torinwalker Posted August 29, 2003 Posted August 29, 2003 We're all owners of old, old machinery. Is the tired engine on your tractor not performing the way you think it ought to? Hopefully this discussion will shed some light on tuning tips that you can use to bring your engine back up to peak performance. Most engine manuals tell you the same old trick: Turn your throttle and idle jets all the way in (soft stop) and turn them out to some prescribed number of turns. This will allow you to start the engine and warm it up. When the engine is warm, apply full throttle and turn the throttle jet in until the engine slows down, then out until it slows down, then position it midway between the two points. Next, throttle down to idle (and hold it there with your finger, at some RPM - usually 1200), then follow the same procedures for the idle jet. Voila! Your engine is perfectly tuned. Yeah, right. There are a dozen other factors that play a part in the tuning process - everything from gas type and gum in the carb to carbon on the plug, valves, and cylinders. The question is, what symptoms associate with what causes?
Kent Posted August 29, 2003 Posted August 29, 2003 I fine tune mine (carefully) with the engine at at least 3/4 throttle and the mower deck engaged.... Seems to work for me.
torinwalker Posted August 29, 2003 Author Posted August 29, 2003 Since this is my very first engine (that I have restored and attempted to tune), I have quite a bit to learn, but I followed one very simple principle: If I can restore the component (well, all of the components) back to the way they were when the engine first came off the assembly line, my engine should haul like a starving ass to the carrot. My engine, a Briggs and Stratton 10HP (243431) is almost there. It has come from not starting at all, to starting and running reliably. It just hiccups while accelerating or decelerating, and it's not quite perfect while running constantly - yet. A few things I noticed while restoring my engine: - The head gasket was worn in spots - could permit a loss of compression - The carb was gummed up, especially near the idle jet inlet, and some of the jets turned (were worn) too easily. The throttle shaft also had some play. - The plug was the wrong type - close, but not perfect. - The cylinder head and valves were coated in a thick brittle coat of carbon. - The coil was shot, and I bent the points before I realized just how important and sensitive they were! The learning curve was a little steep at first - I was playing with something I had never done before, and I let the unknowns of the mysterious little engine blind be from standard, tried and true, logical diagnostics. For example, carbon on the plug doesn't seem like an obvious problem when you've just installed a new coil (backwards). You tend to focus on what you think is the problem instead of following a logical approach. Temperature also plays a big part and makes it more difficult to diagnose the problem area - at least, when you're a newbie. After a bit of trial and tribulation, temperature seems obvious. Little does one realize just how carbon on the valves and a hot engine wreak havoc on engine smoothness. So, I began replacing and cleaning to bring my engine back to "factory specs", but it didn't turn out the way I had hoped. It still runs rough, and occasionally spits flame, but the battle isn't over. So far, I have replaced the coil and was extra careful with the spacing. This ensured I get a good, strong spark. It was also the pointless version which helped eliminate one touchy variable from the mix. Next, I rebuilt the carburetor and replaced the jets, float spring, main gasket - I haven't replaced the worn throttle shaft bushing yet. Before I started the engine, I replaced the head gasket and crudely scraped thick black soot from the piston head. The value seats looked clean enough, so I didn't touch them. Some carbon was left, as it was a quick hack job. I wasn't sure if a perfectly clean and shiny steel surface was necessary, since a few bad turns on the carburetor was going to quickly mess it up again. The spark plug was the most innocuous, but the most troublesome of the group. A new spark plug went in and immediately turned black with carbon. At first, I shrugged my shoulders and kept blaming the coil for lack of spark. How little did I realize that the carbon conducts the spark to ground - and I knew that carbon is conductive! It just failed to dawn on me. The carburetor gasket was so old that it stuck hard to the metal. I had to shave it off with a razor blade, and I wasn't albe to remove all of it. After all that, and following the standard tuning procedures, I had a running engine (and a running tractor!) With the engine in it's present state, I am able to get it to run fairly reliably. It's not perfectly smooth, but I can fine-tune the throttle jet until it rarely coughs or spits. It's suprising how much the engine performance will change with only a slight turn of the throttle jet. There are a few things I need to do before I can get the engine running perfectly: 1. Re-clean the cylinder (piston, plug, valves) and remove any carbon that could contribute to premature firing. 2. Re-re-build the carb - double check to remove the residual gasket, and replace the throttle shaft bushing to get rid of the play. I'm not sure which of the two will have the most dramatic influence on RPM stability under static load - the vibrations of the throttle shaft (or so I'm told) will alter the ability to "fine-tune" the engine. Though, carbon deposits causing premature firing could also significantly alter stability and power. Torin...
