Running Rich?

[rdraidr]

Wanted to pick your brains; when the bick is cold and I add the choke, I get a miss/backfire. The exhaust smells like unburned fuel. When the bike warms up, no issue. I've cleaned the carbs, but did not do a wholesale replacement of items. I've also run seafoam through them. Thoughts?

Thanks.

[WingAdmin]

It's supposed to run rich when you have the choke on - that's what the choke does. It should not be enrichening to the point that you get a miss/backfire however. Have you balanced the carbs recently? How about checked your plugs?

[virgilmobile]

A bunch of possibilities here.
Start the bike from cold...keep it under 1000 rpm.....shut it down after 6 seconds....LIGHTLY tap each exhaust header to verify if in fact each cylinder is firing.They should be just getting warm.

Just one dead cylinder will pass gas through to the exhaust.
And yes it will run on 3 cylinders too.

Do check the looks of the plugs,they tell how the engine is running too...Have a look here...viewtopic.php?f=15&t=13929

If all are cylinders are firing,it can be one of the fuel enriching valves leaking or not closing off...Check the actuator lever on each one while operating the "choke".

Poor compression or uneven compression will cause poor running when cold...that's when it's really noticeable.Compression should be within 5psi of any other cylinder.Usually above 125 psi.
A dirty air filter.....they don't last forever.

What else did I forget.???

[rdraidr]

Of course the choke makes it run rich....

It could be a lot of things, but here's what I checked. First, this was a transfer engine from a donor (wrecked) bike which replaced a blown motor (prior owner). I did not do a lot to the motor other than clean it up. It was "running" when I found it. I had previously sync'd the carbs.

I pulled the plug wires, one at a time (replaced each time) to hear a change in RPM. Pulled #1 (RH front), nothing. Pulled #2 (RH rear) stumble and barely run. Pulled #3 (LH front) stumble. Pulled #4 (LH rear) nothing. Each wire was getting spark. Pulled out the compression gauge.
At idle: #1 - 70psi, #2 - 110psi, #3 - 115psi, #4 - 75psi. I've run it a while with no smoke on start-up and clean looking oil.

So, I'm thinking about a valve job.

Thoughts?

[rdraidr]

Thinking about it a moment more, I should pull all the plugs and then test the compression. Possibly do a wet test.?

Right?

Thanks

[virgilmobile]

Truth be known....With a cold engine,remove all the plugs....Attach the compression gauge to one cylinder..OPEN the throttle wide open and crank the engine.No more than 3 seconds or so to get a good reading.
Repeat for each cylinder.
A compression reading should be no more than 5 psi difference between any 2 cylinders.
A 10 psi difference will lead to a uneven balanced engine.You'll never get it to run just right.Been there,done that.

You can get different readings if the throttle is left closed and the carbs are not synced as they will restrict the available air going to the cylinders...so open the throttle fully.

>>>>>If your compression is way off or very low as you said,do the valve adjustments and check the timing belt marks before doing a valve job.<<<<<

Remember..a cylinder must be able to breath.The intake must be clear(air cleaner) and the exhaust not restricted.
A engine will run fair on compression as low as 90psi on all cylinders.
We usually find the high mileage wings running 125psi or more.
70 psi is just too low to fire the fuel effectively.

[rdraidr]

Can one perform a valve adjustment on a 1200? I thought they were hydraulically adjusted. I've ordered a new timing belt and will verify the setting - scary thought that the valve train is miss-aligned.

Thanks

[virgilmobile]

This is the very first mention that it is a 1200.
Yes the valves can be adjusted,however it is usually done only once,at new and after head work.
It's assumed that the hydraulics will handle it from there.
Don't just arbitrarily change the belt in the hope it will fix the compression.It's just one thing to verify that is spot on.
Test and check everything.

[rdraidr]

Opps, you're right - guess I assumed since I was in the 1200 forum....still not a good thing to do.

Will check all I know to do. Thanks for the input.

[rdraidr]

Pulled all the plugs and held the throttle open; unplugged the fuel pump, of course.

I came up with ~ `165psi per cylinder. The deviation between them was less than the 5psi marks on the gauge.

So, I'm now thinking the valves are fine. Rings are good. Slides are good at wide open at least.

I took each plug, one at a time, and tested them for spark on the engine block - all good there, but I've heard of bad plugs, even new.

Thoughts now?

[virgilmobile]

Keep us posted of the compression results,air cleaner out,throttle open.

[rdraidr]

OK, those were the results; air cleaner out, throttle open, plugs pulled.

Did we cross?

[rdraidr]

Put it all back together. Set the choke and she fired up. Ran it for a few seconds and shut it off. Touched each exhaust pipe and they all were warm. Pulled each plug, and I could hear the RPMs change, some more than others(?).

Wondering if I can have old and leaky plug wires; not getting all the juice to the plug?

[virgilmobile]

We just missed the timing Of the posts.Your compression test indicate a good engine.It's probably time to tend to the carbs.SOme Sea Foam may clear it up or a tear down and hand cleaning.
It sounds like the spark is OK as long as the plug look like there firing clean and are the right ones.

[virgilmobile]

Sorry mate.I get a brain fade once in a while....your first post...uneven cimpression at a idle...later post...even compression open throttle...duh...sync the carbs.
The ones that were low also don't fire very well at a idle,the engine does have a off idle rattle too ...Right??? It has to be the throttle settings off just a bit.This explains the uneven cimpression with the closed throttle.
You know...that's one way to check the carb sync too. Even compression open and closed throttle.
I think you got a new test procedure here.

[rdraidr]

Wingadmin suggested balancing the carbs as well. I did this not long ago; at least I thought I did.

Took it out today for about a 50 mile ride mostly at 70mph. Pulled a hill really well; had power to spare.

No gas smell when I returned.

This stuff drives me crazy.

I'll do the carb balance again. It's good practice.

Thanks.

[Ghostrider52005]

Not trying to be simplistic here but Im a simple minded guy boardering on retarded .
IF the bike starts fine cold and runs fine warm and all it does it get rich with the choke on I would just add less choke if it even needs choke to start and not worry about it.

[rdraidr]

Not trying to be simplistic here but Im a simple minded guy boardering on retarded .
IF the bike starts fine cold and runs fine warm and all it does it get rich with the choke on I would just add less choke if it even needs choke to start and not worry about it.

The only issue to date is the smell of unburnt gas and the back-fire that occasionally occurs when the engine is cold. Let it warm up and nada to the backfire. No simlistic questions to me. I tend to overthink issues.

On another note, I ordered a set of timing belts and in the package came an article about an air cut-off valve. Says it can cause similar results to what I'm experiencing. Anyone have any experience with this?

Thanks.

[micfitz]

Sounds like a faulty slow air cutoff valve. This is normally held open by a spring but if it’s faulty and stuck closed at idle or the diaphram is leaking then the mixture will run rich until the rpm is increased into the main jet range. This condition makes it impossible to fine tune the Pilot screws or synch the carbs. I’m no expert and could be wrong about this. I’m just an expert at removing and replacing the carbs