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Found a '79 CB750L anniversary edition for a great price and brought it home yesterday. Of course, it ran great at the dealer (even from a cold start) but started giving me problems on the way home. For one thing, it just smells like the fuel mixture is way too rich. Also, it started stalling when idling... and because I had to start it up so many times I ended up draining the battery too.
So a quick jump later, and a fun ride home riding the throttle at stop lights, I've got her parked in my garage. It was dark by that point, so I haven't done any thorough inspection of the bike yet. The first thing I'm going to do when I get home tonight is pull the plugs and check em out. But my thought is that there's gotta be something going on with the carbs. The only thing I did after signing the papers and before leaving the lot was flip the fuel valve to "ON" because the dealer had it on reserve. Maybe there was some debris in the line or something fouled up the carbs. Does this sound reasonable? I'm assuming that the idle stalling has to do with the pilot jet. I would adjust the pilot screw, but on the dealer lot she was idling at about 1100rpm after taking the choke off. Is there anything else I should be looking for? Any ideas as to why it seems like it's running so rich?
Thanks!
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It sound like you are on the right track. I would try draining the carbs first. There is a screw on the bottom of each float bowl. loosen it and let the carbs drain.I would open the petcock and try to flush out any debris that might be in the carbs. If that doesn't work you probably will have to remove the carbs to clean them. Will the dealer give you any help?
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Yeah, the dealer would probably give me some help. He's actually a friend of mine (and also drove out to jump the bike,) so I trust him. The problem is, I'm in the north suburbs of Chicago, and he's just across the Wisconsin state line. I'm going to try to tackle this myself, because I'd hate to get stranded on another 50 mile ride.
Thanks for the advice though! I'll definitely drain the float bowls tonight. I figure it's been a while since the bike has seen some riding, and we hit a few rough roads on the way. Something got in there. With only 17k miles on it, I can't imagine that it got nearly enough love and attention. Looks great though. No rust anywhere, and no scratches.
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Do what rick v says and you may have sucked some crud up and plugged the slow jets so may need removed and cleaned. Don't stick a drill bit through, use a broom bristle or strand from a wire brush.
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Thanks for the advice. This is obviously going to be a weekend project for me. I'm going to just pull the carbs off and clean them and see how that goes. If the performance is still lacking, then I guess I'll rebuild 'em.
One thing I noticed was that this bike idles very slow with the choke on. About 600rpm. It will die if it doesn't have a little bit of throttle open.
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I'd say that's normal. Idle should speed up as it warms.
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This post was updated on .
Ugh... okay now I came home tonight and found it leaking gas (slow drip) from the float drain tube. I traced it back to the #1 carb (left side when seated)
What the heck?! I know it wasn't doing any of this at the dealership.
So I turned the fuel supply off. Anything I should look for when I tear this apart?
ETA: Now I'm finding gas in the air box. Is this maybe from the crankcase breather or would it be coming back from the carbs? Also, pulled all the plugs and they're all carbon fouled. Not too bad, but definitely too rich. It's like every step I take I'm finding something. I'm amazed that she ran so well.
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Man, I don't think these carbs have ever been opened up. Not too dirty, but definitely some corrosion on the brass parts. I can't get the needle set screws out of the vacuum cylinder. I also can't get the primary nozzles out either. On any of the carbs.
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yep, i guess thats normal for these bikes, especially if they sat for a while I have the same bike, i finally got it started today, does yours still leak from the bowl, and what was it, mine does that every now and then, Im thinking its just some muck clogging the needle, mine also only runs on choke and dies when you give it too much throttle or take it off the chocke, any suggestions?
Jon M
1979 CB750L Limited Edition
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Cleaning & rebuilding the carbs definitely solved my stalling problem. I don't know if the thing still leaks though, because I turn the fuel supply off when I park it. A habit I never picked up with newer bikes. Even though I know the petcock itself leaks in the ON position (and thankfully not RESERVE), I'm pretty sure the carbs don't leak anymore.
Basically my air/fuel mix was way too fuel rich because of worn float valves and float levels that were too high. My spark plugs were also gapped wrong. Too much gap. Since doing that work, it hasn't stalled at idle once. It still runs a little rough here and there, but I think I know what that's about. I need to do a whole bunch of things that I probably can't afford until it's too cold to matter anyway. I finally got my valve shim tool the other day, so that should help. I think once I got the clearances set, the timing adjusted, carbs synced, and leaky airbox boots replaced the bike will finally run smooth.
Contrary to my paranoid ramblings in other posts I've made about the bike, I no longer believe it has a compression problem. Once the compression tester gets here, and I've got enough time to do the test, I'll know for certain.
Mine didn't die with throttle though. that might be another issue. My bike seems to run better the faster it's going.
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