Idle rpm is going down

[sihi]

Hi after all maintenance . Idle rpm is still not good. It go slowly down when is warm. when it,s cold it doesn't hold at all. It,s bit hard for me explain it how it behaviour.I attached video. Idle mixture screws are set on 1 and half turn.

 

[tkent02]

All maintenance? What maintenance have you done? How did you come up with 1 1/2 turn?

 

[sihi]

I checked tappet clearance, .Cleaned air box , carbs , new intake boots with new O-rings. Before I readed (and set ) that mixture screw should be at 2 -2,5 turns but I also readed when is mixture very rich than rpm go down. thats why I set screw on 1,5 turn.

 

[tkent02]

Synchronize the carburetors if you haven't already done it and then use the highest idle method to adjust the mixture screws.
If that doesn't work well a thorough carburetor cleaning may be in order.

 

[sihi]

Did you saw the video which I attached . Vacuum sync is not that bad . I use ultrasonic cleaner for every single peace of carburetor . I am 100% sure that carbs are clean like my dinner plate. Of courese vacuum sync can be better. But for highest idle method they recommanded 900rpm but I CAN NOT go under 1800 because than it go slowly to 0

 

[tkent02]

You didn't mention the ultrasonic cleaning, nor the vacuum synch.... Maybe try the screws farther out like 2 1/2 to get the lower idle speed working, then do the highest idle from there?

 

[sihi]

I have it before on 2.5 turn and it was same problem. maybe I try 3 turns if the problem persist . Than as say service manual it can be Ignition timing or (and) seating + guides of valves. What you thing? I never adjust timing or replace valves. Is it anywhere guide how to check that ignition timing?

 

[8ball]

Are you trying to adjust the idle with the cable adjustment?

 

[Chris G]

Are you trying to adjust the idle with the cable adjustment?

That's what I first though, I know the video shows a carb sync in progress but no mention of trying to sort the idle using the carb idle adjuster, I don't own a 650 but I would try a base line of 2.5 turns out from lightly seated ref the mixture screws, would also be easier to have your gauges hung from the bars so there in your eye sight when adjustets are made.

 

[sihi]

That's what I first though, I know the video shows a carb sync in progress but no mention of trying to sort the idle using the carb idle adjuster, I don't own a 650 but I would try a base line of 2.5 turns out from lightly seated ref the mixture screws, would also be easier to have your gauges hung from the bars so there in your eye sight when adjustets are made.

Yes. I am trying adjust idle rpm with throttle screw to reach 2000 rpm . Which is the best for vacuum sync. But after as its on the video I let rpm go down. In my opinion the idle rpm is steered be pilot jet and if in low rpm it tends to die than is because mixture is so rich.if in idle rpm is very high than mixture is lean . Isn't right? Thats qhy I screw only 1,5 turn to get more air in mixture so rest go through pilot jet.Iam still new. So I appreciate any advice. Thanks

Ps: gauges is to short to hang them over bars

 

[8ball]

The idle adjustment screw is on the carbs, not the cable, and should be a knob usually between the #3 and 4 carbs. The mixture screws that are on each carb are air screws. The farther out they are, the leaner the mixture

 

[sihi]

The idle adjustment screw is on the carbs, not the cable, and should be a knob usually between the #3 and 4 carbs. The mixture screws that are on each carb are air screws. The farther out they are, the leaner the mixture

Aaaa thats why. I thought that is leaner when is crew in. That explains everything. I hope it's so easy. BTW I know exactly where is idle mixture screw and where is idle mixture knob (and now different between them ) I will post here results later. Thx

 

[sihi]

Thank you very much for good advice. It was idle mixture screw I have to make 3 turns out to settle idle rpm on 1200. And knob isn't touching butterfly at all now. I also released throttle cable so it isn't tensioned like before for lifting butterfly up. Now is only mixture screw which is steering idle rpm. I think it supposed to be like that.

 

[Steve]

There is a LOT of conflicting information here. :-k

I watched the video. A couple of things that I noticed were that the carb sync is good enough to run, but needs to be adjusted to run CORRECTLY.

Also, you seem to be adjusting the cable to change your idle speed. The idle speed adjustment is on the carbs, but NOT where 8ball says it is. His information is based on the older VM carbs. Your idle speed adjustment knob is BELOW the carbs, between #2 and #3.

The mixture screws on your carbs are NOT on the sides of the carbs. Again, those adjustments are on the older-style VM carbs. Your mixture screws are on the top of the outlet of the carbs, and they adjust a MIXTURE, not just air. Turning them out will RICHEN the mixture. When I rebuild a set of carbs, I start with them out three full turns from lightly-seated, which is rich enough to allow it to start easily, sometimes without using the "choke".

Any settings recommended here are usually just something that works to get it to start, adjustments will have to be made that are specific to your bike. When you get done making your adjustments, you may find that one or two of your carbs will be at 2 1/2 turns, one at 2 3/4 and one at 3 1/4 turns. It is easier to start slight rich and lean it out to "best-running".

Suggestion: Start by properly adjusting the throttle cable and idle speed. The cable should have a little bit of slack at the grip. Adjust the adle speed with the knob below the carbs. The factory manual specifies doing a sync at 1500-2000 RPM, but I have always done it closer to actual idle speed. Do a GOOD carb sync. Hang the gauge so it is vertical. Having it laying down like the video shows puts too much drag on the sliders, they need to hang freely. When the carbs are properly balanced, leave the gauges connected. Watch them as you adjust the mixture screws. When you get a proper mixture, the vacuum readings will go UP because the engine is running a bit faster without changing the throttle opening. Slowly turn the screw in until the vacuum drops slightly, then back the screw out about 1/4 turn. Repeat for the other carbs.

 

[sihi]

turning idle mixture up allows vacuum go above diaphragm , this cause that needle go slightly up and make the mixture richer. Is that right Steve?

 

[Steve]

Not really. Adjusting the idle mixture just lets the engine run properly. You won't get enough airflow under the slide to create enough vacuum to lift the slide until you have the throttle about half-way open. That is hard to do with the bike sitting still, you need to be moving to do that.

Look at this picture of the carb, you might understand a bit more how it works.

Air enters from the airbox on the right. A tiny portion of that air goes through the pilot air jet in the lower-left corner of the throat (shown in the picture) and goes past the needle to the tip of the pilot fuel jet. There, it mixes with fuel that has come from the bottom of the float bowl, through the main jet, then through the pilot fuel jet and becomes the pilot mixture. The mixture then travels through a passage to another passage that is above the throttle butterfly. There, you can see that there are multiple openings into the bore. One is on either side of the top of the throttle butterfly (sometimes there are a total of three holes there), another one is out a bit, closer to the engine. That one has a screw in it so you can adjust how much flows through it. The one hole near the butterfly that is always open can not supply enough fuel for the bike to run, so you need to add some with the screw adjustment. The other hole(s) will be uncoverd as the throttle is opened just a bit, they will provide additional fuel to the mix before there is enough air flow to drag fuel past the needle and, eventually, the main jet.

.

 

[sihi]

I did not pay attention to that drowning before. I got it now. Thank you Steve for good explanation.