MZ Question: Blowing head gasket

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Hello,

As many of you know I am now the proud owner of an MZ ETZ 301 Saxon Fun. I have a couple of minor issues with it - and they *are* minor considering the bike cost £270!

First of all, there is a slight stain on one of the cooling fins on the engine block. It happens to be the fin that is below the head gasket. I believe the head gasket may be blowing a little. If it is, it is a little strange as the bike starts and runs OK, in fact I rode it to work this morning. I tried tightening the head nuts to the specified torque (19lbft believe it or not) but they were already tight. Is there anything I can do as a bodge fix to stop it from blowing? Or will I need a new head gasket (the owner says he replaced it recently and I believe him as I have the old gasket...)?

Secondly, and this may be related to the above, but the bike doesn't idle. I have to keep the revs up a bit with the throttle. This isn't too much of a problem, but it means that I need to be on the ball and stay on the throttle all of the time. Would a leaking head gasket cause this? At the moment I plan to take the carb off and give it a clean to make sure it isn't a blocked idle jet.

The bike also has another issue that I'm not too bothered about, and that is the kick start spring is not tensioned. The guy told me he just didn't know how to do it. The bike starts fairly easily and so its not much of an issue, but it means I have to use a piece of wire to hold the kick start in place after I have started the bike. I just mention this because its a bit of a ballache to start the bike if it has died because it doesn't idle! If I can cure the idle problem then I will be happy!

Thanks,

Mark.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

You just identified pretty much all the problems you get with that bike.

1) Probably is leaking a little oil from the head gasket or it could be blowback of leakage from the exhaust header. If it's just a little, I wouldn't bother.

If it is a bigger leak, whip it off and either replace the head gasket or throw it in the bin and refit the head without one. If it has already been binned, you might want to take the barell off and lap the head in or just bung some gasket goo on there.

EDIT: Replacing the head gasket on an MZ 2-stroke takes approximately 3 minutes and requires the use of one tool.

2) They were designed to not idle properly so you keep blipping the throttle at a standstill to ensure it gets a steady supply of oil. I believe they need a bigger idle jet to fix this.

3) I'm pretty sure the kickstart return spring is under the cover rather than in the middle of the engine. It's probably broken or missing or could have been fitted incorrectly.

Now for the best bit.

Head gasket £2.50
Kickstart return spring £5.59
Clutch cover gasket £4.62

Available from www.mz-b.de website includes full set of exploded diagrams of all parts of the bike.

You send them a parts request using their online form, they email you back with a price and availability, you decide if you want to place the order.

They do this to avoid misunderstandings as English is not their first language.

I have used MZ-b many times and they are every bit as efficient as you'd expect a German motor spares company to be.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

When I was looking at an MZ 2 stroke a few years ago it had a broken kickstart spring. May be a common thing.
Hopefully it's located under the clutch cover and therefore quite easy to get to. If it's further back, swear.

And clean your jets. This is the closest I'll get to telling you to cool your jets in the workshop forum.

ms51ves3 · Super Spammer Joined: 08 Jun 2007 Karma :

For the clutch cover gasket why not use a cereal box? It's just as good as any gasket you can buy.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

The only thing that stops the throttle falling off is the bar end. make sure it hasn't been put in too tight.

I haven't actually guddled inside one of those engines but I would imagine the kickstart return spring has a 'hook' that fits over the sprocket quadrant and a 'tail' that in all probability presses against the crankcase itself.

With this sort of thing you usually need to push the quadrant in with the spring in place, rotate it into position which tensions the spring then hold it there while you fit the shaft through it.

You then have to fiddle the cover back on without the whole lot pinging back off again. I seem to recall it being necessary to put your finger through the hole in the cover for the kickstart shaft so you can keep pressure on the shaft while you slide the cover into place and nip a couple of screws in.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

Lone-Wolf · World Chat Champion Joined: 13 Jul 2004 Karma :

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

I found 2 things slowed the idle speed down on that bike.
1. Was slow traffic / lots of idling, but every time you hit the open road and blasted the bike out it would be fixed until next time.
2. Was switching the lights on, this would slow the engine down at any engine revs.

If you had both 1 and 2 at the same time the engine may stall or nearly stall depending on how bad the 2 above were.

So I often switched the lights off at that time and also when I wanted to overtake a lorry.

Don't have it anymore, I defected to japan.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

0.4mm idle jet diameter has been mentioned to me in a very much second hand and roundabout manner.

