revs at 2,000 rpm....HELP. 67 fhc

[autoalain]

Folks, 3 hd8 carbs and the pistons are all up about 1/4 inch, (when running) all carbs were rebuilt, took
my time, and did it right( I hope), backed off idle mixture screws all the way, mixture screws
in about 2 turns each, closed input vacuum to tank, timing dead on with timing light 11%.
made sure the chokes were off on all 3 carbs. cannot lower idle, no matter what I try, and LOTS of backfires
from the exhaust, all floats were set at 7/16 when set, but have not yet verified level
in bowls, idle now at about 1800- 2,000. any suggestions??? this was the 1st start up after engine
rebuild, I have built about 30 different engine (not jags) so I not a bad mechanic (i hope) Mike.
p.s. exhaust clear, no black smoke or oily smoke)

[autoalain]

NOTE to my above, the butterflies in all 3 carbs fits PERfECT, no daylight when installed, the rods that hold
the butterflies no play and did put the new seals on the shafts.

[bitsobrits]

Well, obviously you're getting extra air from somewhere. An incorrect float level won't cause this. You've checked out all the obvious locations like spindle shafts with propane/starter fluid/etc, yes? And you are clear about the difference between the slow running screws vs the mixture screws, yes? Start it up with the slow running screws fully in (gently) as that can help define if it's an adjustment issue rather than an assembly issue. The car shouldn't idle at all with the slow running screws full in. An air leak at the intake manifold gasket is also a possibility, but less likely.

[lowact]

Then, a vacuum gauge should show if there is a leak. What car is it, what state is the positive crankcase ventilation, might this be allowing in air?

[Jack the lad]

As a previous reply has said, you are getting too much air into the engine. I would loosen the piston dampers and let them lie on the top of the dash pots as you start the engine and rev. it lightly. They should all rise together and an equal amount, if they don't you know where to look for the air in problem. If they all settle in a high position then you have a problem with the linkages (most likely cause of your problem). Come back to me when you have tested the piston damper rise and fall, cheers John.

[DWW]

How are the fast idle screws set?

[Philk]

Also, do you have a balance meter? Are the carbs balanced evenly (with all linkages between them undone)?

[autoalain]

Yep, have a balance meter, did not use it yet, on revving engine all 3 pots rise the same, positive crankcase ??, do not know what to check with that, I will pull apart floats to check levels, what brothers me is
the constant backfires from exhaust, lots, would this mean too rich??? of just bad mufflers? I will try
the spray trick all around with propane , forgot about that, it should revel some air input I hope.
thanks for ALL the ideas, I will investigate each one. Mike.

[mgcjag]

Is you valve timing set correctly...and what's your static set to..Steve

[bitsobrits]

positive crankcase ??, do not know what to check with that

There is no positive crankcase ventilation system with the 6 cylinder engines. Just a crankcase breather that vents into the airbox, so not a possible cause here.

Also, incorrect timing cannot cause such an 1800 rpm idle by itself.

I would start by ensuring the fast idle cams are not stuck (can happen even with fast idle screws backed off), the air pistons are free to move, the carbs are disconnected from the throttle linkage, and the slow running screws are fully (gently) home and see where it tries to idle. If the high idle persists, that will leave only the butterflies, butterfly shafts seals, and intake gaskets as possible culprits.

Mechanically setting up triple SU's on an XK engine is very straightforward, assuming everything is healthy and you have read and understood the procedure in the manual.

[autoalain]

Thanks for post to Steve, got cold here in Montreal again, will double check choke stuff to be sure
it is closed, as soon as it warms up will try propane test all around to check for leaks, stand
by guys will have an update in a week or two.