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11 HP Briggs surging


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07-06-09, 08:32 PM   #1  
11 HP Briggs surging

Model=252707, type=0145-01, code=79021911 mounted to a Murray frame.

Ok, I did a search for this problem and read a bunch of older threads (though still pertinent) and can't find anything quite like whats going on with the engine I have (I just bought the tractor at auction so don't know the history).

The motor runs fine at idle but once the throttle goes to full it surges. The first thing I did was to take the carb off and give it a thorough cleaning I Didn't soak it for a day but did take out and clean all needle valves, jets,etc then put in new gas and it still surges (I did set the idle and main screws so the engine runs like a dream). I watched the governor linkage and it is fluttering so I held it steady and viola' the motor ran like brand new (I had a friend old it steady while I adjusted the main). At this point I'm not sure if the problems is in the carb as I would think it would run bad if I held the throttle linkage steady instead of letting the governor flutter it. So at this point I reset the governor arm to no effect, I replaced the governor spring same thing, also made triple sure all the linkages & springs are in the correct place. Kind of looking for clues from here...I suppose it could still be in the carb but I'm a little skeptical at this point. I did buy a carb kit but don't want too use if it's not necessary. I'm wondering if the governor weights are somehow sticking a little in the engine???? it seems to throttle up and down fine though.

Thanks for any help! Doug

 
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07-06-09, 10:41 PM   #2  
It's not the governor. It's fuel starvation. You either are not getting enough fuel through the carb, or you are getting air leaking in between the carb and engine. Sounds like it's on the verge of having enough fuel, but not quite. It does this no matter how far out you back the screw under the carb bowl?


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07-07-09, 06:49 AM   #3  
Thanks for the quick response!

I tried backing the high speed screw out as far as possible but it started running pretty rough so I turned it in until it started running bad and then put it in the middle of those spots (like the manual says) but the only way to do that without the motor surging was hold the throttle steady as it was bouncing around a lot(when held steady the motor ran great). I did try adjusting it while it was surging but it never stopped surging just started running worse when you got too far out or too far in (all on fast throttle position of course). I'll try taking the carb off tonight and installing the kit and let you know.

 
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07-07-09, 07:16 AM   #4  
i had the same problem on a different engine

got most of the surge out by cleaning carb, replacing a slightly leaking fuel line (between tank and fuel pump) but a slight surge still remained at full throttle and the bothersome part was it was irregular - might run fine for 20 seconds, do a slight surge, then run for 45 - 60 seconds and repeat

and like you i was thinking governor - if i held the governor arm, no surge

i traced mine to a vacuum leak, a real slight one - we used to spray silicone at intake manifold gaskets while engine was running, at the dealership i worked at (years back) for similiar problems - ie, the silicone spray would temporarily seal any tiny pinhole leak in the carb to manifold gasket or the manifold to cyl head gasket, - if there was a pinhole vacuum leak, that sealing it would clear it - and that would confirm it was a vacuum leak

cause of the extended surge cycles running up to 60 seconds, silicone would get sucked thru before the next surge, so i used clear lacquer spray - I basically shut engine, sprayed the intake manifold at the cylinder head junction and at the carb base, let cure for a minute or two, restarted, and viola, my surge was history. I've replaced the gaskets since - the lacquer was only for temporary use

i had just pulled engine week before and to remove it, i had to loosen the nuts that held the carb to the intake manifold - and that must have broken the seal on the carb insulator gasket

try it - at least you'll eliminiate the vacuum leak as a possibility if it doesn't cure it

 
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07-07-09, 08:36 AM   #5  
Posted By: larryccf cause of the extended surge cycles running up to 60 seconds, silicone would get sucked thru before the next surge, so i used clear lacquer spray - let cure for a minute or two, restarted, and viola, my surge was history. I've replaced the gaskets since - the lacquer was only for temporary use
I wonder if that stop leak spray that they invented for plumbing leaks might be quite effective at doing the same temporary task?

