What is the function of the floating valve on the carburetor slide ?

Curious as to what the function is of the floating valve on the front of the carburetor slide.

 

Just got my daughter an '07 150RB and its giving me fits. Compression is right at spec.

I have 1 exhaust valve .002 under (waiting for shims to correct) others at spec. Have cleaned the carb twice.

Have a 138 main, 42 pilot, 60 bleed (50 on order) - came with a 150main and 48 pilot.

Replaced aftermarket fuel screw with OEM one. Accelerator pump working correctly.

Hot start valve is closing correctly. Replaced intake boot. Thing is a PIA to grt lit and refuses to Idle down.

Spark "looks" good. Moving to ignition system next, but want to see if I overlooked anything in the carb.

We run race gas in our bikes to avoid the moisture issues with pump gas.

I've had 450r's since '06 so pretty familiar with the new thumpers - this is my first little guy though.

where do you have the fuel screw set at? Mine liked 1.75 turns out for best idle with a 42 pilot. I thought mine liked 2 turns out until I put a tach on it and tuned it. I don't run race fuel, so you may have different results, I run 93 octane pump fuel and drain it after each ride and dump it in my truck.

Many times if your idle is set too high it will hang, try lowering it some, 1/4 turns at a time. Jetting should be 45 pilot with that 138 or a 140 with a 42 pilot. I feel you are lean and that will make it hard starting. Also your jetting is off for race fuel. Race fuel on a stock motor makes less power. I understand why you are using it but go back to pump 92-94 and solve this issue first.

Edited by weantright

Just got done checking the coil - resistance is out of spec explains the high speed miss I can't jet out either.

 

I started at 135 main and 40 pilot which was in the neighborhood. When I got bike it was WAY richer 150 main and 48 pilot and really ran like crap. 

Actually, the straight race fuel should require leaner jetting as there is no alcohol in it like pump fuel. Race fuel is also a consistent blend - pump gas changes with the seasons. Alcohol has about a third the energy capacity of gas. Oxygenated fuels (race fuels included) require richer jetting. Straight gas requires leaner jetting than oxygenated fuels. So while using race gas without re jetting will cost you power, a flat statement that you get less power using race fuel is a little misleading. This is not to be confused with those misguided soles who try to run Aviation LL100 which has the wrong distillation rates for our high performance engines.

 

Of course this is just my opinion from 35+ yrs of riding and racing.

 

But we're off topic of the thread ..... what's that goofy slide valve for ???

Edited by oldfrt613

Not mis-leading, you WILL loose power on this motor using race gas or any octane over 94. It wasn't a blank statement on race gas it's a proven fact on this motor.

Like I said - your off topic, really have no desire to argue about gas ...... but thanks for your opinion

...But we're off topic of the thread ..... what's that goofy slide valve for ???

 

I read somewhere, a while ago, that the plate on the FCR is an anti-friction plate rather than a valve. Dunno... just sayin'.

9474302.jpg

I did a little more searching.

Since the slide moves up and down on rollers, it has some clearance designed around it to insure free movement.

This clearance would result in air leakage around the slide. The purpose of the plate is to compensate for this clearance and 

seal the engine side of the slide. It would be more accurately be described as a wear plate, but since it gets pulled in by the vacuum

I guess it could be considered a valve. Leakage around this plate will cause issues in the slower speed circuits at small throttle settings.

Some places recommend replacing every 25 hours according to Dirt Rider, but my guess only the guys who don't pay for their own parts would do this

(its a little pricey). 

Edited by oldfrt613

From one oldfrt to another, thanks for this tidbit of wisdom. Curiosity was eating away at what limited attention still remains!

I don't know what it's for but if the plate is upsidedown, the engine will run like its too leen, backfire and crackle. Knowing from experience.

I believe that plate is a vacuum break to prevent the slide from sticking due to the high vacuum of a 4 stroke motor

That's why the slide is on rollers and has clearance around it - and needs the plate to seal - if it were the typical slide, it would be a motha to keep free

The assembled slide on the left is incorrect. It is supposed to be flat/square side down. The plate is called a vacuum release plate. It enables the slide to move during times of high vacuum such as at idle or when the throttle is closd at high rpm.

