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B&S Engine wont start


BlackTop's Avatar
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10-07-09, 03:47 PM   #1  
B&S Engine wont start

B&S 17hp OHV
31C707
0154E1

Its acting like a weak battery.
Turns over 1/4 to 3/4 rotation then locks up.
Pull the spark plug turns over fine.
If I put the jump box from my car on it "sometimes" it will start. But I almost have to boil the battery to do that.
When and if it starts it runs "ok" a little backfire at low idle as well as small puffs of white smoke out the intake.
Runs great at higher idle and full throttle.
I pulled the carb off today and gave it a decent cleaning, could have been more detailed.

I have been reading and reading and reading for two days.
Everything I have read says to adjust the valves. I have done this three times thinking I might not have gotten it just right.
But nowhere in my reading can I find what to do if that dosent fix it, short of a new cam at the price of about $100.

I know with any old machine a GOOD tune up is in order. My first step was cleaning the carb. Will be replacing the spark plug, air filter, fuel filter, and doing a proper carb rebuild or maybe just replacing it.
Not that important right now as it runs "ok".
I need to get it to turn over first.

Please help me get my mower running again.

 
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cheese's Avatar
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10-07-09, 06:51 PM   #2  
How did you adjust the valves? Are you sure you got them right? Just a few thousandths of an inch can make the difference. I still think they need adjusting. Does the oil smell like gas?


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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10-07-09, 07:45 PM   #3  
I pulled the valve cover off got out my torx bits and a wrench and using a feeler gauge set the valve lash. Must admit the smallest feeler I had was .008". So as I was setting them rather than by feel for light drag I put a little extra on them to compensate for a thicker gauge.
I'm about 90% they are correct. I've done them three times so far lol.

No the oil does not smell gassy. The solenoid on the fuel bowl on the carb is operating properly when the ignition in turned on and off. When I pulled the carb apart I checked for movement of the plunger and it is free and clear of any gummy tarnish.

This mower is only 5 years old.
It has had normal wear and use however I know the previous owner has not kept the best maintenance.

 
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10-08-09, 05:23 AM   #4  
Insufficient valve clearance will cause hard staring as you describe. Close may count with hand grenades and dancing but not with valve lash on these OHV engines.

Cheese stated a few thousands can make a big difference. I think it is more like a couple of thousands.

Valve Clearance

Intake .003 - .005 in. (.08 - .13 mm)

Exhaust .005 - .007 in. (.13 - .18 mm)

 
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10-08-09, 08:18 AM   #5  
Ok I bought some new feelers this morning with the proper sizes.
After I properly set the valve lash how can I determine if the MCR (Mechanical Compression Release) Is working properly.

FYI I am setting the valves using the method of finding TDC on the compression stroke and taking the piston down 1\4" by using a scrap piece of wire as a feeler.

 
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10-08-09, 08:21 AM   #6  
Oh yeah one more question. Which valve is which?
I believe that the exhaust is the top valve. Am I correct?

 
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10-08-09, 08:33 AM   #7  
Easiest way is to look at where the intake manifold and exhaust manifold go into the head, intake manifold is closest to the intake valve, exhaust-exhaust.

Brain cramp but I think the top one is the intake...but follow the manifolds to be sure.

 
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10-08-09, 11:18 AM   #8  
Valves are adjusted perfectly. .0035" on the intake, .005" on the exhaust.

When i tried a restart it was still a no go.
Pulled the spark plug turned over the motor and fuel spilled out the spark plug hole, also started popping out the carb.
Put the spark plug back in and it fired up with some hesitation.

Do ya'll think this could be a prob with flooding?
But at the same time I think its running lean at low idle, maybe that explains the backfire every 3-5 seconds and white puffs out the carb??

 
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10-08-09, 12:07 PM   #9  
Posted By: BlackTop Valves are adjusted perfectly. .0035" on the intake, .005" on the exhaust.

When i tried a restart it was still a no go.
Pulled the spark plug turned over the motor and fuel spilled out the spark plug hole, also started popping out the carb.
Put the spark plug back in and it fired up with some hesitation.

Do ya'll think this could be a prob with flooding?
But at the same time I think its running lean at low idle, maybe that explains the backfire every 3-5 seconds and white puffs out the carb??
During your "tune up" did you check or change the oil?

 
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10-08-09, 01:27 PM   #10  
checked oil. seems to be ok, does not smell gassy.

 
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10-08-09, 05:13 PM   #11  
Ok here is the latest.
The valves are set perfect, see above post.
I gave her a FULL tune up. New air filter, new spark plug, oil change, too the carb off and cleaned it again. Also gave the carb a great tune. She now runs perfect. No more backfiring, no more white mist out the carb, no more popping and sputtering.

