Revs hang, idles for a while then dies

[Ben Coyle Racing]

Had vacuum gauges on the bike, carbs balanced and the same..

It idles ok for a short while, once I rev it, it won't drop back to idle unless I turn down idle screw, its hangs around 4,000 - 5,000 RPM

When it does idle also, I give it a little throttle and it theres a short delay before its revs,

What could this be ?

I was thinking the carb rubbers but not sure ?

[RedexRobB]

Im assuming it was fine before?

In which case i would double check vaccum pipes are on properly and have no cracks in them. Also recheck u have balanced properly and your gauges are all zero'd if using the dial types. Check the pipes on the gauges too.

May want to check ur air box is seated properly aswell. All suggests an air leak to me.

[Ben Coyle Racing]

It has ram air system and I don't have vacuum pipes, the holes for those are bolted up.. ( Sorry I didn't put that )

And yeah the carbs where balance correctly, nothing up with the vacuum gauges,

any other ideas?

[Mori Man]

I see you've posted up for manifold rubbers - your on the right track.

When bike is running spray some WD40 around each one and see if the revs drop for a brief moment, should help you identify which one is causing the problem.

Alternatevely apply pressure to back of carbs forcing them into the head - that can also seal up any air leak and get a stable idle again.

Been a while since I looked in there but thought the vacuum spigots were a part of the head - if so connect them up again as intended , the SP manifolds have spigots in them too with blank caps for balancing.

Good luck hunting the problem down but as Rob said , air leak most likely.

MM!

[Big Al]

this can be a hard one to solve and may take time to eliminate all possible faults. Totally agree whith what has been said, put link pipes back onto the inlet manifold spigots. Use original pipe or something with a reasonable wall thickness as this side of the system will be under vacuum. i've listed a few other things that may help if you cant find any air leaks, all of which i've done on my L3 with the same problem:-

1. back remote idle screw right off and check throttle is fully returning to shut position - engine off
2. check choke plate at back of carb assembly is moving freely and not hanging up
3. sticky throttle at the bar
4. the collars that hold the carbs to the rubber connectors must be alligned as in the manual (there's is a simple diagram to help) if not the throttle mechanisum
on the back of the carbs can get caught up on the tiny screws that do the collars up. a really thin smear of SILICONE grease (not sealant) will help you put
the carbs back on.
5. with the carbs off check the air by-pass screw adjustment. drain fuel out of carbs first. gently turn up-side -down. 4 screws one for
each carb located down small bore in casting hidden slightly by rubber pipes on swivel joints (carb heaters). setting in manual H and L settings are different.
These screws have a very fine needle on the end be very gentle when turning.
7. IF ALL ELSE FAILS strip and clean the carbs the manual has a very good step by step section and good exploded diagrams to help. just be
methodical and do one at a time, cleanliness is the name of the game.

i'm going to hang my neck out and say that if it's not an air leak its either dirty air bypass screw needles or blocked idle jets.

Good luck getting problem sorted.