Dirty Carbs, no throttle over idle!?

[TucmanXJ]

I just bought a semi-neglected '79 XS1100 Standard. It has a set of Mikunis that are dirty inside after sitting still for 3 years (or more).

First:
Changed contaminated oil/filter for fresh. Fuel had been draining thru #3 carb's cruddy inlet valve into the airbox and down into the breather tube etc.

Changed to new fuel, new NGK oem plugs... voila the bike started & ran ... but AT IDLE ONLY. Bike smoked for about 15 mins then it cleared right up. Engine now idles great but it will not accept any throttle over 1000 rpm. Carb slides just tremble slightly then the engine falters if I open the throttle.

Did a disassembly of the right side carbs to see their condition - other than varnish everything looks normal. Fuel lines and vent tubes are clear and routed normally. Petcocks work fine.

Right now I'm cold soaking the carb bodies in Berryman's carb cleaner (basket type) to clean the carbs & orifices. Will be replacing: inlet valves, needles, jets, pilot airscrews and gaskets with oem items in my K&L kits.

Does anyone have any experience with their XS11 engine faltering & dying once the throttle is opened past idle? Any theories as to what the cause(s) might be?

Working thru it ... step by step.

RJ

[Ken Talbot]

Tucman, your carbs are dirty. It really is as simple as that.

You'll want to start by reading through the various technical atticles here on the forum, starting with this one . Actually, even before that, you want to get those bodies out of the cleaning solution unless you took care to remove the butterfly shaft seals. Prolonged soaking with ruin those seals, and you'll have real problems.

You will find that it will take more than soaking to get all of the wee orifices and passages clean. You'll need to blow compressed air and or carb cleaner through them all to make sure they're open.

Take a few minutes, read the articles, then dive in.

[red bandit]

Hope you removed the shaft seals......or you will be after soaking in Berrymans. Your doing a lot more work than necessary taking bodies off rack. No need to replace parts. Carbs are just dirty. ASK QUESTIONS FIRST!!!

[TucmanXJ]

first cleaning didn't do so well ....

Just pulled the offending carb outta the soak basket after only 20 mins. then blasted it through & through with LOTS & LOTS of air & carb cleaner.

Why the soak? Simple ... #3 carb was extra dirty inside in ALL the vital areas. Looks noticably better now than my first cleaning attempt. Butterfly seals still feel tight - no play in them after a brief dunk.

Will concentrate on getting more air & cleaner THRU the carbs (rather than relying on soaking). Other carbs; #1 and #2 look a bit better ... not separated.

By the way ... the needles, pilot airscrews and choke linkage were coated with years of hard baked oil and varnish. Its a wonder the bike even started.

Been a few years since my last cleaning job but it's all coming back now.

thanks, RJ

[TopCatGr58]

Hey RJ,

Aside from relearning how to clean your carbs, you will also want to look at the timing cover components on the left hand side. After sitting for years, the grease can also get hardened, parts rust, etc., and the mechanical advance parts and sliding timing plate can become stuck NOT allowing enough timing advance!

Also, hope you pulled the TOPS of the carbs off, inspected the vacuum slide rubber diaphragms for holes, as well as cleaning the slides, ensuring that they are not sticking.

Next, check for vacuum leaks, both where the carb boots attach to engine, as well as the synch port caps, the vacuum advance hose...it attaches to the #2 carb body metal port, not the intake boot port!

Let us know.
T.C.

[Ken Talbot]

Re: first cleaning didn't do so well ....

Originally posted by TucmanXJ
Just pulled the offending carb outta the soak basket after only 20 mins. then blasted it through & through with LOTS & LOTS of air & carb cleaner.

Whew!

[TucmanXJ]

OKAY - advance mechanism looksee

So far no real change to the NO throttle-up even with newly cleaned carbs. As suggested - its time to inspect the Ignition Advance & Timing Plate. Diving in.

hand me that sensor please ....

... Mr. Spock "Fascinating"

[TucmanXJ]

Advance Plate testing: looks normal

Just took a look at the Advance Plate & Vacuum Canister / hose condition.

Centrifugal advance mechanism looks very clean, factory paint dot on timing plate retainer screw is still in its oem place / unbroken. Moves freely.

Static canister test:
Slight suction pull on vacuum hose makes advance plate move CC. Engine OFF.

More testing:
Will have to wait until engine cools so it will start better & then test Timing setting at 1000 rpm idle with a light.


DIFFERENT BIKE >
P.O. of my XJ11 had removed the oem advance plate & vacuum unit completely. My guess- it was running with static advance only. Seemed to perform well.

[TopCatGr58]

Tucman,

No, the PO didn't remove anything from your XJ, it didn't come with any mech. Cent. Adv. or Vacuum pot at the timing plate. The XJ's TCI has both curves programmed into it, but it does use a vacuum SENSOR to send electronic signals to the TCI!

Back to the carbs. Did you happen to check what the jet sizes were, as well as the position of the needle on the vacuum slide...it's adjustable. Also, the pilot jets should have had screws capping the jet tower OFF, cause it draws it's fuel thru the MAIN JET and tower via a little tunnel between the towers!

What are your float levels set to, should be ~25.7mm.

