I'm stumped: 3hp no start

Mini Bike & Go-Kart Parts

#1
This is the engine for my build-off bike. The engine will not fire. I got one backfire with starting fluid and another one ignited fuel vapors coming from the tank cap (never had that happen before:doah:). Here's what I checked:

1. Spark--hurt when my hand got too close to the spark tester, so it's good. To be certain, I reset the coil gap.
2. Spark Plug--gapped at 0.030
3. Compression--is fine. I pulled the valve cover to be sure both valves were operating properly.
4. Gaskets on carb and tank--tightened to make sure no air leaks.
5. Plug was slightly wet from ether but I don't seem to be getting fuel. I have not disassembled the tank/carb.
6. Flywheel key is fine.
7. Carb was cleaned and rebuilt with a B&S kit.

This is the engine I swapped out the bushing crankshaft for a bearing crankshaft. I was careful to line up the timing marks. I don't think there would be a different cam for a bearing crankshaft. Even if it was off one tooth, I should have had a backfire.

Thoughts?
 
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#2
Update: I pulled the carb and checked the pick up tubes and made sure all orifices were clear. The carb to tank gasket showed evidence of leaking, so I changed out to a new one. The bowl was full and its pickup tube was clear.

I broke the starter rope so as I was starting to rewind the spring, it broke. Whaddya get for a 53 year old rewind starter??? ......Nuttin':surrender:

Tomorrow's another day and I'll use the other shroud.
 
#3
Do you still have points? I would start with spark timing. It tried to start backwards so it points in that direction. First is be absolutely positive about the flywheel key. Even a small shift in the crank/flywheel alignment can mess with you. If there is a line on the key, change it. Be positive about the point gap. Every now and then we would find the little plunger that lifted the points worn (not eyeball visible) and it would make them temperamental. Just replace it is a good idea. No matter how bad the carb is it will still run on a prime, so not likely to be a carb issue. Did you set the valve lash?
 
#4
Do you still have points? I would start with spark timing. It tried to start backwards so it points in that direction. First is be absolutely positive about the flywheel key. Even a small shift in the crank/flywheel alignment can mess with you. If there is a line on the key, change it. Be positive about the point gap. Every now and then we would find the little plunger that lifted the points worn (not eyeball visible) and it would make them temperamental. Just replace it is a good idea. No matter how bad the carb is it will still run on a prime, so not likely to be a carb issue. Did you set the valve lash?
Valve lash was checked when I was reassembling and in spec. Also made sure valves were opening and closing. I converted this engine so it no longer has points--reset the air gap, too. It has to be something simple and I can change keys, though the one I installed looked good.
 
#5
You didn't replace the flywheel did you?

Edit to add, I may have found the answer to the question I was asking in your other thread. On the older engines (I don't remember the year it changed) there was a difference in the coils and the flywheel, you couldn't swap them independantly. Was just wondering if you changed one and not the other.
 
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#7
Make sure that when you installed the coil that you didn't put it on backwards. The blade connector for the kill wire should be facing the cylinder.

Jim
 
#8
Should have a nice blue spark, lay plug on head and spin engine to check, try dropping some ATF into the cylinder, rings may need a little lube to seal...................Tom.
 
#9
You didn't replace the flywheel did you?

Edit to add, I may have found the answer to the question I was asking in your other thread. On the older engines (I don't remember the year it changed) there was a difference in the coils and the flywheel, you couldn't swap them independantly. Was just wondering if you changed one and not the other.
I used the same flywheel. I've been searching the polarity question, and can't find a date when the polarity changed.

try priming the carb with gas, they sometimes have a hard time starting after a carb rebuild.
I've used ether, but not gas. I'll give that a go.

Make sure that when you installed the coil that you didn't put it on backwards. The blade connector for the kill wire should be facing the cylinder.

Jim
Yep, the kill wire is facing the cylinder.

Should have a nice blue spark, lay plug on head and spin engine to check, try dropping some ATF into the cylinder, rings may need a little lube to seal...................Tom.
ATF is something I hadn't thought of. Could make a difference. I was working in the direct sun yesterday, so seeing spark was hard...sure felt it though!

Thanks all for input.:thumbsup:
 
#10
Back fire is always timing, valve or spark. Magnetron conversion issues (I had one as well) are on older engines, but you will get no spark if the polarity is wrong.

Knowing you are fully cognizant of the operation and parameters of this engines, I hesitate to offer desk top troubleshooting. But you said you got shocked while using the spark tester, and that the fuel fumes from the tank ignited from spark.

Are you leaking spark? The last tec I did, I had several problems, but one of them was the fact that the magneto wire was sliced near the flywheel, and allowing a spark jump once in awhile.

I know you got this. It's disconcerting to have something "done" or rebuilt, then have to go back to the drawing board. Been there. Hang in there Pete.
 
#11
I used the same flywheel. I've been searching the polarity question, and can't find a date when the polarity changed.
:
Easiest quick check is use your other flywheel off the other engine, inspect the key while it is apart. You can do this swap in 20 minutes and you will have the shroud off replacing the rope so you are half way there.
 

