Governor fault, small 2-stroke generator

Subject: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 18 Aug 07 - 10:26 AM

Long shot, but does anyone know about the adjustment of governors on small 2-stroke generators (Yamaha, 500 watt), and governor faults?

Mine was tending to hunt (rev up and down) and I took it to repairers who just screwed the governor up until the engine ran flat out - result, far too many volts. The governor is operated by a lever coming out of what I think is the crankcase but it could be an extension of it. The lever is pulled in one direction by a spring anchored to an adjustable plate, and the position of that plate is controlled by the governor adjustment screw. The end of the lever has a push-rod that pushes the throttle butterfly open (via a cranked arm). The direction the spring pulls the arm opens the throttle.

Something inside the crankcase (or the extension of the crankcase) pulls the lever in the other direction to close the throttle butterfly.

Well, I've solved the over-revving and excessive voltage output by screwing the governor adjustment screw out so reducing the tension on the spring. But now the hunting is back.

I understand in theory how "flywheel" governors work - more revs, more centrifugal force, arms rise and reduce throttle - but I don't know whether this is a flywheel governor. There is I think another sort of governor used on 2-stroke engines - that is operated by crankcase depression. Walbro carburetters use crankcase depression and its variation to operate a little fuel pump on chainsaw hedgetrimmer and strimmer engines that need to work at any angle.


Does anyone know how crankcase depression governors work?

Or has anyone any other ideas about the hunting? The carburetter has NO mixture screws to adjust as far as I can see, and that is a first as far as I know. Every other 2-stroke I've ever taken to bits has had 2 mixture screws (one for idling mixture, and one for full-throttle mixture) and a throttle stop screw to regulate the idling speed. I have got a stop screw to limit how much the governor can close the throttle, and it's already all the way in so stopping the governor closing the throttle too much

Subject: RE: Governor fault, small 2-stroke generator
From: gnu
Date: 18 Aug 07 - 12:20 PM

I am sure Spaw or John or someone will be along and know what to do, but, in the meantime, a 2-sroke gennie? Gosh, that's the first time I have ever heard of one. And, you say there are no mix screws on the carb????

So... here's the number one dumb question. Can you plug the oil feed and put mixed gas in the tank? And , here's the dumb reasoning. If she's hunting, perhaps it's the constant oil feed rate screwing it up?

Subject: RE: Governor fault, small 2-stroke generator
From: gnu
Date: 18 Aug 07 - 12:25 PM

Oh yeah. I assume you have cleaned ALL filters (my old man always said, start with the easiest and then the cheapest "link"). A dirty air filter is the easiest and cheapest, and could easily cause your problem.

Subject: RE: Governor fault, small 2-stroke generator
From: Darowyn
Date: 18 Aug 07 - 01:22 PM

I guess that the crankcase lever is actually operating from a flap in the cooling shroud and responds to airflow from the fan blades on the flywheel, shutting down the throttle when the revs pick up.
I have a mower that works that way, and which has the non adjustable carb too, although it's a four stroke.
It had exactly the same hunting problem, and being unable to find anything that would act as a damper on the throttle so it would be slower in responding to changes, I eventually took the whole kit and caboodle off and fitted a lever throttle and cable so I can control the engine speed manually.
When I can be bothered, I shall add a needle valve adjuster to the main jet.
I should try cleaning the air filter before you get radical with it though- hunting is a classic symptom of rich mixture especially in two strokes.
Cheers
Dave
(Two-stroke guru as well as musician)

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 18 Aug 07 - 03:02 PM

It runs on mix - 50:1 so no separate oil feed. Almost all small gennies up to about 1.5kW are 2-stroke in UK

Air filter is brand new - and fault is present with or without air filter. Exhaust is fairly clean so mixture is probably about right, and there is no sign of four-stroking which is the classic indication of a slightly rich mixture on a 2-stroke.

Fan speed inside cooling shroud is the obvious idea Darowyn, why didn't I think of that? Mind you the lever seems to have a very powerful push for something on an air-flap.

I wonder if there is a flap damper or if there is supposed to be a friction damper or oil-filled damper (remember SU carburettors?). Much more dismantling required. The fault is a recent development, and when it started I too thought shit in carb or shit in airfilter. The additives in modern petrol are a real bugger for leaving deposits.

