Questionhad this for ever, always ran ok. now it seems to have a weak spark. I've check the gap ( 30 thous ) and clean the points. won't start. I'm sure it is a weak spark (used my finger) that ought to tell you something ( ha ) I've never change anything, just wondering if it would be the points/condenser. guess thats about all there is. Any help would be appreciated. Thanks
Dave
AnswerDave
If you can put your finger on the wire and you get nothing that is 1 problem. I would get a coil and points condenser.Breaker point ignition - Possibilities are bad, dirty, corroded, or loose points or points that are grossly out of adjustment, a bad condenser, or a bad magneto coil. See the section:y) pulls on a spring which is attached to the 2nd hole from the top on the governor lever. For engines with no speed control, there is a fixed plate or tang to which the spring is attached. Some amount of adjustment is possible by bending this plate.
The carburetor throttle plate has several holes in it. The one that is probably used is that closest to the little cutout (which I can't show with ASCII art) and the tip of the throttle plate return spring. You can probably confirm this by looking for which hole has the paint worn off!
__ _
Open <-- / \ --> Close | |
|o=========. ,=======o| Top hole
\ O / '=============' | |
\_/ Carburetor +-- ===========o| Next hole
_ Throttle | | |
|o| Plate +-straight-+ | |
| | | | |
|o=====o---/\/\/\/\/\/o========== ---+ | |
| | Spring | |
| O | | |
Speed Control | |
or Fixed Tang Governor |_|
(linkages may cross) Lever | O |
+---+
See: Neil's Tecumseh Throttle and Carburetor Linkage Page for some slightly better diagrams. :)
Initial tests
Add a small amount of gas to the fuel tank - perhaps half a glass or so. Just enough to assure that it will reach the carburetor even if the mower is slightly tilted or jostled.
Inspect around the fuel hose and carburetor body for fuel leaks. If gas starts dripping from the air inlet or anywhere else, there is still a problem with the inlet needle and seat. Disassembly will be required.
Only a few seconds are needed for the gas to fill the carburetor bowl.
Assuming there are no leaks, install the air filter and reattach the spark plug wire or reinstall the spark plug. Attempt the normal starting procedure - prime if recommended.
The engine should start on the first pull! Immediately move the throttle selector to LOW if you have this option. Confirm immediately that it stabilizes at a reasonable speed - stop it quickly if it sounds like the mower is preparing for takeoff - your governor connections are incorrect or binding. If it runs at a fast speed with the speed selector set at LOW, the governor spring is probably in the wrong hole. Check it.
Listen and feel for any significant unevenness, surging, or other unusual behavior. Stop the mower, wait a few seconds, and restart. It should restart with a single pull without priming.
Mow for a few minutes. Stop the engine and confirm that it restarts without priming. Listen and feel for any indication of lack of power or other unusual behavior.
Go take a dinner break. Then confirm that the engine will now start - priming may be needed since it will now be cold.
Maintenance of point-type ignition systems
In most cases, missing or total lack of spark will be due to dirt, pitting, or corrosion of the points or a failure of the condenser. Timing may affected as well by excessive wear. The following procedures should restore the ignition system to good health:
First, test for spark. If there is a spark, try replacing the spark plug since this is the most likely cause of ignition problems. With a spark present, there could still be ignition system problems but this is much less likely.
You may be able to test the points to some extent if you can get to the wire that connects to the magneto or the STOP switch. A multimeter on the low ohms scale will the permit you to watch the opening and closing of the points.
If this confirms that the points are operating the condenser could still be defective, the breaker arm could be sluggish, or the point gap could be grossly out of adjustment.
To proceed further:
* Remove any trim pieces and the shroud/blower housing to access the flywheel, magneto, and points assembly under the flywheel.
* Check the flywheel magnet to magneto core air gap. While it is extremely unlikely that this increased, it is an easy test. The correct value is usually .015 inches but some engines use other gap spacings. A non-magnetic feeler gauge is best for this. If it is much larger than specified, adjust it and test for spark again.
* Remove the flywheel. See the section: Flywheel removal.
* Test the flywheel magnet. No actual strength is usually published but if it attracts a steel screwdriver from at least a 1/2" distance and seems strong, the magnet is likely fine. If it is weak (or missing, though this is mostly a theoretical possibility!), the flywheel will need to be replaced.
* Remove the cover over the breaker points assembly, if any.
* Inspect the points. There should be no serious pitting, corrosion, evidence of arcing or sparking. Nor should they be welded together!
If any of these problems are present, replace the points and condenser as well - a bad condenser may be the cause of the points failure it is not really possible to fully test it.
You can also test for electrical operation of the points using a multimeter on the low ohms scale while rotating the crankshaft (you will have to use the blade - careful) or operating the breaker arm manually.
Or better yet, just replace the points and condenser. The cost is minimal (probably under $5 for a rebuild kit) and you have already done most of the work.
* Note the mounting arrangement and remove the old points and condenser and install the replacements. Do not tighten the locking screws at this time.
Setting the point gap and ignition timing
Perform the following whenever the breaker points assembly is replaced or where a timing problem is suspected.
* Rotate the crankshaft so that the cam that operates the points is at the highest location and the points are wide open.
* Adjust the point gap setting to specifications using a feeler gauge. This is nearly always .020 inches.
* Set the crankshaft position. This is usually done statically and does not require a timing light (Darn!).
o On many engines including Tecumsehs, there is a timing dimension in the engine specifications. This is the distance of the piston below Top Dead Center (TDC) at which the points should just open.
While measuring piston position with a scale through the spark plug hole, rotate the crankshaft until the piston is precisely at TDC and note this distance. (There are special timing gauges for this purpose with lock screws to hold the setting but a little ruler will work just fine.)
Now, turn the crankshaft in the opposite direction from normal rotation (usually counterclockwise as viewed from the flywheel end) until the piston moves down .25 inches or so and then turn it slowly in the normal direction of rotation until the piston position is precisely at the timing dimension listed in your engine specifications.
o On some engines there will be timing marks on the flywheel and engine block or the manual may tell you to line up the one edge of the flywheel magnet with one of the magneto pole pieces.
The flywheel should be temporarily re-installed without tightening the nut.
Rotate the crankshaft until the timing marks are precisely aligned.
Carefully remove the flywheel without disturbing the crankshaft position.
* Adjust the timing. Loosen the locking screw on the points assembly. Rotate the points assembly until the points just open (use a thin piece of cellophane or a multimeter on the low ohms scale. Lock the position by tightening the set screw.
* Double check that your settings have not shifted.
* Replace the cover over the points assembly, if any.
* Reinstall the flywheel and associated hardware and tighten to the specified torque (30 to 33 ft-lbs). Make sure the cupped washer, if any, has its cupped-side facing the flywheel. (Defer tightening to full torque if the engine is not presently mounted solidly on the equipment. Just don't forget!)
* Check, and if necessary, adjust the magnet to magneto coil spacing using a non-magnetic (preferably) feeler gauge or shim stock (typically .015 inches though some are .005 to .008 inches, see your engine manual).
* Replace the shroud/blower housing and any trim pieces that were removed if no other servicing is to be performed on the engine.
