Help! Dropping Cylinders as I Ride...

[BlueOxD350]

Hello, I'm the new guy today... and have a big problem on my hands. I'm leaving Thursday for a 1200 mile trip, but my bike is giving me fits. Here's the scenario:

She's a 79 XS11 Special, with 28,000 miles on it. I was given the bike 3,000 miles ago and have had no problems with it to speak of.

When the bike is cold, with full choke it fires right up. Idle for 1min, half-choke, 1min, no choke. Ready to ride.
I pull out of my drive and on to the road, and it runs smooth, accelerates quickly, and at 70mph it just sails along.

However, in five miles, it will drop a cylinder. (#1? by my right leg as I ride). Still riding, I pulled the plug (getting shocked in the process - so there is spark) but it runs the same. Five more miles, it will drop the next cylinder (#2 if my numbering is correct). Same symptoms - if I pull the boot, I get shocked, but it runs the same - bad. Alas, five more miles later it will die (I'm assuming it dropped another cylinder at that point). If I wait 10min or so, it will fire right up and off I go again. And the same thing will happen, only more quickly.

If, as it starts acting up, I just pull over, set it to half-choke, and let it idle, it will clear up in a few minutes, firing on all four again.

I've scanned all 504 posts this morning and didn't see anything that fit ... although my scan was hasty at best. I'm infamous for having those "I've never heard of anything like that..." problems. Anybody have some friendly advice to help me get on the road by Thursday? Thanks a bunch!
-Dan

[luischia]

Something alike happened to me once, it turn out to be a clogged fuel line, it was not completely clogged, but just let go through enough fuel for idling, but if you start to accelerate, the level on the carburators will began to drop, and the corresponding cylinder to fail.
Depending on the distribution and lenght of the fuel lines to the carbs, it will start dying in order from the shorter fuel line to the longest one. basically, from left to right.
It can be something else though, but this happened to me, I hope it is something easy to fix on your bike.
The line that failed in my case, was the one from the fuel tank to the octopus. (I'm only using the left side petcock)

[DiverRay]

BlueOx,
1. Check the fuel lines for kinks.
2. check the vent lines going to the airbox and make sure they are clear.
3. Check the vent on the fuel tank, it's in the cap. Make sure it's clear.
4. Do as luischia said, check for partial blockage in the fuel delivery system.

[BlueOxD350]

Thank you both for quick, and very informative, replies. I'm heading out there now to see what I see ... it's funny how you get a "complicated fix" stuck in your mind and can often overlook some of the more simple troubleshooting.

[webbcraft2150]

Originally posted by DiverRay
BlueOx,
1. Check the fuel lines for kinks.
2. check the vent lines going to the airbox and make sure they are clear.
3. Check the vent on the fuel tank, it's in the cap. Make sure it's clear.
4. Do as luischia said, check for partial blockage in the fuel delivery system.

Yea, what he said and try new plugs (non-platnium). My 80g had that nasty habit, chased electrical and fuel systems. Found my rig simply does not like NGK's, they came in it from the factory but they would give up the ghost after couple thousand miles, intermittenly at that, finally found she like el-cheapo AC's.

[trbig]

Just for your info....

The #1 cylinder is on your left as you sit on the bike... numbered in order to the right. #4 was the one you described.

Your coils will spark #1 & #4 together... one will be on the combustion stroke and the other will be on the exhaust... basically a wasted spark... and #2 & #3 fire together.

One fuel line runs the left two carbs and another line feeds the right two.

That being said, if you have a problem with the outside cylinders together, or the inside two together.. start looking at electrical problems. If it's the left two or right two together... look at fuel problems first.

Welcome to the site and good luck!


Tod

[JWSanders]

That sounds suspiciously like a pickup coil wire problem, too.

Pull off the left side cover (timing cover) and give the wires coming from the pickup coils a tug from front to back to make sure they aren't broken. They can look fine on the outside but be hanging on by a thread on the inside.

[79XS11F]

Sounds like a fuel supply / delivery issue. Given that it's the fuel paired cylinders that are affected. do both 3 and 4 go off line at the same time?
Rob

[Dads11special]

Here's a dumb question - would that be the left side as you are sitting on the bike?

[TopCatGr58]

Hey BlueOXD350,

I'll agree with the fuel folks! You've got a special, and don't know if you're aware of that wonderful little device called the Octopus! If the PO didn't remove it, then it, too, can go bad preventing proper fuel flow! You can test this by turning the petcocks to PRIME. IF it keeps running and doesn't shut down on you, then you can be pretty sure it's the Octy. Either the vacuum lines to it are leaking, or the internal valve is stuck, corroded and not moving enough to open enough to allow a quick enough fuel flow, so it runs dry while riding!

