Still problems AFTER rolling rd

[chr15w]

Took the car to BD Engineering in Sittingbourne yesterday and dissapointed with power results but thats another story.
When driving at about 65mph @ 2700rpm no problem when trying to get past this speed in 4th or 5th the car coughs and backfires and loses power until I lift off and return to 65mph.
On rolling rd she behaved impecably and easily got to over 100+
On way home problem returned as before! Andy @ BD Engineering suggested that a new coil should be fitted to cure a starting problem and that this might help with the other problem.
Fitted new coil and she starts perfectly, took it out on M/way and car was perfect for about a mile then the problem returned, Doh!
The problem didnt show on rolling rd so cant blame BD Eng for not curing it, it appears to occur when hot and under load.
Andy suggested it may be fuel starvation and that I should check petrol pump but the pump has been there for a number of years with previous owners and Im assuming no probs, Im running a Rover 3500 v8.
Any suggestions gratefully received

[Sidecarbod]

Originally Posted by chr15w

Took the car to BD Engineering in Sittingbourne yesterday and dissapointed with power results but thats another story.
When driving at about 65mph @ 2700rpm no problem when trying to get past this speed in 4th or 5th the car coughs and backfires and loses power until I lift off and return to 65mph.
On rolling rd she behaved impecably and easily got to over 100+
On way home problem returned as before! Andy @ BD Engineering suggested that a new coil should be fitted to cure a starting problem and that this might help with the other problem.
Fitted new coil and she starts perfectly, took it out on M/way and car was perfect for about a mile then the problem returned, Doh!
The problem didnt show on rolling rd so cant blame BD Eng for not curing it, it appears to occur when hot and under load.
Andy suggested it may be fuel starvation and that I should check petrol pump but the pump has been there for a number of years with previous owners and Im assuming no probs, Im running a Rover 3500 v8.
Any suggestions gratefully received

What carb are you running?

Also do you know what ignition system you have? If your not too sure then try to describe it. Does it have a matchbox sized black box on the side of the dizzy? does it have a larger silver box that is attached to the chassis? does it have points? Is it an after market jobbie?

Regards,

Pete

[chr15w]

Originally Posted by Sidecarbod

What carb are you running?

Also do you know what ignition system you have? If your not too sure then try to describe it. Does it have a matchbox sized black box on the side of the dizzy? does it have a larger silver box that is attached to the chassis? does it have points? Is it an after market jobbie?

Regards,

Pete

I have a Holly carb (not sure of size) and electronic ignition, Luminition to be exact

[craggle]

What type of fuel filter do you have and where is it fitted? Any idea what fuel pump you have too?

Craig.

[Clive]

Check your spark plug gaps!

[wilf]

Sounds like it good be a fuel volume delivery problem - just enough for a rolling road run, but insufficient flow at WOT on the road for any period of time. Check filters for blockage, and what fuel pump do you have, and where is it?

Also, it just could be an ignition issue - just try closing the plug gaps up by 5 thou and see if it makes any difference (at least it is cheap to try!).

Lastly check float levels in the carby.

[lutman]

Does it do the same when fuel tank is full or only when fuel is low?
More noticeable in corners or under acceleration ?
I had a car where when low (ish) fuel it had similar and found it to be contamination in the tank, flushed it and all ok - but would suggest this is a remote possability and last resort.
More likley is the fuel filter idea, not forgetting some pumps have a filter internally that can be forgotten about. Change/clean the filters - whilst doing that the tank could be drained collecting the fuel in a bucket or similar, run that fuel through a cloth or an old pair of tights (if you've finished wearing them !) just to see what debris is in the tank.

[chr15w]

Pump is difficult to view but I can read "facet" this may not be the full name but is all I can see
The filter is a "Filter king" and is bolted to the N/S wheel bulkhead about 2" under the radiator pipe
As the car was rolling roaded yesterday the plug gaps and float chambers where checked and adjusted so I dont really want to play around there unless I have to

[wilf]

Filter king filter is dead easy to check - the bottom bowl just drops off after you loosen the nut thing at its base. Careful of the little spring under the filter element tho'. And also be ready for a little fuel spillage.

Facet pumps - not my favourite, but should be OK for a 3.5 RV8.

You may need to get a fuel pressure gauge rigged up and check that at WOT.

[Neil O]

If it coughs and backfires, surely it's more likely to be ignition rather than fuel starvation.
I had fuel starvation on my Dax once, and the engine would just die off. Unburnt fuel in the exhausts would be the backfire wouldn't it?

Dizzy module problem perhaps?