Idle at 6000RPM, what to do?

Hello guys,

im new around here so first of all let me say hello to everyone. I recently bought an 84 seca, with the intention of converting it to a café racer. But the bike ran so good that I did not had the heart to chop it, so I decided on a restoration job.

I took the carburettor off, and gave it a good clean with brake cleaner and a brush. Then I took the diaphragm caps and re-chromed them. I did not adjust anything on the carb itself nor did I dismantle it, except the idle screw which also got a chrome treatment.

After reassembly the bike started right up, but it raced up to 6000rpm! Nor the throttle cable nor the choke cable were attached, so it could have not got stuck anywhere. After that, I dismounted the carburettor, bench sink it and readjusted the pilot screws to two turns open with no success... bike still races at 6000rpm.

I have than unplugged each spark plug cap separately and discovered that only one cylinder causes the bike to jump into high revs. I have then tried to close the pilot screw completely on that cylinder, but this also did not affect the RPM. Butterfly valves were closed, and also the slides operate in a normal manner... This is were my knowledge ended... Anybody got an idea what it could be?

 

Check for a vacuum leaks. Would it happen to be cylinder #3 that is causing the trouble? Is the vacuum line for the petcock installed?

 

Hey, first of all tnx for your reply. Funny thing, when I bought the bike the vacuum line was not even attached. (Cylinder Nr. 2 was without a cap) I also witnessed some really strange pilot screw settings:

C1 - 1.2 turns
C2 - 1 turn (troublemaker)
C3 - 1.7 turns
C4 - 2turns

Ill try hooking up C3 to the vacuum line, and readjusting the pilot screws to 2,3/4 turns We ll see what happens next

 

c2 or c3 it does not matter as long as each port is capped and 1 is hooked to the vac line on the petcock.
did you try to back off on the idle knob, you said you removed it and reinstalled it.
what did you use for the gap to bench sync?

 

I actually used a needle, but prior to adjusting the sync screw i winded up the idle screw, so the needle would just fit below the Nr.2 butterfly valve. Than i readjusted the idle, to a barley open position.

The bike rests on its central stand, and the front forks are mounted as low as they can go, could this be a reason for the gasoline to run trough the carburettor into the intake manifolds?

 

If the float levels are high and your carb manifolds are leaky vacuum wise ,that can cause a run away idle

 

needle is good.
about the forks-are you saying that your bike is tipped forward on the center stand? that the forks are above the triple tree and not in the stock location/height? untill you solve your problem level the bike to stock standards

if you have fuel flowing (carburettor into the intake manifolds?) like that that could be the problem of high idle. if you look at the rear of the carbs is fuel flowing from the little brass jets or up the needle in the throat under the slide?
it sounds like your floats are out of adjustment or needle valves are stuck or defective.
did you do a wet fuel level set?

it is time for the church of clean chat.

 

what size 84 Seca do you have
how to clean carbs
IN THE CHURCH OF CLEAN

follow link to see internal view of carb
Something New, Something Naked

setting float height fuel level

bring tube from left side of carb bank to right side of carb bank when you test carb 1 to test for bike to be level left to right
fuel level must be the same

 

^ what they said! Your carbs aren't ready for the matinée show just yet.

 

tnx, i ll set the old girl (its a XJ550 with B28 mikunis) back straight and let her run for a while, so the excess fuel in the intake boots will be burned off (if there is any). I ll report back what happens over the weekend.

 

If there is excess fuel getting into the intake boots, then there is excess fuel getting into your oil. Fix the problem before you ruin the engine.

Don't run the engine at all until you get the carbs properly cleaned and set up (including making sure that the float needles (and the needle seat gasket) aren't leaking).

 

Hello guys,

Did some more work on the lady. Completly dissasembled the carbs, cleaned them with white vinegar and acetone, replaced all seals, replaced the needle valves and all bushes with new ones. Did a level check, which indicated that the level is at tho lower tolerance, -3mm or even less. I have also changed the carb airbox and intake boots.

But the problem with the high idle still remains (now at 8k), what do you think, is this carb gone, or could it be an elctrical ignition problem?

 

just to confirm wet set to 2mm +-1mm below carb body flange as pictured which is -1 to -3mm.

unanswered question from above did you try to adjust the Idle knob? it controls carb #3.

did you replace the orings on the pilot screws and install in proper order on screw
spring, metal washer. oring (last on, nearest point)
can you confirm if the enrichment (choke) circuit plungers are closed by pushing down on them?
just asking to rule it out

How close to Hamm do you live?
My son and his wife live there.

 

Hello, tnx for your replay. here is a photo of the levels that i adjusted, yes i know that they are a bit low, but i want to find the cause of my problem, so by this setting i ruled out a the float height.