Governor is esssential on a generator where you leave it unattended and the electrical load can vary yet you need constant volts...

Subject: RE: Governor fault, small 2-stroke generator
From: JohnInKansas
Date: 18 Aug 07 - 03:53 PM

I don't have any direct experience with Yamaha, other than staring at the kid's bikes that have taken up space in my garage, and little with two-stroke engines in general. Anything larger than a chainsaw here generally has a 4-stroke.

Most small engines in recent applications may have an "idle" speed but are expected to run "full throttle" any time they're being actually used. The governor can only regulate the "wide open speed" with any accuracy at all. The ones I've seen usually do use an "airflow" sensor of some sort for this regulation. With this kind of governor, some speed hunting is generally unavoidable at light loads, and many engines used in similar applications have virtually no "adjustability."

It's necessary to note that if you haven't RTFM - and believed what it tells you it will probably sound like an engine in this size range is running incredibly fast. It's meant to do that.

On most generators found here, the voltage should be regulated by controlling a field winding in the generator, and engine speed variations should not affect the voltage, by much if at all. Is it possible that the "service place" screwed around with the voltage regulator in addition to messing with the engine speed regulation?

If the generator has a fairly good voltage regulator, properly adjusted, engine speed variations should be "tolerable," although you'll need specific information for your set to assess whether something really needs to be fixed. Engine speed variation may cause a frequency variation, if it's a simple system, but that's not usually considered objectionable in small units of this kind. (Just don't try to run your clock off it.) Light bulbs and motored appliances don't really care much about incredibly accurate frequencies, and everything in most "electronics" is "DC inside" which isolates the innards from outside frequency hunting.

If something really is out of spec, you're best bet is to check with the generator set manufacturer for a maintenance (and or rebuild) manual for the generator set.

(They may have a FAQ where you can find some info, but most FAQ sites rely on the ability of someone to ask an intelligent question and that seldom happens.)

You'll probably also need to separately look for maintenance/service/rebuild manuals from the engine manufacturer. My Briggs and Stratton manual was about $35(US) a couple of years ago, and covers essentially all engines they've made in this century, so if you get a similar one from Yama maybe you can set up your own shop and make enough to buy few rounds.

An option: for a tiny unit like this, if it has a DC output, is to use the generator to charge a battery and get yourself a 500W solid state inverter for AC power. The battery will take care of voltage regulation, and a "fair" quality inverter should give you good enough frequency control. My 500W inverter was about $70(US), although it might be a bit more with the higher voltages in your place.

John

Subject: RE: Governor fault, small 2-stroke generator
From: gnu
Date: 18 Aug 07 - 10:34 PM

Oh... it runs on mix. Soooo, that's why there are no mixture screws on the carb. Interesting.

No problem. Buy a Honda 4-stroke. Well, any, but, the Hondas are quiet... just don't loan it out to a buddy that forgets to shut off the gas feed valve and fucks it up. No fun.

Subject: RE: Governor fault, small 2-stroke generator
From: JohnInKansas
Date: 19 Aug 07 - 12:15 AM

Coleman® now offers a "solid state generator" here in tiny sizes like the one discussed. The implication from the sales literature is that the motor runs at "whatever speed" and drives a DC (or variable speed rectified AC) generator/alternator, probably with very little regulation of either engine speed or the DC output. A solid state electronic inverter provides the stable frequency/voltage output regardless of what the motor does.

But who believes advertising?

_{Why are all those hands going up?}

John

Subject: RE: Governor fault, small 2-stroke generator
From: JohnInKansas
Date: 19 Aug 07 - 02:50 AM

Inverter EF1000iS appears to be the smallest "electrical power unit" currently marketed in the US as a "consumer product." It's rated at 1100 W. There are no generator products listed in the current US model line that are other than 4-cycle engines, and I think that's been the case for several years.

I find a few smaller units – down to 600 W – offered for sale (used) but all that I looked at are also 4-cycle.

It appears that all current US Yamaha models are "electrically governed" for engine speed control.

