SU HiF6 weird problem on a 3.5 Rover.

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jagger
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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Fri Jan 25, 2019 4:11 pm

Denis247 wrote:
Thu Jan 24, 2019 10:16 pm
I'd remove and block all pipes coming from the carbs if I were fault finding this. I've even known a faulty vacuum advance to cause this type of problem, sucking in air, or even cracked pipe between the two. Also any vacuum feed to brake servos or other vacuum devices (my car has vacuum operated heater controls), one way valves or dodgy pipes. Basically, take everything off, and if fault persists check for manifold leaks, it may not be the actual carbs causing the trouble. Just my 2c.
Thanks Denis.Very sound advice.I shall do that once my jumbo economy sack (not) of throttle plate screws gets here.

I'll be fitting the solid plates from the HiF44s to isolate those emissions valves.I have managed to form a line of logic that involves them in this episode.The old plates and valves were quite probably gummed right up from several decades of being out of sight and parked up for long periods.I've put a few miles on it this year which must have come as a bit of a shock.I only got the carbs performing nicely for the last 500 miler and then this hanging tickover started,during that trip.So maybe they'd been loosened up enough through a good run to start opening and messing with the mixture.Since fitting the brand new plates with brand new valves (which seem to be slightly longer and open further) the revs have just risen more.

Also,the brake servo operation has been questionable recently, since the fitting of new brake lines and whizzo steel hoses.So the advice about blocking off hoses really started to bite as I typed that.It may be a bit of air in the system or it may be a fault with the genuine antique servo unit.The hose is new.There was a serious vacuum in it last time I whipped it off.

Must admit that rebuilding and tweaking a Holley on my mate's Defender was a delight compared to this.Just had to un-monkey it back to factory settings for it to perform flawlessly.The logic involved there was very uncomplicated.I obviously haven't found all my previous owner's monkeys yet.



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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by Ian Anderson » Fri Jan 25, 2019 7:24 pm

Does this Landry have vacuum assisted brakes?
If so block the vacuum at the carb in case the servo diaphragm has ruptured.

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Fri Jan 25, 2019 9:58 pm

Yes.Ian,it does.

It'll be getting cut off once I get the carbs back on.I'll D/C stuff one at a time to try and find a culprit.First step is the throttle plates to isolate the emissions valve.

I really am looking forward to finding out what's going on.I was starting to like the SUs before this happened and don't really fancy going to injection (even though I've got a set).

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by Denis247 » Sat Jan 26, 2019 11:34 am

Re "I'll D/C stuff one at a time to try and find a culprit.". You may have TWO faults. Personally I'd do it the other way around, block everything and then open then up one by one. TWO faults can be a bugger, and unusual, but it does happen.
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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Sat Jan 26, 2019 1:07 pm

Oh yeah Denis.I believe that. :D

And again a good idea that I'll adopt as my own. :wink: The brake servo isn't being used so can be blocked off,the vacuum advance isn't important without load either,and the emissions crap (plenty of those available in a high mileage black death edition V8 like mine) pumped into the carbs behind the throttle plates always sounded like a fudge (something beginning with F anyway) to me.Nitrous oxide maybe but not that foul smelling eye stinging mush that gets pumped out of the rockers.

The 2 quid a shot throttle plate screws (if you include postage) won't be here until Monday so I won't know any more until then at least.

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by unstable load » Sun Jan 27, 2019 8:36 am

jagger wrote:
Fri Jan 25, 2019 4:11 pm
I'll be fitting the solid plates from the HiF44s to isolate those emissions valves.
I have heard of the poppet valves being soldered shut before, it'll be a LOT cheaper....
Cheers,
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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Sun Jan 27, 2019 9:36 am

I've seen a few photos of soldering up the poppet valve.Not pretty most of them.As I've got a set of flat plates I can use those to test.I know I can seal the hole better than I've seen done before.A nice patch of carbon fibre should do it.Having seen the price of replacement plates I can see this being in my future.The screws are even more annoying on the price front but they should arrive tomorrow.

I don't think the brake servo is interfering due to the stored vacuum in the hose.Seems the non return valve is working fine (when it's not running of course).

I don't think the vacuum advance is involved due to two different dizzies giving the same result with a new silicone tube.

Then again,I haven't been thinking that straight lately. :)

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Tue Jan 29, 2019 12:27 pm

Well I've managed to drop the tickover.

Assembling by the book on the bench everything seemed to go fine.One and a half turns in on the slow idle screws and fast idle set on the cams.I removed the throttle operating levers to aid fitting on the manifold,refitted them and started it, and got an improved 2000 rpm tickover.On lengthy inspection it turned out that the fast idle cams were operating on the throttles at tickover despite both being fully closed.I've managed to stop that only by turning the fast idle adjustment screws round in the throttle lever plate to give at least a bit of clearance on the cam.It's not perfect but it runs.

