544 B20B help
 

I am trying to fix a couple of problems. My 544 has a B20B engine. It currently diesels(run on) and has hesitation on acceleration. Timing is at 11 and advances to 23 at 3000 rpm. I know it should advance more. It has a vacuum pot that is blocked off and the carb vacuum is blocked off. It has a Weber 2 barrel carb. Will it help to connect the vacuum? I have lowered timing but seems to not solve the run on. I have had the heads off and there is not a carbon build up.

https://i.postimg.cc/y3XZVQf4/2021-07-20-13-02-38.jpg

https://i.postimg.cc/H8CM1D99/2021-07-20-13-02-49.jpg

I'd start by checking the timing but there are some more bits of advice here

https://en.wikipedia.org/wiki/Diesel...tential_causes

Can you clarify the vacuum question? For example, have you got a connection to the distributor for advance / retard? (Doesn't look like it - but there are some electronic devices that might be fitted that do it differently - so tell us more about the ignition system too please)

Right now the vacuum on the pot is sealed off. It has always been that way. The carb port is sealed off as well. I could connect the vacuum from the carb to the pot. However I do not know if this will matter.

I can't answer that for you at the moment.

Have a look in the distributor and have a look in the engine bay for a box of tricks that is after market for running the ignition system.

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Explanation:-

The original mechanical system would have used vacuum to adjust the timing.

As the engine speed (rpms) increase the spark plugs need to spark sooner because the amount of time taken to burn fuel is essentially constant but the speed at which the piston is compressing air is not.

From your first post it sounds like that something is changing so it is possible that an after market something or other has been fitted to do the job that was originally done by connecting a vacuum pipe between the carb and the dashpot on the side of the distributor.

I think you need to find out what has been fitted. If nothing has been fitted and the vaccum pipe isn't there then your first post will need some different explaining!

B20B ignition timing is 10 degrees advance at idle speed vacuum disconnected ..
you have disabled part of the system which isn.t going to help . The vacuum advance increases the advance when cruising which helps economy and also makes for a quieter smoother engine . You need to start with the system working as factory ...

have you had the head skiimmed over the years ? is the non standard carburettor calibrated properly? has it a heat insulating block between carb and manifold ?

lots to consider !

If ignition isn't causing the run-on, then engine running too hot or mixture too weak are the other common reasons. I take it by 'pot' you mean distributor?

As above and what compression ratio do you have and fuel octane? But as above get the correct distributor or a 123 distributor setup and working properly first, check tappet clearances and then the carb setup. Think I remember a B18B distributor with the vac advance rather than retard is a good option.

Plus 1 to all the above especially a change to the fully mechanical distributor. The one you have is working mechanically but will have different springs and maybe weights to giving you a different ignition curve. These engines were designed to run on 100 octane (Ron) and that is hard to find in the UK. 99 available in many places. 97 the best compromise but a couple degrees of retardation over standard may be needed. 93 is bad for these engines. They will run of course with a bit more retard but not well. 97 is worth the extra for performance and smooth running. Maybe even a bit extra MPG.
97 octane “super unleaded” in Britain is roughly equivalent to 91 octane premium in the United States. If you can find higher than that, go for it.
Of course a nice pair of SU's should give you benefits all round if they are fresh and not worn out.
Anti run on valves are available. These work a solenoid when you turn the ignition off, which opens a valve that floods the inlet with air which kills the engine. Quite expensive!

You have identified a number of problems which may be unrelated.

First off, the ignition system problems will not directly cause dieseling or run-on. Dieseling / run-on is caused by a hot spot in the combustion chamber that is continuing to ignite the fuel mixture (in an untimed manner) after the ignition system is turned off. The hot spot is typically a carbon deposit somewhere in the combustion chamber that is acting as the source. The problem may be exacerbated by a fuel mix or ignition timing (too much advance) that is elevating combustion temperatures. The problem may be precipitated by a fuel mixture that is rich leading to carbon deposits. The carbon deposits may also be caused by excessive oil burning.

