Engine Running Problem


Old 08-02-02, 06:29 PM
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Join Date: Sep 2000
Location: Columbia, SC
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B&S Quattro 4HP revs UP and down and UP and down

One year old B/S Quattro revs up and down rhythmically. Pumps out black smoke from the exhaust in time with the rhythm. No adjustments on the carb. Replaced air filter and spark plug. Ran great until yesterday. Bad gas? User error? Any ideas? Thanks.
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Old 08-02-02, 07:33 PM
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Hello Allen. Welcome to our Small Engine forum.

Engines with running problems as your describing usually have carb problems. Most likely the carbs needle isn't fully closing causing excess fuel to fill the fuel chamber or bowl.

This could happen from debris entering the carb and or bad fuel. Water in the tank or gas can, can contribute to the problem.

If that happens to be the case, the carb will have to be removed, cleaned and reassembled, most likely using some new parts from a carb kit.

Another 3 possibilities could be the governor linkage. Possible it's dirty, gummed up, bent or has damaged linkage. Possible the fuel tanks gas caps vent hole is restricted and or blocked.

Also possible the throttle linkage is incorrectly set. If this is the case, it's adjusted for an engine speed which is too high and the governor is attempt to control the engine speed counter to the throttle.

Most likely I have not covered all of the potential possibilities. The other resident small engine service and repair professionals may offer additional suggestions, advice & help.

Check back on your topic several times for additional replies.

Read the other postings and replies offered on this topic in the RECENT & ARCHIVES postings, within this forum, for additional help & information on this topic.

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Old 08-03-02, 05:49 PM
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Location: Columbia, SC
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It worked! Diassembled carb and gas tank. Thorughly cleaned carb and gas tank. Cleaned dirt and gunk from the linkages. Bought new gas. Runs like a champ! Thanks!
Old 08-21-02, 04:54 AM
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Okay...I put the champ in the garage for two weeks. Yesterday I take it out and it runs the same as it did before I did all the work that made it run well. The gas I bought was new. All it did was remain in the garage. I don't get it. Any ideas?
Old 08-21-02, 06:06 AM
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Hello allenzachary, I happened to tie into a Quattro last night that was "hunting" for its idle/running speed on the rich side like yours. You state you did all Tom said but I take it you didn't replace the carb diaphragm which on this carb is all that is replaceable. Get a diaphragm (about $4.00), put it in and I bet you have a fine running engine.....Mike
Old 08-21-02, 05:57 PM
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Location: Columbia, SC
Posts: 219
Great idea...but pardon my ignorance: I don't know what a diaphragm is. If you describe it I'm sure I can figure out what it is and where to put it. Should I just go to my local small engine repair shop and ask for a diaphragm? Is it standard on all b/s engines? Do I need a special one for the Quattro? Thanks for your insight. Allen
Old 08-21-02, 08:05 PM
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The diaphragm is the rubber gasket-like piece between the carburetor and the gas tank. Replace it and you'll be fine. Tell the parts store what engine you have and he should know which one to get. An inexperienced parts man might need the engine model #. It uses the same diaphragm as the 3.5 hp classic also.
Old 09-02-02, 07:49 AM
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Location: Columbia, SC
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You guys are geniuses! Replaced the diaphragm and ba-da-bing! Runs like a champ again!

I'll talk to you again in a couple of weeks when something else goes wrong. ; )


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