Engine: 2.1 Carb B21A: Backfiring Redblock - Help Please

[LankyTim]

That split breather pipe wouldnt affect running, it would just allow piston blow-by and other gases generated in the crank case escape out into the atmospehere instead of being burnt in the engine.

[MissDMeanor]

Ok, still no joy with the old girl.

A friend & I have spent one hour & one breakdown in her trying to find the source of the problem.

Having been in the car whilst driven my mate (mechanical engineer) ascertained that the problem is fuel related i.e. starvation. The leaky pipe will help the engine run lean and does also need replacing. So, the only thing to do is replace the fuel pump with a new one - if that still doesn't solve it, replace the carburettor with a new/working one (possible hole/split in the diaphram).

This was the conclusion.....until we felt the heat coming from the coil. Ok, a rethink. It must be electrical. Checked the points which were ok but opened the gap up a bit and tighten the screw which had come loose. Still running like pooh with the coil getting very hot.

Next, revised plan of action - new coil, then new fuel pump, then working carb.

And I was meant to be in Kent this coming weekend as I'm supposed to be Godmother to a child - oh dear

[malb]

Another couple of ideas and a quick test.

I have a pair of Nov79 245's, my original van and another which had be converted back to a wagon. My original is basically stock under the bonnet except for two things, it has a the air filter box up front beside the radiator, feeding the carb via a tube and adaptor kit of a 144 with similar SU carb, and it has the air pump for the exhaust disconnected.

The converted wagon has a 2.3 motor bodged to replicate the original 2.1 intake and exhaust systems. It has the same manifold as my original.

You photo of the split tube feeding the flame trap never seemed right to me so tonight I took a photo of my original engine inlet manifold for comparison.

Your manifold is obviously slightly different to mine regarding the placement of the PCV port(entry from flame trap), the solenoid, and the airbleed screw (brass screw on carby side of solenoid and PCV port).

My engines have a single SU carb, Do you know what carb is fitted to yours?

The air bleed screw adjusts idle speed and exhaust CO by controlling the air flow rate from the carbon canister mounted below the washer bottle. Other carbs may have this type of function built into the carb itself.

The solenoid closes the the passage from the carbon canister port if the ignition is off. I am on my forth solenoid at present, but all replacements have been ex wrecker. If the solenoid fails, the engine is denied the air which normally purges the the carbon canister, and the fuel system can be pressurised in hot weather or develop a vacuum in cool weather as there is no controlled air flow in or out of the tank to maintain atmospheric pressure.

I suggest that you disconnect the cable to the solenoid, and turn the ignition to the run position, and then reconnect the solenoid. If the solenoid is OK, you should hear a click when you reconnect. Don't be surprised if you also see a small spark. If you don't get the click, the solenoid is shot and needs to be replaced. The engine will run only under considerable sufferance if the solenoid is shot. (50% throttle for a very uneven idle).

The other area to consider in regard to back firing is the air pump unit that would originally have been mounted over the alternator at the top of the motor. If this is still fitted, and there are problems with plumbing or anti backfire valves, they can make the engine backfire alarmingly. Mine came off about 20 years ago and I blanked off the distribution manifold at the outlet with a plumbing fitting (3/4 in cap). Ultimately pulled the distribution manifold comply this year and capped the injection ports into the head completely. Sorry no picks of this section as it went to god years ago, but is is covered briefly in my 74-77 and 74-90 Haynes.

Regarding air leakage from the split in the flame trap tube, this should not have a killer effect as the system is calibrated to operate with air flowing from the filter through the trap and into the manifold. The flow rate is controlled by the porting in the manifold, so the engine should not lean out because of the split.
Hopefully these two bits of info might help.

[Mike_Brace]

The two things that spring to mind from the days when I played quite a lot with B21A's. First I would fit new points and condensor - this could be the cause of the hot coil. The other thing worth checking is the cam belt. With it on exactly tdc is the cam notch lining up or 1/2 a notch out. If half a notch out it needs to be so the the pulley mark is slightly to the right of the cover mark not the left.

