Topic: 1978 CB550k - Running poorly after 30 minutes of riding.

[tylersilicate]

I had a post a few weeks back about my bike sputtering and backfiring. I thought I had fixed the issue by changing out my spark plugs and doing some routine maintenance. But I never really fixed it. If I ride for over thirty minutes(I assume this is when the bike starts to get hot) it starts responding very poorly and will eventually conk out. I can let it sit for a minute and then it will crank up and ride fine for maybe 30 seconds and will start doing the same thing. It does fine on my work commute every day (~15 minutes) but anytime I take it for a distance it starts to act up.

Any ideas?

[WarwickE36]

A coil might be failing, if it has stock points the condensers could be suspect as well.  Its a place to start, I would say its more likely electrical than fuel. 

Are all the pipes equally hot when it fails? if 1/4 or 2/3 are cold, that's most likely another sign of electrical failure.  If it were say 1/2 or 3/4 its more likely fuel. 

[mrbreeze]

Warwick is correct. Thats a real easy way to seperate either of those causes. Once you figure out which system is causing the problem......its much easier to troubleshoot.

[Spanner 1]

Fuel starvation.. !!!....... vacuum in the tank and/or plugged-up petcock. Ride with the gas cap cracked open and see if any improvement... but better, undo your petcock and clean it's passages... good luck.

[mrbreeze]

That very well could be the problem Spanner but I'll tell you this. A plugged up fuel petcock will give you the same symptoms as having a bad coil conection. Years ago, I put Accel coils and wires on my bike. You have to do a little fabricating to get those coils mounted properly because they are bigger than the stockers. Well....I was in a big ole hurry so I tie wrapped them into place and called it good. I didn't have any problems for over a year and mostly forgot all about my hasty job of mounting them. What happened over a year later was one of the coil wires got pushed out of the coil but not all the way. It was an intermittent problem that drove me nuts and I was sure it was fuel starvation also. Couldn't find anything wrong with fuel delivery or carbs and then I rembered the coils that I was always meaning to get straightened out. Sure as sh!t........I got my hand up in there while it was acting up and wiggled things around. Low and behold......it picked up and started running like it should.The thing about checking the temp of the pipes is a diagnostic God send. If its 1-4 or 2-3.....you check ignition. If its 1-2 or 3-4 check fuel. Very easy to do and it won't send you down the wrong troubleshooting road.

[dave500]

ignition gremlins result in most of the carb rack removals and tear downs it seems,make sure your ignition is spot on,you cant guess,it must be perfect!,check it all twice,,dont glance at it,use your finesse.

[tylersilicate]

In regards to the first two posts.. I took it out this morning and it seems #4 is cold (slightly warm but not scalding like the other 3) just #4 though. So could that be a coil / electrical problem?

[mrbreeze]

It could be either one but at least you have it isolated to just 1 cylinder. You could have a clogged jet (not gettin' fuel to that cylinder). You could have a fouled plug or a bad plug wire or cap. Time for some detective work on your part!!!

[Tews19]

I am interested to see where this goes.... Never thought about the temperature to the cylinders until The SHop that did my carbs told me I have two cylinders running 20 degrees colder then the other two..... SO I may have an electrical problem? My bike drives great minus the occassional high and hanging idle... If I move the throttle forard tho I can sometimes make it drop...

[tylersilicate]

After riding it again just a minute ago.. It started immediately acting up (after sitting 4-5 hours) all 4 pipes were warm this time.

[TwoTired]

Tell us what the spark plug deposits look like.  (all four)

[Spanner 1]

O.K., now I'm goin' with crappy main fuse connection......

[WarwickE36]

Never thought about the temperature to the cylinders until The SHop that did my carbs told me I have two cylinders running 20 degrees colder then the other two..... SO I may have an electrical problem? My bike drives great minus the occassional high and hanging idle... If I move the throttle forard tho I can sometimes make it drop...

More likely not fully cleaned idle circuit, i.e. idle jet, passages, potentially float height at well.  Pull the carbs re-clean everything making sure its perfect then set float height while you're in there.

Are you running pods?  If so its more likely the pods screwing with your AFRs...get a stock box and filter and see what happens.

If its a stock steup make sure there are NO intake leaks especially on the carb/manifold side, but carb/filter side matter almost just as much... Check for loose clamps, holes or weather cracking in boots, airbox has all its nuts and bolts holding it together.... You can check for air leaks using brake cleaner just squirt it around the areas I mentioned it the RPMs rise you have a leak.  Fix it and re-test