Idle circuit help

[Larry D]

My bike is stock through and through. I'm getting very close to getting it tuned in but I'm getting some mixed signals.

While riding on the interstate back and forth to work (+-70mph) I'm getting about 32 mpg, my feeling is it should be a little higher. It's running fine at speed and accelerates nicely when twisting the throttle.

I've been having difficulties getting the transition from the idle circuit to open throttle correct. The has always run on the rich side so, I decided to try and figure it out.

I pulled the plugs and cleaned them, set the idle air screws to 1 1/2 turns out and went for a nice ride to ge the bike up to temperture. Before I got to my driveway I rode along at minimal throttle for 1/4 mile or so and chopped the plugs. Since it's always run a little rich, I was expecting to find nice tan, clean plugs. Nope, they look like always....black, not oily, more of a soot.

Also while riding it was popping some on acceleration not much but some, which I thought would indicate a lean condition. So, I'm showing rich while doing 1/4 throttle plug chops and popping, which is I thought meant lean....

I've actually been playing around with this for a couple days. I had it pretty nice at one point, but the idle air screws were only about 3/4 of a turn out. It got me worried about burning up a valve, so I reset them to 1 1/2 turns out.

I'm home, digital camera is ready, the bike is warmed up and I'm open to suggestions.

[bwringer]

I can't remember -- do these carbs have the stock size pilot and main jets?

With interstate riding, I usually get around 33 to 35 mpg with my 850.

[TheCafeKid]

I have argued with people about this over and over, but, there are those that suggest that popping on DECEL is not ALWAYS a lean condition, but a rich condition. Their theory is that as you've fed a bunch of gas thru the carbs, then chop the throttle, a fair amount of gas goes unburnt because the air flow is cut off with the butterflys being slammed shut. Because the airflow is cut, the air/fuel mixture in the cylinder falls out if its particular window of the perfect combustable mix and some of that unburnt gas vapor is exhausted out of the head into the pipes, where the temp is extremely hot right at the head. Since its also getting a bump in air with the push into the pipe, it combusts in the header, causing your pop pop pop noise. Its plausable i suppose, but goes against everything that IVE been taught about how it generally works.

General rule of thumb, if the bike runs better cold, then starts to get sluggish thru a particular stage of the carbs when warm, its rich in that area.

Also, generally, these bikes, especially the big ones, get WORSE mileage on the highway (70+mph) On my 1100ES, and on my ex 1100G, i got the BEST mileage when i was in the twisties at about 42mpg or better.. I generally get about 37ish on the highway...

[Larry D]

Brian, I have no reason to believe the pilots or mains have been changed. I've never looked at them though.....

Josh, Should I just keep turning in the idle air screws incrementely until the off idle hesitation quits. The it stumbles, hesitates, bobbles, whatever you want to call it, when accelerating from an idle condition....like, accelerating out of a turn in second gear.

I had it very nice at one point, but when I checked how many turns out I was, they were +- 1/2 to 3/4 turns out............

How do I know when ,or if, I've turned them in too far ?? Besides burnt valves......Just keep checking the plugs ?.......

[TheCafeKid]

Brian, I have no reason to believe the pilots or mains have been changed. I've never looked at them though.....

Josh, Should I just keep turning in the idle air screws incrementely until the off idle hesitation quits. The it stumbles, hesitates, bobbles, whatever you want to call it, when accelerating from an idle condition....like, accelerating out of a turn in second gear.

I had it very nice at one point, but when I checked how many turns out I was, they were +- 1/2 to 3/4 turns out............

How do I know when ,or if, I've turned them in too far ?? Besides burnt valves......Just keep checking the plugs ?.......

