Low Idle/Stalling when HOT

[ChicagoRob]

I've got the boy's 80 550L back on the road after doing a top end build (used cylinders/complete head/new rings) and correcting an electrical demon. (Another Electrosport RR went out on me. Grrr.)

Anyway, I got the float levels correct and the plug chops are looking good and it's running great until it gets hot. Not warmed up, I mean 6k rpm highway cruising hot.

Exhaust/carbs/air box are all completely stock. It does have Green Dyno coils and the electronic ignition, though. I'd swear that the valve clearances are all within spec and that the air box & boots are all properly sealed.

Here is the symptom, I'll pull up for a stop and the revs will drop down below 500. Sometimes it will stall out, sometimes not. If I blip the throttle, most of the time it go back up to the 1k range and stay there. Sometimes not. Besides that, it still runs well. No hesitations, no popping, no surging anywhere in the power band.

Any thoughts?

[Nessism]

How about setting the idle speed higher with the adjustment knob on the carbs?

[ChicagoRob]

How about setting the idle speed higher with the adjustment knob on the carbs?

I've tried that but when it's not in this condition it idles way too fast when it's warm. Up around 2k.

I kind of expect it to act like the 1100. Idles low when cold so it needs a little choke, then settles in at 1k when warm and hot. As it stands now, I have to adjust it down during the warm up phase, then adjust it up as it warms up. This just doesn't seem right, you know? This kinda sounds like a rich condition but the plugs aren't showing rich.

[mike_of_bbg]

Rob;

Check your voltage at the coils.

This sounds a lot like what my bike was going though. After a particularly annoying session last week I finally got her home and looked through a lot of things. Turned out I was only getting 8.5V at the coils. Did the coil relay mod and no stalling at idle yet (the RPMs do occasionally dip from 1100 to say 900 at hot idle but it doesn't stall). It used to take quite a bit of cranking to get her to start and now she starts faster than my 21st-century fuel injected cars do.

High heat can cause resistances to increase, plus the voltage dip of dropping to idle makes this a big suspect. One more thing to look at, anyway.

[ChicagoRob]

I forget to mention that it has a coil relay mod and a new 220A AGM battery. Sorry.

I'll check it out anyway. Can't hurt.

Rob

[Nessism]

I don't know what to suggest other than making sure there are not any intake system leaks, such as from the intake boots and/or their O-rings, and tweaking the pilot screws. The 550's tend to like 3 - 3.5 turns open on these screws. A vacuum sync is also required if you want a properly smooth idle.

[don]

Just for Schlits beer and giggly boobies try taking it for a trip that would get it to produce your symptoms but with the fuel valve on PRI. Befor I spent a whole year trying to diagnose a problem on my 550, it would do the exact same thing. Normal around town riding, no problem, extended riding or high reving riding and it would act "flooded out" at the stops. It turned out, in my case, the petcock was going bad. Worth a try I guess.

Do a search on "gas in airbox" or all posts by "Don", you'll see what I mean.

Good luck.

[TheCafeKid]

I don't know what to suggest other than making sure there are not any intake system leaks, such as from the intake boots and/or their O-rings, and tweaking the pilot screws. The 550's tend to like 3 - 3.5 turns open on these screws. A vacuum sync is also required if you want a properly smooth idle.

Agreed. Also just pulling the plugs and looking at them without doing proper plug chops on the circuit (pilot in this case) that you're having trouble with wont show you much. If you're not doing plug chops, you're looking at either whatever circuit you were in last, or an overall read.
Ive also found that if your area uses ethanol in the fuel, plug chops aren't really as helpful as they used to be. They'll tell you if you're really rich, or really lean, but the plugs dont colour like they do with straight gas. They'll either be black, white, or grey, and thats about all you'll get...

[niclpnut]

Hey mate. Mine is/was doing the same thing. Tracked the problem down to a bad charging system.

I was having to constantly adjust the idle screw even after fresh carb cleaning and sync. Thought it was the coils on mine too, so I did the relay mod. However after trouble shooting the charging system I found that the stator was going out, slowly draining the battery.

It was intermittently charging.

Problem got worse as it got warm. Without rpms up I wasnt generating enough voltage to give me a good spark, and it would begin to stall at lights. A blip on the throttle to raise rpm and it would be good for a min, then begin to fall.

