If i have to take these bloody carbs off 1 more time........

[Drunkn Munky]

Right lads im admitting defeat and looking for some help with a bloody air leak somewhere thats causing me to lose the will to live.

Symtoms:
Revs not returning to idle as they should, slow to return and gets worse the higher the idle is set
Unstable idle
Engine will eventually cut out if idle is set to 1300-1400 rpm

Obviously ive gone over the usual suspects, rubbers, clips and all pipework to the carbs several times and found nothing, tried 30 and 35 rubbers both new sets, all clips are fine and not split, carbs are seating correctly and ive checked over the carbs for any cracks etc.

History of the carbs:
They were setup on this bike with this engine fitted and run perfect.
Engine was then swapped for a standard motor, refitted carbs and it run perfect.
This engine(the RLR one) was then refitted and thats when the problems started.

The carbs were balanced from the very beginging and ive re checked them serveral times since with the drill bit method, i dont have a carb balancer as ive never had an issue with the drill bit method.

Suggestions on a postcard please

[Neosophist]

The drill bit method isn't perfect.

This will let you set the butterflies perfect but due to engine differences (ie slightly different vaccumn on each cylinder) this is why you need a vaccumn gauge.

Balacing the carbs will only get you a smoother idle.

Lets just go with the drill-bit method first of all.

So have you actually checked for an air-leak?

Get some carb or brake cleaner (this stuff is really flammable)

With the bike running... spray around the carb rubbers and listen for rev changes.. if your revs drop when you douse a rubber in fluid that rubber is leaking in air and the joint needs to be fixed.

Make sure clips are tight but not overly tight.. too tight and they will deform the rubber.. too loose and they wont hold the carbs on.

Next.. you mention it gets worse with temperature change.. this could be mixture setting, relating to float heights and pilot screw setting.

You must first ensure you have NO air-leaks, if you do you wont' be able to set a mixture or idle speed properly.

Presuming the carb cleaner doesnt' reveal and air-leaks you can presume mixture settings... perhaps too rich if its getting worse with heat.

For this back your screws in half a turn...

[Drunkn Munky]

Sorry neo i should have explained better, ive already checked the that the carb rubbers are not sucking air but when you say "if the revs drop when you douse the rubbers in fluid". Surely you meant the revs will RISE if there leaking and sucking carb cleaner???

Im not convinced its carbs settings, ive used the drill bit method a 100 times and got near perfect tickover everytime. As i said these carbs were setup on this engine and running perfect before i swapped in the standard engine which was only run for a 1000 miles(again running perfect) before refitting this engine.

I wouldnt say it gets worse with heat, i can only think you got that from me saying the engine will eventually cut out if you set the idle to where it should be @ 1300-1400 rpm, it will idle @ that rpm but will occasionally drop to the point that it will stall, sometimes it wont and returns to idle but sometimes it will stall. Increasing the idle only makes the revs even slower to drop to idle.

[amorti]

I keep thinking that (loose?) tight valves might give you similar problems, but they'd have to be pretty desperate.

On Triumphs it's quite well known for them to run rougher as they approach the 12k service (valve shim) and magically be fine afterwards, and they usually need at least half the inlet valves re-shimming due to closing up.

[Drunkn Munky]

The motor has barely done any miles since being built so i think its fair to say we can rule that out, cheers anyway

[oldgreyandslow]

I feel your pain!

Carb cleaner sprayed round the rubbers definetly made the revs rise on mine, you did say you've checked all that side of things though.

So all I can offer is sympathy, unless you want to kick my cat?

[Drunkn Munky]

TBH its not like i havent done this before, i know all the issues and pitfalls but this time its really got me pissed off. Rubbers have been off and inspected atleast 5 times today alone, even the slightest dodgy looking clip has been replaced.

Ive just refitted the carbs again slowly tightening up the clamps with the engine running until they seal yet the front ones are now giving a very slight rise in revs when sprayed with carb cleaner, idle is terrible, throttle response is now crap resulting in the revs hardly dropping at all. I know the problem is with the front 2 carbs but the rubbers are perfect as are the clips and yes the carbs are seated properly so WTF is causing the leak?

As for kicking your cat ive just taken out my anger on the twat of a tree surgeon next door whose just let a whacking great branch fall on my workshop scaring the living shit out of me.

[arsey30]

Is it running on all cylinders. [check ex pipe temp]
Is the fuel tap delivering a good flow.
The spray to the front carbs may be picked up by the air box snorkel.


Dave.

[Drunkn Munky]

Hi dave,

Yes all 4 are firing, fuel is being supplied by a portable tank hanging from the roof at present and gives good flow, vacume is blocked off while using this. Ive also tried the fuel tank to rule this out. Ive already thought about the spray up the snorkle and eliminated the possibility of that.

Ive now tightened the clips way beyond how tight they should be and have seemed to stop it sucking air from the rubbers but its still not right, revs still dont drop cleanly and it will stall if left alone. Im not happy, something is seriously a miss somewhere.

[Neosophist]

Hmm.

Overly tight valve cleareances can cause symptoms too, are they all in spec.

If you have a vaccumn gauge you could see if any cylinder has low vaccumn pressure (this can indicate an air-leak)

Is your vaccumn pipe for the fuel-tap ok? If not being used (ala HRC mod) is it blanked off correctly? This can be a vaccumn leak point.

I use propane to check as I have a big gas bottle and spray the gas around the rubbers... the idle will change and smooth out if you have a leak (carb cleaner does this too) as your essentially correcting the air/fuel ratio.

If your getting this by spraying the rubbers then they are deffinatly leaking.. make sure you use a straw or as Dave said it might be beign drawn in through the snorkle.

As for leaks.. is the carb ok, no cracks? is the manifold stub clean and smooth, is the rubber ok and not got a split or hole in it ( can be difficult to see)

maybe a thin smear of silicone around the carb stubs before planting them on the rubbers to check its sealing properly (allow silicone to cure before starting)

I hate vaccum leaks, can be a right pain.

Apart from carbs / carb rubbers and vaccumn points there isn't really any other places or a vaccumn leak besides the carb balancing screws.

Are they all present? Do they have the alunimium crush washer on and are tight?