Fuel quality / octane rating can play a secondary role. If you are incurring persistent low level detonation that can raise combustion temperatures creating hot spot ignition sources.

The sure fix for decarbonizing is removal of the head and mechanical cleaning of all of the surfaces. A slower solution that may work is to gradually mist water or methanol into the carb intake while the engine is running. The steam reacts with the hot carbon to create a combustible gas gradually resulting in removal of the deposits (turbo charged cars that run water / meth injection for detonation control usually have remarkably clean combustion chambers). You can try the additive in the tank solution; but, I have no faith in those snake oils.

Some later carburetors have an internal run-on control device which shuts off fuel to try and eliminate run-on. Perhaps whatever carb you are using has such a device so you may want to check that out. Pretty hard to retrofit an anti run-on device - shutting off external fuel supply is useless because of the large reservoir in the float bowl. My 142 has D jet fuel injection and the injectors turn off when the ignition turns off - fuel injected cars never suffer from run-on.

As to the ignition timing. Since a B20B in a 544 is a hybrid you need to check the part number for the distributor. Volvo used a wide mix of ignition control strategies on the B 18 and B20 engines. The distributors on B18 engines used static advances around 20 deg. The part number on your distributor will confirm that you are using the correct distributor with the correct advance curve for your B20B's vintage and market (advance curves changed during production and depending on the market - emission requirements). If the distributor is correct then lack of advance may be caused by a sticking / jammed centrifugal advance mechanism.

This is the distributor I have. I know it is not correct but I cannot find the correct one. This one has worked for many years. Also pic of cylinder inside.
https://i.postimg.cc/pXqDBxjj/2016-06-21_14.24.22.jpg
https://i.postimg.cc/SND04XBv/2016-06-21_14.24.06.jpg
https://i.postimg.cc/8Pty8XkW/2016-04-24_14.57.41.jpg

The MG engine is fairly similar to the Volvo. Here is a link to the potential causes of dieseling in our MG engines. Please note that the combustion chamber is in the head, not the block.

https://mgaguru.com/mgtech/engine/ro101.htm


By running with the vacuum disconnected, you are getting no vacuum advance from the distributor, only mechanical advance. Consequently you are probably running too retarded. This will contribute to overheating and perhaps your other issues.

[QUOTE=lelshaddai;2755553]This is the distributor I have. I know it is not correct but I cannot find the correct one. This one has worked for many years.

It is pretty clear now that the first move is to get the correct distributor and get it timed correctly ...

Perhaps this the time to bite the bullet and get a 123.

The most reliable will always be the original with points 👍

The 123 is a lovely bit of kit especially as original ones are getting worn and harder to source. They don't do anything different to a original in proper working condition in the sense they have the same ignition curves but there is less maintenance. If you want to keep original totally fine but I can't see any reason why not to fit one.

Understand you have taken the distributor apart to take pictures, i.e. cap and rota - but have you removed the screw that holds the points in place ? or is it missing ? that won't help :-(

Distributors.

All aftermarket electronic ignition units will fail sooner or later in my 50 year driving experiences ... They don't really give anything noticeably better , and you are stuck , you will never get it going ...... with points you will get on your way with a screwdriver . the more simple the better .👍

That's if it is in proper good condition to start with after 50 to 60 years. The 123 are a pretty reliable bit of kit and my thinking is it's one less thing to go wrong on a ageing car, there's always stuff that needs doing if running them daily. If you have a dizzy in good condition and you're happy to maintain it then no need to change, if like in this instance it isn't and not correct a 123 is a good choice. But if he wants to source a original one, recondition it and maintain it then it will obviously work and be reliable as well. For me there's no valid argument against either option.

The distributor appears to be from a late B20 from the last of the 140s or the earliest 240 before they received the OHC engine. It doesn't even show up on that list posted by Derek. I thought all the B20s in the final 140s and the 240s in the US were K jet starting in 1974 or 1975. However, carb equipped 140s and 240s did continue on in Canada well into the '70s so perhaps it came from a Canadian spec B20.

