choke lever and mixture screws

[marp68]

A bit embarrasing to ask, but.....

When is the choke ON? When the lever is pulled up or down? Now when it's warm outside, it doesn't seem to differ, and I don't remember...

And, when does the mixture gets richer? When it's screwed further out?

The idle mixtrure screws are now set to 3/4 turn out, as according to the Clymer manual. But what if I want to adjust the mixture better. Do I just turn one of them at a time in and out to get the highest RPM and then adjust the idle speed to correct RPM again?

/Martin

 

[5twins]

Down, yes, and yes.

 

[retiredgentleman]

marp68;

If you try adjusting the mixture screws with the engine idling at 1200 rpm, you won't see or hear any difference.

I recommend you do the "dead cylinder" method. With one cylinder running at about 300 or 400 rpm, you can easily adjust for the highest smoothest rpm.

 

[marp68]

Okej, thanks 5twins. I seem to get a bit senile...

Regarding the dead method, I used that but only to adjust the idle speed screws to set the correct idle speed. Before doing that I turned the idle mixture screw out 3/4 turn as specified in the Clymer. One of the mixture screws was adjusted approx 1 turn out. The sparkplugs seemed okej both before and after making the changes. But now, when it's warmer outside the engine react more unstable.

So if I also want to calibrate the idle mixture, I use the dead method as well:

-let the engine idling on one cylinder,
-adjust the idle mixture screw to get the highest RPM,
-then adjusting the idle speed screw to about 1000 RPM,
-doing the same on the other cylinder
-finally adjusting both idle speed screws at the same time to get about 1200 RPM

 

[retiredgentleman]

marp68;

The "Dead Cylinder" method is used to adjust the mixture screw...............it has nothing to do with setting engine idle rpm.

The idle speed screw is used as part of the "Dead Cylinder" method. The idle speed screw is used to lower the rpm down until the engine is almost stalling, perhaps 300 to 500 rpm. At that point, adjust the mixture screw for the highest idle, which might be 400 to 500 rpm. If you have trouble detecting the rpm peaking, you can again lower the rpm with the idle speed screw, which makes the mixture screw more responsive.

After both cylinders have had the mixture screws adjusted, you can adjust the idle rpm to anything you wish, using the idle speed screw.

 

[marp68]

sorry, I meant that I used the dead method to synchronize the cylinders idle speed, not only the idle speed itself...

I will try adjusting the mixture according to your description next week, when I back home again.

Cheers,

 

[marp68]

It's hot here in Sweden right now and the engine seemed to run badly at idle. I started from scratch and tried the dead method with the mixture screws. Couldn't get one cylinder to run at 400-500 rpm, it stopped, had to put it at 1000. So I let both cylinder run and statred to adjust the mixture screws anyway. And of course, it was difficult to see any change. I however noticed alisghtly rise of rpm when turning the screws out (enricher the mixture, right?). The standard settings is 1 1/4 turns (xs650B), but now it is approx 2 turns? Could this be due to the hot weather (25 degrees Celsius in the shadow)?

Anyway, I went out for a ride and the bike responded nicely.

I will redo the dead metod with the screws adjusted this way, to see if one cylinder now can run at apporx. 500 rpm.

M

 

[marp68]

Down, yes, and yes.

So, lets see if I understand the mixture function correctly... By screwing the needle out, more air gets down the circuit which sucks more fuel through the pilot jet?

Any good text/link to how ecatly the enrichening/leaning function works?

 

[5twins]

On the stock 650 carbs, we're dealing with a true mixture screw. It controls fuel flow, or more correctly, the fuel/air mix from the pilot jet. Opening it up lets more fuel/air mix in and makes things richer. Closing it reduces the amount of fuel/air mix and makes things leaner.

 

[retiredgentleman]

marp68;

If you can't get the one cylinder to idle at 300 to 400 rpm, here's a tip.

Your carb butterflys may not be sychronized properly. If they are not matched, then one butterfly will seat against the carb throat first. With it seated, the other butterfly is cracked open enough that it will not allow the rpm to go down below 1000 rpm.

This is what should be done. When PO's take carb butterflys apart, they fail to properly re-aline the butterflys on the throttle shafts. You can't just randomly re-tighten the 2 butterfly screws and call it done.

Make sure the throttle speed screw is fully backed out of the way, so the throttle is allowed to close fully. You need to leave the butterflys screws loose, while you open and close the throttle. Let the spring tension make a little "snap" as the butterflys close fully.The closing of the throttle will cause the butterflys to "self aline" against the carb walls.

Now, with the butterflys,"self-alined", tighten the butterfly screws (blue lock-tite is good to use).

With this done, your carbs can now fully close off the butterfly pair.

 

[marp68]

I CAN get it to go down to 400 rpm, but after some turns the engine dies, so I can't/don't have time to adjust the mixture screw.

A correction... The right standard adjustment for the mixture on xs650B is 3/4 turn, not 1 1/2 as for the xs650 D which I said before. Since I couldn't adjust it on one cylinder, I tried doing it when both were running. I then adjusted it to almost 2 turns.

The engine responded okej when riding it. After riding the bike I had a look at the sparkplugs again, which looked okej, just at grey tan. That's how it looked before with only approx. 3/4 turn. Shouldn't there be a difference, you think?

Hmmm I think I have to make some more adjustments, testing rides and checking the plugs aftrwards...

 

[5twins]

You don't have to get the cylinder speed down to 400, just reduce it some from 1200. The slower you can get it, the easier it will be to hear changes and effects the mix screw adjustment is having.

