Sat Apr 13, 2013 5:46 pm
Well I have been messing with this cub for some time now and still cannot get her to run. I need some advice. Here is what I figured out thus far.
When I try and start it all I get is a series of pops. Sounds like it is firing on 2-3 cylinders then will not fire on any. If I keep cranking it will then fire on a couple of cylinders, but not enough to start the engine or even kick the starter off. Also no amount of adjusting the carb seems to effect the popping at all. Not knowing where to start I checked the following:
-Compression seems to be okay, ratings: 100-93-90-100
-Carb has been rebuilt and seems to work and flow as it should, good flow when main meter jet is pulled, also good clean main meter jet.
- Checked all gaps, set points, spark plugs to setting in manual. Also retimed the magneto.
-Spark however seems to be a little odd, I used one of the cheap little spark testers from AutoZone, The first time I tried it I had spark on all 4 cylinders but the 3rd and 4th cylinders gave a much brighter light in the tester. I then tried it again after adjusting the gaps and timing and found that all cylinders had spark but the light was faint, and not as bright I would think it should be.
I did notice however that the rotor in the mag seems to have an awful lot of play in it. The rotor will move at least a 1/8 of a turn without the main shaft moving. I feel that this is not supposed to be happening. Can this be my issue as it is throwing off the timing and not letting the rotor make the connection with the post in the cap at the correct time? I am at a loss as to where to go from here. Any help is greatly appreciated.
Sat Apr 13, 2013 8:09 pm
When did it run last?
Have the spark plug wires been replaced?
I remember a few posts regarding the spark plug wires and cubs not running, and I think I remember that Cub wires need to be Solid Core Only ?...something like that. Something to check at least.
Persistence will pay off !
Sat Apr 13, 2013 8:15 pm
the first thing I would do is run a wire from the battery to the distributor by passing all other wiring. A bad switch will give the problems you are talking about. If that does not work then make sure that the plugs are firing when they are supposed to. Set at 1 TDC the see if the next plug that fires is 3 then 4 then 2 then 1. Popping sounds like it could be out of time. But do the switch bypass first.
Sat Apr 13, 2013 8:23 pm
thank you for the replies. The last time the engine ran I found a that the carb was gummed up and needed a rebuild. So I rebuilt it and once I put it back together it has not started since. The wires on the Cub seem to carry the spark as they should. Also I can not by pass the wiring as this model has the magneto on it, not a distributor, but thank you for hte reply. I am simply just lost on this one.
Sat Apr 13, 2013 8:55 pm
If it was running with a gummed up carb, and nothing else was changed or worked on until you rebuilt it & put it back on, 99% chance it's something with the carb. Even if I was sure I rebuilt it right, I'd break it all the way back down & triple check everything before moving to anything else.
Sat Apr 13, 2013 9:08 pm
Do all that Cecil advised. If that don't fix it, check and make sure that the terminal for the kill switch wire isn't shorting to ground. There are cardboard washers between the side of the mag and the condenser wire and if it is missing it will short out. Try that.
Sat Apr 13, 2013 9:15 pm
woops didn't catch the mag part. The first thing I would do now is spray some carb cleaner in the carb and see if it starts and runs on the carb cleaner. If it does the problem is with the carb. Keep me posted and we will get you thru this.
Sat Apr 13, 2013 9:24 pm
I did not try carb cleaner, but tried good old starting fluid. That had little to no effect. That in addition to the large amount of slop in the rotor keeps me leaning toward the spark/magneto being the issue. I am no expert but feel that I can usually diagnose the area of the issues and this time I am in the dark. When I got this Cub it has been in a garage for 15 years and all I had to do was put a new coil in it and it ran great, for about 2 years. So I just cant imagine how sitting for a few months at most have caused all these issues, but thank you all for the replies so far. I know from the knowledge on this site it will all get figured out.
Sun Apr 14, 2013 1:27 pm
make sure the little marks on the gears in the mag are timed correctly
Sun Apr 14, 2013 4:46 pm
The magneto and the carb I think are going to pulled off and gone through from top to bottom. I have decent compression so its either fuel or spark.
Tue Apr 16, 2013 5:08 pm
Was able to get the Cub running today. While that is progress there is still an issue.
Once I finally got it running, the engine seemed to smooth out and sounded good. So I let it run at at about 1/4 throttle. After about 10 min the engine began to studder and pop and died. I was able to get it running again, but this time the engine sounded like it was either dropping a cylinder or something but it was not running smooth. It would still run like this but I could not seem to smooth it out with any type of adjustment. I then shut it down to check things over and then could not get it started again. I just can not understand how the engine ran like a top for 10 min and then did an entire 180 without me touching anything. If anybody has any idea what is going on I am willing to try and look into anything at this point.
Tue Apr 16, 2013 5:32 pm
A.J.; I know these kind of problems can be a real pain. The only advice I would give at this point is to work on one system at a time. Pick either the ignition or the fuel system and get that to 100% before going to the other. The trouble with working on both it's easy to miss some thing, and quite possibly you may get it fixed and have no idea what was wrong if it should happen again.
Tue Apr 16, 2013 6:10 pm
Birddog, Thank you for the reply. I thought I had done a good look over but it looks like it was not enough. I think I will start with the carb. Besides cleaning and checking all gaskets, setting the float height, making sure both pieces are level is there anything else I should keep and eye out for?
Tue Apr 16, 2013 6:50 pm
I don't want to deter you from your plan, and going through the cub one system at a time is a good idea. But this sounds a bit like a magneto with a couple of issues. I suspect the pinion and rotor may need replacement due to the slop you mentioned. That slop is the same as retarding the spark, and will make the cub rub poorly. Also, you may have a failing coil. Once it gets hot, it breaks down, which is why it runs for a while, then runs poorly or not at all. Two things you could do to check. One, see if it starts again once cool, and repeats the pattern. Two, immediately after it starts to run poorly or not at all, check the quality of the spark at a plug. It should be bluish-white and snap very strong, not yellow and weak.
Tue Apr 16, 2013 6:56 pm
I'm in Rick's corner. Magneto problems are primary.
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