torinwalker Posted August 29, 2003 Author Posted August 29, 2003 Checking for spark: A gentleman from Briggs and Stratton was kind enough to provide this very informative tidbit concerning coils and spark plugs. I was having trouble getting spark from a new coil I installed. I suspected the gap between the magneto and the flywheel, and I suspected the magnet on the flywheel itself, but I failed to look at the plug. For some who have never fiddled with an engine (but who want to), this will be very informative: Torin... Thank you for contacting Briggs & Stratton E-Customer Support! Let's look at what is required to create a good spark. Flywheel: The flywheel magnet must generate a sufficient magnetic field to start the chain of events in motion. A fair test is to hold the flywheel on edge with the magnet facing up. Place the blade of a 10" #3 (1/4") straight blade screw driver against the magnet. Release the screwdriver. The magnet should have enough strength to hold the screwdriver straight out. If we pass this test, assume the magnet is OK. Rotational speed: Remember speed is a factor. The engine must be pulled over at a minimum speed of 250 RPM before the coil will even think about firing. Thick oil on a winter day or a heavy parasitic load may cause problems. Customers come into play here as well. Shorter or elderly individuals may not have the leverage or strength required to reach the RPM necessary to activate the Magnetron's electronics. Spark Plug: The spark plug is a major element of the equation. A new spark plug may require around 10,000 volts to jump a .030" gap when the engine is cold. This drops to just 4,000 when the engine is hot as electrons are more easily emitted from a hot surface. That's one of the reasons the old vacuum tubes in radios had to warm up before the radio would work. Electrons are also more easily emitted from a sharp edge than a round one. A spark plug begins to require more and more voltage as normal wear causes the edge of the center electrode to become less defined. And finally, an internal short or carbon/oil fouled plug simply shunts the high voltage burst straight to ground, resulting in insufficient spark or no spark at all. Ignition Coil: The ignition coil is probably the easiest thing to check and therefore the first thing to check when embarking upon ignition system troubleshooting. Install the Briggs & Stratton spark tester, part number 19368, between the high tension lead and a good engine ground. Spin the engine over (at least 250 RPM) and watch for spark in the tester window. As simple as it seems, this is a fairly comprehensive test. The tester electrode gap is .166" wide. Those wise in the way of electrons have calculated that it takes around 13,000 volts to jump this gap. We need 10,000 to jump the gap on a cold spark plug. Add it all up and we have voltage to spare. Engine quits while running? Hook the tester up in line with the spark plug and start the engine. When the engine quits, monitor the window. If spark is present, the problem is not in your ignition coil. By the way, this test stresses the coil well beyond the demand it would see in operation. Think about it. We're asking the coil to build enough voltage to jump TWO gaps - the tester as well as the plug. If your engine starts and runs OK cold and hot, you've got a healthy ignition coil. Note: because Magnetron Ignition coils depend on the flywheel magnets to operate, they will function even if the flywheel key is sheared - unlike breaker point systems. One additional test you can perform: check the impedance (resistance) of the secondary circuit at room temperature. Hook an ohmmeter test lead to the spark plug terminal of the high tension lead and another to the lamination stack (ground). Your resistance reading should range between 2,500 and 5,000 ohms. If infinite (no continuity), an internal open circuit exists. Replace the coil. If infinite but the engine runs, your problem is an internal break of the high tension lead, a poor attachment of the spark plug terminal or improper mating of the high tension lead to the coil. A pin within the coil body, skewers the lead. If the pin does not contact the wire core, there will be no continuity. The coil will often have enough available voltage to jump the gap, so you see spark. The internal arcing that occurs within the high tension lead will eventually create enough resistance that ignition system performance will suffer. If your resistance reading is much lower than 2,500 ohms, an internal short exists. Replace the coil.