 

You adjust the pilot/fuel screw (and idle speed screw) for a perfect idle with a hot engine. Then you do the needle, finally, the main. Then you adjust the AP. Any other order and you'll never get it right.

 

Race gas will make less power. The compression ratio of your bike simply is too low to require it. Sure, it may last longer in the tank but adding stabilizer will accomplish the same thing, be cheaper and make more power.

Running VP 93 octane T4, have no desire to argue about blanket statements on race fuels when you can't possibly make that statement for ALL race fuels

T4 has a MOTOR octane of 93

 

Premuim pump is R+M/2 octane 0f 91 (93  in some places) T4 R+M/2 is 100 octane.

 

Higher octane always makes less power. It is used to prevent detonation on modiifed high compression (cam/piston) combinations that make more power but must have a slower burning (higher octane) fuel. So the trade off of a fuel that makes less power is more than compensated by the mechanical improvements.

 

 

There is no arguement. Only facts.

 

 

Show mw a race fuel that has r+m/2 octane of 93

ROFL!!!!!! An 'unbiased report' from a company that only sells VP. :lol:

 

Please. :lame:

 

I will say a non-ethanol fuel will make more power than an ethanol laced one due to the lower BTU content of alcohol. To get that just go to puregas.com to find it at about $3.50 a gallon. Or visit a marina. However, the 2% change in power is insignificant and better tire pressure will have a greater effect.

http://atv-utvtech.com/product-review-articles/performance-product-reviews/vp-racing-fuel-the-secret-potion-of-performance/

 

" This is a guaranteed stable racing fuel for racers

who need to know what they are putting in
their tanks. You can run it every day or save it
for the big race. This isn’t a high-horsepower
fuel; it’s a predictable, safe and reliable fuel
that runs better than pump gas" MXA magazine 4 star rating
 

 

I will say a non-ethanol fuel will make more power than an ethanol laced one due to the lower BTU content of alcohol. To get that just go to puregas.com to find it at about $3.50 a gallon. Or visit a marina. However, the 2% change in power is insignificant and better tire pressure will have a greater effect.

 

2% increase is insignificant ? You've said over and over it will make LESS power, now its an insignificant increase. I don't have access to any pump gas without alcohol except auto STC aviation fuel which is only 89 octane.

We have high humidity most of the time in the midwest. I can tell you there is a noticeable increase in throttle response with this fuel, and it certainly has at least as much power as the pump gas around here. Octane is a measure of the resistance to pre-ignition and not a performance indicator. I agree there is no advantage to running any more octane than what is needed to prevent detonation, but octane is not an indication of power output, its only one of the variables in final power output. Pump gas with 10% ethanol is a moisture magnet and inconsistent, especially in our area. I ran pump gas right up to the point the state required all pump gas to be cut with 10% ethanol (I used the be able to get 100% premium gas at rural stations). I wish I still could, but I can't so we run "race" fuel in all our bikes.

 

I can't understand why you have such a problem with people running race fuel (yeah - I've noticed you bash everyone who does). It provides a fixed variable in bike tuning that you cannot get with pump gas.

 

As it turns out, my issues with this particular bike was a bad coil. The coil on this bike is built into the spark plug cap. This is the third such failed coil I've run across on this model motorcycle - must have something to do with the heat. I've not lost a coil which was mounted on the frame so it was a new one for me.

...Higher octane always makes less power. It is used to prevent detonation on modiifed high compression (cam/piston) combinations that make more power but must have a slower burning (higher octane) fuel. So the trade off of a fuel that makes less power is more than compensated by the mechanical improvements.

There is no arguement. Only facts...

This is not a completely true statement.

The more correct statement should be: "generally, an engine will make the best power with the lowest octane fuel that will not pre-detonate"

It's not so much that higher octane makes less power; if you don't setup the engine to run it, you fail to exploit it's potential.

If I could afford it, I would run T4 instead of pump gas without hesitation.

I have a drag car with a 10-5-1 compression motor that I have jetted and tuned for 93 octane pump gas with 10% ethanol. I have another engine that is 14-1 compression and I run VP C-12 in it. I tried the C-12 in my 10-5-1 motor and it ran slower, I had to advance the timing and lean out the main jets to get the C-12 fuel to run the same ET. Just an experiment I did and it would not justify the cost of the C-12 fuel. Now If I ran a 100hp and above NOS I would run the C-12.

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