New problem - Clunks when starting...

So, my bike has been running really well. Had a forum member help me get the valves balanced with his mercury sticks. Engine sounds great. Starts right up in the morning. However, today when I came home for lunch, it had starting problems. After turning the ignition on, open the choke, engine cutoff to run, and shifting to neutral, I pushed the starter button and there was a heavy "clunk" that vibrated my front end, then nothing. It is like something heavy in the engine came loose when it tried to start, then got jammed. Very weird. I tried again. Another clunk. The third time there was no noise, but the fourth time it started cranking and eventually kicked in.

Same thing happened when I got on to come home. It is a very scary noise. Sounds almost like a piston is broken, or something, until it starts to run.

Not sure if it matters, but both times the engine sputtered and popped badly until I turned off the choke. Then, it dropped to idle around 700 rpm and sounded very smooth. The ride was great with no rpm fluctuation while idling at lights and such.

I still haven't tuned the mixture, yet. It sounds good, though (except for today when it sounded REAL lean with the choke on).

 

heavy misfire from overload of fuel?
did you try it w/out choke?

 

Might be your starter clutch. Is there also a grinding/whirring noise? If so, the starter clutch is probably not engaging properly. This could be a problem with the clutch being worn out, or it could be caused by a change of oil (some synthetics will cause this).

 

Don't think I heard a grind or whirring noise. Just a heavy clunk, then nothing. Like something jammed. But, this morning I see that there is fuel leaking from the air box. Grrr! I'll try without choke. Then, I'll see what the deal is with the fuel level.

 

Well, I did notice a whirring noise after the clunk. Kind of like it was winding down. Is that indicative of a starter clutch issue? Any other way to test it?

One other thing about the fuel... I recently read something that gave me the thought that I should be closing the petcock when I finish riding. Is that the right thing to do? Since I got the bike running, I haven't ever closed the petcock except when I've had to remove the tank. Is it normal to close the petcock when the engine gets shut down?

Today, when I got to work, I let the bike idle for a few seconds, then goosed the engine a bit, then shut down. I also closed the petcock to see if that helps. Could be that too much fuel is getting into the carbs while it sits, and it is flooding the bowls. Does that sound reasonable? When I bought the bike a few months ago, I was told that the petcock is reasonably new. Might need a new one?

 

Unless the petcock has been replaced with an aftermarket one, it's automatic. "ON" is only "on" when it gets vacuum. Otherwise it's off.

You could have a float issue in which case your carbs could be filling your crankcase with gas. VERY BAD. You need to figure this one out-- if you didn't overfill the oil, and it's getting "added to" with gasoline, it will dilute the oil and cause engine damage if you run it.

 

OK. I'll plug my tube into it again and check the float level. I checked a couple of months ago, and the levels were spot on. But, since there was fuel dripping out of the air box this am, it must be overflowing somewhere...

I'll also check the oil again. Thanks for the heads-up.

 

Well, I'm embarassed to say that my bike was VERY low on oil. Not sure if that was the problem, but I sure hope not. I've ridden the bike maybe 15 times since I got it, and I haven't changed the oil yet. It was on my list of things to do... The PO told me that he thought it was fine on oil, so I didn't think anything of it. The little window is so hard to see through, that I thought I was looking into oil when I looked at it. This time, I got in really close and could see some metal in there and decided to add some oil to see what happens. I added about 3/4 of a quart and then I saw the oil line.

Dang. Now I'm stressed that I might have cooked my engine. It was running when I got here, so I'm going to keep my fingers crossed and say a prayer, hoping God listens to bonehead newbies...

 

If mine can recover from a slightly spun main bearing, thanks to the gas-in-the-oil issue pointed out above, yours can most likely recover from this, but if you somehow managed to cook a main or rod bearing, it's a lot of work. Pulling the motor isn't much fun, but once it's out its pretty much a breeze until you have to lug the engine back into the frame.

 

Put the bike on the centre stand when checking the oil and let it sit for maybe 10 minutes before you check it so the oil can find its level, if its not on the stand it will appear empty or low(if you havnt done this already) the level should be just below the top of the glass. Get an inline fuel filter, clean the carbs, check the vacuum diaphragm in the petcock it may need replacing and/or the seal behind the lever. Check the in tank fuel filter, is there dirt in the tank etc. SEARCH the forums all you need to know is there.

 

Thanks, Switch. It doesn't seem as bad today. Haven't heard the "clunk" since adding the oil.

Appreciate the advice, Bushy. Unfortunately, the PO removed the center stand to make room for the crappy 4-1 exhaust with a stupid "performance" muffler. LOL So, my center stand are a couple of cinder blocks with 2X4 on top! When I've checked it, I have just held it upright, and bent over to see. But, that obviously isn't the best way to do it. So, I'll have to have someone hold it up for me.

Anyway, got a fuel filter. I've cleaned the carbs, and they are working properly. I'll check the petcock diaphragm. That's a good idea. Fuel might be leaking into the carbs a little at a time.

Thanks!