Idle knob did not affect the RPM neither did the choke . I did replace the o rings on the Idle screws, but i did not know where the circular silver bush goes which came with the rebuild kit?



I ll try to re check ih the idle screew were all assembled in the right order, but when i turned them all the way in, it did not affect the high rpm, regarding that this must be an issue witg the main jet.

Maybe it would be wise to clog up the main jet with some silicone plugs to pinpoint the problem to an exact carb .

 

It would NOT be wise to clog any jets with anything.

It would be wise to take a can of spray carb cleaner and identify where your (likely) vacuum leak is.

The idle mixture screws do not appreciably effect idle speed. Did you make sure to remove the old o-rings from the idle mixture screw wells?
The idle speed screw (between #3 and #4 carb along eh bottom of the carb rack) does, as does the throttle plate synch, and a host of other small details that need to be addressed individualy, and methodically.

Did you completely follow the advice given in The Church of Clean?


The circular aluminum "bush" is a plug that is meant to tamperproof the idle mixture screws (an EPA mandate). They are not needed.

 

Sorry, there is no vacum leak, i allready replaced all boots and clamps.

 

the orings in that kit are not the correct ones for the mixture screws way to thick. the bush is the seal plug for the mixture screws you can use a "rubber"plug instead
fuel levels way to low you can just check them all at the sides of carb 1 and 4 that can cause lean condition as well.
did you replace gaskets for the manifold boots?

it has been sugested in other posts to seal the enrichment circuit hole in the bottom of the carb bowl to eliminate that circuit as a problem.

 

I did replace the gaskets also. Tnx guys, i ll re-adjust the levels one more time and let you know if it solved my problem.

 

If you cleaned them properly and bench synced them you should not have a run away idle condition with out air getting sucked in somewhere. My advice would be to remove the carbs again and make sure all your throttle blades are closed with the idle screw backed out. Then inspect the carb manifolds for any damage or gaskets that could be out of place where they bolt to the head.

 

But did you test for a vacuum leak?
Replacing parts is no guarantee that there is no leak.
Did you replace the throttle shaft seals?

 

He has air pulling in somewhere.

 

did you soak the enrichment plungers in acetone this will cause problems because the tip is mounted in rubber?
I will post a photo in morning of the oring you have in your kit and the proper sized one there is quite a bit of difference in size

 

In addition the orientation of the spring, washer and o-ring must be correct.

Gary H.

 

Hello,

1. removed the pilot mixture screws, ... i did leave one of the old seals in one of the holes
2. adjusted the level againg, pain in the ass process, did manage to get 3 carbs in the tolerance, but one is really stubborn. its acctually quite hard to raise the level for 1-2 mm, since the tang is so sensitive. ( are there any replacement floats sold anywere?) please also explain how a lower level can result in a richer mixture?

Will try to assemble it again on the bike and re-check for vacum leaks. But a vacum leak sould not provide so much power (my opinion), because after releasing the clutch the bike felt like it had the throttle half open.

I did not replace the throttle shaft seals, they are up next if the next test does not resolve the problem. Choke plungers were not soaked in acetone,i did noticed the rubber seals, they looked ok.

 

So just because replace things doesn't mean that there isn't a leak.

A run-away idle like that is screaming "AIR LEAK SOMEWHERE!!!"

The mixture screw o-ring that you didn't replace, would not cause this.

You must bench sync your carbs to carb 3, not carb 2.

You have not done the throttle shaft seals..... I bet I know where there's a lot of air getting sucked in--- ahem

Make sure there is a vacuum port cap on each port that doesn't have the vacuum line on it, AND make sure that the vacuum line doesn't have any breaks, AND make sure it's connected properly to the petcock. If its not, it's no different than an open vacuum port-

Just a little air leak WILL cause a run-away idle, so much so, that even ONE leaky throttle shaft seal will cause that.

Could be a leak at the manifold-to-head surface. You DONT know til you actually check it, rather than assuming.

Could be jets got mixed up when reinstalling into the carbs.....

Could be a number of things.

You must systematically eliminate possibilities.

What was it Spock said about eliminating possibilities, regardless of how unlikely....?

 

The unlit propane torch trick is an easy way to check for vacuum leak. Just run the engine and point the unlit torch at the intake boots for a few seconds, if the leak is there, the RPMs will creep up. If not, repeat the procedure somewhere else next to the carbs (throttle shaft ends for example), and so on.

 

Could also be screaming "I NEED A VACUUM (RUNNING) SYNCH". At least one cylinder is producing way more power output than the others, and that self-reinforcing cycle is what can cause the run-away condition.

Of course, you've got to figure a way to throttle down the engine before you can perform a running synch...........

