red67

i have an early 2 litre aluminium block
i drive it once or twice a week between 2 and 8 hours each time
on start up recently it only fires on 5 cylinders

when it's up in operating temperature (sometimes a little time after) the sixth will cough and backfire a few times and then kick in and all is fine after that.

i checked the ht leads and all electric connections are fine.
the plugs are top quality and pretty new (i've only run it the last 8 or so weekends). but i've not checked them this weekend.

when i got the car in september last year i couldnt get it to fire-up. one of the plugs that was in the car was really heavily sooted. i replaced them all and changed the oil, oil filter, fuel filter and air filter at that time and it ran like a dream without any problems. so i'm curious to see if it's the same plug that is sooted again when i check.

has anyone else come across a simliar problem/solution?

mo_gearhead

Are we talking about a car with carbs... or F.I.? You dont say how you have confirmed it is "running on 5 cylinders at startup". But assuming that to be true, it sounds like a possible electrical problem. I think we may need more info. about what year it is, induction system, mileage on engine, what tests you have done, etc. Is the previously "sooty" cylinder the one now not firing all the time? Any unusual engine (lifter/valve) noises?

red67

its carburetors. 1967, original matching numbers gearbox, engine and chassis and original bendix pump etc. it was completely recondontioned before i got it.
i can hear that it runs on 5 and can hear when the 6th kicks in.
i dont know if its the previous sooted plugged cylinder not firing - i'll pull all the plugs out when i go to the car next, think i'll replace them again as a first cause of action. the distributor and points and ht leads all look immaculate.
i've not had the valves or the carbs adjusted or looked at to date.
theres no adverse knocking or valve noises to my knowledge but i'm no expert. i can always hear the tappits when its warm i think thats it, its normal sounding to me. here's the engine firing with 6 when its warmish... i reduced the idle speed a little since this video...
http://www.youtube.com/watch?v=Sp1nno1O9cI

red67

ps the exhaust emissions are clear (they not black or anything) so i dont think its a cylinder ring worn or anything, which maybe could have sealed itself when warm and allow compression.
but maybe i need to get those carbs tuned if they are sooting up the plug/plugs.
i guess i need to get my *** over to the car to check them first.

Droops83

Hey sounds like you have a nice car! The Webers on your car really need clean fuel. The idle jets clog very easily. This is my initial guess of what your problem is. I would pull all the idle jets and make sure they are clear. A quick blast of brake or carb cleaner followed by compressed air will do the trick. It is a good idea to run more than one inline filter to make sure your fuel is clean.

It is also a very good idea to do a basic check of your engine's overall condition. If you do not know when your valves were last adjusted, adjust them! Check the compression, and leakdown if necessary. If one of the plugs in particular is fouling up quicker than the others, at least do a compression/leakdown test on that one. Make sure the dwell and timing are set correctly and all the ignition components are in good order. Then, verify the correct fuel pressure (3.5 psi) and float levels. Then fine tune the carbs. If you don not know how to do this, it is a good idea to bring the car to someone who does. Well hopefully this helps a bit, let us know how it goes.

---Chris A.

Mike Murphy

It sounds like one of your cylinders is fouling the spark plug, due to improper fuel mixture or oil leakage on that cylinder. After you put in new plugs, run the car for about 100 miles and pull the plugs if one plug looks different than the others, that's a clue as to which one it is.

red67

many thanks for the good advice guys
i went to the car today and tried to fire it up without doing anything. sounded like it was firing on 4 and struggling. so i pulled out the plugs and replaced them one by one. every single one of them was totally black and sooted looks like its been running really rich. i could only get my hands on 5 plugs today from my supplier so i get the 6th thursday from him.
on getting that i'll definately take it to my mechanic and get the carbs cleaned and adjusted and valves adjusted. my technical proficiency is pretty much non-existant but i think i'll try and learn to check and clean the idle jets regularly as you say. also great idea with 2 fuel flters if the weber carbs get clogged easily - i never considered that. many thanks again. i'll let you know how it turns out.

Mike Murphy

Yeah, what's happening is that your plugs are getting fouled. You are either running too rich, or the plugs are the wrong heat range.

Peter Zimmermann

red: Chris' comments are right on the money. Establish that you have a sound engine (leakdown test) before throwing away time and money looking for a problem elsewhere. Another thing that should be done is to have the car low on fuel, below 1/4 tank, when you give it to the shop. Have them pull the fuel guage sending unit and look into the tank. If it's really ugly in there have them pull the tank, flush, clean and seal it. That way you're starting out with clean fuel. This is similar to having a television that doesn't work, and having a repairman out to discover that someone unplugged it - do the basics first. You haven't mentioned if someone has added a CD ignition box to the car, or replaced the points with an electronic system. This can make a world of difference, the CD alone can clean up those plugs, and please be aware that plugs used with a CD require a wider gap than those used without a CD. In most instances the plugs that will work the best in your car (with CD) are W5DC Bosch gapped at .030". Without a CD you can go hotter, to a W7DC gapped at .024". In some cases W6DC plugs will work well (CD or no CD), and give you the advantage of being safer to use during extended periods of high speed driving. When experimenting with heat ranges always check them to confirm that you're not damaging the engine! A good alternate plug is the NGK BP6ES (CD), or the hotter BP5ES (no CD), gapped the same as above. Other plugs are available, but all of the plugs that I've mentioned are proven over many, many years, in a very large number of cars.
Pete

red67

thanks pete.
i don't know CD is (sorry i'm a newbie) but the distributor and points look exactly as in the haynes manual pictures from the orgiinal car - so i don't think its been upgraded to an electronic system - it's all old school.
i've been following haynes manual guidelines with plugs - i've just put in W5DC bosch's with gaps of .55mm (.022") this was from haynes manual guidelines. the ones i pulled out where platinum tipped boschs.
crap in the fuel tank i never thought about either - good place to start you're right guess you gotta start at the source.
i had an additional thought regarding the source - if it's the fuel octane rating i'm using now the car is in europe causing problems also (or adding to them) - (it was a US car originally). i've been fuelling it with 98 octane unleaded but thats a purer grade than US i think so it should have less impurities in it and help the issue rather than add to the problem.
i think my mechanic will be happy to see me when i give him the list of what i want him to do.

Peter Zimmermann

The W5DC with the narrow gap (no CD) would normally be OK, especially with your potent fuel, but they're so cold that they don't like to be started, run a few minutes, and then shut off. We had a heckuva time diagnosing fouled plugs in an early 911 a number of years ago. The customer said that every Monday morning the car ran crappy. We finally figured out that he started the car every Sunday morning, pulled it into the driveway in order to get his lawn mower out, then shut it off. When his grass was cut he put the mower, and the car, away. On the third start without being driven, on Monday morning, a plug fouled! We put a CD on that car and the owner never had another problem, the car smoked less, got better mileage and ran better! By the way, .022" gap is fine, for some reason we preferred .024", which seemed to work a little better in SoCal conditions. If you add a CD open up that gap to .030".
Pete

red67

haha. that's brilliant detective work pete. sounds like i should really look into upgrading to CD. (but what does 'CD' actually stand for?) i want to try to keep the car as close to pure factory original as much as possible, but if the plugs are sooting up on me again after having everything looked at and sorted then i'm switching.

red67

actually pete would you recommend getting it done straight away with the other adjustments?
it's not de-valuing the car or being unrespectful to its originality or purity?

ron mcatee

CD means "capacitive Discharge".

Peter Zimmermann

Yes, if your shop has considerable early 911 experience there should not be a problem with them installing a CD unit. If it were me I would definitely have it done.
Pete