KZ250 Muffler Options

citizendeck

New Member
Picked up a new-to-me 1980 KZ250 D1 I'm fixing up to teach my cousin and some friends to ride. The muffler is rusted and in need of replacement. I'm looking at a couple options from Dime City Cycles right now, but does anyone have any previous experience with a good replacement for the OEM muffler? Not looking to make it sound louder or "improve performance" really, just want a good (economical) swap for the original part to get the bike on the road. Will replacing the stock muffler with an aftermarket part require re-jetting at all?

I've got a set of Harley pipes on my CX500 that were pretty much a straight swap, no re-jetting necessary. New bike, new questions though. And this one isn't nearly as well documented as the CX...
 
use one side from a 450 or 500 twin
the main thing is to keep the thing as long as stock and bigger as in bigger hole through the muffler(harley muff) is not better
 
Weren't they a 2-2 exhaust setup as standard? If you've got a 2-1 on there it makes life a little easier if you're prepared to fit bits on. on the bright side, it's not a 2 stroke so pipe choice isn't as critical. Like previous poster said, if you can't find a 250 muffler, use a half a 500cc+ twin setup. I hope you've got a decent choice of breakers near you, that can really help keep the costs down. Don't forget to check your jetting after - if your pipe differs in efficiency afterwards by a wide margin then you may have to rejet to suit.

This one caught my eye because my bike is a GPZ305 - basically your bike with some stupid ideas thrown in - like "lets make the engine bigger and overstressed" and "nylon is FINE to make the oil pump drive cog from". Oh... and my favourite - "let's make the gauze filter on the oil pickup hard to get to, restrictive and prone to make the engine blow up." Did I forget - "Let's make it so the bike dissolves in a UK winter". Can't forget that one :p

That said, I bought my bike for less than it would cost to buy the cafe racer bits fitted to it, and am planning on being VERY cautious with the maintenance!
 
Thanks for the response Khaos. The KZ250 is actually a single, so only one carb and exhaust to deal with. I found an aftermarket part that's the same length as the original. Now to deal with the tach and what may be a failing starter clutch. Tach isn't showing any movement whatsoever so it's hard to know if I've got the pilot and idle screws set correctly. And the engine sometimes makes a grinding noise when trying to start, so I'm hoping to replace the parts soon and be able to tune the engine and carb/exhaust properly.

How's the 305? I'd been searching for something in the 250-350 range to build up and 305's sounded like a nice middle contender, but that does sound like a pain to deal with. Got the 250 for enough of a deal that replacing parts isn't too much of a hassle (yet). As long as I get her running and on the road sooner and not later ha.


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Khaos said:
Weren't they a 2-2 exhaust setup as standard? If you've got a 2-1 on there it makes life a little easier if you're prepared to fit bits on. on the bright side, it's not a 2 stroke so pipe choice isn't as critical. Like previous poster said, if you can't find a 250 muffler, use a half a 500cc+ twin setup. I hope you've got a decent choice of breakers near you, that can really help keep the costs down. Don't forget to check your jetting after - if your pipe differs in efficiency afterwards by a wide margin then you may have to rejet to suit.

This one caught my eye because my bike is a GPZ305 - basically your bike with some stupid ideas thrown in - like "lets make the engine bigger and overstressed" and "nylon is FINE to make the oil pump drive cog from". Oh... and my favourite - "let's make the gauze filter on the oil pickup hard to get to, restrictive and prone to make the engine blow up." Did I forget - "Let's make it so the bike dissolves in a UK winter". Can't forget that one :p

That said, I bought my bike for less than it would cost to buy the cafe racer bits fitted to it, and am planning on being VERY cautious with the maintenance!

Nylon drive gears are common also on Yamaha and Suzuki. Over time they do tend to crack, but surprisingly, they rarely actually fail.

305cc is a very small increase in capacity on a basically sound motor. Honda did exactly the same with their C/CA/CL/CB72 back in the sixties. A 250 and a 305cc version with basically the same gears, shafts, castings etc. We used to punch them out to 350 and rev them till they finally cried enough. Different motor, but you get what I'm saying.

Can't help you with that oil filter screen though and all bikes dissolve in a UK winter - so do cars :-( .

CitizenDeck, starter noises are often a sign that the starter clutch needs maintenance before it fails. They are a simple device and should be easy and cheap to fix before it fails.
 
My mistake with regards the engine - I was thinking of the GPZ250 - and engine which was perfect as a 250, but overstressed as a 305cc, which is what happened when learner laws changed and made the GPZ250 obsolete overnight. As a 305, there are a number of problems.

Firstly - the cam is in the head, and relies on good oil flow. This is not good, because (1) the oil pickup pipe is small and restrictive, (2) it's fitted with a gauze filter, which is prone to block, and (3) is hidden behind the oil pump which is (4) driven by a nylon sprocked that is prone to stripping the teeth. (5) The camchain tensioner is also a weak point.

If you're going to buy a 305, then be aware of this. You want to know what the TRUE mileage is - in the UK, we can now check this through the government DVLA website. Any vehicle over 3 years old has to have a yearly safety check, and the mileage is recorded. When I went to buy my bike I queried the mileage, then proved the bike had significantly more miles on it. I also pulled them up about the uneven brake levels from the rear brake.

You want to be asking when the valve clearances were checked - and check them yourself the first chance you get anyway. You want to see receipts to prove the oil and filters have been changed regularly - and I mean ideally new oil every 1000 to 1500 miles, and a new filter every 2-3000. You want to make sure (again, first chance you get) that the nylon sprocket driving the oil pump is in good sound condition, with no signs of any cracks or bad wear on the teeth. Then you want to dig further in and make sure that the oil feed pipe behind the oil pump has a clean gauze filter. You need to do this every time you change the oil. Do this, and you'll have a better chance of a reliable GPZ305. Don't take my word for it - there's a german website - http://www.gpz-305.de/English/index_english.html - that will give you some great information.

