View Full Version : OT...Repairing old motorcycle intake manifold boots???

04-17-2008, 08:36 AM
Hey guys! The rubber intake boots on some of these old motorcycles... they crack after time and need to be replaced.
However, a lot of them are not available anymore.
I just rebuilt a KX80 for my helpers boy to race and the damm intake cracked when we where putting the carb on.
I've tried every source but cannot find one.
Anyone know if there is a magic Goo out there that'd fix this?

04-17-2008, 08:57 AM
I have fabbed adapters out of aluminum with a chunk of goodyear green stripe hose to connect the carb to the adapter, trick is to figure out how to make the transition into the reed cage ....every one is a little different...Good luck Shawn

04-17-2008, 09:00 AM
Sikaflex will give a flexible repair which holds up, I once patched a nail hole in a tire one Saturday night for a 200 mile round trip on the Sunday, the tire survived and continued hold air until the tread was gone,

A.K. Boomer
04-17-2008, 09:14 AM
Torker, stay away from anything to do with radiator type hose as it will swell as soon as gas hits it, there is some industrial type hose that is rated for oils and would most prob. be OK, If the boots are offset in diameter you may have to make adapters and that will suck, it will also slightly upset flow if not tapered --- Those damn things always weather check...:(

04-17-2008, 09:22 AM

This might give you some ideas.

- Scott

Bob Farr
04-17-2008, 09:27 AM
Anyone know if there is a magic Goo out there that'd fix this?
Thanks! Russ

How about using the old one as a pattern to mold a new one? Here's a few links:




04-17-2008, 09:51 AM
Shawn.. this one has a real ugly angle into the head.. I thought about tryingto machine one from alu.
Nick.. where do you get Sikaflex?
Boomer.. yup, I already know about the gas swelling up rad hose. I see a lot of that done here when I take in old bikes.
Scott and Bob... I was wondering about casting new ones. I'm actually suprised that the aftermarket hasn't covered this.
The snowmobile aftermarket is all over this. You can get intake boots for almost any old sled.
I really need a quick fix as he has a race over in Alberta this weekend.

04-17-2008, 10:44 AM
Sikaflex is the stuff modern car windscreens are bonded in with, Polyeurethane Adhesive Sealant is the generic name for the product, it comes in a variety of curing speeds. It's also used to stick side panels on busses, roofs on hightop conversion vans, I used it to stick GRP wings on a car once, provided you clean the surfaces to be bonded it doesn't come off!
If you ask windscreen replacement shops they will often sell you a tube, sometimes they'll give you half a tube if it's the end of the day as it doesn't store well once open,

04-17-2008, 11:08 AM
Sikaflex sounds like it might be a better fix but I've had pretty good luck repairing cracked motorcycle intake manifold boots with "Shoe Goo" or "Plumbers Goop", "Mechanics Goop" or any of the similarly named products which are all the same thing. It's very useful stuff for all kinds of repairs and I carry a tube during bike trips.

04-17-2008, 11:21 AM
torker what about building a plate that is thick enough to machine then hand port the proper radius,and attach a four stroke type intake?we use this kind on yamaha banshee's.just a thought.

04-17-2008, 03:31 PM
Bob.. I wasn't sure if Goop stood up to gas.
531.. Ya.. I could do that...if there was room and I had time. There's very little room inbetween the carb and airbox.
BTW nice looking boost bottle setup you got there... but does it actually work?
I messed with one on a TY175 quite a bit. used the boot off an RD350. Tried different bottle sizes etc but never really noticed a huge difference.

04-17-2008, 10:45 PM
Maybe these guys can help: http://www.intakehoses.com/

04-17-2008, 10:53 PM
Thanks Steve! You see the problem with most of these intakes is they have an aluminum plate cast into them(or glued in.. however they do it????). The plate often has an "O" ring groove cut into it to seal the intake to the head or the reedcage.
See the ones that 531(funny name huh?) shows and imagine the rubber boot and the plate all in one unit.
Not real easy to make when there are several angles involved.

04-17-2008, 11:44 PM
I'd love to have a rd350.. not seen one in years..

The one of older brothers would stand up at 45mph.. of course you'd have to drop quite a few gears and nail it. I was much lighter then.

I liked to have lost my license on it.

Rookie machinist
04-18-2008, 12:22 AM
Sikaflex can be found at some lumber yards it's used in commercial glass and building caulkings. You could also try dow corning 795 I know this stuff sticks pretty good and stays flexible. If you want the 795 send me a pm as long as it can be mailed I'll send you a tube, I also might have some sika if your interested.

04-18-2008, 12:29 AM
David, I have two RD350's in my yard. I put them in the save pile so the bonepickers can't rape anymore parts off them.
rookie.. I phoned the windshield shop and they'll let me have a near empty tube. Only need a little bit.

Peter N
04-18-2008, 02:53 AM
I'd love to have a rd350.. not seen one in years..

The one of older brothers would stand up at 45mph.. of course you'd have to drop quite a few gears and nail it. I was much lighter then.

I liked to have lost my license on it.

