recent purchase '82 RJ SECA idling high rpm when warm

Thanks Durk
Think I can manage that. Very informative.
Just one thing - I assume you replace the seals, and/or 'o' rings (we are looking for worn, split, etc?) Anything else? And what size are they, where do you get them from individually.....I dont think you get them with a basic rebuild kit......?
Excuse my ignorance, I SHALL do a search for them, but in the meantime, if you know......?
Many regards
Dale

 

Get ahold of XJ4Ever. Even shipping to the UK, it won't take long to get your parts, the correct parts, in hand.

Your Seca has Hitachi cabs, not Mikunis; although the "theory of operation" is the same.

The diaphragms are part of the slide assembly and are located directly under the "hats." They CAN develop pin holes or tears over time; often they're fine.

Anybody that's "never had to replace" a throttle shaft seal hasn't worked on too many carbs; or he's not very good at what he does.

 

****************************LATEST UPDATE*******************
As I've obviously got vacuum leak somewhere (probably at the throttle valve seals) I've pulled the carbs, done a wet float set (2-4mm), checked the filter to carb boots (clean), the carb-to-head manifolds (there is some cracking, but it doesnt go all the way thro', and I didnt get any +revs, when I sprayed around them anyway, when idling) Sealing them all the same....
The vacuum spigots are clean....
Broke the carbs, checked the diaphragm (in #1, a bit of dirt above needle?) Got the rest to check........THEN........ :lol:
took the fuel rail apart....old black disintegrated part of 'o' ring? smeared all over it! Every 'o' ring at least worn, one with bits broken off...possible reason for high idling(?) Perhaps.....going to get into the throttle shafts tomorrow and see the state of their seals (bet they are poor also...)
Thanks fitz for xjforever prompt - will no doubt be purchasing this weekend from them....

til tomorrows next episode..... :wink:
Regs
Dale

 

*********************LATEST TODAY***************
Just stripped carbs down, cleaned them, checked diaphragms, (one has very slight wear in two places, but cant see light through...?)

Removed the throttle shafts and seals the seals look ok to me, but I cant compare with new alike (?)

I have replaced the 'o' rings on the fuel rails, which when compared with the new I've put on you can tell they were worn (thinner), and one was damaged also (the one on rail between 1 and 2 carb, I think, where there was sludgy leak all over the rail...) - could this have been the cause of high rpm's once at machine temperature??

I made two attempts to send pics of the existing throttle shaft seals (and the replaced 'o' rings, but wouldnt accept from camera, or my mobile (too big and I dont know how to put them to 500 x 500) - from your experience must I replace them? (I know someone has been in to these in the past, as the butterfly screws have been removed before - maybe someone has replaced the seals not long ago....but NOT the 'o' rings??

You'll probably advise that replace them anyway, (the throttle seals) cos the only way of telling if theyre worn or not, is to put the carbs back on the bike (and eliminating all other possible vaccum leaks), and if the problem still remains, then it is the throttle seals....??!!
They are a little 'loose' on the shafts, one or two....

Let me know, from your experience, how to proceed....

Regs.

 

Just removed the replacement fuel line 'o' rings - theyre correct diameter, but too thick, and wont allow line to slip into carburettor....
ordering some from xj4ever, along with throttle shaft seals.....adios

 

All good advice from other people... BUT - usually, before you start changing shims etc, I'd advise you MAKE SURE that the idle adjusting screw is set properly (I always get into trouble from others on here for suggesting this simple check above everything else - However, it proved to make a significant difference on my XJ).

This adjustment screw is EXTREMELY sensitive to minute adjustments because, as it acts directly on the throttle, it opens/closes the butterflies on the carbs. You might find that backing it off a little once the engine is warm allows you to drop the idle speed back to 1000rpm. Just my two-penn'orths-worth...