*I* would suggest that you check your sizes. I have too many times made assumptions about the carbs on an otherwise stock bike and found that i was wrong. Over the years people have likely found and tried to fix the little problems and flat spots associated with these carbs. If you didnt pull the plugs covering the adjustment screws yourself, then LIKELY someone has monkeyed with them before. I myself am having the SAME conditions you are experiencing rolling from 0 to 1/8 turn of throttle in ANY gear at ANY RPM, and have figured out that indeed my pilot jet is TOO SMALL. If you're not getting ANY reaction from the screws passed a half turn, which is nearly closed, then you may be suffering from the same problem. The symptom is a bobbling, or a semi instantanious stammer of the motor just off idle, its surging, its lean. I have recently been reading both Factory Pro's tuning guide, and a couple of other guides and sites regarding carb tuning, and they are all consistant as far as this goes: the pilot jet, and float settings will effect the carbs at ALL RPMs and gears because you, for at least a second, step thru the pilot circuit on your way to the others. I would check and note your sizes, both of the pilot and the main, and even take a peek at your needle clip seating too. If the main isnt stock, and im not sure what that is on your bike, make it so, and then work from there. In all the guides on the CV carbs, the MAIN is where you work back from. If its not one or two sizes from being right, it will cause you problems when tuning the rest of the circuits. Also, i almost forgot to mention, and this is perhaps more important than anything, your float levels MUST be set properly. Set them at the mid point of the range (in your case 22.4mm is perfect) and leave it. they ALL must be the same! Also, only work one thing at a time. I have made the mistake of trying to change multiple things at once, just because i already have the carbs out so why not? Well, its impossible to tell which of your changes may or may not have made a difference.

to summarize, check your sizes, check your float levels, and i would suggest stepping up one size on the pilot and go from there. Of course this is ALL provided that you're sure you have no air leaks from the boots or airbox, and that your valves have been recently adjusted. Hope this helps, and if you need anymore, i will try to lend what limited knowlege i have.

[Griffin]

Larry,

I was having some issues with the stock carb setup on my '81 750E. I'll PM you what my solution was.

As you know, I had it purring like a kitten before I sold it. The plugs were always a nice grayish-tan color as well.

[Larry D]

*I* would suggest that you check your sizes. I have too many times made assumptions about the carbs on an otherwise stock bike and found that i was wrong. Over the years people have likely found and tried to fix the little problems and flat spots associated with these carbs. If you didnt pull the plugs covering the adjustment screws yourself, then LIKELY someone has monkeyed with them before.

I myself am having the SAME conditions you are experiencing rolling from 0 to 1/8 turn of throttle in ANY gear at ANY RPM, and have figured out that indeed my pilot jet is TOO SMALL.
I notice it in first gear when coming out of the clutch and in second coming out of a turn and third as well. Don't notice in other gears, I'll pay closer attention tomorrow.

If you're not getting ANY reaction from the screws passed a half turn, which is nearly closed, then you may be suffering from the same problem.

The symptom is a bobbling, or a semi instantanious stammer of the motor just off idle, its surging, its lean.
So this condition is a lean symptom in the pilot ? I thought this meant it was rich. I've been turning the idle air screws in, making it even more lean.

I have recently been reading both Factory Pro's tuning guide, and a couple of other guides and sites regarding carb tuning, and they are all consistant as far as this goes: the pilot jet, and float settings will effect the carbs at ALL RPMs and gears because you, for at least a second, step thru the pilot circuit on your way to the others. I would check and note your sizes, both of the pilot and the main, and even take a peek at your needle clip seating too. If the main isnt stock, and im not sure what that is on your bike, make it so, and then work from there. In all the guides on the CV carbs, the MAIN is where you work back from. If its not one or two sizes from being right, it will cause you problems when tuning the rest of the circuits. Also, i almost forgot to mention, and this is perhaps more important than anything, your float levels MUST be set properly. Set them at the mid point of the range (in your case 22.4mm is perfect) and leave it. they ALL must be the same! Also, only work one thing at a time. I have made the mistake of trying to change multiple things at once, just because i already have the carbs out so why not? Well, its impossible to tell which of your changes may or may not have made a difference.

to summarize, check your sizes, check your float levels, and i would suggest stepping up one size on the pilot and go from there. Of course this is ALL provided that you're sure you have no air leaks from the boots or airbox, and that your valves have been recently adjusted. Hope this helps, and if you need anymore, i will try to lend what limited knowlege i have.

Thanks for the explanation. I'll tear into the carbs and check out the sizes the next time it's going to rain for a couple days. The way it's been raining lately, it shouldn't be long.

I set the float heights when the carbs were cleaned but I'll check them at the same time. No leaks and I have 442 miles on it since the valve adjustment. The bike runs well except for this one issue.

[Larry D]

Larry,

I was having some issues with the stock carb setup on my '81 750E. I'll PM you what my solution was.

As you know, I had it purring like a kitten before I sold it. The plugs were always a nice grayish-tan color as well.

Okay. We need to get together and ride soon. I seem to be so busy lately on the weekends, I have to squeeze in 45 minute rides here and there. I've been trying to ride into work, but me and the rain don't get along to well.

[TheCafeKid]

Larry,

I was having some issues with the stock carb setup on my '81 750E. I'll PM you what my solution was.

