Hey guys, new here. I have a mower that I put together a few years ago and haven't had any issues with it until recently. It one day just started to lose power when I hit a patch of thicker grass. I initially thought it was the fuel pump as I fought that issue when I put the engine on the mower. The engine that's on it was fuel injected and didn't have a provision for the pulse line. I couldn't get one of those pumps to work to save my life so I just put an electric pump on it and it's ran great for 4 years now except for idle at low rpms but I was good with it. Anyway, I had a new pump I'd bought a while back that I put on it and it still did the same thing. So, I went and bought a third electric pump to which would never keep the system primed. It's not filling the clear plastic filter but I eventually went back to the the pump I first replaced the original with. It keeps the system primed but doesn't keep the filter full neither. So, I pulled the plugs and one was fouled. Replaced both with new NGK plugs to which it was doing the same thing. So now I thought it was one of the coils. After some research and coil and flywheel swapping I've wound up with the flywheel that was on it when it ran and a conversion kit to replace the DSAI modules. Still doing the exact same thing and I've also replaced the carb to which it runs so much better at idle. Also, I thought maybe the pickup tubes and valves were leaking and letting the pump suck air into the system so I made new dip tubes and installed those. At this point I'm at a loss. Unless it's something really dumb it seems to only be affecting the cylinder on the left if you're facing the carb. I've adjusted the governor as the directions say but still no luck. Any help would be greatly appreciated.
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CV740 loses power under load
- Thread starter mark029
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Export threadTo me this sounds like either a blown head gasket on the left side or valve clearance is off on the left side. I would pull the plug wire off the left side and see if anything changes. If nothing changes, check the valve clearance on that side. If the valve clearance on both valves, I would be pulling the head off and replacing the head gasket. If the engine doesn’t run when you pull the left side plug wire I would pull the right plug wire and repeat these steps on the right side. What I am doing by pulling the plug wires is to find out if both cylinders are working properly. If nothing changes by doing these tests is to find out if both cylinders are mechanicaly working properly, if so then I have a fuel or ignition problem. Make sure you read my signature!!
Well, I've had both valve covers off and everything in there looked fine. I've seen these bend push rods before and then it just snowballs from there. This thing runs too good at idle and some load for it to be anything major I think. I'm going to do a compression test on it today when I get home. I feel like it's something dumb and I'm just over looking it. The fuel issue has me puzzled with the filter being partially full. It's before the pump and maybe it needs to be after the pump? But it's ran that way for years. I'll pull the valve covers back off and check the clearance this evening too.To me this sounds like either a blown head gasket on the left side or valve clearance is off on the left side. I would pull the plug wire off the left side and see if anything changes. If nothing changes, check the valve clearance on that side. If the valve clearance on both valves, I would be pulling the head off and replacing the head gasket. If the engine doesn’t run when you pull the left side plug wire I would pull the right plug wire and repeat these steps on the right side. What I am doing by pulling the plug wires is to find out if both cylinders are working properly. If nothing changes by doing these tests is to find out if both cylinders are mechanicaly working properly, if so then I have a fuel or ignition problem. Make sure you read my signature!!
I would still check each cylinder by putting the plug wires, one at a time. You need to diagnose which cylinder is causing the problem. At that point you you can run a compression test. Better yet, go the an auto parts store and rent a leak down tester, most will do this for free, and perform a leak down test. This will give you a better picture of the condition of each cylinder.
bertsmobile1
Lawn Royalty
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- Nov 29, 2014
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With a leaking head gasket the engine will run perfectly at idle when the cylinder only partially fills
However when the throttle platte opens fully it will leak
A common symptom of a blown head gasket is knocking ir backfiring when the blades are first engaged then the mower runs fine till you turn them off & on again.
However when the throttle platte opens fully it will leak
A common symptom of a blown head gasket is knocking ir backfiring when the blades are first engaged then the mower runs fine till you turn them off & on again.
Ran a compression test on both cylinders yesterday and both are at 150#. I haven't witnessed any knocking or backfiring but when I pulled the plugs, the left cylinder plug is extremely black. Looks like fuel is puddled up in the intake as well. I'm going to pull the valve covers today and see if there's any issue with the valve adjustment on that left side specifically.With a leaking head gasket the engine will run perfectly at idle when the cylinder only partially fills
However when the throttle platte opens fully it will leak
A common symptom of a blown head gasket is knocking ir backfiring when the blades are first engaged then the mower runs fine till you turn them off & on again.
Decided to pull the intake off last night and noticed the bolts on the right side weren't tight. Not sure how loose they were but I noticed that the 1/4" impact driver didn't hit at all when removing them. It just spun them out. Maybe it was pulling air in right there. Pulled the left valve cover and nothing seems out of place there. I've had both of those off already and didn't see anything wrong.
So this problem is still ongoing. I've cut grass with it several times this season and it seems to get worse each time I cut it. I've pulled both plug wires one at a time and you know well that something is wrong when I remove one. The engine runs fine at wide open throttle with or without the blades engaged. When I start cutting and run through some thicker grass is where the problem occurs it seems. That or when I hit a substantial bump in the yard. I've adjusted the governor several times but that does nothing to help it. When this happens, I have to stop and let the engine catch up. Also, the engine will not stop with the switch. I've ordered two switches and both have been wrong. I'm about ready to roast marsh mellows off this thing.
Reading back through this thread at the advice and a little research led me to pulling the heads off. Both appeared to have blown gaskets and both heads were a little bit warped under the exhaust valve. Also found the wire going to the oil sensor between the cylinders had been chafed. Fixed that, resurfaced the heads and replaced the head gaskets. It’s still doing the same thing but it really only seems to do it when I hit a bump in the yard. My yard isn’t the best but this problem just came out of nowhere. When this issue came up I was going to put a kit in the carb but just opted for an aftermarket carb. Should I have just rebuilt the original?