80 XS650 starts, idles, will not rev at all

SDR80SX650

SDR80SX650

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I just bought an 80 XS650. It ran great for 3 days. Today I went for a ride. It started acting like it might be out of gas, first small signs of stumbling, I switched to rez and turned around. Less than a mile later it seemed to really run out of gas. I pulled to the side of the road, opened the gas cap to find plenty of fuel. The bike still starts and idled fine but the smallest twist of the throttle makes it spit and sputter. The exhaust smells very rich with fuel. There is very little stock about this bike. I read a few other threads. Changed the spark plugs and checked the slides and needles. Slides take about 15 second to drop with port covered. Fuel is flowing to the carbs. The battery is only showing 8v motor off dropping to 5.5v with the motor running. I know the carbs were cleaned last summer.

I am going to charge the battery and see what that does. Any thoughts?
 
Yes, these bikes won't run right with a battery that low. The ignition needs a near fully charged battery to function correctly. Your battery may just be going bad or the charging system may have quit.
 
definitely get the battery voltage up and check it out after that. But, I had this happen to me and I swore it was ignition related ('90% of carburetor problems are ignition' :laugh:) and after 3 weeks of fruitless ignition investigation and parts swapping I wound up having to replace the BS34's with Mikuni VM's. Runs fantastic now.
 
Ok, sorry I haven't posted any progress of lack there of. Been busy with other projects. So, I charged the battery and it is holding fine. Still having troubles tho. I went through the carbs. They were plenty dirty so I thought that might be it but no. I put the carbs back on and fired her up. Ran great for a minute and a half then back to slightly rough idle and not able to rev at all. I do have a new detail to the symptom tho.

Starts and idles fine, well ok but won't rev unless I tilt the bike to the right. Then it idles better, pretty good and revs no problem. I have been through the carbs twice now. I thought the float was sticking or a float was flat (filling with gas). No luck there either. I can't figure any other reason that could cause the lean of the bike to affect its ability to run. I have checked fuel, it is flowing very well to the carbs.

Ideas?

P.S. I am running Mikuni's
 
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Sure sounds like carb problems to me. Go to the "Tech" section and find the Carb sub section. Lots of info in there as to float levels etc.

Have you set the float levels correctly? Are you sure the pilot circuit is clear.............pilot jets, passage ways, and mixture screw starting setting. Are the rubber plugs in place under the pilot jets?
 
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I pulled the carbs and completely disassembled the trying to make sure everything was clean and clear. There was fine sediment in the float bowls. I assembled everything exactly as it was prior to dis-assembly because it ran fine before this problem and nothing has been changed. I do not have access to a compressor so I was not able to blow the many small passages out like I would have liked. The mixture screws were 1 1/8 turns out so that is how I put them back. One of the floats was hanging up on its hinge pin, it was slightly bent, I was able to straighten it and get the float to move freely. (I am certain) The rubber plugs are in under the pilot jets and in good condition. Diaphrams are in decent shape, Approximately 30-35 second for the slides to reach bottom with port covered. I do have a fuel filter, it is new and clear so I can see the fuel flowing through. I have checked the flow, all good.

I am going to take the carbs off again and re-double check them.

When bike is idling and leaning to left, with air cleaners off, and I try to rev I have noticed small drops of fuel spitting out. I have not seen this with the bike leaning to the right. Also I noticed the difference in the angle of lean, (left to right), (running poor to running well), is fairly slight. 10 degrees or maybe less and the problem is all or nothing, it does not progress with the angle. If I lean the bike right and rev it a little, hold that rpm and lean to the left there is a 1 or 2 second lag before the rev drops to a rough idle.

I have not checked the ATU or to see if the timing is advancing. I thought about that. If that was the issue it should at least start to increase rpms when throttled, yes? This is not the case. There is 0 increase in rpm when you twist the throttle if the bike is leaning at all left of straight up and down, just increase in roughness of the idle. Also I can't see how timing could be affected by the left/right tilt of the bike. I don't know. I am ready to check the tire pressure at this point...

Thanks for all the thoughts.
 
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You say you are running mikunis and your "Diaphragms are in decent shape"

what kind of mikuni's have diaphrams?
 