As you know, I had it purring like a kitten before I sold it. The plugs were always a nice grayish-tan color as well.

Actually Brett id be interested in seeing your solution as well. While my current problem is associated with my 1100ES and its podded carbs, It may be helpfull info to me and something to try as well. I have come to the conclusion that its nearly impossible to tune all the annoying little burbles and flat spots out of vaccum carbs for pods. If i had one, id be swapping them out for an airbox, and jetting for that. Unfortunately i dont, but it will be on my active shopping list when i get back from the WV trip later this month. I dont think i will miss that 2 or 3 horsepower, and i will certainly enjoy the torque gain and smoothness in any weather or temp...I hope...LOL

[Larry D]

I haven't been able to get it right yet. Last night I turned the idle air screws out to 1 1/2 turns out and it made the problem worse. I rode to work this morning and at every stop, I had to keep feathering the throttle to keep it from dying. The bike runs beautifully on the mains, but simply won't idle at the "normal" setting. It will idle nicely if the idle air screws are turned 1/2-3/4 turns out. I did the highest rpm method a few days ago and that is where it worked well. But, having the air screws barely open, has me a little worried. So, I set it back to something close to "normal", but the bike does not like it.

I'm wondering what damage, if any, may occur running the idle circuit at only 1/2 turn out for a few days until Griffin and I get it fixed.

Thanks.

[almarconi]

Larry..tell me it isn't so . When my bike was running like crap I looked at your bike with envy. I watched the video you made of the bike running..I'd never seen a 750L start that easily before. I only wished my bike would run that well.

On a more serious note, is it possible the carbs just need to be cleaned again? It doesn't take much to clog the pilot jets. Possibly some fine rust particles or dirty gas.
Did you check the rubber carb boots for leaks?
As stated earlier, you may want to try some #45 pilot jets to see if makes a difference. Normally the screws should be set in the 2-3 turns range.

[Larry D]

Larry..tell me it isn't so . When my bike was running like crap I looked at your bike with envy. I watched the video you made of the bike running..I'd never seen a 750L start that easily before. I only wished my bike would run that well.

On a more serious note, is it possible the carbs just need to be cleaned again? It doesn't take much to clog the pilot jets. Possibly some fine rust particles or dirty gas.
Did you check the rubber carb boots for leaks?
As stated earlier, you may want to try some #45 pilot jets to see if makes a difference. Normally the screws should be set in the 2-3 turns range.

Actually the bike runs down the road fantastic, I'm just having a hard time with the idle. I would bet you a paycheck that the carbs are clean, no air leaks.

I can get it to idle well, it just takes the idle air screws being barely turned out, which has me wondering if I'll do any damage with them set that way.

Thanks for the compliments. I'll have to put up some updated pics...

[gustovh]

I set the air screws on my 1100 lt at 2 1/2 turns as a base, then did the high idle adjustment. One is 3/4 one at 1 1/2 , 1 1/2, and 1. I am not worried about burning up my motor. I do get that nice tan color on my plugs. Just my 2 cents.
V

[Larry D]

I set the air screws on my 1100 lt at 2 1/2 turns as a base, then did the high idle adjustment. One is 3/4 one at 1 1/2 , 1 1/2, and 1. I am not worried about burning up my motor. I do get that nice tan color on my plugs. Just my 2 cents.
V

Yep, I did the same. That's how I got the screws set at 1/2-3/4 turns out. I know everyone here says to set them at about 2 1/2 turns out and tune from there, which is what I did.

1/2 turn out just doesn't seem right to me.....I'm going out at lunchtime in the parking lot and set them back to 3/4 turns out and ride around some.

Well, that's what I did. 3/4 turns out and had to turn down the idle knob to around 1200 rpm. Idles much better and no dying at stops. Guess I'll run it that way for awhile and see if I burn anything up.....

[maro]

Yep, I did the same. That's how I got the screws set at 1/2-3/4 turns out. I know everyone here says to set them at about 2 1/2 turns out and tune from there, which is what I did.

1/2 turn out just doesn't seem right to me.....I'm going out at lunchtime in the parking lot and set them back to 3/4 turns out and ride around some.

Well, that's what I did. 3/4 turns out and had to turn down the idle knob to around 1200 rpm. Idles much better and no dying at stops. Guess I'll run it that way for awhile and see if I burn anything up.....

Larry,

What was your final resolve and how are you making out now with your low rpms and mixture screws?