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Carb? Stuttering after a while

Posted: Mon May 25, 2020 3:56 pm
by Bornfree
Our car has not being used for 3 years or so. Started up ok this week, choke sticky, so have lubricated jet so it returns to position, when pushed in.

For the three drives we have done, car starts up and goes well, warms up and then choke can be pushed in. After about 4 miles cruising about 50 mph it runs a bit more roughly by stuttering/spluttering/juddery losing power. Pulling choke on doesn’t improve. I’ve pulled over, checked the jet needle is fully in (choke off) and checked that nothing is loose. Can then start up and all seems ok and runs ok, and we’ve got to our destination another 3 or 4 miles away. I’m a bit of a novice but wondering if the fuel mix could be changing with the engine warming up, or is there some air leakage or is there something else happening? (It’s got electronic ignition, unleaded head.) Any thoughts and help much appreciated! Thank you.

Re: Carb? Stuttering after a while

Posted: Mon May 25, 2020 4:18 pm
by ManyMinors
Firstly, have you drained and re-filled the petrol tank? If the car is still running on old fuel that could be the cause. It "goes off" fairly quickly now.

Re: Carb? Stuttering after a while

Posted: Mon May 25, 2020 5:04 pm
by MattsGPOvan
Ditto.... Put super unleaded the octane rating will last longer.😉

Also 3 years .... shame on you .... enjoy your British icon and put a smile on your face and all around you.😎.

Re: Carb? Stuttering after a while

Posted: Mon May 25, 2020 5:07 pm
by Bornfree
It had very little fuel in, so it was filled with 20 litres before we drove it again.

Re: Carb? Stuttering after a while

Posted: Mon May 25, 2020 5:23 pm
by pgp001
Driving a few miles and then stuttering and then starting OK and doing the same again.
Have you checked the vent hole in the petrol filler cap, it could be blocked and disturbing the fuel supply.

Phil

Re: Carb? Stuttering after a while

Posted: Mon May 25, 2020 8:17 pm
by Bornfree
There are some vent holes in the stainless filler cap, but none that obviously go outside, 2 inside the rubber seal, and 2 outside. I’m presuming they are connected. I can blow into the centre ones, but it’s quite hard to work out where the air is going to when your lips are in the middle bit!

Re: Carb? Stuttering after a while

Posted: Mon May 25, 2020 8:21 pm
by Bornfree
MattsGPOvan wrote:
Mon May 25, 2020 5:04 pm
Ditto.... Put super unleaded the octane rating will last longer.😉

Also 3 years .... shame on you .... enjoy your British icon and put a smile on your face and all around you.😎.

Don’t worry, someone else had kept it safe for us in their garage until we bought it. It’s going to be used!! :D

Re: Carb? Stuttering after a while

Posted: Tue May 26, 2020 1:16 pm
by newagetraveller
Remove the petrol filler cap before you go for a drive. If the problem goes away then it may be the filler cap.

Re: Carb? Stuttering after a while

Posted: Tue May 26, 2020 2:03 pm
by mowogg
Have you checked the filter in the fuel pump? It might be partially blocked and unable to keep up with the required supply?

If as suggested removing the cap does not fix it i would start to be suspicious of the coil. Do you know its history? Modern ones are often the issue

Re: Carb? Stuttering after a while

Posted: Tue May 26, 2020 2:56 pm
by simmitc
Check the air filter - has something being building a nest / spinning a web and clogging it?

Check the float chamber - is there any debris in there that could be sucked up to block the jet and then fall away again - perhaps some "varnish" from old petrol that dried out?

I would have suggested the condenser, but not if it has electronic ignition.

Re: Carb? Fuel pump? Stuttering after a while

Posted: Mon Jun 22, 2020 9:39 pm
by Bornfree
So no spiders in the air filter :) So far
loosened the petrol cap
replaced the jubilee clip on the petrol feed to the carb as it was loose and tightened it up.
changed the coil to a new one I had.

But still it goes well for a few miles, then while cruising at around 50 it stutters and loses power (choke makes no difference). So now thinking which do I look at next?

Fuel filter or carb float chamber.

I did have a look at the nut on the fuel filter a couple of weeks ago but couldn’t budge it, but perhaps I need to have another go?

