Seriously rough running engine -SORTED!!!

[martinbrowning]

Hi folks,
Some weeks ago I posted a topic about a seriously rough running twincam; car developed misfire, rough running and kangaroo-ing up the road with loss of power. All plugs heavily fouled so suspected an electrical fault.
I replaced: coil,dizzy cap,HT leads, condenser, points and plugs. Used quality parts throughout (Distributor Doctor). Engine started and idled well so thought problem solved.....WRONG
Following advice from this Forum I have also replaced HT and LT leads from coil to distributor. Decided to take car out today for a post winter shakedown before it's MOT next week -
1. car started ok and idles well, exhaust whitish to clear.
2. Took car out and within a few seconds misfire back accompanied by black exhaust and lack of power.

Brought car home, cleaned plugs again (which were ALL heavily fouled) and started it. Idles ok but as soon as you use throttle problem returns and difficult to get it above about 2000rpm. Engine only running for a minute maximum but plugs heavily fouled again.

Sledge hammer tactics I know but thinking of changing carbs with another pair on the bench which have minimal running time on them.
ALL THOUGHTS GRATEFULLY RECEIVED!!!

Martin B

I can't believe it, and am most suitably embarassed and shamed. Took off the air filter to make working on the carbs easier. Then took out the pump jets and cleaned through with compressed air. replaced the jets and tried the engine - all working really well. Replaced air filter assembly in preparation for road test........problem returned.
Ta dah!!!! clogged air filter element. Cleaned element and all is sweetness and light againJ ust can't believe that I didn't think of that. Sorry to one and all for bothering you .

[Elanconvert]

hi martin
checked your previous post and can't see what carbs you have?

fred

[Gray]

One not obvious fault I've come across is a loose float valve in Webbers, but would only affect two cylinders.

[martinbrowning]

Hi Fred - car has twin dellorto's

"Gray" - yes, strange problem as it seems to affect all four cylinders.

Martin

[Elanconvert]

if you have ruled out electrical issues [and I can testify to the unreliability of 'new' parts]
I would maybe think that grizzly's stuck pump valve might be worth investigating.......
have you tried gunsons colortune? swapping carbs would give you some answers if you know the replacements are ok, but a bit more work........

fred

[Chancer]

Have you by any chance used a rebuild kit on the carbs? That is assuming that they are webers.

Years ago I had an identical problem after rebuilding my old webers, they were the type with a crenellated washer Under the jet cover, I did not realise that it was this that vented the float chambers (later carbs have an air passage to Inside the air filters).

I threw away the crenellated or castellated whatever its called washers and replaced them with the seals that came with the rebuild kit, it looked nicer and I figured it would stop fuel leaking out if the vehicle overturned.

The result of my ignorance was the identical symptoms that you have, float chambers that are not vented to atmosphere, even if you dont have that set up make sure that however your float chambers are vented that it is not blocked by perhaps the wrong air filter.

My mistake was only resolved on the Rolling road at Hailsham Dynotune, an expensive way to solve a very basic problem.

Mmm, thinking back I cant recall the plug electrode colour, I'm thinking that my engine leaned out, it felt like fuel starvation.

[Grizzly]

I'd be having a good look at the Carbs..... Remove the top covers then check the floats are correctly adjusted, remove the one way valve from the bottom of the Float chamber and make sure it not stuck, with fuel in the Float chambers open the throttle fully whilst checking the two pump jet plungers go down at a reasonable speed and not stuck (if you look into the air inlet can you see a jet of fuel squirting out of the Pump jets at the top of the venturi with no dripping (you can do this on the car with the help of a small mirror but its awkward so much easier if you remove the carbs)), check for sediment in the bowl chamber, check the alloy crush washers are ok under the Pump jets (while your there the small hole in the bottom of the jet is clear by blowing down it with the larger hole in the side covered), remove the Main jets (check for crud and clean well).


Have you got an after market fuel filter that could have plugged or collapsed? or a Collapse or kinked fuel line?

[Matt Elan]

Did you buy spark plugs from eBay or Amazon? There are a lot of fakes around so it's always worth getting some real ones....... The fouling is a typical symptom of fakes. It's a cheap diagnosis to get some real ones from a decent motor factors and try them out.

[john.p.clegg]

Martin
Can't see rotor arm on the list?

John

[martinbrowning]

Thanks for all your replies and advice; will look closely at the carbs although it seems strange that BOTH should develop the same fault (ALL plugs fouled). Checked advance with a timing light - some scatter but operating correctly. Put a set of LED sensors in line between each plug and lead - they flash with each pulse to the plug. All merrily flashing away with no fault showing as revs increase.

John - yes, sorry, new rotor arm fitted as well. A "red" one from Distributor Doctor in place of the rev limiting one fitted.

Looks like the carbs need to come out and onto the bench.

Martin

[john.p.clegg]

Martin
Not very good at poker but I'll show my hand now...my money is on electrical if all four cylinders are "missing",if it was a fuel problem the plugs wouldn't be sooty,and intermittent problems like this are a pig to locate,my next step would to rig up a 12v test lamp on the dash ,somewhere it's obvious ,connected across the coil + and earth, ( assuming -ve earth ), and go for a drive...if the lamp doesn't flicker when the problem occurs...then I'm wrong...

John

[Elanconvert]

martin
does the coil get very hot?

fred

[david.g.chapman]

Hi Martin,

Forgive me if you have looked at this - but could it be old fuel?

I have similar problems trying to start up after just 2 months over the winter, with 10 litres of 95 RON in the tank at the start of the 2 months. The car was difficuilt to fire with plugs fouling very easily. Adding 10 litres of fresh 97 RON got the car going, and a fill up of 97 RON has transformed the car's cold weather starting and running.

If you are not sure about the fuel drain the tank with one of those pump syphons you can get on the internet for a fiver, and try fresh fuel.

Just a thought...

Dave Chapman.

[Matt Elan]

Have you changed the plugs for known good ones?