After completing the re-installation of carburetors and air cleaner I thought trying to start the motorcycle for the first time in a few years was going to be easy. Turns out it wasn’t so easy.
I went out to the shed ready to hear the bike run for the first time and double checked the gap on the spark plugs, installed the plugs, and setup my auxiliary fuel tank with a golf tee plugging the carburetor vacuum hose since there is no where to connect the hose until the tank is reinstalled.
It’s ready to go. Turn on the key, looks good. Choke engaged. Bike is in neutral and clutch lever squeezed. Kill switch is in the Run position. Press the Starter button. Nothing!
Now I had cranked the bike over previously while performing the compression test. What happened? I determined that I could jump the starter with a wire between the battery positive and starter relay, but that doesn’t provide power to the ignition circuit to start the bike.
There are three switches that can interrupt the starter circuit. One is a sliding contact switch in the clutch lever that requires you to have the clutch disengaged to start the engine, the second is the rocker switch for the engine stop switch with Run and Off positions, and then the starter button itself.
I first took a look at the clutch switch since it seemed that it would experience the most wear and tear every time you shifted. I took that switch apart and it didn’t look too bad, so I cleaned it up and put it back together. Still nothing. I then learned that you could bypass this switch in the headlight bucket. The wires are spliced in that location with opposite male/female connectors. Still no go.
So now it’s time for the multimeter and a large plot of the color coded wiring diagram to start checking the continuity of the wires. I confirmed first that the wires to the clutch switch and the switch itself are working fine, but I am leaving it bypassed for now to free up a hand for other tasks. Just make sure the bike is in neutral before you try to start it…
At this point I was explaining to my son what I was trying to do and went to show him that the starter button wasn’t working. What? Now it works! Stop the wire checking and lets see if it will start.
Cranking, but not starting… Pull the plugs again and check for spark. 1, 2, and 3 have spark, but 4 does not. Trial and error showed the that spark plug and the spark plug wire were ok, but the spark plug boot had issues. Nothing available at the local auto parts store, so I had to order some NGK spark plug boots online.
I continued to try and start the bike knowing that it would be running on three cylinders and eventually it did start, which is when I found out that the tachometer cable is broken too so I couldn’t really tell if it was idling properly. Add a tachometer cable to the order. What I could tell is that it was actually only running on two cylinders, number 1 and number 3 since the number 2 exhaust pipe was cold to the touch after running for a few minutes.
You can also see the comparison of the spark plugs from when I first took them out and after running the bike for a few minutes. 1 and 3 look ok, 2 is very wet, and 4 hasn’t been run much.
A week later, the NGK spark plug boots and tachometer cable arrived. Replaced the boots and tachometer cable and fired it up. It was idling really low… probably why it was fairly hard to start the first few times. Raised the idle to 1,100 and all cylinders appear to be firing and the engine revving nicely. Only problem now is that it has an intermittent misfire/backfire occurring at idle, but not when the engine is revved to 2,000 rpm or higher… More work for another day. Link to a twenty second video of what it sounds like. The pops occur at the 9 and 13 second marks, but the camera did not pick up the sound very well since it is so quick. Video
The new NGK spark plug boots below. The two model numbers that I used are XB05F and VB05F. Both are 5 kΩ resistor spark plug boots with the X having a 102° angle, cylinder 2-3, and the B having a 120° angle, cylinder 1-4.
After the new boots were installed I investigated the original boots further. The number 4 spark plug boot was rattling, so I took a couple of them apart.
From left to right they are in the order that they were taken off the bike with cylinder 1 on the left. Someone was definitely messing with them before since 2 and 4 are in the wrong positions and what happened to the spring that is supposed to be inside boot number 4? (Edit: as seen in the follow-up post, https://twowheeljunkie.wordpress.com/2014/07/14/misfire-solved/, the boots were actually in the correct position, but still an issue of what happened to the spring for the boot that should have been on cylinder no. 2)
Up next, synchronizing the carburetors and solving this misfire/backfire issue.
