Can't idle below 4k

See this post for details on what has been done thus far with carbs:

http://xjbikes.com/Forums/viewtopic/p=56517

Idle has been all over the place, but I have not been able to get it below 3-4k without letting out the clutch while in gear. This makes cruising at city speeds a breeze, as I can go hands free. . But clearly this is not a good thing.

By turning the idle screw, I can increase the idle, but not decrease it below that fast race.

Workshop instructor thinks it might be the timing plate, or perhaps something with the throttle cable. I know this subject has come up before, but what else should I look for?

 

I'm wondering if the throttle is being held open by a misadjusted/mis-synched carb, i.e. one butterfly plate is holding the throttle open.

 

It's simple, the engine can't run that fast without getting air!
Either the throttle isn't closing or you have a leak in the intake manifold.
Take the rubber boots off the intake between the carbs and the air box and check to make sure that when you close the throttle all the way the butterfly valves actually do close. They should only be open the width of a business card at idle but you should be able to back off the idle screw and have them close all the against the side of the bore.
If that's ok you probably have cracked intake rubber manifolds or leaking seams where they bolt on to the engine or something like that.
The mixture can be too lean and make it idle too fast but only when it warms up, not when cold.

 

It seems to get worse as it warms up, so the mixture is a bit suspect.

I'll check the boots as well.

 

What do you see with a Colortune? Is it too lean?

 

I'll let you know.

 

Loosen-up the Cable Adjuster all the way. If the Cable Adjuster is too tight or is isn't swiveling in its mount ... that will open the Throttles and you can't adjust it out with the Idle Adjustment Rod.

On the Cable. At the end of the bend. Thumb wheel. Loosen. Twist cable adjustment knurl and listen to the rpm's rise and fall!

 

I ' m wondering if the POS Vacuum fuel valve petcock contraption has developed an air leak.. resulting in a High idle.
Those things were crap when newish.. now, 20 years later??

 

If the Petcock had a Vacuum leak ... quite the opposite would occur. The Bile would stall from fuel starvation.

Although 4,000 rpm's isn't outside the realm of possibility for and air leak ... I would suspect linkages or improperly adjusted Butterfly settings.

You need to see if the Throttle Shaft is hanging-up. Try lubing the linkages and the Throttle Shaft Seals (Internal Pivots) with some Marvel Mystery Oil.

Still ... you NEED to know if the linkages are allowing the Butteryfly's to Close. That kind of power -- 4,000rpm's -- needs Main Jet influence to make the engine run that fast.

 

Tried to do a bit of colortuning. Everything looked blue, but then at 4k rpm I would expect that.

I'll pull the rubber boots and/or carbs and see if the butterfly valves are behaving. Will also check for throttle cable movement.

Coupla questions:

1. Carbs have yet to be balanced. Since they are cleaner and have no jet blockage, I'll do that soon. I have noticed by taking a temp reading with an IR probe off the header pipes, there is a wide discrepancy in the readings from cylinder to cylinder. Might this be related to the high idle?

2. Possibility of a timing plate problem causing the high idle?

 

Also should mention, as a possible clue: The bike starts pretty easily, and given the high idle doesn't really doesn't need any choke for long. When it starts, it idles at around 3k. But as it warms up, the idle goes to 4k.

Seems strange.

 

If there is a wide discrepancy in the temperature readings from cylinder to cylinder that would indicate different amounts of fuel mixture in each cylinder due to unbalanced carbs or it could be due to blocked idle jets, leaking seals or some other problem. Anyway, something is not right if it's different from one to the next.
I don't think there is anything you can do to the timing plate that will change the idle much since it's not adjustable. If you take the bolts out and turn it the engine will run poorly or not at all.

 

Interesting. I see your reasoning, but I'm wondering why adding a stronger spring to my petcock vacuum diaphragm would seemingly cure MY racing idle.

 

His engine isn't idling.
It's racing.
I doubt the Petcock has anything to do with it at all.
4,000 rpm's indicates that the Butterflies are open and the engine is getting fuel from the Main Jet Supply.

Stuck Diaphragms?
Linkage springs?
No or stretched return spring?
Sync -- way off.
All including Pilot Mixtures incorrect or needing the Colortune when the engine is below 1,150 rpm's.

