Running on one cylinder

[duluthmuffler]

Just limped my bike back to work, after a short 15min. ride. I started to notice a miss on just the right cylinder. It slowly got worse and worse. Kind of acting like "out of gas, or dying battery" By the time I had gotten back to work, the right side wasn't firing but only occasionally. Spatting. The symptom was its worst when it was in gear/under load...running on one cylinder mostly... in neutral it didn't seem to be so bad.

I did some preliminary checks. The tank valve on that side flows gas ok. When in neutral and at idle, if I remove the right-hand spark-plug wire, the bike will stall immediately (This bike is set up with a double lobed cam and dual output coil...not sure if removing the plug wire and stalling is tell-tale of my problem, another problem, or not a problem...pretty sure it would do the same on the left...)

The left side works fine. The right side will have a successful igniting stroke every so often if I open the throttle wide open.

Is it spark or fuel?
I'm hoping it runs better after cooling off or something so I can go home.
This is on a blue 77
Thanks!

 

[XSLeo]

On the dual output coil the spark travels from the coil down the plug wire, across the engine to the other plug, up the wire to the coil. Pulling either plug wire off breaks the circuit and stalls the engine.
So pulling a plug wire in your case isn't really effective. On a points ignition with to coils it works.
My best guess is a dirty carb on the side not running. Idle circuits is a good place to look at first.
www.amckayltd.com/carbguide.pdf
Possily a fouled plug.
Leo

 

[duluthmuffler]

Found a bunch of related posts after I submitted my thread... sorry for posting then reading... here's an interesting bit from XSLeo

"If one side has plugged idle circuits it won't run on that side until you rev it up high enough where that carb gets into the mid to upper range then that side will start to run, thus the sudden increase in power.
I might try removing the idle mix screws, count the number of turns out first. Use a can of carb cleaner, put the straw in the hole the screw goes in, cover with a rag. spray the cleaner. This can knock a blockage back into the float bowl. Put the mix screw back in and set to what it was.
Test ride, if it runs on both cylinders at idle then the carbs need a bit of attention."

 

[duluthmuffler]

Thanks Leo!.. I'll do some reading and cleaning this weekend

 

[duluthmuffler]

So I've downloaded and printed and bound my handy Carb document. Thank you guys for putting it together! What a resource. I cleaned up both carbs using the ChemDip product. And have read in other posts about not dipping the carb bodies because of the butterfly shaft gaskets.. I'd love to dip the carb bodies too... Is it okay to dip them if those gaskets will be replaced?

I put the carbs back on after their cleaning... with no change in how it was running.

Using that tip about grounding the spark plug on my dual output system was a great tip Leo. I pulled the plug and ran it and viewed a tiny yellow spark. I then swapped the plugs and tried running it, and both sides are running now. And I've installed two new fresh plugs, which improved things even more. However...

The cylinder that was not running before is now smoking, and doesn't have the same pop the the good side does...

I did install a new cam chain on this build.... this motor is still in its break in stages...
would "loose" head bolts be cause?

Once the bike has cooled off and I'm done with work, I'm going to check the cam chain tension, and valve clearance, and check the head bolts for proper torque... all stuff the carb guide instructs to do first.

Why would one side run nice while the other is off? Still carbs? Do them again?

..any other thoughts?

 

[XSLeo]

Yes, unless you are experienced with carbs in general, these carbs in particular it may take at least three tries to get the carbs cleaned. That's about average for not to bad a set of carbs, if really bad a few times more might be needed.
Search carb cleaning and you will find many methods of soaking your carbs with out the very harsh and hard on the rubber parts Chem dip.
Depending on how fouled the nonrunning cylinder is it may take a few miles to burn out the fouling.
On the headbolt torque I like to torque to stock specs on initail assembly.Let it set over night retorque everything to spec except the 8 large nuts. Those I torque to 30 lbs.
Let set over night, retorque as desribed. Then start it up and warm it up. Shut it down then the next day retorque as before. Then start it, ride it for about 50 miles. During tis first 50 miles get the bike up in say 3rd or 4th gear, about 30-35 mph. A firm to hard roll on, accelerate briskly up to around 45-50, back off throttle and coast in gear back down to the 30 to 35. Repeat as many times as you can, during the first few miles after about 25 to 50 miles tyour rings are about as zseated as they are gonna get.
Doing this on a bit of a long hill works even better.
This hard roll on, coast loads the rings and seats them in quickly.
Now return home, drain the oil, pull the filters, both sump and side cover. Inspect the filters and oil for any and everything.
Let it set over night, retorque the head. Probably by now when you bring the nuts and bolts up to torque they are not turning more. If so this means they are holding the torque. It may take another few heat cycles to get to the point when you are torqueing the nuts and bolts won't turn more.
After you reach this pont you can check the torque during the winter shut down procedure or the spring wake up procedure.
Leo

 

[gggGary]

Run a compression test. Can we see pics of the plugs? Will that cylinder run if you rev it far enough under load or not?

 

[xjwmx]

may take at least three tries to get the carbs cleaned.

