faltering engine

[eth]

My 1098 traveller is faltering severely like im going too slow in too higher gear, it occours at about 1750 to 1900rpm (guessing, no taco).

So far to remedy the problem I have:

Changed the plugs and leads, plugs all nice tan and even colour
Cleaned ht cap, small amount of pitting on the poles
Strobed electronic ignition all seemed stable and correct
Compression tested at 140 to 150psi over all cylinders
Tappets set

All to no avail! Should I junk the electronic dizzy and spend ££££££ on a recon mechanical setup?

[JOWETTJAVELIN]

Seems to be a lot of this spluttering, coughing and power loss going on. Mostly it turns out to be fuel-related.

I'm doing some thinking about my own car which sometimes kangaroos only when fully warmed up. So far, after a lot of testing and ruling-out (it never is the ignition, btw), I blame poor manifold design, on the Series II at least. But then again I deliberately allowed the water to reach 90c, took it for a long drive and nothing at all went wrong.

[eth]

Im reluctant to diagnose fuel problems for the reason that it only happens at a very confined rpm range and the su carb only has one jet, I think? Once your going she goes well. It reminds me of my old yamaha yb100 when the copper contact the point was riveted to fractured around one of the points causing a miss in sympathy with rpm. It took months to find the fault. I should have just changed them out of principle, lesson learned but I dont have that option as I have no points. I have two more ideas 1. The coil has taken a bash at some time and has a deep dig in the case could this be suspect? 2. When I purchased the car sept last year it had 4! Rotor arms in the glove box . . . Should I be suspicious?

[JOWETTJAVELIN]

Now that you mention the coil has taken a bash then yes, this could have upset the windings. You say you have an electronic ignition kit fitted, so there won't be any cb points to worry about.

Unless someone without a clue has installed the elec. ignition, consider the 4 rotor arms lucky spares.

[bmcecosse]

It's 'never' the coil...........it either works - or doesn't. Carb piston rising and falling as it should? Oil in the damper piston? Air cleaner clean? Could well be faulty advance curve on the ignition - does the vacuum advance work ?

[eth]

The carb seems fine, I inspected the slide and topped up the oil just this morning before juddering and shaking my way to work. Unsure if the vacuum advance works I could not detect any change in engine note when sucking on the pipe and forgot to check when I was strobing it. I would like to swap over a known working dizzy before I waste £80 or more on more unnecessary parts. I found from experience disconnecting the vacuum all together and running it had a negligible effect on performance I don't think it alters the timing all that much

[bmcecosse]

It does make a big difference - so disconnecting it should show an effect. Sounds like it's not working. Strobing is a waste of time - adjust for smoothest idle, then road test to make sure it's not pinking.

[eth]

I agree that the vacuum advance could be faulty but disagree that strobes are rubbish. Being all but deaf i dont stand a chance of hearing my engine gently pinking so have little other option than to strobe it. Logically i cant see it being the vacuum advance because the only way to coax her past the faltering is with more throttle which should surly make the problem worse if that was the case.

[liammonty]

I'm inclined to agree that it's ignition related- not fuel. The SU rarely gives any bother like you describe (not like Webers and other fixed jet carbs). I don't reckon a faulty vacuum advance is the issue either- it would be most noticeable when trying to accelerate using light throttle openings at lowish speeds, in my experience, causing a momentary hesitation which then clears. It won't cause hesitation when running at a constant speed, so I'd be surprised if it was that. I think it's definitely worth changing the rotor arm, as the ones that are available these days are know to be utter c**p and are prone to arcing, I believe. The following link is to a supplier of decent quality parts (including rotor arms) for Lucas distributors, that might be useful :

http://www.distributordoctor.com/red-rotor-arms.html

Also, just because you've got electronic ignition, don't rule that out as the problem- it might be worth swapping back to points and condenser to rule it out as the problem if nothing else works... Good luck!

[eth]

i have already purchased a new rotor arm, just waiting for it to arrive. As for electronic ignitions i dont trust them as far as i could throw one whilst still attached to an a series. I'm very reluctant to spend out on a recon mechanical dizzy until i know the old one is at fault.

[liammonty]

Shame you can't borrow a dizzy... Didn't realise you had an 'electronic dizzy' as such- I'd assumed it was a standard one with an electronic conversion hall sensor thingy (like an Aldon Ignitor) in it- hence suggestion of changing back to points etc to test it. Good luck with the rotor arm!

[bmcecosse]

You can strobe away for all your worth - but what will you set it to?? Any figures posted 40 years ago are irrelevant now - today's fuel is so very different. If the vac advance is not working - then the ignition timing at idle will have to be set much too far advanced to compensate - and will be very wrong when running - especially at lower revs...... Test the vacuum advance.....