So why is it still hard to start? Even by hand once it hits that compression stroke it is near impossible to turn.

How can I check the MCR to make sure its working?

 
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10-08-09, 05:46 PM   #12  
In the above post you say you have fuel spilling out the spark plug hole...Later you said you took it off & cleaned it again.. Still same???? Try replacing the float & needle & seat & installing a kit, that should fix the flooding problem...To check the MCR & if the valves are adjusted correctly as you say they are,, with the valve cover off,, slowly turn the engine by hand..Watch the exhaust valve & as the piston approaches TDC compression,,the valve will ""do a little dance"" & slightly open than close again...The movement is slight so watch close, this is why the valve clearance is so important.... Hope this helps... Roger

 
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10-08-09, 06:27 PM   #13  
No more fuel spilling out. I think I may have flooded it earlier. It only did that once and the oil never smelled like gas.

Will check for a "little dance" as you say. Get back with ya'll tomorrow.

 
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10-08-09, 08:33 PM   #14  
It might be that you have a bad connection causing the hard starting. Battery terminal, solenoid connections and the starter terminal...
Might try turning the engine by hand where the starter leaves off see how it feels.

 
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10-08-09, 08:39 PM   #15  
The fuel spilling out is not from common flooding. You can't flood the engine enough by choking it for fuel to spill out the spark plug hole. This is a carb problem, leaking fuel into the cylinder. Gasoline can't be compressed, so it hydro-locks the engine causing your problem. Usually this coincides with gas in the oil (which is why I asked if the oil has a gassy smell). Apparently yours has not been doing this enough to have noticeably contaminated the oil yet. Sounds like the valves aren't the issue. The compression release function on the cam could be defective, but I doubt it. The fuel in the cylinder is definitely an indication of a problem that will cause your symptom, so I would address that before anything else.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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10-11-09, 11:04 AM   #16  
Ok here is what I have been able to discover.
After sitting for a day or two there was no fuel in the cylinder. Pulled out the plug manually turned engine over no fuel came out.
Pulled off the valve cover checked the valve lash one more time...it is fine.
Turned the engine over by hand and the exhaust valve does not dance around or open any on the compression stroke. This leads me to believe that the MCR on the camshaft has failed.

While chasing these gremlins I decided to do a little wiring check. To make sure my battery was charging properly and I had good connections.
Found the two wires coming out from under the flywheel and at a slightly high idle they produce 13.5v. However when I run the engine up to full throttle they produce 22-22.2v.
Is there a voltage regulator that I need to replace.

You guys are so great on here. I really appreciate all the helpful information you have shared.
Here's to yaBeer 4U2

 
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10-11-09, 12:23 PM   #17  
Posted By: BlackTop Ok here is what I have been able to discover.
After sitting for a day or two there was no fuel in the cylinder. Pulled out the plug manually turned engine over no fuel came out.
Pulled off the valve cover checked the valve lash one more time...it is fine.
Turned the engine over by hand and the exhaust valve does not dance around or open any on the compression stroke. This leads me to believe that the MCR on the camshaft has failed.

While chasing these gremlins I decided to do a little wiring check. To make sure my battery was charging properly and I had good connections.
Found the two wires coming out from under the flywheel and at a slightly high idle they produce 13.5v. However when I run the engine up to full throttle they produce 22-22.2v.
Is there a voltage regulator that I need to replace.

You guys are so great on here. I really appreciate all the helpful information you have shared.
Here's to yaBeer 4U2
Your engine has a Dual Circuit alternator. Dual Circuit alternators use a polarized plug with two pins. One pin provides DC current for charging the battery; the second pin is an independent AC circuit for headlights.

To correctly test DC output measure amperage.

Current for the DC side of the alternator is unregulated and is rated at 3 Amps. With the engine running at 3600 RPM, output should be between 2 - 4 Amps DC.

To correctly test AC output measure AC voltage.

With engine running at 3600 RPM, AC output should be no less than 14 Volts.

If you do not have problem with battery charging or lights I would leave it alone.

 
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10-11-09, 01:08 PM   #18  
Do you still have the problem you originally had?

Quote:
"Its acting like a weak battery."

"Turns over 1/4 to 3/4 rotation then locks up."


If you are still having this hard start problem and you are confident the valves are correctly set, the battery is fully charged, battery cables are good and all start system electrical connections are sound it is time to look at the cam.

Getting to the cam will take a bit of work.

 
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10-11-09, 02:59 PM   #19  
Yes I still have that exact problem.

I've just been trying to eliminate every other possibility that may be causing it other than the cam.

Unfortunitly I think its come down to the cam.

 
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