The tickover screws are wound almost all the way out to achieve a 650 rpm tickover when warm and that brings the plate closer to the fast idle cam to the extent it was holding the throttle plates open.Not easy to see when you are fitting the throttle arms back on the back side of a pair of carbs.Both carbs are balanced ok but I need to mess with the cold start some more (it's a bit bush mechanic at the mo) and see if there's a better way around the problem.

Emissions inputs to the carbs are bridged together.The servo and vacuum advance,and thier hoses, seem sound,Mixture will need chasing for a bit I'm sure but at least it won't be revving it's nuts off as I'm trying to set it.I'm also pretty sure something else will come back to bite me but that's just what this problem has done to my confidence. :D

Test drive later hopefully.
Last edited by jagger on Tue Jan 29, 2019 2:30 pm, edited 1 time in total.

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by DaveEFI » Tue Jan 29, 2019 1:36 pm

Seems to me you need to set up all the linkages etc by the book. The fast idle cams shouldn't do anything with the throttles closed, and 'choke' not in use.
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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Tue Jan 29, 2019 2:40 pm

DaveEFI wrote:
Tue Jan 29, 2019 1:36 pm
Seems to me you need to set up all the linkages etc by the book. The fast idle cams shouldn't do anything with the throttles closed, and 'choke' not in use.
Tried that Dave.On the bench it all looks lovely and per the book.I was well chuffed and thought I'd just drop them back on and everything would be sorted.But fitted to the car the idle screws need to be backed out more than the one and a half turns specified in the manual to get a tickover .Which holds the throttle open and stops me from dialling in a tickover below 2000 revs.That's when the bush mechanic in me kicked in.I know it's a bodge but it's the one I used to get this thing running for when the snow hits.Quite how the cold start got like that I do not know unless the new throttle spindles are machined incorrectly or the replacement throttle plates themselves are allowing the throttle arm to move further than before.I don't much feel like stripping them again to replace the old throttle plates to check.Not this afternoon anyway. :)

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by Mc Tool » Wed Jan 30, 2019 9:00 am

I'm remembering the hassles I had with a duff pcv I had ( 2l ohc ford engine ), idle all over the place depending on just how open the valve was stuck at the time.
Is there a crankcase leak allowing air into the case (like intake gasket ,dizzy o ring ect ) and thusly allowing a bit of air flow thru the carnkcase and on to the intake side of the throttle plates . I'm thinking something along these lines may explain why it's a bit erratic /temp related. Maybe even a bit of excessive blow by in one pot ( sticky ring,
comp test? )😊
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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Wed Jan 30, 2019 2:03 pm

Thanks Hamish.Yep,it's a bit of a weird one.All worth thinking about.

If it wasn't minus something out there I'd go and have a look again.It drove ok yesterday apart from a strange misfire/backfire on closed throttle which I believe is what the poppet valves are meant to combat.Then again it could be the new dizzy farting about (not a top quality one going on price). or the mixture being wildly out.It's an old engine with a nice coat of black death inside and three fairly worn cam lobes at the back so it's not like I'm starting from the front page of an SU tuning book.You know the old engine,ignition,etc must be in tip top order before commencment.I can guarantee that it isn't.Got photos to prove it.My avatar is the "rebuilt" engine I bought to just drop in last year. :D

I'd like to whip them off again and check out this throttle/cold start relationship because it ran fine with that set up previously.So something has changed in that relationship during the rebuild and I'd like to find out what.Why the tickover screws are jsut about all the way out is still unansered.I've bush mechanicked it into running but I'd like to mechanic it properly if possible.Or I could just go and rebuild one of the other engines......

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Tue Feb 12, 2019 6:00 pm

The cool off period went well.I have returned to action. :laser:

Well it turns out I wasn't far wrong about the throttle plates.The flat set I fitted from my other HiF44s are a fraction smaller on the vertical plane allowing them to close further,by quite a bit actually, and interfere with the fast idle cam.I measured them horizontally but not vertically before I fitted them I must admit.I'm guessing they're a racing mod as the carbs they came off have no cold start assembly fitted and so didn't have interference from it.So I've refitted the new replacement poppet plates and the throttle all works together now and rests in the correct place (as indicated by the oil stains and carbon).I'll refit and test tomorrow hopefully.
Attachments
flat plate.JPG
Flat throttle plate closed (no idle screw)
poppet plate.JPG
Poppet throttle plate closed (no idle screw)

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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by jagger » Sat Feb 16, 2019 3:30 pm

Well that put paid to seeing if the carbs were set up right this time.Wondered why it wouldn't start.Looks like it shed a bit from the dizzy worm drive so carb tuning is the least of my worries. :D


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Re: SU HiF6 weird problem on a 3.5 Rover.

Post by scudderfish » Fri Feb 22, 2019 9:42 am

That'll certainly make tuning an interesting challenge :)

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