.png "Powered by vBulletin")
I had my bike apart for some catch up maintenance, I replaced the intake o-rings, thoroughly cleaned the carbs and replaced all o-rings, checked valve clearances and measured all valve shims. When I got everything together I tried to start it up but it won't start. It kind of wants to catch but it wont, and it pops and backfires. I thought perhaps my cam chain jumped on the sprockets, as I'd turned the engine checking clearances a bit before I remembered to put the tensioner back in. I checked the cam timing as per instructions today and everything seems dead on. The #1 mark on the exhaust cam points straight at the front gasket surface when 1-4 on the advace are TDC. There are precisely 20 pins between the specified marks on the cam sprockets.
It seems obvious that I did something wrong though (who knew??). I'm pretty sure I didn't cross the plug wires, I double-triple checked them. Of course that's not always enough with me, but assuming they are right that leaves fuel, right?
I know that lean conditions will cause popping and backfiring, but can it be bad enough to make it fire directly out the tailpipe, like a gun shot? All the fuel screws are at about 2 1/2 turns out, the air screws are at 1 1/2. The carbs were all dipped, rinsed with spray cleaner and blown out with compressed air. all jets and stuff were thoroughly cleaned as well. All new o-rings from Mr. Barr. The petcock is working and all bowls fill with fuel. The airbox is pretty well sealed. I did the 'bench balancing' as per instructions. I just can't imagine what I'm missing. The carbs are off it again from checking the cam chain, I'm not sure if I need to open them up again, or not. I thought of a possible test (haven't tried it yet), if I put it all back together and cranked the engine with the plug wires disconnected for a few seconds, should the plugs be visibly damp? Any tips or hints? Help? Please?
<<<Final Update>>>
Just because this post ended up being such an odyssey I will put the spoiler here. The main cause of my backfiring seems to be that somehow I left all the ignition timing adjustment screws on the breaker plate loose, so there was quite a bit of 'break dancing' going on under the points cover. Funny, I don't remember touching it before all of this. What was I saying again? Oh yes - By the time SteveN mentioned 'checking easiest things first like ignition timing (always good advice), I'd already discovered a cylinder with no compression, so obviously the bike would not have run well, backfiring or no. The cause of THAT was that our heroine neglected to (okay she was scared to) check and adjust her valve clearances for many thousands of miles. She was damn lucky not to have burned an exhaust valve or two, that's how tight the valves were. After putting MUCH smaller shims in, setting the timing, and bench adjusting the carbs the bike runs FANTASTIC! Today I fine tuned ignition timing with a timing light and it runs even better, I guess I'm ready to vacuum sync the carbs and it should run even better yet. Still pretty smooth though.
So service those valves regularly, kids! It's very easy using Basscliff's tutorial, which includes several variations of other members. It's also a good idea to do a compression check every tune up, to keep tabs on your engine's health.
It seems obvious that I did something wrong though (who knew??). I'm pretty sure I didn't cross the plug wires, I double-triple checked them. Of course that's not always enough with me, but assuming they are right that leaves fuel, right?
I know that lean conditions will cause popping and backfiring, but can it be bad enough to make it fire directly out the tailpipe, like a gun shot? All the fuel screws are at about 2 1/2 turns out, the air screws are at 1 1/2. The carbs were all dipped, rinsed with spray cleaner and blown out with compressed air. all jets and stuff were thoroughly cleaned as well. All new o-rings from Mr. Barr. The petcock is working and all bowls fill with fuel. The airbox is pretty well sealed. I did the 'bench balancing' as per instructions. I just can't imagine what I'm missing. The carbs are off it again from checking the cam chain, I'm not sure if I need to open them up again, or not. I thought of a possible test (haven't tried it yet), if I put it all back together and cranked the engine with the plug wires disconnected for a few seconds, should the plugs be visibly damp? Any tips or hints? Help? Please?
<<<Final Update>>>
Just because this post ended up being such an odyssey I will put the spoiler here. The main cause of my backfiring seems to be that somehow I left all the ignition timing adjustment screws on the breaker plate loose, so there was quite a bit of 'break dancing' going on under the points cover. Funny, I don't remember touching it before all of this. What was I saying again? Oh yes - By the time SteveN mentioned 'checking easiest things first like ignition timing (always good advice), I'd already discovered a cylinder with no compression, so obviously the bike would not have run well, backfiring or no. The cause of THAT was that our heroine neglected to (okay she was scared to) check and adjust her valve clearances for many thousands of miles. She was damn lucky not to have burned an exhaust valve or two, that's how tight the valves were. After putting MUCH smaller shims in, setting the timing, and bench adjusting the carbs the bike runs FANTASTIC! Today I fine tuned ignition timing with a timing light and it runs even better, I guess I'm ready to vacuum sync the carbs and it should run even better yet. Still pretty smooth though.
So service those valves regularly, kids! It's very easy using Basscliff's tutorial, which includes several variations of other members. It's also a good idea to do a compression check every tune up, to keep tabs on your engine's health.
. Thanks muchly!
.
Comment