MZ/MuZ Riders

hello, i have a etz 250 and i was just wondering what is the correct spark plug to use. a NGK B7HS as it says in my haynes manual or a NGK B8HS which my mechanic says is ok and what other people say to use too. i understand about the heat range thing but could using one or the other spark plug affect the performance of the engine. i ask this as i have a slight problem with my bike. the bike starts ok but even when warm has a different idle speed every time i use the bike sometimes 1200rpm sometimes 1600rpm. the bike runs well ( good acceleration ) but after about 10 mins of 60mph the engine seems to hesitate and pull back as if its running out of fuel, if i slow down or change down gear and accelerate its fine and then back up to top gear and it starts doing it again, also around town 30-40mph its fine.. have checked fuel line .ok. contact breakers .ok. new air filter and i use high octane fuel.. any ideas.. thanks........

Hi tynsham.

I'am thinking you have a week mixture problem, due to low float height or restricted fuel flow from the petrol tank.
First check your fuel flow from the petrol tap.
Check needle valve in carburetor is clear.
Set float height as per book very important,
Throttle needle set 3rd grove from bottom
Then set slow running mixture screw to get the slowest tick over you can -1000rpm,
NGK B7HS should be ok for all running, but some use B8HS for motorway use.

hi, i shall check out all the things you mention and see what happens. many thanks...

Interesting that you mention using a B8HS for the motorway Skorpion, I was on the A14 the other week and my ETZ 251 seized up, with a B7HS......it was a hot day and I'd been running at about 70mph for a while, my friend who came to my rescue reckoned it was down to a weak mixture.....now got a 150 main jet but I think that's maybe a bit too big (standard is 130). But I wonder if a B8HS might have prevented the seizure?
I need to investigate as I'd like the new piston to last a good while.... although the old one was in there for who knows how long before I bought the bike, and I've done about 12,000km on it in the last two years.

A B7HS seems ideal for most types of riding. But an B8HS will run a little cooler for hard sustained use.
But it's a bit odd no one has said anything about oil.

I'd doubt increasing the main jet size would solve the problem.
In fact if the petrol/air mix is too rich it may create other problems like diluting the injected oil.

Use the very best you can find - fully synthetic if possible.

you fellows in the uk
i had good luck on 2 smokers in the late 60's
running LODGE OR KLG
there may be some one with new old stock
that will work in the mz
dave
my Yamaha ym1 305 took the same plug as my bmw r50S 1961 w240t1 i think
yes its been a while like 42 years