Mike

[Mister T]

Reading thru the posts I do not see that you looked at the distributor for a worn points mounting plate or loose shaft as Malb suggested , as bad as this engine backfires it as to be an ignition problem , possibly a rotor arm that is shorting to the shaft , I have seen this many times with cheap ignition parts .
If you have a dwell meter check to see if the dwell angle changes radically , approx 5 degrees max should be Ok , but do look at the rotor for tracking where it fits to the shaft if in doubt instal a new Bosch part.
One more point to check , that the coil is getting 12 volts constantly especially when the engine is backfiring.
Mister T.

[MissDMeanor]

Thanks for your posts guys.

OK, she was serviced recently and I have checked the points, etc but it may be prudent to replace points and condenser in case they are faulty.

My friend has reminded me that he also cleaned the carb out with a carb flush of some sort when he fiddled with the mixture. He thinks that may have damaged the diaphram in the carb.

I will also check what you have suggested guys and get back to you. One of my problems is that I haven't got many tools and cannot get out and about much - feels like I've had my legs chopped off or that I'm on a ban

Anyway, I'm guessing that I'll just have to replace parts until the problem is resolved. I don't think I'll ever find what the cause was as severely misfiring for a while, I would imagine, will cause other things to expire

PS she starts fine and ticks over a bit rough but ok - the misfire is under load

PPSS I will take a better picture of the carb and post it up for you Malb - I'll be able to check which carb it is then too

[MissDMeanor]

Originally Posted by malb

You photo of the split tube feeding the flame trap never seemed right to me so tonight I took a photo of my original engine inlet manifold for comparison.

Your manifold is obviously slightly different to mine regarding the placement of the PCV port(entry from flame trap), the solenoid, and the airbleed screw (brass screw on carby side of solenoid and PCV port).

My engines have a single SU carb, Do you know what carb is fitted to yours?

Hi Malb

I'm so sorry - I said I'd post a piccie up but life sort of got in the way. The carb is a Stromberg 175 CD-2 (I only know that 'cos they've helpfully stamped it on the top for me lol):



And yes, the bay arrangement is different - here's a better picture of the pipes and carb etc:


Thanks to Jim C I have managed to obtain a refurb kit for this carb. I'll be having a go tomorrow and will probably start a new thread with pictures for that in the hope that it helps someone someday

[Matthews 855 T5]

This is an interesting post. Have you checked for fuel delivery? I had a major pita problem with my b21a years ago, it turned out to be the fuel tank sender had a pin hole so was reducing the amount of fuel fed to the carb. Does it stall? Does it pink?

I think yours may be due to the recent service and fitting poor parts, I often had problems with condensers and points but back then they only cost a pound or two. Hope you fettle it soon.
Matt

[MissDMeanor]

Ok folks, now we're moving forwards in more ways than one.
My friend (an engineer (with the big hands) & I spent the weekend on Mildred.

The first thing we did was refurb the carb (see other thread) and were quite disappointed to see that it was actually in quite good nick with no tears or splits in the diaphragm. It was also not gunked up with rubbish we may have been able contribute to the way she ran.

After refitting the carb we checked the plugs. Nos 1 & 2 looked slightly odd but nothing to write home about and the other two looked normal.

We strobed her and she was a mere 40 degrees out! So, after adjusting the timing she runs much sweeter and starts on the button now. Although we did notice that the timing changes but Mike Brace has given some excellent advice to solve this. So far so good.

I took her for a spin and she is 90% better but still not good enough to drive any distance. She still has that sudden complete loss of power which imo is dangerous - someone driving behind is likely to clonk her up the bum.

So, it is now possible for me to drive her the short distance to work (to send parcels off). I've been using Rosie, my current mode of transport, who doesn't cope so well some days:




It doesn't handle all the weight very well so I thought I might put bigger wheels on it and lower it a bit

The next plan of action for Mildred is to order the pipe that had a gaping great hole and any others that are beginning to perish; fit the brand new carb I managed to get hold of (thanks JimC) and fit a new cambelt - great advice from Mike Brace.

After that, if she still coughs I'll be looking at the fuel pump and probably replacing again the condenser etc. The coil seems to be fine now we sorted the timing out - i.e. the coil isn't burning hot when she's running now lol

[minesa240x3]

Sorry to hear that your still having problems,but you will sort it soon.Fantastic pictures and explanations as you try solving your fault.Others will undoubtedly benefit from your experience,well done and best of luck,
By the way does Rosie corner well,And true to the 200 series the back and front wheels are spaced differently,