suddenly a rough running engine

hi there,
I went to start my car today and it took ages to start, usually it starts after about 3 stabs at the starter.
I went on a club run 2 weeks ago and it ran perfectly, just sailed along the motorway at about 80klm per hour...fine.
Today it finally started, sounded if it was running on 4 cylinders, will not rev at all . Could not use the car.
Checked the dizzy, nothing amiss inside, its a converted to electronic type.
how could it become so sick after being parked after the last run?
I checked the spark to the cylinders and all are sparking.
The carburetors were completely rebuilt last year by Midal in Sydney.



Staff member
I would be looking at the carbs, if it is indeed only firing on four. Pull the elbows off and just see if the slides open smoothly by lifting them with your finger. If they do, try to get it started, and look under the slides with the engine ticking over to see if you can see a mist of petrol.
hi there,
thank you for the advice, I too suspected something suspicious in the carburetor area.
I will do your checks and let you know the result...

hi there,
today I removed the air cleaner and elbows.
put my finger into orifice and tried to raise the slides.
very hard to raise, but will raise.
so removed the plungers and the slides went up easily.
topped up with light oil, replaced plungers and did test again, result was the same, will raise by difficult.
Q:- when accelerator linkage moved, should the slides move up?

cobraboy:- felt the manifolds after getting started and rough running, all ports on drivers side getting hot.
did the same on passenger side ( RHD car), and number 1 and 4 cold, others getting hot....
checked the spark with a testing gadget that is just placed on the wire and it lights up showing a spark is present,
and all show sparking.
Q:- how can it spark and the exhaust be cold?

Harveyp6:-The needles are still attached to the slides

what is my next move?

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Staff member
Q:- when accelerator linkage moved, should the slides move up? Not on their own, no. The linkage moves a throttle butterfly, and the slides go up and down due to vacuum pressure, so they are not directly linked.

Q:- how can it spark and the exhaust be cold? It will only fire if the fuel is there at the correct ratio.

what is my next move? Is there a fuel mist below the passenger side slide when ticking over?
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I had this last week running on 4 cyl and it was cured by a light tap with a screwdriver handle to my NS carb float chamber. I assume that my float needle had stuck closed. Ran like a dream after that.
hi there,
thanks Quattro for answering my individual questions, I learn something new every day.
Having only removed the elbows so far, thinking about removing the LHS carbi, I was at a loss of not knowing what to look for in the carbi itself, so
"devilsplaymate's idea will be my first hit.....I remember doing that to my old series one land-rover, taping the fuel pump to make it tick and start pumping.;)
back again, went to shed, started car, tried to tap body of carbi, but not like conventional SU with a big float chamber to tap.
So it did nothing!
So now the only option is to remove carburetor, when I take it to pieces, what do I look for that is faulty?
are there any springs that will jump out and fly across the shed, never to be found again?


Well-Known Member
If you are taking a carb to bits then I would remove it and then retire to a clean place so that you cannot lose any bits.

However before you start ……. you will likely need parts to re assemble.
With HS6 all you may need to do is remove the float chamber lid with the cab in situ and check there is fuel in there, you can do this with the carb still on the manifold, and may even re use the lid gasket.

With HIF6 you will need to pull the carb, the paper spacer gaskets will need replacing, as will the square 0 ring on the bottom float chamber lid.

As Quattro has said, before you do this, run the engine with the LH elbow off, look in the carb intake and rev the engine, you should see the slide rise and at the bottom there should be a good spray of fuel being sucked out of the jet at the bottom. If you have a good spray of fuel then I would leave the carb and look at plugs and leads first.
hi there,
the engine would not rev so could not check the slide for petrol spray, so removed carbie.
Will take into local carbi specialist on Friday for a checkup and see what they recommend!
this is a most unusual event, used the vehicle and no problems, parked it and 2 weeks later try to start it.
Then this happens, I remind myself "its just a hobby", everything one does costs $100 +, my Morris minor broke its oil pump , gearbox out, clutch out and remove pump..... waiting for a new one...."its just a hobby" ....
2 cars sick , might join the old duke and hand in my license...just kidding :p
hi there,
today I collected my carbi from the local carburetor repair shop, rover p6B V8 SU.
They said that it was running perfectly and demonstrated on a 6 cylinder engine.
Installed the carbie and started the car.
It started easily, but with the same performance as before.
Seriously rough running, sounding like running on only 4 cylinders.
Checked the distributor firing order on the dizzy and leads, all correct.
Changed over plugs on 2 cylinders to see if it was dud plugs, but started up as before , doing the same thing. rough running.
Have now come to a halt on sorting this unusual problem, so what is the next thing to check?


Active Member
Does the "running rough" include any knocking? Just wondering if the spark is jumping across contacts in the cap, had it happen on my Range Rover years ago. Replacement was the only cure.
A couple of months ago my car started running roughly and wouldn't idle. I checked all the usual things - even stripping the carbs - without success. I had filled with petrol the night before the problem started and half-suspected that was the cause, but the car was running so badly I doubted that it could be. Having used 12 gallons in 95 miles, I filled it again somewhere else and within a mile or two all was well. Since the problem here seems to point to two specific cylinders it seems unlikely that dodgy petrol is the issue, but I thought it worth relaying how significant an effect it can have.


Active Member
hi, are you taking about the dizzy cap or spark plug cap?
no knocking sounds.
I am talking about the distributer cap. It was trying to fire two cylinders at the same time and caused a severe knocking.
I also have suffered poor fuel on 3 occasions over the years , but that caused a misfire , coughing & spluttering when trying to accelerate
Hi there.
today I did more tests regarding the plug leads etc.
eventually found that the cap was not sending a spark to 1and 4 cylinders from the cap end.
So now have to find a cap, Supercheap can order me one for $49 plus postage, so that is my
only way forward. Wins have them for 9 GBP plus post, but going with the local option.
I always use 98 octane , 95 if thats all that is available.