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Garden Tractors / Mowers / Scooters

Briggs and Stratton, Intek Misfiring


Hi All, I have an 18HP V-twin Briggs Intek (407777) that's misfiring as soon as it revved up from...

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  #1  
Old 07-13-2012, 12:54 PM
Neo Neo is offline
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Default Briggs and Stratton, Intek Misfiring

Hi All,

I have an 18HP V-twin Briggs Intek (407777) that's misfiring as soon as it revved up from idle.
It was also continuously popping at idle but does not do that since I adjusted the vales.

Observations....
It now runs well on idle (since adjusting the vales).
If I open the throttle quickly it pops once with black smoke.
Randomly misfires (every 1 seconds or so) once rev'd up.
Gets worse when fully warmed up.
I can't tell if it's one or both cylinders that is misfiring.
It will run on one (either) cylinder when spark plug cap(s) are removed.
Removing either spark plug cap while the engine is running stops the misfires.
Does not seem to be revving up that high at full throttle... but this is the fist Briggs I have worked on so this could be me.
I tried a little choke. It seemed to reduce the misfires a bit but you have to apply a lot of choke (almost to the point of flooding) before it does that.

Done so far...
Replaced both spark plugs.
Stripped down the carb and cleaned it out.
Compression tested - 200PSI Cyl1, 180PSI Cyl2... prior to Adjusting the vales.
Removed and rolled the push rods on glass ... all 4 dead straight.....Is it supposed to be steel for exhaust and aluminium for inlet?.... why aluminium?
Adjusted the vales.... again and again. Even a touch too tight and back again ... no improvement.
Checked all inlet manifolds for leaks.
Check the connections to the ignition coils ... all good.
I pulled off the flywheel and the Shear key is in good condition.
Sprayed in some carb cleaner (without effect) so I'm going to re-clean the carb... but I think the Misfires are too short and sharp to be anything to do with the Carburetor.

Possibilities?...
I'm hoping it's not the cam .... This engine has only done 214 hours and I know it has been serviced occasionally in that time too ... Could the cam really wear that fast?
How would I prove it's the cam without changing it?

Any other thoughts would be welcome???


All the best.
Neo7
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Old 07-13-2012, 03:07 PM
sprkplug sprkplug is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Any evidence of a mouse having taken up residence under the flywheel cover? What procedure did you use to set the valves?

A quick thought: the two ignition coils each use a ground wire, with a female spade connector. Those two wires eventually merge into one "kill" wire, which connects to the equipment's wiring harness. At the junction where those two wires connect together, there will be one, or sometimes two, diode/s. This is to prevent backfeeding into one module from the other... sometimes those diodes fail, and the result can be similiar to what you describe.

It's dangerous, but I have removed the shroud, unplugged both wires at the coils, and started the engine to see if that fixed the problem. BE AWARE!!! The engine will not shut off with those wires unplugged!!!
You might make up a couple of individual kill wires that you could ground out to shut it off.

Please be careful.
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Old 07-13-2012, 03:08 PM
Road Torpedo Road Torpedo is offline
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Default Re: Briggs and Stratton, Intek Misfiring

I would run through your carb. just for the hecky derns. If there too lean, they'll pop.

Bad valve seats, in particular, loose seats will cause your problem. Warped valves will cause your problem.

Ultimatly, it MIGHT be your cam. They make some cams with plastic teeth AND plastic cam lobes. If your lobes are worn, maybee not from hours but from cheap quality, then that will cause your symptom.

I would almost bet you have a loose valve seat somewere.


Quality is just not there anymore in assembly. You never seen the old ones do that and if you did, there was a reasonable explanation and it wasnt due to quality.
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Old 07-13-2012, 03:21 PM
sprkplug sprkplug is offline
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Default Re: Briggs and Stratton, Intek Misfiring

RT is right on about the valve seats. That's exactly why I asked about the mouse nest, as the debris from the nest will cause the engine to overheat, loosening up a seat, or in some cases a valve guide.
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Old 07-13-2012, 04:11 PM
Pat Barrett Pat Barrett is offline
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Default Re: Briggs and Stratton, Intek Misfiring

