high idle - tinkered with carbs - regret

[Blank Slate]

The bike starts up great, runs great, but after it has warmed up after a 15 min ride and I'm stopped at a light, the idle gets high (2500-2700).

So I decided to tinker with the carbs to lower the idle.

The 3 screws that sync the carbs were turned 4.5, 3.5, and 5.75 out. I read on the forum that they were supposed to be 1.5 out. So I did that to all 3, and the bike idled like CRAP. Eventually I put them back close to how they were originally, and bike sounded great again, but I went for a ride this morning and there is a lot of popping coming out of the pipes in low gear. Bike still has great power, but in low gear or slowing down, it's popping occasionally. Before messing with these settings, I don't think I ever heard popping from the exhausts.

I read the manual and I understand that the 3 screws I touched are carb syncing screws for 1,2 - 3,4 and then sync them all together. And on the other side of the carbs is the idle screw.

Now, I just want the popping noise to stop. I figure that I don't have the 3 screws exactly how they were before, maybe off a 1/2 turn here or there. Is the only solution here to re-sync the carbs with that vacuum apparatus?

[bikerphil]

You need to find someone with a set of gauges (or purchase your own) to properly sync your carbs. The 1.5 turn out setting you read is a rough starting point for the 4 idle fuel mixture screws.

[donebysunday]

You need to find someone with a set of gauges (or purchase your own) to properly sync your carbs. The 1.5 turn out setting you read is a rough starting point for the 4 idle fuel mixture screws.

Need to start from the beginning, please, if you don't mind, OK ?
The reason the bike was reving up after warm up is you have the idle speed set way high on 1, 2 or more carbs. Sync the carburetors, this is the first thing, see what happens to your idle after that.
This may help there are three carbs inside each carb, one is the enrichment (choke as it's commonly known, simple term) carb, it increases fuel feed like a choke but not a choke. No adjustment at all.
Next, low speed/idle circuit, adjustment is in the towers just behind the intake boot and in front of the slide diaphragm cover on the top of the intake bell of each carb, 2 1/2 turns out is a good starting point on the carb/s.
Then the high speed carb/s where the engine starts using the main jet. This is where sync is so important. If the carbs sync is not right one or more carbs are running rich while the others are lean (causes poor idle and more vibration from the cylinders trying to pull the lean carb or lean carb dragging behind (lean cylinder will pop on deceleration, popping caused by insufficient idle/low speed mixture) the other cylinder/s.
So to start, (1) sync the carbs, (2) adjust the idle mix to it's smoothest running idle (IMO), I think 2 1/2 turns out on the idle needles will be close + or - . You may have to adjust your main idle speed screw as you get close as the idle should change (higher or lower) as you adjust sync and then idle mixture.
Comments welcome every one, please, I'm only human !

[Blank Slate]

Lots of good information Donebysunday. So to start, “2.5 turns” means I screw the thing down hard until it cant move right anymore, mark it with sharpie, and turn it 2.5 revolutions left?

[lowprofile2000]

Lots of good information Donebysunday. So to start, “2.5 turns” means I screw the thing down hard until it cant move right anymore, mark it with sharpie, and turn it 2.5 revolutions left?

Don't screw it in Hard, be gentle or the tip will break. I learned the hard way. There is a joke in there somewhere now that I re-read that....

[donebysunday]

Lots of good information Donebysunday. So to start, “2.5 turns” means I screw the thing down hard until it cant move right anymore, mark it with sharpie, and turn it 2.5 revolutions left?

DO NOT TURN THE IDLE MIX SCREWS IN HARD !!!!!

THIS IS HOW TO BREAK THE TIPS OFF DEEP DOWN IN THE CARBURETOR BODIES/PILOT TUNNELS.

Lightly seat !!!

They are very fragile and the demise of many a beginner. Lightly seat, then turn the idle mix screws back out + - 2.5 turns.

First sync the carbs with the screws in the linkage between #1/#2 then #3/#4 now you have #1 and #2 equal and #3 and #4 equal, now you adjust #2 to #3 so having 1/2 synced and 3/4 synced your bringing 1 and 4 along for the ride when you sync 2/3 there by syncing all 4 together. This is done with the engine running.
If you can't get it to idle you will either need to pull the carbs and do a bench sync by eye (looking through the carb at the light under the butterflies) get the same amount of light (crescent moon under the butterflies of all the carbs equal).

There is a tedious way to do a bench sync on the bike using piano wire or darning needles. I'll not go into that yet.

ADJUSTING PILOT SCREWS BY EAR vs. COLORTUNE
By Ken Talbot



Tuning is a bit of an interactive process at the best of times. You may have to sync first, adjust the screws, then sync again, etc. Try starting at two turns out from lightly seated:

- warm up the engine and sync the carbs with a mercury tool or vacuum gauges
- adjust the idle down to approx 700 or 800 rpm
- adjust one pilot screw out slowly while listening very carefully to the engine sound and watching the tach needle
- listen for the engine speed to pick up a bit then fall off
- if it doesn't pick up, adjust the screw slowly in, again listening for any increase in idle speed
- when you her the increase, adjust past it a half turn or so, then come back to it again until you've got the sweet spot
- adjust the idle speed back down to your low starting point
- then work another screw, again looking for its sweet spot
- each time you get a screw adjusted, drop the idle back down
- once you've got all four screws set, resync the carbs
- take one more pass through the pilot screw adjustment for each carb, still working at 700 to 800 rpm
verify that the sync still looks good
- adjust the idle back to 1100 or so depending on your personal preference


- go for a ride!

You do know the difference between idle mix screws and sync screws, yes ?

