newly built motor fail, need advice

#1
Every thing scrutinized again and again and cranking again and again til my shoulder is sore.
The plug fires outside the cylinder, then after cranking for a while starts to get wet.
It feels like it has the 11-1 compression it should have, and tried at 34* and 28* timing.
The cam-crank dots are lined up. Tried all idle speeds on the carb. Checked the lash
again and again. It won't start. Tried 2 different new coils. E3 and 3910x tried. Tried carb
cleaner and ether. I can't get it to even try to start. ??????
 
#2
I would say try any other spark plug you have lying around just so you don't go running around chasing problems that might not be there. Spark plugs can throw you for a loop sometimes.

What engine is this? Is this the dual carbs motor or something else?
 
#3
Hello friend, this is adding speed parts I had on the shelf to a NR clone short block with Arc rod.
One of the carbs from my 2x motor, new cam, ambush 2.7 fw, the usual hop up, 28/25 .075 NR head.
A new 3910x was tried today, still nothing. Thanks for the get-back, I'm dead in the water.
 
#8
When you say it feels like 11:1 compression what do you mean? Is it hard to crank? Does cam have a working compression release? If you have spark. I would drain floatbowl, pull out plug, crank to make sure it’s not full of fuel and keep gas off. Just give a quick spray of either and if cam timing and you have spark it should start and run for a few seconds.
 
#9
Hey Ole
It takes quite an amount of effort to turn the starter cup by hand past the compression stroke.
Yes, it's a brand new cam. I'll follow your protocol in the morning and report back. Thanks..
 
#10
When you say it feels like 11:1 compression what do you mean? Is it hard to crank? Does cam have a working compression release? If you have spark. I would drain floatbowl, pull out plug, crank to make sure it’s not full of fuel and keep gas off. Just give a quick spray of either and if cam timing and you have spark it should start and run for a few seconds.
That's exactly what happened, but I couldn't ever get it to do it a second time!
Next i'm going to scrutinize the head and use another head gasket and try to
fire some carb cleaner again like it did once this morning. It's really making me
cranky that it won't crank.HAHAHA
 
#11
You should use starting fluid (either) I know other stuff works but it does not burn clean like either. But it did start and run ok, then after it ran out the prime your saying it would not do it again?
 
#12
That's right, Ole, It wouldn't hit again and I followed the same process. I have starting fluid and will use it.
I have the carb off, should I put it back on and try to fire gas? What are you thinking about the compression
aspect of the situation?
 

chrisr

Active Member
#13
You need spark, gas and compression all at the right time. If the plug is getting wet (soaked) that plug wont fire. You need a dry good plug that is gapped at around .030 and with the gas shutoff, try a little starting fluid to see if it will fire; if it works you need to work on the carb, if not, double check your flywheel timing is correct.

Ballpark way to check timing, with the head off or with a dial indicator to check when the piston comes to top dead center, you should see the tail end of the magnet piece that is in the flywheel about halfway under your coil.
 
#16
When you say it feels like 11:1 compression what do you mean? Is it hard to crank? Does cam have a working compression release? If you have spark. I would drain floatbowl, pull out plug, crank to make sure it’s not full of fuel and keep gas off. Just give a quick spray of either and if cam timing and you have spark it should start and run for a few seconds.
Still working to get it started, cleaned the carb and tried a NGK plug, still only fires ether once in a while, not gas.
After comparing the compression of this motor with the one in my working mini it's clear something is wrong with it.
My good motor is a lot harder to turn over. Or is because the rings haven't seated in the new build? Could a valve not
be seating right?
 
#17
Still working to get it started, cleaned the carb and tried a NGK plug, still only fires ether once in a while, not gas.
After comparing the compression of this motor with the one in my working mini it's clear something is wrong with it.
My good motor is a lot harder to turn over. Or is because the rings haven't seated in the new build? Could a valve not
be seating right?
Before you try anything involving tearing down the motor, try setting your exhaust valve lash a thou or two looser.
 
#19
Hello all, O happy day! I tore the motor down, didn't see anything strange.
Back together w/ a new head gasket, lash .002, choking it, it starts after 5-6 pulls.
I run it about 15 minutes. The magnetic oil plug had 3 tiny metal strands attached.
Is that normal for a new build?
 
#20
Hello all, O happy day! I tore the motor down, didn't see anything strange.
Back together w/ a new head gasket, lash .002, choking it, it starts after 5-6 pulls.
I run it about 15 minutes. The magnetic oil plug had 3 tiny metal strands attached.
Is that normal for a new build?
Sometimes those metal strands are burrs left from the aftermarket cam being ground. I always take a soft stone to the edges of the lobes whenever I open a new cam. Not to radius it, just to knock the burrs loose.
 

Top