172.5 for the main jet. I've also ordered a jet needle that has multiple slots for adjustment. Unlike the Barron's kit, the All Balls did not have a slotted jet needle. So, now I have some room for adjustment and see if these solve the issue.

Thanks for your help.
 
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