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hardline

Knocking - 10HP CI B&S

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hardline
To keep this as short as possible... I have a pair of 3410S, a 1972 and 1973. I used them in the 80's for my lawncare/landscaping business. They are all I kept of the equipment I had, and are used for my property and hobby now. The 1972 has been sitting for basically 20 years, I have tried to get it running several times during that time, and am stuck on this engine issue. I pulled it out a couple weeks ago and broke down the carb, tanked it, and put it back together (on the previous attempt, it got a kit), cleaned out the gas tank, new filter and line, etc.. It starts fast/easy on it's own fuel now, but does a bit of surging. I have worked on the mixture without much result, but it seems to level off on its own at some point. If I throttle up, it will alternately surge and knock. There seems to be quite a bit of knocking in general. It did not knock when I stopped using it 20 years ago, so I don't believe it's in the journal. It also seems to be short on power when throttled up, but I need to check/set the governer nuts before I can be sure. This is starting to get long. I suspect the problem is in the ignition, and the carb will level out once this is taken care of. It did have new points on my last attempt, they are looking older now, but still behaving the same. I ground the valves 2 tries ago, but they probably didn't need it, they are set correctly. I am thinking about things like replacing the magneto, or remagnitizing the flywheel, but would like to do testing first. I have been away from these for a long time and could use some direction on what to try and what information I need to gather to post for troubleshooting. Looking for ideas. Thanks for any help, Chris
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RedbarnRick
Hi, I don't have any 10 hp but have several 16 hp. CI engines, the first thing to check is the points and condenser, just replace the condenser (napa) and keep original as a spare. file the points with a metal nail file gently then reset to .010 or your engines spec. check to see if there is any oil coming from the points plunger, hook a spark tester to the plug do you have good strong spark? Did you replace the long needle jet? Is it clean, the ethanol fuels leave yellow jello in the smallest orifices, use a copper stranded wire strand to clean small holes out. Once running spray some wd40 around the throttle shaft to see if it's leaking this will cause an erratic engine rpm, if it smoothes out the throttle needs rebushing. If none of these helps you might have a timing issue due to the flywheel key way getting worn or a sudden stop will shear it the key slightly. Does it have a fuel filter and is it installed the correct direction, also some of these early tractors have a shutoff on the carb that has a tubular screen inside that clogs with white residue. Stay tuned as some of the real experts chime in on these great old engines.
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HubbardRA
Sounds to me like you have a leak either between the carb and manifold or manifold and block. Use either carb cleaner or starting fluid to check for leaks. Start the engine and get it running fairly smooth, then squirt the starting fluid all around the gaskets on the manifold. If it hits a leak you will know it. The engine operation will change dramatically.

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hardline
Thanks for the input, this is what I have so far: I fired it up and it leveled off fairly quickly. It really starts fast/easy, faster than I ever remember, it almost didn't need choke. I sprayed carb cleaner on both ends of the manifold, and on the throttle shaft ends, there was no change in the engine speed. There seems to be a minimal amount of surging now, but the knocking is still definitely there. I do have a capfull of marvel in the gas, which is potentially clearing up any internal carb issues. I did break down and tank(in an ultrasonic cleaner) the carb 2 weeks ago, it is spotless and appears to be doing pretty good. The carb kit I put in a couple years ago included a new nozzle and needles. It was cleaned, tanked, sprayed out, brushed, etc. a couple weeks ago. The fuel filter and gas line are new, and in the correct direction. there is no shutoff on this carb. I will replace the condenser, then the points tomorrow and see if there is any improvement. These were new also, but I need to go through this step anyway. I read something about moving the armature bracket position on the block, never had a need to before...??? I do not have a spark tester, I could see what kind of distance I can get the high tension lead away from the plug. One point I should make, but not sure it should matter on something this size. I used these in the Chicago area years ago at ~800ft above sea level, I now live outside Denver at 6800ft. The other 3410 doesn't seem to care, but it has a newer engine with a magnatron ignition. I will post again after some initial ignition work/testing.
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BLT
A long shot. You might have a carbon build up on th fire deck of the head. This also causes kncking. The head is easy to remove and can be done with engine in place. If you see a carbon imprint of the piston, your problem could be solved.
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hardline
I had the head off when I ground the valves a couple tries ago and cleaned it at that time, it was almost spotless anyway. Though I have made attempts at this several times in the last 10 years, it has only run a total of less than a 5 hours during the process. Thanks for the thought. Chris
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