I have a DR trimmer with a B&S 5 hp quantum model 12F707 type 0633-01 and code 96060556. The trimmer had been surging some when it ran which I deduced was a gas problem. It usually started with the first 3 pulls. After it ran for a while and needed a string replaced, we tilt the end up. Usually after that it would need to cool or wait a few minutes to start. I figured it was the oil getting in the cylinder when the front end was lifted.

Anyway one day last week after a string change and it had been running, it wouldn't restart. I just left it figuring it was time for a new plug and filter, etc. Replaced the plug and air filter and sprayed down the carb with carb cleaner and even sprayed some into the gas to clean it up. It wouldn't fire. This has a starter and old battery so I jumped the battery and cranked on it and no engine ignition. Checked the plug and plug wire and was getting plenty of spark.

Took the carb off, soaked it in Berryman's cleaner for a day, blew out all the passages, soaked it again for another day or so, blew it out again, run a small bread wrapper wire through all passages and all clear. Put in new kit. Put it back on and the same thing. I can crank and crank on it and it doesn't feel like it is getting fuel. The spark plug is still getting plenty of spark. Starting fluid doesn't make it fire although it did make if back fire a couple times.

I think I get good enough spark it isn't the armature. I'm about at my wits end over this. Thanks for any help.

I have a DR trimmer with a B&S 5 hp quantum model 12F707 type 0633-01 and code 96060556. The trimmer had been surging some when it ran which I deduced was a gas problem. It usually started with the first 3 pulls. After it ran for a while and needed a string replaced, we tilt the end up. Usually after that it would need to cool or wait a few minutes to start. I figured it was the oil getting in the cylinder when the front end was lifted.

Anyway one day last week after a string change and it had been running, it wouldn't restart. I just left it figuring it was time for a new plug and filter, etc. Replaced the plug and air filter and sprayed down the carb with carb cleaner and even sprayed some into the gas to clean it up. It wouldn't fire. This has a starter and old battery so I jumped the battery and cranked on it and no engine ignition. Checked the plug and plug wire and was getting plenty of spark.

Took the carb off, soaked it in Berryman's cleaner for a day, blew out all the passages, soaked it again for another day or so, blew it out again, run a small bread wrapper wire through all passages and all clear. Put in new kit. Put it back on and the same thing. I can crank and crank on it and it doesn't feel like it is getting fuel. The spark plug is still getting plenty of spark. Starting fluid doesn't make it fire although it did make if back fire a couple times.

I think I get good enough spark it isn't the armature. I'm about at my wits end over this. Thanks for any help.

When you say you replaced the filter, was it the air filter or the fuel filter?

Mark

Air filter. That model didn't come with a fuel filter. One of the reasons why I overhauled the carb. I cleaned the plastic fuel tank out as well.

If starting fluid did not make it fire then your issue is not fuel related. I would guess judging by the backfire that the problem is a sheared flywheel key or a sticking valve. When the engine was hunting like you said, that means it was running lean. In some cases when an engine has been running lean, it can damage the valves or seats.

Thanks Justin. I cranked on it again last night for a while. It kinda brumbles along (for lack of a better word for the sound where it sounds like it is firing a little bit and trying to run. Also does it with the throttle in the choke and run position with no difference between the two. When I move the throttle to the stop position which also kills the armature, it definitely starts turning slower without the brumbling sound. This tells me I have some fire and compression so the valves may be working somewhat. It didn't really backfire much but I didn't use starting fluid last night and the back fire I was getting was an occasional pop.

I will check the flywheel and hope you are right. I wouldn't think that it sheared because it ran until we shut it off but who knows. Is there an easy way to check it such as turning it by hand or do I just need to pull it and look? As I recall, remove the nut and a little tapping around the flywheel will knock it loose or I may need to put a puller on it. Is there a special way to tighten the nut back.

I looked at the drawing for the valves which are behind the head. If I remove that head do I need to replace the gasket or are they reusable? I guess when I remove the head I'll see the valves. Although according to the engine diagram, maybe I can remove the muffler and see if the exhaust valve is working.

All this with the valves just brings up more questions. Can I squirt some oil around them or maybe lay it on its side so the valves sit in oil for a while? What would be the fix for a sticky valve(replace or clean up with emory cloth)? For this model the valves ride along side the cylinder which all all attached to the top half of the engine body and then the body splits. Is this one of those all weekend and expensive jobs where I'd end up wishing I'd just bought a new engine?

Thanks for the help. In the meantime, I'll try to search the archives for flywheel and valve.

Too see if they key is sheared all you have to do is remove the nut holding the flywheel on, and you can see the key's position. As far as the valves go, you need to take the cylinder head off to make sure both valves are seating properly. Sounds more like a flywheel key though.

Well Justin you figured it out. I dug around for a while and found the right socket and removed the top nut with my electric impact wrench and the key was just fine.

Took a look at removing the head and removed the sparkplug. Stuck my thumb over the plug hole while I spun the impact wrench on the flywheel bolt and had no compression. I could hear the piston moving air but not past my thumb. I removed the head (the bolts were barely snug cause it took no effort to turn the ratchet) and sure enough the intake valve stayed sticking out a little. Removed the carb intake and sprayed around with brakleen (was out of carb cleaner) and sprayed around the valve seat. I was able to bump it close after a while. Guess I'll go back tomorrow and clean it up good with carb spray back around the valve guide until I can turn it and it closes all the time and maybe get some marvel mystery oil for the gas which someone recommended on one of the other threads.

Moral of the story is that I should have just stuck my thumb over the spark plug hole a long time ago checking for compression.

Question I have is do I need a new head gasket or just reuse the old one. I will probably just use the old one unless I hear different. Don't know about torqueing them down but I'll probably just snug them down on a standard alternating back and forth basis and then crank on them again while alternating. At least they will be tighter than when I removed them. And as always, I'll use antiseize on all bolts.

Thanks again.

Well I got it back together tonight and got it running. Sprayed the intake valve with some carb spray till it worked free. Put it back together. Used the same head gasket. Started on first crank. It surged some but I'll try opening up the needle valve a little.

Then I moved over to the Murray and replaced the jack shaft and put it and the mandrel back together.