Plugs fouling - causes?
Discussion
MGB with 1950 Oselli which was built some time ago. Was set up on rolling road last spring and Weber 45 re jetted and new high pressure fuel pump. Started misfiring at end of summer after not much use. Checked compression ans was 180 on 3 cylinders, 175 on other. So all good. Cleaned plugs and ok for another few miles, then wouldn’t start. Changed plugs for new iridium ones and same again - wouldn’t start after a 5 mile run and plugs v black as pics inc on the treads. Have bought a borescope to have a look - specifically what should I be looking at?? Could it just be overfuelling? And help appreciated. 
I would check that the float valves are remaining shut, as with a high pressure fuel pump they'll be hard pressed to stop the flow.
Also check the float levels, as high float levels can cause rich running as well.
Even if there's a small amount of dirt in the float valves that could enrich the mixture.
Any smell of fuel from under the bonnet at idle?
Are the manual chokes shutting off fully?
Is the idling smooth?
Also check the float levels, as high float levels can cause rich running as well.
Even if there's a small amount of dirt in the float valves that could enrich the mixture.
Any smell of fuel from under the bonnet at idle?
Are the manual chokes shutting off fully?
Is the idling smooth?
The plug ceramic does not look too bad.
A 5 mile run is perhaps not enough?
HP fuel pump seems suspect though, a carb normally doesn't want high pressure, you want enough pressure and enough flow rate.
Is it the best plug for the job?
Problems with big carbs pottering about on short runs with light loads are not exactly a novelty.
A 5 mile run is perhaps not enough?
HP fuel pump seems suspect though, a carb normally doesn't want high pressure, you want enough pressure and enough flow rate.
Is it the best plug for the job?
Problems with big carbs pottering about on short runs with light loads are not exactly a novelty.
looks like a fuel mix problem?
or the spark gets wrong or to weak fault somewhere?
your plugs are new or were new, so look at the system before it sparks, are those still healthy?
old cars bobine things or battery or in the thing that directs the spark were the plug cables come out... lol at my poor English, also on old cars next to that distributor ah, a small bobine/condensator?
if the spark is to weak and the fuel mix to rich it als can get you there.
or the spark gets wrong or to weak fault somewhere?
your plugs are new or were new, so look at the system before it sparks, are those still healthy?
old cars bobine things or battery or in the thing that directs the spark were the plug cables come out... lol at my poor English, also on old cars next to that distributor ah, a small bobine/condensator?
if the spark is to weak and the fuel mix to rich it als can get you there.
Agree with an earlier poster in that I’d be looking at the electric fuel pump overpowering the floats in the carb. Had a similar issue with an Alfa, and as it had a pressure regulator fitted I was able to dial back the pressure to something more acceptable. Cured the issue in my case.
As above, most likely overwhelming the carbs with too much fuel pressure. Fuel pressure on Webers should be somewhere in the 2 > max.5psi range. You will need to measure what pressure you are getting at the carb and reduce pressure to ideally 3.5psi using either a good quality fuel pressure regulator or by fitting a fuel return line to the tank and running a flow/return system with restrictor.
I'd wager correct pressure will resolve your problem, but if not you will then need to look at spark plug temperature to check you are running a hot enough plug and camshaft specs to check that the engine hasn't been fitted with a hot 'race' cam that makes loads of power up high under full throttle, but isn't suited to part throttle opening and normal street driving conditions.
I'd wager correct pressure will resolve your problem, but if not you will then need to look at spark plug temperature to check you are running a hot enough plug and camshaft specs to check that the engine hasn't been fitted with a hot 'race' cam that makes loads of power up high under full throttle, but isn't suited to part throttle opening and normal street driving conditions.
Webers - a (my) cautionary tale.
I have an Alfa Romeo 'special' with twin Webers. When I originally fitted the engine, I used a Weber service kit but they were a bit scruffy and so I thought I'd get them refurbished / renewed at some time. But they worked just fine until......
The car would start just fine but the plugs would soot up on two cylinders, indicating a (presumed) problem with the adjustment of the 2nd pair. I leaned them off went for a good fast blast, pulled over in a rest area & checked the plugs. Absolutely fine. A couple of days later I tried to start the car and struggled. Only way was to enrich the mixture, started just fine but then the plugs were fouling. I messed around with the bloody things for weeks then thought sod it and I brought - at great expense - some shiny new carbs.
They arrived by courier, early one morning and I went to fit them. It was only when I went to remove the old ones that that I found out the problem. The choke was jammed slightly open, obviously this meant that the car was running rich but when I leaned off the carbs the fouling was cured but then, as I have said, starting was hard when the engine was cold.
The b
h about the whole thing was that with those Weber carbs I never needed the use of the choke to start - indeed I had disconnected the choke cable. Presumably, due to lack of use the choke lever had 'gunked-up', enough to overcome the return spring pressure. Some fool, who wont be named, must have touched the lever and opened it slightly and the gunked up choke lever didn't return to close the choke.
Still, I have some shiny new carbs. And a hole in my bank balance!
Sometimes, look for the little things......
I have an Alfa Romeo 'special' with twin Webers. When I originally fitted the engine, I used a Weber service kit but they were a bit scruffy and so I thought I'd get them refurbished / renewed at some time. But they worked just fine until......
The car would start just fine but the plugs would soot up on two cylinders, indicating a (presumed) problem with the adjustment of the 2nd pair. I leaned them off went for a good fast blast, pulled over in a rest area & checked the plugs. Absolutely fine. A couple of days later I tried to start the car and struggled. Only way was to enrich the mixture, started just fine but then the plugs were fouling. I messed around with the bloody things for weeks then thought sod it and I brought - at great expense - some shiny new carbs.
They arrived by courier, early one morning and I went to fit them. It was only when I went to remove the old ones that that I found out the problem. The choke was jammed slightly open, obviously this meant that the car was running rich but when I leaned off the carbs the fouling was cured but then, as I have said, starting was hard when the engine was cold.
The b
h about the whole thing was that with those Weber carbs I never needed the use of the choke to start - indeed I had disconnected the choke cable. Presumably, due to lack of use the choke lever had 'gunked-up', enough to overcome the return spring pressure. Some fool, who wont be named, must have touched the lever and opened it slightly and the gunked up choke lever didn't return to close the choke.Still, I have some shiny new carbs. And a hole in my bank balance!
Sometimes, look for the little things......
For what it's worth, back in the 80's I ran a MK2 Escort with a highly tuned 1600 engine (Kent for those Ford fans).
This engine ran twin 45's and used the standard fuel pump - I had no fuelling issues at all.
An electric pump is a nice to have, but is best fitted with a tank return pipe to bleed off excess pressure.
This engine ran twin 45's and used the standard fuel pump - I had no fuelling issues at all.
An electric pump is a nice to have, but is best fitted with a tank return pipe to bleed off excess pressure.
Billy_Whizzzz said:
Thanks all. Fuel pressure gauge arriving today so will investigate. May go back to SUs…!
Also check the carb to manifold mounting nuts, they need to be tight enough to stop air leaks but loose enough to reduce engine vibrations transferring to the carb.Those plugs don't look too bad to me for a tuned carb engine of that era btw, you may be barking up the wrong tree.
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