Rebuilt top, won't start, kicker binds up, and backfires

aconley003

aconley003

New Member
While I've visited this site for the past few years, I'm only now posting my first thread. I ride a '72 cb350 k4 (twin) that's been modified a bit from stock. I'm running a smaller 12v battery, new rectifier and simplified electronics, mufflers from a Thruxton, kick start only, stock carbs and engine, and pod air filters. Before I embarked on the top end rebuild it was smoking consistently from the breather hose and running a bit choppy in terms of idle. I've put it back together but now it won't start. Here's what I've done:

So I tore down the top because the blowby was making all my pants smell bad. I found that the original ring gaps had worked their way near one another, and there was a lot of carbon build up on the tops of the pistons and all throughout the head. I cleaned everything, and installed new rings (pistons and cylinders were still within spec), gaskets, oils seals, lapped valves (guides were in great shape) and did trickle-down tests. I put it back together and remounted in the frame.

-Tappets were adjusted to .002 and .004 respectively (prior to setting chain tensioner: could this effect clearance?)
-new points installed and dialed in with light tester (but advancer could be out 180 deg possibly, but I doubt it)
-Installed new plug wires with NGK splicers into original coils.
-New Condenser
-charged battery
-cleaned carbs (adjusted floats, cleared jets)

So now the lights/horn/signals all work. But when I kick it over, I've got nothing. After 6-9 kicks I get a huge backfire from the left pipe and somewhere in the kicks I get a minor backfire from the right where the header meets the muffler (I need a new clamp). It doesn't even feel/sound like it wants to kick over (no coughing or anything). Then, the kick lever will occasionally bind completely jarring my entire body as I sink my weight into it. But then the next kick goes all the way through smoothly (perhaps binding up with an ill adjusted rocker? or the cam chain binding somewhere?)

I haven't checked for spark yet. Perhaps the coils are bad or the wires/splice kits. But bad current wouldn't mess with the mechanics of the kick lever? Any ideas? Thanks
 
So when you put things back together, did you put the cam sprocket on correctly? Didi you set the timing? why have you not checked for spark before you put the plugs back in? A newbie error is not enough fuel in the tank when trying a restart. get back when you find out about the spark.
 
Tested the spark and it seems fine. There was good bluish-purple spark on both sides. I appreciate the note about the fuel, and there WAS plenty of fuel. But I apparently forgot to turn off the petcock for an hour or so and came back to find my garage floor full of gasoline. So my guess here is that the fuel-shutoff pins in both carbs are shot. I'll put some of them on order soon. So now overly flooded carbs would prevent a solid starting, but still wouldn't explain the occasional binding of the kicker.

I did several checks on the cam shaft positioning, sprocket and timing marks. It took me two solid tries but I ensured that it was all correct and that the correct bolts went into the correct holes on the sprocket. When I adjusted the cam chain tensioner I did it according to the correction on benmirada.com, which indicated that I rotate 90 degrees past TDC before releasing the tensioner. Presumably, this pushes into the chain in its most slack position. But Mirada was working on a 73, which I don't assume would be much different from my 72.
 
You have advancer put in 180° out of rotation. Swap the coil wires (blue and yellow) and try a few kicks.
 
I switched the coil wires and gave it a few kicks. It coughed a little more than it had before (which was nothing at all), but didn't act as if it wanted to turn over. Granted, it was 20 degrees out when I tried, so maybe it was a bit too cold. I gave it 7-8 good kicks and it didn't seize up all all. Since I lost most of my fuel to my garage floor, I will pick some more up after work and try it again. I

I did set the floats, but may have gone the wrong direction with the tang. I will also correct float height and report back.
 
Although you checked carefully when you put the cam back in, its still easy to get it wrong. The symptoms you describe sound very much like your 180 out on the cam.

Take off the points cover. Take out number one plug. Turn the motor over by hand so you can watch the points. Use something soft (I use a lead pencil) in the plug hole so you can see when No.1 is at TDC. If you got the valve timing right the correct set of points (firing No.1) will spark.

