Fuel mixture assumptions incorrect?

Rode 250 miles down here yesterday and the bike was running OK. It was slow "out of the hole," as they say - I'd hit the throttle and there would be a slight delay, then it would really take off. Plenty of power. Ran it around 6k rpm most of the way. Didn't want to idle, though, so I'd have to give it a little throttle at intersections.

I figured it was running too rich, right? Isn't that what hesitation generally indicates? Bike smelled a bit gassy, also. I turned all my mixture screws in just a little and rode around town a couple of miles. Now the bike is stalling when it idles down and at the moment it won't start. Giving it any throttle at all while operating the starter shuts down any firing that it happening.

I just pulled the plugs. #1 was pretty dark, #2 was REALLY dark and sooty, #3 & #4 looked quite good. So I cleaned #2 and turned it in a little more, then backed 3 & 4 out to about where they had been.

Still doesn't want to start. Is there another way I should be approaching this?

FYI
Carbs were thoroughly cleaned and completely rebuilt including throttle shaft seals. I'm quite confident about the job I did and that float levels were set correctly. Valves were also adjusted and re-shimmed as needed.

Thanks.

 

Forgot to mention that this is the '81 650 Maxim.

 

If as you say the carbs were cleaned & bench synced properly, get 4 new plugs & set the pilot mixture screws at default, just turning them in and out as you feel don't cut it, your probably going right past the ideal setting, think 2 degrees in or out at a time. What method did you use for the running sync' ?

 

Thanks, Wiz. I use a single vacuum gauge to sync. My mixture screw adjustments originally started at default, then I backed them out slowly while listening for the motor to come up. Once it starts to sputter I turn them back in a little. Basically Rick's method, I guess.

On additional factor that complicates things a little: This was my first experience working on Hitachi carbs and I didn't realize that you could over-tighten the mixture screws. I ended up screwing them down a little too far such that the needle tips got a bit pinched. I made sure that the washers, o-rings, and springs were all still OK, though.

The long and short of it is that I'm not sure if the default setting is still an accurate place to start.

 

Yes on default-depending a little on altitude air filter, exaust etc.
2 1/2 is SOP but is too lean for me with the k&n filter.
I end up much farther out when all is said and done.

One thing though......Instead of just going by ear, pull the
plugs after each adj rather then just riding it for a while.
Ride around for sure, but I check after a few miles and as
the wiz said-no more then a degree or two at a time.

Even trying to be carefull on my first carb clean, I managed
to squish my o-rings. Makes adj'ng them a bit of a pita.

 

URK.

HOW "pinched?" Can we get a pic? You might need to replace them.

2.5 turns is only the factory-recommended "base" setting, not necessarily where you'll end up when you're done.

 

I ended up quite a bit farther out when I first adjusted them but like I said it was hesitating. I'm 250 miles from home and need to get back today. I've got the camera on my phone but a more thorough analysis of the screws will have to wait until I get home. I just need to this thing running.

For now my plan is to put in new plugs, reset my mixture screws, and resync. I've got a long drive and it's my anniversary. If it doesn't work I may be looking for a place to stay...

 

Got it running, resynced, idle set, and it seems OK. Hesitation is gone. Hoping that I run it as is for the 250 miles home without too much concern a out whether or not it's too lean.

 

Just read the plugs when you get home; you might have accidentally "nailed" it. Good going. Ride safe.

 

Normally Fitz is on the mark but here I disagree.

Don't ride 250 miles on plugs that haven't been checked!
If the they are very lean the bike will run great-that long
a trip and you can damage her badly.

 

I made it home without incident. Thanks for the assistance. None of the plugs look too bad.

I'm a bit puzzled about how the bike is idling, however. When I pull the bike to a stop it will be idling at about 2500 rpm and will slowly drop until the engines quits. It probably takes about 15 seconds. It did it when the bike was running rich and it's still doing it now.

Any ideas?

 

Yes, but if I understand the principal correctly, that extra fuel (that doesn't get burned) actually acts as a coolant, right? This would be more of an issue if you were rolling around town but not so much where you've good strong air flow during highway driving like I did today. I never had any indication that the bike was running hot.

 

Don't bother worrying about thermo-dynamic theory. I doubt you hurt the motor.

Explain "none of the plugs look too bad" if you would, please. Or give us a pic.

Quite honestly, it sounds to me like you still have pluggage in your idle circuit AND/or you're not really in sync. I don't want to start a whole new pi**ing contest, but a single gauge for doing a carb sync isn't the most accurate way to do it; two baby bottles would be better even because it's comparative.

Unless your float levels are way off. Were they wet-set, with the rack off the bike and level in all planes?

The hanging idle is still screaming "sync" to me though.

 

Here's what they look like after arriving home Saturday following a 250 mile trip. Ran the bike at 5500-5800 rpm most of the way but I did have lots of stop signs and lights between the highway and my home in the middle of town.

I honestly think this is very unlikely. I was extremely thorough while cleaning the carbs up.

I switched to the single gauge early on last year while working on my first bike, the 550. I had built myself a four tube manometer but I was struggling with it. I didn't quite understand the process and the motor would take off on me such that it almost sucked the ATF into an intake a couple of times. Made me nervous. Maybe I'll try that thing again now that I have a little more idea what's going on.

Yes, they were wet set off the bike and were carefully leveled with each adjustment. It took me a LONG time with these carbs but by the time I was done I was very confident that they were all within spec.

I'll check it again within the next couple of days. Thanks!

 

From the looks of those plugs you're still (evenly) lean when on the mains.

Are you running a different air filter, aftermarket pipe, or is everything stock?

 

I'm running the Hi-Flo air filter purchased from Len which I think is supposed to be basically equivalent to the OEM filter. Exhaust is stock.

 

Those Plugs look like they just came out of the box.

"Hesitation" = Lean.
The Mixture, transitioning from Idle ... to OFF Idle, ... Needs sufficient Fuel to sustain Combustion.
If its too Lean, the Engine waits for the Main jet Supply.

Get away from that LEAN Condition.
That looks "Critically Lean"

Don't get seduced by the extraordinary power the engine will make when the mixture is Critically Lean.
The explosive mixture flashes too hot for an aluminum air cooled engine to withstand.
The heat will melt aluminum and burn through the Piston Crown.

 

Go to Starbucks. Order a Caramel Frappuccino.

The plug tips should be that color!