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Mike_H

Trouble starting...

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Mike_H

Having an issue getting my old girl fired back up. I "bought" a 1977 7016H basket case for a case of beer. The tractor itself is in good shape, but the engine lost ignition, and PO tried to get it running, but lost interest. When I picked it up, I got the tractor, the engine, and three boxes of parts. I rebuilt the engine (with all Briggs stuff) and am at the point of trying to start it again. Just for clarity, I'll list what I've done...

Point are gone...in its place is a new mega fire ignition module. I was fighting to get spark with this until I flip-flopped the leads. The primary wire from the coil is connected to the negative side of the mega fire module, and the positive side goes to ground.

The coil is new. PO cooked the old one while troubleshooting.

Carb is rebuilt with all new parts.

New piston, rings, valves. Intake valve guide was replaced as well.

New plug, fuel lines, gaskets, battery, etc.

I have about 120 psi compression, my indicator says I'm getting spark, and I believe I'm getting fuel...the spark plug smells of it, and I am getting backfires.

Leads me to my question...While trying to start yesterday, I would crank it while its choked and I would get a loud backfire through the muffler, then a small pop a cycle later, then nothing. I also got a few pops through the carb.

I'm thinking the timing is off, but I know the flywheel key was in good shape when I put everything back together. Kinda scratching my head on this one. Any ideas?

Oh, one more thing...How fast should the starter/generator turn the engine over? Mine seems slow, and it will stall out the first time I try to crank. Hitting the key again seems to get it past the compression stroke, and once its spinning, there is no problem keeping it going...Is is possible the engine isn't spinning fast enough to fire up?

Thanks

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powerking_one

Mike,

I would suggest that the crank/cam timing is out and the previous owner didn't get it "right". As I recall when rebuilding a 300421 12HP in Landlord, the gear timing marks were very hard to see and align. With 120lbs of compression, that seems wrong also in that for a "healthy" C.I. Briggs single it should be more in the 90-100lb range.

My 2 cents worth,

Tom (PK)

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ReedS

A set of points would be helpful here as they could help verifying cam timing.(Points closed at TDC or very near TDC) You will need to verify that both valves are closed/ or are closing at the appropriate time, along with seeing the timing mark on the flywheel lining up to the coil.

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BLT
quote:Originally posted by Mike_H

Here is a video of her turning over...just want to verify my starter/generator is spinning her fast enough...


id="quote">
id="quote">That doesn't sound bad turning over. I have a 101 with a 12 HP that starts OK turning over slower. Did you pull crank or cam out of engine during its rebuild?

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Mike_H
That doesn't sound bad turning over. I have a 101 with a 12 HP that starts OK turning over slower. Did you pull crank or cam out of engine during its rebuild?

id="quote">

I did pull EVERYTHING out. The PO had not torn into it as far as I have, and I wanted to ensure it was in good shape, as I want this thing to run for another 35 years. I'm almost positive I checked the cam to crank timing marks, and they lined up...there were two dots that meshed. The service manual I used (downloaded from this site) was kinda confusing on the whole timing thing though. When I roll it over by hand, the motion appears correct for a 4-stroke engine (ie, the intake valve is open on the 1st downstroke and closes as the piston begins the compression stroke, both are closed on the power stroke, and finally the exhaust valve opens).

I think I'll pull the head, and roll it over by hand. I should be able to look into the shroud, and see the magnet coming past the coil at the right time...or not.

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fishnwiz

Are you sure that you did NOT get a partial shear of the flywheel key on the 1st backfire? It does not take much of a partial shear to put the timeing off.

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Mike_H
quote:Originally posted by fishnwiz

Are you sure that you did NOT get a partial shear of the flywheel key on the 1st backfire? It does not take much of a partial shear to put the timeing off.


id="quote">
id="quote">No, I'm not. Its real difficult to see anything timing related on this beast without getting the engine out of the frame. I haven't figured out how to pull the shroud without yanking the dang thing. I've had it in and about about 3 times now...

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ReedS

Do you have a photo of the new coil? Where was the coil purchased and what was the part number on the coil? I ask this as the coil should be p/n 298968. I have seen more than my share of incorrect coils installed on these engines, it can be confusing as a number of times I have seen the Magnetron coils advertised as "replacing" the point type coils which is not true. They produce spark on every revolution, though it is incorrectly timed, hence your backfires. The magnetron coil can be used if the flywheel is repolorized. I suspect your coil to be incorrect.

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msiebern

I have installed several of the megafire style modules, and have had a couple of Briggs that would backfire. I put in a set of points to eliminate it firing every on every stroke. Both of the engines responded to this setup and now start very quickly and run very smooth. Before pulling it all apart, it would be an easy check by just adding a set of points and running the megafire through them. Just my 2 cents worth.

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Mike_H
Originally posted by msiebern

I have installed several of the megafire style modules, and have had a couple of Briggs that would backfire. I put in a set of points to eliminate it firing every on every stroke. Both of the engines responded to this setup and now start very quickly and run very smooth. Before pulling it all apart, it would be an easy check by just adding a set of points and running the megafire through them. Just my 2 cents worth.

id="quote">Mike,I pulled the points plunger, and plugged the hole. Can't do that. Reed,I am 90% sure I have the correct ignition. It definitely NOT a magentron (i.e. it does not have the "extra" stuff that goes with magnetron). I ordered it from a local farm store here, but this project has taken me a while to get finished. The coil looked just like the one that came out, just less "crispy" :D It had one wire that goes to the points and the spark plug wire.

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ReedS

Well there aren't too many options now, you could verify several things, static cam timing for one, valve closure, and static ignition timing. If all check out ok and your confident the mag is correct, the symptom is backfire or in other words incorrect spark timing. The only other thing controlling spark timing is the Mega-fire module. I've never used one so I can't speak for or against it, all my tractors run points and all run decent that way. There is also the Nova II module, I know they are essentially the same but perhaps a different brand module is the next thing to try since there's no going back to points easily. At worst if all else is good and ignition timing is still not correct you could go the magnetron route if going pointless is a must.

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Mike_H

I made a video tonight...I'll let you guys look at it...I'm thinking sheared key... Mechanically, it looks good. The engine seems to be doing the right things at the right time. Only thing I noticed is that the magnet in the flywheel is quite a bit past the coil when at TDC on compression stroke. I know the ignition event is supposed to happen before TDC, but I'm not sure how far. I'd say the magnet is 15 to 20 degrees past the coil at TDC.

Hopefully it will be clear to those of you who have much more experience than I.

Here is the vid..,

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Mike_H

Sheared Flywheel key for the win! I pulled the motor and the flywheel this afternoon, and sure enough, Ya'll were right.

20150314_131936_zps0xqyfxs8.jpg

Local Family Farm and Home had the Briggs OEM replacement 3 pack...picked that up, threw it on, and put the old girl back together. Started right up!

Now that the main hurdle has been cleared, I've got a couple other small issues to address..Leaky carb (I think its the fit of the venturi tube), my wiring harness is a mess, and my throttle linkage is not returning to idle correctly.

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