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JohnF2015
JohnF2015, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1009
Experience:  Owner/Service Technician at S & J Small Engines
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I have a JB Onan 7.5kw genset that burns points after less

Customer Question

I have a JB Onan 7.5kw genset that burns points after less than 10 hours of use. I change the points and it runs fine again. I have also changed the condenser many times but it does not help. This unit applies 12V during starting and then cuts back to
6V after starting. With new points it starts quickly. Once it starts to miss badly, I can check the points and they appear to be only slightly burnt. Is there a solution to this problem?
Submitted: 1 year ago.
Category: Small Engine
Expert:  Curtis B. replied 1 year ago.

Have you checked the coil voltage to see if it cuts back to 6 after start? Usually the points burn because the voltage is not being cut back.

Customer: replied 1 year ago.
I checked that several times the past couple of years and it does switch over. It could though switch back if the contact that causes it to switch to 6V closes. I removed the distributor plate and brought it home yesterday so I could examine the contact and adjustment more closely. I will adjust it so that it opens ASAP so that it stays open while the engine is running. The adjustment may be somewhat tight allowing it to oscillate open and close while the engine is running.When starting with 12V there is far more sparking between the points than when it is running off of 6V---of course that would be expected.Will the engine start okay if it runs on 6V during the start cycle?Is there a conversion kit for electronic ignition?John
Expert:  Curtis B. replied 1 year ago.

Some engines will start ok on 6 volts. You would just have to try it. As for electronic ignition, would need the engine numbers to check.

Customer: replied 1 year ago.
I do not understand the answer that some will start on 6V. Seems like the answer should be it will or will not---not maybe.I assume I could try it by adjusting the centrifugal contact gap so they remain closed all the time---right?The way it works now the gap should be .020 when the engine is stopped and once the engine reaches speed the contacts close switching the voltage from 12 to 6V.
Expert:  Curtis B. replied 1 year ago.

Engine uses the 12 volts to make strong spark. Some engines are easier to start than others. If your's is easy start, 6 volts might be all you need.

Expert:  Curtis B. replied 1 year ago.

There is no yes/no!

Expert:  Curtis B. replied 1 year ago.

There is no yes/no!

Customer: replied 1 year ago.
Is misadjusting the centrifugal contacts an acceptable way to force the engine to run on 6V all the time?
Expert:  Curtis B. replied 1 year ago.

YES

Customer: replied 1 year ago.
Okay--I will try it in a few days. The engine is at a cabin I have in the mountains. One clue it may fix the problem is if it will start at 6V and using 6V during starting there should be next to no or very little arcing across the points during starting. Now, with 12V, I can see noticeable arcing during starting which does not occur once it switches to 6V. Of course the thinking is that it may be switching back and forth between 12 and 6V. If this works I may try experimenting with the gap across the contacts so it uses 12V during starting but only for the very least amount of time. The only reason I would hesitate to use 6V exclusively is that during the winter it is naturally tougher to start due to the extreme cold weather.While up there I can also get the engine serial number so you can tell me if there is an electronic conversion kit which would totally eliminate the problem.
Expert:  Curtis B. replied 1 year ago.

Sounds good, thanks.

Customer: replied 1 year ago.
As I mentioned in my last mail message it was going to take me several days before I could travel to the location of the Onan gen set to try a few things. I installed a new set of points and the engine started right up and ran smooth as it normally does. The only way it would start is on 12V and as soon as it started the centrifugal contacts closed switching it to 6V. The engine will not start unless it goes through this sequence. I tried holding the contacts closed to see if it would start on 6V but that trips the overload protection which I have to reset after several minutes. The engine will not turn over if the contacts are held closed before operating the start switch.The contacts seem to operating properly and I adjusted them to .020 as outlined in the manual.My guess is the engine will run fine for about 6-10 hours. Then start to miss until it gets bad enough for the engine to simply stop. At that point it will not start until new points are installed or the old ones are cleaned. They appear barely blemished but must be cleaned regardless for the engine to start. When cars had points they would burn over a 12-24 month period and you could visually see that were badly burnt and/or pitted. Just looking at the Onan points you would never guess the engine would not start due to the points.The engine runs very smooth with new points and starts right up.When starting the points arc noticeably on the 12V but when the contact closes there is barely any spark between the contacts using 6V.None of this makes a lot of sense to me.I also checked the timing to make sure it was dead on.The engine numbers are model 7.5 JB FL16581D, SER # ***** Is there a conversion kit for this engine?Any other ideas?
Customer: replied 1 year ago.
Are you actually familiar with my gen set? I gave you my engine model number and serial number. You referred me to a 6.5 KW
conversion kit which is a completely different set up than my unit. I also ask you if you had any other ideas based on the feedback I sent.
Customer: replied 1 year ago.
This information is useless to me. I have a JB, 7.5KW engine as I mentioned in my reponses to you with the serial number you ask for.
Customer: replied 1 year ago.
I have not gotten a response from anyone.
Expert:  JohnF2015 replied 1 year ago.

Hi, my name is***** will try to assist you with this problem.

The first thing that I would do is set the points at .018 inches, I have found in my 30 years that this tends to work better than the factory suggested setting. The next thing that I would look for if to make sure that you aren't getting a oil film back into the point area, I have seen some of these engines that get a small amount of oil back into the points and that oil will burn onto the points and cause this same problem.

Customer: replied 1 year ago.
Okay--I have been setting them at .021 but will change it to .018 you suggested. I have never noticed any oil around the points or on the points. I will though check a little closer.I know though if the points are only slightly over 21 it will not start. Same with the timing--it must be dead on. Closing the points though might help. The engine is at a cabin in the mountains and it will be a week at least before I get up there.The other issue is that it has to run 6-10 hours before the points burn. I will set them at .018 as you suggested and see what happens.One question right now---is there a conversion kit for this engine to upgrade the ignition to electronic??I am certainly not experienced as you but I am very mechanically inclined and do all of my auto engine work and have my entire 70 year life.You may have noted by reading my response strings that the points are only slightly blemished when the engine starts to miss and eventually stops. By looking at the points you would not guess they had a problem--at least I would not.Thanks for working with me. This question was sent via my wife's pay pal account.John
Expert:  JohnF2015 replied 1 year ago.

I am going to have to do some digging to try to find out on this one whether there is a conversion kit available or not. I can't find anything that is referenced at this time but I will make a few phone calls to my suppliers and see if they have an answer for that then I will get back with you.

Customer: replied 1 year ago.
Okay---Thanks.Could also asked them about this gen set in particular regarding the point issue. The dealer who originally sold this set and installed at a vacation cabin for another guy said it always had a problem with burning points and her could never figure out why. To me it might be a design issue from the start.
Expert:  JohnF2015 replied 1 year ago.

I will do some research and let you know what I come up with. It may be tomorrow now before I have any answers but I will respond back here as soon as I can get more information.

Customer: replied 1 year ago.
Thanks.