Also, aside from the MAIN jets, did you remove the main jet NEEDLE=emulsion tube from the middle of the carb body up thru the top of the carb?? IT has many little aeration holes that are also easily clogged with varnish and gum!
T.C.

[TucmanXJ]

XS11 fuel system

T.C. At first I'd assumed that indeed my 1982 XJ11 had a stock YICS engine in it. Not so, at DMV inspection Model Serial # 3J6 was on the engine case. Tucson Ride Now YAM Dlr said it was a 1980 G engine without YICS. This swap was confirmed by the changed Ignitor bolted on top rear fender, larger spaced oem mount holes betrayed the matter. I just sold it, shoulda taken some pics of the No-Advancer/Plate empty space - it sure looked peculiar but it ran well.
--------------
BACK TO the '79 XS11 Fuel Gremlins:

GOT FRESH FUEL, AIR, SPARK, BRAND NEW BATTERY, NEW OEM PLUGS, NEW OIL/FILTER. Engine CRANKS & TURNS over FAIRLY QUICKLY & STARTS EASY with CHOKE ON. WILL NOT ACCEPT -ANY- THROTTLE PAST IDLE.

I very carefully & meticulously cleaned every millimeter of the Mik carbs; all jets, mains remain at stock size 137.5. The low, medium jets & needles were cleaned, clips remain at center oem position. Blew fresh carb cleaner & air through every port, & orifice including mid-jet tunnels (removed cap & pulled the small jets, 2 were replaced with brand new ones). Although I can't measure the float heights (no verniers) they all match in height & are void of gas. All bowl inlet valves were carefully replaced with new K & L units. Both fuel lines are new. Bowl vents, air lines are clear. There do not appear to be any vacuum leaks at the boots or manifolds.
Although the carbs were gunked up - after their double cleaning one could eat from them.

CV Rubbers seem supple, not holed or cracked. The throttle slides feel just a tad loose in their bores. Butterflys are intact and feel solid. Linkage is correct, and cable operates as it should.

So far the Advance plate & line seems correct, vacuum pull on the correctly placed #2 carb port line (is not connected to the manifold port) results in 5-8 degrees plate movement. Adv. plate will go thru a wider arc manually although with some spring resistance, it doesn't bind.

TAN colored OEM timing paint dot is unbroken. Adv plate & ring retaining screws have virtiually no wear, no tool marks at all. No grease, no rust - very clean timing area.

FULL choke setting will permit 2,000 to 4,000 rpms. At even minimum throttle application the slides appear to quiver in their bores, then the engine falters & eventually dies just past 1,100 rpms. At 1100 rpm engine idles fairly smooth with only an occaisional carb spit as it warms up.

Will check both vac petcocks to see if they are flowing sufficient fuel for correct operation. Beginning to suspect these Mik carbs are just plain worn out. Is it possible that excess slide wear will cause faulty CV operation?

Airbox is off while I get these carbs sorted out - I hope.
RJ

[red bandit]

Either wrong pilot jets, are they 42.5? Or carbs still dirty. You mentioned varnish!!! Just because you can't see any dirt doesn't mean they are clean. Clean em again, let the spray carb cleaner sit in em and soak. NOT Berrymans. It takes time to dissolve varnish.

[randy]

TucmanXJ;

Just a thought here... Those slide diaphrams can be a bitch to get in place and stay in place while you install the top cap. Is it possible that the rims slipped out of place? That would cause you to loose vacuum when you open the throttle. I find that a little dab of contact cement on the rim helps keep them in place for the top installation.

[TucmanXJ]

Ken T's slide question & test

Ken Talbot sent me a msg ...

quote: When I turn throttle the slides just sit & quiver, not raising. Their surfaces are clean; rubber looks & feels normal.

So he said - quote Aha, now were getting somewhere. Slip a fingertip under each slide, lift it to the top of its bore, then pull your finger out quickly. What happens? Does each slide quickly snap shut, or do they slowly creep back down to the bottom?

Just went out there & tested the throttle slides in their bores by lifting them up. "The carb slides return down kinda sluggish-like, defintely not snapping back."

This may be the cause of the no higher rpm trouble ... e.g. the carbs seem like they are just plain worn out (?)

RJ

[planedick]

Fall slow

Slides returning slowly is normal. There is a small hole in the top for air to get in and to actuate so it creats a vacuum when you let them fall so they should fall rather slowly indicating a good condition. Having the airbox off might be a problem. The vacuum between the throttle plate and the slides is the scource of the vacuum to raise the slides.

[TucmanXJ]

FUEL NO GO SOLVED!

NO FUEL EH? - LOOK FOR the OBVIOUS....

In my tuning & testing the Vacuum Petcocks fell into my blurry view ... applied vacuum to the carb boot lines. Only a small dribble of fuel came out, not nearly enough for a thirsty monster like the XS!

On PRIME setting they flow like Niagra Falls.

Sure enough - the venerable VACUUM operated PETCOCKS are in BAD shape, blocked by crud/gum etc.

In Prime - bike now Starts, Idles and "RUNS like a Scalded Dog" Hey it even has smooth running quality - everything works now. Throttle slides operate as they should.

thanks guys, RJ