Topic: Aftermarket Airbox to Carburetor Boots smaller than OEM?

[Krazykuul]

To save you all from reading a bit... I learned that the 77-78 (K3 and K4) CB550K bikes use a different (longer) style of airbox to carburetor boot.  They are difficult to source and I only found one guy who supplies them... read on for more info.

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My cb550k came with a new set of rubber boots between the airbox and carbs.  Included with the bike were some parts, and there is one old boot that was torn up from the previous owner.  It is a 1 or 4 cylinder (outer) boot.  The part that goes into the airbox with the venturi is much larger and snugger fitting than the replacements on my bike right now.  It also looks a little longer too.

I have noticed with mine that the 1 and 4 cylinder boots appear a bit more restrictive than the 2 and 3 boots.  Even if you look at pictures on ebay, they appear the same way.  I have heard of this mentioned once before on this forum I think, but cannot find it (it was in a post about someones bike not running right).

My symptom is that with the same fuel setting across all 4 cylinders, cylinders 2 and 3 sparkplugs look good while 1 and 4 get carbon buildup.  I am thinking the restrictive boots make cylinders 1 and 4 run rich.  I have gone through and everything is in spec, coil and condensers and wiring good.  Bike runs awesome, just this slight annoyance.  I am dialing down the fuel screw on cylinders 1 and 4 to hopefully get the sparkplugs all even and looking good.

Anyone have any knowledge, or know where to get some good replacement boots?  Id like to try making some out of rtv if that is even possible.

[Scott S]

 The 1 and 4 boots are smaller and angled to clear the sides of the intake plenum. Be sure to line up the tang/nipple on the boot with the dot on the plenum.

[Krazykuul]

Its just weird that I have an original torn up one and the venturi is bigger, and matches the size of the 2 and 3 cylinder boots.  On the 1 and 4 cylinder boots i have installed, the venturi is so much smaller it almost fits inside the venturi on the 2 and 3 cylinder boots.  I am riding right now, the bike rides great.  I will probably leave it as is.  However, i was just hoping someone with more knowledge of this issue chimes in, because like I said, i heard of someone mention it on another post in this forum before, i just cant find it now, nor can i find anyone inquiring about this possible issue with aftermarket boots from ebay.

[Krazykuul]

Also, there wouldnt be any issue of obstruction or not fitting if they were bigger, it would just be a lot harder to remove and reinstall the carbs on the bike, and youd have greater risk of tearing the boots like the previous owner did.

[Scott S]

 Pics would be helpful here.

[Krazykuul]

I got some pics.  I found that i had a straight (center) boot too.  So i have both types for you guys to compare.  Check out the pics and see how different they are.  The most obvious difference is that the older boots are longer and it would make it harder to remove the airbox/carbs from the bike, and easier to tear them up and need new ones.

To me, it appears that on the new set I have, the straight (center) boots are less restrictive and the angled (outer) boots are more restrictive.  That couldnt be good for performance.

[bryanj]

Which 550K do you have? As one of them is totally different

[Krazykuul]

1978 CB550K, it is not a supersport

***GOOGLE DRIVE LINK TO PICS***

[Deltarider]

Be sure to line up the tang/nipple on the boot with the dot on the plenum.

What dot???

[Deltarider]

1978 CB550K, it is not a supersport

The K3 and K4 have different - longer - boots than the CB550, CB550K1 and CB550K2 have.

[Krazykuul]

See my previous post for an updated link.

You can see that "nub" that he is talking about on the older boots in some of my pics.  The newer set I have doesn't have the "nub".  They are easy to line up without it anyway, because you can see casting marks in the rubber across the horizontal axis on the newer boots (and vertical axis on older boots)

[Deltarider]

If you order parts and don't specify - in Honda speak - what model you have, you run the risk ending up with the wrong parts. Honda did not specify models in years.

[bryanj]

Because its a 77/78 the boots are totally different to the earlier years and the F model.
There was a member on here haand making replacements and that is the ONLY source for these

[Little_Phil]

http://forums.sohc4.net/index.php/topic,182852.msg2116264.html#msg2116264

[Krazykuul]

You all are right!!  I failed to come across this knowledge until last evening.

I contacted Paul at mybluebike2004@yahoo.com, and he promptly got back to me to let me know he is still doing his thing.

DavidSilverSpares doesn't have them on their website listing for 77-78 bikes, so if they don't sell them anymore, it seems that Paul is the only guy who can supply these parts!

Thank you all for the help!  I wish I didn't have to start a new thread for this, but hopefully I can help that from happening again in the future.

[bryanj]

Silvers NEVER sold them for the 77/78 only the head to carb rubbers

[Scott S]

Be sure to line up the tang/nipple on the boot with the dot on the plenum.

What dot???

 This dot.

 There's a dot on the plenum and a tang on the boots/velocity stacks for #1 nd #4. Align the dot and the tang so that the angle of the outer velocity stacks is correct.

[jakec]

The 1 and 4 boots are smaller and angled to clear the sides of the intake plenum. Be sure to line up the tang/nipple on the boot with the dot on the plenum.

Which way does the nib on the boot face? up? down?

[Scott S]

Inward, to line up with the dot on the plenum.

[jakec]

Sorry, didn't see your photo.

[Deltarider]

Thanks Scott! First time I learn about this. I'll have a look at mine. I hadn't observed dot nor tang, but I'm confident I always mounted them correctly.