This site has a "parts and service" button that indicates that you can "view" owner manuals and parts catalogs, but offers only "buy" for the service manuals which you would likely need. You can "browse shop and maintenance items" but it doesn't say (without going deeper) whether you can get the shop items.

The parts and service section "recomends" that you register and log in, but it doesn't appear to be required. You do need to enter a specific model number for your machine in order to get into viewing the part lists. There is a caution that parts for older stuff may be unavailable, and they appear to say that you must buy parts through an "authorized Yamaha dealer."

If you can find a similar Yamaha site for your international region, you should find something similar. The US site is fairly "user friendly" although they don't go too deep into the details.

I've heard rumors that the use of 2-cycle stuff persisted a little longer outside the US, so you may even find some current stuff of that kind at the site for your region - if you can find it.

John

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 19 Aug 07 - 03:10 AM

Thanks John. 2-stroke is still common here. I have just bought for the princely sum of £30 a spare brand-new 700 watt modern generator, via ebay.

Yamaha told one of their agents, who told me, that the unit has not got a voltage regulator, only a rectifier pack. I have a replacement rectifier pack (via the Yamaha agent) - but so far I have not yet found where it is fitted. I expected it to be inside the control box, but it isn't. I have not yet taken the electrical bits of the generator itself off the engine since I was concerned about lining the bearings up again on reassembly. I've had that problem when stripping and rebuilding motor vehicle dynamos and alternators before now, and once succeeded in ripping the commutator of an electric lawnmower to pieces by not lining new brushes up correctly. Sounds like maybe I should put a load on before bitching further!

The repair place told me that the problem HAD to be the voltage regulator, and that they hadn't touched it.

Until a few months ago hunting was not noticeable. When the output voltage is roughly in the right region, the hunting causes the vlotage to vary fromabout 200 volts to about 260 volts. Here the normal is 240.

I also am familiar with the running speed, and it came back from the repair place running a LOT faster then when it went in.

It just seems so wasteful to throw the thing away!

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 19 Aug 07 - 05:48 AM

The exact model is an ET-500. No longer listed on either the UK or USA Yamaha sites.

It is not an air-flap governor - at least not an airflap on the flywheel and fan. I've had the cowling off and there it isn't. The usual governor lever is mounted onto a spindle that comes out of the crankcase between the motor and the dynamo. With the engine not running that spindle is easy to turn. When the engine is running the lever has a surprising amount of pull - about 6 ounces at a guess at the end furthest from the spindle.

I've had the carb totally to pieces, and I mean totally. No change. No adjusting screws (apart from a stop screw on the throttle butterfly that stops the butterfly from closing totally, and which was and remains srewed right in ie setting the highest "tickover speed" (if there was one which there isn't). With air cleaner back on and new fuel (50:1) the engine note is perfect ie just a hint of four-stroking at steady speed, and just a hint of blue haze in the exhaust, so the mixture is spot on for max power.

The governor arm has three holes in it for the spring that opens the throttle. The spring was in the middle one. I've moved it to the inner one so that the spring has less leverage on the arm - but not much change! Trouble is, to get at the spring and change it to the other hole means dismantling things again.

Loading with a 60W lamp produces a change in engine note and a slight drop in revs, but voltage gauge still showing 300 volts!

Vexed now!

Subject: RE: Governor fault, small 2-stroke generator
From: The Fooles Troupe
Date: 19 Aug 07 - 06:05 AM

Both 2 & 4 storke gennies (especially at the lower power end - up to about 800 watt) are sold here in Aus - 240V 50 cps is normal mains. Larger ratings seem to be mainly 4 stroke - the small ones have only recently become popular and cheap - Chinese of course...

I vaguely seem to remember that 2 stroke engines do not like running at idle or below a certain percentage of max load for any extended length of time - something to do with damaging the bearings or rings...

Most small motor motor-mowers are designed to 'run at full (manual) throttle setting' when mowing - they have a sorta feed back throttle arrangement.

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 19 Aug 07 - 09:14 AM

Yep, it's that feedback throttle thing that has been pissing me about.

