Petcock positioning ends sputter!

Nashville Kat

Nashville Kat

Well-Known Member
Today, just by accident, I got my bike running much better-

I've started to experience a common complaint I see on these boards- My bike was fading out again just as it got up to speed and started to hum-

(I was hoping to find a thread here)

I'm just coming off break-in, and the motor sort of always never got up to a constant run-

I figured it was some kind of carburetion, but I've been thinning the mixture (Not accurately I fear), and it was getting worse- The other day ran it without the air filter, and same thing-

but I noticed at speed that gas was coming out the air intake (besides annoying leaking elsewhere, often descibed here)

I should have realized- TOO MUCH gas, not too little.

But it seemed to be the opposite, because it ran fine under load and then faded when up to speed.

Also another clue- The slightest closing of choke lever IMMEDIATELY cut power- too much gas to air
(Lever was loose and closing on its own, but now tightened)

Still I didn't get it- I mixed in more oil- seemed to help a little- but not much

I took out petcock filter- more surge acceleration but same top end fade-

Growing frustrated I wanted to come on here and ask about alternate carbs- I still do, because i think the carb is still the weak link here

Anyone know where better ones are available? Cart carbs? Motorcycle? Lawn mower? Anything!

So anyway, I had the thing running back about as well at first, but nothing great,

and before bringing the bike inside I let it cool down- then I went outside and noticed that I hadn't shut the petcock!

So instead of bringing it in and dripping, I decided to close it and run any gas out of the line-

so I took off and clutched the engine- the thing ran great! It was still just SLIGHTLY open, and then got the right amount of gas!

Too open- same trouble
All closed- engine stopped-

It had never occurred to me to adjust the fuel line by CLOSING DOWN the petcock-

but it seemed to work great- I rode a couple of miles and it motored better than ever-

Crazy!



([url]www.thehearpe.com- my film script, but my bike photo is on the last page- multi-speed Micargi cruiser
 
The stock petcock is garbage. Get solid, positive ball valve.

SBP Fuel valve assembly

Valve.jpg
 
Interesting.

We were talking about something similar last night here. With the newer 2.5 Liter tank full of fuel the carb on my neighbors bike was flooding out. Once there was less fuel in the tank everything worked out. The weight of the fuel forced more fuel through the petcock. By turning it off a bit the flooding stopped.
 
The valve needs to be consistant regardless of fuel level or setting the carb will be a karp shoot, at best.
 
I have a mark on my stock petcock, that indicates where off is.

I am pretty sure that Mark will put a mark on his indicate where he needs to set his petcock as open. I personally don't understand this, fluid dynamics. Somehow I have a feeling that the weight of the fuel would also be dependent fuel mix ratio too.

Right now I am trying to figure out how to get "Howard", my pool vac, to climb the wall without going too high and coming out of the water, or staying on the bottom and not vacuuming the sides. Which is dependent on how much crude is in the filter basket, skimmer basket, how dirty the filter cartridges are and where the valve is set between skimmer and vacuum function. The better this works, the less time I have to run the pump and the less time I have to spend brushing down the sides of the pool.
 
Yeah- the bike is running much better now- but this fix is tenuous-

The petcock I believe is just a shutoff valve from the tank- and is not really meant to be an intregal part of fuel delivery regulation-

So I'm still wondering if there is a better carb out there ?
These don't really have a float tank do they? Just that needle vaklve that raises up-

I'm thinking if there is too much gas when it really starts to suck, that maybe the needle position might be best at the LOWEST notch- but I haven't tried it yet.

If thge petcock lever is closed when perpendicular to the line, and open when parallel, mine seems to work best angled in between- yet it seems to vary a little bit, which is frustrating-

I had to load the bike in the car several weeks ago, and drained a half of tank through the petcock-

it took forever! So very little gas goes through it anyway-

I'm probably going to put in an inline filter- but wonder if that will just negate this petcock setting, and be a waste of time and money-

I'll be playing around, and post here if anything happens-

I put some BMX bars on today- and get a few inches of rise on the bars-
but most importantly- a more secure perpendicular grip on the bars-
 
Guys, you're missing the point here. The amount of flow through the petcock should not be a factor when it comes to how much fuel is being burned or offered to the engine. That is a function of the float, needle valve and throttle needle. If the float is out of adjustment or if the needle is hanging open then you'll have excess fuel. If the throttle needle is lifting too high for your conditions that will also cause a rich burn. Using the petcock as a fuel metering device, or blaming it because it doesn't work like one is wrong. The problem Nashville is having sounds like either a float level or throttle needle adjustment. Too rich? Raise the 'C' clip on the needle. Fuel dripping from the carb? The float is too high and allowing too much fuel to enter the bowl and excess fuel to be drawn in during running.
Tom
 
Don't think I was telling him to use his valve as a metering device............in fact on the contrary.
 
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