Mikuni RS Flat Slide Accelerator Pump System

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Been riding with the accelerator pump operational since my RS34 carbs were installed several years ago, and have recently been thinking about disabling that fuel system.
Will trial-ride with the pump rod removed, and update with my impression.

In the mean time, I look forward to receiving member thoughts and suggestions...

I disabled mine for a season a few years ago. It seemed to run better but at the time my bike was a stock 81 LTD with RS34's running 125 mains. I will be interested to hear your results as my bike is an almost identical build to yours.

Matt bx wrote: I disabled mine for a season a few years ago. It seemed to run better but at the time my bike was a stock 81 LTD with RS34's running 125 mains. I will be interested to hear your results as my bike is an almost identical build to yours.

I like the way the engine runs too, so I made a few changes to the carbs in addition to removing the pump rod.

115 main jets seem good for my engine setup, which runs incredibly well on regular gasoline.

I don't understand why you would want to remove the accelerator pump system. Thats kinda the point of going to RS carbs to me.

DoctoRot wrote: I don't understand why you would want to remove the accelerator pump system. Thats kinda the point of going to RS carbs to me.

Agreed, though the pump being disconnected for me is barely if at all noticeable. This is a road bike that doesn't get raced, though it does love accelerating through the winding roads around the town where I live.

At this point, I have removed the plunger w/spring, and the three rubber fuel hoses between the bowls. The fuel-feed hole in the #3 bowl was tapped-plugged with a #4-40 brass screw, and I replaced the o-ring bowl gasket to seal off the system. This is all temporary and easily reversible when/if desired.

Now we'll see if that despised overflow drip has been eliminated. So far, so good!

These RS34's were a reasonably priced alternative to the BS34 CV carbs that came with my bike, which have severely-limited tuning capability by comparison.

:woohoo:


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Was it setup correctly beforehand? mine came from the factory opening way too late. It should be opening almost immediately after opening the throttle, these carbs are known for their super snappy throttle response due in part to this feature. I still don't understand why you would want to disable it other than to simplify tuning. I feel ya on the drip. Happens on every set of RS carbs I have touched.

DoctoRot wrote: Was it setup correctly beforehand? mine came from the factory opening way too late. It should be opening almost immediately after opening the throttle, these carbs are known for their super snappy throttle response due in part to this feature. I still don't understand why you would want to disable it other than to simplify tuning. I feel ya on the drip. Happens on every set of RS carbs I have touched.

Found this lightly used set on ebay. It was missing the plunger rod, but still had the factory jets.

Honestly, I don't sense a loss of performance without the pump. It was adjusted to start before half throttle opening.

There is less residue laying in the stacks now, probably since no fuel is splashing off the back of the slides.

I believe this mod has solved the fuel drip mystery. Hallelluliah!

:woohoo:

Interesting. I always assumed the drip had to do with the floats or needles because the drips came from the overflows.

DoctoRot wrote: Interesting. I always assumed the drip had to do with the floats or needles because the drips came from the overflows.

Correct, but what causes that when the bike is just sitting and undisturbed?

:evil:

Matt bx wrote: I disabled mine for a season a few years ago. It seemed to run better but at the time my bike was a stock 81 LTD with RS34's running 125 mains. I will be interested to hear your results as my bike is an almost identical build to yours.

Still not a single drip or drop from any fuel overflow...

:kiss:

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When you disabled the system did you cap off the nipples on the float bowls? Or is that #4 screw keeping all the gas from entering the plunger chambers?

I just bought some RS34's and am looking to disable the accelerator system, still waiting for them to get to me so I have not had a opportunity to check them out.

Injected wrote: When you disabled the system did you cap off the nipples on the float bowls? Or is that #4 screw keeping all the gas from entering the plunger chambers?

I just bought some RS34's and am looking to disable the accelerator system, still waiting for them to get to me so I have not had a opportunity to check them out.

I used a #4-40 x 3/16" countersink brass machine screw (hardware store item), with a tiny drop of Loctite 271 on the threads.

After removing the fuel hoses, I stuffed a piece of coated elec. wire in each tube, with just enough protruding for removal. The #2 and #3 bowl tubes pass through.

An uncut bowl gasket will be needed for the #3 carb. The one provided for the pump bowl has a segment removed.
Reference ebay items 233626068037 and 233626069109



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