B&S 18HP V twim OHV not starting

14 years ago

B&S Model 407777

Serial 0128-E1

Completed 200hrs

I have replaced the oil and spark plugs

replaced Oil, Fuel and Air filters

Seveal weeks ago the engine cut out after several hours of operation the oil was low so I top it up. All was ok until I hit a rock and bent the blade. Following the blade replacement it ran fine but eventually it started to backfire and run poorly. I cleaned the Carb with no success. I checked the valve clearances and found then to be incorrect. I adjusted both fuel and exhuast to 0.005 and it ran fine for 0.5 hour before it lost power and black smoke started coming from the exhaust. I again cleaned the carb but it only got worse now it will not start(i did not let the engine cool).

Is it a Gas problem or have I set to large a gap on the valves?

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Comments (4)

hankll
14 years ago
Without being detailed, it is carb related, with the black smoke. As though it is flooding. Check the float seat and replace, sounds like it could be bad or installed incorrectly if you replaced it. Just my .2 cents worth......
tomplum
14 years ago
A lot depends on how familiar you are with that carb. Some versions have main jets that fit in the bottom of the transfer tube that can get out of place. Seals for the tube are available separately or come in the kit. It would also be worth a look under the valve covers again. Were the valves adjusted at or after TDC to start with? Good protocol is to ensure that the studs are tight for the rocker arms and to note the position of the valve guides themselves. If one appears to be in a different position, take a closer look. They can come out from the head, which holds the valve, which can bend the push rod.
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retired_again
14 years ago
Similar problems are becoming common on Vanguards. Here are a couple of ideas.

1. sometimes the Mikuni fuel pump starts to seep fuel into the crankcase (from the vacuum line). Fuel fumes in the crankcase are expelled into the air filter compartment from the breather and ingested through the carburetor air stream. This results in a rich fuel air mixture.

Remove the air filter and disconnect the breather hose from the air filter housing. flex the breather hose so it is facing away from the carburetor inlet. Run the engine to see if there is a change.

2. Where did that engine oil go? If oil fumes were expelled from the breather, perhaps the air filter received a coating. How could this happen? I don't know -maybe by excess tipping? If the air filter is contaminated, a rich mixture might occur. Sometimes the wrong filters have caused this type of problem. Aftermarket filters have also caused problems because they are manufactured with more restrictive paper.

3. sparkplugs that are the wrong heat range or sparkplugs that are misfiring may allow black exhaust to be expelled. Sometimes the mis fire may not occur until the engine gets real hot.

The experts may have more suggestions if these ideas do not help.
walt2002
14 years ago
First thing to do is remove the carb float bowl and be sure you don't have a bunch of water and or crap in it. IF above suggestions in posts fail to solve the problem, try disconnecting the "Kill" wire from both ignition coils at the base of each coil.

Walt Conner

B&S 18HP V twim OHV not starting

Comments (4)

hankll

tomplum

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retired_again

walt2002

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