Series 3 Carb problems

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TheMegaMan

TheMegaMan

Well-Known Member
Posts
516
Location
Cambridge
Been out for the longest run in the Landy today, since it's been back together. Unfortunately, I had a few running issues that I think are carb (Weber) related, but I'm not entirely sure...and I suspect actually at least 2 separate problems.

Firstly, when letting it drop back to idle, it's 50/50 whether it stalls or keeps running at 1200 or so revs. If I wind the throttle stop down any further (since 1200 is a bit high), it pretty much invariably dies. I'm having to keep blipping the throttle to be sure to keep it running when pulling up at junctions. Landy pedals are not exactly set up for heel and toeing! Dirt in the idle jet?

The other problem I had was after trundling along at a reasonable speed for a few miles, I started getting a misfire, which got successively worse the further I went. On the overrun, I was getting some serious popping and banging from the exhaust - some proper backfires. Applying the throttle again, it really coughed and spluttered again and only just pulls. Runs slightly better at higher engine speeds than low, but definitely misfiring throughout.

I stopped for a few minutes, check dizzy cap, etc, didn't see anything wrong so set off again, and it was OK for a while (still had the unpredictable idle speed issue), but it started doing it again.

Possible fuel vaporisation issue? Engine was hot, but not excessively so, and it was a cool day, so if that's the problem, I'm not going to be able to go anywhere in the summer. What else could it be?

Cheers!
 
I had various problems with carbs, Weber erratic idle, Zenith flat spots and lack of power. Finely fitted SU initial problems with icing but made a shroud that fitted over exhaust manifold and now runs sweet. It pulls from idle and is much more responsive.
I think the problem is that there are to many cheap copies of carbs that would be suitable if the quality was some where near the original spec.
 
I don't know much about webber carbs but is the air-fuel mixture set correctly, that might account for the erratic idle. Pull a couple of spark plugs out and check the colour. Are you still using the points and condenser because modern condenser are pretty rubbish, that's why I went to electronic ignition. Have you put some lead additive in your petrol? It took me weeks to sort out the bad running with mine and it was a mixture of the three things above.

Col
 
TheMegaMan said:
Been out for the longest run in the Landy today, since it's been back together. Unfortunately, I had a few running issues that I think are carb (Weber) related, but I'm not entirely sure...and I suspect actually at least 2 separate problems.

Firstly, when letting it drop back to idle, it's 50/50 whether it stalls or keeps running at 1200 or so revs. If I wind the throttle stop down any further (since 1200 is a bit high), it pretty much invariably dies. I'm having to keep blipping the throttle to be sure to keep it running when pulling up at junctions. Landy pedals are not exactly set up for heel and toeing! Dirt in the idle jet?

The other problem I had was after trundling along at a reasonable speed for a few miles, I started getting a misfire, which got successively worse the further I went. On the overrun, I was getting some serious popping and banging from the exhaust - some proper backfires. Applying the throttle again, it really coughed and spluttered again and only just pulls. Runs slightly better at higher engine speeds than low, but definitely misfiring throughout.

I stopped for a few minutes, check dizzy cap, etc, didn't see anything wrong so set off again, and it was OK for a while (still had the unpredictable idle speed issue), but it started doing it again.

Possible fuel vaporisation issue? Engine was hot, but not excessively so, and it was a cool day, so if that's the problem, I'm not going to be able to go anywhere in the summer. What else could it be?

Cheers!
Click to expand...

Could be the carb. On the other hand, it could be the timing.

A few thing to check are, parts quality, old stock Lucas caps, points, capacitors, etc. are often rubbish. New Lucas the same. Try and source Bosch parts, still made in Germany.
Also, timing set to the standard marks with a strobe light may not work now, due to unleaded fuel, and wear in the distributor drive. Try setting final timing by ear, or using a dwell meter.
 
Thanks for the suggestions.

I neglected to add that I'm running electronic ignition, so shouldn't be a condensor/points/dwell issue. I did wonder whether the dizzy was loose, and had moved (was the first thing I checked when I first stopped), but it was all good, and if it had moved, it wouldn't have recovered itself, would it?

Yes, using Redex RDX18 additive.

The idle jet was set my the MoT tester when it was on the exhaust analyser during MoT, so it *should* be OK. I've avoided touching that so far, but suspect I will need to.

I'll check plug colour and carb filter when it stops raining!
 
Agreed, coil could break down hot, could there be carb icing, if its cold damp weather, If the idle was set on an analyser there a good chance its too weak, carbs need a richer idle. Also look for air leaks and stiffness in the throttle linkage. I agree its probably at least two separate issues, very tricky.
Sadly you may have to doubt every new part.
 
I'm thinking too rich mixture maybe being caused by needle float valve flooding the carb.. Can yo restart immediately after stalling. Plug colour will tell.
 
Managed to take a quick look at it today.

