Author Topic: wont start  (Read 5294 times)

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Offline Boomhowar99

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wont start
« on: March 26, 2012, 12:49:26 am »
I rebuild two motors this weekend. Both identical 12hp flatheads. They both got the valves and spring kits. Cams are timed right and flywheel keys good. both getting fire and fuel. One started right up and runs good the other one just backfires and wont start. Ive rebuilt plenty of motors and never had this problem and need help. Any advise would be appreciated greatly.
James Urhahn

If it aint breaking then you aint running it hard enuff!

Offline russell jennings

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Re: wont start
« Reply #1 on: March 26, 2012, 01:47:56 am »
i would start with the basics,fuel,air,compression,spark......try to single one out then go to the next.i have had new out of the box spark plugs not work or miss fire! start small then go bigger.
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Offline Boomhowar99

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Re: wont start
« Reply #2 on: March 26, 2012, 02:30:12 am »
I got all of them. This is this first time Ive ever had a motor ported and polished and head polished. could it just be carb adjustment not right with the porting not letting it start?
James Urhahn

If it aint breaking then you aint running it hard enuff!

Offline russell jennings

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Re: wont start
« Reply #3 on: March 26, 2012, 10:00:57 am »
it is possible to be over ported,i learned that the hard way with a 340 rotax snowmobile race motor. you may need to fatten up the starting or low side of the carb. what does your spark plug look like?? wet or dry??
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Offline Zippy 13N

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Re: wont start
« Reply #4 on: March 26, 2012, 10:09:33 am »
I had the same problem with one of these motors last year.  And a guy told me to check the spark plug gap.  Wouldn't thank it would make a difference but he did it to his and it fixed the problem.  Might not fix it for you but its worth a shot.  Just my  :twocents:
Derrick Nichols

Offline bountyhunter

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Re: Re: wont start
« Reply #5 on: March 27, 2012, 09:03:25 am »
Find prob yet

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Offline Boomhowar99

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Re: wont start
« Reply #6 on: March 27, 2012, 10:45:50 am »
No havent had time to mess with it yet. Been really busy with work. It will be later this week or this weekend before I can give it a try again.
James Urhahn

If it aint breaking then you aint running it hard enuff!

Offline saltyAMF

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Re: wont start
« Reply #7 on: March 27, 2012, 06:30:04 pm »
usually when stuff backfires and wont start its 180 out timing wise
joshua "MEAT" coleman

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special thanks to MY NELMRA GUYS, George Herrin, EC DISTRIBUTING, E3 spark plugs,and my wife for putting up with it all!

Offline GoberRacing71t

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Re: wont start
« Reply #8 on: March 27, 2012, 09:05:20 pm »
If the engine is on the mower (or even if it ain't) take the spark plug out and try turning it over by hand. When mine was doing that the belt had jumped off of the clutch pulley and was dragging. This was causing the starter to turn it over too slowly to start and it was also back firing and getting the starter hot. Like everyone told me...it is usually something so simple that you just over look it.

Yes, I felt kind of dumb! :tard:
Tony Gober
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Offline brokemotor

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Re: wont start
« Reply #9 on: March 28, 2012, 12:01:26 am »
If it backfired , check the flywheel key.
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Offline Boomhowar99

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Re: wont start
« Reply #10 on: March 30, 2012, 03:18:08 am »
Ok. I have fuel and fire. Cam is on time. Flywheel key is good. All I have is backfiring still. Went over everything several times.

The starter on it is off a 8hp flathead, could it be spinning it the wrong way and not letting it start?
James Urhahn

If it aint breaking then you aint running it hard enuff!

Offline The Tank

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Re: wont start
« Reply #11 on: March 30, 2012, 07:47:54 am »
Ok. I have fuel and fire. Cam is on time. Flywheel key is good. All I have is backfiring still. Went over everything several times.

The starter on it is off a 8hp flathead, could it be spinning it the wrong way and not letting it start?


The starter spins the same way. If you checked all that and everything was fine then it sounds like you have a valve problem.
Frank "The Tank" Woods

AKA "The Intek Outlaw"

Offline Zippy 13N

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Re: wont start
« Reply #12 on: March 30, 2012, 10:40:01 am »
The starter spins the same way. If you checked all that and everything was fine then it sounds like you have a valve problem.

Yep sounds like you need a valve job, or possibly a bad valve.
Derrick Nichols

Offline Jim Knutson

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Re: wont start
« Reply #13 on: March 30, 2012, 10:50:52 am »
Check to make sure you dont have the coil on upsidedown.
If you quit when you're behind, you will never win.

Offline Smowkin Joe

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Re: wont start
« Reply #14 on: March 30, 2012, 11:54:10 am »
Check to make sure you dont have the coil on upsidedown.
This one is surprisingly easy to do, and then overlook. :doh: :doh: :doh: :doh:
Joe Erlenbusch