problem idling during warmup

[DimitriT]

I like to ride the 550 during the colder months but I have a nagging issue with how well it likes to idle.

The bike starts on half choke every time. It seems to be able to idle at 800-900 RPM when I take it off choke after a 15 seconds.
That tells me its running a bit rich and I can probably turn the pilot screws in another quarter turn (something I'm going to try).

But here's when it gets weird.

I ride the bike for 10 minutes. Now mind you its cold so the bike is not fully up to temp after this.
Bike rides fine though and will idle so long as its moving. But once it comes to a stop the idle drops off and the bike dies.

But if I don't stop and manage to get on the highway I can keep riding for another 15 minutes. At this point the bike is
fully warmed up and will idle perfectly from here on.

I'm trying to think of what can cause this. Seems like something gets warm enough after 10 minutes which gives the bike
trouble in idle but once it gets fully warmed up it no longer has this issue.

Could it be something in the clutch? One thing I haven't tried is to put it in neutral and see if it still dies when I come to that stop.

Any ideas are welcome.

[Rob S.]

I'm certainly no expert, but what does your bike idle at when fully warm?

I've found, over the years (decades), that the manuals are a tad optimistic on idle speeds. My Z1 was supposed to idle at 900, but I've never seen one do that.

I think the recommended idle speed for my 11e is 1,100, but I keep mine higher. I think between 1,100 and 1,400 is good for these inline fours.

[azr]

Could it possibly be your intake or airbox boots are old? while they are still cold and hard they are causing a leak but once they warm up and are a tad more pliable they seal up a leak?? also, is this a new problem?

[DimitriT]

I'm certainly no expert, but what does your bike idle at when fully warm?

I've found, over the years (decades), that the manuals are a tad optimistic on idle speeds. My Z1 was supposed to idle at 900, but I've never seen one do that.

I think the recommended idle speed for my 11e is 1,100, but I keep mine higher. I think between 1,100 and 1,400 is good for these inline fours.

The manual says 1100 to 1200. When fully warm it idles at 1200. It's impossible to know the real speed since I'm not sure how accurate the tach is. I'd like to hook up an electronic tach and measure it one day.

I should mention that once the bike is fully warmed up it is rock solid on idle. Tach needle drops perfectly when I close the throttles and I never have it go below 1100.

It only has difficulty while its warming up but not fully warmed up. Like I said, when its cold it will idle weakly around 800-900 which might mean its a touch rich.

[DimitriT]

Could it possibly be your intake or airbox boots are old? while they are still cold and hard they are causing a leak but once they warm up and are a tad more pliable they seal up a leak?? also, is this a new problem?

Yea its possible that its some sort of intake leak but I doubt it. You would think for starters that the rubbers would get looser as they warm up and leak more?

I wouldn't say its a new problem. When I got the bike it had fuel issues and I've been fixing them one at a time. The bike used to be all over the place with the idle and the pilot screws would bottom out when I tried to set the mixture. I found out the float heights were wrong, fixed that and now it is almost there except for this weird problem.

I should add I set the float heights using the recommended procedure and a vernier depth gauge. But I never actually measure them wet. I have the float bowl tube to measure them wet and I will do this in the winter.

[azr]

Well it's an easy thing to check the next time you have the carbs out. As well does that model have o-rings behind the intake boots? (never had that model so don't know)

[BigD_83]

Have you had a chance to vacuum synch the carbs yet, and set the idle by the "highest idle" method?

[DimitriT]

Have you had a chance to vacuum synch the carbs yet, and set the idle by the "highest idle" method?

Carbs have been synced and valve clearance checked recently. Oil and gas are fresh. Charging system looks to be in order. I did set the idle according to that method although there's at least half a turn of the pilot screw where I don't notice any change in idle. The bike gets about 50 mpg.

Only thing I noticed on the bike. When I have in gear with the clutch pulled in, there's a fair amount of drag on the clutch. Meaning the rear wheel wants to spin. Now I'm not sure what's expected here. I don't feel it when the bike is off the center stand. I did set the clutch cable play according to spec.

