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B&S , 250cc engine problem

This is a discussion on B&S , 250cc engine problem within the Small Engines forums, part of the Tech Support Forum category. Hi , I have a snowblower that is mounted with a b&g 250cc 1150 series engine , recently the engine


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Old 03-09-2011, 03:59 AM   #1
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Hi , I have a snowblower that is mounted with a b&g 250cc 1150 series engine , recently the engine starting acting on me , know I can not start it with the pull cord , it wont start , but if i use the starter it will start , i already checked the spark and fuel , it seem ok , but I also checked the compression , and I only got 25 psi with the pull cord , and about 75 psi with the starter , the engine is 3 years old , I also put some oil in the cylinder to see if the compression would get higher , but no it was still at 25psi with the pull cord , so the rings should be ok? . What would be the correct compression on this engine , and do i check the compression this way ? thank you

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Old 03-09-2011, 10:32 AM   #2
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I wouldn't worry about the compression...those engines have automatic compression releases so you won't get an accurate reading anyways. Does it have fresh gasoline (under 30 days old)? If not, drain and add fresh. If the spark plug has never been replaced, get a new one while you're at it. How does the engine run once it gets going? Is it smooth? Is the primer working?

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Old 03-09-2011, 02:09 PM   #3
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The flywheel has to turn at least 720 RPM's (if I remember correctly) in order for the ignition to start functioning. Your not short roped are you? Kinda hard to reach the needed speed with a short starter rope, also with cold thick oil. Follow the manufactures suggestions on oil weight to use...
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Old 03-09-2011, 02:59 PM   #4
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thanks for the replies , when the engine start , with the starter , it runs fine , but sometime it will die on me when i am snowblowing , and even when the engine is hot it will not start with the pull cord . the gas inside the tank is old so i will change it , i always use the best octane available here in montreal , octane 94 , and i will change the plug . hope this will do it , here there is a lot of snow recently so it as to be fixed . thanks

I run synthetic oil in in , some leftover from my car oil , and the pull cord is the original .
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Old 03-13-2011, 03:32 AM   #5
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Hi, the use of high octane fuel is at least part of your problem. The higher the octane rating the slower the burn as well as a higher flash point temperature. in these small engines high octane is not recommended for the reason you describe. it is harder to ignite and it burns slower. While this is beneficial in a high compression performance engine ( slower burn so instead of a quick explosion there is a slower explosion allowing the fuel to "push" on the piston longer providing performance benefits and prevents pre-ignition from such a quick burn), it is not recommended in a air cooled low (7 to 1) compression engine.

try putting regular 87 octane fresh fuel and it will resolve your problem. also, the ignition system will produce a spark at 1 rpm's. As soon as the coils field to ground is broken (such as the points opening) the energy is redirected to the only other ground, the spark plug, rpms are irrelevant. the compression release disengages around 250 rpm's and your starter turns the engine around 200 rpms.

Kevin
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Old 03-13-2011, 12:14 PM   #6
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Quote:
Originally Posted by kbowley View Post
Hi, the use of high octane fuel is at least part of your problem. The higher the octane rating the slower the burn as well as a higher flash point temperature. in these small engines high octane is not recommended for the reason you describe. it is harder to ignite and it burns slower. While this is beneficial in a high compression performance engine ( slower burn so instead of a quick explosion there is a slower explosion allowing the fuel to "push" on the piston longer providing performance benefits and prevents pre-ignition from such a quick burn), it is not recommended in a air cooled low (7 to 1) compression engine.

try putting regular 87 octane fresh fuel and it will resolve your problem. also, the ignition system will produce a spark at 1 rpm's. As soon as the coils field to ground is broken (such as the points opening) the energy is redirected to the only other ground, the spark plug, rpms are irrelevant. the compression release disengages around 250 rpm's and your starter turns the engine around 200 rpms.

Kevin
Hi,
Briggs & Stratton recommends a minimum of 250 RPM before spark is present. To quote Briggs & Stratton, "The engine must be pulled over at a minimum speed of 250 RPM before the coil will even think about firing."

I do agree about the octane, 94 offer no benefit for a low compression engine such as this one.
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Old 03-14-2011, 04:35 AM   #7
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Please tell me what Briggs manual states that. I have read every one and have never seen that, it simply is not true if they did. I also dont believe they said, "before it even thinks about firing" Do you know what RPM's the electric starter turns the engine over at 75 degrees with 10w30 oil? I absolutely assure you that one cannot pull that engine over at 5 revolutions per second. Just for your info, the electric start on a garden tractor turns at 150 RPM's on a Briggs 12 hp IC, however, when warm they usually start with just a bump of the key. Many engines will start with just a small tug through the compression stroke.

