Having idling issues

thank you for looking at my post. Any thoughts or comments are greatly appreciated

i have a 1982 Yamaha xj650 maxim

I'm having issues with idling. I'll start my bike and it will rev up to like 2500 to 3000. I'll adjust my idle screw down to around 1400 - 1500.

Once I start riding it's ok until I slow down or stop. Then it drops rpm so low that it dies unless you give it throttle.

Also. I might be having a throttle issue. While riding the rpm accelerated up by there. Self some. When I rev the bike up to 5,000 rpm while in neutral. The Rpm drops fast from 5,000 to 3000 rpm. But then really slowly decreases from 3,000 to 2500 or 2000 rpm. But doesn't drop to normal idling rpm.

I tried looking for a vacuum leak using propane. But I didn't notice any rpm changes when using the propane.

Also I'm curious if there's a issue with the throttle tightness or if it's sticking some. When i open the throttle all the way open and let go. It does snap right back

So any help, comments, or thoughts are appricated

Thanks

Tim.

 

I would check tightness of the clamps, were your carbs recently pulled and cleaned? When was the last time valves checked and adjusted? To me it sounds like your synch could be off, what do the plugs look like? Black, brown , white. ? You could pull the throttle cable off arm at carb see if idle is better ... just a few items to check.

 

Hi Tim,
When was the last time the bike ran without the afore mentioned symptoms? Did you do any work on it prior to this happening?

There are several things that could be causing this. Basics are the starting point. Are you valve clearances in spec? Carbs synched?

 

you need to do a running sync and adjust the mixture screws
when the idle drops, one cylinder stops working and the others can't keep it running

 

I'm going to look into the items you talk about today and I'll report back. Thanks for the hlep

 

I just recently bought the bike. This is my first bike I'm not sure if the symptoms where there when I bought it. Was able to ride it for a mile than had a gas leak that I fixed already

I did clean the carbs. But I didn't bench syncs the butterfly valves. Because honestly I didn't know I had to.

 

Ok. Could you tell me exactly where the adjustment screw is on my carb I know it's on the lower part of the carb

 

@Jetfixer
Here are my spark plugs


Left outer, left inner
-—

Bottom view of lefter outer, left inner
------


Top is right inner. Bottom right outer
-----------


Whats your diagnoses?

 

2 of your cylinders are running rich ( black soot) other 2 are ever so lean indicated by the color of the insulator. If it were perfect your plug should be a light brown . One other thing when you rev engine and drop back to idle do you get any popping of the muffler? This is also an indication of engine out of synch IE one or more cylinders getting more fuel than another. You can try to do a running synch if you have a mamotter or as I have a 4 vacuum gauge synch. What are your idle mixture screws set at 2.5 out is good starting point.

 

Sorry for taking so long to reply. @Jetfixer

I do not really have any popping sounds out of the muffler.


I have a friend who's gonna let me borrow his vacuum gauge.

My question is where are idle mixture screw located I've been doing research. But i can't figure it out in my own.

Thanks
Tim

 

there are three (3) located as you look straight down they are located between the carbs towards the cylinder head , synch 1to 2 and 3 to 4 and synch 2 to 3 look in the information over load hour it is more detailed in the file . My vote is the vacuum gauge method . basically get them all to have about the same reading even across .

 

Ok thx @Jetfixer. I will go out and get the gauge instead. I also look into the information you told me bout.

Thanks again

Tim

 

the screws are phillips head and will rotate out of reach when you turn the throttle.
don't get them too far out of whack, 1/2 turn on those screws is a whole lot.
you should sync at about 1100 rpm but if you need to start at 2000 or even 2500 rpm to keep it running, that's ok.
as the sync gets closer to right the rpm will climb, just use the idle knob to turn it back down and do a final around 1100.
your motor should be warmed up, then keep a good fan blowing right on the engine while you work
personally i like the two bottle homemade tool but they all work, use what you like
get a long screwdriver

 

Thx you for your response @Polock. I did some research into the homemade tool you described. I'm gonna work on my bike this weekend

 

So from reading different threads the adjustment screws are hidden under brass caps that need to be drilled out.

Any suggestions on how to do so?

This a picture from another thread

And this is mine. Sorry it's hard to see po painted it black


Close up
Thx for any help
Tim

 

use a small #20 NEW drill bit hit trigger maybe twice an easy out or pick and pry out..be careful you do not want to hit the mixture screw under plug.

 

Thank you @Jetfixer. I will do that. I will report back with how it went

 

there are pilot mixture screws (4) which are under the brass caps , those screws are adjusted to set mixture

then there are sync screws those are the 3 screws you see in the photo between the carbs

 

Sync screws move with the throttle, mixture screws don't