I had one that drove me crazy, similar description, The wire that goes to the bowl solonoid was shorting out and causing the solonoid to snap closed and then the wire would intermidently contact opening the solonoid. I've heard of people using side cutters to snip the end off and re-installing it, eliminating it's effectiveness. It's an anti-dieseling device, I'm told, shut the fuel off when the switch is cut off.
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Old 07-13-2012, 07:11 PM
Ed Radtke Ed Radtke is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Low oil shutdown?If so,unhook it.
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Old 07-14-2012, 03:45 AM
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Default Re: Briggs and Stratton, Intek Misfiring

Thanks to everyone for your suggestions.... But my biggest thanks goes to Pat Barrett.....Man you hit the nail right on the head.
Turns out I'd wired up the solenoid incorrectly an is was only getting a couple of volts. So I guess it was letting go and momentarily blocking the jet. I have been trying to crack this problem for over a week now. So you've done me a big favour and I really owe you a beer ... hope you live near Sydney

The poping has stopped but I'm not completely in the clear yet.
Seems that if I open the throttle too fast she splatter, hesitates and blows heavy black smoke until I back off the throttle then open it gradually to full throttle.

Just completed a fully strip down and clean up of the carb....Any other ideas gents?

All the best.
Neo
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Old 07-14-2012, 08:23 AM
sprkplug sprkplug is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Glad to hear you resolved the problem Neo! I have to admit that the solution has me scratching my head somewhat though. I do this line of work for a living, so problems such as what you describe hold great interest for me, as I may run into them myself someday.

In that light, may I ask how you were able to wire up the fuel solenoid incorrectly, and in such a manner that it only had a couple of volts feeding it? I certainly don't know what application your engine was used on, but I'm wondering where such a low voltage exists on a typical setup for this engine?

Also, there are two wires feeding into the fuel solenoid, one is a fixed ground and the other a switched 12 volt power source. Why was it necessary to rewire the solenoid, had the engine suffered wiring damage?

Again, not trying to pick on you at all, I've had instances where I've spent a few days trying to sort one out, so I've been there! Just want to understand your specific situation so I'll be better informed if I'm ever faced with a similar problem.
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Old 07-14-2012, 07:08 PM
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Default Re: Briggs and Stratton, Intek Misfiring

Quote:
Originally Posted by sprkplug View Post
In that light, may I ask how you were able to wire up the fuel solenoid incorrectly, and in such a manner that it only had a couple of volts feeding it? I certainly don't know what application your engine was used on, but I'm wondering where such a low voltage exists on a typical setup for this engine?

Also, there are two wires feeding into the fuel solenoid, one is a fixed ground and the other a switched 12 volt power source. Why was it necessary to rewire the solenoid, had the engine suffered wiring damage?

Again, not trying to pick on you at all, I've had instances where I've spent a few days trying to sort one out, so I've been there! Just want to understand your specific situation so I'll be better informed if I'm ever faced with a similar problem.
Well just to give you guys the background story..... I bought an old Toro Wheelhorse but the engine turned out to be totally stuffed. I liked the mower but needed to know if the Toro Transaxle was working before investing another engine. The Briggs was fitted in an MTD Yardman which I was recently given because it has transaxle problems. So I decided to transplant the Briggs from the MTD to the Toro. The Briggs wasn't running quite right in the MTD but it would prove the point. Once I got into the Toro it got a lot worse but I had no idea that a wiring issue would cause the symptoms I had. Maybe because I've never worked on a Carb with solenoid before

Anyway the electrical connecting plugs where quite different (between the 2 mowers) so I had to make some conversions which proved more complex than I had imagined lol!

I haven't trace the wrong connection I made but my guess it's getting it's positive feed through one of the Toro's relays or dash lights and that's why it only has a couple of volts on it.

BTW along the way I have discovered that Briggs have some real issues with cams and have discontinued the one on my engine. So to replace the cam on my engine I have to replace the hole block. It's stuff like this (and the overall build quality compared to a Kohler) that will make this the last Briggs I ever own

All the best.
Neo
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Old 07-14-2012, 07:21 PM
sprkplug sprkplug is offline
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Default Re: Briggs and Stratton, Intek Misfiring

As the late, great Paul Harvey would've said: "Now you know, the rest of the story".

I would guess that an issue with the ignition wiring played a part in this scenario.