 
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07-07-09, 08:40 AM   #6  
While the engine is surging spray some carb cleaner along all the mating surfaces between the carb and block, if the engine tempo changes you have an air leak and can take the appropriate action. You may have a crack in the intake. Have a good one. Geo

 
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07-07-09, 09:55 AM   #7  
Also check the throttle shaft. The carb you have is known for getting worn out where the throttle shaft goes through it, creating an air leak, sloppy throttle control, and allowing unfiltered air to enter the engine. It's usually worst at the end of the shaft that the linkage connects to.


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07-07-09, 11:32 AM   #8  
Posted By: ecman51` I wonder if that stop leak spray that they invented for plumbing leaks might be quite effective at doing the same temporary task?
not familiar with that stuff - but i think silicone spray, carb cleaner, any fine liquid that will enter and termporarily block pinhole lead will work plus known to not do any damage to the engine

i only used the lacquer as i knew it would cure real quick and skin over any pinhole leak (remember, i shot it with lacquer while engine was off) and the surge was so irregular it would have been difficult, i'd have to kept spraying for a couple minutes or more and gone thru 2-3 cans of spray trying to make sure it was a pinhole leak

i've since replaced the gasket between the carb and the plastic insulator block and surge is history

it's aggravating when doing maintenance on one item, introduces a whole new problem - i'd pulled the engine to replace the timing belt (my mower is a honda 3813 with overhead cam)

 
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07-07-09, 02:37 PM   #9  
Posted By: cheese Also check the throttle shaft. The carb you have is known for getting worn out where the throttle shaft goes through it, creating an air leak, sloppy throttle control, and allowing unfiltered air to enter the engine. It's usually worst at the end of the shaft that the linkage connects to.
Hate to ask but if it IS the throttle shaft being sloppy what options are there?

 
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07-07-09, 02:58 PM   #10  
Posted By: Sledgod Hate to ask but if it IS the throttle shaft being sloppy what options are there?
If your lucky only the shaft has worn to a point beyond being serviceable.
There may be a bushing in the upper hole that can be replaced. If you have a drill index,( 7/32, & 13/64 come to mind for some reason) you can match the shaft size to a drill, and use it to feel how sloppy the hole/seat in the body is. If you remove the throttle valve/butterfly valve from the shaft it should slide out and you can see how bad the shaft is worn.

 
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07-07-09, 04:07 PM   #11  
Well took the carb off and cleaned it about as clean as I can get it, I installed the kit (at least what came with it anyway) and was able to somewhat get rid of the surging at high speed and with no load by fine tuning the high speed adjustment, however it still very slightly surged but was a ton better than what it was. So off I went on it's maiden voyage...the instant the blades kicked in (for that matter when I put it in gear) it started surging again about half as bad as before but at least it's a step in the right direction, not something I would mow my lawn with every week though thats for sure

I had noticed doing the carb kit that there was a small amount of play in the throttle linkage so I brought it into the garage and tried spraying small amounts of starter fluid near the throttle linkage to see if there was an air leak there but nothing happened (which doesn't necessarily mean it's not a problem). I tried adjusting the high speed again but no success. I'm starting to wonder if I'm going to have to check my head gasket...maybe something else or just pull the dang thing and rebuild it (not sure it's really cost effective but would be interesting to at least get experience on small engines). Thanks for all the responses! this is a great site!

 
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07-07-09, 08:28 PM   #12  
I have to ask...What are you using to clean the carb???? Are you soaking it in a bath cleaner for carbs ,,or only spraying it with a spray cleaner..To me it seems like you still have something pluged,,, Just a thought.... Roger

 
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07-08-09, 05:53 AM   #13  
Just a carb cleaner spray. I can't see anything else that could get plugged as it's pretty much all new parts. I'm not saying that there isn't something that isn't clogged just can't see what it might be.