This is no basis whatsoever for altering a fundamental part of your motorcycles fuelling system. Unless of course you happened to have a spare jet that fits and a drill.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

Have any of you seen the MZ Workshop Videos?
It shows you everything inside and how to strip it down and up again.

https://www.bikechatforums.com/viewtopic.php?t=140295&postdays=0&postorder=asc&start=0

Its under MZ in the first post.
I noticed the Videos did not appear on the internet until the company went bust so I assume there are no copywrite issues.

I turned the videos in to DVD format so I could watch them on my TV.
I class them as an educational tool and general entertainment since I do not have the bike anymore.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

Ichy · World Chat Champion Joined: 15 Jul 2005 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

At the time it was the only bike I had so I had to improve it.
Mine also had CDI.
Don't make the same mistake as others do about super unleaded.
People keep saying there is no point unless the compresion requires it.
But there is far more than just octane in many of the super unleaded fuels.
The main extras are stronger cleaners and other things.
The advice is try it and see what happens.
Some engines will show no difference, others will improve.
The amount of improvement will depend on so many variables the simple answer is try it and see.
The MZ 2 stroke engine does excessively suffer from burning deposits when around town and excessive idling so extra cleaners in the fuel could well help and may improve the idle problem.

Put another way, what if your problem is the carb needs a clean.
The best solution is as you mentioned cleaning the carb.
But the other option is to put petrol through with extra cleaners in to try and clean it out.
If the problem is dirt some ware else in the engine that the petrol comes in to contact with it could also clean it.
In an old engine its often advised to put petrol in with extra cleaners to try to clean it out.
Only problem is the cleaners are weak so takes a long time.
Saying that if you do not notice a decent improvement after 1/2 a tank you can always fill up with normal petrol next time.
I know the extra cleaners are in Shell V Power, BP Ultimate and Tesco 99. The other brands may only be as good as normal unleaded.

I remember the original grips on the bike.
at least I do the left hand one.
It was solid rubber.
It was closed at the end (no handlebar weight or bung).

As for the ethanol part.
My point was that the bike is east german.
They stopped making the old 2 stroke in 1994.
The berlin wall had only fallen a few years before and ethanol was not normal or common back then in east germany or the ex soviet union.
So I doubt the bike is designed to handel ethanol even at our 5% level.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

I can assure you that given a sufficiently large main jet, an MZ 2-stroke can and will run on pure ethanol, never mind 5%.

Take this as fact.

A badly worn carb slide can be another cause of non-existant idling.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

By that reasoning I could also run normal unleaded... with a load of redex in the carb! Wink

I think I'm going to take the carb off at the weekend and give it a clean. I went to Halfrauds at lunchtime and now I have a bottle of TTS and a can of carb cleaner in my top box! Smile

When I take the carb apart I can see if the slide is overly worn. Anyone know what kind of carb is fitted to my bike?

I've also ordered some high temperature silicone sealant which I plan to daub on the sides of the head gasket to try to seal it a bit.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

I still have the owners manual for the bike.
The Owners manual is for the
ETZ 125
ETZ 150
ETZ 251
ETZ 301

For the ETZ 301 it states
Carburetor
Bing Type 84/30/110
Intake pipe diameter 30
Main Jet 118
Venturi tube 7
Needle Jet 72
Jet needle 4E1

Needle position from top 2
Idling Jet 45
Idling air regulating screw (open turns) 1...1 1/4
Gas Slides 197
Idling Speed approx 1200 rpm.

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

If you want a laugh the owners manual states the exact same carb and settings for the ETZ 251

Yet the 125 and 150 have different carbs / settings to each other.

The ETZ 251 got only 50 to 60 mpg and performance was bad from new.
It was running way to rich so the needle had to be set to as lean as possible.
It then got 60 to 70 mpg and performance improved.
But thats with normal (slightly faster acceleration than adverage cars) riding around at 60mph or lower.
It was said the carb was overfueling since its was setup for the ETZ 301.

I assume you have noticed the bike handles far better and has faster acceleration when you only have around a gallon of fuel in the tank?
That meant I had to run on reserve all the time and I did run out once when I had a faulty batch of petrol (halved my fuel consumption).

Tank holds 24 litres.
It claims that 1.5 litres of that is reserve but mine used around 4.5 litres for reserve.

luke27 · Nova Slayer Joined: 15 Oct 2008 Karma :

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :