Bike Has Spark, Won’t Start
- Thread starter MiffedFan
- Start date
So I think this thing is broken somewhere and I just can’t see it.
To review:
Gaskets have been changed on the bike
Cylinder head has been tightened to the foot pounds mentioned earlier in the thread.
CDI, magneto and spark plug changed, we have spark
Fuel was changed to a ratio of 32:1
We have compression and when the clutch is released we can feel the engine engage, no ignition, not even an attempt, we hear the engine chugging along, but no ignition
I removed the car to confirm suction at the intake manifold, there is suction.
I did a test with the spark plug out and held a piece of paper over the spark plug hole while cranking the engine, no fuel residue or moisture appeared on the paper. Would that be normal since the fuel is supposed to be atomized into the combustion chamber?
I put liquid fuel into the intake manifold, through the carb, also added fuel under the spark plug again, both times no fire.
Magnet definitely spins when the engine spins.
We do have a pretty long after market muffler on the engine right now. The original muffler is shorter. Could that be causing a back pressure and preventing ignition?
Trying to give as much info as I can to figure this out.
To review:
Gaskets have been changed on the bike
Cylinder head has been tightened to the foot pounds mentioned earlier in the thread.
CDI, magneto and spark plug changed, we have spark
Fuel was changed to a ratio of 32:1
We have compression and when the clutch is released we can feel the engine engage, no ignition, not even an attempt, we hear the engine chugging along, but no ignition
I removed the car to confirm suction at the intake manifold, there is suction.
I did a test with the spark plug out and held a piece of paper over the spark plug hole while cranking the engine, no fuel residue or moisture appeared on the paper. Would that be normal since the fuel is supposed to be atomized into the combustion chamber?
I put liquid fuel into the intake manifold, through the carb, also added fuel under the spark plug again, both times no fire.
Magnet definitely spins when the engine spins.
We do have a pretty long after market muffler on the engine right now. The original muffler is shorter. Could that be causing a back pressure and preventing ignition?
Trying to give as much info as I can to figure this out.
Greg58
Well-Known Member
Motorized Bicycle Carburetor install and rebuild
Pictures from taking the carb off the bike and taking it apart to puting it back together and some info. on how and what it all does well sort of and ways to change the min jet for those who want to and areas that can bite you by plugging off and sort of how to fix them. I hope this will sort...
motorbicycling.com
So I thought of this this morning and so I went back to the previous carb to eliminate any issues with the carb. We are back to the racing carb from Amazon that would have come with a colored air filter. The bike was actually running previous to this current issue with an identical carb. We changed the carb back to the original carb and the bike has not started since. I have tried it with this carb as well, no go. I will be changing the muffler back later today as the bike did run with the old/original muffler before we switched to the original carb.
All of those changes have been made, but it still does not start. We are likely going to replace the entire engine. We’re run out of options and steps to try.
MEASURE TWICE
Well-Known Member
I know timing of spark is important so I mentioned about key an keyway if damaged, but wonder if there are other things like markings to check. I used to use a timing light on automobile and motorcycle engine, but those probably have what small engine don't.
On Briggs engines, though different again from the two stroke china girl mb engines, there use to be points and condenser. Now elctronic module for the Briggs eliminates points and condenser, but magneto lamination distance from flywheel with magnet was an adjustment to a very small amount to optimize spark.
If a new engine is purchased and runs fine, hopefully with lots of hours on it and old engine maybe has some parts that can be used if necessary if something is needed in the future, they might come in handy. Though of course if there is a part that is bad and unknown which it is, then maybe difficult to use effectively.
I remember seeing a large plate and movable pointer that was being used on a civil aviation piston engine with propeller removed, to set timing, maybe for both valve and spark, when reassembling and getting ready to test after servicing.
On Briggs engines, though different again from the two stroke china girl mb engines, there use to be points and condenser. Now elctronic module for the Briggs eliminates points and condenser, but magneto lamination distance from flywheel with magnet was an adjustment to a very small amount to optimize spark.
If a new engine is purchased and runs fine, hopefully with lots of hours on it and old engine maybe has some parts that can be used if necessary if something is needed in the future, they might come in handy. Though of course if there is a part that is bad and unknown which it is, then maybe difficult to use effectively.
I remember seeing a large plate and movable pointer that was being used on a civil aviation piston engine with propeller removed, to set timing, maybe for both valve and spark, when reassembling and getting ready to test after servicing.