If you had the Carbs off ... see that the throttle cable connection isn't jammed up under the head.
That will do it every time.
Don't pry it loose if that is the case ... pull the Carbs back and set it free.

 

The cable seems to be free and clear of everything. We took care when reinstalling the carbs the there were no hangups. But since it was racing even before we touched the carbs, it may be the cable has never been pulling it's full range. I won't know until I look at the butterfly valves. I'll give the idle jets a good look as well. The throttle snaps back, so I don't think it's the return spring.

I think my next step should be syncing. As I don't have a manometer (yet), I'll have to wait for Saturday's workshop. It will be interesting to see what that first manometer reading looks like.

 

Not so fast.

The next step should be putting a small degree of slack on the Throttle Cable.
There is an adjustment on the cable. The Plastic "J-Shaped" fitting that corrects the angle of the Cable exiting the Throttle Grip Mount.

There is a Locking Ring and a Knurl adjuster. Un-lock the Knurl and back-off the slack on the cable.
That might be enough to allow the Linkage to Close and make those high rev's back-off without doing a lot of other unnecessary adjustments and troubleshooting.

Loosen the Locking Ring.
Adjust the Knurl and listen to the rev's as you turn it. I have a high degree of confidence you will be able to bring the rev's down making a Cable Slack Adjustment.

 

Rick - I'll take a look at that, tomorrow hopefully. I'm all for doing something simple and easy to alleviate a problem.

Thanks.

 

Ok, it almost definitely is not a problem with the throttle cable. The throttle has full range, and the cable shows just a tiny amount of slack left over when the throttle is closed. The idle adjuster is past the stop, and it still idles at 3500-4000 rpm.

We checked the timing, and it appears to be advanced by about 5 degrees, maybe a bit more. So it's idling high because of the advance timing, or the timing is high because of the high idle. Probably the latter, unless the electronic ignition is to blame.

I suspect a vacuum leak in the manifold intake boots. They do appear to be a bit cracked in places. Hard to tell how significant without removing them.

In the event they aren't sealing correctly, will I have to buy a new set? I think they are about $20 apiece, maybe more. Or could I use a gasket sealant - paint it on, squeeze the boots to get the stuff into the cracks, let it dry?

 

If the cracks are deep ... fill them with Black, 1-Ton, 5-Minute Epoxy.
You can sand it down after it Cures.

If the cracks aren't too deep ... you can Brush-on some Black, Liquid Electrical Tape.

(Don't use the sloppy brush that's attached to the jar-top ... Let some drip off the applicator and brush it on with a Artist Brush.

If this was jusut a straight air leak ... the engine wouldn't sustain a steady 4,000 rpm's.
In order to get 4,000 rpm's ... there needs to be FUEL and an AIR FUEL Ratio correct for the engine to be running that fast.

I think you should investigate:
Needle Jets raised or alltered.
Stuck Diaphragm Pistons.
ALL Linkage related issues ... including Butterfly's not closing and allowing the Mill to get a sip of Main Jet Gas.

Pilot Jet really Pumping-out some Gas through the Pilot Mixture Screws.
Which means:
There would have too be enough AIR in the Pilot AIR Passage to sustain the Ratio without ample Fuel coming from the Pilot Jets. You need to turn the Screws IN.

Go back to Factory Preset = 2.5 Turns Out on the Pilot Mixers and work from there!

 

Thanks Rick. Now the usual follow up questions :

1. Any clues on what to do about the dreaded manifold bolt, the one that keeps breaking off? The usual PB Blast and careful patience?

2. Does the epoxy/liquid tape fix work? Or would it be worth it just to replace the boots?

I plan on pulling the carbs this week and (hopefully) give them the Rick Massey Old Fashioned Carb Cleaning Method (RMOFCCM©) .

Just to make sure I'm clear on the terminology: When you say turn the pilot mixture screw "in", you mean closed? As in, righty tighty?

When you say 2.5 "turns" out, are those full 360 degree turns? Sometimes "turns" can mean "turn of the hand", which usually translates to 180 degrees.

 

Replace the Boots ... IF you can FIND them and afford them ... no question?

"Turns" = 1 Full Revolution. 360-Degrees.

The IN = Down, Right, toward closed.
The OUT = Up, Left, opening.

