Intake Carb Holder Replacement

[LakeOber]

Hello everyone,

New to the site. Just picked up a 1980 Special this week. I am excited to get back to riding after 7 years. Bike appears to be in great shape and was well cared for by the PO. The only thing I am noticing immediately that looks like it needs some attention is the intake carb holders. 2 of them are cracked and appear to be all the way through. I would like to replace these at some point this summer. 2 questions regarding this:

1. Will it cause any damage to the bike if I don't take care of this immediately? Like I said, plan to take care of it at some point this summer.

2. How difficult is it to change these out? Afternoon project? Any tips I should be aware of when removing them?

Thanks!

[kboehringer]

Not a hard job.... but not quick either...

LakeOber,
Welcome.

Frequently, the carb boots LOOK like crap but are NOT cracked all the way through. The only way to tell for sure is to pull them and look at them. I strongly suspect, if the bike runs well, that they are not cracked all the way through. The area where they CAN crack through is just a MM or two in front of the clamp area to the carb. I've seen one or two cracked through in that area.

If they are all the way through you will be changing the fuel/air mixture by adding air between the carb and motor/head. That will create a very poor running condition.

Some folks have smeared RTV silicone over and into the cracks and have had some success with that. Looks like crap but can work as a TEMPORARY fix and might (in some cases) look a little better if done carefully.

There are aftermarket NEW boots available and I have two sets of these on two of my 5 XS11's (the others have RTV for the moment). The replacements are NOT cheap, and this hobby is not a good one for a severe penny-pincher. I believe I paid like $80 for each set.

The replacement will take you (a new guy to the XS11?) a good day+ to do properly. You will have to:

• Pull Seat
• Pull Tank.
• Push air box back
• Remove carbs (always a PITA for the un-experienced)
• Clean the carbs (you got 'em off anyway!)
• R&R Boots.
• Put it all back together carefully and slowly!
• Carb Re-Sync would be very strongly advised.

Go ahead and get them on your wish list.... Replacing them is a good idea but normally not absolutely necessary UNTIL they crack all the way through.

Sincerely,

[jetmechmarty]

$75 -Just do it. Don't fool with the broken crap. It's not worth it.

https://www.siriusconinc.com/pro-det...roduct_id=1786

[LakeOber]

Great information! Thank you both!

[sthomag]

Let me share with you my experiences with replacement carb boots.

I had two small problems with them. The first was that they had mold seams in the interior, and they resulted in ridges in the throat. Those were easily fixed with a small sanding drum in a rotary tool. Just make sure you only take off enough material to make a smooth surface. Don't worry about surface roughness: that doesn't bother airflow.

The second was they didn't seal to the head properly. I only noticed that after I had thrown the little included gaskets away (I've read elsewhere on this site that they don't help much). There were little gaps between the boot and the head's sealing surface. I fixed that with some Permatex Anaerobic Gasket Maker.

Other than those two things they work fine, and it's a lot easier to remove and install the carbs, now, too.

[skids]

If you need to do a carb vacuum synch, make sure that your tubing is not to tight. OR, just allow the nipples to cool down before you pull off the hoses. The brass nipples on the aftermarket carb boots can be pulled out if you are not careful when they are hot.

[kboehringer]

Don't worry about surface roughness: that doesn't bother airflow.

Really? I guess those of us that have race experience and "PORT and POLISH" our heads and intakes should just stop all that silly polishing. Flow bench data means nothing.......

[DiverRay]

Really? I guess those of us that have race experience and "PORT and POLISH" our heads and intakes should just stop all that silly polishing. Flow bench data means nothing.......

The thing to remember is the XS1100 head has a LIP between the intake boot and the head, unless someone has worked on it! The Boot is about 1mm larger than the port in the head, and that will do a LOT more than the poor surface inside the boot. So no, a little scuff on the inside of the boot will NOT make a difference. JMHO

[motoman]

The thing to remember is the XS1100 head has a LIP between the intake boot and the head, unless someone has worked on it! The Boot is about 1mm larger than the port in the head, and that will do a LOT more than the poor surface inside the boot. So no, a little scuff on the inside of the boot will NOT make a difference. JMHO

Tottally agree. If anything, a little scuff to a certain extent will actually atomize fuel intake more......which is ALWAYS a good thing.

[3Phase]

The exhaust is supposed to be shiny, intake is supposed to be left slightly rough so fuel doesn't condense on the walls and form rivulets.

[CaptonZap]

When BSA was developing the 350 and 500 cc Gold Stars, they originally mated the outlet of the Amal GP carb to the inlet tract in the head.
At some point, for some reason, a slightly larger carb was installed, and the increase in performance was noted, as it was expected. Later, when the head port was enlarged to match the carb, a decrease was noted. So it was factory blessed to have a small step between the carb and intake port.

FWIW

CZ

[Bonz]

Nice history lesson, CZ! You thinking of doing the rally this year?

[CaptonZap]

HH,
I thought I saw my name on your list of attendee's, so I guess I'm in.

This guy has some interesting ideas about porting, among other things.

http://mototuneusa.com/power_news_--_think_fast.htm

CZ

[Bonz]

Yeah you told me about that before. It is interesting.