Series 3 Carb problems

tottot said:

Have yoy done a compression test ?

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Well, I did one a couple of years ago when I was getting the engine running again before taking it out - the figures weren't particularly good. And it's then sat under a tarp until I refitted it at the end of last year, and has run around 20 miles since.

I probably should have investigated before refitting it, but the summer weather was disappearing and I really wanted to get it back on the road for the winter. So I guess I need to do some work with it in situ, instead...

Figures were, bar (psi):

Wet is with a few ml of oil squirted into the cylinder.

I should be able to take a look at it tomorrow, and will measure these again, as well as checking the tappets.

rynner said:

i bought a 'new' dizzy with the same rotor arm as yours, possibly from the same seller,it had obviously been gouged and scraped by a screwdriver and was in about the same condition as the one pictured,it was replaced after SEVERAL emails and my 88 ran ok, afterwards,
i also replaced the weber carb a while afterwards as they do wear just that made the old girl run like she had had a full service,spot on!and better mpg,
atb and good luck

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It was in reasonable condition when it arrived, to be fair, but it's sat outside for a couple of years since then. I didn't think it was that bad, but I'll give it a clean up.

The carb was also new in 2019, but also sat outside while I was rebuilding the chassis. It had certainly got a bit gunky with old fuel left in it, but I did take it apart and give it a pretty good clean at the beginning of the year. I *think* it's clean now (fresh petrol), but if you're telling me it's a float chamber problem, then I could be persuaded to take it apart and check the needle again. I certainly don't think it's worn out, as it's hardly done any road miles so far.

TheMegaMan said:

Well, I did one a couple of years ago when I was getting the engine running again before taking it out - the figures weren't particularly good. And it's then sat under a tarp until I refitted it at the end of last year, and has run around 20 miles since.

I probably should have investigated before refitting it, but the summer weather was disappearing and I really wanted to get it back on the road for the winter. So I guess I need to do some work with it in situ, instead...

Figures were, bar (psi):

Cylinder Dry Wet
1 10.1 (146) 11.0 (160)
2 9.5 (138) 10.0 (145)
3 8.8 (128) 9.5 (138)
4 8.5 (123) 8.5 (123)​

Wet is with a few ml of oil squirted into the cylinder.

I should be able to take a look at it tomorrow, and will measure these again, as well as checking the tappets.

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That is not ideal, but it should still run OK like that.
Try setting the valve clearances. If that doesn't make any difference, it might be a good idea to remove the head, take the valves out and lap them in with grinding paste, and then replace the head using a quality composite head gasket. Under no circumstances use a copper head gasket. If there is one already installed, throw it away.

Comp figures not to bad for an old series, but pressure not coming up when wet on number 4 points to poor valve seal. + 1 for Turboman's suggestion.

I didn't think the compression was _too_ bad, which is why I didn't redo the engine while it was out. But I realise it isn't perfect.

However, I now wonder whether I did that test with the engine cold. I repeated the test today after it had warmed up properly, and I got some much better figures:

Figures were, bar (psi):

So actually, I'm quite happy with that.

Reset the tappets. Checked and adjusted timing. I'm on an electronic distributor, so can't do timing statically, but I used a timing light. Am I correct in assuming this should be done with the vacuum advance to the dizzy disconnected? I've set it at TDC which I think is correct for an 8:1 engine. But as soon as I connect the vacuum advance, even at idle, it jumps to guessing around 10 degrees BTDC. Is this expected? It does seem to run smoother like that.

I should point out that it's not an original S3 engine....I think it's a 5MB engine from a 90/110 according to the 11Hxxxxxxx engine number. But the pulley seems to be completely alien. I've got my own mark on the pulley when I determined where TDC was, but I have no other angle marks to work with.

Anyway, after all this, it still wasn't running as cleanly as I would have liked, so I decided to clean the carb out again, too.

Some gunk at the bottom of the float chamber, and I'm sure all jets are now clear. But the really interesting thing is the throttle spindle. There is a tab on a linkage from the choke that holds the throttle stop slightly open when the choke is partly open. This seems to be significantly bent, such that it was never going to effect the throttle stop. So I've bent this back into position, and along with the clean up, it now seems to be running better, and I can at least adjust the idle speed slightly from within the cab using the choke. I was wondering why pulling the choke a little wasn't raising the idle speed as I was expecting it to.