The Briggs Inteks are consumer engines, similar to the Kohler Courage series. Kohler builds the Command as a premium engine, the same as Briggs produces the Vanguard. Both built to meet a certain price point.
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Old 07-15-2012, 03:48 AM
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Default Re: Briggs and Stratton, Intek Misfiring

Hmmm .... thanks for that. I know the Kohler Command engines But might check a Vanguard sometime too

Anyone got any ideas on the "splatter, hesitates and blows heavy black smoke" issue?


All the best.
Neo
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Old 07-15-2012, 06:35 PM
Road Torpedo Road Torpedo is offline
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Default Re: Briggs and Stratton, Intek Misfiring

A loose valve seat.
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Old 07-15-2012, 08:54 PM
Motormowers Motormowers is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Sounds like a bad cam. The exhaust lobe is worn down and not letting the valve open to the point it releases the exhaust pressure from expansion so when the carb is full throttled fast the excess combustion pressure has to go somewhere so it goes out the intake and through the carb causing drawn fuel through the emulsion tube to puddle in the venturi and flood the engine on the intake cycles. Slow throttle response wont do it as much. Remove the valve cover and turn the engine over with the spark plug out. See how much rocker movement you have on both rocker arms. Should be equal when valves are adjusted properly. When the cam gets real bad it will pop badly out the carb on hard throttle. Gotta love those Inteks.
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Old 07-15-2012, 11:29 PM
Road Torpedo Road Torpedo is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Plastic has no place inside an engine
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Old 07-16-2012, 03:00 AM
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Default Re: Briggs and Stratton, Intek Misfiring

Quote:
Originally Posted by Motormowers View Post
Sounds like a bad cam.....
See how much rocker movement you have on both rocker arms. Should be equal when valves are adjusted properly. When the cam gets real bad it will pop badly out the carb on hard throttle. Gotta love those Inteks.
I found it hard to measure the travel of the push rods (with the digital verniers I have) but I did measure the valve stem drop.
  • Cyl 1, Inlet 6.95mm, Exhaust 6.96mm
  • Cyl 2, Inlet 7.02mm, Exhaust 6.76mm

I'm guessing these look quite consistent and healthy? .... What do you think?

Is it possible to check for a loose valve seat?... without taking the head off?

Also I can get a new Carb for around $135 delivered. So I'm thinking of just swapping it out and be done with it.... Although I can't confirm it's the carb really can I?


All the best.
Neo
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Old 07-16-2012, 08:43 AM
sprkplug sprkplug is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Sounds like the cam is just fine.
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Old 07-17-2012, 12:46 AM
Road Torpedo Road Torpedo is offline
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Default Re: Briggs and Stratton, Intek Misfiring

Well...you eaither have a crappy carb that is crappy no matter WHAT you do or HOW you repair it...yes it does happen OR...............................................a loose valve seat or warped valve or bent valve.
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Old 07-17-2012, 07:35 AM
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Default Re: Briggs and Stratton, Intek Misfiring

Hi Gents,

Will this two part test work????

If I run the engine and remove one plug cap, rev it up quickly (test 1), then replace that cap, then remove the other cap and rev it up quickly again (test 2).

My guess is if I get the same black smoke with either of caps off then I'm looking at a carb problem. But if I get black smoke on just one side (of the two) then I'm looking at a valve problem, on that side.


What do you think?


All the best.
Neo
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Old 07-17-2012, 03:51 PM
Road Torpedo Road Torpedo is offline
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Default Re: Briggs and Stratton, Intek Misfiring

I assume this is a two cylinder. If it is, what i have done in the past to diagnose a cylinder trouble is to pull a plug wire while it's running.

If the engine all of a sudden dies out when one of the wires are pulled from possibly the only cylinder keeping the engine running, it will die or near die or atleast run worse with alot of black smoke.
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Old 07-18-2012, 02:44 AM
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Default Re: Briggs and Stratton, Intek Misfiring

I've been reminded that it's a twin barrel carb so the above won't work....

Ok, Take 2.......

If I run the engine (for a short time) with a spark plug out of each/either cylinder could that harm anything?

And/or if block off the inlet manifold (at he cylinder head) with a thin sheet of metal and have the spark plug out could that harm anything?

Could these tests help me point to the smoky root cause?

And I want to have another go at cleaning/soak that carb. I've read that removing all non-metal bits and boiling a carb in water/lemon juice does wonders???.... Didn't think I had much to loose as I'm considering buying another Carb anyway.

All the best.
Neo
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