Looking for a way to test throttle shaft seals

I've flooded the rack with propane 3 or 4 times suspecting a vacuum leak but nothing showed up. Thinking it might possibly be the throttle shaft seals....cause it isn't a very big leak at all....just enough to give it a slow return to idle and a roughness at idle.

Is a shot of carb cleaner directly on the shaft seals a good way to determine if they are bad or not?

The rack needs to be pulled and split but do the throttle plates need removed or can the new seals be pressed in from the outside?

Thanks.

 

Everything has to come apart.

Because of the way the linkage is manufactured, one side is "blinded" necessitating removal of the throttle shaft from each individual carb to get at the "trapped" seal.

To remove the shaft from the carb, the butterfly plate needs to come out. Sorry.

I'm NOT an "X" expert, do you have Mikunis or Hitachis? Butterfly removal is a slightly different proposition depending on manufacturer.

 

I was afraid of that! Len has the special screws and screwdriver listed immediately following the shaft seals....took that as a bad sign.

Oh well, so be it!

I have Mikunis, I was hoping to find a documented thread on the repair but my searching has been for naught.

 

I replaced my seals last month and it was really pretty straight forward. Fortunately I didn't need that JIS screwdriver Len sells and I replaced the screws with the Allen head replacement. Just take your time and it isn't a bad job.

I should note that my carbs are Hitachi but I wouldn't think it's too much different on the Mikunis. Fitz could probably answer that.

And yes, carb cleaner sprayed on the shafts will quickly show a leak, my old ones sure did.

 

If you want to see how bad they reall are just pop the E-Clip off of the #4 Carb and remove the nylon washer. Look at the seal and you might be able to pop it out with a dental pick. The seal should be soft and no cracks. If the seal is stiff and cracked you know what needs to happen. Just remember that outer seal is not going to be as bad as the center ones that really take the heat. So if that outer seal is bad the inner ones are in worse shape for sure.

MN

 

I evaluate them when I have the Rack stripped, just before flushing passages.

I hold the Rack VERTICALLY and drip Marvel Oil to lube the Throttle Shafts.
With Oil at all the Shaft openings.
With the Oil in place, I work the Linkage and see what happens to the Oil.

If it drips out quickly; I let the owner know the Shaft Seals are cracked or worn.

 

The Mikunis differ from the Hitachis in that they have the butterfly screws SPLIT-PEINED ("staked") over on the ends, preventing them from being unscrewed without tearing up the threads in the shaft.

You have to hold the butterflies open and file the screw "nubs" off the backside before they can be unscrewed.

This has to be done VERY CAREFULLY to prevent accidental damage to the carb throat.

Best practice is to find a dowel (or broom handle, or ???) the same diameter as the carb throat, and slice it to create a "half-moon" sectioned plug that you can slide in to hold the butterfly open and provide a solid platform for filing against.

 

Very good write-ups by schmuck and some of the other guys at xj4ever.com

Read both the Cleaning Your Mikunis and the Hitachi Throttle Shaft Seals write-ups. Pertinent info in both.

 

It's looking like the throttle shaft seals won't need replacing. I shot liberal amounts of carb cleaner around them, from all angles, and no change in rpm's at all.

I backed out the mixture screws a touch and went for a ride....it seemed to run pretty good, good power off idle and thru the gears. Took a look at the plugs....all very clean but looked too white to me.

Backed the screws out some more and went for another ride....the power was down and the hanging idle was back with a vengence! Pulled the plugs and they were still white....that seemed odd but thinking I had gone too far out with the screws I turned them in about 1/4 ± each.

That seemed to do the trick, lots of power and the hanging idle is nearly gone....only shows up when the motor is real hot, and then it's pretty slight.

Think I'm in the ballpark now and will try the Colortune again in a day or so.

 

All the fiddling with mixtures can trhow your vac sync off slightly too; you may need to revisit that once you've got the mixtures dialed in.

Keep in mind that when it comes to the mixtures, 1/4 turn is a HUGE adjustment.

 

Sorry, forgot to mention that the carbtune was hooked up while I made the A/F changes.

Yeah, I found out about the 1/4 turn....these bikes are soooo touchy! :lol:

 

The Pilot Mixture Screw's Fine Tuning Range is just a matter of Degrees.

Once the Adjustment is made to sustain IDLE ... The "Fine Tuning" will be a matter of a minute [ my-nute ] tweaking of the Mixture Screw.

The width of a Nickel -- more or less -- will tune-out "Poppidies" or infrequent stumbles.

 

Rick, I don't quite understand this statement??

 

I also have found that out. :lol:

 

The Tip of the Pilot Mixture Screw rises through the O-ring at about 2-Turns, ... letting AIR get into the Combustion Chamber.

Further bring the Needle UP allows the AIR to begin Siphoning FUEL from the Pilot FUEL supply's connected Passage.

