Diff'rent Strokers

[kiwi mvx]

Hi Guys, I have done approximately 8500 km on my engine since I rebuilt it with no dramas and a lot of that riding has been open road stuff pushing it along pretty hard so I guess by MVX standards it has been reliable.

One thing that seems to have a huge impact on performance is the state of the battery. When the battery was starting to die it began fouling the front two plugs a lot and backfiring when starting. The charging system seems only just adequate so I put a led park light in and tend to ride it with only the park light as opposed to low beam. I also fitted a new battery and there was an instant improvement in performance as a result of this.

I have run B8ES plugs in the front two cylinders and a B9ES in the rear. From the time I rebuilt the engine I used 130 main jets on all cylinders as a conservative approach given the MVX's reputation for seizures and melting pistons. I have pulled apart many sets of carburettors and they all have various jetting combinations using 125, 128 and 130 main jets.

Today I changed the main jets from 130 to 128 and took it for a ride. The bike felt cleaner through the mid range and just generally ran cleaner all round. I did a plug chop and all the plugs were a light tan brown colour, probably about right but maybe risky for a MVX, I;m not sure? time will tell!

Just wondering if anyone out there has had a crack at any plug/jetting combinations?

[Mr FFF]

125 is the correct size main jet so even your 128's would probably be on the rich side. I have tried to run 9 rating plugs in the rear cylinder but it just won't have it oiling every single time. I have had the best results from NGK B8IEX Iridium plugs

Hope that helps

Ian
_________________
MVX250 1983 MVX250 1984 GT380J 1972

Valves are for toilets unless they are power valves.
Claim to fame. Have beeten Casey Stoner over a championship season.

[kiwi mvx]

Thanks Ian, it's good to know 125 is the standard main jet, perhaps the sets of carbs I have pulled apart were re jetted by previous owners in an effort to prevent engine seizures?
Interesting your bike wont run a 9 rating plug on the back cylinder, my bike never fouls the rear cylinder but had a fair appetite for plugs on both front cylinders. Nothing is ever straight forward on a mvx, perhaps that is part of the appeal.

[kiwi mvx]

Hi Guys,
Well after approx 10 000km of what I would say hard riding the MVX finally seized after my initial rebuild. I had been progressively leaned out the jetting to 128 mains down from 130 mains and running B8 ES plugs in the front two cylinders. About 30 minutes before it seized I was thinking the motor never felt better (everyone knows that feeling aye!). I cant be 100% sure but I suspect I may have hit reserve while in a passing lane going up a long hill under full load. This resulted in some pretty spectacular fish tailing up the road and an emergency get out of the fast lane without geeting run over action plan. The motor did not overheat.

The front left cylinder sitting on the bike seized. Not only seized but also cracked the piston.

Despite all that if the house was burning down the mvx would still be the first bike I get out of the garage.


I have a new piston but does anyone have a set of .25 rings for sale?


Photos to follow

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