Or you can try the "ride and adjust" method. Set your mix screws to the factory spec of 3/4 turns out and idle speed to 1200. Go for a ride and take a small screwdriver with you. Ride a few miles/Kms and pull over. Note idle speed and open the mix screws 1/4 turn. Ride another few miles/Kms and pull over again. Note idle speed. If it's the same or has gone up, open the mix screws another quarter turn. Keep doing this until the idle speed drops off. You've now found the setting where the mix screws are too rich. Make a note of that and reset them to 3/4. Run more tests, this time turning the screw in 1/4 turn at a time, until the same thing happens - idle speed falls off. Now you've found the too lean setting. Best setting will be somewhere between those two points. I prefer to stay to the rich side of it. That helps reduce popping on decel with my aftermarket (louder) mufflers.

 

[marp68]

Okej, I'll try that. So if I understand you correctly, if it gets too rich the idle speed will drop? As when it gets too lean...

I've also noticed that when I set the idle above 1200, the rpm doesn't drop fast enough after letting go of the throttle when driving. It sort of stays on about 1500 rpm for a while and slowly drops. It takes about 10 sec until it drops to normal/set idle speed. The lower I can set the idle speed/closer to 1200, the better, then the rpm drops almost immediately when releasing the throttle grip. But then I've noticed that 1200 is a bit too low, since sometimes the engine tends drop even more, jump one turn end sometimes die. It's hard to get the idle speed steady. It sort of moves around a bit, not much though. Maybe an airleak somewhere, manifolds or dirty carbs, or the aftermarket mufflers.

When driving the bike, the engine responds good though and doesn't jump turns. So it's only the idle that is not steady/acts strangely. Letting go of the throttle, it backfire a little. Probably due to aftermarket mufflers (Dunstall copy), air leak (which I haven't found yet) or to rich fuel/air ratio. I'm about to change to soft material inside the mufflers, which could solve this problem a bit.

 

[5twins]

If you're backfiring and popping on decel and can't tune that out with the mix screws, you probably need a larger pilot jet. That may stabilize your idle speed as well. Have your air filters been changed as well? If you're running aftermarket mufflers and, say, pod filters, some minor re-jetting is usually required.

 

[retiredgentleman]

marp68;

I'd say your carbs are not synchronized. One butterfly is open slightly more than the other, which can cause the idle to hover higher than it should. Refer to my earlier posts in this thread.

You don't have the mixture screws adjusted properly yet and you may have small air leakage as well.

 

[marp68]

Thanks for the tip about the butterfly. Seems easy to assure they are in sync. Regarding the pilot jet, I didn't know it effected the idle. Think I'll check all inside things during next winter.

Okej, so i went for a day trip and just by chance adjusted the mixture screws to 1-1,5 turns. Since it was very hot weather, I wanted to be sure it wasn't too lean but not as rich that I set it before. It seems that my backfiring/popping are not as many and as strong as before. More of a deep smooth popping, almost as it normally should sound like on deaccel. The idle behaves still strange though. And the choke during start doesn't do much help in hot weather, as it did earlier in the springtime, when the weather was colder (15 degree Celsius).

I'll do the ride/adjust method during the week.

I have new normal air filters (not pod), but I haven't checked the manifolds yet, using carb spray or start gas. Shouldn't it has to be something that only effect the idle but not higher rpm, since the engine runs well then on higher revs/driving?

Well, this seems to be what older bikes is all about. But also the charm with them... The pulse and feel during the ride yesterday was awsome. And the looks from other people isn't that bad either...

 

[wilbur60]

I have a 1980 xs with 4000 miles on it. It has sat for the past 10 years. It did not run when I bought it. I took the carbs off and cleaned them out and replaced the needles under the floats. I have set the float at least 6 times hoping to get it right. I cannot find any adjustment screws for air mixture of for anything other than the idle setting. The previous owner burned up the stock air filter box so I replaced the stock air filters with some K an N filters which probably means rejeting. At this point I have:
1. After running it at 4000 rpms (+ -) it will not return to an idle on its own. I must get it to slow down by putting the engine under a load (In a high gear letting the clutch out) to slow it down or wait for it to slow down which takes a while. If I rev it up to release the sticky parts it only raises the idle higher, up to 3700 RPM's. Rather uncomfortable at a stop sign.
Is there a spring that should be closing something but obviously is not?
2: At 4500 RPM's and up it starts missing and has no power. Appears to be starving for fuel.
Is it the jetting, ya think?

 

[ippytattoo]

If you have the BS34's that came stock on an '80 then the mixture screw is under a little pressed in cap just in front of the carb boots. MikesXS has a good photo that is labeled here. And your high idle sounds like a lean condition either due to lean jetting or possibly an air leak causing the lean condition. You can check for leaks around the carb holders and throttle shaft seals by spraying carb cleaner around the boots and throttle shafts while the engine is idling.

 

[OgreOwner]

The needle on the pistons has several places where you can place the circlip into. The Clymer manual says that you move that circlip up and down on the needle to rich or lean the mixture. The adjustment means taking the top off the carb and pulling the piston to get at the needle.

 

[wilbur60]

Not sure how the carb cleaner test for air leaks works. Assume the goal is to see the carb cleaner spray being sucked in a small hole.
The air leak idea sounds good, though. That could be why it is popping and backfiring through the carbs. Seems to get better (less popping) as it warms up.
How do I tell what size jets to get if I need to re-jet?