You can remove it, but it would be easier for now just to run it on PRIME, just try to remember to turn it back to OFF when stopped to help reduce the chance of overflow at the carbs!
T.C.

[BlueOxD350]

Wow. I'm amazed at two things. 1) I didn't find this site sooner. 2) What a great bunch of folks willing to help out the frustrated... Thanks to all for their input.

So what I've learned: so it's #3 and #4 cylinders that have a nasty habit of dying out on me. It seems as though #4 goes first, followed shortly by #3. Then she dies.

Luischia - I flushed all the fuel lines. Some particulates, but no major restrictions. At least now they're clean.

DiverRay - No kinks in the fuel lines. There are no vent lines going to the airbox (are these the ports at the cylinder side of the carb? because they are capped off) The fuel cap leaks (bad gasket) so I guess it vents okay - but the vent looks clear, too.

Webbcraft - do more people see this same problem? I just went back to NGK's as a starting point to troubleshoot... but maybe I should go AC again?

TRBig - Thanks for the diagnostic starting point - since it's #3 and 4, I'm going to run with the fueling issue...

JWSanders - I see the posts on the pickup wire problem, but since I get shocked like crazy when I pull a plug wire at 70 (maybe not the smartest idea, but it lets me know there's spark) is this really something to check now?

79XS11F - #4 goes first, with #3 shortly thereafter. Although in my diagnostics today, I've had an instance of #3 down while #4 is firing... Generally, I'd say they go together.

Dads11 - Right side while on the bike. So #4 is the first problem-child.

TopCat - I don't have anything that looks like an "octopus" - I'm assuming this would be an inlet from both petcocks, and an outlet to four carbs. Either way, I don't have one. I have no "prime" on my petcocks, either. On, Off, Reserve, Off. There's a fuel line from one petcock to the other, and then each petcock serves two cylinders directly. Also, I need to shut my petcocks off each time I stop to keep from filling my crankcase with fuel (eventually).

I do think that it's being starved for fuel. My petcocks have (or had) a long (2") filter sticking up into the tank ... with the lines being clear, perhaps the filter is plugged up... I'm going to pull these to check if they're plugged in the morning - any idea if these are standard and replaceable, or just flush clean and reuse? Also, I pulled the float bowl drain plugs out of both #3 and 4, turned the fuel on, and get a drip about every second. Any input on if this is not enough? I guess the filter will tell a story all it's own in the morning...

Again, thanks everybody!

[AlanB]

Hi BlueOx,

We thought that all the Specials had a "Prime" position on the cocks, and an extra pair of prime lines direct to the carbs, bypassing the octy.

It sounds like your bike has had the octy removed, and the "prime" outlets linked; Highly recommended!

The octopus was a remote, vacuum operated fuel valve, which lines from both cocks go to, and with two outlets to the carb pairs.

What are the first three digits of the frame/engine number?

Fron the factory, these numbers should be the same, and define the actul model of the bike; It makes remote diagnosis a whole lot easier!!!!

If you have fuel starvation issues, try running with the fuel cap open; if it runs OK, the cap vent is blocked, and air cannot get into the tank to replace the fuel; this is a diagnosis, not a cure!

AlanB

[TopCatGr58]

Hey BlueOx,

A mere drip is no where near enough to keep the float bowls filled! It should have poured out! One thing that has not been mentioned, but will require a little more work, is the actual fuel "T's" themselves. They can get gummed up and clogged. But even after that, small particles in the fuel like you mentioned can also clog the SCREEN that is under the float valve seat!

So...first, pull the fuel lines from the petcocks, and have a bowl handy, and then turn to ON, if flows steady, then move to the carb fittings, again if flows steady there, then it's the carbs, the screens....my next bet, or the "T" fittings. You have to take a carb off of the bank to remove the "T" fitting for cleaning, but not the valve seat screens! Just the float...CAREFULLY, read the tech tips, and then the valve seat!

I'm surprised that it doesn't have a PRIME position!? It's usually with the handles pointing forward.....IIRC!
T.C.

[JWSanders]

Ah, I didn't read close enough into it. Probably is a fuel problem. But it never hurts to check them. Only takes a few minutes.

One thing's for sure...they will break eventually.

[amasher69]

hi, i just had the same problem. change the fuel lines with auto line. the lines don't "kink" untill they get warm. once i changed them no problems.