Pros and cons for next thing to rule out please?

Re: Carb? Stuttering after a while

Posted: Tue Jun 23, 2020 6:28 am
by Murrayminor
Bornfree wrote:
Mon May 25, 2020 5:07 pm
It had very little fuel in, so it was filled with 20 litres before we drove it again.
That could be the problem.
A vehicle that's laid up for a lengthy period with an empty fuel tank can develop rust inside the tank, you filling it up with fresh fuel can dislodge the rusty particles and even flakes.
When you are running it from cold everything has settled to the bottom of the tank, as you drive the contents are shaken and stirred so your fuel pick up could be getting partially blocked by rust therefore causing the symptoms you describe.

A clean of the fuel system my be in order.

Re: Carb? Stuttering after a while

Posted: Tue Jun 23, 2020 6:28 pm
by Bornfree
Mm could be. I got the filter out of the pump today and it's very clean, although not cylindrical, a slightly twisted shape.
IMG_20200623_173235495.jpg
Su pump filter
IMG_20200623_173235495.jpg (2.77 MiB) Viewed 645 times

Re: Carb? Stuttering after a while

Posted: Wed Jun 24, 2020 9:57 pm
by noidea
does the pump run fast when it happens

Re: Carb? Stuttering after a while

Posted: Thu Jun 25, 2020 5:25 pm
by Bornfree
noidea wrote:
Wed Jun 24, 2020 9:57 pm
does the pump run fast when it happens
To be honest I've not noticed any change in the ticking I can hear.. I think I need to take it out for another run and listen carefully. Are you thinking it's pushing too much fuel through to the carb?

Re: Carb? Stuttering after a while

Posted: Thu Jun 25, 2020 9:35 pm
by noidea
MINE IS DOING THE SAME BUT RUNS VERY FAST WHEN ENGINE IS HOT .BEEN TOLD THE TANK NEEDS CLEANING MINE HAS ALSO STOOD FOR A LONG TIME

Re: Carb? Stuttering after a while

Posted: Fri Jun 26, 2020 1:35 pm
by newagetraveller
Dirt in the float chamber?

Ignition coil breaking down in the hot weather?

Re: Carb? Stuttering after a while

Posted: Fri Jun 26, 2020 2:58 pm
by MOGGIEMOS1@
Hi guys and gals please help to solve my problem ive tried everything...new distributor with points set at .15..new condensor....timing set at between 3AND5dg BFTC...ive drained the fuel tank and added new unleaded (recent engine rebuild to allow unleaded)...carb cleaned and drained of old fuel...3in1 oil in dashpot....spark plugs gap set 0.25..new coil...leads...plugs...ive tried everything it runs as sweet as a nut but the minute I take it out on the road its got no power until I pull the choke out then its better but not how it should be...ive adjusted the fuel mixture according to the Haynes but something is telling me because ive fitted a new distributor (which gave me the same problem as ive got now) could the timing be out possibly retarded but if so how should I set it despite the manual references...with my strobe gun....any help would be much appreciated thankyou

Re: Carb? Stuttering after a while

Posted: Fri Jun 26, 2020 3:14 pm
by MOGGIEMOS1@
I forgot to mention I'd swapped the dizzy from a 25D to 45D. Thanks

Re: Carb? Stuttering after a while

Posted: Fri Jun 26, 2020 5:06 pm
by myoldjalopy
MoggieMos -At least it starts! If the timing is out either way the engine could lose power - but if too retarded, it would tend to overheat. Too advanced would also cause loss of power but would tend to start knocking. You could try loosening the dizzy clamp bolt and slowly rotate the dizzy both ways to see if you get a smoother idle and then road test it (tho' you say it runs 'sweet as a nut' at idle).
Yet the fact a bit of choke improves things suggests that it might be too weak a mixture (which would also cause overheating) due to insufficient fuel flow or carb setting wrong. Does the pump perform well when pumping into a jar? If the plugs look pale/whitish after a good run it woud suggest a weak mixture.
Of course, other causes coud be binding brakes - and I'm assuming the new condensor and coil are good quality........many have found this is not always the case......and good compression on each cylinder.