Anyway, I now seem to have beaten it, even if I don't know what I did(!). Moved the spring on the actuator arm in to the innermost hole (I may have had it the wrong way round above, I had previously moved it to the outermost) and found I needed to wind the spring tension up a bit on the adjuster, and bingo, no load engine just four-stroking and meter showing 240V, put caravan on to it (fridge and battery charger, so probably about 250 watts) engine note deepens with hint of more four-stroking and meter steadies at 235 volts.

On to the next task!

Subject: RE: Governor fault, small 2-stroke generator
From: JohnInKansas
Date: 19 Aug 07 - 12:19 PM

Since all the engine intake air on a 2-stroke usually goes through the crankcase, and the piston back-stroke compresses it in the case to inject it into the cylinders, there's usually a pretty good airflow through there and a pretty good pressure cycle. Quite likely the governor could be an airflap (or more likely a piston/diaphragm?) on the inside. It would be expected that inside the crankcase it could produce a pretty hefty push on a stiff external linkage.

In most conventional (automotive) rigs I've seen the rectifier is about as close as possible to the alternator, and usually mounted directly on (or inside) the gen case. In older auto alternators, it often was two or three diodes pressed into separate holes, and there wasn't a single "rectifier" part bolted on somewhere.

Have you tried the local library for obsolete engine manuals?

John

Subject: RE: Governor fault, small 2-stroke generator
From: GUEST,ThatGuy
Date: 19 Aug 07 - 05:04 PM

PMFJIH-There are a lot of bad theories here- even the 'two stroke guru' is dead wrong. Modern small engines use an internal flyball governor. It does NOT "shut down the throttle when the revs pick up" - it OPENS the throttle when the engine load increases and it does so by working against a spring. The OP's Yahmaha is not overvoltage because it is running too fast- frequency is related to shaft RPM, not voltage. It sounds like the Yahmaha has multiple problems 1) engine performance and 2) electrical issues. The engine performance could be from carbon in the muffler (needs to be cleaned on a regular basis) or leaking crankshaft seals or both. A good small engine shop can tackle those. As for the electrical problems, well that is what electrical shops are for.

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 19 Aug 07 - 05:25 PM

Funny, when I was at school the emf generated by a conductor moving in a magnetic field was proportional to velocity and to the strength of the magnetic field. The calculations were done on the number of lines of force cut in unit time.

On the Yamaha, it is the spring that opens the throttle, trust me, I've pushed and pulled the linkage while the engine is running, and the spring opens the throttle, and the governor lever (operated by who knows what inside the crankcase) closes the throttle.

And if you google "Medway Mowers" they are supposed to be the gurus of small garden machinery round here. Experts on small electrical machines seem not to exist, the throwaway culture having rendered them obsoltete.

Silencers do not usually need cleaning. When did you last clean one out on your car or motorbike?   

How does any governor know that the load has increased? Only by a drop in revs.

Since the gadget is now apparently running stably under load and producing the right voltage, I am unlikely to split the crankcase to find out how the governor works as a matter of idle curiosity.

But if anyone has a workshop manual for a Yamaha ET500 I'd be most curious...

Subject: RE: Governor fault, small 2-stroke generator
From: John J
Date: 20 Aug 07 - 01:21 PM

Silencers on 2-stroke engines DO need cleaning! A clogged silencer will cause too much back-pressure = poor performance. I would be surprised if running on 50:1 petroil would premature cause exhaust clogging, but you never know. It's v important to use decent quality 2 stroke oil.

JJ

Subject: RE: Governor fault, small 2-stroke generator
From: JohnInKansas
Date: 20 Aug 07 - 01:46 PM

I've done a little bit of poking around to satisfy my own curiosity, and find that 2-stroke engines still are used some in marine applications and in Go-Kart racing. I don't find anything in the Go-Kart info as small as your generator, but some boat books seem to be still available(?).

An example:

Yamaha Outboards, 1992-98
(SELOC Publications Marine Manuals) (Paperback)
by Chilton Book Company (Author), Kevin M. G. Maher (Editor)

The description says:
"Covers all 2-250 Hp, 1 to 3-cylinder, V4 and V6, 2-stroke models, including fuel injected units. Also includes advanced oil injection and counter-rotating drive."

Comparable current engines that appear to be about like yours - and for which not manuals seem available - are rated slightly above the 2 hp minimum size indicated, so something at least very similar to yours might be included. I'm not familiar with the Chilton SELOC (marine) series books, although I've seen numerous fairly recent Chilton automotive books.