If I get time tonight I may try and take the float bowl off tonight and see if some crud from the gas tank didn't get in it and plug up something. I had previously drained the tank and put fresh gas in but maybe some crud is still in it. I had a cousin of mine look at it late last night and like you guys he thought it was running too lean but couldn't fix the problem by adjusting the high speed screw so back to the carb drawing board I go.

 
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07-08-09, 07:47 PM   #14  
You'll probably have to soak it in a cleaner,, blast it out with the spray stuff & chase everything with a blast of compressed air..Lots of tiny holes to get plugged in there... Also double check the float level...A low float canalso cause a lot of headaches... Roger

 
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07-09-09, 12:12 AM   #15  
Still a carb problem. Something is still clogged.


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08-04-10, 06:22 PM   #16  
Ok,

I know this is over a year afterwards but I got time in the last few weeks to go over this tractor again. I Found 2 really loose bolts on the cylinder head and so pulled the head off & cleaned out the carbon and put a new gasket on and re-torqued the bolts, then tried starting it and it still surged, I put the carb in parts cleaned for 2 days and blew it out completely but still surging (I tried adjusting the carb real slow but you could only get it so it had a little less surging).

At this point I said what the heck and I pulled the motor and completely tore into it. The governor control shaft was broken in half and I had to replace it. Also broke the glaze on the cylinder and put in new rings, new Crank seal and pan gasket (while cleaning out what looked like RTV sealant chunks in the pan). I also cleaned the rust off of the flywheel and magneto (adjusting the gap to spec), cleaned and re-gaped the spark plug. Last night we got it all put back together again and after adjusting the governor for the right high speed RPM it ran like a champ....absolutely NO surging

However, After running and test mowing the lawn for about 15-20 minutes it started missing and was getting worse so I shut it down and put it in the garage. After thinking about it over night I couldn't come up with a reason as to why it was doing that. I went out tonight and started it up and lo and behold it ran like brand new again So I started mowing again but just like the night before after 15 minutes or so it started missing again and would get worse...I tried adjusting the high speed needle but it didn't change the missing problem so I'm thinking it might be a bad magneto...I've heard when the get hot they can do odd things if their bad....any clues? Could the motor be overheating because I did something stupid (it IS 90 degrees here)?

BTW, Sorry about the uber long post but I try to be thorough

 
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08-04-10, 07:56 PM   #17  
did you do a static adjustment on the governor after you fixed i?

 
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08-05-10, 07:50 AM   #18  
Posted By: 38racing did you do a static adjustment on the governor after you fixed i?
If by that you mean loosening the governor control arm bolt and turning the control shaft clockwise until it stops and re-tightening the bolt on the control arm then yes I did that. If thats not what you mean

Once the motor was back together and was running I bent the tang on the governor spring linkage to get to the desired high speed RPM. Ran great for about 15 minutes then the problems started. I'm going to try and get it to do it again tonight when I get home and when/if it happens I will immediatly check spark to see if the coil is shorting out when it gets hot. Anyone know how to check it with a multimeter?

Thanks for the help Beer 4U2

 
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08-05-10, 03:26 PM   #19  
Ok, just ran it until it got hot and started missing again and the spark when it was missing and the spark when it was running fine are the same... after checking the spark when it was hot it wouldn't start anymore just sit and spin and maybe a half-hearted pop now and again. I'm thinking the coil is fine but after doing some research on the net I'm beginning to think my valve lashing is out of whack...I didn't check it when the motor was apart like a moron (looked good visually - DOH) So I'm not sure what to do check next in the wild hope that's not the culprit

 
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08-19-10, 12:28 PM   #20  
Ok valve lashing was good but broke down and bought a new Magneto and installed it and blamo everything ran great, no problems anymore... I know not a lot of people are looking at this post but if it helps one person not go through the dumb mistakes I went through then I will be happy. Have a great day all!

 
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08-19-10, 01:08 PM   #21  
Glad to hear it all worked out and that it runs good!

 
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