torinwalker Posted August 29, 2003 Author Posted August 29, 2003 I wonder, is there an inexpensive tach available that will tell you how fast your engine is rotating? I was working out a voltage divider to provide a 5V pulse from straight off the sparkplug. That way, I could determine the highest RPM while turning the throttle jet. The ears are great for that, but hey...why not add a visual aid for increased accuracy? From spark plug ----+ | / \ 2.999M - 0.25W / | +----> 5V to freq counter, oscilloscope, etc. | / \ 1k - 0.25W / | to chassis <--------+-------> to counter gnd. I'm sure there's a better way, but I have a counter already, and the circuit costs $0.10 to build. How do you guys tune? By ear only? Torin...
powerking_one Posted August 29, 2003 Posted August 29, 2003 So, what's your point? We (club members) probably didn't know that the Magnetron (or any coil for that matter) depends on the flywheel magnets to operate. Tom(PK)
torinwalker Posted August 29, 2003 Author Posted August 29, 2003 You just made my point. If you (club members) don't know how to repair or tune your engines, this conversation could provide insight. How many people find tractors that have dead, or poorly performing engines? How many tractors obtained could only be a coil or a spark plug or a carburetor rebuild away from fully operational? More notably, how many tractors have been abandoned because its owner had no idea how to diagnose a simple engine problem? Torin...
Dadsy98 Posted August 29, 2003 Posted August 29, 2003 For about twenty dollars there is a vibrating tachometer (Trysit Sirometer) available at your Briggs & Stratton service. B&S part number: 19200. Foley-Belsaw also has one for $18.50 part# EGR5978521 I got one awhile back and it's not too tricky to use. Foley- Belsaw has an inductive tach test meter for $69.95 part# EGR5955481. it looks handy to me. I tried using my Fluke 8060A on the negative side of the coil. Didn't give me a usefull read out. Steve
jkmustang1 Posted August 29, 2003 Posted August 29, 2003 My B10 was put away because the points went closed and would not reopen. :) That's what the original owners nephew told me the day of the sale. It was taken to a shop and they could not get it running so it was put up and another tractor was bought. To me it sounds as though the plunger broke. Now that I have a job and will have a little tractor money again. I will start getting the things needed to make it run. It was put up so long ago the original battery although junk is in the box. I am sure there are a lot of tractors like my B out there.
RayS Posted August 29, 2003 Posted August 29, 2003 I don`t see how it would run right using a magnetron coil with out having the fly wheel repolarized. Most Briggs dealers will tell you that you have to get the flywheel repolarized to use the pointless ignition. I put one on before and it would run but not very good. I put the right coil back on it and the trigger module and haven`t had a bit of problems. Ray
JimV Posted August 30, 2003 Posted August 30, 2003 I have done several coil conversios on old briggs engines and have never had an engine that I couldn't get tuned well.I really don't think it's got to be that technical.I had an old sportster that I could get to kick over with one or 2 kicks every time. A little trial an error is usually all you need. I have seen alot of club members tractors running and they all sounded pretty smooth, even the ones the smoked. Clean points and the right gap will usually do the trick unless you have deeper problems like carb settings sticky valves plunger problems are a different story.
torinwalker Posted August 30, 2003 Author Posted August 30, 2003 JkMustang1, It looks like you could still repair that engine with the same coil I used. It has a trigger built into the leading edge of the coil laminations (there is a cylinder side and a "this side out" side. Don't make the same mistake I did and install it backwards...) As the magnet sweeps the coil, the electronics inside (I dunno... a zener configured to avalanche?) trigger the spark, obviating the points altogether. I would worry about that little pin that goes in and out. I wouldn't want that thing swimming around inside while the motor is running. RayS, I read that engines older than 1952 used a different material for the magnet and lost their strength after a few years. More modern engines have none of those problems. As far as repolarising, don't you mean remagnetize? Torin... P.S. Ahhh... that's better. I had hoped this kind of conversation would spark up!
