42A707 Briggs Runnig Weak!

AlbertiAugust 5, 2014

Hi All,

I'm a new member on GardenWEB with my 1st post today!
I just read many posts regarding the 42A707 18HP.
The discussions that seem to relate to my problem talk about hard starting followed by erratic running, as if on one cylinder. Some folks point to the compression release mechanism, if indeed there is one on my machine.

Please bear with me. All of you know the frustration we go through till the problem gets resolved.

What I've done:
Rebuilt the carb & 3-bolt fuel pump with a Briggs kit.
Cleaned EVERY carb passage with a .012" spring steel wire then fluid & air. New plugs, too.
Hoses are new, clean tank & fuel filter with fresh gas.
Pulled the flywheel to clean & inspect. All good.
Choke plate closes & opens fully.

I keep a clean engine, good fuel & regular oil changes, etc.
Cooling fins & shrouds are always kept clear.
At this point it starts hard, will run at an idle but won't tach up on full throttle, then dies. Choking doesn't help, only to start. This condition occurred suddenly, however, this season it did seem to be slow to rev up (about 2-3 seconds) once it started. Sounds (and smells) like it's running rich.

Still a hard start and sounds like it's running on one cylinder, however when I pull either plug wire it dies, then a loud pop. Engine will not develop enough power to engage blades or hydrostatic drive.

Hope there is a simple fix that I've overlooked.
I'd appreciate the forum's help on this one.


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some thoughts:
1. this uses the "easy spin" starting. there is not mechanical compression release. check valve adjustment.
2. check the compression with the regular style compression tester. Usually, these have around 90psi.
3. If compression is weak on one cylinder, pull the cylinder head to check for a loose valve seat.

once the above is verified to be ok, examine the fuel system. From your description, I have the impression there is not enough fuel. On older equipment, the fuel lines deteriorate and the fuel pump is unable to draw fuel from the fuel tank. Air is usually drawn in from cracks in the fuel line and around the clamps on fuel line connections. Also, the pulse line from the crankcase may need attention. Make sure the o ring on the oil filler tube is ok.

    Bookmark   August 5, 2014 at 11:41AM
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Hello Bluemower,

Thanks for your prompt reply.

It appears (to me) the good news is I won't have to mess with a compression release problem.
The bad news says I may need to pull heads & do the valves.

I don't have a compression tester. Is there a clever way to compare cylinder pressures for a poor farmer like myself?

With regard to sufficient fuel supply, I've done the checks/repairs as follows:

1. replaced fuel line & clamps
2. cleaned sight glass fuel filter
3. pulled fuel line off carb & let gas flow free from full tank
4. replaced pulse line & clamps from engine to carb
5. rebuilt carb & fuel pump
6. replaced o-ring at filler tube end (no oil weeps there)
7. removed pulse line at carb, cranked engine & can feel a slight pulse hose end

I guess I need to fashion a compression tester to see if I have the 90psi you mentioned.

Thanks again for your help.
Don't hesitate to send anything further I may need.

    Bookmark   August 6, 2014 at 7:27AM
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