I think the designation means that the distributor is equipped with vacuum advance whereas the typical B20B engines would be equipped with vacuum retard. The typical distributor on a B20B pre 1974 would be a JFUR4. I don't have any data on the later distributors. It might be equipped with very little centrifugal advance which may be the cause of your lack of advance or the advance mechanism could be stuck. Pull the points plate off and see if the centrifugal advance operates smoothly. If it does, then you may have to dig up the specs for a late B20A or B (perhaps Canadian spec) to find out what the specified advance is. The advance curve may be wrong for your particular B20B depending on whether you have a high or low compression B20B. If so, you may have to investigate replacing the advance mechanism.

As an observation, if the distributor has not been rebuilt then it probably has shaft wear which causes timing problems at higher RPM. The distributor on my 1971 B20E worked fine at low RPM; but, as you increased the RPM you could see the timing marks bouncing around quite a bit starting around 2500 - 3000 RPM. A new 123 distributor might be one way to address your distributor uncertainty and eliminate any wear issues.

The top of the piston looks moderately clean. The bigger problem would be the actual combustion chamber. In particular are there deposits on the exhaust valve which runs hot and provides more opportunity for hot ignition sources? Since the engine appears to be out of the car I would assume that you are going to do an engine clean which may address most of the run-on problems.

If I want an original correct dizzy I need a
JFUR4 0231146078

Anyone have one of these?

Something different!
 

Hi lelshaddai sorry I cannot help with a distributor. But I am hoping you can help me with a long time issue. I am fitting USA style bumpers on my 544 and need dimensions for the cut outs in rear panel where the towel rail support bars pass through. Ideally the diameter of the holes, distance from the bottom edge of the rear panel and distance from wing seam to centre of cut out hole. I would be very grateful as I dread getting the cut outs wrong!

Hey Farmer, I will try and get those bumper numbers out with pics today.

Great,many thanks

Is the 123 only electronic ign? I wanted to keep points if I can. I tried Petronix in the current distib and had trouble hooking it up the the coil since it still has the armored cable. Will only the 0231146078 work our can I use 0231146077 or 02311460009?

Farmer, here are the pics and measurements.

The holes about 1 1/2 in diameter. They are 1 1/2 inch, on center from the fender connection. They are 5 1/2 on center from the bottom. These are estimates. The holes appear to be 35" apart on center.
https://i.postimg.cc/zL7xgcL7/2021-07-22-10-35-44.jpg

https://i.postimg.cc/ZBqVFxpS/2021-07-22-10-35-49.jpg

https://i.postimg.cc/DSqj2Znt/2021-07-22-10-36-27.jpg

https://i.postimg.cc/RqFDc4LH/2021-07-22-10-36-56.jpg

https://i.postimg.cc/LngQbD74/2021-07-22-10-37-05.jpg

https://i.postimg.cc/NLzPDSdP/2021-07-22-10-37-30.jpg

https://i.postimg.cc/JswYVJVN/2021-07-22-10-39-26.jpg

https://i.postimg.cc/f3DHkNbk/2021-07-22-10-39-30.jpg

Thanks so much for that and taking the trouble to post photos. It will be a great help to me. Do hope you get your B20 motor sorted.

Contact Adam (swedishandgerman) on here, he is your man when it comes to distributors. He'll know which one is best to have and probably will have one he could sell you. He is in England is the only issue for you.

VP autoparts have an American branch - they might be able to help

Here are pics showing the inside of the distributor (the type you are talking about: JFUR4 0231 146 078) of my 1970 B20B.

As said earlier, it forms part of a vacuum retard system, specifically for emission control purposes. In this system suction for the vacuum “pot” on the distributor is obtained from a very specifically located port on the rear carb (of the twin SUs). The port is in the region of the throttle plate, on the underside of the carb, such that when the throttle plate is closed the lower edge of the throttle plate lies just upstream of the port (and suction at the port is high). As the throttle opens, the edge of the throttle plate moves to a point downstream of the port and suction rapidly falls away.

As a consequence, I don’t think the vacuum connection in this system would have any effect on the ignition timing except when the throttle is almost closed.

I have blocked off the port, as most people seem to do.