Mikuni RS34 or other help needed (revs not going down)

[nanno]

Alright chaps,

I sincerely need your help on this one, because I am running out of ideas.

As some remember, I am playing around with my Mikuni RS34s on my Z1000J with K&N Duals for a while now and I think I have dialed them in very, very nicely, with the following jetting:

Pilot 17.5, Mains. 125, Needle 4th notch from the top, mix-screws 2 turns out, fuel levels on 17mm, slides are synced and don't rattle at all when idleing (i.e. sync should be fine), vacuum ports are sealed and the plugs of them not cracked, accelerator pump is set to the specs of the Mikuni manual.
Furthermore I also tightened down the inlet manifolds when hot and also made sure that the carbs are fitting snuggly and checked everything with brake cleaner (no effect).

So far so good. Now comes the funny part, as long as the bike is cold (up to 60-70°C oiltemp), it runs brilliant, accelerates like a donkey on steroids and if you close the throttle the revs go down brilliantly, just as they should. As soon as the bike gets hotter, if I keep the revs up (lets say over 4000 - 5000 rpm), they just won't go down anymore UNLESS I force the slides down. The bike works fine if I keep the revs below that mark, also it accelerates like a good one, both cold and warm, with no flat spots in the jetting at all.

One of the things that came to my mind, while writing... could it be the ignition advancer - I had that on my XS11, when the vaccuum line broke (the advancer on that one was operated by vaccuum, like on old cars).

Any help would be highly appreciated.

Cheers,
Greg

[Al]

A&R would be a good place to start.
Are there any splits in the carb mounting rubbers? Can be vary hard to spot and sometimes only reveal themselves when you tighten the jubilee clips.
Are the rubbers sealed to the head. The cast in steel baseplate will bend and can lead to air leaks as the motor heats up.
Have you got a PPT arrangement fitted or are you using a return spring for the push throttle return?
You might try to release the screws holding the bank of bodies together and then do them up again in-situ. If assembled on the bench they can be less than square.

AL

[nanno]

Regarding your questions:

Rubbers are soft, can't say anything about the baseplate, but I will put them on some glass and check whether they are gapped.
I have a ppt setup with two cables, both setup to have minimal play in them.

I shall try to loosen the carbs and will do as you suggested.

The odd thing is, it only happens, when the engine is hot (and the carb-bodies get hot(-ish) too).

Thx a lot for your input.

Cheers,
Greg

[prowlerz1]

have you checked the valve clearances?????

[nanno]

Not in a while... no... why ?

But as I can hear them, they shouldn't be too far off.

But I shall check that tomorrow.

Cheers,
Greg

[nanno]

Alrighty, I improvised an additional inlet manifold gasket (between head and manifold) from gasket paper and it did indeed make the situation slightly better. But once the bike was really 100+ degrees and doing the brake-cleaner test again it showed that it still didn't seal properly.

So I have just ordered a new set of manifolds and hope that they will do the job.

Also when the bike is cold (i.e. tomorrow), I'll drive back to my shed and check the valves, just to make sure, that there's nothing wrong in that corner.

Thx to all for your help so far. But I have to admit, for the few minutes, the paper worked, it gave me a short glimpse on the things to come... oh and I will love those RS34s...

Cheers,
Greg

[Al]

Hope thats all it is Greg. Do you have any sort of support for the carbs and filters?
Someone here had a bracket looped up over the top frame rail and my CV's when used without the airbox have a bracket from two of the cam cover screws to stop them falling off or vibrating the fuel out of the float bowls!

AL

[Rich]

Try some Blue Hylomar on the joint

[Dodgy Z1B]

Try some clear silicon, use it to seal allspeeds where they slip into exhaust thingy and are held in position with springs on rd400 works a treat, I know its the other side of the engine so a bit less heat for it to deal with.

[nanno]

Nope, carbs are not supported.

Rich, I will try that tomorrow. Will use some red Dirko, but that should be equally fine (I think).

New manifolds are ordered anyway.

The backside of the old manifolds has some severe markings, because they have been mounted on two different cylinderheads and the last time I overtightened them a bit, which rubbed off a bit of the rubber around the bolts.

Cheers,
Greg

[Pigford]

There are different types of rubbers to suit different profile carb stubs!!!

Make sure yours are the right ones....I had this with my Z1000 (RS36's) and Ray Debben got me the right ones - after Jeff (Z1enterprises) told me to check it out

I also had an "invisible" leak right next to where the screw fixing is, by the base plate of the manifold

[Ginger Bear]

These; http://www.z1enterprises.com/Carb-Holde ... r-314.aspx

Not these; http://www.z1enterprises.com/Carb-Holde ... r-442.aspx

[nanno]

So these:

http://cgi.ebay.at/ws/eBayISAPI.dll?Vie ... 1439.l2649

were the wrong ones ?

(The Z1Enterprises shop seems not to work at the moment)

Edit: Appears to work again, yes mine have the groove at the right position (I can feel the carbs "snap" in to that) - so that should be fine.

Cheers,
Greg

[nanno]

Just checked, the ones installed are the ones you recommend GB (ending in -1135).

Checked the valves and reset the exhaust valves (they were all on the tighter side) and dirko'ed the inlet manifolds for some extra seal towards the head.

Let's see if it does the trick.

Cheers,
Greg

[nanno]

I owe you an update, I think:

1) Dirko did the trick
2) the cables hung too, when hot.

So today I modified a GPZ750 Turbo throttle assembly to fit with RS34s. Mind you, whoever said, that they work "out of the box" with Mikuni RS 34s or are a "direct replacement" on the Z1000J, has obviously never tried it.

I ended up milling out the cases, turning up a throttle cable adjuster (for the RS34s) and replacing the electric internals from the GPZ switch with the ones from my Z1000J - so yes... it was a kind of straight fit, because I didn't have to turn out the cases, because the bars are the same diameter.

But... did I mention how much fun working RS34s are ?

Quick re-jet to 125 mains (jetted up to 130ies yesterday) and I was rewarded with super crispy throttle response and absolutely mad acceleration. Steady idle at all temperatures and the oil temp stayed at about 90 degrees Celsius... (without an oilcooler and riding very fast).

So now I will wait for my new manifolds.

Cheers,
Greg