 

Thanks Nige
Been there and done all that a long time ago, and the lowest revs, I can get (even now I've adjusted shims) in operating temperature is 1500-2000, with idle screw turned down to lowest before it will just cut out.
Its been established that its a vacuum leak, and its and/or between the air intake carb boots, the vacuum spigots, the carb to head manifolds, or THE THROTTLE SHAFT, AND FUEL-TO-CARB SUPPLY PIPE SEALS, AND O-RINGS.
Im just on that case now, done the investigation, found the worn parts and ordering the necessaries.......watch this space.....!
Thanks for your reply.....
Regs.
Dale

 

**************LATEST******************
Done wet float level test. Broke carbs, and removed carb to head manifolds (cracked in various places - just sealing with silicon now) Air box to carb boots examined closely and are ok.

When I dismantled carbs, found that fuel supply o-rings were worn and had deposited on one part, a sludgy, residue (cause of vacuum leak?)
The throttle shaft seals look ok, but I have sent for both seals and o-rings from Chacal, and will replace both.

The carbs were filthy on the outside, and I have meticulously cleaned them, the best I can - the insides jets etc and bodies seemed relatively clean, (the firm I bought this from, told me when it was sent back that they had had the carbs off, and worked on them) apart from the float bowls, which had a sort of brown stain in the bottom of them, (rust from inside tank, in fuel?) which I cleaned out.

Can't proceed any further (dry bench synch, vacuum synch on bke etc), until my carb parts arrive, and I can reassemble everything.......
Have attached a pic which I have now managed to reduce, of the used o-rings. Hope you can see it.
Later
Dale

 

Please Note: The pic includes new o-rings, that I attempted to replace with, but they were too wide in guage, (wouldnt insert into carb fuel shaft when fitted) so I've sent for proper ones from chacal......

 

PIC OF SHAFT SEALS REMOVED FOR REPLACEMENT(?)

 

***********LATEST JULY 13**************

Replaced throttle seals with new ones. Replaced carb fuel-pipe o rings with new ones.

Thoroughly cleaned carburettors, every nook and cranny. (as mentioned following the many threads, over the past few weeks/years!)
Passed the 'clunk' test

Installed new bolts and spring washers in float bowls
Put an extra seal of bike innertube on top of already silicone-sealed, cracks in inlet manifolds.

Made an apparatus to hold carbs completely level (copied from thread on this site) from pvc plumbing equipment, and wet-set the float levels again -they were in fact the same as when I did it from holding it in a vice!!)

All are in spec - #s, 1-3, 2-3mm below gasket level, #4 is 3.1-2 below gasket level mark.
Bench-synched carbs, using a fine-guage paper clip.

Re-installed carbs to machine (after some deliberation and help from this site(!) - see other thread!!)

Started up with choke-initially idled steady at 1150, then all of a sudden, when warmed up,(and choke off) shot up to 2400 and stayed at that(?)

Turned it off.

Idle screw is fully 'out' and throttle is loosened right off.

I know I've just changed valve shims to spec, so requires vacuum synch, and I have bought a 4-dial guage to perform this task, but....?

The idle mixture screws are about 1/2 way out from seated position when bench synched - would turning them back down tighter slightly, bring the idle down....?

This smells of vacuum leak again, otherwise....?I only sealed the mouths of the inlet manifolds with red high temperature instant gasket seal, (12 hours ago) over the old gaskets, and I havent tried a 'spray carb cleaner around them' test yet....

:? Is this situation normal, before doing vacuum synch, after valve shim adjustments.....until you've vacuum synched, using guages.....???

Thanks....

 

Did you make sure that the choke (actually an enrichment circuit) actually closes completely?

When you say the idle screws are "half way out" what do you mean exactly? We measure the initial settings of these screws in the number of "turns" and "half way out" might be more than the 2 1/2 turns from bottom recommended.

The inlet manifold should have a proper o-ring or gasket (not sure which for your model). I'm not sure how well the red instant gasket would work, but I wouldn't recommend it.

High idle is quite normal if you haven't set the pilot mixture screws correctly or synced. Get to doing that stuff.

