VERY LOW IDLE AND BOGS UNDER LOAD

[DarkMonster620]

2004 M620

Last Desmo service, October 2015, performed by me, last oil/filter service, performed at dealer April 2016.

Customer states bikes idles very low after "fast idle" is disabled, engine idles at about but no more than 1000rpm+-50; while riding it, it will suddenly bog down when given gas.

Values measured with Socio and Centurion: TPS 2.7° Trim 18  Inj time 2.4ms air bleed screws, 2.5 turns out on both cylinders

OEM exhausts with cat wont heat up, after a while riding it or idling it, they are still just warm and was able to grab them without gloves, cat part was also just warm to touch; for some reason HEAVILY leaning towards the exhaust being "fubar" since, exhaust coming out is cold and if I place my hands on either exhaust engine will shut down.

Any ideas?

[clubhousemotorsports]

when you can grab those exhausts what is the engine temp?

Possibly a clogged cat?

seems odd that an oem exhaust would be that cool at running temps.
Is the bike fueling correctly?
why does it have 18 trim if all stock?
air fuel or CO?

it sounds like something is not right there I would look at the plugs
compression/leakdown
check CO at the ports
check air filter for mouse nest

[DarkMonster620]

Sorry, CO measured at the measuring ports in headers avg for both 3.4% front 3.4 rear 3.6 . . . airbox has resonator cut off . . .

In my bike with open top airbox and Termis I run 23 trim setting and CO avg was 3.8%, usually rear a bit richer than front . . . This is one of the few Monsters from Gen 1.5 that has OEM exhaust set up, plugs are nice, no leaks doesn't smell like gas when idling, just has a real low idle and will bog when under load

Sadly at home I don't have too much equipment, Gunson CO meter Socio/Centurion for diagnostics and no bike to compare since mine is just occupying space.

[clubhousemotorsports]

can you put your exhaust (cans)on his bike to test?

[DarkMonster620]

Did that, OEM cans, bike ran better and I got burned !!! Didn't know I had them laying around

Still idles a bit low with airbleeds at 2.5 turns out . . . gonna check tomorrow morning, when is NOT raining, and screw them to 3 turns out . . . Didn't bog as hard

[Howie]

Remove the mufflers and see what happens or go old school diagnostics.  Hook up a vacuum gauge to one of the ports for throttle synch, or better yet, both with a tee.  Note reading.  Bring engine speed up to 3-4K RPM.  Vacuum reading goes down, clogged exhaust.  

Eric beat me to the exhaust.

[DarkMonster620]

Remove the mufflers and see what happens or go old school diagnostics.  Hook up a vacuum gauge to one of the ports for throttle synch, or better yet, both with a tee.  Note reading.  Bring engine speed up to 3-4K RPM.  Vacuum reading goes down, clogged exhaust. 

Eric beat me to the exhaust.

Will do . . . now, where did the missus placed my vacuum meter?

[DarkMonster620]

Went OLD school, vaccumm for both intakes was about wvenat idle and 3500RPM . .  took cans off, made lots of noise, bike didn't bog as hard . . . Re-installed my old OEM cans and from 1 to 10 it was an 7.5 . .

Would an expanded tank that builds up preasure be an issue?

[Howie]

As long as it is venting properly, no.  Clogged cats make me wonder what your CO levels are, particularly at cruise. 

[DarkMonster620]

As long as it is venting properly, no.  Clogged cats make me wonder what your CO levels are, particularly at cruise. 

Idle CO avg for both, 3.9% . . . at the rear, front cyl 3.8% vert cyl 3.9%, trim setting 18, any lower CO would drop avg of 0.4  . . .

After a while of riding or just sitting in my uncovered car port, bike wouldn't start unless I opened the tank cap and a BIG "POOOF" would come out and then bike would start normally . . .

Customer has bike now and states that after a while riding, it will bog but, NOT as hard as before . . . for some reason, I am leaning towards the tank internal venting . . .

[Howie]

POOF not good.  Poof in or out?

[ducpainter]

Idle CO avg for both, 3.9% . . . at the rear, front cyl 3.8% vert cyl 3.9%, trim setting 18, any lower CO would drop avg of 0.4  . . .

After a while of riding or just sitting in my uncovered car port, bike wouldn't start unless I opened the tank cap and a BIG "POOOF" would come out and then bike would start normally . . .

Customer has bike now and states that after a while riding, it will bog but, NOT as hard as before . . . for some reason, I am leaning towards the tank internal venting . . .

It's not uncommon on steel FI tanks for the vent tube in side the tank to become clogged solid with rust.

They can be cleared, but it's a PITA.

Blow compressed air through the vent hose. That will tell you. That doesn't answer the low idle issue, or the bogging. Usually they just stop running.

[DarkMonster620]

POOF not good.  Poof in or out?

OUT

It's not uncommon on steel FI tanks for the vent tube in side the tank to become clogged solid with rust.

They can be cleared, but it's a PITA.

Blow compressed air through the vent hose. That will tell you. That doesn't answer the low idle issue, or the bogging. Usually they just stop running.

Sadly, plastic tank

[ducpainter]

OUTSadly, plastic tank

I see now way for that plastic internal tube to become clogged. Perhaps the screw in fitting might rust and clog.

The pressure vent is built into the cap. It's a little rubber diaphragm. Might be stuck. Pressure in the tank would not inhibit the flow of fuel.

[DarkMonster620]

Gonna get it back Saturday for a few hours . . . will take fuel cap off