[eth]

Fair point about timing and modern fuels but has anyone invented an electronic/mechanical ear for the deaf to detect pinking ... thought as much lol. I have been offered a spare dizzy and coil for a MGB 1.5l would this be interchangable? In the meantime i will have to test the vacuum advance.

[liammonty]

The vacuum advance won't actually make much difference at all at idle- the take-off is blanked by the throttle plate... However, it would make a big difference at low revs at light to mid throttle, but none whatsoever at full throttle. Still don't reckon it's the problem though- Coopers, Marinas and numerous other vehicles have run without it! It helps pick-up and economy hugely, but its absence shouldn't cause 'bad' running per se, just less efficient. Definitely worth checking to rule out however. I did wonder- I had similar symptoms to those you're experiencing due to the vacuum advance hose splitting, which meant the mixture was leaning out hugely as the carb was sucking in loads of air it shouldn't have been- check for air leaks whilst checking the advance is working.

BTW, I got my old DM2 refurbed (with 25d innards) as I needed it recurving after I built a new engine, and it's great. Cost a small fortune though, so don't do it unless you know that's the problem! Regarding the MGB dizzy- I think pretty much any 25d or DM2 (or 45d) will fit straight in (though of course the advance curve will be different, but that wouldn't matter). I'm sure somebody will say if that's not the case!

[eth]

Well thats good news, a chap at work is lending me his spares on Tuesday. On this topic has anyone produced a dizzy for the a series with an advance curve to meet the needs of modern fuels? Or would this mean having a laptop on the passenger seat, I suppose a login password would offer far better anti theft

[JOWETTJAVELIN]

If you post up your location in your profile someone local may be willing to pop round and help you out.

[bmcecosse]

I can assure you my vac advance makes a BIG difference at idle - if I take the pipe off (and blank the tube so no air goes in) the idle goes to hell. The engine starts - and the vac pulls the timing up to get a nice smooth idle - and top make the engine 'responsive' to the throttle. Almost as soon as the throttle is opened the vacuum falls away, and hopefully the engine is accelerating so the centrifugal advance kicks in. I suppose that could be the problem here - centrif advance jammed/broken spring - worth checking it out! this is where a spare/known good dizzy is handy - drop it in and see if the problem goes away!

[liammonty]

I'm sorry BMC- we'll have to disagree on this one. The HS2 carb is designed so that the throttle flap COVERS the vac take-off port at idle, reducing the signal (which would otherwise be very high at idle- complete vacuum). As soon as the throttle is opened slightly, it uncovers the port and gives a signal, which is obviously greatest just off idle, and tapers off as revs are increased (and vacuum is decreased). My 1030 engine's got a late HIF38 fitted, and that does give full vacuum advance at idle, as the vacuum take-off is positioned on the manifold side of the throttle, but NOT blanked off at idle. This was what BL did later to try and improve emissions at idle on Metros. Anyway, until you get your 30 year old strobe out of it's box and use it, how do you actually know what the advance is doing at idle anyway? BTW, blanking off the vac advance on any of my cars (Minors or VW) results in brief hesitation pulling away, and a slightly 'flatter' engine, but makes no difference to the idle, as long as there is no air getting in to the carb.

I can't believe I'm going on about this- it is far too dull. Just hope the OP gets his car sorted!!!

[bmcecosse]

I well know what the HS2 is 'supposed' to do with the vacuum - but it's not exactly a seal (especially if the carb has done a few miles) - and it does leak through and pull up the idle . Take the hose off at the dizzy and feel for the vacuum ! In any case - I described how MY engine responds to disconnectiong the vacuum at idle - and I have an HIF 38..... But I can assure you the HS2 operates just the same - there is enough vacuum leaking through to pull up the timing - at least partially - at idle. This allows the engine to be started against relatively lowly static advance - and the vac then pulls up the timing to give a nice/smooth/responsive (and possibly emissions friendly) idle.

[eth]

Update, spent all day tinkering and succeeded in making the car useless. I started by swapping the coil, no luck. Then the carb still no luck so I swapped back, at this point the car became un drivable so swapped the carb out again fearing i had upset the original and still the same. The problem has now manifested itself such that if you sustain high revs without load the engine dies down to a splutter, more throttle it continues to splutter, less and it returns to a rough tick over. Spark testers have confirmed that its still sparking whilst spluttering. The fuel pump tested fine and have tried gravity feeding the carb also. Tappets have been checked ... re compression tested ... Tried different oils in the dash pot ... swapped ht leads ... checked for air leaks and then I ran out of ideas and day light. Emoticons cant describe how I feel right now, I'm at a total loss.