Ambo revs fall significantly with clutch pulled in

[Ambo_bubba]

Got an Ambo I've recently put back together and been posting a bunch as I work through little issues.

I'm pretty sure I've got the carbs about as well dialed in as I can but now after about 10 miles of riding, it starts to stumble and die at idle.

When I get home I test it while still got I pop it in neutral and let it idle sits right around 1200ish. Then with the clutch pulled the revs drop significantly to the point where it starts to stumble and die. If I then start it back up it idles high at almost 1500...

This only happens while it's nice and hot. Any thoughts on where to start? Thanks!

[bigbikerrick]

I would verify the valve clearances first .  Make sure they are not too tight.
Rick.

[Ambo_bubba]

Will pull the covers off and check. I did reset them about 50 miles ago with a 100 mile break in maintenance on the engine

[Antietam Classic Cycle]

In my experience, this happens sometimes after a complete rebuild, and goes away as the engine breaks in. Pulling in the clutch moves the crank forward slightly, against the front main bearing's thrust face. One scenario: The radius of the crank may be slightly larger than the beveled edge of the bearing and when the two meet, the engine slows down. Second scenario: there is little too much forward crank movement, and the connecting rods are binding slightly.

[Ambo_bubba]

Interesting input... At what point do you consider it broken in enough that I should start chasing other causes?

Is upping the idle to around 1500 acceptable in the meantime to deal with the issue?

[Antietam Classic Cycle]

Interesting input... At what point do you consider it broken in enough that I should start chasing other causes?

Is upping the idle to around 1500 acceptable in the meantime to deal with the issue?

It's usually gone by 500 miles. Since Loops are supposed to idle in the 850-900 rpm range, 1200 rpms should be sufficient.

[Ambo_bubba]

Roger that, will up the idle slightly and dot my is and cross my ts on the clutch cable and valves and then check back in here in a couple hundred miles.

Thanks for the wisdom!

[Dimples]

I had a similar problem with my Ambassador. It idled fine in neutral, but pulling in the clutch made it start to stall. I removed the clutch push rod and discovered the throwout bearing was disintegrating.

[Ambo_bubba]

Worth checking, throw out bearing is new as are all the clutch components...

[guzzisteve]

It is most likely the clutch and not the crank. Adjust the arm more for further engagement.

[Ambo_bubba]

Adjusted the valves (they were a hair loose, but not by more than .01in), adjusted the clutch per Greg Benders site. Started right up, pulling the clutch in and out made no difference at all. Was optimistic and went for a ride, same result as earlier, pulling the clutch in kills the bike, leaving it in neutral fine. Other thing is typically when it does this the oil light flickers and comes on as it dies. After a couple stumbles and keeping it going it'll stay on at what I consider an idle (can't tell from the tach since it's bouncing all over the place) so I have to keep the Rpms up to slightly higher than where I have the idle set when it's not doing this to keep the light off. 

One observation I made was at the same time the idle stumble starts, the tach gets super wonky and bouncy to the point where it never settles on anything.

Other thing I noted is I have a very slight weep from the head gasket on the left cylinder, just below the spark plug.

Any thoughts? It really only happens after about 10 or so miles of riding around town. Even if I let it warm up for a bit extra long the bike rides great up untill the 10 mile mark

Thanks!

[Antietam Classic Cycle]

Perhaps it's time to re-torque the heads and then adjust the valves.

[Ambo_bubba]

Will give that a shot, was going to do a pan off oil change and re torque at 300 miles but thinking I'll do it at 200 instead.

[Aldo]

One observation I made was at the same time the idle stumble starts, the tach gets super wonky and bouncy to the point where it never settles on anything.

Thanks!

You mention a tach.  Does it have an Eldorado dash with electronic tach?  If so, unplug it and see if it improves.

[Vagrant]

If it were me after thr re-torque I'd hit the interstate and put on 200+ miles changing the rpm on a regular basis. JMHO.

[pressureangle]

As an analogy, classic cars with carburetors and automatic transmissions need a richer idle mixture than manual trans cars to accommodate the torque converter load at idle. Perhaps put a half turn in the idle mixture screws and see if it improves.

[Ambo_bubba]

You mention a tach.  Does it have an Eldorado dash with electronic tach?  If so, unplug it and see if it improves.

It's got the civilian dual gauge dash, with an electric tach. I'll give this a shot

[Ambo_bubba]

If it were me after thr re-torque I'd hit the interstate and put on 200+ miles changing the rpm on a regular basis. JMHO.

Sounds like it's time for a road trip