Bottomed-out is all the way down until the Jet is as tight as it can get in its threaded hole.

Two and a half turns out would be: 2 X 360 + 180 from all the way in.

 

Ok, I pulled one of the boots off. There are cracks, but they do not go all the way through.

The gasket, as you can see, it pretty much a mess.

 

If they dont go through ... the Epoxy followed by a coat of Liquid Electrical Tape will do the trick.

I hope you didn't break a Cap Screw getting them off ... if you didn't you are a Lucky Guy!

You can MAKE new Gaskets. Real Easy. I'd say the gaskets were your problem.

Coat the Gaskets with "Indian Head" gasket sealant by Permatex. That will plug any air leak and seal them permanently.

A "Paperboy" Single Hole ... Hole Punch will make the holes you need for the studs.
You can make the outside and inside big holes with some sharp, small scissors.

 

Since you've got the rack off check your bench sync too.

 

Oh yeah, checking float height, everything, since I am doing the RMOFCCM©.

I think I am just gonna replace the boots and gasket. One of the boots had a through and through crack where it joins to the carb. A couple of the gaskets more or less disintegrated when I pulled the boot off the manifold.

Which brings up a couple of questions:

1. What's the best way to scrape off the remains of the gasket from the manifold? I don't want to damage the aluminum.

2. Whoever put those manifold bolts back used some sort of anti-thread freeze. It was whitish and powdery when I removed the screws. It almost looked like plumbers tape. I've heard milk of magnesia works great to stop threads from freezing.

What sort of substance (if any) should I use on those bolts?

 

Permatex NeverSeize Anti-seize Compound.

Aluminum Based Paste.
Bolts, fasteners and Spark Plugs treated with the Compound -- Don't seize.

I use it to lube Header Pipes into the Collector.
Coat Axles.
Smear it on the Side Stand Pivot.

Anything you need to take apart later ... gets a smear of the stuff.

As for cleaning the Old Gasket off of the Aluminum.

I use a High-speed wire brush on the end of the extention wand of my Dremel Tool.
I basically work like a Dentist and brush it off until the wire brush shines the Mating Surface.

You can soften the Gasket by rough (320) sanding it and using Carb Cleaner to wet it and loosen it and then go after it with a razor blade.

I used to do it like that to all Gaskets that used adhesives until the BandAids got soaked with blood and started falling-off into the internals of the engines I was working on.
They're tough to get out because the magnet won't pick 'em up!

 

Rick, you're a madman. . I don't think I would have the courage to take a Dremel tool anywhere near the engine block.

Another question came up: On my #4 carb, the brass retainer that covers the air jets beneath the diaphragm - that brass screw just won't budge. On the other three, no problems. Any suggestions?

Also - an observation. Remember I said that the #2 header pipe was not nearly as hot as the other 3? Colortune confirms it is indeed firing. When pulling off the chrome dome on the #2 carb, I noticed the the rim around the slide, and its internal cylinder were a bit greenish and looked very dry. All the others looked ok. It also looked like the diaphragm may not have sealed all the way around, although I can't be for sure. Think that might be the problem with #2?

 

That would be a major contributing factor to that Cylinder not firing as it should.
I "Seal" the Diaphragm to the Body by smearing a very light coat of Waterproof Grease in the Diaphragm Ridge Locating channel.
The grease only holds the edge down -- all around -- until the Hat is Placed on and screwed-on tight.

The Dremel Tool is a Wire Brush Bit. A mini wire brush bit.
It just "Brushes-off" the Gasket material and does no harm to the Block what-so-ever!

Using the Extension Wand attachment makes it a precision tool.
You could brush-off paint from your fingertips and not lose any skin!

 

Rick - while waiting for the new boots, I have a general question here.

If there is a leak in the boots between the carb and the manifold, wouldn't that make the engine always run lean? IOW, carbs don't know about all that extra air the engine is getting.

Lean means faster idles?

 

The answer to the question is Yes ... the Idle would increase.
Idle.
Maybe up to 18-hundred or so.
To get that thing up to 4-Grand ... you NEED Main Jet Gas.
Linkage.
Idle Rod.
Sync way off.
Lazy return spring.
Tight cable.
Something that's opening the throttle fly's some.
4-Grand is Power ON.

