Rebuilt Engine not turning over...

cgguy09

cgguy09

1971 CB350 K3
Hey team,
Just got done rebuilding my engine, but she won't turn over. It seems every fourth rotation or so I get a little back fire & a flame out of the back end.
Here is the status:
Gas Tank: Full
Spark Plugs: 12 months old, good blue spark.
Compression test (cold): 155-160 for both cylinders.
Valve Gaps: Within spec 10~11 mm on Exhaust 5~6mm on Inlet.
Points: timing light shows light at F & LF.
Exhaust and Inlets are screwed in tight (I tried a leak test with no results).
Carbs: Haven't been torn apart, worked just fine 2 weeks ago. I've noticed gas on the spark plugs when I've pulled them after attempting to start the bike.

I feel I preformed the adjustment on the points correctly...but my intuition would tell me the problem would stem from this... I know the compression is low, but its on a cold engine. I'm kind of at a loss & am going to break for the evening and hopefully get some recommendations for tomorrow.

As always thanks guys.
 
What motor?

Edit: if it's the CB350, I want to say a weak electrical system. If your battery is low at all, it will be hell to start.
 
Sorry Rich,
1971 CB350 K3.
The Battery was fully charged and measured the correct Voltage, I have a good blue spark on each of the plugs.

Deacon,
I'll take a look at the spark advancer tomorrow. I thought that could only go on one way though...
 
Next time you check spark at the spark plug: as soon as you see it, check that the cylinder you pulled the plug from is at TDC by looking thru the plug hole. A flashlight or even a pencil in the plug hole should make it obvious.
 
Big Rich said:
Next time you check spark at the spark plug: as soon as you see it, check that the cylinder you pulled the plug from is at TDC by looking thru the plug hole. A flashlight or even a pencil in the plug hole should make it obvious.
Click to expand...

That was something I looked for, I put a socket wench extension in there & confirmed the spark occurred when the cylinder was at TDC on both cylinders.
Thanks for the recommendation though, lets me know I'm thinking along the right path...
 
I know you can't mean 5-6mm etc. valve lash - you mean 0.005mm or whatever it is right? At 5-6mm your valve wouldn't move :p When you rotate the engine by hand, are the valves moving as you would expect them to? Have you done the static timing test with a test-light to confirm the right plug would fire as the matching piston is reaching TDC of the compression stroke?

150-160PSI isn't low compression - that's great IMHO.
 
cgguy09 said:
Deacon,
I'll take a look at the spark advancer tomorrow. I thought that could only go on one way though...
Click to expand...

The advancer can only be installed one way, but if you took it apart to clean it up, it can be re-assembled 180 degrees out. I did that on my 450.

CC
 
Re: Re: Rebuilt Engine not turning over...

CCRider said:
The advancer can only be installed one way, but if you took it apart to clean it up, it can be re-assembled 180 degrees out. I did that on my 450.

CC
Click to expand...

Yeah that was a source of head scratching with willow at the very first DTT get together.
 
Hooking up the coils backwards will have the same effect as 180° advancer.
Left coil should be blue, right is yellow.
 
Uh oh, I knew I shouldn't bored out those valves....Just kidding. My bad Tim, you'll have to forgive me I'm a simple man, I just tend to move decimals around as I please. But yes, I rechecked everything yesterday & confirmed it was in spec. Thanks for the vote of confidence on the Compression test, I was a little worried about that...

I haven't checked the movement of the valves, that is something I'll do this morning. I have a pretty good idea how they should open and close. I looked in the manual but didn't see any explicit cycle noted, but I'll figure it out.

I did (sort of) take apart the spark advancer apart. I just took off the breaker-cam (cylinder) for cleaning. That was about it. I'll strip that back down & see if it was installed backwards. At that point I'll go back through & redo the points gap/ignition timing.

Thanks guys, as always appreciate the input.
 
Tim,
No the Cam is made so it can only install one way and it has to be put in a certain manner when the cam chain is at a certain rotation.
 
Is it possible the Cam Chain Tensioner could be inhibiting it? I messed a little with that before I put it back on. I wouldn't think that would affect it but I'm not sure...
when I pulled it off the spring and plunger were pulled and locked half way back..thats about how I re-installed it.

Okay so I did a little test, I took off the CCT holder and plunger and put pressure on it myself. Once every engine rotation the engine seems to stick when it gets to the TF mark. The engine won't turn when I put pressure on it.
When I say once every engine cycle I mean every other time it passes LF.

I don't know that much about the Cam Chain Tensioner but this doesn't sound right... maybe a problem with the cam chain itself.
 
The occasional backfire you're hearing leads me to believe that your plugs are firing while the exhaust valve is open. I'd focus on making sure your ignition timing is correct.
 
Bit of an update:
I properly tensioned the cam chain and I couldn't manually turn the engine at the alternator.... This tells me Ive assembled the engine somehow incorrectly...I'm fairly positive I messed up with the cam chain, I'm going to break it back down & put it together...wish me luck & speed
 
Might have just been 1 tooth out on the chain - easy thing to do and would be nearly impossible to set the valves properly.
 
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