 

If nothing else, open the airbox, be creative, and make a baffle of some sort to stifle the airflow to the carbs to pull the idle down temporarily.

Another question--- are you sure you didn't put any butterfly in backward or upside down?

Just running through possibilities....

 

It could be as simple as a carb hat screwed back in not tight enough. It happened to me once

 

Dumb question . . . But - Did you reset your idle screw proper or just twist it on in there?

 

Since he said the idle knob didnt affect the idle, I'm assuming he rabbit in and out to check, therefore I didn't bother to bring that up.

But, maybe I should heed my own advice of " never assume....."

 

He also said he bench synched them, and a proper bench synch shouldn't give him 6K.

But hey, I've done things worthy of a palm slap to the forehead, so maybe . . . .

 

I had an air leak and it didn't turn out to be the carbs at all. Instead, one of the gaskets between #1 intake manifold and the engine was sucking air. When I removed the intake manifold about 1/2 of the gasket was nowhere to be found. Installed a new gasket and the problem was solved. I initially found the leak with a propane torch.

 

poor photos but you can see how different (larger) the ring on left is compared to 2 on right
ring on left is from Kit op showed the 2 rings on right are the correct size
the cross section of the rebuild kit oring is much larger diameter then the correct orings from xj4ever.

would make it very diffucult to get the soft bottoming of the mixture screw before backing it out to 2-1/2 turns initial setting. I doubt the needle tip would even protrude through the carb throat.

edited for o ring ID

 

But which is the wrong one?

 

The fat one is incorrect

 

I did an edit on that to change rich to lean.
the lower the fuel in the bowl the more air is used to pull the fuel from the bowl which results in lean.

 

The way I understand it, the engine will always suck the very same amount of air-fuel mix thru the carbs, then if less fuel is available due to a low level in the bowls, the mixture will automatically be leaner than needed.

 

so what causes it to be "automatically leaner" if it is "sucking the same amount...."
its like the soda bottle and the straw when you blow across the straw. the air flow fights gravity to pull liquid up

good reading on carb tuning

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

• 3. Low end (full throttle / 2k-3k) talks of float hight
• • • Float height (AKA fuel level & how to..)
  • To get best low-end power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
    • Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tangtouching but not compressing the float valve spring.
    • If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
    • If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
    • Example: change float height from 15mm to 14mm to richen up that area.
  
  Marc W. Salvisberg
  

 

Less fuel in the same volume of air-fuel mix, that's what I call leaner.

 

Tnx guys for all your replys, i did manage to set the fuel level on all 4 carbs now, i have also discovered that sometimes a choke plunger got stuck but only after, opening and closing it for like 40 times. I did install the orings with the rebuild kit, they fit - fully screwed in the needle protrudes trought the carb body for 2mm, as with the original ones. A test with a seringe showed that they do seal.

Out of curiosity i did a blowjob on the carb (not a plesent experiance), all 4 of them seme to behave in the same way concerning the air leake trought them. So in the next days i ll mount them on my bike, and try to seal off each carb seperatly (without the airbox boots) to determine which makes trouble. And ill try to make a video if it can be uploaded here.

 

the thicker o rings may affect where you want your base setting of of the mixture screws to be standard starting would be 2-1/2 turns so 2 turns may be a better starting point for you , in my experiance it will start and run easily from 1-3/4 turns ( with thinner o rings).
just want to be careful of running them to lean for extended periods of time,
the bike will start and run with out the air box boots. it will be a good time to do a visual on how the slides are working in the response time to open and close through the throttle range.
you will have to post the video on an online place like you tube then paste in the link to have it show up in the post.
its a great looking 550 you have, when you have it running correctly you will be very happy with it. well worth the time and trouble spent.

 

If you do a research on Google with "blowjob" I think you'll be surprised (and maybe shocked) what you'll find.

 

well, i ll rephraise it, i tryed to imitate the engine by sucking air trought the intake of the carburator and it was not hooked on the gas supply

 

Good thing, you don't want to inhale atomized fuel. That's assuming you can create enough vacuum to pull fuel up from the bowl.

 

This is getting out of hand

 

+1. We have ladies present.


Gary H.

 

SUCCESS!Got her to work! Must have been the blowjob, or the float level one further question, there is a distinctiveknock knock knock sound coming from the area of the sprocket/shaft. This noise goes away with an increase in the idle speed. (somewhere around 2000 rpm it cant be heard any more) Is this a sync issue, can i sync it without the YiCS tool?

 

you can sync with out tool
my bike made a distinctive knock with oil changed to spec added 2 ounces (56 cubic CM) of oil, sound went away
front chain sprocket has a plate that holds sprocket tight in place that wears out could be you need a new one . it was the only part my local dealer had on the shelf $4.00