Misfiring and Black Smoke

[dfinn]

Misfiring and black smoke problem.

I'm not sure if I posted my question at the correct place, but here goes.


Re: Rover 1973 Rover P5B V8.


I need some advice on this black smoke and misfiring which started suddenly.

The car was running perfectly up until last Saturday when I decided to take it for a spin as I do most weekends. However on this occasion when I started the car it was misfiring and wouldn’t pull your socks off and the engine's power output is the equivalent of a Honda 50. The engine is hard to start when hot and also stalls at idle, cold starting is fine apart from the misfire.

The spark plugs are black from carbon build up.

There’s a good spark going to all 8 plugs.

I stripped down both carburettors and give them good clean as I thought the choke may be stuck, but it doesn’t appear to be. I’m nervous that I may have to dig deeper but I’d like to try all the simple stuff firstly.

All comments/advice would be gratefully appreciated.

Kind Regards

Dan

Paid up member.

[harvey]

Are the carbs the original HS6 or have you got HIF6 fitted?

[Deleted]

May 19, 2015 12:48:24 GMT dfinn said:

Misfiring and black smoke problem.

I'm not sure if I posted my question at the correct place, but here goes.


Re: Rover 1973 Rover P5B V8.


I need some advice on this black smoke and misfiring which started suddenly.

The car was running perfectly up until last Saturday when I decided to take it for a spin as I do most weekends. However on this occasion when I started the car it was misfiring and wouldn’t pull your socks off and the engine's power output is the equivalent of a Honda 50. The engine is hard to start when hot and also stalls at idle, cold starting is fine apart from the misfire.

The spark plugs are black from carbon build up.

There’s a good spark going to all 8 plugs.

I stripped down both carburettors and give them good clean as I thought the choke may be stuck, but it doesn’t appear to be. I’m nervous that I may have to dig deeper but I’d like to try all the simple stuff firstly.

All comments/advice would be gratefully appreciated.

Kind Regards

Dan

Paid up member.

Manual or auto choke? If manual, has one or both jets stuck in the lower cold start position. This would cause a rich mixture and therfore black smoke and misfiring. If autochoke, it may suddenly have failed sticking in the cold engine position causing a rich mixture.Piston sticky in the suction chamber?

The biggest help to you is the sudden outset as that means something has suddenly become very out of adjustment rather than over a long period of time.

[norvin]

All good advice from resurgam. Have you checked to see if the carbs are flooding.

[johnwp5bcoupe]

A simple check to see if you have stuck chokes (assuming they are HS6's see harvey's post) is to remove the suction chamber and piston to see if the Jet is more or less level with the body?

If you have an AED fitted the Jet's are fixed

[dfinn]

Thanks guys, it’s a manual joke (SU HIF4 carburettors) I’m going to remove the suction chamber again and report back.

Dan.

[harvey]

May 19, 2015 14:50:15 GMT dfinn said:

it’s a manual joke (SU HIF4 carburettors)

Presumably it's a typo and you mean HIF6, in which case the choke mechanism is a barrel fitted with "O" rings which perish and give the effect of running full choke all the time.

[dfinn]

There’s good news and bad news Guys, the good news first, the car fires up, and the black smoke is all most gone.


Oops a typo for sure (joke/Choke) it’s hard to be humble when you’re as great as I am!!! :-}}


The bad news, there’s a small leak from one of the fuel bowls so I’ll have to remove the carburetor and sort that problem out before proceeding with balancing and tuning.


Would any of you have the correct procedure for tuning and balancing the carbs, or point me in the right direction as to where I would find the information? (SU HIF4 carburetors)


The problem I have presently is…..a tiny misfire or rough running engine with air filters off. When I go to rev the engine it appears to choke itself somewhat. I’ve been fairly adventures the last few days so I’m guessing a few settings may have been altered. The car is fitted with Lumenition Electronic Ignition Systems, I’m not sure if that makes a difference or not to any settings.

The only test I’ve still to do is a compression check; but I don’t have the gauge, could you recommend where I’d get hold of a suitable apparatus.


I’m as well to get a repair kit and do the job right at this stage, where can a buy a repair kit?

Kind regards

Dan.

[johnwp5bcoupe]

May 19, 2015 15:34:02 GMT harvey said:

May 19, 2015 14:50:15 GMT dfinn said:

it’s a manual joke (SU HIF4 carburettors)

Presumably it's a typo and you mean HIF6, in which case the choke mechanism is a barrel fitted with "O" rings which perish and give the effect of running full choke all the time.

