1979 Honda XL500S – Hard to Start
Checking the wiring has been straight forward but without a running engine this project has taken a little longer than expected.
I did manage to get it started once but since then it’s only been good exercise for my right leg. The first issue I found was the ignition switch was wired wrong and didn’t turn the engine off. This was quite easy to fix but it meant that it didn’t turn it on either.
I changed the plug, just in case, and got another coil for it as there was a small crack in the original one. Once the key was wired properly there was good spark, however it still wouldn’t start.
I checked the fuel tap and discovered that the on setting didn’t work as expected but the reserve setting did. With not much fuel in the tank, the main tank didn’t work until you filled it to the top. There was a post online about this problem and the fix was to shorten the pipe on the fuel tap assembly that goes up into the tank.
Once the fuel was sorted and flowing into the new Mikuni Carb, it promptly dumped it out of the overflow and all over the crankcase. Bugger.
So off with the carb and another good clean, took the jets out and blew compressed air through them, made sure the float wasn’t sticking and re-read the Mikuni manual. The Mikuni carbs don’t have a traditional butterfly type choke and this one had an “enrichment” lever on the side of it, a separate system designed to work as a choke.
With the key on, fuel on and enrichment lever on, in the down position, the engine started but wouldn’t idle or rev. Yay.
Once the engine would start things went better from there. It was just a matter of getting the pilot jet (mixture screw) and the idle jet sorted out to play nicely with each other. I started experimenting by turning both jets in until they stopped and then writing down the amount of turns out until the engine would start, idle and rev cleanly. This took a bit of time but eventually I was able to get it running, ride it around for a bit and see how it went, then adjust the settings a little bit more.
Once it would start and idle I noticed it was running a bit rich by the exhaust smoke and a little backfiring. One issue I found with the pilot jet was that it would screw out to so many turns but after a ride to test, it would be back to where it had been before. I managed to fix this by adding a little bit of grease to the thread, which then seemed to stop the screw from moving. I found some really helpful information on tuning the carb in the manual and some forum posts online at Thumpertalk.com
So now that the engine is running I will just need to check the wiring, brakes, change the tyres and whatever else it needs to get it road worthy.
1979 Honda XL500S – Hard to Start