3tj Cutting out.

[sethbrown]

Hi all,

After finaly sorting all the other problems the last 3 times i have taken it out it keeps cutting out when warm. Everytime i pull up at a set of lights the revs drop right off and it cuts out sometimes it starts straight away and other times like my last outing it kills the battery trying to start it again.

Anyone any ideas?????? other than the scrap yard that is! lol

thanks Seth

[Evilchicken0]

I'd say either it's fuel starved ... but then the revs would rise or maybe the valve tolerances.
I had a 3en2 which wouldn't run with the EXUP valve, it would gradually strangle and didn't matter if I revved it or not ... no idea what it was !!!

What's it like starting from cold ?

[rockTJ]

When were the valve clearances last checked??? If they are tight when the engine is cold they are only going to get closer as the engine warms up.....

Other than that - air leak from the carb rubbers?? Someone more technically minded will come along with a better answer soon. Hope you get it sorted.



Chris

[Evilchicken0]

When were the valve clearances last checked??? If they are tight when the engine is cold they are only going to get closer as the engine warms up.....

Other than that - air leak from the carb rubbers?? Someone more technically minded will come along with a better answer soon. Hope you get it sorted.



Chris

Actually it goes the other way, the valve heads expand so the vavle seals when it's hot - cutting out does happen though

[sethbrown]

Thanks ill check the carb rubbers etc tonight. really hope its something simple bike is really starting to do my head in now!!

As for the exup coment i have already removed this and put a metal plate over the hole however it seems to do it regardless of having that in or out. what do these exups actuly do? mine seems to run better with it out dose that sound right?

thanks

[rockTJ]

When I had my hillclimb mini we were told to run the valve clearances (especially on the exhaust) at about 50% to 75% more than the std road engine. As the engine temp rises the valve clearances nip up to nearly nothing. If they are too tight to start off with then at running temps the valves dont close and the exhaust ones burn out and the inlets loose you a shed load of compression. Ah the days of 1400cc metro lumps and scatter cams

On the road I suppose you're never under that much load for too long. Someone told me that the FZR's are known for having chocolate valves oh well make hay while the sun shines I say.

Chris

[Evilchicken0]

One way to get an engine to produce more power is to rev them harder and the way it's done is making the stroke shorter so the piston doesn't travel so far per revolution. That's ok, but it means the engine is weaker in the low to mid range, it has little torque so it takes longer to reach the top end where the power is. If you have a narrow exhaust pipe it increases torque so your low / mid range is increased but when your at high revs you want a bigger bore to flow more gas otherwise you'll strangle the engine. The exup closes at lower revs making the pipe effectively smaller bored, and opens to increase it giving you nearly the best of both worlds.
That's why you would use a 2" LCB on a competition Mini but only a 1 3/4 on a rod car.

The valeves on the FZR have to rev high, maybe not as high as todays engines but by the standards of mid 80's design ... high. They also need to be light and that means there's trade off against strength so they wear or stretch, remember they can be going at 14k rpm or 233 times a second

[levo]

Start it up and then spray carb cleaner around the rubbers........... if the revs rises they will want replacing /fixing.

[sethbrown]

Thanks all for the info, I got fed up over the weekend and started from scratch checking carbs resetting floats etc (which were all over the show!!) put it all back together and its running sweet now!!! Really not sure what the prob was in the end but hay it ain't doing it now and that's good enough for me!! the only thing I did do after this is reattach the exup now it runs really rough with that in!?! It's back out now and running really nice, will I be ok leaving this out? Will it harm the engine in any way?

Also!!!! Lol! Being the newbie to biking that I am?! I want the set the preload up on the front forks at the moment it just seems a bit soft. How do I know when they are set up correct? Any advice or is this really a personal preference sort of thing?

Thanks again all

Seth

[Evilchicken0]

If the bike runs ok without the EXUP then leave it out.

The forks could probably do with new springs - the Japanese ones are quite soft, and fit some new oil too. Adding a little oil with make them a bit harder too but remember forks should be supple rather than hard.