That reminds me all carb sprays are not created equal. Berryman's has a bit of a cult following. I like Autozone house brand because it burns my skin. Really bad! I figure it must have something going, to do that...

 

[duluthmuffler]

Wow! Thanks for the expert break-in regimen. On my rebuild, I left the pistons in the sleeves so the rings are at "what they are" status. I'm saving up for that 750 and rephrase rebuild... This rebuild was aimed at new gaskets and a new cam chain.

Yesterday I checked the cam chain tensioner and backed off that nut about a 1/16".
Also the exhaust valve clearance (is "lash" the proper term there?)... was a bit small...intake was fine.

At this point both cylinders were running, and the problem side was still smoking and running weakly without much "pop" like the other side.

After I checked all this I ran the bike for a while. Rode it around the parking lot, trying to put a bit of a load on it... It seemed to be stable and the smoke dissipated. I think that Leo is correct in that it just took awhile to burn off the "fouling"...

It was running well enough that I thought I'd finally ride it home so I could do more tuning from my own garage... just as I was about to leave, I thought to try adjusting the problem cylinders idle speed screw... I sped that side up and balanced the overall speed to that low unbalanced/balanced speed and felt that it had dramatically improved. Both sides are running pretty well now.

So I think my problem is fixed, and now I'm just at the tuning stages! It backfires a bit while its cold.. I know now that I've got those large replacement jets from mikesxs, and some hard and broken gaskets here and there. I'll do a proper carb synch next , and see if I can't improve some grounding for my ignition too. I think its a bit suspect.

My problem I think was my carbs paired with an old spark plug, and not knowing how to test that plug.

Thank you guys for the power of knowledge. I will have some really happy carbs very soon. Happy riding!

 

[duluthmuffler]

So I'm getting a fouled plug(s) very easily - which is what was happening last year I'm pretty sure. Q: To foul, does the gap need to be bridged? Can a plug foul by being coated with gas/oil? Can plugs become varnished? Pictures to come this evening.

Q2: When fouled by oil would there be a lot of smoke involved? Would it get very smokey before it stopped working?

i know that its fouled plugs because I have swapped plugs and the dead cylinder switches sides. (Prior to this, I reversed points/wires and carbs and the dead cylinder did not switch sides).

This winter I cleaned the gas tank, cleaned the petcocks, new 2 single coils (green), wires, boots, cleaned my carbs 10 times (I need a smaller pilot jet 27.5 vs. 25 - 1977) I'm running the points and single lobe set-up again. Valve lash is good, timing is good, cam chain is good. Exhaust has some holes. Carbs have a little bit of a whistle, so I think butterfly shaft seals. I'm running 1.75 turns out. Before the fouling, things seem very happy. 2nd kick start-up cold, responsive revving up and down.

I've not yet synched the carbs, but now that I can do the dead cylinder method that'll be a synch.

Here's another piece of my puzzle. As a shortcut , when I put this motor together, I used the cylinders with pistons left inside from a junk yard motor. Wear on the walls didn't seem too bad at the time... but what do I know.

The valves/top were re-done by a shop two years ago, so I know they are fresh. I've not yet done a leakdown test. Compression was 135-ish on both.

I had been getting a lot of backfire, and things smelled hot. But I'm not totally trained in the symptoms of lean/rich. But I moved it 1.5 to 1.75 turns out. Now I would guess my symptoms are lean and rich. ???

The latest foul came when I was engine breaking a lot down a big hill, then sloww through my neighborhood. Big pilot needle? Junky junkyard rings? I just want to ride!

 

[duluthmuffler]

Dead cylinder comes to life sometimes at higher RPM. But its very sparse and sporadic.

 

[TwoManyXS1Bs]

Engine braking down a long hill, followed by oil fouled plug(s) usually means bad rings. The oil gets sucked up past the rings during closed throttle coasting. Probably just junkyard roulette, and you found a bad one. Proper fix is cylinder hone and new rings at a minimum, rebore with new pistons/rings more likely. Only way to tell for sure is to pull the cylinders, pistons and rings, and have them inspected and measured...

 

[pamcopete]

That reminds me all carb sprays are not created equal. Berryman's has a bit of a cult following. I like Autozone house brand because it burns my skin. Really bad! I figure it must have something going, to do that...

Yea, I like that. I also like cleaning solutions that make me dizzy or interfere with my breathing . The ones with the skull and cross bones are my favorite. They gotta be the real deal.

 

[duluthmuffler]

Maybe these pics will help finalize the bad ring prognosis.

I'm not being very scientific with all this. But I'll try to explain it the best I can. I've got three spark plugs, #1 and #2 are newer last year with 50 miles on them, and #3 was from before. I left the carbon on #1 to show you guys. #2 and #3 were cleaned with emery cloth and wiped off.

#1 has a lot of carbon but it has been the best running. Tonight the plug eventually fouled after trying to sync my carbs.

#2 Looks clean but never ran. This is what it looked like after the other cylinder ran for 30 seconds.

#3 This plug didn't foul tonight but has. This is what it looks like at the end of my "testing"

 

[TwoManyXS1Bs]

Shiny/dark porcelan. Yep. Oil...