Nic

[ChicagoRob]

I think that I found it.

Believe it or not, cleaning the foam around the air screen (the boy and a friend had over-oiled it) solved it.

I finally figured it out when I noticed another symptom: it was having great difficulty revving over 7k on the highway. Everything is stock so the jetting was correct, voltage to the coils was above 12, everything was sealed and I had gone over the carbs with a fine toothed comb so there wasn't anything left but air. I first tried without the airbox lid and it ran like crap. But when I tried it with the lid but not the foam, Bingo! I had to use some rubbing alcohol to get the foam oil out, but it's all good now.

Is that foam supposed to be oiled?

Rob

[bmac]

Foam

Yes, very lightly is the rule. Brand new from suzuki they are LIGHTLY oiled. Glad you solved that dilemma. There is nothing worse than going over in your head what could be the culprit. Bob

[TheCafeKid]

They're supposed to be oiled but here's a tip I've used to make sure I don't over oil. Oil a rag then wipe the rag off on the filter. K&N are easy to over oil but they also run dry pretty quick.
As the bike warms up to operating temp the natural result is for it to richen up. When it's cold an over oiled filter may not show any problems because it needs more gas when cold anyway. But as it warms up it will run richer and need more air, the over oiled filter will choke it off and your bike will drown.
It'll be even worse when it's hot hot out like today (my god is it hot...100! In June!!) After you've fixed your filter you may, should the temps stay like this, and you still have a wet boggy issue at idle and just off idle, open your air screws an 1/8 turn (or if you have CV carbs, leave em alone or back em off an 1/8). While running too lean is dangerous, running too rich isn't much better as it will carbon up your piston heads and valves..

[ChicagoRob]

Bad news, that fixed one problem (poor high rev performance) but not the stalling problem.

Thanks for the oiling tips. I did the rag one.

I think that I've finally figured out what it is and boy, do I feel stupid. It's overheating. Now I've ridden/driven a lot of air cooled vehicles, atv's, motorcycles and heck, I even own an aircooled car that we only drive in the summer but this is my first experience with overheating.

I'm 99% it's overheating because the tube that goes from the cylinder head cover to the airbox is showing signs of melting. It's never done that before.

I also think that I know why. I painted the barrels/head/cover black (VHT Engine paint) to dress it up a bit. I guess that I got it on a bit too thick and it's acting as an insulator. Does this sound plausible? Is there a special paint to use that won't cause it to overheat?

Thanks,

Rob

[Nessism]

Paint is not the reason unless you sprayed it 20 times.

Did you vacuum sync the carbs and change out the intake boot O-rings when you did the top end job. Can't see any specific reference to these critical details in this thread other than people asking.

Regarding the air filter, the oiling technique is detailed in the factory service manual. Dump some motor oil on it and squeeze out the excess. I use a paper towel to blot out the extra oil but don't go too far. You need oil on the filter to trap dirt.

[ChicagoRob]

Thanks Ed. I guess that's good news.

Yes, carbs are sync'd (I have a Morgan Carbtune) and the intake boots and orings are newish (1 season, tops). I'll order some new orings and replace them just because.

Compression is 120 across all four, I've put in new rings so I rechecked the ring end gaps yesterday when in the cylinders and they are between .3mm and .2mm. It used to have points with the mechanical advance but now has a Dyna S. I checked the timing and it was timed to the first mark (with timing light attached to #4 plug wire, not static), not the advanced mark, so I corrected that. It also has Dyna Green coils. When it's showing this symptom, there's at least 12.5v measured at the coil input. (Coil relay mod and a Honda regulator with the sense wire attached to the coil relay trigger wire and a new AGM battery) All of the valve's lashes (sp?) are at the high end between .06 and .09.

It runs great when it's not smoking hot. It's completely smooth across the entire powerband. No throttle inputs hesitate, surge or pop. Cruising is smooth. I'm really happy with it except for when it gets hot and stopped at a light. When it's rolling again, everything is fine.

I can't get past the fact that the ventilation hose has started to melt. It really shouldn't be doing that. At what temp is it considered overheating?

Thanks for all the help,

Rob