Last request for help! Sorry for long post...

The dear old Series let me down big time last weekend on an event, so this weekend I am trying to sort it out but with no success.

2.25 Petrol. Carburettor - BM Parts (Bearmach?) Zenith pattern, replaced original carb about 6 months ago, has run fine up to now, idled at +/- 500 rpm like a sewing machine, although has always popped back a lot through the exhaust on long downhills. Slight blow at manifold/exhaust joint after fitting new exhaust. Carb has done about 2K miles, averaging 18-20 mpg.

Symptoms - engine hot with lots of slow driving & idling (temp gauge below half as normal tho), suddenly refuses to idle and stalls. Only able to get it running by increasing idle speed to silly amount, and even then it was racing up and down and stalling without any intervention from me. I'm suspecting a big air or internal fuel leak, so yesterday I -

  • dismantled carb and did the "Zenith fix" - flatted the top/body mating surfaces back to 100% flat and mirror finish (and boy did it need it - top and body were badly warped and the surfaces apparently machined with a chainsaw). Could get a 1mm feeler between top and straight edge at several points before I started
  • attempted to seal the redundant passage in the body as noted on several "how-to" websites, only on this version of the carb there wasn't one
  • set float height to 33mm as per book (this may need adjusting 1mm or so as I have removed metal from the top and body, but it should be the basis for a running engine I reckon)
  • blew through all jets with airline
  • checked fuel pump delivering - yes it was
  • sealed air cleaner to carb flexible pipe with gaffer tape where it was deteriorating
  • cleaned and remade all joints on assembly with smear of orange Hermetite (manifold/adaptor/carb) as well as correct gaskets
  • broke and remade manifold/exhaust joint with Firegum - now no blowing at all.

It now runs better (in that it will at least run unattended) but only with a high idling speed, and the revs are still chasing up and down with a noisy patter from the exhaust. If I try to reduce the idle to something normal, it just waits a bit and then dies. It's still obviously VERY WRONG. Medium and high speed running is (and always was) fine.

I have now totally run out of ideas. Can anyone suggest anything else before I a) shell out 150 notes for a Weber, b) start looking for a diesel transplant, or c) let the dog have a go on the basis that he can't do any worse than I have?

All suggestions gratefully received. If you've read this far, thank you for staying with me :-)

Reply to
Richard Brookman
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so Richard Brookman was, like...

Forgot to say - also altering the idle air adjustment screw has no effect. All the symptoms of an air leak, bit where?

Reply to
Richard Brookman

Inlet manifold? Try squirting some wd40 around the inlet... though not too much and beware of the risk of fire. The idea is that the WD40 will momentairily plug any leak and it would run fine. Another trick is to stick one end of a rubber hose in your ear hole and use the other stethascope stylie to snif around the carb joints and inlet manifold joints for a leak. To get the idea of what your listening for try it next to the intake. Any leak will sound similar but lesser IYSWIM.

I had this on an Old sierra replacement engine. After 2 weeks of trying to sort it I gave up and began to break the engine down into parts to sell. As I removed the carb plate (after trying the head gasket twice on this replacement engine) I saw a large tear in the inlet manifold where the guy who I bought the engine from had clearly used the inlet as a point to hoist the engine out of the donor. It was covered by an accelerator cable plate so you couldn't see it.

I also had varying revs on a V8 at idel casused by a holed diaphram in the advance retard unit. Try bolwing / sucking on this pipe to check if it's holed.. If you go purple or suffocate then it's fine.

Other than that I'm stuffed for ideas too.

Lee D

Reply to
Lee_D

On or around Sun, 3 Jul 2005 13:48:25 +0100, "Richard Brookman" enlightened us thusly:

[snippage]

definitely sounds like an air leak. manifold-to-head joint, manifold-to-carb joint... is the carb mounted on a plastic or other insulating block?

as lee said, you can get air leaks in the dizzy unit.

Has it got a brake servo? if so, is the pipework and servo itself sound?

Check also that no plugs have unscrewed and disappeared from the manifold.

Reply to
Austin Shackles

so Austin Shackles was, like...

Possibly manifold to head, although why that should suddenly start to leak I can't think. Manifold to carb is belt-and-braces sound. Yes, the carb is mounted on a plastic insulator, also in good condition.

I've tried, honest, but I can't get my head far enough under the bonnet to suck the pipe! However, I've run it with the vacuum advance disconnected (very lumpy) and when you reconnect the pipe it perks up a couple of hundred rpm, so the dizzy diaphragm would seem to be OK.

No servo.

Visual check suggests everything OK - no cracks in manifold, and all plugs present and correct. There is one empty screw hole in a raised boss just behind the carb mounting, but there's no sign it's lost anything recently, and blanking it with a finger makes no difference.

By process of elimination, it's got to be something with the manifold, or else the almost-new carb is shot beyond redemption. I guess the manifold is the next victim of my attentions.

Thanks for the help.

Reply to
Richard Brookman

so Lee_D was, like...

Good idea - I'll give that a go. I've tuned enough twin-carb setups on bikes to know what I'm listening for.

