Only Backfires Through The Carb Regardless Of What I Do (1450)

[giddyup306]

Yesterday when I went to mess with it here's what I found...

After trying several times to set the points yet again I noticed that the trigger for the coil had somehow completely broke! The little fork that goes under the nut broke completely off! I have no clue how this happened. I did get the engine to run, but it ran violent. It must have broke at that point. See that machinist put the wires that to to the stator on the wrong freaking side. In noticed this after I had everything including the PTO and clutch installed so I just extended the wires 6-8". I ran them along the points wire and then made a loom with electrical tape so it would at least look like it belonged there. The wires are about 2" too long, but they're not in the way of anything so I left them. So really I don't know how it broke, but whatever...

At this point the battery was dead, so i decided to check the valves. Since the "t" mark is either non-existent, or too rusted to read, I put my finger over the spark plug hole to find the compression stroke. I then pulled the head off and used a dial indicator to find true TDC. The intake was set right at .010", but the exhaust valve was set way too tight. At this point the battery was still not charged, so this is where I left off.

I did manage to get the engine to start and run, but it only ran for 2-3 seconds then died. After that it wouldn't even attempt to start. I thought that maybe it was flooded so I took the plug out, cranked it a few times, and blew it out with compressed air... Still nothing. I probably should have left the points alone at that point but I didn't thinking I could tweak it a bit and get it to run.

At this point I'm 99.99999999% sure it has to be something other than timing. The plug is new and set at .035", the points are new Kholer points. The shaft is a new shaft. I thought maybe it wasn't staying set, but it is. Turning it over by hand I have compression, and the valves are set correct (well now they are). The carb is brand new and the only adjustment it has is for the idle set screw. It's getting fuel to the chamber, too... What can possibly be preventing this engine from running? Is it possible that the govenor is preventing it from starting? This is the only thing I can think of...

[Matt G.]

You still have not told us if the ignition timing is correct or not. If it is off far enough, it will not start.

[_DX3_]

Possibly the coil? After replacing my stator and putting my engine back into the tractor, my 1250 ran like crap for a few seconds and would backfire loud enough to make the neighbors think I shot someone. After following the suggestion to check the coil specs I put the coil from my 128 on and it fired and ran great until it would get hot say maybe 10 to 15 minutes. This is when I found out the PO had put on a Nissan spark plug wire which had a bunch of resistance built into it causing the coil to overheat and die. Now I doubt you have the plug wire issue, but the coil could be bad. Mine even showed spark but the coil trouble shooting sequence showed my coil was very weak.

Coil Specs:
http://www.onlycubcadets.net/forum/showthread.php?t=11

[giddyup306]

Originally Posted by _DX3_

Possibly the coil? After replacing my stator and putting my engine back into the tractor, my 1250 ran like crap for a few seconds and would backfire loud enough to make the neighbors think I shot someone. After following the suggestion to check the coil specs I put the coil from my 128 on and it fired and ran great until it would get hot say maybe 10 to 15 minutes. This is when I found out the PO had put on a Nissan spark plug wire which had a bunch of resistance built into it causing the coil to overheat and die. Now I doubt you have the plug wire issue, but the coil could be bad. Mine even showed spark but the coil trouble shooting sequence showed my coil was very weak.

Coil Specs:
http://www.onlycubcadets.net/forum/showthread.php?t=11

I'll be bob darned! I had a bad coil!!! All this time... Believe it or not, but when I pulled out the plug to check for spark it had spark every time! I have seen coils fail under load, so I decided to go that route (the only way I caught them is with a scope). I decided to check the resistance of the coil. From + to the tower I had 8K ohms, from the case to any terminal it was OL. Now when I checked from + to - I had 3.6 ohms. This is still technically within spec since the spec is 4-8 +/- 10%. I would have scoped it, but my batteries were dead... At this point I didn't care if it needed a coil or not. It was getting one along with a new plug wire. When I called the small engine shop, she said that they probably had one. Well, "probably" isn't enough for me to justify driving to get it. She then asked if I had a part number. Even if their was one, it wore off along time ago. I was then on hold because she didn't know how to look up the part. When I got there the guy tried telling me that it was the condenser. I might agree with him if it wasn't brand new, and I tested it before I went to get the coil. He told me that "they either work or they don't". Horse hockey! He's still arguing with me, so I told him that I have seen coils start and run a vehicle, but fail under load. Then he asked if I saw that type of coil fail like that. I then told him that it was out of spec so he'd just STFU. He was like "well if it's out of spec...". If I was a small business owner, I wouldn't try and downsell a $55 part for a $5 part.

$70 and 30 minutes later I went to crank the engine over. It wanted to start. I reset the points and that baby fired right up on the third try. After it was running I seated the rings just watched that little beauty idle. You guys have no idea how happy I am that this darn thing runs! Even on a cold start it fires right up without even touching the choke. :biggrin2.gif: I started this project 5 years ago off and on and I was always convinced that it was a timing issue.

Now more fun stuff! The clutch stays engaged and the thingy (technical term) that raises and lowers the snow blower doesn't work (but the tractor will move back and forth). Can someone guide me with links on how to fix and repair these two things?

Other than that I just need to put everything back together. This tractor is just going to be used with the snowblower, and I plan on making a cab for it as well as getting regular V tires, along with some wheel weights. In the winter this could be a nice little money maker @ $10 a driveway.

Thanks everyone for the help!

Oh and I forgot to mention that the plug wire they sold me is the wrong one! I need to bring that back as well as the old coil so I can tell him were to put it. lol

[ACecil]

Glad you got your cub going!

[_DX3_]

Persistence, gotta love it. Glad you got that problem figured out. I am sure with the great guys we have in here, you other problems will be fixed soon.

[R Bedell]

LOL.....soon or later, a lot of us have been down this road or will be. One goes round and round endlessly, then all of a sudden, you discover the problem. It is a learning experience for you as well as others here. Glad you shared you experience here.

[eastonct124]

You didn't have a "Backfire". You had a "Pop". I didn't think of getting specific.
A pop always sprays cool wet gas back out of the carb.....not a flame (backfire).
That happened to me on the old Broadmoor I have. It drove crazy....turned out it was the points needed filing and gapping.
Ran fine afterwards.
Good to hear it's running.
The clutch is simple fix...probably not adjusted right.

[Methos]

Glad ya got it fixed!