1988 SB50 sputters high speed

[vette66_00]

Dump the fuel.... Take off the petcock clean it.

[Wheelman-111]

Greetings:

Ah, DL Hoover's Theory of Spontaneous Vacuum Formation. I agree with 'Vette, and would add a look at the function of the carb float assembly.

[fastplastic]

inside your gas tank/petcock you have a filter if thats clogged just enough it will limit your flow of fuel when you need it the most check that and try not to burn up your motor

[smanke]

I had the gas tank off a couple weeks ago and cleaned it and the petcock. The filter on it wasn't dirty. So can someone explain why gas is flowing out the carb drain when the engine isn't running? I disconnect the fuel line from the carb and the flow stops out from the tank and the carb. So there is a mysterious vacuum being created with everything hooked up and the engine off. How is this possible? What should I check with regards to the float besides the level? The float level is at spec.

[Wheelman-111]

Greetings:

Pull the carb off again. Find a short length of - for Gosh's sake, CLEAN! - fuel line and hook it up to the fuel inlet fitting. With the bowl off, blow through the fuel line. As you do this, raise up the float with fingertip pressure to ensure there's a tight seal at the float needle/seat interface. You can perform a similar test on the petcock, using clean vacuum line to activate/deactivate the valve that controls fuel flow.

Both petcocks and float needles can get "sticky" as they wear. If the phenomenon you describe is consistent, then I'm stumped too. Vacuum isn't created from nothing.

However consider the possibility that it was a coincidence, or somehow when you yank on the lines the float and/or petcock get jostled just enough to "unstick" and operate normally for a moment.

[smanke]

I'm not saying I'm certain there is a vacuum going on with the engine off. But how else would gas continuously be able to get to the carb bowl drain with the engine off? I've pulled the lines off the gas tank petcock and no fuel flows out when the engine is off. I will try your tests now and post the results.

[fastplastic]

it not vaccum you put the carb together wrong and your throttle needle isnt setting correct to

[smanke]

I know I put the carb together correctly and the needle sits properly. I'm not mechanically challenged.

[Wheelman-111]

Greetings:

The bowl takes a good 15-30 seconds to empty itself when you open the drain screw. If it flows longer than that, the petcock must be letting fuel get by in the absence of vacuum - thus it must be stuck open. Plugging in a fuel line or unplugging it won't change that, unless the act of unplugging the line knocks the iffy petcock shut.

The carb float needle will run and run until the fuel level rises, lifting the float and shutting off the flow at the seat.

[smanke]

I have pulled the fuel line from the carb and left the other end hooked to the fuel petcock. I left the vacuum line hooked up. I hit the electric start and gas comes out at a steady flow from the tank. As soon as I stop turning the engine over it comes to a stop. So I think the petcock is operating normal. Maybe it's the needle valve sticking? I'm so frustrated with this thing you have no idea!

[Wheelman-111]

Greetings:

Recommend you replace the float needle and hone the seat with some polishing compound on a partially-stripped Q-Tip. Search Colgate.

The needle can Look fine and not be. On one early Aero carb I had, it just wouldn't work until I replaced the needle. Get a Honda one.

Alternatively, USPMale used to sell nicely recon-ed carbs at a fair price.

[smanke]

So you are saying use toothpaste to hone the needle seat with? I will buy a new needle too and see what happens. Do you know if I could get a whole carb?

[Wheelman-111]

Greetings:

PM USPMale to find out if he still sells/reconditions them. AvoiD eBay "specials".

[smanke]

I don't exactly understand what uspmale is. Could you explain your post. Where can I possibly find a carb?

[vette66_00]

USPMALE is a user here. PM (private message) him.


Click here to go to the COMPOSE a message... http://www.hondaspree.net/phpBB3/ucp.ph ... de=compose Then type in "uspmale" into the TO: box.