Have you got a compression tester? This is the quickest way to see if your valve timing is right. If you got bugger all compression, your cams in wrong.
 
Hot500 said:
Although you checked carefully when you put the cam back in, its still easy to get it wrong. The symptoms you describe sound very much like your 180 out on the cam.
Click to expand...

I realize it's a technicality, but it's impossible to be 180° out on the cam. There's no such thing.
 
Sonreir said:
I realize it's a technicality, but it's impossible to be 180° out on the cam. There's no such thing.
Click to expand...

I stand corrected :( What terms do you use to describe when valves are opening and closing out of phase with the correct pistons.
 
That usually only happens if you're off by a tooth (or a few teeth). Rotating the cam 180° just changes which stroke is the intake/power and exhaust/compression strokes. Everything still works.
 
I'm trying to get my hands on a compression tester since all I currently have is a fuel line pressure gauge. I am fairly certain that my cam sprocket is on the correct tooth/setting and that the shaft isn't on the wrong stroke. On a compression stroke for the left cylinder at LT it falls as per normal right after rotating past LT (like it did prior to the rebuild). When setting my points and adjusting the rockers I had to hold in in place on FT and LT while making adjustments. And the same thing was true for the right side as well.
 
You don't adjust the rockers at TDC. You do it around 90° TDC. There needs to be zero tension on the arm when you adjust the tappet.
 
Fair enough about the zero tension. My manual indicates adjustment at LT or at the top of the compression stroke. I made my adjustments here making sure that the tappets were loose, or not touching the valve springs. Thus, the valves were all closed when the adjustments were made. I didn't, however, watch the tappet during the full cycle from compression stroke to compression stroke to see if the gap opened up 90 deg past TCD.

I did, however, set the cam chain tensioner 90 deg past TDC.
 
A bit of progress... I switched the coil wiring and had no binding up of the kick starter. I switched them back and it seized on the third kick. So I adjusted the advancer 180 deg as suggested (and ensured that the wiring was back to standard). Now it doesn't have any issues in that regard.

I also rechecked the tappet gaps and three out of the four were fine. I opened the left exhaust back into spec and rechecked everything. I even checked the gapping at 90 deg past TDC just to be sure that nothing opened up wider and it didn't (in fact the tappets were closer to the top of the springs indicating to me that they were in the process of opening the valves for the next rotation).

Other hiccups: 1. right carb is totally flooded out, which makes a bit more sense why this side keeps backfiring when I kick it to start. I will open it up tomorrow and readjust the float for better results, hopefully.

2. I tested the battery before starting and it measured 13.2 V. After several attempts at kicking it I remeasured and it came to 9.8. I assume that this is a dead battery, which could explain A LOT about why it won't turn over. But this is my second battery within a year. So I chased some wiring around and found that there is a wire disconnected from the stator. It is the one that attaches to the little tang. Might this disconnected wire be what's frying my batteries (or more accurately, not allowing them to charge)?
 
The green/red wire is the neutral wire. Shouldn't affect charging.

Battery does sound like it's on it's way out. An initial test is to put the battery on the charger for 24 hours, disconnect it, wait another 24 hours, then read voltage. You should have pretty close to 12.5V.
 
Compression woes. Tested yesterday and then again today. First I only got 90 on right and 110 on left. Today I squirted oil in and was able to raise both sides to a consistent 120. The bike has been quite cold and the test was at about 35 degrees outside. This might add 10-15 or so psi, but this is still way too low for proper engine functioning.

I also adjusted float height and air/screw mix. I will reset the timing and give it a few more kicks, but do you all think I will need to take the engine out again and give it some more valve work?
 
The bike will run and idle OK at those numbers, but it'll feel sluggish when you're riding it. If you're looking for why the bike won't start, compression isn't your issue (yet).
 
Fuel and/or fire then? It has a little backfire every other kick, which my limited skills points me towards a fuel/carb issue. The plugs are due for a change anyway, so I will grab some new ones and eliminate as many variables as I can.
 
Give it half a dozen kicks and then pull the plugs. If they're dry then your problem is carbs. If they're wet, then the problem is (probably) spark.
 
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