At 2-1/2 Turns Out ... the AIR begins drawing enough FUEL to support Combustion and ::: ( depending upon various conditions ) ::: the Engine will IDLE.

Further Turning of the Mixture Screw ::: ( depending on Fine of Ultra-fine Thread ) ::: moves the Metering-end of the Screw away from the Orifice allowing more AIR and accompanying Pilot FUEL Jet Gas to enter the Intake.

The Metering End of the Screw ::: Depending on Pilot FUEL Jet Size, Pilot AIR Jet Size and the Engine's "Health" reaches a point where the Pilot Mixture Screw reaches Maximum FLOW::: further bring it Out past FULL having no increase beyond that Point.

Finding the WINDOW of Open with Siphoning occurring ...
and
Totally WIDE Open was "Guess work" until COLORTUNE arrived.

Now, with prerequisite cleanliness and within specs for tuning, ... The Pilot Mixture Air~Fuel Mixture for achieving IDLE can be Observed.

Bunsen Burner BLUE is the Starting Point for Adjusting the Pilot Mixture Screws.
Supplemental RICHNESS is needed to sustain combustion during the Momentary IN-rush of AIR during the IDLE -to- OFF Idle Transition.
::: 4 to 6 Rapid "Eye-blinks" :::

This TWEAK is added to the Point where the Bunsen Burner Blue was established.

It might be only the width of a Credit Card.
Some cases, ... a Nickel.
But, ... FAR less than 90-degrees. (1/4 turn)

From BLUE

 

Thanks for the explanation Rick....it makes perfect sense!

Whether or not I can actually apply this info in a meaningful manner remains to be seen but it seems like I need to go back and find the starting point of the BB Blue....and go from there.

My plugs were pretty white, based on that I was afraid it was too lean and went from there. I probly have it too rich even tho the plugs are still white cause I'm out around 3 1/2 turns ± on all 4 screws which is probly too far.

I also have Dyna coils and Iridium plugs gapped @ .040."

 

If you CRITICALLY Lean:

Did you clean the AIR Metering Ports of the Emulsion Tubes?
Are the Diaphragm Pistons rising or sticking?
Are the AIR Jets correctly placed?
Are there AIR Leaks?
Is the Fuel Supply adequate?
> Some filters are not sufficiently porous.
> Fuel Lines kink.
>> Are the FUEL Jets the right size?
>>> Beenie Screens clean.
>>> Float Heights tested and set.

Buy a Commercial RUBBER REJUVENATOR and Flood the Throttle Shaft Seals.
TEAC Pinch Roller Rejuvenator was the best.

I think this stuff replaced TEAC

http://www.mcmelectronics.com/product/2 ... rm=200-200

 

If it were me, at this point, I'd go back to stock plugs with the original specified gap until I had this sorted out.

I have a feeling that you may see different results.

 

If you can't get mixture results with the idle mixture screws, then it is jet related. Are the jets of the correct size and position. It has been mentioned several times, but the manual has the position of the jets reversed...

 

I did this Fitz but the mixture screws were way out....I'm going back to the colortune and find the 'point of idle' that Rick mentioned, and go from there....with the OEM plugs.

 

The jets are correct OEM, I didn't know about the reversed position....is that for the Mikuni's or Hitachi's?

 

The Haynes has the positions reversed in the Hitachis. You can't really mix anything up in the Mikunis.

I think going back to OE plugs is going to give you a better baseline; I think you're on track.

 

For clarification.
Mixed Jets ~ Hitachi ~ Haynes
AIR Jet sizes and placement.

Main AIR = Smaller ID [ o ]
Pilot AIR = Larger ID [ O ]

CORRECT POSITIONS ( 750 Carb Shown)

 

Re-set the mixture screws to 2 1/2 plus a skosch, set the idle at 1100, sync'd her up and went for a ride. It may not be perfect but it surely is in the ballpark!

Very strong going up through the gears, no miss or hic-cup and sounds like a much larger tuner sport bike....I love that sound!

The idle hangs very occasionally, but mostly will drop back to 1100 like it should. Idle has a slight, occasional, change in tone....not really a poppidie, but more of a slight change in cadence I guess....I think I should be able to tune this out with minute tweaks on the mixture screws.

Over-all, I like it.

Tomorrow I'll put the OEM plugs back in and see what they look like after a short ride....I didn't look at the Iridiums today....wifey had supper on when I returned and I was summoned! :lol:

 

You'll never be considered a hard-core Biker until you decide to do one more thing after getting the Dinner-call.
Something simple.
Tightening a miniature hose clamp.
That you strip.
And, ... look for the spare that should be right where you keep them.
But, you don't find one.
Damn.
But, it's 14-minutes to six and the hardware store is in range.
Your superior skills in calculating Time, Distance and Speed send you hand to you hip pocket.
Wallet and keys.
Poof.

 

LOL!! Been there so many times Rick......
Hey...cold food ain't all that bad....you get used to it after awhile! :lol: