15.5 ohv popping from carb

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  #1  
Old 07-19-10, 07:58 AM
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15.5 ohv popping from carb

hi all i have 31c707 15.5 ohv i notice that i satrted looseing power and a popping sound kinda sound like back firing from the carb or popping here what ive done i replace the spark plug put some seafoam in the gas adjusted the valves a few times i adjusted the valve to this speck 003-005 in
005-007 on the ex can any one help!!!
 
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Old 07-19-10, 05:55 PM
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Did you position the piston correctly as below before adjusting ?

Just to clarify, The top valve is the exhaust/Bottom is intake.


Remove the valve cover then rotate the engine over by hand until you reach top dead center compression stroke, Then remove the spark plug. Once at TDC insert a small screw driver in the plug hole touching the piston and rotate clockwise past TDC until you see the screw driver move down inside the hole 1/4". Now loosen the jam screw in the center of the adjustment nut and adjust, Hold the adjuster nut with your wrench while tightening the jam screw. It may take a couple times to get it right because when tightening the jam screw it could throw the adjustment out so check after tightening.
 
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Old 07-19-10, 11:59 PM
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Does it only do it at full throttle? If so, and the valves are adjusted properly, then the camshaft is probably the problem.
 
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Old 07-20-10, 05:50 AM
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yes cheese it is @ full it pop i just put a new cam and tappete/lifter in this motor this spring
why the heck is it eating cams now that is 110.00 for new cam and lifters + 6.00 for sump gasket
 
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Old 07-20-10, 11:15 PM
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Yeah, I forgot...that was you that went through this just earlier this year. Is it making the same noise as before when the cam went bad? I wouldn't suspect the cam to be bad this quickly. If it is, the only thing I can think of that would contribute to this problem is improper lubrication or improper valve clearances.
 
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Old 07-22-10, 07:26 AM
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when i rebult the motor if u remember i ask u what u used to lube the motor with as i was putting the motor together i used vasoline as a prelube then i filled the motor with 30 weight motor oil and after i fugar out i had sheered the fly wheel key i change again and i adjusted the valves to the speck in early post i don't know what the heck is going.
 
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Old 07-22-10, 07:40 PM
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DOesn't sound like you did anything wrong. Check the valve travel again, see if one of them isn't moving far like last time.
 
  #8  
Old 07-23-10, 06:33 PM
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will do tomarrow long day @ hospital
 
  #9  
Old 07-26-10, 02:42 AM
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looks like its cam time again. for the life of me don't understand how this cam wore out in 4 months i mowe 2 strip 20' wide 80' long and that is it cheese please give me ur input or anybody give me ur input
 
  #10  
Old 07-26-10, 02:46 AM
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cheese let me bounce this off ur head oil slinger not kicking the oil up enough to lube the lifter/ cam. can it be possibal . let me know what u think.
 
  #11  
Old 07-26-10, 11:38 PM
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Yeah, it's possible if the slinger is damaged or the mower is operated on enough of an incline to keep the slinger out of the oil, or totally submersed in oil. The fact that the cam is made of such cheap chinese junk metal that you can cut it with a pocket knife doesn't help matters much.
 
  #12  
Old 07-27-10, 03:29 AM
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how about this i get another cam and lifters send them to a place and have them harden/tempered im @ my wits end or adding something like z-max to the oil to reduce friction or tlefon let me know what u think what do u think about thicker oil maybe i know if u go to thick it wont lube the crankthe more problems to come let me know what u think
thanks for all ur help
 
  #13  
Old 07-27-10, 03:33 AM
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look a prevous note too from me has there ever been a data sheet put out on cams going bad recall from b&s or something like that let me know
 
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Old 07-27-10, 10:50 PM
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Briggs knows about the problem, but they are taking advantage of the problem by charging high prices for the replacement camshaft instead of revising it to a better product and offering it in a recall or at least a reasonable price. There have been some warranty issues related to it, I would contact Briggs and tell them your plight and see what happens.
 
  #15  
Old 07-29-10, 12:47 PM
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cheese what are u getting for a cam and lifters. send me a pm. b&S told me basicly oh well i would have to buy another cam and lifters. i gave them hell.what some of my other ideas let me know...
 
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Old 07-29-10, 03:44 PM
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We have been experiencing a similar problem in the classic car world with flat tappet cams. The oil companies have removed much of the zinc additives from the latest version of oils. Most folks have switched over to diesel oil which has higher zinc levels. Others have started using a product called ZDDP. Maybe this is a similar situation -- just a thought.
 
