Hi fellas, have a 3.5hp B&S on my 45 & starting has become an issue. A few months back I replaced the diaphragm, pulled apart & cleaned the entire carby,cleaned out the fuel tank and have replaced the governor spring. Have a new spark plug with plenty of spark visible. All has been going fine until recently. Now, it starts after second or third pull with choke on, blows a little grey smoke (not allot, which disappears after a few seconds),it runs for 15-20 secs then it will slow & stop. Try to start again, it may start, runs for 10-15 secs then slows & stops again. Have adjusted mixture screw and idle speed & this morning I am unable to re-start at all. Last week had same issue and finally got it started and ran fine. Stopped a couple of times during cutting the lawn & re-started no probs. Any ideas / suggestions? Thanks- Ross
Ross, the first thing to try to settle is whether it is spark, fuel or compression. I suggest you try the B&S compression test (remove plug lead, then flip the blade plate backwards toward the compression stroke, and see if it bounces off compression). It isn't all that likely to be the problem, but it is possible. Second test: try to check whether it actually has spark when it doesn't run. Now that it won't start at all, that should be easy to check.
If you have spark and compression, you should check that the flywheel key has not sheared. All of those checks should be done first because then the only thing left is fuel, and that is a bit more complicated to check, and more likely to give uncertain results. The first fuel check is, while it is refusing to start at all, squirt a small amount of petrol into the cylinder or inlet pipe and see if it will start and run briefly.
If you get to the end of that set of tests, you should know definitely which system is at fault. When you have that information, let's talk some more.
ok, finally got it started this morning after removing the air filter & pouring fuel into the carby (screw down the air filter cover but i forget to place the air filter back in position) and its running well. So I cut the grass & just before I finish the engine dies. I then try to start & it wouldnt. I try with the choke on & it starts runs for 10 secs & dies. Start again & it does the same- runs for 10 secs & dies.. Maybe a fuel blockage somewhere?? Any thoughts are appreciated. thanks Ross
Well, it seems to be fuel supply, and the pattern of symptoms you have described sounds like the fuel pump diaphragm is misbehaving. You said you have worked on it recently - it may have a wrinkle or a leak. Sometimes if the diaphragm's rubber valves are working badly it will run once it gets going, but doesn't like to get going. I suggest you have a close look at the diaphragm.
I suggest you try the B&S compression test (remove plug lead, then flip the blade plate backwards toward the compression stroke,
Just in jest (I couldn't resist it), mate, Ross is a Scott Bonnar Model 45 cylinder mower owner....I wouldn't like to see him with half his fingers missing, flipping the reel backwards...Sorry grumpy...
Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member. Kindest Regards, Darryl
ok found the problem. The gasket that sits between the carby & the fuel tank (attached) had partialy perished (assume due to vibration) & pieces had fallen to the bottom of the tank. Carby was then trying to draw them hp through the pick up tube which was blocked with the perished pieces. Cleaned them off, hit the jets etc with compressed air & now running fine!! Strange, as the gasket was brand new a few months ago. Heard of this before? Any ideas on a fix? Cheers Ross.
I think one possibility is that the new gasket a few months ago was very old stock. Another is that you've been using fuel with ethanol in it, or that you used some kind of gasket sealant on the diaphragm, or it was distorted when you installed it. One of these things seems more likely than the others, to me, but I won't mention which one in case I'm being unfair to a local spare parts merchant.
