Carb diagnosis

Tor

Tor

Well-Known Member
My father's South African 1973 V8 auto runs HIF6s and has a throttle hesitation issue that we've struggled to figure out. So far, it can only be compensated for by enrichening the mixture on the one side to the point where the car returns 10mpg urban.

With proper synchronisation and balancing the MPG and general response have improved a lot, but the minute you stop the engine and restart, as one does when shopping, it's a complete pig to drive. Putting foot helps, but it takes a good second or two to bite from standstill (and there's no power until it does). The LHS carburetter is the offender, and RPM wavers while accelerating until it reaches peak running temp. While warming up the engine needs a lot of choke.

It gets worse in right-handers, as power comes and goes in a steady, frustrating rhythm.

It's getting a replacement set of carbs fitted but this sort of issue makes one curious. Fuel line filters have been replaced and the car is generally well looked after by a P6 expert. Electric fuel pump. Carb spindles have lengthwise play (along the axle) but very little "up-and-down" play.
 
Forgetting the fact that there's plenty of other things that you should have worked through first, so making the assumption that is all OK I'd suggest that the needle has dropped down in the piston on that carb.
 
Or a low fuel level in the float chamber?

A carb overhaul beckons (see other recent posts). Also check the throttle linkage and make sure both carburettors reach full throttle together.

Chris
 
The needles were both sitting in the dashpots when those were removed and cleaned. Can an over-rich mixture override a too-low float level?
 
Thanks for that, but turning the mixture screw right in made the car run evenly through the range. Anyway, the carbs are being swapped over today, and I'll post any findings by our guy Alan there. I already sent him your previous detail postings on setting them up so I'm waiting for some emails when he opens up the old ones...
 
In the end the carbs were replaced with a rebuilt pair. Here's what our guy found:
" -The [intended replacement] carb bodies were adjudged O.K., as were those that came off your Dad's car. The spindles & butterflies were both good with no excessive play & the poppet valves operated cleanly. What I did find,however, on the carbs I removed & replaced with the ones I had rebuilt to Workshop Manual Spec was both floats were leaking & the springs in the suction chamber were wrong. The seals in the cold start valve seals were in a poor state. Fortunately I have accumulated a fair amount of parts both used & unused for these HIF 6 carbs & was thus able to effect a good rebuild, The carbs were not all the story as I checked out the distributor & found the advance/retard servo diaphragm was ruptured, I fitted one I had repaired & we were back to square one briefly."

From square one, the car was taken out on a road trip, rather optimistically as it hadn't been tested, and acted up after an hour to the point that my dad had to limp back from the Paarl winelands and book a rental to save the day:

"What I found when I managed to get the car to my house that there was no points gap. This was due to wear in the bush in the points mounting plate being equal to or greater than the points gap. This occurs on the older design which has a roughly triangular plate which swivels around a mounting pin & wears. The later design has the plate rotating around a larger diameter bearing & is less sensitive to wear. currently the car runs O.K. but, is prone to start misfiring at about 4000 r.p.m. or so, I suspect coil &/or plugs but will sort this out in due course."

So, bodged, perished AND worn out. Now it runs, though!
 
Sounds like it just needs a proper Tune Up now and all will be well :wink:
By this I mean checking, cleaning or replacing plugs, air filters, points etc and setting up dwell, timing and mixture :)
It's frustrating chasing problems if you don't start at the beginning. Sounds like you are nearly there now 8)
 
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