Air Intake Boots-How cracked is cracked

While recognizing that the question "Is is is,or isn't it" occupied the nation

for a considerable time,the question whether cracked is like being

pregnant or playing horseshoes may be messing with mine.The airboots

between the cylinder and the carbs have what I think are superficial

cracks,yet the machine is running rough,and stalling under slight load,also

cyl.#4heats up much faster than #'s 1&2,& moderately faster than #3.Can

I take heat-resistant silicone caulk and seal the slight cracks externally,or

should the carbs come off,to allow closer inspection of the boots? I have

cleaned the coil connections,synched(as best I could) the newly rebuilt

carbs,and made sure the pilot screws were out 2-1/2 turns...? I'm at a

loss as where next to look. TIA.

 

Welcome to the malady that hits all us XJ owners.. You can be pretty certain that if there are superficial cracks, then at least one of them goes all the way through. In order to get at all 4 of the boots, you will have to remove the carb rack. At this point, all 4 should be replaced. However, some members here have had good luck resealing them using black RTV and inner tube rubber. It is a quick and dirty fix that while it isn't exactly pretty, it usually works (depending on where the cracks are -- if they're cracked around the clamp mounts, then you are looking at replacing them).

If you do decide to replace them instead of repairing, you have to be VERY careful when removing the bolts that hold them to the head. There's 26 years worth of galvanic oxide in the threads, and that stuff is like superglue. You have to use a good penetrating catalyst like PB Blaster , applied to each bolt several times a day for at least 1-2 days prior to attempting removal. DO NOT use WD-40. It is useless in this situation. Each time you apply the PB, take a hammer and screwdriver and give each bolt a couple cracks to help the PB break up the oxide. Once you have done this ritual for a day or so, get your 5mm allen key and try the bolts.

If you snap any off, STOP RIGHT THERE. Remove the head from the engine and bring it to the nearest machine shop to have the bolts drilled and Heli-Coiled. Trust me. Do not attempt to fix it yourself or use an EZ-Out on it. The bolts are too small, and the EZ-Out will wind up snapping off on you, then you're in big trouble. You can drill out a bolt, but you can't drill out an EZ-Out. (I learned this the hard way!)

 

heres a question for somebody that changed the intakes, and found a crack all the way thru
how big was the crack on the outside, that you could see ?

 

A customer of mine who owns an auto repair shop showed me this trick to check for intake leaks. With the gas on but not lit, run the nozzle of a propane torch around the carb boots. If there's an air leak, you'll hear the engine rev up as soon as it sucks in the propane. You may also want to jiggle the carbs while doing it to replicate rough road conditions.

 

On mine there were cracks everywhere. The biggest one was on the #2 boot, it cracked right behind the clamp that holds it on the carb, almost 3/4 of the way around the boot. On the inside it was about a 1/4" long split.

 

Mine looked pretty bad. Mrs. gave me new ones for X-mas.

When I pulled the old ones off I found the insides were like new. Problem was just on the surface.

Bottom line, check them before fixing or replacing. Looks can be deceiving.

 

I had the same as MiCarl, on closer inspection the cracks were no more than half way through. One on my other engine was split where the boot connects the head between the bolt holes and the intake tract. The outside looked fine, but it was leaking. Best way to tell is to check for leaks using wd40 or propane. Be very careful using propane as there is a very real danger of an explosion!

 

I had tried starter fluid(sprayed on each boot)w/o a change in RPM or

engine sounds.The boots were removed in the spring(when the carbs were

rebuilt,at that point the cracks were superficial.However.when I put

them back,I didn't replace the gasket.

Sounds like that's my next step.Thank you all for the input.

 

I found that mine where cracked but not all the way threw. I used the RTV sealent and it looks great, bike still has them on and running

 

There's a neat product called Liquid Electrical Tape, which purportedly works wonders for this problem, with considerably less mess than RTV would be. I found a bottle of it in the boat equipment section at Walmart.

 

We sell this product where I work.

I, too, was going to suggest it as a fix, but was wondering how it would hold up to fuel?

 

Looks to be the same product Rick was running through his "tests". Seems to have held up to the rigors of carb diaphragm use. Haven't heard back from the beta on that yet so no news is good news.

 

+1
same situation, minus the mrs.

 

Robert, when you say diaphragm use, did Rick just paint liquid tape onto the carb diaphragms? And more importantly.....did it work?

 

Painting liquid tape sparingly on carb diaphragms should work OK.

I used a product called PlastiDip in spray can form. Applied it sparingly over the 4 carb diaphragms - they looked as good as new. It does seem to stiffen up the diaphragms slightly but I've had mine back in the carbs for about 10,000kms and no detectable problems yet.

Might get around to opening them up again next year for a service but so far it's the least of my worries.

 

Lincstriker, I did indeed mean just that. As I said, the beta test results haven't been posted. Rick said he'd let us know what all came of his efforts. I'm looking at some pretty shot diaphragms right now and am thinking of doing my own little experimentation.

 

I'm in a similar situation Robert, I have a spare set that are suspect to say the least, so I think I'll just give it a go. I'll post my findings, but it won't be for a while yet.

 

I almost bought a jar of the liquid tape the other night, I was going to apply it to my son's carb boots, they look a little worse for wear. but the bike seems to run great, so the must not be all the way through yet. I figure I should put something on there to keep them from getting worse.

 

Mine were pretty bad so I got a new set from a fellow member on this forum. After reading horror stories about broken bolts in the head I decided to use RTV sealant on them. Works great.

 

mine looked like the original boots... they were cracked pretty bad.. I can't afford $100 for a new set of rubber, so I got some black high temp RTV and it works wonders