No idea how this got bent. It took a fair bit of effort to straighten it out again. I'm sure it was right when I fitted it, and the only other person who's been near it would have been the MoT tester when was checking the emissions. Not sure why he would have needed to have tampered with this, though. Hmmm....

Anyway, rain stopped play, today, but it does seem better. I'll take it for a proper run sometime in the next few days to be sure.

hi there,
you have to disconnect the vacuum pipe only if you use the timing light and the running engine, if you simply use a 12V bulb with the engine stopped no. About the degrees of advance it depends, in my case with a 96 octane fuel, I have to adjust it to 6 BTDC

LA LA LAND-ROVER said:

you have to disconnect the vacuum pipe only if you use the timing light and the running engine, if you simply use a 12V bulb with the engine stopped no. About the degrees of advance it depends, in my case with a 96 octane fuel, I have to adjust it to 6 BTDC

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OK, good, that's what I thought and what I did. I was just surprised that the amount of vacuum at idle resulted in such a change in timing when I reconnected the pipe to the carb.

I may well play around with this, and adopt the 'by ear' approach. I want to eliminate the random element I seem to have in the system before doing this, though, and of course make sure I can load up the engine enough to ensure I can be sure I don't get any pinking.

Sounds like you are getting there. Bent tab a mystery but you have it doing what it should. Well worth doing a by ear check, it's the way I always did mine, with engine warm running at 1000-1200 rpm [ set on the linkage screw ] turning dizzy get to max rpm then back a tad.

in my opinion, when you have an engine that runs regularly in phase set for octane, you can give an ear adjustment to make it work smoother, but it must not have detonation problems for example already at 10 degrees, otherwise with more 'advance you may have a knocking at highest engine speed ....

So took the Landy out for a run again, today (the first time since cleaning the carb on May 28th).

The good news is that it seems to idle a lot better and more consistently than before. Plus, now the tab is back where it should be, I can trim the idle speed to bring it up a bit when it was still warming up.

However...

...I'm still getting the chronic misfire. It's fine at relatively low engine speeds, but when the engine gets to about (guessing 2500-3000rpm), the toque drops right off and if coughs, splutters and backfires. If I ease up on the throttle and apply it *really* gently, then I can speed it up a little more. Managed to get it up to a tad over 40mph top speed.

A real bu99er to diagnose this, as it's only showing up when the engine is loaded at speed. Tricky to stick a timing light on it when moving...

I'm thinking there's something wrong with the electronic dizzy, that's screwing the timing at high engine speeds.

It could be fuel starvation, but it's a very distinct change when running well to suddenly misfiring, whereas I would have expected fuel starvation to be a bit more gradual. Plus, the issue seems to occur at a particular engine speed under both moderate and heavy acceleration (although no so much when really feathering the throttle). It doesn't seem to occur at lower engine speeds when booting it really hard, which would surely use more fuel than being more delicate at a slightly higher engine speed.

Am I right in my thinking, or am I looking in completely the wrong place?

Coil?

To save me the trouble of re-reading the whole thread, did you lap the two mating seats of the carb? These new carbs are not great quality, people have found that the two halves dont mate properly and air can get sucked in between the faces. The remedy is to take it apart and use very fine emery paper on s sheet of glass to gently flatten the surfaces properly.

Col

I had a very similar problem on an old 205 I used to run, turned out to be a poor earth on the CDI.

I'm not sure if or how that would transfer to a distributor set up, but earth points can do very strange things indeed.

The coil was new, and again, I'm puzzled why there would be such a definitive cut-off with engine speed. But I guess they aren't too expensive, so will try and get a new one to swap over.

No, I didn't lap the faces of the carb, but I think there was a fairly even mark around the edge of the gasket. I'll get a new gasket and give that a try.

Earths are the cause of so many issues. I have paid particular attention to ensuring panels are all well connected, but I'll check it over again.

I'm not going to get a chance to do much with this for another week or two, but will report back when I do.