[JTGS850GL]

How about those intake boot O-rings? Were they changed out as well? Things in that area tend to leak when they get cold. Rubber gets harder and shrinks. As they warmed up they get more flexible and expand. Just a possibility.

[DimitriT]

Intake boots are new as are the o-rings. The only think not new in the intake system are the airbox side boots and the airfilter. The air filter is stock and can probably be cleaned and oiled. How often does it need a cleaning? It's probably been 10k miles since the last one. Thing is I never see any dirt coming off it when I clean it.

[DimitriT]

Just wanted to follow up on this problem.

I was able to get the bike to the side of the road when the problem was happening and had a little time to try and isolate it.

When the bike gets in this state the idle is weak and slowly dies off. But it can take ten seconds to die off as it warms up.
This gave me just enough time to pull ignition cables off the spark plugs to see if there was one cylinder in particular which
was weaker and could be causing the bad idle.

It turns out pulling the cable off cylinder #4 made no difference in the idle. So I know that's where I should look.

I had to put the bike in storage for the winter but yesterday I opened up the valve cover and checked tappet clearances
and the exhaust #4 tappet was below spec. I swapped the 2.60x shim for a 2.60 shim and got that clearance in spec again.

I guess its possible that while the bike is warming up that tappet clearance may tighten up enough to give me bad compression
and once the head warms up fully the clearance loosens up back to spec and I get good compression back. That would explain it.

Next I will drain that #4 carb and screw in my wet float height measuring tube and verify its correct. I set
the float heights dry so I can't really tell if that resulted in the right height. It's also possible I have a bad or dirty float valve.

Last thing to do is to clean and reoil the air filter. Won't be able to test run it until the Spring though.

[JTGS850GL]

I would doubt that going from a 2.60X to a 2.60 would cure what you're describing. The difference between those two shims is less then .05mm in most cases. If the swap brought #4 into spec then you still had some room to spare. Good thing you did check the valves though.

One cylinder cutting out would not cause the engine to die. It may cause the idle to be a little rougher but it shouldn't cause it to completely shut down. My guess is you still have other issues beyond what you've found on #4. Keep plugging away at it. You'll trace it down eventually.

[gustovh]

You have mentioned all that was done, but I have not seen any compression #s. My 850L used to have the problem that you describe, even with a valve adjust the compression #s were a bit low until it was fully warmed up.

I did a cold check, mid temp check, that is when it would not hold an idle and one fully warmed up. It showed a steady increase of a few #s with each check. The bike is still that way with over 53,000 on it, I just let it warm up longer and slowly reduce the choke until it will idle on it's own. It runs like a striped monkey being chased by a big cat.

So IMO there is nothing wrong with your machine.

V

[DimitriT]

Nothing like a nor'easter to get you into the workshop

I did the wet float height measurement on cylinder #4:



and compared it to #1:



both looked fine.

Here's a picture of the plugs (1 to 4 from left to right):



They also look fine. #1 might be a touch rich.

But there was one surprise. I did the compression test. Now this was cold and dry:

#1 - 130
#2 - 15
#3 - 125
#4 - 128

Yes #2 is 15. I tried it multiple times and am sure it is correct. I did a tappet clearance check just the other day so I'm guessing #2 has a stuck compression ring. Very odd but it might explain my idle problem.

Now since the bike runs fine once it warms up I'm not really looking forward to a top end tear down unless it needs something else.

Good to know though.

In the spring I'll do a warm compression test once I get the bike outdoors.

BTW, while I had my hands dirty I cleaned the foam air filter. I was surprised by how much schmutz came out of it this time. Not sure why I let it go so long. It was all embedded deep in the foam and took a while to get out. Oh well.

[Nessism]

Where are the pilots screws set? How is the air cleaner?

The 550's are jetted lean from new. My old 550T took 3.5 turn on the pilot screws otherwise the idle would hang. You also need to have the carbs vacuum synced otherwise the idle won't be stable.