MB165

Active Member
#12
youre close, double check the basics,
compression, how much psi?? 8000 series don't have much, maybe 60psi for a minimum
spark, you can get a zap but still have weak spark, will it jump a gap?
check the ignition timing.
try firing it up off a can of carb cleaner, that alone should rule out all but the carbie
cam timing correct?
 
#13
I remember the last Tecumseh I was working on, I didn't torque the flywheel down all the way. It was "tight"...but not the 55lbs of required torque that the flywheel key needed..and it was throwing my spark off until I torqued it down to the right spec.

You didn't mess with the cam timing did you??
 
#14
I remember the last Tecumseh I was working on, I didn't torque the flywheel down all the way. It was "tight"...but not the 55lbs of required torque that the flywheel key needed..and it was throwing my spark off until I torqued it down to the right spec.
Very true. I used to find a lot of flywheels that had kicked timing just a tiny bit. That was my comment on looking for a shift line on the key. I have never seen a Briggs flywheel that was on to tight, saw many of them that were too loose though.
 
#15
Back fire is always timing, valve or spark. Magnetron conversion issues (I had one as well) are on older engines, but you will get no spark if the polarity is wrong.

Knowing you are fully cognizant of the operation and parameters of this engines, I hesitate to offer desk top troubleshooting. But you said you got shocked while using the spark tester, and that the fuel fumes from the tank ignited from spark.

Are you leaking spark? The last tec I did, I had several problems, but one of them was the fact that the magneto wire was sliced near the flywheel, and allowing a spark jump once in awhile.

I know you got this. It's disconcerting to have something "done" or rebuilt, then have to go back to the drawing board. Been there. Hang in there Pete.
Ooooh, this little baby ended up having way more issues. Sometimes it pays not to follow the rebuild instructions in the manual and do what your gut says to do.:facepalm: I tested the spark in the workshop with only an incandescent on, nice solid blue spark. No leaking. What caught on fire was the ether as this dumb @$$ forgot to drill out the vent holes on the cap after clear coating.....but read on.
Easiest quick check is use your other flywheel off the other engine, inspect the key while it is apart. You can do this swap in 20 minutes and you will have the shroud off replacing the rope so you are half way there.
Yep, did this along with a new key. Then I tried an aluminum flywheel that I knew had the correct polarity. Had plenty of spark with all three, no fire though.

youre close, double check the basics,
compression, how much psi?? 8000 series don't have much, maybe 60psi for a minimum
spark, you can get a zap but still have weak spark, will it jump a gap?
check the ignition timing.
try firing it up off a can of carb cleaner, that alone should rule out all but the carbie
cam timing correct?
Ah, Briggsie-San, you are getting closer to the issue. No go with a shot of ether in the intake port w/o carb attached. Don't have a true compression tester, but I have one with a rubber tip that I wedged in place....30 psi. Pulled the head to make sure valves were sealing, and checked lash all were good.

I remember the last Tecumseh I was working on, I didn't torque the flywheel down all the way. It was "tight"...but not the 55lbs of required torque that the flywheel key needed..and it was throwing my spark off until I torqued it down to the right spec.

You didn't mess with the cam timing did you??
Flywheels were at 55 lbs-inch. The Bellville washer is kind of tired, though. I ordered one from OldMiniBikes and supplier cancelled order. As to cam timing, that's where I was anxious. I eliminated everything on the outside first before I opened her up to find.....:shrug:.

Very true. I used to find a lot of flywheels that had kicked timing just a tiny bit. That was my comment on looking for a shift line on the key. I have never seen a Briggs flywheel that was on to tight, saw many of them that were too loose though.
.....metal shavings in the bottom of the sump. After many pulls, I noticed more oil than expected on the piston. Rotating the piston down showed the walls were getting scored by the rings. Per the rebuild instructions, I did not hone the bore beforehand. Ring gap was in spec as was the edge to piston groove clearance. Timing, btw, appeared to be correct. What wasn't happening was compression.

So my nice, clean and purdy 1964 Briggs ended up being toast. This was after 2.5 hours this morning.

The next several hours were spent building a "new" engine. I had a sleeved block and correct piston, so this engine got the usuals done plus a honing. Transferred parts over, made absolutely certain cam and crank were timed (a bearing crank, no less). Put on the white shroud, the gold tank and carb. Filled her with 19 oz of oil (20 overflowed), took her outside and after 10 "I really want to start" burps, she fired up.

Compression was the culprit in the end. Now all I have to do is clean the new block, paint it gold, and clear. I'm adding a new starter clutch and recoil spring for it when Amazon delivers.
 
#16
I am glad you fixed it but bummed that you damaged the block. Did you find the rings carbon jacked or what was the culprit? We never honed unless there were scores in the wall that we filled with JB Weld (yes, it really worked). It may be how you can save the engine.
 
#17
Franken-Briggs Running

I need to adjust the crank bearing seal (a little leak), but aside from that the engine runs really well with no blue smoke!
https://youtu.be/Pph72simCHM


BTW, the rattling you'll hear is the Workmate shaking. The engine is not making any interesting noises!


:thumbsup:THANKS TO EVERYBODY WHO POSTED THOUGHTS AND IDEAS. I USED THEM AS A "TICK LIST" AS I TROUBLESHOOTED. :thumbsup:
 
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