Balance weights free to move to furthest extent?
Is there an accelerator pump on that carb and if so is it functioning as it should?
Wear on throttle body where throttle spindle passes through it?
Just an idea or two.

Stanleysteamer said:

Balance weights free to move to furthest extent?
Is there an accelerator pump on that carb and if so is it functioning as it should?
Wear on throttle body where throttle spindle passes through it?
Just an idea or two.

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Is there still Bob weights in the dizzy if it’s electronic?
What about a leak in the vacuum pipe?

Hicap phill said:

Is there still Bob weights in the dizzy if it’s electronic?
What about a leak in the vacuum pipe?

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Depends on how complex the electronic ignition is. Most just replace the points and condenser with a trigger etc, but the dizzy still distributes the spark and has bob weights in it to advance the spark when needed.
More complex and far more modern systems use the computer to fire the spark through the coil packs, so no dizzy at all.
It is always worth checking the vacuum pipe to see it is properly connected at both ends and has no leaks.
But the symptoms would be different, part throttle hesitation instead of full throttle.
https://www.liveabout.com/testing-vacuum-advance-distributors-classic-cars-726193

Not been able to spend much time on this recently. I had a quick look on the driveway the other day, but it behaves impeccably when just idling and running under no load. But went for a drive again today, and it's still misbehaving.

I've not yet run through the list of things to check on here (carb lid, for example), but I'm drawing to the conclusion that it is a fuel starvation issue. It's very quickly an issue when starting off, but it's less of a problem after very gentle acceleration. Maintaining a constant road (and engine) speed when approaching a hill, causes misfires when the throttle is applied harder to keep the speed up. So I now don't think it's directly related to engine speed, but to fuel flow. I suspect the fuel pump isn't keeping up, and the float chamber in the carb is running dry under acceleration. Backing off on the throttle for a while allows it to refill, so all is well for a while until I accelerate too hard again.

So are there are tricks to checking the fuel level in the float chamber? Or how to check how well the fuel pump is coping? Where the best place to buy a good quality fuel pump (or brand) if I need a replacement?

I have a V8 fuel filter in line with my pump which might be reducing the flow, but I find it hard to imagine I'm exceeding what a V8 might want to drink. I may well experiment with a cheepo transparent filter body and bypass the V8 filter, in a hope of being able to see what's going on, although seeing this as I drive along is going to be a challenge. Bonnet off time, I think. Maybe a remote GoPro looking at the filter as I drive.

When they came off the assembly line, the petrol engined landies didnt have a fuel filter at all. Adding one changes the pressure in the fuel feed line and alters the flow dynamics slightly. Keep the filter as small as.possible and as close to the carb as.possible. Alternatively, fit an electric fuel pump.

Co!

TheMegaMan said:

Not been able to spend much time on this recently. I had a quick look on the driveway the other day, but it behaves impeccably when just idling and running under no load. But went for a drive again today, and it's still misbehaving.

I've not yet run through the list of things to check on here (carb lid, for example), but I'm drawing to the conclusion that it is a fuel starvation issue. It's very quickly an issue when starting off, but it's less of a problem after very gentle acceleration. Maintaining a constant road (and engine) speed when approaching a hill, causes misfires when the throttle is applied harder to keep the speed up. So I now don't think it's directly related to engine speed, but to fuel flow. I suspect the fuel pump isn't keeping up, and the float chamber in the carb is running dry under acceleration. Backing off on the throttle for a while allows it to refill, so all is well for a while until I accelerate too hard again.

So are there are tricks to checking the fuel level in the float chamber? Or how to check how well the fuel pump is coping? Where the best place to buy a good quality fuel pump (or brand) if I need a replacement?

I have a V8 fuel filter in line with my pump which might be reducing the flow, but I find it hard to imagine I'm exceeding what a V8 might want to drink. I may well experiment with a cheepo transparent filter body and bypass the V8 filter, in a hope of being able to see what's going on, although seeing this as I drive along is going to be a challenge. Bonnet off time, I think. Maybe a remote GoPro looking at the filter as I drive.

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Mechanical or electric pump?

Manual, will have a glass sediment bowl, might be blocked up.

Electric, can you hear it running when you switch on?