Engine tuning as a result of changing exhaust system

Dear all,

I have recently bought an '87 Kwak GPz305 which is standard except for
the exhaust. For those who don't know the bike, it is a 2-cylinder
air-cooled 4-stroke, which comes with a pair of exhaust pipes. In '90
the owner replaced the exhaust with a Motad 2-into-1 system. It was
fitted by a garage in Croydon. I was wondering what adjustments you
would have to make to the engine to accommodate this new exhaust system.
In particular, if I were to be able to source a replacement pair of
'original' pipes, what would need to be undone in the way of tuning?
This isn't something I plan to do myself, so I'm asking more out of
curiosity than anything else, but any advice would be very welcome!

Thanks folks,

Adam

 

The biggest selling point of the old style Motad silencers/systems was that
_no_ changes needed to be made to carburation at all. Depending on what bike
you fitted them to, there were often some flat spots in the mid-range
though.
On a GPz305 I doubt you'd notice much difference between the motad and
standard system anyway.

JB

 

From what I remember, Motads are a direct replacement and don't necessitate
any rejetting of the carbs. It's only when you upset the air/fuel balance
(like fitting race cans) that you need to up the jet sizes to prevent a lean
running condition. What is wrong with the way your bike runs with the
Motad?

 

(oops, bad form etc)

Ok, I just re-read your post - you think that the jets might have already
been changed to accommodate the Motad and that fitting OE cans will need the
jets changing back. I very much doubt that they'll have been changed.

 

Porridgewog SV1k said the following on 02/04/07 10:28:

No worries! I'm just interested. I'm happy with the way the bike runs
with the Motad system. Is rejetting the carbs the only thing which
people need to do when fitting different exhaust systems, then?

 

Champ said the following on 02/04/07 10:25:

Thanks for your help! The bike has only done 11k miles and has been
garaged for its entire life, so is in good nick!

 

Adam Gamsa says...

Change the oil and filter every 3000 miles using a good quality semi-
synth oil and a genuine oil filter, service the engine regularly and
it'll last forever. If you don't bother keeping to that schedule start
looking for a new camshaft and cylinder head.

--
Lozzo
Triumph Daytona 955i SE (Black with added black bits)
Suzuki Bandit 600S (Green with added shit bits)
Yamaha SR250 Delusion (It's "Special")
I ride way too fast to worry about cholestorol.

 

Lozzo said the following on 02/04/07 10:41:

Thanks, I will - it sounds easier than finding parts =) Anyone know
where I can get hold of a service manual/Haynes manual?

 

Adam Gamsa says...

Ebay

--
Lozzo
Triumph Daytona 955i SE (Black with added black bits)
Suzuki Bandit 600S (Green with added shit bits)
Yamaha SR250 Delusion (It's "Special")
I ride way too fast to worry about cholestorol.

 

Thats the one with the elastic band instead of a chain right ?

 

pile of shite.

Sorry if that offends but I had two friends who got one each not long
after they came out. Endless returns to the shop for fix after fix.

 

or output shaft as the keys failed and the bike made lots of churning
noises and 0 mph.

 

Statistically there must be one I suppose.

 

Bear says...

If looked after according to the service schedule the GPZ305 is a bloody
reliable bike, trouble is not a lot of them were serviced regularly
enough, which got them a nasty reputation for blowing up. KR1s and the
KR1Ss were just fucking shite through and through, no matter what you
did to them.

Honda just couldn't make a reliable camchain tensioner for quite some
time. I didn't mind the enclosed disc on my VF400, it taught me to ride
smoother and not use the bloody thing. I ended up becoming incredibly
quick and hardly braking.

Daytona 675 oil consumption, Daytona and Sprint 955i fuel couplings and
a few others come to mind.

They really were horrible bikes.

The first of the powervalves, like the one mr P-W Buckley owns were evil
handling bastards. I refer sir to this post I once made :

http://groups.google.co.uk/group/uk.rec.motorcycles/browse_thread/thread
/491d77651ed762f6/b655ede50a36afe6?lnk=st&q=&rnum=1
&hl=en#b655ede50a36afe6

<small voice>

I don't like BMWs

</sm>

--
Lozzo
Triumph Daytona 955i SE (Black with added black bits)
Suzuki Bandit 600S (Green with added shit bits)
Yamaha SR250 Delusion (It's "Special")
I ride way too fast to worry about cholestorol.

 

Sounds like someone's forgotten the two stroke triples.

Well, they still haven't sussed carb icing after 20 years.

GPz900/750R at camshafts/tensioners.

Partly the result of having a slightly bigger list of models to choose
from.

That horrible 550 V-twin - XZ?

--
| ___ Salad Dodger
|/ \
_/_____\_ GL1500SEV/CBR1100XXX/CBX1000Z
|_\_____/_| ..88045../..23727.../..31893.
(>|_|_|<) TPPFATUICG#7 DIAABTCOD#9 WG*
|__|_|__| BOTAFOT #70 BOTAFOF #09 PM#5
\ |^| / IbW#0 & KotIbW# BotTOS#6 GP#4
\|^|/ ANORAK#17 IbB#4 YTC#4 two#11
'^' RBR Clues: 00 Pts:0000 Miles:0000

 

I have a genuine Kawasaki Service Manual for the GPZ305 - contact me by
email if you are interested (watch out for the spamtrap in my email address)

 

<snip>

Every manufacturer has its bad moments. When corners cut in development,
in the rush to get the models out, results in catastrophe.

Honda's such nadir was the early/mid-1980s.

BMW's is now.

Triumph's was a couple, maybe three or four, years ago, but I think they
recognised the danger signs and pulled themselves together just in time.

Ducati... well, only between 1970 and 2007.

Moto-Guzzi - the mid-1980s, and a decade thereafter, when *every* model
was shite.

Suzuki - the interregnum between the old GS series and the GSXR. Think
GSX fours, with their terrible electrics, the ill-fated Turbo, the crap
early vee-twins, the leccy windscreen tourer with its supermarket
trolley-sized wheels, the GR650 twin with its centrifugal flywheel
crank......

Kawasaki - beyond the occasional lemon, they have rarely put a foot
wrong, and it's hard to point at a duff Kawasaki launched since, say,
1984. GPZ1000R, KLR650, that's about it.

Laverda - everything, following the re-introduction of the brand in the
1990s. An unrivalled catalogue of mechanical catastrophe, irate dealers,
desperate press, and despondent customers. I suppose they kept the RAC
and AA in business.

Yamaha - the early 19080s, when they insanely dropped the 50 twin in
favour of a series of crap vee-twins and triples and lacklustre fours,
with the possible exception of the XJ650. Redeemed by their launch of
the RD350.

Very few manufacturers build truly crap bikes these days. But the
lacklustre machine, that should never have been let off the
drawing-board, and is then priced so far above the opposition that
nobody buys it, is still with us. Oh, we're back in the Z1000 thread.

 

Fair play, at least they sold one of the wretched things to Doc Gonz0.

--
platypus

"Merely corroborative detail, intended to
give artistic verisimilitude to an otherwise
bald and unconvincing narrative.”

 

Tim said the following on 02/04/07 21:36:

Oh dear, sounds like I might have invested my hard earned £400 in a
stinker. Oh well, it should still do what I intended it to - namely to
serve as a machine to learn about how 4-strokes work. I just won't be as
distressed if it doesn't run when I put it all back together. That and
finding a buyer when I want to sell it on...

 

actually, I think Ebay is shaft-driven.