These I guess...
7c8bdc70ae0efe9fb7a6fda3fc22786a_8755.jpg

4c170527dc3640fb23d559edd0aa2b8d_8756.jpg
 
SDR80SX650 said:
I pulled the carbs and completely disassembled the trying to make sure everything was clean and clear. There was fine sediment in the float bowls. I assembled everything exactly as it was prior to dis-assembly because it ran fine before this problem and nothing has been changed. I do not have access to a compressor so I was not able to blow the many small passages out like I would have liked. The mixture screws were 1 1/8 turns out so that is how I put them back. One of the floats was hanging up on its hinge pin, it was slightly bent, I was able to straighten it and get the float to move freely. (I am certain) The rubber plugs are in under the pilot jets and in good condition. Diaphrams are in decent shape, Approximately 30-35 second for the slides to reach bottom with port covered. I do have a fuel filter, it is new and clear so I can see the fuel flowing through. I have checked the flow, all good.

I am going to take the carbs off again and re-double check them.

When bike is idling and leaning to left, with air cleaners off, and I try to rev I have noticed small drops of fuel spitting out. I have not seen this with the bike leaning to the right. Also I noticed the difference in the angle of lean, (left to right), (running poor to running well), is fairly slight. 10 degrees or maybe less and the problem is all or nothing, it does not progress with the angle. If I lean the bike right and rev it a little, hold that rpm and lean to the left there is a 1 or 2 second lag before the rev drops to a rough idle.

I have not checked the ATU or to see if the timing is advancing. I thought about that. If that was the issue it should at least start to increase rpms when throttled, yes? This is not the case. There is 0 increase in rpm when you twist the throttle if the bike is leaning at all left of straight up and down, just increase in roughness of the idle. Also I can't see how timing could be affected by the left/right tilt of the bike. I don't know. I am ready to check the tire pressure at this point...

Thanks for all the thoughts.
Click to expand...

First thing, 1 1/8 turns on the mixture screw is not correct for a 1980. Have you read the Carb guide that is in the Tech section? There is a table that gives the specs for your carbs.

You must confirm that the float levels are set correctly.

Do you have stock exhausts and air box, or as I suspect, pod filters and some kind of straight pipes? Tell us what jets you have in the carbs, the numbers are stamped on the jets.
 
I have read other similar threads and tried many of the suggestions. I have read the carb tech guide. I know the starting adjustment is 3-3.5 turns out. I tried that adjustment as well. I only know the bike ran very well in the configuration I bought it with so I set it back that way. I do not want to get 10 or 20 little, possibly incorrect for this bike, changes down the troubleshooting process and find I am worse off than I was.

Lots of mods on this bike.
full

I
I am pulling the carbs again tomorrow. I will have jet info and pics for all...
 
sounds like maybe floats are rubbing /sticking. One minute too much fuel the next insufficient .
 
When you have the carbs off, the pilot jet out, spray the carb cleaner in the pilot jet hole while watching the metering holes at the throttle plate. You should have good streams of spray coming through. Any blubbering, spitting or failure to come out?
Wear eye covering of some sort, carb cleaner can and will blind you.
 
Here's the 4 little holes in the main bore that cleaner should come out of. Remove the mix screw and it's little o-ring before blowing the cleaner through. Block the mix screw hole with your finger. Be aware that you may not be able to do a proper cleaning without compressed air .....

OutletHoles.jpg


I think your float levels are off. That's the only thing I can think of that would cause the bike to run differently when tilted. Eventually, you're going to want to change those air filters too. They're the cheapo pods and cause all sorts of tuning problems. In fact, they may be responsible for your way off spec mix screw settings. They partially block the air jets in the bell mouth .....

CheapPodFlange.jpg


Try running the bike with the filters removed to see if there's any change.
 
Main Jets 132.5
Pilot Jets 45 (factory 42.5)
Pilot Air Jets 135
I have cleared and cleared and re-cleared all passage ways in both carbs.
Blast of cleaner into pilot hole sprays out metering holes.
There are no obstructions in these carbs.

I am a little unclear as to float setting. (27.3mm or 22mm)

My suspicion is kinda focused toward the floats due to the effect leaning the bike has.
 
I have notice the air cleaners look like they could be blocking or at least partially blocking the air jets/ports. I have tried running without them, no diff. Too much dust here to leave them off long, even for troubleshooting.
 
Float setting is 27.3 if you have brass floats, 22 if you have plastic ones. If your carbs are all original 1980 models, then they would have brass floats. The plastic floats came along in '81 but can be retrofitted to the '80 carb set. You just need to use their 22mm setting if they're fitted.

You have the stock size mains in there. They're too small for your mods. Get some 137.5s.
 
Thanks for the float clarification. I have brass floats so I am going to go set them to 27.3

137.5's should I be worried about adjusting the main jet size for elevation?
 

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