XJR400 Bad Running

[Mike Shelby]

Hi - Just got me this . . .



But . . .

At the moment it's running really bad, no power, fuel leaking I think from the back of the carbs (and carries on leaking when switched off for a while then then it stops), also had really old black sooty plugs which looked well worn out which I've changed for new ones - does anyone know if the carb inlet rubbers from another Yamaha will fit as mine are perished and cracked so wondering if it's sucking in air?

The bike will only get to about 60mph and just sounds choked, sluggish and not very lively so I'm hoping to get the carbs off tonight and check all the jets etc.

Also has slightly pitted forks but Kayla tells me ones from a TRX850 will fit so will be on the lookout

Other than this it's quite a nice bike and I think quite a bargin for what I paid.

[Kayla850]

...Also has slightly pitted forks but Kayla tells me ones from a TRX850 will fit so will be on the lookout

Other than this it's quite a nice bike and I think quite a bargin for what I paid.

Whoa there... I said they might fit Actually, they should fit, thinking about it. They'll be longer though, so you'll have a bit of fork sticking up- it might be easier to find a decent set of 3EN2 forks and rob the stanchions from them to rebuild your XJR forks.

[Evilchicken0]

Try the FZ600 inlets they were the same dia as the FZ400. Or just put an FZ600 engine in there.

[Maelstrom]

How old is your motorcycle?
If you have Mikuni BST carbs on that bike then you will have to replace all the seals that stop fuel leaking into the throat.
see http://www.litetek.co/Guide_MikuniBDST_ ... gAssy.html for some examples. First strip the carburettors, clean everything, check diaphragm rubbers, and replace all the seals. Check those inlet manifold rubbers while you are there. They may be cracked on the outside, (UV light damages NBR), but the cracks may not go all the way through. Then set all the carb settings back to standard and check the condition of the air filter. Anything less than that and you are just wasting your time and ours.
Check my Yamaha 400 kits here http://litetek.co/ReplacementPartsYamaha.html to see if any match the XJR and I will also do the same later today to see if I can do the kit for the XJR.

cheers
Blair

[Maelstrom]

This is the only place I could find a parts listing.
http://www.megazip.ru/ru/bike/yamaha/view/1231
Strange for a bike that has such a long model run.

Anyway the carbs on this bike are nothing like the other 400s. They do not have the 'special' o-rings and seals that the Suzuki and Yamaha 400 sportsbikes use. That is good from the point of view that it limits the possible causes of your problem.
Giving the carbs a total overhaul is still a necessity, I believe, simply as a matter of course. Otherwise you could spend a lot of time chasing your tail.

From my quick look over that website the early models had paper float bowl gaskets and the later ones an o-ring. With the later models having an o-ring that seals the main jet holder. Both have o-rings on the float neeedle seat.

You should also check all the choke plungers and cable to ensure that they are seating correctly.
cheers
Blair

[Mike Shelby]

Thanks for all the replies - it's a 1993 by the way (4HM1) - After much haggling from what they were asking at £700 I only paid £525 for it with 10 months MOT so expected and knew there would be things needing doing.

I took the carbs off last night and took the float bowls off to check the jets - as I lifted the carbs off I heard a rattle inside the outer rhs carb - opened it up to find the main jet and washer had fell out and was loose in the bottom under the float!! Anyway put the jet back in and checked all the others and one more wasn't as tight as it should be either.

I checked the inlet rubbers and although they look bad on the outside the cracks don't appear to go right through.

Put it all back together and went for a ride - much better now than it was and not leaking any fuel at all - but still don't think its completely right as it seems fluttery on the throttle at certain revs and still seems vastly underpowered - now thinking ignition coils, leads and plug caps. The ignition coils are cable tied on and not even sure if they are the correct ones as they aren't bolted on where they should be.

Can I use ignition coils/leads etc from another bike such as one of my 3TJ's which do run nice to test on this bike or are they model specific? Don't want to damage the coils or the bike and don't know enough about this sort of thing - soz

Also the throttle cables badly need replacing - anyone know if they'd be the same fitment/length as another Yamaha with twin cables?

I've only got my 3tJ's to compare this bike with as they're all 400's - not expecting it to be as quick and snappy as those as the XJR should only be 53bhp standard but feel sure it should be more lively than it is at the mo.

Has standard heavey exhaust at the moment to but will try out of interest a motogp can from one of my others to see if the exhaust is restricting it at all.

I haven't seen any kind of M-Max derestrictor on this bike yet so possibly it might still be restricted to 112mph - although the fastest I've managed as it is now is 80mph - it was struggling to do 50mph before I had the carbs in bits so at least there's some progress!

Thanks again

[Evilchicken0]

You can fit other coils, most manufactures use a similar coil in all their bikes as long as they May be chevame firing order.
Look at the needles to see if there's any wear on one side its a sign the emulsion tube is worn.
Maybe check the valves I think they'll be like the XJ engines.

[Mike Shelby]

Just an update -

This was doing my head in so set about it again . . .

Had the carbs off for a 2nd time just to double check everything was clear in there again which it was, so put it all back together and used some black silicone sealer on the carb rubbers just to seal the cracks - so couldn't understand why the outside cylinders appeared to be running rich - with black plugs yet the inner 2 cylinders were a nice brown colour. Spent a whole day - tank off . . . tank on . . . tank off . . . tank on etc!! kept adjusting mixture screws but still the outside cylinders looked to be running way to rich no matter how much I altered the mixture screws.

Then decided it can't be the carbs - so turned my attention to the coils . . . the coil feeding the outer cylinders 1 & 4 was my next target as the inner 2 & 3 looked to be running perfect. Took off the coil and disconnected the wires to find the spade terminals were so tarnished/corroded - so cleaned them up and put it back on and hey presto!! Runs like a chuffin' dream now!! Much more power and must have only been running on 2 cylinders.

Also for anyone who has an XJR400 - I changed the trottle cables for new ones as they badly needed doing and it's something you've gotta do while the carbs are off but I didnt buy XJR400 ones as they were £29!!! Instead I bought a new cable from global bike online for a Yamaha TW125 for £15 (twin cable push/pull just the same) and it fits straight on! - just a little longer in length but if you route it around the left side of the headstock instead of the right it fits fine.

I've also found out that anyone needing new inlet rubbers the exact same is used on a Yamaha XS400 (bearing in mind they are a 2 cylinder engine) so you would need 2 pairs if ordering as they are left and right specific.

My next problem is gonna be how to remove a chewed/rounded off alan bolt out of one side of the lower fork yoke when I come to change them - previous owner has made a right mess of it and as it's recessed can't even get molegrips on the head - all suggestions very welcome. Might even have to look for a replacement yoke if I can't get it out.

Mike

[Evilchicken0]

Could you use an easy out - a lefthand thread into the allen bolt head. Or drill the head off

Nice one with the coil

[Kayla850]

My next problem is gonna be how to remove a chewed/rounded off alan bolt out of one side of the lower fork yoke when I come to change them - previous owner has made a right mess of it and as it's recessed can't even get molegrips on the head - all suggestions very welcome. Might even have to look for a replacement yoke if I can't get it out.

Mike

A good quality cobalt drill should make it easy-ish to get the bolt out and if you're careful you should be able to save the thread. Early Fazer 600 yokes might be the same though if you get stuck.

Good news on the running issue though