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This is on my friends craftsman mower. The machine is a 2014 model.

The machine backfires and pops through the carb under load. Checked the valve lash, all good. Nothing sticking. He has replaced the carb with a brand new one and brand new coil too. Starts and idles fine. If you try to go to full throttle it starts breaking up. While running and having the problem, I hit it with carb cleaner and the effect was minimal but leaned towards chocking it out vs picking it up so it was not starving for fuel. The more I played with it the more it appears that it was purposely being limited. If you have ever had a Polaris ATV as an example where they have a rev limiter for reverse, that is what it is acting like. As if it has a rev limiter. However it's not getting anywhere near an RPM that it SHOULD be limited on. This machine has a "tractor" mode on it. Seems the safety measures are all or none (it either runs or doesn't). Nothing I would think of that could act like a limiter.

Where should I look? What am I not thinking of?

Is this a over head valve or a L head series ?

If you can work the throttle by hand what does it do ?

It is conventional overhead. Has regular ol' rocker arms. I will check the throttle and I will let you know. I suspect it will make no change because it's being held back via ignition

The only way it can be held back via ignition is that the magneto coil is not gapped right. Check it with a buisness card. Regap it with a card is what i mean.

You might have a blown head gasket also. I would almost bet good money on the gasket.

I just re read your post. Yep head gasket !~!~!~!

And what the @#!*!#* is it fitted to ?
no engine has any sort of rev limiter except the EFI ones everything else is in the mower.
And being that there are 3 different OHV B&S engines rated at 19Hp an engine number might be a bit of a help too.

Buggy there is no rev limiter on that engine at all. Well the governor is a limiter in a way. But I don't think that's your issue with your engine.

I have worked on many of these, that's why I asked you if it was a OHV type engine. I myself don't a engine number,it's on the valve cover if you look at it good.

The reason you are getting blow back out of the carb is that the head gasket is blown right there between the cylinder and valve rod valley. The compression is coming back out thru the carb via the rod valley. When you take the gasket off it will have a bad spot on the back side of the gasket.

Rotary parts has a better gasket than the OEM ones. It is beefier and last longer..

Be sure to check/change your oil also. Gas can get in the crank case because of the gasket being bad.

Bert will agree with me on this. We have been working on these things for a long time. We do this for a living.........

I will check it out again in person tomorrow. The guy said the model number is a 33R877.

He did tell me that he took the head off to make sure that everything looked ok. The valve lash if I remember right was .003 and .005. The guy is no dummy either. Seems if it was a head gasket, it would be a pig to start and would never run good at all. I mean it fires and idles fine and you can slowly start running the RPM's up and it is fine until it gets to a certain point and then it starts running like crap.

bertsmobile1 said:

And what the @#!*!#* is it fitted to ?
no engine has any sort of rev limiter except the EFI ones everything else is in the mower.
And being that there are 3 different OHV B&S engines rated at 19Hp an engine number might be a bit of a help too.

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It's a craftsman mower. I didn't THINK there was any kind of ignition limiter on it but figure if they have gone that far with a mower now a days you guys could school me on it. That is just what it reeked of when shooting it with carb cleaner had nearly no effect on it. My thoughts are that it had nearly no effect because fuel is not what it's problem is.

Also what is th clearance supposed to be on that pickup to flywheel?

A buisness card or 12 thousands for the magnetron coil.....

Maybe the guy took the valve cover off instead of the head ?

That blow out is only visible from the backside of the gasket and it is small. If you take the head off and just look at the front of it and put the head back on you are pissing whiskey as a old friend used to say. LOL

BuggyMasters said:

I will check it out again in person tomorrow. The guy said the model number is a 33R877.

He did tell me that he took the head off to make sure that everything looked ok. The valve lash if I remember right was .003 and .005. The guy is no dummy either. Seems if it was a head gasket, it would be a pig to start and would never run good at all. I mean it fires and idles fine and you can slowly start running the RPM's up and it is fine until it gets to a certain point and then it starts running like crap.

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(I mean it fires and idles fine and you can slowly start running the RPM's up and it is fine until it gets to a certain point and then it starts running like crap.)

