Abby’s Guide > Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) > Discussions > Engine runs at half throttle with vapor/smoke out of the carb throat.
Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions |
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trouts2
Location: Marlboro MA
Joined: Dec 8, 2007
Points: 1328
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Engine runs at half throttle with vapor/smoke out of the carb throat.
Original Message Feb 10, 2011 5:58 pm |
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Issue about vapor or smoke through the carb. A 7hp Tecumseh L-head went to half speed while clearing and could not be throttled higher. The engine was in parts when I got it so I can only go by reports about that. I thought it might be carb related so went through the carb. These was gas in the float so I put the head back on and fired it up. It still only ran to half throttle. Seems to run somewhat well at half speed and lower but does sound not “usual”. There seems to be an extra snap sound (non-metal) which I think is coming out of the carb but not sure. It could be from the muffler. There is either smoke or vapor out of the carb. Not a lot and disburses quickly. I thought it could be timing causing the intake to not be closing fully. The engine has solid state ignition so I thought it might be a broken flywheel key. Pulled the flywheel and the key is fine. It seems to be the intake is not seating fully. What I don’t understand is how can that happen instantly. The machine has run well through the prior storms and in the middle of the last storm it went to half throttle. I was told it was spitting gas out of the throat but what I see is vapor or smoke. It’s not much or a strong flow. The valves are at .008 intake and .010 exhaust. The spec is 8 and 12. The next move is to lap the valves. If that does not cure it then possibly there’s a crack somewhere in the head under the valve head. ?? Anyone ever have something like this or suggestions if not seat or wall crack?? If a valve problem is it usual for it to show itself all of a sudden?
This message was modified Feb 10, 2011 by trouts2
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friiy
Location: Las Vegas, The Desert
Joined: Apr 12, 2008
Points: 600
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Re: Engine runs at half throttle with vapor/smoke out of the carb throat.
Reply #4 Feb 10, 2011 10:45 pm |
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Check the engine by doing a leak down test.... see if you have air howling through the closed intake valve.. ... The valve could be gummy-----the stem might have bad gas residue dried on it that is slowing its travel ( have seen this on the intake before-lots and it gets worse as the engine gets hot...) Try spraying a penatrating oil on the intake stem through carb or throught the spark hole with the valve open, let it sit for a while and turn the valve face with a popsicle stick to help wash it around... Let us know what you find.. Friiy
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trouts2
Location: Marlboro MA
Joined: Dec 8, 2007
Points: 1328
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Re: Engine runs at half throttle with vapor/smoke out of the carb throat.
Reply #6 Feb 11, 2011 8:05 am |
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Jtrebor,
The carb was rebuilt a few months ago and got a touchup cleaning yesterday before testing. It was run very rich and would not produce black smoke. I figured it was not firing fully with the vapor/smoke and was the valves so took it apart again. Friiy>>> Check the engine by doing a leak down test.... see if you have air howling through the closed intake valve.. I got it as parts so could not do a leakdown . Going by the symptoms I was told the carb was gone through and the engine reassembled and run. It seemed like valves so I opened it again. It was a mistake at that point to not have done a confirmation leakdown test. I should be able to lap the valves today and after do a leakdown.
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CharlesW
Joined: Jan 9, 2011
Points: 76
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Re: Engine runs at half throttle with vapor/smoke out of the carb throat.
Reply #8 Feb 11, 2011 6:11 pm |
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The slap noise maybe the tappet with lots of play - going up to hit the valve that is slow or gummy.. Friiy Or the piston tapping a valve that is hanging open.
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CharlesW
Joined: Jan 9, 2011
Points: 76
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Re: Engine runs at half throttle with vapor/smoke out of the carb throat.
Reply #10 Feb 11, 2011 10:03 pm |
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They're on the block , not on the head on this engine.. Friiy My bad. Totally missed the "L head" in the original post.
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