One Cylinder V-twin SOLVED Now with two cylinders!

[swooshdave]

Need a sanity check here:

Spark- Lay spark plug on head. Have spark.
Compression- 100 psi+ each side

Start bike, left header cold after 30+ seconds, runs rough like a single.

Rev to 3k and header gets hot and seems to sound right.

It has to be the idle circuit, right?

I had that carb in the ultrasonic cleaner for about an hour. Blew it all clean but didn't pay close enough attention to the idle passages. Maybe it was clear, I would have thought I would have noticed if it wasn't but not 100% sure. Will go in again and only focus on the idle circuit.

850T with VHBs

[canuck750]

Compression is pretty low, a healthy engine will have 150 ~ 160 psi per side.

Did you check the compression with the carbs off or the throttle held wide open?

[swooshdave]

Compression is pretty low, a healthy engine will have 150 ~ 160 psi per side.

Did you check the compression with the carbs off or the throttle held wide open?

No, press fit compression tester. Just held it to the spark plug hole and hit the starter button. Regardless of the compression reading since they were equal that seems to eliminate compression issues as the cause for once cylinder not to idle, correct?

[tris]

If you can, switch the carbs side to side and see if the problem follows the carb

[rodekyll]

Is it possible to have jets mixed up/in upsidedown/slide backwards?

Otherwise, I'd think the idle circuit is a logical place to start.  Sometimes if you rev it and use your hand for a choke you can suck the obstruction out of the jet.  We used to call that an Italian tune-up, so it's appropriate to use here.

I'll be trying that tomorrow on my Honda outboard, which hits one cylinder all the time, and the other three randomly.  I know mine is a fuel problem because I can add ether and it revs normally, and I can choke off the air to a suspect and pick up speed.  The problem is what to do about it without removing the miserable stack of four, placed vertically behind a big plastic intake screen.  I hate that job.

[luthier]

When that happens, pull the plugs and I bet you'll find the one that isn't firing is wet. You left the fuel taps on or on reserve and one side , the lower one gets flooded. The only way to get it going again is to clean the plugs again. Then make sure, one tap goes forwards and the other goes backwards.

[swooshdave]

Is it possible to have jets mixed up/in upsidedown/slide backwards?

Upside down?

I know the main jet and idle jets are interchangeable but I have the idle jet (50) in the right place, which means not attached to the accelerator.

[swooshdave]

If you can, switch the carbs side to side and see if the problem follows the carb

Great suggestion. It's on my list of things to try.

[acogoff]

    Just saying here, in case you missed it. A sparkplug that is shot will fire in open air just fine but under pressure it will not.

[swooshdave]

    Just saying here, in case you missed it. A sparkplug that is shot will fire in open air just fine but under pressure it will not.

Then why would it work at higher rpms?

[Idontwantapickle]

Then why would it work at higher rpms?

That's what they do.
It is a good idea to check the carbs but as the rule goes most carb problems are ignition and most ignition problems are carbs. 
It's easy to change the plugs but sometimes hard to tell if they are actually working without some sophisticated tools and techniques. Always be willing to start over with a fresh outlook if your troubleshooting dead ends.
If the carbs are clean and jets are correct and level is right but still has symptoms then get new plugs and maybe condensers. Watch the points for arcing. If that all checks out swap the carbs right to left just to check.
But in the end you'll facepalm when you discover it was probably exactly what your intuition told you it was to start with.
Hunter

[swooshdave]

That's what they do.
It is a good idea to check the carbs but as the rule goes most carb problems are ignition and most ignition problems are carbs. 
It's easy to change the plugs but sometimes hard to tell if they are actually working without some sophisticated tools and techniques. Always be willing to start over with a fresh outlook if your troubleshooting dead ends.
If the carbs are clean and jets are correct and level is right but still has symptoms then get new plugs and maybe condensers. Watch the points for arcing. If that all checks out swap the carbs right to left just to check.
But in the end you'll facepalm when you discover it was probably exactly what your intuition told you it was to start with.
Hunter

It's got a Dyna on it so no points.

Yes, I absolutely know that when I find out what it is it will be simple, just hard to find.

NGK BP6ES sound right? I bet I have some of those for my Bultaco.

[Kiwi_Roy]

No, press fit compression tester. Just held it to the spark plug hole and hit the starter button. Regardless of the compression reading since they were equal that seems to eliminate compression issues as the cause for once cylinder not to idle, correct?

Don't forget to open the throttle for the compression test

[swooshdave]

Don't forget to open the throttle for the compression test

Will do!

[Groover]

Was going to say check the condensers by seeing if your points are sparking excessively when running, then I read that you have Dyna ignition, so that doesn't apply anymore. Spark plugs still spark somewhat with failing condensers. Could it be a failing Dyna ignition or part of it? Not familiar with that ignition.

Good luck.

[rodekyll]

Yes, BP6ES.  Hand-check the gap.  The 'pre-gap' is like 0.038 -- HUGE!

[unclepete]

When I got my T-3 and finally got it started , it ran on one cylinder .
It would start with choke and run on both , but with choke off it would drop to one cylinder . Dead cylinder would pick up about half throttle .
The small #50 jet was clogged . Bike had sat for about a year . 

[swooshdave]

Yes, BP6ES.  Hand-check the gap.  The 'pre-gap' is like 0.038 -- HUGE!

I tried again this morning after cleaning the idle circuit REALLY GOOD. Just started it and same thing. Ok, can officially cross that off.

I don't have a BP6ES on hand so I grabbed a plug out of the Ducati. Fired up, idled on both cylinders.

Problem solved! Plus the carbs are clean! Really clean!

Thanks to everyone for their suggestions. They were all good.

On to my next problem...

The plug gap should be .025, correct?

[swooshdave]

When that happens, pull the plugs and I bet you'll find the one that isn't firing is wet. You left the fuel taps on or on reserve and one side , the lower one gets flooded. The only way to get it going again is to clean the plugs again. Then make sure, one tap goes forwards and the other goes backwards.

My taps are clearly marked R and O which I assume means RESERVE and OFF. And they are sided so both handles go forward for Off. And the hoses are not connected so both taps have to be on. I'll address the fuel lines later.

[swooshdave]

https://youtu.be/1EheaCQecdA

Both pipes hot. I think this is the right lumpy, lumpy sound.

[Tom H]

I tried again this morning after cleaning the idle circuit REALLY GOOD. Just started it and same thing. Ok, can officially cross that off.

I don't have a BP6ES on hand so I grabbed a plug out of the Ducati. Fired up, idled on both cylinders.

Problem solved! Plus the carbs are clean! Really clean!

Thanks to everyone for their suggestions. They were all good.

On to my next problem...

The plug gap should be .025, correct?

If the Duc plugs were not equal to the NGK BP6ES, go get a set. Sounds like the plugs were the problem if I have read this right to get the bike to idle properly.

Now get the right plugs!!

Glad it's running!! Good luck!!

Tom

[swooshdave]

If the Duc plugs were not equal to the NGK BP6ES, go get a set. Sounds like the plugs were the problem if I have read this right to get the bike to idle properly.

Now get the right plugs!!

Glad it's running!! Good luck!!

Tom

Duck plug was just to test the plug out. Totally wrong plugs, but I made sure they were shorter so no valves were hurt.

Fresh set of NKGs installed.

New stainless brake lines. Bled brakes. So much easier than those Norton Lockheeds to bleed!

Will sync carbs in morning, test ride and then to the show.

AAA is on speed dial. 

[balvenie]

Happy Trails mate

[twhitaker]

This goes to reinforce the earlier statement that carb problems are electrical. Good find.