Started, then died, unknown cause

So, I started my 750csr for the first time in who knows how many years, it was given to me and I've been working on trying to get it running, etc etc. So, it started this morning, was running pretty good, a slight miss at idle but that can be sorted out later. It was idling and running and revving just fine for about 5 minutes, then it just died, and I have not been able to get it restarted since. It has spark, I checked that first, and I can smell fuel in the exhaust pipes, so I am assuming that fuel is getting into the cylinders. Is there something quirky that I need to look for. All the fuses are good, checked them with a multimeter. It seems like it should start, it has all the necessary components.

Thanks

John Jones
1982 750 CSR Twin

LOL no of course not haha

How's the battery?

it's not perfect, but I can get a good couple of minutes of solid good speed cranking out of it before it goes dead. it was good enough to start it for the first time in who knows how many years.

Have you checked it since you ran it. Maybe it's not charging properly. Could be the battery, or could be the charging system on the bike. You may have just run for 5 minutes draining the battery until the spark got too weak to keep it going. I'd try taking the battery to a wal-mart, they'll charge them for free, and see if that gets it going again. If it does, check the stator wiring and functionality. Even if you're getting spark, if the battery is low, sometimes it's not a strong enough spark to get ignition.

I think it's a carb issue, the spark is strong, but when I took the tubes off of the backs of the carbs going to the airbox and the right hand side carb was overflowing into the airbox, I pulled it off and it was soaked. I pulled the carbs off and turned them upside down and pulled off the bowls and the float on that carb doesn't have as much movement as the other one when the carbs are upside down. The needle and seat appear ok, I think the float may be out of adjustment, how do I set the floats?

John Jones

On most carbs, there's just a little metal tab which is what the float valve rides on, and you bend it up and down a little. Should only need small changes. To check the level, hook some clear fuel line to the drain on bottom, and open it up. The fuel will rise up to the level where the valve closes. Specs may vary by carb, but you're usually looking for 3mm off from the line where the bowl connects to the carb body. It's kind of a trial and error activity. The easiest way is to set the carbs level somewhere off the bike, and just feed the gas in through a funnel with some fuel line suspended over the carbs.

Patton has a nice little diagram of how the clear tube test works, if you dig around the carb section, you should find one pretty quick.

Thanks!!

Sometimes a float gets stuck, and you can just knock it loose by tapping the side of the carb with a screwdriver handle or some such. Worth a shot before you tear everything apaprt at least. But if it's been sitting, it probably won't hurt to get in there anyways. The finding fuel at the pipes makes it sound rich, and the overflowing carbs would definitely cause that, so it sounds like you're on the right track.

Am thinking the carbs at hand don't have overflow circuits, and must rely on non-leaking float valves with correct float height and float function. The existing float height tang setting may be perfectly okay, and may be attempting to close the float valve at the prescribed fuel level. But the float valve is failing for whatever reason to fully close when it's supposed to.

The float valve consists of a needle and a seat. Incoming fuel fuel flows through a small hole (orifice) in the seat and into the bowl. The rising float tang is supposed to press the needle point into the orifice and thereby stop fuel flow through the float valve when the prescribed fuel level is reached.

Float valve failure -- leakage through a supposedly closed float valve -- may result from dirt or grit or other crud between the needle point and seat orifice. Or may result from a worn or damaged point on the float needle. Or a crusty deposit at the seat orifice. Under these conditions, fuel keeps rising until it enters the carb throat, and then flows back toward the air box, and also flows forward toward the engine.

There's a reasonably good chance that the carbs were functionally okay before the bike sat unused for an extended period during which varnish accumulated in the carbs and in the fuel valve due to gasoline evaporation and deterioration.

Would recommend first assuring that the float valves are perfectly clean and functional before making any float tang adjustments.

Would also recommend checking the crankcase oil for any sign of fuel contamination, such as an odor of gasoline or diluted condition. And if in doubt, would change both the oil and filter, and block any further fuel from entering the carbs until the carb overflow condition is corrected.








Good Fortune!

Thank you very much for the information, I saved the diagrams. I did take the needle and seat apart today and make sure they were clean, etc, there wasn't any buildup on either the needle itself or the seat. The bike is now running, barely. With the choke all the way pulled out, it runs at very high rpm's until it warms up and then it starts what sounds like a carb backfire, more like a random hissing coming out the other end of the carbs at random. If I push the choke in a little bit the idle drops but it doesn't seem happy at the lower idle. Giving it any more than a little tiny bit of throttle results in the bike hesitating and then dying immediatly. Damnit I hate carbs. I'd even take old fashon mechanical fuel injection over these headaches lol. Not to mention I have really no experience messing with Dual Carbs. One has always been enough of an annoyance to me on cars. Now that it's running, I can start figuring out little by little what is causing the little annoyances, like why I can't give it anymore than a tiny bit of throttle.

Thanks

John Jones