 

Thanks Manbot

Sorry. I meant the synch screws, (when doing the bench synch) not the pilot mixture screws, are all screwed approx 1/3 to1/2 way 'up', effectively when only ' a sliver of light', can be seen when viewing thro' each carb mouthpiece/venturi.

Could it be that the butterflies are set so wide open (guage of a small paperclip), that this is causing the high idle (if a vacuum leak is not the culprit, - or the pilot mixture screws not set 2 and 1 half turns out?)

Cant remember if they (the actual pilot mixure screws) are screwed right down, or not, - will look tomorrow. - and do vacuum leak test!

:wink: I can get some new manifold gaskets (if tests necessitate) off a site in Europe - £10 (inc pp)
Thanks.....

 

Oh, and the enrichment circuit is closing properly as well.....
Regs.

 

Yes and Yes. A bench sync only gets you close enough to get the bike started. You got that far. Do a running sync, and your butterflies will be set properly for the different vacuum your 4 cylinders produce.

Then set the mixture screws (2.5 turns is also just a STARTING point). The Gunson ColorTune plug works great for this. After setting the mixtures, sync again, etc, until all the cylinder mixtures are tuned and all are pulling the same vacuum.

 

Just been trying to synch, using vacuum gauges. Waited til op temp reached. Got the 1 and 2, and 3 and 4 as level as poss, but when temp reached, still high idle. 2.5-3.0 rpm.
Kept tweaking synch screws, and got it down a bit more. Idle screw, is all way out....turned off. Throttle is slack, with 0-10mm til plays takes up.
When I blipped throttle would only come down slowly, to @2000rpm
Tweaked again.....turned off
Turned on again, and racing up and up, to 5krpm+!!!
Have I blown a gasket or something? Really worried....
Will try again when cooled down (I didnt have a fan on)
Regs.

 

HELP!! :!:
Ive let the motor cool down for 1/2 hour, and started again, and it just keeps racing up to 5+K!!!
Turned off.

I did notice a little 'pop' of air, up from carbs/manifold area, when I pressed starter button to restart engine, just before I got this problem (between 1 and 2?)

Turning the synch screws out, is having no effect now ( I could press down on the throttle linkage, before, and that would bring RPMs right down til it cut out almost... this has little, or no effect either.......... :cry:

The throttle is not sticking, and idle screw is all the way out, anti-clockwise?

Please someone tell me I haven't done something major down below?

I was doing so well, it would idle very low, with adjustment, (til op temp) and now this.... :cry:

Any ideas? Had this experience before when trying to synch?

 

You didn't blow a gasket or anything.

You're over-adjusting. You probably have it so far out of sync now that you're going to need to pull the rack and re-bench sync. Don't feel bad, we've all done it.

And then don't attempt to sync until it IS up to operating temp.

 

Thanks fitz

Made me feel better, knowing its something that many people have endured in the past....

Just took the carbs off, and there are no butterflies stuck wide open or anything, - but on closer inspection #s 1, 2, and 3 are all at 2-3mm!! #4 looks more or less fully closed.
Explains the 5k+ idle!!?

Like you said, in my effort to get lowest idle I could, I have overadjusted (I dont think I tried to actually synch until op temp. tho(?)) to the point of 'no return' so to speak.
I actually got a decent synch, on 1 +2, and 3 +4, (3 and 4) slightly higher/lower, cant remember which now) on the dials of the guage, but I wanted a lower idle......!!
This time when I bench synch, I'm going to use a lesser guage base (a certain guitar string I have in my posession) than the paperclip I used at first, enabling the butterflies to close to a tighter gap, when throttle fully 'off' and therefore the lower idle can be attained(?)

:roll: Think this is logical in theory, and find out if in practice?
Regs.

 

Several members recommend a business card torn into even strips instead of the paperclip or string. Because it's flat and bends to mold the curve of the inlet, it gives a more narrow setting so that it doesn't rev as high.

Might give that a try too.