Author Topic: 18.5HP Missing at top speed  (Read 6447 times)

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fordman84

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18.5HP Missing at top speed
« on: May 28, 2008, 03:12:07 pm »
Hey guys, I have a stumper here.  My dad has a Craftsman riding mower (I think that is the problem...haha, I worked for Sears Service Center for a couple of years so I can say that) that has started having problems.  First, it is about 3-4 years old but I don't know the numbers off it.  It is a single cylinder B&S, 18.5 HP I think, maybe 18HP.  He called me a while ago and said that it has been running funny, so I went out this weekend to look at it.  The stupid thing will start and run at low to mid-speed.  however, as soon as you try to get it up to full power it starts sputtering and I noticed some blow back through the carb vent tube (the plastic one coming out from under the engine cover/cowl).  He has replaced the carb already and that didn't help.  I rebuilt and put the old one back on, still no help.  He also replaced the coil/plug wire because the old one melted a bit by the muffler.  One of the first things I noticed is that the fuel filter doesn't fill with gas.  It will run, but there is just a bit of gas at the bottom and looks like the filter is acting as a wick to pull the fuel up.  I think that is an issue.  I replaced the filter, no help.  I think the pump might be bad to start with.  The thing I am most afraid of is that the OHV's might be out.  When I was at Sears and the other shop, OHV was just starting to be big in riders, so I didn't get to work on them much.  Could this be a case of a valve not seating back properly?  Wouldn't that happen at all speeds instead of just the top end?  If you think it might be the valves, how can I check/adjust/replace one?  I have done a lot of old valve jobs, and I have worked on OHV's in cars a little bit. 

I am stumped and hope someone can recognize the symptoms or tell me something else to look for. 

Offline Dylan

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Re: 18.5HP Missing at top speed
« Reply #1 on: May 28, 2008, 03:28:39 pm »
my friends 16.5 OHV would idle fine and run but as soon as you put load on it it would start to die.. and it would bearly run... took it in.. and they said the cam lobe was worn down..
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Offline tgames64

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Re: 18.5HP Missing at top speed
« Reply #2 on: May 28, 2008, 04:25:56 pm »
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He has replaced the carb already and that didn't help.

Has this new carb been adjusted properly?

Quote
I think the pump might be bad to start with.

Inexpensive to replace, do so and take that factor out of the problem.

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fordman84

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Re: 18.5HP Missing at top speed
« Reply #3 on: May 28, 2008, 09:08:30 pm »
I am hoping since it is only 4 years old at most, that the cam isn't worn already...but who knows.  As for the carb, there aren't a lot of adjustments that can be made.  There is only one adjuster screw and it has one of those darn limiter caps on it.  When I tried to remove it, I felt I would be more likely to break the screw so I left it alone.  It sounds to me to be tuned right though.  There is a nice smooth idle at medium speed, but as soon as you crank it up any more it starts cutting out.  It will still run, just has no power since it is missing. 

Offline minijeep

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Re: 18.5HP Missing at top speed
« Reply #4 on: May 29, 2008, 12:35:24 pm »
Have you checked to make sure that the vent in the fuel tank is not plugged up?  If the tank is not vented the pump will not move enough fuel....but the problem will seem to go away at low speed. 
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Offline bountyhunter

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Re: 18.5HP Missing at top speed
« Reply #5 on: May 30, 2008, 03:02:38 pm »
main jet pluged

fordman84

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Re: 18.5HP Missing at top speed
« Reply #6 on: June 02, 2008, 08:29:55 am »
main jet pluged

But on two different carbs, one of which I went through and cleaned/rebuilt?  Anything is possible I know.  My father ended up taking it to a local shop out by him.  I'll report back on what he says was wrong.

Thanks to everyone for your ideas though, I just can't get out to where he lives often enough so he took it to the "professionals".   :P

Offline bountyhunter

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Re: 18.5HP Missing at top speed
« Reply #7 on: June 02, 2008, 08:50:38 am »
sorry missed the carb change!! :bash:

fordman84

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Re: 18.5HP Missing at top speed
« Reply #8 on: June 04, 2008, 10:17:57 pm »
sorry missed the carb change!! :bash:


HAHA, not a problem.  So my dad called the guy a the repair shop and asked what the issue was.  He got a return call a few hours later, and I am not sure what to think of this.  Granted, I haven't worked on a lot of OHV smal engines, but this doesn't seem right.  They say that the cam is rubbing on the muffler.  That is how it was passed on to me.  My dad has rebuilt cars and is pretty mechanically inclined, so I don't think he is one to mis-hear. 

Anyone know if that s even possible?  Could it be the "exhaust valve has rubbed on the cam and worn it down"?  I am perplexed :confused:

Offline nor66

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Re: 18.5HP Missing at top speed
« Reply #9 on: June 04, 2008, 10:36:24 pm »
Cam could not rub on the muffler!!!  Thing only thing riding on the cam is the lifters. It sounds to me that when you move your throttle to max speed it is applying the choke, your linkage might be out of adjustment.
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Offline Squidd

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Re: 18.5HP Missing at top speed
« Reply #10 on: June 05, 2008, 01:23:11 pm »
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They say that the cam is rubbing on the muffler.
Usually the muffler bearing takes care of that....:rofl:
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Offline nor66

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Re: 18.5HP Missing at top speed
« Reply #11 on: June 05, 2008, 02:10:01 pm »
 :lol2: :lol3: :rofl: Oh yea I forgot about the MUFFLER BEARING!!!!
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Offline mowinmachine

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Re: 18.5HP Missing at top speed
« Reply #12 on: June 05, 2008, 03:08:37 pm »
Check the blinker fluid too!

 Anyhow, I'm not sure what that shop is smoking. There's no way internal parts could rub on external parts. My guess, which might as well be as good as any is that you might have a plug with a faulty insulator, which if shorting could cause misfiring at higher speeds. I've actually had this happen more than once. Sounds like you all replaced the coil, wires, and so on, but what about the plug? A bad plug can cause a lot of problems and they're cheap to replace.
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Offline briggsracer1892

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Re: 18.5HP Missing at top speed
« Reply #13 on: June 05, 2008, 03:43:05 pm »
Dont forget the power steering it also affects the cam!!!!! :D :confused: :woo: :3gears: :lol2: :lol3: :owned2:
sit down, hold on, shut up

fordman84

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Re: 18.5HP Missing at top speed
« Reply #14 on: June 05, 2008, 10:20:54 pm »
Yeah, I would expect them to tell me the canooter switch is bad.  Those things are always going bad! 

I am gonna give the place a call and see what they are doing.  THanks for confirming what I thought.