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Old 07-30-10, 01:09 AM
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I don't have any ideas other than get an older briggs engine with the metal engine shroud and swap engines...those had the cast iron camshafts built like a cam ought to be built, not the chinese pot metal pressed-together cams they use now. (no, you can't use one of those to replace your cam...they changed it just enough to keep you from doing that). The tappets are supposed to be hardened. If your valve clearances are too loose, the cam lobes beat the tappet every time they come around and wears it too fast. I don't know what else could be the problem. I've never had one that I just installed go bad on me in a short amount of time.
 
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Old 07-30-10, 08:49 AM
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cheese u know i was thinking. what if the valves in the head causing the cam to ware out for ex. if some carbon got in to the valve guide and is putting some more pressure on the cam. than what is tolrated but it is not a whole lot like ozs. or the valve spring has gotten more risistive it is the exhuast valve that is causing the problem.and with the extra heat. could this happen? do u know what the spec on the valve spring (how much pressure does it take to collapse the spring)?????
 
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Old 07-30-10, 09:36 PM
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No, I don't, but I can't see a spring getting stronger. Usually the spring gets weaker and you check spring height to confirm its' viability. If there was carbon in the guide enough to cause the cam to wear, it would also be enough to float the valve at much of any rpm. Do the valves work freely all the way through their travel path? If so, I wouldn't suspect them as the problem.
 
  #20  
Old 08-02-10, 12:04 PM
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seams to i took the spark plug out so the motor would turn freely and it seams to move smoothly no sticking, delay movemet. i been looking for another cam (used ive already put 1 new one in. i can not aford to spend over a 100.00 bucks again just for it to do again untill figuar this out. i found some cams used but the person didn't have the liferts that went to the cam/motor. im i going about ths the right way tring to get cam/lifter set or should get another cam and try i out.ur input is needed and dont pull any punches tell me what u would do!! i'm lost. hehe i tell u what i was going to do was have the cam lobes and the face of the lifter coated with Polytetrafluoroethylene . dont know if ti would work or not....
 
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Old 08-02-10, 09:21 PM
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$90 for a new cam and lifters is all I can recommend. I have used old cams before but you have to be really careful about the lifters. If you see any wear pattern at all, even just the way the light reflects on the lifter face, don't use it. What would I do if it were mine? I wouldn't. I have enough other engines around that I'd take that mess off and put a better engine on... so I can't help much with the "what would you do" scenario. If I were in your position, I might be inclined to try a used cam if my lifters were flawless, the cam was flawless, and it was $20 or less. It's a gamble and is it worth pulling the engine and taking it apart again to save a few bucks? Depends on your situation I suppose.
 
  #22  
Old 08-03-10, 07:02 AM
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i going to chk around to see if i can find another motor im going to check it with a fine tooth comb beore i buy if i could afford ti i would just get me a new motor but 450 is a lot on fixed income to spend @ one time and nobody will let me pay it out then pick up the motor i even told a few shops they would not evevhave to order the mortor till it is all paid off they said no...
 
  #23  
Old 08-03-10, 09:42 AM
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Check around in the paper, craigs list, ebay, etc... for engines or riding mowers that need work. You can find mowers with good running engines for $100 and under. They might have bad decks or transmissions, but who cares... you just want an engine. Look for the older briggs with the metal engine shroud 14hp and up. The engine you have should be worth fixing, but I can't guarantee it won't happen again. The cams usually last several years, not just a few months. I don't know why yours did this.
 
  #24  
Old 08-05-10, 05:59 AM
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cheep pig metal i took the cam out the other day and mic the lobe it was made with 040 lift it has 030 lift on it i found a 18hp c31777 w oil filter the guy said it runs rough he thinks it is a carb problem i want to go look @ it. he wants 50.00
the motor i had was c31707 15.5
i know it will fit. bore is defferance from all the spec that i found and looked up.
has medal shroud
 
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Old 08-10-10, 06:43 AM
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hi cheese i went to that guy house the other day he had a lot of motors and guess what. the all same problem the cams he was thinking it was the carb i pulled valve cove on 6 of the ex valve bearly moving i told it was cam he did not beleave me he rip the botton of o 2 and i said see. all the motor had gas smell to the oil medal shaving in sump i just laugh he got mad,
he got a bunch of motor from a
guy and and thouhgt he was going fix them up and sell the and get a lot of money i told him he going spend @ least 120 per motor to replace cam and lifters an gasket he had 15 or 20 motors he was pis*** off
 
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