 

Sync could also be an issue. When I bench sync'd it, it sure seemed be off.

Also - the pilot adjust screws were way different from each other.

One of these pieces has to solve the puzzle. I can't manometer the sync with that idle so high.

 

ok please for me just check this cause I had this same problem, make sure that your hose clamps on your boots are all facing the same direction, they should have a little clip on them, and if they arnt directly on top or bottom than it will catch on the thing which opens your butterfly valves. it took me weeks to figure it out, I rebuilt the carbs cleaned them did everything I could think of. so just check that maybe its the same mistake I made

 

Set the Pilot Screws ... ALL ... just a few Degrees short of 3-Turns Out from the Bottom.

See what happens.
Let us know.

 

The boots, gaskets and rubber caps came in today. Yay!

Removing the remnants of the old gaskets is a real bugger! Some of that stuff has petrified. Lots of scraping, spraying some 3M adhesive remover, scraping with a small screwdriver, razor blade, and yes - Dremel wire brush.

How anal do I need to be here? Does the entire surface need to shine? There are parts that have tiny bits, so small I can't even feel them with my fingers. So I have to shine all the way around the bolt holes?

Normally, I wouldn't even ask. New gaskets should easily fill those gaps. It took me over an hour to get 99% of the stuff off just one cylinder.

 

Nobody's gonna sneak-in and peek to see that you got all the material off the mating surfaces.

I guess if you can't feel it ... it ain't really there.

Button it up!

 

I jsut set my pilots and so far it has been idling good!!!!!!!! hopefully its that way tomorrow, but you know how that is.

 

Idling good is a GOOD Start.

It's what the Bike does, now, "Out-of-the-hole" that we have to work on.

If there is Bogging-down or Hesitation ... some real Tweaking needs to happen.

I know you are up for it. You want that Bike "On-the-edge" of fine-tuning.

 

Grrrr, now a couple of my float needles aren't sealing. They are the original stock ones, so I guess it was just a question of time. Probably sitting dry these past few days was enough to push them over the edge. Good thing I did the test on the bench, with a catch basin underneath. It would have been a real drag to have primed the carb on the bike and have a little flood of gasoline on the garage floor.

Oh, the things that can go wrong...

So now, more hurry up and wait. Waiting for needle valves from Chacal that (hopefully) will work.

Oh well, more time to get those manifold openings bright and shiny!

 

Roll-up some 1200 Grit Wet-O-Dry Finishing Paper and stuff the slender roll into the Float Valve Bodies and ... Do the Twist. Shine the Inside Diameters of the Float Valves.

If the 1200 Gets looking like its clogged-up with tarnish or brass ... snip it off and use a "Fresh" section of the rolled-up finishing paper to shine the Insides of the Float Valves Clean.

That ought to put an end to the sticking floats.

Eyeball the Geometry .... too.

You may have to sling the wire over the opposite side of the Float Tab for a straight UP / DOWN movement of the Pin!

 

Rick - the rubber tips of the old floats needles are pretty scored. That's why I tried to replace them a few weeks ago, with crappy aftermarket needles that leaked like crazy. So I reinstalled the original ones.

Before that, I had that idle problem. After that episode, it grew worse. We all know the rubber boots to the manifold were cracked and had disintegrated gaskets. Maybe a combo of the leaky boots and leaky float needles is the root of that high idle?

 

Ok, I found a great product to get rid of the baked on gaskets:




It was so easy, spray... wait a few minutes... scrape it off. The stubborn parts took a few application.

Now the surface is squeaky clean. Heck, even this guy would give it a thumbs up:

 

I understand the situation with your boots and floats.

What concerns me ... is that the "Idle" you have is 4-Thousand RPM's.
4,000 RPM's isn't Idle, anymore. It's POWER-On.
In order to have enough Fuel to make 4,000 RPM's ... you need the Main Jets.

So, I suspect a Problem with the Linkage and the Butterfly's.
You MUST not have the Butterfly's closing when the Throttle is closed.
Main Jet Supply is getting in.
You should ... if the High-rev situation persists ... pull the rack and:

Examine the linkage.
Bench Sync the Carbs with thin slices of Business Card.
Make sure that the Sync Screws are not tight and keeping the Butterflys Open.

