'jerky' running on my 74 V8

DamianZ28

Active Member
Hi all, car is running lovely now I've covered 1100 miles since full engine rebuild, fresh oil & filter & 500pcs and at 1k miles I fitted new cam, as funds were available. So yes all running smoothly but as of late when driving along and say I change down to 4th from 5th gear to go up hill for example, it'll 'stutter' for want of a better word, almost like some is pulling coil lead off & back on extremely fast then it's ok!, incidentally the coil lead going into the cap did have minor surface 'dust rust' on it which cleaned off fine but still doing the same, very frustrating. The timing is currently set to -8°,any less as in -4 to -6°BDC then its really bad, have fitted an electronic ignition kit, new leads , new coil/ disty cap ect. carbs all rebuilt.
Could it be moisture in the fuel ? Pump is an engine bay 'sucker' electronic Huco & works really well. Its only recently started to do this which is the odd thing, could it be timing perhaps ? Heads & block were skimmed, am running composite head gaskets. A real head scratcher as I think its something simple I hope!
 
Do you have a fuel filter fitted? If so check it’s not gummed up. If not, check if there’s dirt in the float chamber that could be causing a blockage.

Also, I didn’t notice any info on the condition of the carbs. Check the spindles for wear, you can spray carb cleaner around them while the engine idles and see if it changes at all. It shouldn’t.

On ignition, does it have points still or electronic ignition? If electronic check the plug gaps, they can be opened to 0.032” (0.8mm) to make use of the extra power.
 
Mine did similar when we brought it. 45 years of grime in the fuel tank, showed up especially downshifting to accelerate going uphill. Another clue was the fuel gauge didnt work, as sender was rusted up. We removed, tank, cleaned and sealed, and cleaned out fuel line and renewed filter.
 
Hi guys, thanks for the replies, carbs were 80% rebuilt but still have old needles, new fuel filter. I refurbished the inside of the tank with a frost kit, sender is also brand new. Ignition has electronic kit but ill check the plug gap, good tip thanks!
 
A new cam will require the carbs be retuned to suit. Normally it results in lean running which can burn your valves. However try adding thicker oil to the carb dashpots. That will richin up the mixture during accelleration.

What is a frost kit? if its an additive to the tank you may well have gummed up everything. I'd flush it all out....The actual tank walls are lined with a lead solder so they don't rust unless scratched.
 
Hi Mike, carbs have been adjusted after cam was fitted, mixture is good. Fuel tank was originally a mess inside, filthy & surface rust from lack of use/damp before I bought the car. Frost kit had acid based cleaning solution, decontaminating solution & then a tank sealer which adhered to the clean metal on the inside, I had the sender (new) out a few months ago & all was very clean with no loose debris, still a clean grey finish to the inside.
This has only started in the last say 200 miles or so, the electronic ignition kit is new old stock kit, possibly it has an intermittent fault, poss the new coil has become faulty, not sure, the car doesn't back fire or actually stop, just hesitant but for a split second then ok, as I said almost like some is pulling coil lead off & back on extremely fast, not just uphill but just in general driving, either a fuel issue but the filter is new & full when engine is running or its electrical & ignition fault somewhere
 
Hey @DamianZ28. Veering off topic, with my apologies, did you get your latest P6 painted in that shade of blue you wanted, and fit a set of Cragars? Coz if ya did, we're gonna need pics!
Hope you find this bothersome fault and get it rectified.
 
Hi Alistair, no not yet sir, possibly next year, there's a small possibility l maybe able to purchase the alloy wheels in the summer if the budget allows! New central heating boiler and new roof first though....watch this space!
 
Sounds like an electrical problem to me. Undo and clean as many ground/earth connections as you can readily reach, including the battery, and its positive lead, and the coil. Where is the Huco pump supplied with power, and grounded? Also check youir fuses for clean. Deoxit as many connections as you can.
 
Hi there, I checked all the connections, most I have renewed with fresh connectors, I'm hoping it a dodgy ignition module (Powerspark version)

The Huco pump is wired from the ignition supplied via the fuse box, earthed with a small eyelet/nut & bolt through the inner wing. Battery is new & I checked the connection the other day.

I drove it yesterday evening & its wasn't great, intermittent again, before I set off I had to retard the timing as it was dreadful going up the road, had to turn around & go back home quick & set to about -8° BTDC, one thing I noticed is the strobe light didn't work straight off then it did, its brand new & was working fine before this issue, tested it on a friends classic & worked fine, so if the module has an intermittent fault then would this in turn effect the strobe gun function as a potential weal spark to number one lead ? ( where the clamp goes on to) .

Once up & running say at 50~60mph its fine but still has the hesitance about it but dreadful at low speeds & pulling away.

Speaking to various Rover V8 people who know their stuff & I get mixed opinions, some say refit the points & condenser while others say keep the conversion module ! So I've ordered a new module but also a set of news points & condenser for a safety net.

I did notice the other day while it was running rough that the fuel filter was completely full, this normally is not even 3rd full when running & has always been fine, I though well maybe there is an issue with one of the carbs, but yesterday it was fine.....need a new hobby lol :-$ , if funds permitted I would replace the whole lot with a new manifold edelbrock & Holley 390 carb jetted to suit the 3500!
 
-8° BTDC is confusing, do you mean 8 deg BTDC, or 8 deg ATDC
Sure a dodgy spark module will show up on a strobe, the flash should be regular. Try it on all the other leads near the plug boot, see if any leads are maybe breaking down, if they all mess around you know its the module, or wiring.
 
Can you get a pressure gauge on the fuel line? Maybe the tank return is blocked...Should only see 2-3 psi, more could overpower the needle & seat.
 
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