gpz500 spark plug change

[slightlytasty]

Recently bought a 1998 kwak gpz500. Gave it a bit of a home service but the damn spark plugs are impossible! They seem to be 18mm but I can't get a socket down the hole to get them out. It's tiny. I even tried an 18mm box spanner but that wouldn't fit either. Do you need a special kawasaki plug wrench? Any ideas?

Bike also seems pretty down on power, tops out about 110 on the clock. Has restrictor certificate with it but I took the carb and air box out and couldn't see any washers. Cleaned the air filter, Took the exhaust off. It seems clean and airtight. Any ideas?

It has done 47k miles so maybe has shit compression but til I can get the plugs out I can't test. What compression should it be?
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Own Aprilia RSV and 955i Speed Triple and 2002 FZS600, had Bandit 650, SV650S, GPZ500S, DR650

[stinkwheel]

You need a big, long thinwall tube spanner of the cheap and nasty variety. I THINK it's a 14mm from memory (remember plug spaners are measured by the thread not the hex-size. If you ask for an 18mm plug spanner people will look at you funny). If you get an expensive one it'll be too thick to fit

Like this one:
https://www.bitzforbikes.co.uk/photo/790030.JPG

Compression should be equal on both sides and shouldn't increase significantly when you repeat the compression test having put some engine oil in through the sparkplug holes.

I find blue-tak on a stick useful to clear the stones and crap out of the sparkplug recesses. If you haven't cleared these out, the plug spaner won't be able to fit down far enough.

110 seems too fast for a restricted bike but too slow for a standard one. I suspect it isn't restricted but check for a 'stop' in the venturi chamber restricting the distance the throttle can open.

Are you thrashing it hard enough?
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“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.

[gerkin]

i have a er5 i usually flush the crap out at the spark plug bottom with a hose ,try a little degreaser first if it is oily or greasy!!there is a drain hole fitted which exits on side of cylinder head! works fine for me

[tsmith]

yep, you need one of those tools to change the plugs. MPS and M&P sell them

i use an old electrolux vac and the tube fits down the spark plug holes a treat to suck out all the crud before I swap out them out. Use NGK DR9EA

GPZ produces 52 rear wheel HP when new and just about manages 130mph flat out. Yours is probably in the mid 40's now depending on engine condition so I'd expect around 110-115mph

As long as your throttle opens fully, the only other common restrictions are via washers in the carb inlet rubbers. If it's a German import these have restricted slides in the carb tops (extra holes drilled in them) to bring the power down to 27ps

[slightlytasty]

Thanks everyone, can't believe I got such a quality set of replies in such a short time. That was my first post but I'll be definately using this place again.

I'll get the right plug wrench and get testing and come back to you
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Own Aprilia RSV and 955i Speed Triple and 2002 FZS600, had Bandit 650, SV650S, GPZ500S, DR650

[veeeffarr]

[stinkwheel]

The plugs are in a recess about 8" deep with a drain hole at the bottom. They are seriously long plugcaps. Providing the plug is in and isn't removed until everything is dry, pulling the caps off and squirting water down there won't do any harm.
____________________
“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.