patrician12 Posted August 31, 2003 Posted August 31, 2003 I find 90% of the running problems are carb related.Most tractors are only used 5-6 months a year and occassionally in snow.The gas gets gummy and under those welch plugs in the carb you will find most your problems.Stens sells these plugs so it is not a crisis. Here is a good trip.I just picked up a Ward's Gilson tractor with a 10 horse Tecumseh on it that has been still for years.The gas tank I flushed,changed the fuel hoses,soaked the carb in gunk and rebuilt it.The engine started well but runs erratically,hunts,puffs etc.Bad points???Should I take off the flywheel and check?NO!Here's what to do.Get a can of propane with a valve and a 1/8 inch. hose.This is the kind the hardware store sells for plumbing.I sure everybody has one you guys are all handy.Shut the fuel off to the carb,put the hose in the air horn of the carb,open the valve to the propane and start the engine.If it runs perfect or near to it you need a carb,a cleaning or a main jet etc.But in short order you didn't have to check points.I don't know about you guys but everytime I get a tractor on the cheap that doesn't run except for one time it was carb problem.In most respects these carbs are close to Holleys carbs in the fact that metering needles and jets use o rings and gaskets for seals and this is there weak point.Even the larger carbs off the 16hp single cylinder Briggs engine that look like they came off a car are of this weak design.They all monitor fuel poorly and leak gas(even when new).
torinwalker Posted August 31, 2003 Author Posted August 31, 2003 Patrician, I have to agree. The carb (and possibly some carbon in the cylinder) is the number one reason for this instability. I'm going to rebuilt my carburetor again today to remove the residual gasket I spoke of earlier, and to change the bushing on the throttle shaft. I'll let you know how much closer it gets to OTS (Off the shelf) performance. Torin...
patrician12 Posted August 31, 2003 Posted August 31, 2003 These carbs are of terrible quality.You're correct, how do you deal with worn throttle shafts!It would be a great advance if all the carbs were like the ones used on my twin cylinder Briggs motors.Very much like automotive bowl type.
torinwalker Posted August 31, 2003 Author Posted August 31, 2003 You do what I just did. You use a screw extractor and you pull the bushings from the carb body. You then press-fit new ones in their place, and if necessary, install a new throttle shaft. (Mine was fine.) The result was actually quite suprising. Now that the vibration from the engine doesn't jostle around the throttle, it's more steady, and the engine is more steady. I knew that was going to do the trick!!! Unfortunately, I only replaced one of the two bushings. I'll order another and install it next week. That should reduce the rough running even more. Now all I have to do is clean the head and valves to remove that pesky carbon, and it should run very smoothly. You're right. These carbs ARE crap. My sister's car has a very nice injector/carb hybrid (I don't know if it's a hybrid, really). Instead of using a venturi to draw gas from the long stemmy thing, they use a high pressure nozzle (an injector) to inject aerosoled gas into the carb body. The pulsed fuel injection is electronic, so I doubt it would be a better solution. Oh well. What's so strange about the car-like carbs on the larger 16HP engines? Torin...
RayS Posted August 31, 2003 Posted August 31, 2003 Repolarize or remagnetize its the same process. Briggs started using the magnetron around 1982. Pretty sure that everything before then would have to be repolarized. I tried the magnetron on my HB 212 and it wouldn`t work. My dealer told me that I would have to send it in and get it repolarized if I wanted to use the magnetron, so I use the magneto and a trigger module. Briggs has a address where to send a flywheel for repolaring but I am not sure what it is. There is tons of information on this archived on this site and the address as to where to send is also archived somewhere. Tiny Tach also make a very acurate tach that is inexspensive. ray
torinwalker Posted September 1, 2003 Author Posted September 1, 2003 Oh, I see what you're talking about now. You're talking about the trademarked product "Magnetron". I was mistaken. I was using a magneto with built-in trigger module, not a Magnetron (tm) coil. My apologies. You're probably most definitely right. What I was referring to before with respect to not having to send in the flywheel concerned the strength of the magnetic field. While I was rebuilding my engine, I had trouble getting a strong spark and suspected a weak flywheel magnet until the guys from B&S told me it wasn't possible for such a new engine - he said the magnetization problems were corrected after some time during the 1950's. Beyond that date, the magnet should be strong enough to last for well beyond the lifetime of the engine, even after harsh vibration and heat which would have destroyed earlier magnets. Torin...
Recommended Posts