Manifold boot repair?

My neighbour's 1982 Suzuki GN125 has had its carb (Mikuni VM20SS if I
recall correctly, with a #35 idle jet) mangled a number of times over
the last 25 years by various shops as well as by me. From the mileage,
just over 2,000 kilometres, you can guess why. The carb' has been apart
so many times it's not funny as there have been a few periods when she
left the bike sitting in her basement for three or four years. One
dealer even stripped the slot on the idle jet so that it was just wedged
in, only partly seated (when I managed to get it out and took it in to
buy a new one, the dealer asked "who the blankety-blank did this?". I
told him his shop did! Still, I suspect her more recent problem might
have been caused by me, so I feel responsible to make it right).


Since I've been helping out her out the last few springs (usually just
changing or cleaning plug, changing oil and filter, checking tires and
cables, cleaning chain etc, even checked the valve adjustment once -
that was in spec') acceleration has become more and more tentative.
Last year, there was so much hesitation at low and medium throttle that
I thought the bike was dangerous in traffic and after I couldn't detect
any vacuum leak and a few idle mixture adjustment experiments, I pulled
her air filter and made a K&R one and left the air intake cover off to
make it rideable, at least as far as my slightly more energetic riding
style is concerned. Over the summer, neighbour racked up her customary
75 annual kilometers. She rides the bike so moderately that she thinks
it's fine, but I can tell it's not. Last week after it had been sitting
since October, I charged it up (as usual, it started almost
immediately), ran it up and down the lane with some new gas for half an
hour and then looked for leaks again by spraying WD40 around the rubber
manifold boot. This time, I'm pretty sure there is a vacuum leak around
the manifold because I can hear the idle speed increase.


I had the carb apart last year and spent some time satisfying myself
that the diaphragm rubber was okay.


Anyway, I'm wondering if there is a way to treat or coat the rubber boot
(I'm pretty sure it has never been removed from the engine). My own
visual inspection in-situ hasn't turned up any flaws and I'm hesitant to
try to remove the two somewhat corroded screws that fasten it to the
head for a better look since I'm not sure that I could obtain a
replacement if removal caused further damage.

 

paul c wrote:

[re: 1982 Suzuki GN125 intake boot]

http://www.alpha-sports.com/spst/1982 GN125/12.htm

#25 13110-05300 PIPE, INTAKE (superseded by 13101-05300)
#26 09280-32006 O RING
#27 02112-06168 SCREW (qty 2)

http://servicehonda.com

13101-05300 PIPE, INTAKE $14.03
09280-32006 INTAKE PIPE O R $0.84
02112-06168 02112-06167 $0.21

Soak the screws really well using your favorite penetrating oil, if you absolutely
can't get them out, grind the heads off then after removing the intake pipe, apply
heat from a Mapp gas or propane torch and use a stud remover or a new pair of
vise-grips or a very small pipe wrench to get them out.

 

Thanks very much for going to that trouble, I hadn't thought to search
those sites. (Ordered parts from alpha-sports, if anybody from
servicehonda is reading this, it seems impossible to look up parts there
if one is using a linux os.)


Thanks also for the advice. For something that old, it makes sense to
apply penetrant and waiting a few hours before doing anything else. I
was taught to give one try with the right size Phillips head and if that
doesn't work, go immediately to the impact hammer, bike isn't here right
now, so I'll see whether there is room to try that without engine removal.


Even with the tank off, it makes me a little nervous to apply heat
around the cylinder when there may still be a little fuel vapour around.
Any comments?


A couple of times I've seen people heat a bolt then shoot a spray can of
compressed 'dry ice' something-or-other for a moment or two, I think it
might have been nitrogen.

 

I would not worry about that, if you're a little unsure just thumb the
starter for a few seconds to flush any leftover mixture out of the
cylinder. You're trying to heat the studs, not the head. Yes, I know
the stud will get hotter than the head but the aluminum head will
expand more than the steel stud. Simply getting the stud very hot will
tend to break the bond between it and the head and will make it easier
to remove even if you let it cool before removal.

 

I've also heard it suggested that a dab of valve grinding
paste in the screw slot will let a philips head get a
better bite.

 

Thanks for the offer. She doesn't mind paying a few bucks for a new
filter and oil every year but I know if I'd asked her about the
boot/intake pipe, she would have said "oh, don't bother, it's fine", so
I ordered those with my own nickel! I'm sure it would be the same story
with her muffler which seems in good shape to me but I suppose a
mis-fitted one (I had it off when I checked valve clearance last year,
can't remember the reason for removal but put a 'newish' gasket in
afterwards) might cause some hesitation at low speeds but not nearly as
much as a leak at the intake would.


She liked my insurance advice better. Since the bike is now twenty-five
years old, she could get a "collector" plate here for about a third of
the 300 bucks she now pays for her customary 100 kilometres (liability
insurance is a government monopoly here but they don't pay up if an
at-fault driver is uninsured, you have to pay extra for that! Her bike
is just above one of the rate cutoffs, 110cc, so she pays the same as
she would for a 400 cc bike!).