I Have one :D
Here's, a picture of it. I bought it last year to restore, currently sitting under a pile of junk in a shed waiting for more space.
I used to have one of these about 30 years ago, and I have never had so much fun on a bike, but it took me many years to find another as they are about as rare as hens teeth these days.
It is actually much scruffier than it looks in the picture.


Hey Russ, if I get stuck for any spares can I drop you a line to see what you have?


04-18-2008, 04:53 AM
There are many fixes, electric tape ( justed used that one last week), rubber hose and there is the interchangabilty of different OEMs. The vintage motorcycle market makes a lot of repo parts which fit right up, especially with regard to carb boots. check VMX magazine.

04-18-2008, 05:51 AM
Bob.. I wasn't sure if Goop stood up to gas.

Don't think I'd use it to seal a leaking fuel tank where it'd be subject to continuous immersion but it's been on my intake boots for years and it's holding up. But the Sikaflex sounds better and glad to hear you got some. One of the Sikaflex products was recommended to me for sealing the sawcuts in my concrete floor and it seems to be good stuff.

04-18-2008, 03:50 PM
torker,i am an ex tt-dirt oval racer(9 years)on a yamaha banshee,that i built my own a-arms and swingarm on,as well as building my own engine and doing all my own machine work.it is black and my number is 531 hence the name.not sure if you are making a joke about the boost bottle or not.i am also invloved in sand drag racing through doing machine work on the motors.boost bottles are a pretty big joke with those guys.yamaha banshee's can tend to have lightswitch power,either on (9000+ rpm)or off(bog).a boost bottle stores atomized fuel and air that is coming through your air cleaners and carb when you chop the throttle and close the reeds(i.e.coming down the straightaway full throttle then chopping the throttle to do a 180 degree hairpin turn into the infield).then when you crack the throttle back open the path of least resistance pulls the pre-atomized fuel and air out of the boost bottle as it is trying to get some more air through the aircleaners and carbs.it does nothing for topend,it merely helps some with the bog on the bottom end.the intakes i showed you fit where the stock intake fits,and you can still use the factory air box.i was just showing the picture to give you an idea.upp builds a lot of aftermarket intakes but did not list any for kx's.i watch all of your post in anticipation of your next project,i plan to build a version of your ring roller to radius tubing.keep up the good posting.

04-18-2008, 03:58 PM
RD350, gotta love em
When the drags here were down in Ravenswood, there was a little chainsaw called "the white-ant". RD 350 motor, bored to about 400, in a raked frame. Used to leave worked K2 hondas and Kwak 9s while they were still thinking about the clutch lever.
Ahh, them was the days :D

04-18-2008, 04:43 PM
Torker, I would like to know how that Sikaflex works out for this situation.

04-18-2008, 11:15 PM
Leon...thanks for the real name...sorta awkward calling someone 531 :D
Nope...no joking. Your boost bottle setup looks A-1. Very nice work.
I do know what a boost bottle is for. They are not all things to all runners however.
You utilized it in the ultimate arena. Hi R's to low.
In my case.. low R's to low R's.. not too effective. Very little effect in a trials bike. I still think a different shaped bottle could work in low R situations but haven't had time to work on it. I'm thinkin a coffin shaped bottle may work... round didn't... square didn't. I'd appreciate any advice you could give!

I ride these ol' twin shocks on the back wheel every chance I get and am always looking for ways to pop the front wheel at will. It helps overcome the poor front suspension. The back is poor as well but my back legs are amazing! I have "Monoshock" legs :D
Peter... you wanna WHAT? Buy parts off my babies?
Aint gonna happen :D But I have plenty of old Yammies.. if any other parts are the same.. yup...we can fix it.
BTW.. Thats a damm nice RD you got there. What do you need anyway?
topct.. Ill let you know!

Peter N
04-19-2008, 02:57 AM
Russ, it looks better in the photo than it actually is. I'ts quite scruffy and non-standard in a few places.
It was originally an Italian market model that was imported over here a few years ago, and there are a few local market parts on it.
The front master cylinder & caliper are Brembo rather than Yamaha, and have some unrepairable failures, so need replacing. The headlight uses Tomaselli cafe-racer style clamps instead of the usual tinwork 'ears' that slide over the forks, and the headlight is non-uk standard so needs replacing.Also the speedo is in km/hr instead of mph. Many other little niggles too, like the handlebar switchgear not working.

My aim is to restore it back to UK-original spec and then ride it as hard as my smaller-than-teenage-balls and ageing reflexes will allow.
The blue was not a standard UK colour option either, so will probably be resprayed & decalled to match the UK 'Silver Dust' model that I had years ago, which looks like the one in the picture below.



04-19-2008, 09:54 AM
Peter..thanks for the pics! I'll have a look on my other old stuff to see if there is any matching parts. I'd hate to show you pics of mine. They've sat outside for years and years. I couldn't believe it when I first got the place... there were these two Rd's, a couple of Twinstars, a Water Buffalo.. all sitting in the weather for years. what a shame. The guy had no idea what he had.
There's actually a lot of strange stuff here that should be rescued, Maico, CZ, Bultaco, Jawa,A Harley dirtbike, a couple of nice Elsinores, etc.
I just don't have the time or the covered storage to mess with them all.