Please tell me which manual that states your quote.
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Old 03-14-2011, 04:57 AM   #8
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from the briggs manual i just read
" a power-saving, low back pressure muffler that lets the engine speak with quiet authority . . . a unique dust-sealed ignition system with powerful ceramic magnets that develops a strong, hot spark even at low RPM for easy starts . . ."
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Old 03-14-2011, 11:00 AM   #9
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Hi Kevin,
Please see here:
Ignition System Theory and Testing | Frequently Asked Questions | Customer Support | Briggs & Stratton

In fact, the Briggs & Stratton service manual states "Flywheel must rotate at 350 RPM minimum" (when checking spark). The same manual states that a properly working electric starter motor will turn at a minimum of 1400 RPM.
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Old 03-14-2011, 03:57 PM   #10
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that is incorrect, period. if it were, why would the service manual state

"electric start motors should meet or exceed a crank speed of 120rpm at 40c. test using a hand held tachometer..."

" we compared 5W-30 synthetic oil to a mineral based 10W-30 and a 10W-40 in very cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively and neither engine started."

I mean think about what you are saying...1500 rpms!! So you believe the starter turns the engine 500 rpms faster than it idles? 1500 rpms would be 23 times per second...have a listen the next time you start your engine and see if you really believe that it is spinning 23 times in one second.

I will take a video tomorrow creating a spark turning the engine with my hand past tdc with the plug out...will that be enough proof?
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Old 03-14-2011, 05:22 PM   #11
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Quote:
Originally Posted by kbowley View Post
that is incorrect, period. if it were, why would the service manual state

"electric start motors should meet or exceed a crank speed of 120rpm at 40c. test using a hand held tachometer..."

" we compared 5W-30 synthetic oil to a mineral based 10W-30 and a 10W-40 in very cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively and neither engine started."

I mean think about what you are saying...1500 rpms!! So you believe the starter turns the engine 500 rpms faster than it idles? 1500 rpms would be 23 times per second...have a listen the next time you start your engine and see if you really believe that it is spinning 23 times in one second.

I will take a video tomorrow creating a spark turning the engine with my hand past tdc with the plug out...will that be enough proof?
Hi there,
I am not saying or believing anything, I am simply repeating the information the Briggs & Stratton makes available to their dealers for troubleshooting and repair purposes.

The starter gear is considerably smaller than the ring gear, now I don't have the time nor desire to measure it all up (and it would vary by engine), but that means that the engine would turn considerably slower than the starter motor. So let's just say that on a starter turning at 1500 RPM with a 2" gear, engaging a 12" ring gear, would cause the engine to be turned over at 250 RPM.
Have a good night.
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Old 03-14-2011, 06:02 PM   #12
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If there were no drag on the starter that would be correct. The starter should turn at 6500 rpms at 12 volts no load. the starter is designed to produce enough torque at a given amperage to overcome cranking loads with a given gear reduction. For instance if the voltage remains constant, the starter draw in amperes progressively increases as the starter motor slows until it equalizes at the batteries max CCA. the windings in a single cylinder Briggs starter to turn no less than 150 rpms at 12v 165 amps, if the CCA amp capacity of the battery is doubled to 330 the starter should hold 300 rpms at 40c. This however is above the design load of the starters bearings, gear and windings. it will overheat rapidly at those amps. In practice, the engine will usually start quicker so that overall starter life is about the same. the problem rears its head if a laymen continues to crank a no start condition beyond 5 seconds at the higher amps. the starter overheats much quicker, 20 seconds would cause failure.
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Old 03-15-2011, 03:05 AM   #13
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on my snowblower , the starter works with 120v a/c , from my house outlet , there is no battery on my machine .
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Old 03-15-2011, 03:27 AM   #14
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@RWD, if your engine problem is solved please use the thread tools at the top of this page and mark it solved.

If not, is the same issue still preasent?
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Old 03-16-2011, 02:47 AM   #15
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Quote:
Originally Posted by jrrdw View Post
@RWD, if your engine problem is solved please use the thread tools at the top of this page and mark it solved.

If not, is the same issue still preasent?


ok , i need to go buy a new plug and some 87 octane fuel , i will do it this week , and I will let you guys know , thanks

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