Plug 1 looks fairly good. However, plug 2 is looking rather black. Rich or just oily? I'm a bit confused by this...something odd going on somewhere. I am losing a bit of oil, so it might be number 2 cylinder is a bit worn somewhere, and I'm burning some, rather than it all dripping out of the bottom, as I had been assuming.

Rotor arm has the brass strip set into the body of the arm, rather than glued on top. Does this mean it's one of the better ones?

It wasn't idling so well again today, so checked the idle jet (was clear, as far as I could tell) and the carb filter (also clear). The idle adjustment screw was only about 1/2 a turn from being fully screwed in. Opened it another 1/2 turn, and everything seemed pretty good...for a while. Thought I might have cracked it, so set the idle speed nicely, but then a couple of stops and starts later, the idle speed drops low enough the it just stalls. Also got some backfiring through the air filter on throttle blips.

I also noticed a strange 'rattle' from around the fuel pump/distributor area of the engine, fairly high pitched - higher than engine revolution speed. It sounded like a little metal clip rattling or something, but nothing seems loose. Does the oiled air filter make a noise when air is being sucked through it? I assume the cam drive on the fuel pump doesn't usually make a noise. I wonder whether something isn't right with the distributor...

Another idea that I will try, suggested by @kermit_rr in @jasonmarks 'Coked Up' thread, is to check the ignition timing with a timing light, and see if there is any difference between timings when it's idling well or not. It seems I can now get both behaviours just on my driveway, so I don't need to stop out on the road to do this, I hope.

I also measured the dwell angle as 22 degrees (or is that percent?) on my DVM, but I don't recall whether than was when it was running 'nicely' or not. I'll do this in a more methodically when I have enough time. 22 degrees seems very small (I recall it's usually around 45-60 degrees), but is this actually a useful parameter on electronic injection, since I can't adjust it.

RotorArm.jpg
Plug1.jpg
Plug2.jpg
 
It could be a ropey plug lead on No2 cylinder. Clean the plugs, swap No2 lead with another one and go for a spin. Pull the plugs and see which if any are black. Might be a duff plug. Also check tappet clearances, check inlet manifold & carb base for air leaks and check the exhaust manifold and exhaust for leaks. Let us know how you get on.
 
TheMegaMan said:
Managed to take a quick look at it today.

Plug 1 looks fairly good. However, plug 2 is looking rather black. Rich or just oily? I'm a bit confused by this...something odd going on somewhere. I am losing a bit of oil, so it might be number 2 cylinder is a bit worn somewhere, and I'm burning some, rather than it all dripping out of the bottom, as I had been assuming.

Rotor arm has the brass strip set into the body of the arm, rather than glued on top. Does this mean it's one of the better ones?

It wasn't idling so well again today, so checked the idle jet (was clear, as far as I could tell) and the carb filter (also clear). The idle adjustment screw was only about 1/2 a turn from being fully screwed in. Opened it another 1/2 turn, and everything seemed pretty good...for a while. Thought I might have cracked it, so set the idle speed nicely, but then a couple of stops and starts later, the idle speed drops low enough the it just stalls. Also got some backfiring through the air filter on throttle blips.

I also noticed a strange 'rattle' from around the fuel pump/distributor area of the engine, fairly high pitched - higher than engine revolution speed. It sounded like a little metal clip rattling or something, but nothing seems loose. Does the oiled air filter make a noise when air is being sucked through it? I assume the cam drive on the fuel pump doesn't usually make a noise. I wonder whether something isn't right with the distributor...

Another idea that I will try, suggested by @kermit_rr in @jasonmarks 'Coked Up' thread, is to check the ignition timing with a timing light, and see if there is any difference between timings when it's idling well or not. It seems I can now get both behaviours just on my driveway, so I don't need to stop out on the road to do this, I hope.

I also measured the dwell angle as 22 degrees (or is that percent?) on my DVM, but I don't recall whether than was when it was running 'nicely' or not. I'll do this in a more methodically when I have enough time. 22 degrees seems very small (I recall it's usually around 45-60 degrees), but is this actually a useful parameter on electronic injection, since I can't adjust it.

View attachment 238552 View attachment 238553 View attachment 238554
Click to expand...
Have you solved this problem yet? What was it?
 
No progress yet, unfortunately. I've actually been away from home (shock, horror!) visiting family for my girlfriend's birthday. Felt strangely uncomfortable...

Anyway, before doing much else. I intend to take the rocker cover off sometime - possibly this week - to check the tappets. I'm hoping those are just a bit screwey, as I've never checked them. Worth getting those right before spending too much time on anything else, I think.
 
I went 35miles from home the other day, felt right odd.
The two plugs you have look ok, the tips ar a nice light brown and given a decent run the rest of the head [ of the plug ] would most likely be the same
Have yoy done a compression test ?
 
Last edited:
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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