MZ/MuZ Riders

On Saturday I took my bike out for a blast. Overtook a ducati (silly ducati) on a corner and then parked up. When I returned to my bike 10-15 minutes later I noticed some oil on the ground. I then noticed that one of the bolts from the starter motor cover was gone (left hand side)....I assume this was the cause of the leak! I got home replaced the bolt and topped up the oil... However... since then when in 5th gear and over 5,1k revs (I have a KOSO tacho on the bike)... the engine seems to judder forward and back.. this happens at 120 KPH or above (if it gets there). This 'feature' doesn't happen in any of the other gears that I am aware of. And I can be at 6.5k revs in the lower gears and no judders! Also the bike seems to pop and bang alot when I'm slowing down... more so than usual..actually like it's about to run down to the reserve of the tank (thats how I usually know it's time to fill her up).

The bike usually easily gets above 140 in 5th gear (sometimes over 160!)

I went to halfords and bought £32 (yeah I know, but I love this bike) of 10W30 best quality oil today an did and oil and filter change...just to be sure that it's not oil related... I've not changed the spark plug yet... but that might be my next job (tomorrow night).

Any suggestions? Has anyone else had similar issues?

check the nut and lock washer on your engine chain sprocket

and did the rear wheel move making chain out of line

my rotax 500 always seems to loose its sprocket nut when i get too rowdy
and some times the back wheel axle slips in the swing arm
dave

Thanks dude. I'll check those things tomorrow after work. I did adjust the chain recently

and see if the chain is free ie kink some times an older chain will get stiff spots in it and complain when going around the front sprocket
dave

thanks again. i hope the chain and sprockets aren't goosed as they are only a little over a month old.

update: I adjusted the chain-it wasn't lose, just could have been tighter. Checked the oil and drained a little as it was a little bit over the max mark. Took her out to see if these thing have helped...Nope. Still problem of the bik popping and backfiring and juddering at 5.1k revs

It's odd cause this only happens in 5th gear and when I've at about 120 KPH

Any other suggestions would be appreciated, this is doing my head in... the bike was running brilliant for a good few months...

what happens at 5.1k revs in other gears,may be a fuel supply problem or air leak,mine used to pop like mad on the over run untill i replaced rear pipe gasket with a piece of glass rope which made a better seal.

Hi dude, in the lower gears (4 down to 1), the bike acts as per normal and is without fault. Only in 5th gear... I have this 'slipping' /juddering problem and it pops and bangs more than it ever did. I'm not worried about the popping/banging thats cool .... but I need a good strong 5 th gear to overtake on the bypass etc. I've since been advised that XT engines are known/prone to develop a 5th gear pitting problem. .......

So, I'm almost resigned to taking the engine out and embarking on the scarey journey of cracking open the cases and replacing the gearbox....
...oh joy...

OR, I've just had a quote from my local "friendly" suzuki dealer (yamaha would be more)... for a minimum of £350 for labour alone.

OUCH!!! had the same problem on my zzr1100 but in 2nd gear,found that by holding the lever up with my foot it would stay in gear,let go of the shifter and then it started to jump and slip out of gear,ended up buying a 2nd hand blown engine and swapped boxes over as could not see any thing wrong with gears or selector drum on my engine,worked fine after.good luck with it but make sure your certain of the fault first as gear parts can be expensive new let alone the labour.

Rodge, I'm going to wait before buying the new gearbox. Today I tried to get it to ail again in 5th @ 5.1k revs...and it didn't do it... but it did do it a little later at 5.4+ I've changed the oil to 10w30 (expensive stuff)... so maybe thats helping ?

Before you start buying expensive stuff, why dont you try to check the easy and inexpensive things first.

Since it developed popping and banging it should be an indication that it has something to do with fuel/air mixture. The right carb is vacuum operated which means that the condisions in the carbs (how much they open) may vary from gear to gear at the same revs.

Change the airfilter (or clean if it is a reuseable one) clean the carbs and take look at the fuel tap as well and also the membrane in the CV carb.

A worn out fifth gear (common on early XT's from the 80's) is cured by changing to a newer Yamaha OEM part wich is more resistant to wear, at any rate a worn fifth does not have the symptoms that you describe, it is an audible humming/singing noice in fifth sometimes in combination with high frequency vibrations.

Anders, spot on, that's what I'm doing. I'm checking as many of the easy (inexpensive things as possible first). I've got a spare air filter, so I'll try that too , cheers

I had a mate who "fightered" a CBR 600 and in doing so he removed the fairing which in turn caused all sorts of airflow problems to the air box. His bike would rev and run no problems at slower speeds but as the speed increased so did the flow of air being rammed into the airbox causing the problems you discribe (making the bike run very weak). This was solved by trial and error by decreasing the size of the air intake hole with about 5 pence worth of tape of all things (after he had paid out good money on 2 sets of carbs, numerous plugs & leads and various ignition components along with "expert workshop time". £500 in total)

Moral of the above story -- don`t jump in and start spending money, unlike a true Scotsman

Have you altered the filter / airbox / carbs / exhaust in any way?

If there was an issue with 5th gear pitting or being damaged ,missing teeth, then there would be debris in the oil that you have just replaced, and if there was metal flying around in your gearbox then i am sure that it would have wrecked it by now.

From what you describe it sounds like a fuel / air issue so i would start there before tearing the engine to bits or buying things that are not required.

Kenny.

Thank you Kenny much wise and sensible advice there. I am definately a Scotmans...but I find it easy to part with cash to keep my bikes healthly...

The only thing I changed was one of those little tarty air filter things on the breather... so based on that..I'm about to take it off and put the original back on and see if that helps. Not sure if that'll help as it was on it for weeks before the trouble started.

All the comments Much appreciated

YYYIIIPPPPEEEE!

Took the tarty wee blue air filter off and the bike is back to normal

brilliant

thanks again dudes