The V8 Owners Forum -

Hi guys
I've got a rover 3.5 V8 in my Humber sceptre mk3 with hif44 su,s on it but it sometimes when I'm out and excelerase only get like one third of the power even though my foot is planted it makes no difference, it's fine up till then but it's not all the time , I'm guessing it's carburettor issue ... any suggestions?
Regards dave

Sounds like no fuel is being sucked though one of the jets. For whatever reason.

Fuel supply/restriction blocked filter etc maybe

Possibly one of the dashpots sticking.

Chris.

Yeah the fuel lines and pump are new and the carbs have been stripped and cleaned and I've got oil in the dash pots I've just let it cool down for a hour and gone back out and she's flying again ???

Does it only happen when the engine is good and hot? Fuel vaporisation?

Hi Dave
so how does that happen and how do I get around it ?

My first RV8 - a 1969 P6 3500 - was very prone to this. But only when idling on a hot day or in very slow moving traffic. But it would cut out totally, and not re-start until it cooled down.

Things like fuel pipe routing and so on can make a big difference, so it's difficult to be specific on a one off installation.

Are you using an electric or mechanical pump? Engine driven or battery fan?

Does your fault only happen at low road speeds where the airflow past the carbs etc will also be low?

Hi Dave
It just seems to be when it gets hit like in slow moving traffic then I get one third of the power no matter how much I give it I've got a new hardy fuel pump and all which is mounted on the drives inner wing sow I can put a heat shield around it I thought it was a little tight in there but this is the first time I've came across this I was going to wrap my exhaust manifold but it's to tight to get in there I've been thinking of changing the sd1 carbs to the p6 carbs at a later date as well . There are pictures of that engine bay in The garage scene under humber sceptre mk3 see what you think your views would be appreciated
dave

If you've got one of those infra red heat measuring guns, might be worth checking the temperature of the pump and fuel lines? I doubt the actual carbs themselves make much difference since they will be the same as a maker's installation.

Of course it may not be vaporisation at all. But if it only happens when things get hot it's worth considering.

Hmmm I just been out for a run and stood in traffic and it did it again I got home and felt the pump and it was warm to the touch so that's probably the issue I'm a boat builder carpenter and we have some silver heat shield matt so I'll wrap it around the weekend to see if that will work it'll look a tad unsightly but if it works least I know . I will let you know fingers crossed
Regards dave

For the petrol to evaporate, it has to be more than warm to the touch.

HI Dave
Yeah I was just thinking that . And that was warm not hot .so back to square one but I will still cover them up with heat wrap it's got electronic ignition but it's running the old coil but I still think it could be carb related because I bought them from eBay he said from a running landy and I've had a few teething problems with them I've just bought a couple of sets of p6 carbs and manifolds,I'm picking them up from the nrsa swap meet 1st of March think it wouldn't hurt to service them and try them is it true that the p6 carbs are a better than the sd1s ?
cheers dave

Dave, assuming you've got perfect clean fuel supply at the right flow rate and it's not heat related, check the float chamber condition at the base of the HIF unit - if the plastic floats are old and not 'floating', due to filling with fuel, they can throw up some quite odd intermittent faults.

Also, your coil...change this for a known working one. I had a similar issue on a previous V8. Was convinced it was a fuel issue...checked, cleaned, rebuilt everything on fuel side; NFF/perfect working order. It was the coil breaking down under load when at higher operating temperature.

As they say, '90% of fuel faults are electrical...'

Ok then I will order a new coil I know the one I have is old if not the original from 1988 so it's well due , and that will be another one to cross off
Thanks Dave