Engine rough idle, won't rev
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Khaki Rover
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Location: Scottish Borders

PostPosted: Mon May 07, 2018 5:04 pm    Post subject: Engine rough idle, won't rev Reply with quote
Need some advice on solving a rough running problem. The engine will start reluctantly and idles roughly, but won't rev at all and generally coughs and spits when I press the accelerator. It feels like fuel starvation, but I can't find the cause.
When this first happened (luckily only 1/4 mile from home) I thought the fuel pump had died so I replaced it, but it made no difference. So I took the carb off (Zenith copy) and checked it - main jet is clear, float valve isn't stuck, there's a spray of fuel down the carb when I open the throttle. The inline filter looked a bit dirty, so I cleaned it. The pick up pipe in the tank is OK - it's a military under seat tank so easy to check. And yes, there is fuel in the tank...
The primer lever seems to work on the fuel pump.
I've also checked the ignition - plugs are clean, points are new and gapped, condenser new, static timing on 6 BTDC (can't set it dynamically as it won't idle well enough), distributor cap & rotor ok, HT leads are new. Tried a different coil.
I had the mainfolds off in case there was an air leak (they were replaced a few weeks ago), but nothing obvious wrong. I even did a compression test as I was starting to fear the worst, but the readings are all the same and about right for a 7:1 engine.

Sorry this has been a bit of an essay, but I'm out of ideas. Any suggestions for things to try would be much appreciated!
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Alan Drover
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PostPosted: Mon May 07, 2018 5:26 pm    Post subject: Reply with quote
Evening Khaki Rover.
As you've checked everything else the fault is almost certainly the carburettor. Many years ago I fitted one in an emergency and even with the air bleed screw screwed right in the engine still ran very rich when it should have stalled.
The problem with Zeniths especially the cheap copies is the quality of the castings. If the two castings do not meet properly due to the top one warping, air gets in and the carburettor floods. I was so fed up with the poor quality of these Zenith copies that I collected 5 from my mate who had a load of spares and when I could afford it I would get them remanufactured one at a time by BFS in Salisbury. The first one was done about 9 years ago and is performing faultlessly on my 2.5 petrol engine.
The best thing to do is to try and find a genuine Zenith and get it rebuilt or get a Weber conversion but they can be troublesome and performance suffers.
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Alan Drover.
1975 SWB hardtop with a 2.5 petrol engine, overdrive, front disc brakes, parabolic springs, hand throttle, Defender doors and Wolf wheels.
Also a 1977 Stage 2 MGB GT.
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Khaki Rover
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PostPosted: Mon May 07, 2018 5:56 pm    Post subject: Reply with quote
Evening Alan,
Thanks, I heard the Zenith copies were sometimes poor quality, but it was already fitted when I got the Landy, so I left it. I could never get the idle right - one day it would be 700 RPM and the next 1100 RPM so maybe I should have replaced it long ago.
I do have a spare Weber, but I bought it on eBay and need to check the jets are correct for the Landy before I try it. I'll get it sorted this week and see if that fixes it.
Another question: when I took the manifolds off, there was a one piece gasket for both manifolds, so I replaced it with the same, but the manual shows only two small gaskets for the inlet and nothing for the exhaust. Does that work? I'm not sure about bolting the exhaust mainfold onto the head without a gasket!
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Alan Drover
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PostPosted: Mon May 07, 2018 6:42 pm    Post subject: Reply with quote
Stick with the one piece manifold gasket. The others rely on a flat head to manifold surface, virtually impossible. Ask for Series 2 ones.
The Zeniths I got from my mate were genuine ones.
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Alan Drover.
1975 SWB hardtop with a 2.5 petrol engine, overdrive, front disc brakes, parabolic springs, hand throttle, Defender doors and Wolf wheels.
Also a 1977 Stage 2 MGB GT.
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lovejoy633
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PostPosted: Tue May 08, 2018 10:22 am    Post subject: Reply with quote
There are a lot of dodgy cheap condensers on the market. I would buy another and test it as sadly "new" does not always mean you can rule it out.
cheers
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websnail
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PostPosted: Tue May 08, 2018 2:42 pm    Post subject: Reply with quote
Idea 1,
If you think it's too lean, just pull out the choke a bit and see if it gets better.

Idea 2,
Dizzy well worn.

Idea 3,
Are you SURE all HT leads are going to the correct plugs in the correct order! (had a landy like a pig once, on 2 cylinders!)