That's the exact symptoms of a bad gasket ~!~! No it will run with a bad gasket, but if it washes out and gets bigger then it's a pig to start.

Signs of a leaking head gasket ( can be all or some )
1) hard to start
1) oiled pug
3) oil pooling in carb
4) runs ok slow but gets progressivly worse as the speed increses
5) leaks oil around the head gasket
6) noisy at full throttle
7 ) blows smoke briefly when the throttle opens wide ( when you engage the blades or start to move )
8) crankcase smokes when engine is off ( stop engine & remove the dipstick )
9) oil blowing out of the fuel pump

And as you have already been told your mower is displaying several of them.
Inteck are highly probe to blowing the gasket when previously stated.
When replacing the gasket you need to lap the head and stone the cylinder as it goes hollow on the bridge between the cylinder & pushrod tunnel.
At least 3 or 4 come in every year with new gaskets ( can't be that I have replaced it ) leaking.
I fit Stens ones which are pressed from the same material used for exhaust gaskets and seems to wok a lot better than the genuine B & S ones.
The one size Stens does not use I fit solid copper and never had a single one come back.
The Oregon distributor down here only brings in the small intek gasket and it is also better than the Briggs one.

All noted guys, I will,let you know what I find. Thx

Guys here is a video of what it is doing. My friend says he put a new head gasket in it when he pulled it apart. Looking at this you still thinking head gasket?

http://www.youtube.com/watch?v=qJ3hisw6tZ8

Just got back from a huge birthday bash for 3 friends of ours. 2 brothers and a sister all born within a week. Different years of course.........

Ok back to the engine in ??. Yes it does plus more. The video was a lil short and the camera wasn't on the front of the tractor.

Let that engine run for 5 minutes or so at a medium speed so the carb doesn't blow out the exhaust like it's doing in the video.

When you shut it down take the oil dip stick out and see if some smoke and fumes come out Like Bert posted # 8 on his post. Don't worry about # 9 cause you have a gravity fed system.

Like Bert said and I have seen it too. People say I just put a new gasket on. Something is wrong with the head or a bent rod maybe.

Let us know.

I wish I could see that mower in person.

Change your oil and see if there is gas in it. Or just drain a lil bit out and check to see if it is thin.

It runs the same no matter hot or cold. 30 seconds or 30 mins it runs just like that. I slowly revved it to show that it is fine until you get it up to that point. The backfiring through the carb is the problem.

Boudreaux In Eunice La. said:

Just got back from a huge birthday bash for 3 friends of ours. 2 brothers and a sister all born within a week. Different years of course.........

Ok back to the engine in ??. Yes it does plus more. The video was a lil short and the camera wasn't on the front of the tractor.

Let that engine run for 5 minutes or so at a medium speed so the carb doesn't blow out the exhaust like it's doing in the video.

When you shut it down take the oil dip stick out and see if some smoke and fumes come out Like Bert posted # 8 on his post. Don't worry about # 9 cause you have a gravity fed system.

Like Bert said and I have seen it too. People say I just put a new gasket on. Something is wrong with the head or a bent rod maybe.

Let us know.

I wish I could see that mower in person.

Change your oil and see if there is gas in it. Or just drain a lil bit out and check to see if it is thin.

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When you shut it down take the oil dip stick out and see if some smoke and fumes come out Like Bert posted # 8 on his post. Don't worry about # 9 cause you have a gravity fed system.


This is one of the main reasons I was posting. I wasn't asking if it ran for a certain amount of time.

Boudreaux In Eunice La. said:

When you shut it down take the oil dip stick out and see if some smoke and fumes come out Like Bert posted # 8 on his post. Don't worry about # 9 cause you have a gravity fed system.


This is one of the main reasons I was posting. I wasn't asking if it ran for a certain amount of time.

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Ok I'll try to get back over there tomorrow.

Buggy did you find anything out yet ??????

Boudreaux In Eunice La. said:

Buggy did you find anything out yet ??????

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I have not got back over yet but rest assured I will report back when I do.