Once very useful, the newer Chilton auto books are 295 pp of boilerplate reproduced identically in all Chilton manuals from a 1943 edition, plus one or two pages of the same specs printed (per Federal Regulations) under the hood of any recent auto sold in the US, so they're seldom worth much; but the marine engine books might be better(?).

The book appears to available only as "used" but the prices quoted are mostly fairly low. Amazon is getting a reputation for advertising used books they don't have and can't get, but it might be worth exploring the possibilities as an "extended general curiosity" sort of thing.

I found at least one website that offers the SELOC manuals covering other years, but they want $40 (US) for a subscription to let you download and/or print "any pages you want for any one engine." I didn't save a URL (since I wasn't interested at that price - sorry) but you should be able to find it easily enough in the unlikely event you might want to.

Your particular engine draws a complete blank in all my web searches. Even "modern" ones in the same/similar size range are really rare.

John

John

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 20 Aug 07 - 03:00 PM

I have asked the go-kart people in essex who supplied the (unnecessary, as it turned out) rectifier pack to see if they can get Yamaha to divulge where the rectifier pack goes and how to regulate the governor....

Subject: RE: Governor fault, small 2-stroke generator
From: GUEST,ThatGuy
Date: 22 Aug 07 - 11:42 PM

"Funny, when I was at school the emf generated by a conductor moving in a magnetic field was proportional to velocity and to the strength of the magnetic field. The calculations were done on the number of lines of force cut in unit time. "

The key here is "strength of the magnetic field" which is varied by the voltage regulator. The shaft speed HAS to be a constant 3600 RPM to generate 60 hz (or 3000 RPM for 50 hz).

"Silencers do not usually need cleaning. When did you last clean one out on your car or motorbike?"   

Cars and bikes are usually 4 stroke engines- the muffler/screen and ports on all two-cylce engines need to be cleaned- usually at 100-150 hours of operation. Failure to do so will rsult in poor performance and, in some cases, the hard carbon deposits will become trapped between ring and cylinder wall, scoring the latter.

Don't ask questions if you don't like the answers.

Subject: RE: Governor fault, small 2-stroke generator
From: JohnInKansas
Date: 23 Aug 07 - 12:11 AM

The shaft speed HAS to be a constant 3600 RPM to generate 60 hz (or 3000 RPM for 50 hz).

Incredibly brilliant observation - for ca. 1940; but most alternators now have more than one pole. "Lines of force" is also a rather arcaic concept, not much used in current teaching, design, analysis, or testing, and fundamentally limiting if one uses current easily available test equipment - and knows a little more than elementary math.

- Ever hear of Mr. Maxwell?
- Helmholtz?
- differential calculus?

John

Subject: RE: Governor fault, small 2-stroke generator
From: Richard Bridge
Date: 23 Aug 07 - 04:37 AM

Yes John. Just trying to make the point that the faster an alternator, one that Yamaha said does NOT have a voltage regulator, runs, the more volts it produces.

Subject: RE: Governor fault, small 2-stroke generator
From: GUEST,ThatGuy
Date: 26 Aug 07 - 12:49 PM

>> The shaft speed HAS to be a constant 3600 RPM to generate 60 hz (or 3000 RPM for 50 hz).

> Incredibly brilliant observation - for ca. 1940; but most alternators now have more than one pole.

Actually, all small AC generators have exactly two poles and have a shaft speed of 3600 RPM to achieve 60HZ. Some small gensets cheat and run slightly faster to compensate for droop. Larger gensets have four poles and turn at 1800 HZ.

> - Ever hear of Mr. Maxwell?
> - Helmholtz?
> - differential calculus?

Ever hear of a shop manual? They are loaded with practical answers to how gensets work. You can find one at a book store or library.

Subject: RE: Governor fault, small 2-stroke generator
From: GUEST,UBERKron
Date: 03 Sep 12 - 01:16 AM

its fly weight governer. I discovered this after the generator ran only at WOT. The genend bearing cage had disintegrated and jammed it in the wrong position. This post was entertaining as fook. Armchair pros much?