generator worries

[lakemac]

Not too sure if I have found the right place for my problems??
I am trying to service a 6kva Onan generator that is on a friends 38ft Regal Commador.
By service I mean I am trying to stop it asphyxiating me and my family every time he rafts up to us,and starts it to heat up his lunch with his microwave oven.
I am a qualified electrician and electrically the thing runs fine.
The problem is in setting up the carburettor (and especially the choke) so the thing can maintain a constant voltage and run on a proper air/fuel mixture.
Has anyone out there had an dealings with these gensets???
This summer without gas masks on board would be greatly appreciated.

 

[Silvertip]

Re: generator worries

If this genset is running that rich there are very likely other issues and the most likely fix will be a carburetor rebuild. If generators are not exercised regularly, have a supply of fresh fuel, and the fuel system kept clean by using a product like SeaFoam periodically, they can have the same problem as the engine in any boat. No degree of tinkering will fix that issue. You didn't say if this is an automatic or manual choke. If its a manual, there is no adjustment as it is closed to start the engine and open when running. If it's an automatic choke, then any attempts at adjustment should be done on a stone cold engine. The choke plate should just barely close when the engine is cold. It should be perfectly horizontal in the carburetor bore when the engine is warm. The only mixture adjustment you can make is generally the idle mixture although some do have a high speed needle. If you don't have a service manual, I would suggest you get one. Idle mixture screws are usually turned in until the engine begins to die. Note that position. Then turn it outward until the engine again begins to die. Note that setting. Happiness is somewhere in between those two settings. Adjust for best idle quality. You obviously need to make that adjustment with no load. The same adjustment process can be used on the high speed needle if there is one, but now the engine must be loaded and running at its governed rpm.

 

[lakemac]

Re: generator worries

Thanks for your quick response.
The generator has an automatic choke in the form of a bi-metal coil which heats up after starting. I am considering replacing this with some form of solenoid type setup so the choke only closes on start and opens immediately. It starts with much coughing and spluttering and after about a minute it gets to running rpms but still runs very rich and emits much smoke.
I do have the manual for it but it doesn't give away any clues as to how to set up the auto throttle advance, which is also part of the problem.
Currently if you load it up ,i.e turn an appliance on,it struggles to maintain rpms and volts (again more smoke).There does not seem to be any voltage regulator in circuit and the voltage goes up and down with rpm,threatening to destroy anything turned on at the time.
I have put a rebuild kit through the vacuum advance mechanism but I think setting this side of thing up is critical.Any clues on this?
I have a carby rebuild kit on order.
Thanks again for your time

 

[Silvertip]

Re: generator worries

Gensets are dependent on a load to activate the speed control mechanism. If that mechanism is sticky or the carb is messed up, the engine simply can't achieve its governed rpm so it "hunts" which is why voltage fluctuates. You may not have a choke problem but you may have a float that is misadjusted or fuel soaked, or an inlet needle and seat that is not functioning properly. The choke is easy to see if it's working? Remove the air cleaner/silencer and watch it. You will likely be unhappy with the manual choke setup. Carbureted engines tend to require varying degrees of choke during warm up. Your scheme is either on or off. It will likely start fine but will exhibit the same issues you have now, but due to a lean condition rather than rich. Again, You have a fuel delivery issue -- and you simply need to determine whether it is indeed the choke, or carb. I'm guessing carb rebuild.

 

[jlinder]

Re: generator worries

One of the common problems with generators is that they typically run with a very light load and carbon up after a while. About 15 years ago I worked with a couple of these and we often times had this as a problem.

You would find that even with a light load the generator would start hunting with the engine speeding up and slowing down and the voltage following the speed. It would get so bad that eventually the generator would die.

The solution we used was to plug in something that started to draw power, as much as the generator would support as long as it was not over the generators rating.

After about 5 min it started running smoother so we added some more load, repeating the cycle until we had it running at close to full load.

After about 10 min of that the carbon was pretty much cleaned out and the generator run smoother and cleaner until it was time again to clean it out.

Of course, it is a generator with 1 cylinder (I think 1 cylinder) and there is only so much you can do to get it very clean and quiet.

 

[drewpster]

Re: generator worries

If the engine is cleaning up slightly after a few minutes running then the choke is probably responding as it should. It sounds as though you have a rich mixture problem overall. That points directly to fuel delivery. It is likely that it is the needle valve. Carb floats these days are made of plastic. It has been a long time since I have seen a bad float. It is more likely that the needle/ seat is sticking partially open or the tip is worn allowing too much fuel in the fuel bowl. Make sure your rebuild kit has a new needle. Some will come with a new seat if it is serviceable. Make certain that the float level is correct before putting the carb back together. A slightly high or low float level can drastically effect engine performance. The kit should come with a float level specification and the directions should tell you how to measure it. Check it closely.
Generator carbs are generally simple in design so taking them apart and putting them back together is pretty simple. The critical part is to make sure it is completely clean. If you have access to a compressor use it to blow out all of the passages thoroughly. I do not recommend using spray can carb cleaner to initially clean out the carb. First use a soaking type carb cleaner. Then follow with pressurized air. If you do not have a compressor, spray cleaner will be ok only after first soaking the carb.
I highly recommend taking the carb apart over a table covered with a clean light colored sheet. The point is to catch and to be able to see any tiny hard-to-replace parts that may tumble out. No teardowns on the tail gate in the yard allowed.
After tear down, soak the parts in the cleaner for the amount of time recommended on the can. Be absolutely certain no plastic or rubber parts are left in the carb while soaking. The cleaner can melt them. After soaking wash the parts in warm water and blow them clean. Again, blow out the passages thoroughly. Inspect for any debris by looking through the holes you can, and feel for good air flow through the holes you cannot see through. READ THE DIRECTIONS that come with the kit. It is very easy to miss a detail or fail to set an initial adjustment. (after many years doing this stuff, I still read the directions)
Allot of folks are intimidated by carburetors. They are generally very simple devices. The trick is to be very thorough and pay attention to detail. Work clean!

 

[lakemac]

Re: generator worries

Thanks everyone for your input.
Seems like the carby kit is a good start.A 3 week wait as it is coming from the States.(why is everything on the other side of the world when you live in Australia??)
Will let all know of progress

 

[lakemac]

Re: generator worries

G'day everyone.
The carby kit arrived yesterday a week before time.I have installed the replacement parts as per the supplied instructions and I am going to bolt it back on today. My friend,the owner,has produced the maintenance and repair manual which is somewhat useful but not completely enlightening.Tuning instructions deal mainly with the governor system,which will be handy down the track. From the manual I can tell what the various parts are ,and one in particular is of concern.
The carby is a Zenith brand with three forms of adjustment,these are idle adjustment needle,throttle stop screw and adjustable main jet assembly. The concern is the adjustable main jet.
Surprisingly this is not a replacement part in the carby kit though almost everything else was ,down to things like new float springs etc.
Anyway my concern is this adjustable jet and how it will play its part in the tuning of the carby?
Any clues??