This PDF gives a bit of useful information on the bike as well: http://www.z250.co.uk/CMM%2001%2006.pdf, although it doesn't go into the significant reliability issues far enough as far as I'm concerned. This page shows the experience of some riders/owners of the GPZ305: http://yewemmgee.blogspot.co.uk/2012/09/kawasaki-gpz305.html

Given all this, I still bought one - the green thing that is my avatar It's like anything else - if you know about the weak points, you keep an eye on them - preventative maintenance is the thing (and possibly some common sense modifications).
 
teazer said:
CitizenDeck, starter noises are often a sign that the starter clutch needs maintenance before it fails. They are a simple device and should be easy and cheap to fix before it fails.

Thanks for the confirmation on that. I've got a second KZ250 in the garage waiting its chance for a rebuild. Going to see if the starter clutch is in better condition to test on the first bike... or if I need to buy two starter clutches.
 
Okay, so I actually decided to fit the old CX500 muffler on my KZ250 project. Got a new tach cable (tach wasn't showing any movement) and now the tach is up and running and I was able to balance my air screw and idle screw adjustment to about a 1250 idle speed. Spark plug shows a medium brown color. Fitted the resealed tank on, filled up on some gas, threw a helmet on and took the bike out for a couple test rides.

Seems the engine is running super hot. The exhaust pipe gets red hot at the top engine connection down to the bend area and there's a little bit of popping on acceleration. I also noticed some smoking while she was sitting and idling/warming up and at the end of the ride. Seems like it's coming primarily (if not, only) from the right side of the engine.

Any ideas on what's going on here or what I should be looking to fix/replace?


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Despite the plug colour, it sounds like she may be running lean. Have you checked the oil level as well?
 
red hot header pipe can happen pretty easily on a single wall pipe after a run from the pole-ice
but yank that exhaust off that poor sr and investigate before you melt that engine
and post up a picture already of da pipe
 
and doesnt the cx500 have a crossover balance chamber ?
what i am getting at is the cx500 has one 250cc exhaust pulse spaced from the next but each 250 pulse gets split up and goes out 2 mufflers
your system is too restrictive
 
Khaos said:
Despite the plug colour, it sounds like she may be running lean. Have you checked the oil level as well?

Yeah, oil level is good. I changed the filter and put fresh oil on recently. I cleaned off the dried engine gunk and it seems to be leaking out of the left side of the engine case (alternator cover), so I've got some gasket material that should be coming in today to fit a new gasket.


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xb33bsa said:
red hot header pipe can happen pretty easily on a single wall pipe after a run from the pole-ice
but yank that exhaust off that poor sr and investigate before you melt that engine
and post up a picture already of da pipe

I'll get a picture up soon. I only noticed it running red hot after a test ride last night. It was glowing after a short ride around the neighborhood. I didn't notice the glowing during the daytime test ride, just that it was really hot.

Running was okay through the gears, just a bit of popping on acceleration so I'll do an air screw adjustment to get it a little richer.

Yes, the CX500 does have an h-box assembly connecting the headers to the rear exhaust pipe and mufflers. I pulled it off my CX when I went to pods, mikuni carbs and Harley mufflers. It's the same length and shape as the stock KZ250 muffler I pulled off because it was rusted and falling apart. The CX muffler on the KZ sounds quieter and deeper than the aftermarket muffler I had fitted originally.


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see and unfortunately i had not thought through my suggestion of using a single muff off a multi
using a single muffler off a 500 twin or 1000cc 4 needs to be a donor without crossover balance pipes or shared pulsation chambers,nope you need a donor with true individual pipes and mufflers per cylinder
 
xb33bsa said:
see and unfortunately i had not thought through my suggestion of using a single muff off a multi
using a single muffler off a 500 twin or 1000cc 4 needs to be a donor without crossover balance pipes or shared pulsation chambers,nope you need a donor with true individual pipes and mufflers per cylinder

Not a problem. I'll stick the other muffler back on and see if running condition improves at all.


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Got the new muffler installed. Also put in a new, charged battery and the stock air filter holder and air filter (found off eBay). The PO had a flat paper air filter installed on the air box. Turned the air screw a quarter turn in and adjusted idle speed. Spark plug is definitely showing a darker color now. The exhaust headers are still getting really hot. It seems like steam/smoke is coming off the header pipe itself and not from any part of the engine. Sprayed a little starting fluid around the exhaust header/engine intake connection and there was no change in the idle.


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you dont read plug color for anything but wot mainjet running and it should be very whitish then only 2 strokes read a brown plug
yes the header pipe will burn you,you just had never noticed it before :eek: wtf is the new muffler ? this thread is worthless without some goddam good full view images of your exhaust
 
xb33bsa said:
you dont read plug color for anything but wot mainjet running and it should be very whitish then only 2 strokes read a brown plug
yes the header pipe will burn you,you just had never noticed it before :eek: wtf is the new muffler ? this thread is worthless without some goddam good full view images of your exhaust

Well I definitely noticed it gets hot haha. But I think glowing red is a little too hot. Unfortunately it's dark out and the bike isn't in a garage so I can't get a picture of the full exhaust set up right now. So here's a picture of the muffler it's got on it right now and a link to DCC:
75fa0d1c8876c3e85637ad3dd302a0b5.png

http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-exhaust-parts-22-inch-baffled-glass-pack-muffler-80-84052.html


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