Start the Bench Sync with 3
Close it down on a thin 1/4 Inch wide strip of Business Card.
Match 1, 2 and 4 to the thin strip ... and you'll have Closed throttles which will allow you to set-up the Mixtures better.

If the Throttles aren't Closed because you used a feeler gauge too thick for the job ... you are probably running on Main Jet Output and that has the Rev's too high to correct with the Idle Adjustment Rod.

 

Sometimes with these bike, you want to advertise "parts bike for sale".

Other times... miracles happen.

Installed new floats, had to sand one down a bit so it wouldn't leak. Used washer fluid to reset the float height. Then installed the carbs with their new manifold boots.

Rolled it back out of the garage, put the tank back on. Moment of truth #1 - prime the carbs - Yay, no flood! Moment of truth #2 - Yeah, but will it start? Two cranks and it fired right up, like it hadn't sat idle for nearly two weeks.

And the best part - the idle problem is fixed! When warm, it easily and happily purrs at ~1400. It may go lower, but I'm afraid to try it without first getting the idle mix right and then syncing them. It sure seems smoother when riding at speed too.

I fixed so many things, hard to say which was the problem. Maybe the sync was way off, and bench syncing fixed it. Maybe the pilot adjustment was way off - resetting to factory fixed it. Maybe it was those cracked manifold boots - got new ones. Maybe a bit of all of the above.

Long day, I'm happy atm. Tomorrow - who knows? Lots more tweaking ahead. But there wasn't much I could do with that high idle. Glad that's behind me, at least for the evening.

Thank you everybody for your help and advice! Doubt I could have fixed it otherwise.

 

Well ... that's more like it.
Had to be a combination of ingredients.

So, now the real Tweaking begins.

Good Luck bring it in. There's no more fun than having all the component parts in good working order before you begin the quest of getting an XJ-Engine all smoothed-out.

It takes time.
Patience.
A mind over matter attitude ... and ... most importantly:

A real, homemade, Tweaking screwdriver that FITS the Mixture Screws so you can actually move them a my-nute (sic) amount to put the engine in the Twilight Zone.

Here's where we ought to have a couple of Regional "Kits" that could be shipped-out to a Mamber who is beginning the "Sync and Mix" portion of the adventure.

But, there are "work-arounds" for everything you'll be needing ...
Especially if there is a Tropical Fish Department at the Pet Store.

You CAN Sync those Carbs with ONE Vacuum Gauge.
I did it for years.

Sears Vacuum Gauge
Rubber Hose
Golf Tees
And a restriction device to quiet-down the Vacuum pulses and keep the indicator needle on the Vac-Gauge actually showing you the Vacuum and NOT just fluctuating wildly under the rapid pulses of vacuum of the Intake Strokes.

 

Attempted my first color tuning today. Keep in mind I have not synched yet.

Interesting thing is, cylinders #1 and #2 would not go rich (yellow flame) no matter what I did. #3 and #4 were fine, I turned them just to the point of turning yellow.

Something is still going on with #1 - adjusting the pilot screw on it had by far the most dramatic effect on the idle. Related to this issue - the headers are 50+ degrees warmer on #1 than on the other three.

Synch issues?

 

Oh crap. I didn't use the YICS tool for color tuning.

I know it's a must for synching, but what about color tuning?

 

Mine was doing this same thing.. Turns out the choke cable waant disengaging all the way, I pushed the choke down manually at the carbs, solved the high idle then I adjusted it from there... I'm sure you have already checked that but I thought I would throw in my 2 cents.

 

When the "Choke" is operated by someone who does not know that the effect is proportional, they tend to get heavy handed turning the Enrichment ON.

The net effect is to bend the "Tee-tops" on the Enrichment Valves out of shape so they are Tilted and not straight up and down ... causing them to not fully seat when OFF.

Straightening them can break them off.
If you break-off an Enrichment Valve T-Top ... you have to Drill a hole in the end and solder-in a new T-top from a Brass screw you have filed-down to the size of the Broken-off T-Top and solder it in ... making a new T-top end.

Sizing it is the trick.
Not only do you need to have the correct height ... but, you also need to file the head of the Brass screw to pass through the bore on the Enrichment Valve Body.

Chucking it into a Drill and high-speed sanding it will do the trick. Just be sure to leave enough stock so it doesn't bend; too!