Idea 4,
Beg, borrow or steal a 2nd carb and try that.
Good luck.
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Alan Drover
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PostPosted: Tue May 08, 2018 4:32 pm    Post subject: Reply with quote
Websnail it's definitely the cheap and nasty Chinese Zenith copy that's causing the problems as it happened when I had to buy one as an emergency purchase. If you think of it a complex piece of equipment like a carburettor, which is manufactured then shipped halfway across the world and sold for around 50 or so. The quality has to be non existent. Other terms spring to mind but they wouldn't be allowed on this forum.
BFS in Salisbury once told me that they would have liked to have manufactured new Zeniths but they couldn't find any company who could make the castings to the correct specifications so the only way to get a proper Zenith is to have an old one remanufactured. That's what I did with the ones I got from my mate who used the break Land Rovers. In a bit of a garage clear out today I found another remanufactured one that I didn't know I had.
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Alan Drover.
1975 SWB hardtop with a 2.5 petrol engine, overdrive, front disc brakes, parabolic springs, hand throttle, Defender doors and Wolf wheels.
Also a 1977 Stage 2 MGB GT.
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Khaki Rover
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PostPosted: Wed May 09, 2018 7:37 am    Post subject: Reply with quote
Thanks everyone for the suggestions. I'll spend some more time this weekend trying to get the beast to run. I do have a spare Weber carb, so I'll try that once it's had a quick clean-up. I'll see if I can get another condenser too.
I think the HT leads are in the correct order - I didn't change anything from before, but I'll double-check this too.
I'll keep you posted...
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Alan Drover
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PostPosted: Wed May 09, 2018 11:30 am    Post subject: Reply with quote
Khaki Rover.
Best place to get any ignition parts is from the Distributor Doctor. He doesn't sell cheap unreliable rubbish that is prolific on the internet.
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Alan Drover.
1975 SWB hardtop with a 2.5 petrol engine, overdrive, front disc brakes, parabolic springs, hand throttle, Defender doors and Wolf wheels.
Also a 1977 Stage 2 MGB GT.
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Khaki Rover
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PostPosted: Tue May 15, 2018 7:10 am    Post subject: Reply with quote
Morning all,
Quick update: turns out the problem was the points/condenser. I fitted my spare Weber and it was no better, so I re-checked the ignition and found the points had burned out. I did change them early on in the process, but I only had a cheap set spare and it seems they were rubbish. So with new points and condenser, all is well.
I decided to leave the Weber on for now and see how it goes. I spent some time replacing the jets and generally tidying it up, so it's probably a better option than the Zenith copy.
Thanks everyone for your help - I guess it's another lesson about the dangers of cheap parts...
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websnail
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PostPosted: Tue May 15, 2018 7:25 pm    Post subject: Reply with quote
Glad you're sorted.
Rubbish parts, not for the first time have wasted time! Confused
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Previously my daily drives:
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lovejoy633
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PostPosted: Thu May 17, 2018 7:07 pm    Post subject: Reply with quote
Those symptoms you had are very obvious results of a failed/dodgy condenser which can then burn out your points.
I have had these problems with my spitfire before.
Normally I am a fan of originality and don't do upgrades,
but after so many dodgy condensers on the market, I went for electronic ignition, which all fits inside the dizzy cap.
I have to say, I've never had a problem since........but I do still carry the points and condenser in the glove box just in case.
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Alan Drover
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PostPosted: Thu May 17, 2018 8:25 pm    Post subject: Reply with quote
Evening Khaki Rover.
I was wrong in my diagnosis of the problem as you said the points and condenser were new. Years ago I had to buy a cheap distributor in an emergency and the points lasted about 10 minutes before the heel wore out and closed the gap. I got the correct distributor from a breaker and had it rebuilt by the Distributor Doctor.
I agree with lovejoy633. Go for electronic ignition but don't buy the cheap and nasty rubbish on the internet. You can get ones that fit inside the distributor. I have a Pertronix on my Land Rover and Lumenition Magnetronic fits inside the distributor too. Once fitted and set up no adjustment is necessary and the only maintenance needed is to check the carbon brush inside the cap and the occasional drop of oil in the distributor. What year is your Land Rover?
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Alan Drover.
1975 SWB hardtop with a 2.5 petrol engine, overdrive, front disc brakes, parabolic springs, hand throttle, Defender doors and Wolf wheels.
Also a 1977 Stage 2 MGB GT.
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Khaki Rover
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PostPosted: Fri May 18, 2018 12:36 pm    Post subject: Reply with quote
Afternoon Alan,
It's a 1979 with the Lucas 45D4 distributor. I had been thinking about electronic ignition and now seems like a good time to try it. I actually have an electronic ignition module that I built from a kit years ago (these were very popular back in the 80s when lots of cars still had points) but I never fitted it. It uses the points with a power transistor to switch the coil, so it's easy to go back to the original setup if the electronics fail for some reason. I'll see how that performs, but I like the look of the Magnetronic and Pertronix as they fit inside the dizzy and keep the original look.
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Alan Drover
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PostPosted: Fri May 18, 2018 3:58 pm    Post subject: Reply with quote
Khaki Rover.
Somewhere in my box of bits I have a Lumenition Magnetronic. I bought the but it doesn't fit my 45D4 as it is the latest version for the 2.5 engine and has the sliding points. I'll dig it out. Your 45D4 should have points with a red heel, mine were blue.
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Alan Drover.
1975 SWB hardtop with a 2.5 petrol engine, overdrive, front disc brakes, parabolic springs, hand throttle, Defender doors and Wolf wheels.
Also a 1977 Stage 2 MGB GT.
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