SU HIF4

[norvin]

This is what I use a water gas gauge and fitted on the end is the carburettors part from the Gunson kit which is not very good as it sticks and gives a false reading.

[petervdvelde]

Dan,

I bought SU spares with sucarb.co.uk/carburettor-kits.html. They have all the spares, even bolts, brackets, springs ect. Wadhams may also sell service kits.

Peter

[Deleted]

May 19, 2015 17:46:20 GMT dfinn said:

There’s good news and bad news Guys, the good news first, the car fires up, and the black smoke is all most gone.


Oops a typo for sure (joke/Choke) it’s hard to be humble when you’re as great as I am!!! :-}}


The bad news, there’s a small leak from one of the fuel bowls so I’ll have to remove the carburetor and sort that problem out before proceeding with balancing and tuning.


Would any of you have the correct procedure for tuning and balancing the carbs, or point me in the right direction as to where I would find the information? (SU HIF4 carburetors)


The problem I have presently is…..a tiny misfire or rough running engine with air filters off. When I go to rev the engine it appears to choke itself somewhat. I’ve been fairly adventures the last few days so I’m guessing a few settings may have been altered. The car is fitted with Lumenition Electronic Ignition Systems, I’m not sure if that makes a difference or not to any settings.

The only test I’ve still to do is a compression check; but I don’t have the gauge, could you recommend where I’d get hold of a suitable apparatus.


I’m as well to get a repair kit and do the job right at this stage, where can a buy a repair kit?

Kind regards

Dan.

Dan, what did you do to get the "good news"? Was it something obvious?

[dfinn]

May 19, 2015 12:48:24 GMT dfinn said:

Misfiring and black smoke problem.

I'm not sure if I posted my question at the correct place, but here goes.


Re: Rover 1973 Rover P5B V8.


I need some advice on this black smoke and misfiring which started suddenly.

The car was running perfectly up until last Saturday when I decided to take it for a spin as I do most weekends. However on this occasion when I started the car it was misfiring and wouldn’t pull your socks off and the engine's power output is the equivalent of a Honda 50. The engine is hard to start when hot and also stalls at idle, cold starting is fine apart from the misfire.

The spark plugs are black from carbon build up.

There’s a good spark going to all 8 plugs.

I stripped down both carburettors and give them good clean as I thought the choke may be stuck, but it doesn’t appear to be. I’m nervous that I may have to dig deeper but I’d like to try all the simple stuff firstly.

All comments/advice would be gratefully appreciated.

Kind Regards

Dan

Paid up member.

[dfinn]

Black smoke and misfire resolved:


Many thanks to all for your helpful comments on my original post regarding the black smoke and misfire.

A misfire is basically, one of three things, loss of spark, the air/fuel mixture is too far out of balance to ignite, or loss of compression.

Firstly I checked compression on all 8 cylinders and got an average of 160 to 170 psi which is pretty good. Cleaned and checked the gap on each plug during this process. (Plug Gap, 0.8 mm,)


Secondly I checked for spark and coil voltage, fitted with a Lumenition Electronic Ignition Systems and balance resistor I was getting 12 to 13 volt in and between 7 and 10 volt out on the coil and a good spark on each plug, everything is as it should be. I had previously checked the timing when the car was running.


So that leaves the fuel/air.

I decided to rebuild my carburetors (SU HIF6) they had been left to the elements for 6 years before restoring the car. Ordering the parts on line was the simple part, getting delivery was a totally different story but I eventually received all the parts from Limora three weeks later in four separate deliveries, total cost for all the parts came to 480 euro.


While dismantling the carburetors I discovered the O-rings on the choke assembly had perished allowing too much fuel delivery thus causing the fuel air mixture to be totally out of balance. Reassembling the carburetors wasn’t that difficult, just take lots of photos and follow the fitting instruction which came with the repair kit. All in all I had both carburetors back on the car in a few hours ready to fire up the engine.

Now came the balancing and tuning:

Attached are a few different websites which were invaluable to me in getting the perfect result, it took a while to get both carbs balanced but my patience paid dividends in the end, no black smoke and no stumbling and falling, just a perfectly running engine.

Thanks again to everybody who gave me advise.



britishclassicmotors.com/3301.html

www.autotap.com/techlibrary/diagnosing_misfires.asp

www.youtube.com/watch?v=ASeMfXfjNpw



Best regards

Dan.