Rough running

rich777

Member
So my cars a p6 v8 auto.been stood for 1 month because it was running rough not even driving.my friend who is a ex rover mechanic has been temporary defeated.its running on 1 carb perfectly fine as soon as we go to the other carb with a bit of revs it just pops and bangs.done so far changed float /needle adjusted carbs .points leads dizzy rotar switched carbs but same thing on passenger side carb .from front of car.
Any ideas as to what we can check would be great.
He also took of rockets and everything moving correctly. I'm not sure what he was looking at though but he can't understand what's wrong.
 
Yes I think he turned one down to check the other one .as soon as we give a little throttle it just pops and bangs
 
If you think it's one carb, run engine to NWT, disconnect throttle link that connects both carbs together. Rev each carb separately. The one that pops and bangs is the problem. Chances are the needle has dropped out of the piston.
 
Thx Harvey all needles are good piston and he can see the fuel jet from the side .he can't find anything wrong with it
 
Beat me to it.
Could be your carb problem is ignition.

See what the header temps are after running for half a minute, feel them all. If you have a laser temp reader so much the better.
 
This is actually the second person to be defeated with this. Although my friends had the day off to scratch his head about it.
 
interesting . my old V8 isn't happy starting cold and stumbles and can pop or backfire plus rough running until it gets warm. then it settles down and behaves . both carbs had been refurbed 2 years ago but. car sat ( covid) for most of a year and not cranked over. etc (very remiss of me I know) had one carb overflow with fuel ..( nearside ) but slight tap with mallet and several fire ups and runs/ stops with no faults. put mine down to lacquer /dirt? on one float -fuel valve in carb. all electrics .dizzy .leads. cap .plugs etc having been replaced with new 2 years ago and a full electronic dizzy being used now. set up with colour tune in all cylinders at same time ( hot engine) though inner cylinders run marginally richer than outers. looking at stale fuel and 5% ?ethanol situation though tank has those fuel 'improvement ' pellets you see advertised in it. Apart from a glitch with 'lights' ( resolved) only worry now will be the annual poor handbrake issues. MOT now due so fingers crossed . I did use a laser temp reader and no major unbalance found. previous compression test was Ok with just over 10% differential on pressures. wondering if we sharing 'fuel' issues . or is carb (one?) being HIF type I was pondering the bi.metal part of carb .not being an expert `I understand there is a way they auto adjust selves using a bimetal strip but stand to be corrected . happy motoring .
 
HIF jet adjuster has a bimetallic strip built in, to vary the jet height slightly , and thus mixture strength, to compensate for changes in fuel temperature
 
I remember in the early 1970's a number of V8 distributer caps were cracking & thus tracking between cylinders making the engine fire on two cylinders at the same time making for horrendous knocking as one was well before top dead centre .
 
Have had the same issue on my P6Bs, thanks for the tips here. Checked with the laser reader and looks like I have two cylinders colder than the rest. Deep joy! Still to check distributor cap and also have Lumenition coil and ignition unit, fitted long before I bought it. Any extra guidance welcome!
 
Each carb feeds the end two cylinders on its own side, and the centre two cylinders on the opposite side.
(Written by a member on here long ago) May help locate carb issues.

Check your plug leads are separated to avoid cross firing, especially 5&7
 
Back
Top