Another fuel starvation issue (help?)

Sat Dec 21, 2013 5:16 pm

Hi all,
Having fuel issues with my 1958 Lo-boy. The machine has it's original tank, sediment bowl, and carburetor. Currently has a see through Briggs& Stratton in line fuel filter. The machine has been starving for fuel lately, as evidenced by the fact that I only get a piddle of fuel coming into the fuel filter. Initially thinking it was a sediment/strainer issue, I took sediment bowl off, cleaned bowl and strainer, and put it back together. No dice, If I start the tractor up with choke closed, it will "pull" enough fuel into the bowl to stay running at about 3/4 choke. With choke off, VERY little if any fuel getting into filter. Today I pulled carb off, cleaned the main jet and needle/seat, etc..., and set the float level at 1 13/32", with 3/16" drop. (steel tipped needle btw). Still no dice, WORSE if anything. I've seen issues here where some in line filters seem to have flow issues in these gravity systems, but the filter is new and I seem to get plenty of fuel "free flowing" out of it. Suggestions please????...Also- tractor will run with idle mix screw all the way in. Maybe that help the diagnosis??. Thanks in advance,

:help: :help: Sam.

Re: Another fuel starvation issue (help?)

Sat Dec 21, 2013 11:57 pm

It sounds like a fuel flow issue. You may have some schumtz in the inlet pipe or down around the shutoff valve of the sediment bowl.

If you disconnect the input side of the add on filter and let gas run into a container how strong of a flow do you get? Good steady pencil lead sized stream for 20-30 seconds is what you're looking for. If you get that, the problem is farther downstream. Less than that, and it's upstream (Which is where I'm betting it is by what you've said). Use a clean container and you can dump the gas back in the tank.

If it's upstream it's not real easy but you can remove the sediment bowl (just the glass) and hold a cereal bowl sized container under it and open the valve to see how well it flows. It should squirt out sideways on two sides. There's a little disc in the end of the stem hanging down into the sediment bowl. Poke a wire in from the side and up the tube, be ready for gas to flow. You can also try poking it down the tube in the gas tank through the filler hole. You wont get all the way through either way because of the valve.

If it's downstream connect up your filter and pull the plug on the bottom of the carb, do you get a good pencil lead sized stream for 20-30 seconds? Yes, then it's in the carb. No, then disconnect the line coming into the carb and try again. Good flow there means it's either the inlet screen on the carb or the needle/float is sticking. Bad flow there means get rid of your add on filter and try again.

Two points just to clarify operation, nothing is getting pulled, it's all gravity flow. The choke position has no relationship to how much gas will flow. The choke position will affect how much/little air mixes with the available gas to get it to the right proportions to burn.

Welcome to the forum! :{_}:

Re: Another fuel starvation issue (help?)

Sun Dec 22, 2013 9:26 am

Have read initial post about 10 times. Thinking carburetor issue. There is a screen, suppose to be, at the carburetor inlet. Might be part of a fuel flow problem.

Run Scrivit's tests/checks.

Engine warmed up. Shut off and setting for 4 or 5 minutes with fuel supply ON. Start engine up. Engine should run fine, no choke needed, for about 1 minute. After about a minute engine should start to stumble if the problem were fuel flow related.

If choke needed to keep engine running within first minute of operation - carburetor problem.

Re: Another fuel starvation issue (help?)

Sun Dec 22, 2013 5:50 pm

Thanks both for the suggestions, I'm thinking I (hopefully) missed a piece of crud in the needle/seat or main jet. Time to pull the carb again :( I'll keep ya posted.

Re: Another fuel starvation issue (help?)

Sun Dec 22, 2013 7:15 pm

SamK wrote:.......I'm thinking I (hopefully) missed a piece of crud in the needle/seat or main jet.............
Instead of guessing, hoping and doing unnecessary work, spend a couple minutes and KNOW WHAT'S WRONG by following the steps I laid out. Could be the carb, could be a couple other things from your description. Could be multiple problems. You might get it with a shot in the dark, I prefer to turn the light on and aim carefully.

Re: Another fuel starvation issue (help?)

Mon Dec 23, 2013 12:28 am

Another thought. What type of fuel line are you using? and how old?

Had a neoprene fuel line that the interior lining came lose. Fuel flow would test good when separated from the fuel filter. Attach a filter and only a trickle of fuel into the filter.

Agree with Scrivet, conduct the checks to determine the problem location.

Also, another thought. I use large gravity flow fuel filters manufactured to accommodate several different sizes of fuel line. I have to cut the ends off of the filter nipples to match the fuel line. Check the openings in the end of the fuel filter nipples.

Edit: I don't know how big the B&S fuel filter is. Some are quite small. Could be to small to handle the Cub engine's fuel usage.