3TJ carbs on a 3EN?

[skatsman]

Hi all, new to this forum. I am wondering if anyone knows if the 3TJ carbs are the same size fitting as the 3EN ones? My set is running really rich even with the needles droped to min position. Thought i'd try another set of carbs before buying a set of emolsion tubes from the states. Thanks in advance.

[Evilchicken0]

Usually this would be in the FZR section but it's your first post so the Mods might be easy on you.

Yes they should fit, although it's probably better to use carbs from a 3EN, that way you shouldn't need to mess about with the settings to much. Running rich could mean the floats are to high, the float bowl rubbers might not be sealing or the float valves could be worn. Of course you might have the wrong jets in the carbs too No2 and 3 are a larger size to No1 and 4 to keep the cylinders cool.

To check the float height you need the carbs on the bike and connect a U tube to the drain hole (it's a Yamaha tool but you should be able to rig one up). Then you can see the height of the fuel which is measured against the carbs body.
When you turn the ignition on does the fuel pump (thats the clicking niose) spin over and stop ??? If you then turn the ignition off and on again does the pump still make a lot of clicking - that could be worn float rubbers or the float valves not sealing, you'll also get poor idle.

[4StrokePete]

I tried to fit 3TJ carbs to a 3EN1 a couple of months ago. They wouldn't fit without a lot of work so I gave up. I think it was the choke mechanism hitting the coolant pipes.

[skatsman]

Thanks all, I think I will look for a set of 3en carbs to be safe. I checked the float height and they looked ok with a home made guage. Idle seems fine, cruising at 6K + fine too but really splutters around 4-5K! Give it some full throttle form the lights it feels dead and holds back at about 5k - 7k the comes back to life. Ease the power on and its fine! Really stumped on this one.

[Evilchicken0]

4-5k are the idle jets - they might need cleaning
Up to 8k though is exup teratory. Have a look on the downpipes on the side stand side you'll see a chrome cover. Take that off and you see a pulley wheel. Turn the ignition on and see if the wheel opens and then closes. Check the cables haven't frayed where they come out of the sheath.

[skatsman]

The EXUP valve moves freely, maybe a bit too freely as it tends to rattle on idle. If you hold the pulley it quietend down. The splutter I think is over fueling as it gives a chuff of black smoke around the place in the rev range. Am i correct that black is fuel, blue is oil and white is water?

[Evilchicken0]

That sounds about right on the colours

Maybe you should adjust the exup. Put a pin between the two tangs on the pulley into the hole behind. Find the adjusters near the top of the cables and take up the slack, finger tight only, retighten the lock nuts and check.

[skatsman]

Thanks, I will give it a try at the weekend and let you know.

[skatsman]

Just reset the EXUP and changed the carbs for another set from a 28K km bike, runs better, pulls through the revs ok. Does sound as though its only firing on 3 and there is a slight splutter really low down at 2-3K. Stripped the carbs and had a real good clean.

Bit of an update, runs perfect when cold, no splutter no missing crisp throttle response. Same when it comes of choke, but after 5-10 mins loss of smootheness and sounds as though I have lost a cylinder.

[kaighn80]

are you defo getting a spark across all 4 plugs? are any of the plugs wet when you take them out? can you find that one plug isn't working? if not then I'd be tempted to check balance, but i had problems that seem to be a lot like what you describe, it basically turned out that there are some bushes in the ex-up valve and mine were shot so i replaced them and set everything back up and after that it was fine, they don't cost much so might be worth doing just for the piece of mind that they are done.