This wouldn't account for a failure while running, though, or would it? I'm more inclined to look for heat as the culprit (eg warping), hence the lapping of the carb faces.

If I can work out a way to get my head between the carb and manifold I'll give this a go.

Glad it ain't just me then!

Cheers for this.

Reply to
Richard Brookman

On or around Sun, 3 Jul 2005 20:12:09 +0100, "Richard Brookman" enlightened us thusly:

gasket can fail, and generally they do this relatively suddenly. consider how an exhaust can be fine one minute and noisy the next...

Reply to
Austin Shackles

Inlet manifold occurred to me too, as this was the cause of the undiagnosable problem on the 101. But the symptoms seem wrong - it runs well at higher revs / loads. The 101 would idle fine off load, but as soon as you tried to rev it it would die - just ran too lean and stalled.

Is compression even across the pots?

Are all the ignition bits in good fettle?

Reply to
Tim Hobbs

so Tim Hobbs was, like...

Haven't done a compression test, no - would uneven cylinders give these symptoms?

All ignition parts were renewed and set correctly a few months ago, and it has run fine since then - until last weekend! I also checked/adjusted the tappets as part of the exercise yesterday.

I took it for a decent run this afternoon and it drives like a nightmare! Pulling up a steep hill is the only time it feels right. In top gear, with no throttle (on a straight and empty road, natch) it was doing 30mph on one occasion - ulp - and then 200 yards later, same trick, it would slow to walking pace and then die.

I'm absolutely certain it's an air leak (what else can it be FGS?) but I've done everything I know. I spose the next step is to take off the manifold and start checking the solid bits.

Thanks for the post.

Reply to
Richard Brookman

Have you checked with a dwell meter? If it was an air leak it would be ropy all the time and certainly not pull well under load. The dizzy shaft wobbling about can cause your sort of problems. As can a closed contact breaker gap.

AJH

Reply to
sylva

so snipped-for-privacy@despammed.com was, like...

Another line of enquiry! Thanks for this. Too dark now, but I'll have a look tomorrow. I know I should have checked these, but...

Reply to
Richard Brookman

That sounds very much like an inlet leak. Runs progressively leaner, and your natural instinct is to press the pedal harder which makes the problem worse.

Reply to
Tim Hobbs

In theory yes, although the 101 would run really well for about 20-30 minutes, then it would slowly die away. Stop for 10 minutes and it would cure itself. Then run fine for 5 minutes, then stop for 10 minutes. Then run for 2 minutes and so on, until give up and call RAC. All the whlie it would idle absolutely fine and even.

In fixing the 101 we found a badly knackered dizzy and thought we'd cracked it. Then a split diagphragm, thought we'd cracked it. Claggy fuel filter sock - thought we'd cracked it. Every time, no better...

Richard - you'll have the best sorted broken down Landy in Britain before you finish! Good luck.

Reply to
Tim Hobbs

Have you tried running it with the air cleaner hose off? An internally collpased hose can do this, as can a silted-up air cleaner (give it a damed good clean-out, the silt in the bottom can do a very good impression of looking like its meant to be there).

Richard

Reply to
beamendsltd

On or around Sun, 03 Jul 2005 22:24:38 +0100, snipped-for-privacy@despammed.com enlightened us thusly:

I've had engines with air leaks that run OK at higher throttle openings, mind. depends on the carb and how much fuel it delivers, also, the inlet leak is worse under over-run or idle conditions when the inlet depression is greater. Put a vacuum gauge on it; that's what identified the fault on mine.

Reply to
Austin Shackles

so Tim Hobbs was, like...

No, pressing the throttle makes it run as normal - from about 1/3 throttle upwards it's fine. It's the idle (and the driving around at or near zero throttle - which is quite a lot in town and on slowish roads) that's the problem.

Reply to
Richard Brookman

so Tim Hobbs was, like...

Ah - that's the very thing mine *won't* do.

Thanks, Tim - we aim high here.

Reply to
Richard Brookman

so beamendsltd was, like...

Yes

When the problem first arose, taking the air cleaner hose off the carb killed it stone dead. After my attentions at the weekend it will run with it on or off - no difference. The hose was full of holes anyway (hence my email to you), but I gaffered it up to be on the safe side.

Reply to
Richard Brookman

On or around Mon, 4 Jul 2005 19:09:44 +0100, "Richard Brookman" enlightened us thusly:

opening the throttle makes less inlet manifold vacuum, thereby sucking proportionally less air through the leak, and at the same time delivers more fuel.

On the engine I had with inlet manifold problems (1500 ford), it had an aftermarket manifold which had thinner flanges than the standard exhaust manifold. This manifold, though, allowed of mounting the twin-choke carb from the GT version. However, the manifold had half-holes and shared half it's mounting bolts with the half-holes on the exhaust manifold. Which was fine if using the original manifold. addition of some spacers once I'd eventually worked out what was wrong made it seal fine and solved the problems.

Reply to
Austin Shackles

Hi Richard,

Had a similar problem before, after a lot of trial and error I replaced the condenser - sorted mine out, funny thing was it had only been replaced three weeks before!

Cheers

Mac

Reply to
Mac Harris

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