[Blank Slate]

let’s assume tips are not broken by now..
ill see what 2.5 out feom lightly seated gives.
a real pain is keeping the carbs fed with fuel while testing. im doing the gas tank on, gas tank off, and it only gives me a few minutes to test before fuel runs out.

i need this machine to do the carbs
https://youtu.be/ijAM9skj0S4

[CaptonZap]

And check for air leaks between the carbs and head.
Propane torch style.
Someone here will explain.
Check it after it has warmed up and started to high idle
Expansion caused by heat is a sneaky thing.
I had the same problem, and it was a loose nut on the inner stud of #2 carb.
CZ

[DiverRay]

Pull the seat and put the fuel tank on the frame, but backwards. You should have fuel line to go to the carbs, and you don't run out of fuel. You CANNOT adjust WITHOUT a good fuel supply, as the height in the fuel bowl makes a difference in the adjustment!!!
You should be able to find a 4 gauge vacuum setup for about $125 to $150 new. You WILL need a "T" fitting so you can verify all 4 gauges are the same. I use my hand vacuum pump to verify before each sync, if it's been more than one day.https://www.z1enterprises.com/mainte...tem-tools.html This is Z1, and it's not a bad price. You don't need the "tubes", just plug each line into a carb boot.
The high idle may be from the old rubber on the boot nipples. If you can spin the rubber, it's bad!

[Blank Slate]

thanks guys. im gonna order the tool Ray suggested to sync properly.

[donebysunday]

Lots of good information Donebysunday. So to start, “2.5 turns” means I screw the thing down hard until it cant move right anymore, mark it with sharpie, and turn it 2.5 revolutions left?

I think first we need some identification of what you are working on, pilot needles, carb linkage screws used to sync the carbs, or what ?

On the diagram #34 and 35 is a low speed/idle/pilot needle and spring, one for each carb so 4 of them, there is also a little cap to keep us from adjusting out of the EPA range, most folks through the caps out unless it's a pristine stock show bike. The line showing where they go in the carb is broken but they go straight down to the end of the line then the line picks up again going to the right and then straight down again right into the top of the intake of the carb or should I say the engine side. There is one in each of the four carbs.

Balance or sync screws are in the linkage between the carbs just about where #71 is between number 4 and 3 carbs and 43 between 2 and 3 can't see the linkage between 1 and 2 but it's like #71

https://ibb.co/hstzKp

First set the low speed/idle needles at about 2 1/2 turns out, these are in the vertical tunnel top of the intake of the carb body of each carb between the slide housing and carb boot connecting the carbs to the engine as I explained in the description of the location in the diagram.

Next sync the carbs with the linkage screws in the linkage between the carbs #1-2 then 3-4 then 2-3.
I have the 4 gauge vacuum meter but I can't help myself from double checking with my mercury carb styx (old school but I bought 2 pounds of mercury for it back in 1977) holy crap, my carb styx are 41 yrs. old ? ? ?
So let us make sure we are talking about the same screws, needles and such.

[mack]

Tuning.

Pablo, bring it back here and I'll put it back the way it was when it left here. STOP tinkering! Make a list of all the things you've done to it so I know what else to look at.

[mack]

Pablo

For gods sake, don't go under that valve cover for any reason! When I gave you back the bike I handed you a sheet of paper with the spec's, mileage at the time, shim numbers and clearances, compression etc. etc. and told you to keep it in your tool box. Bad things can happen if you tinker under there. Check with me first. OK?

[Blank Slate]

Sorry Mack !!

Its running great except for a small popping noise in first gear sometimes at low idle. Ill definitely stop tnkering and bring it back to you this fall.

[mack]

Ok

Beg borrow or buy yourself a big box fan like the ones you saw in my shop and set them in front of your exhausts. These are air cooled motors so when ever your running your bike, make sure you have lots of air flow hitting the motor.

Until you bring it back, lets see if you can't correct this yourself. If you sent away for the tuning equipment, this isn't to hard to get rid of.
Step #1, pull the plugs out of the cylinder head one by one and inspect the the plugs. If they are a nice light tan colour the idle mixture screws are correct. If they are white it's running too lean, black and sooty it's set too rich. number the plugs as they come out. Left side as your sitting on the bike is number 1. OK Set up some light wire across the top of your ultrasonic cleaner and hang the plugs in the cleaner so only the threads are submerged and run a cycle to clean the plugs

Make an adjustment if required to each idle mixture screw in quarter turn intervals. according to the colour you saw. Turning the screw clockwise leans them out and anti clockwise richens them.


Reinstall the cleaned plugs and continue to ride it until the balancing equipment is delivered. Repeat step #1 a couple times until the colour on all four is the light tan colour.

Note: The bikes performance will be off at this point because every time you touch an idle mixture screw it throws the balance off between cylinders. Don't worry too much about it unless it becomes a real dog.


Step #2: by now your plug colours should be very close so you can do as Ray said. Put the tank on backward and hook up the fuel lines. Pull the rubber nipples off the intake boots and hook up the gauges or mercury sticks. Start the bike and then balance 4 to number 3 first the balance 1 &2, then adjust the center small one and that will bring the left and right side of the bike into harmony.
Note: Pablo the idle speed will change when your doing this process. Increase the rpm at the grip as required to keep tuning. When you think it's close, shut the bike off and open the throttle up and let it slam closed a couple times. This will seat the screws. Then start the bike again and check to see if the levels stayed the same. Adjust if required and repeat until the levels hold.

Step #3: adjust the master idle screw, the big one that pushes on #3's butterfly shaft and bring the idle down or up to around 1050 to 1150 rpm.

Note: a lower idle will reduce the big clunk going into first gear.