Topic: '82 CB650 running on 1-3 / 4 cylinders

[gmoneymagna]

Hello all! I have an issue and I'd like to pick the your collective brain.

Bike: 1982 CB650SC Nighthawk
Modifications: Minimal. Handlebar replaced. Front fuse box relocated (temporary wrap in electrical tape)
Recent relevant maintenance: In the last 1,000 miles I have changed and gapped the spark plugs, adjusted the valves (x2), changed the oil, added a UNI foam air filter designed for the stock airbox. I have hooked the carbs up to a sync but they were spot in. I have never removed the carbs on this bike for the 4 years  I have had it.
Other relevant information: There has been a right sided, top-end tick for ~8 months that increases with revs. It is not loud or harsh. I adjusted the valves repeatedly in order to make this go away and it did not. It feels to have full power and up until recently ran perfectly. My working diagnosis for this issue is a slight exhaust gasket leak.

The problem: It will only run on 1/4 cylinders (cylinder 4) without help. It needs choke and throttle to start and then quickly dies. Only the 4th exhaust header is warm the remaining three are cold.

Workup so far: I have checked for blown fuses, and unhooked ground wires and so far nothing. I have sprayed starter fluid in the airbox without the filter (3 starts for a total of about 6 squirts of fluid) and the bike with rev up to ~4k rpm then come down. It will run extremely rough with some throttle and dies immediately afterwards. At this point exhaust headers 1 and 2 are slightly warm, 3 is cold and 4 is hot. I recently filled up gas 9 miles ago at a local gas station and used 91 octane (I know >86 doesn't matter) ethanol free gas like I have for years.  At this point I think I am being pointed to low fuel delivery caused gunked up carbs and bad gas. The bike leans left when parked so perhaps this lead to carbs 1-3 being gunked up by mislabeled ethanol gas more than carb 4. I would rather not tow the bike home (I have no truck or trailer). I may go back and pull the spark plugs but I'm not sure exactly what I would be looking for, and  I have never had a plug foul on this bike. I just want to make sure I'm not missing anything before I pull the carbs for the first time.

Thanks for the help!

[jgger]

Disclaimer alert! I'm not a pro!

That being said it does sound like a fuel issue. Do pull the plugs to see if they are black and sooty,  or wet. Lay at least one from a cold cylinder against the motor while it is connected to the plug cap and crank it and look for spark. If you have spark then maybe open the drain screws on the carb bowls to see what you get. If no fuel then pull a fuel line and check for fuel flow from the tank. If there is fuel in the carb bowls you may have gotten a load of water at the last fill up.

If it is a water issue you need to drain it out of the tank AND carbs then replace with fresh fuel.

Hope that gets you going. I would be hesitant to pull the carbs on the roadside, it would be better to get it home first.

[gmoneymagna]

Spark plugs 1 and 2 have sparks against the frame so I stopped testing the rest. Neither were soiled. Drained the float bowls and all had liquid to give. Went ahead and pulled the carbs and cleaned the exterior (first time pulled in 6 years owning the bike). So far the bowls have a thin film of clay colored material in some places that wipes away but overall nothing too nasty in my novice opinion. I am lucky that my year of carbs has a removable pilot jet so I will pull the main and pilot jet and needle tomorrow in all the carbs and spray cleaner and air through them. Either way I have learned a lot about my bike by just pulling the carbs for the first time.

[fizzlebottom]

Hi there. I've got your same bike. It sure sounds like your carbs need a thorough cleaning. You almost undoubtedly have clogged slow and/or pilot jets. You mentioned a thin clay colored material, which points to the fuel going way past the point of being good. You've taken them off the bike and removed the bowls. You need to follow the Carb Rebuilding Guide. These carbs are similar enough to our VB44Cs that you can follow just about everything. The only difference is that ours do not have air cutoffs. You do not need to break apart the banks, so don't do that either.

If you haven't done so already, get rid of the vacuum petcock garbage that our bikes came with. Use liberal amounts of carb cleaner spray and be very very thorough. Once you've got them cleaned (including making sure the float needle seats are clean), shiny, and bench-sync'd, you're half way done. Now comes the hard part: putting them back on the bike. Get ready to swear a bunch.

Good luck.

[gmoneymagna]

Hi there. I've got your same bike. It sure sounds like your carbs need a thorough cleaning. You almost undoubtedly have clogged slow and/or pilot jets. You mentioned a thin clay colored material, which points to the fuel going way past the point of being good. You've taken them off the bike and removed the bowls. You need to follow the Carb Rebuilding Guide. These carbs are similar enough to our VB44Cs that you can follow just about everything. The only difference is that ours do not have air cutoffs. You do not need to break apart the banks, so don't do that either.

If you haven't done so already, get rid of the vacuum petcock garbage that our bikes came with. Use liberal amounts of carb cleaner spray and be very very thorough. Once you've got them cleaned (including making sure the float needle seats are clean), shiny, and bench-sync'd, you're half way done. Now comes the hard part: putting them back on the bike. Get ready to swear a bunch.

Good luck.

Thanks for the comment!

I have taken the carbs off. Aside from thoroughly cleaning the exterior, the internals seemed okay to my noob eyes. In the bowel there were some spots of a clay colored  film I could wipe away. I took out all the pilot and main jets and blasted them with carb cleaner and compressed air, but honestly none of them looked clogged and I could see light through them. Importantly I changed the gas in the tank (probably should have done this first), put the carbs back on with lots of swearing like you said (it was also 100F outside) and the bike runs again! Who knows if it was just bad gas or if I unplugged something in the carbs. I didn't pay much attention to the floats but I have never had an issue with gas leaking and they looked spotless inside.

I did not bench sync, and I honestly am not sure what that is exactly. It is running pretty smooth but I was planning on syncing the carbs on the bike like I've done before. However today I have noticed a spark coming from my spark plug boot when it touches the engine (and my finger!) so I will have to sort that out before syncing the carbs.

Thanks again!

edit: Also I'm not really sure what to do about the vacuum petcock. I have heard bad things about them in general, but the petcock doesn't appear to have a vacuum line to it (maybe it is downstream on the right side of the carb bank). But either way last year I spent 60 freaking dollars on a new petcock that said it fit this year of bike and it's working great so far so I don't plan to change much!