Sluggish acceleration

[GeoffK]

Hi
Have just bought a 1973 BGT and have setup the engine to the best of my ability and have found that it is very sluggish when accelerating from low revs. At about 2500rpm the problem clears and then I t goes OK. My gut feel is that the oil that I have put in the carb dash pot is too thick and during the cold weather it is restricting the initial lift of the carb pistons which clears as the revs increase. Any thoughts? I have set the engine at the following settings:
Tappets 15 thou cold
Points 15 thou
Plugs 25 thou
Static timing 10 deg BTDC
Carb needles flush with piston base
Carb jets 12 flats down from bridge
Carb intake balanced by ear
Tick over 800rpm and fairly even
The coil, distributor, leads and plugs all look fairly new.
Should I use 3 in 1 oil in the dash pots rather than SAE30.
I look forwards to any feedback
Best regards Geoff

[Paul Hollingworth]

I put 20/50s engine oil in my dashpots. You need thickish oil to get the transient enrichment. I'm sure that's what the workshop manual recommends. Buy a strobe timing light and do your timing dynamically.

[Vic Butler]

I use automatic transmission fluid. It doesn't change viscosity and stays there.

[Ian F]

Geoff, do you know what cam you have? My BGT with a Piper cam really picks up at around 2500rpm and the change is very noticeable.
I have used engine 20/50 oil in SUs as recommended. I did experiment with lighter oil many years ago and couldn't really tell any difference.

Ian F

[Michael Barclay]

Hi Geoff
The handbook recommends 20/50 engine oil but you can buy dashpot oil. Classic oil at Bicester heritage sell the penrite version.
Regarding the sluggish pick up - check the Vacuum pipe from the rear carb to the distributor is fully connected and not leaking.
mike Barclay

[Paul Hollingworth]

All oils change viscosity massively with temperature but multigrades the least.

[GeoffK]

Hi. Thank you all for your views on the dash pot oil. I have tried 3 in 1 as that was my gut feeling and it did make an improvement but was not the cure. I now suspect that the timing is thing to look at. Let’s hope Santa has a strobe light in his bag.
What are your views on the other settings? Are they Ok?
No idea what cam is fitted assume that is original equipment.
Best regards Geoff

[Charles Farran]

You don't say what distributor you have - a Lucas 25D4 or a 45D4. Per Haynes - if the latter, then the plug gap should be .0035 in for Champion NYCC or N9YC or equivalent plug. (If the former then 0.032 in for NYCC & 0.024 - 0.026 in for N9YC).
I take it you have cleaned the pistons of both carbs & ensured that they haven't got mixed up between the front & rear carbs & that there is a fresh in line fuel filter? Is the connecting fuel hose between the two carbs in good condition? Are the breather pipes from the tappet cover to the carbs Ok?
Any air leaks on the fitting of the carbs to the inlet manifold?
Cheers,
Charles

[Ian F]

Hi. Thank you all for your views on the dash pot oil. I have tried 3 in 1 as that was my gut feeling and it did make an improvement but was not the cure. I now suspect that the timing is thing to look at. Let’s hope Santa has a strobe light in his bag.
What are your views on the other settings? Are they Ok?
No idea what cam is fitted assume that is original equipment.
Best regards Geoff

Other settings look like a good initial setup to me Geoff.

I think that (in my experience) tinkering at the edges with fine tuning is unlikely to change what you describe as a sluggish performance below 2500rpm. If it really is a big surge of power then it is probably something significant, and things like plug gaps are unlikely to be responsible.

I think you need a stopwatch and some careful measurements of acceleration. Look at the plugs after some hard acceleration at high speed - switch off and coast to a stop and check the plugs. Weak? Rich? Are your carb needles the standard ones?

If you can check with the previous owner about any modifications made (cam/ needles etc.)

Of course it might just be that you have got accustomed to driving your ordinary modern diesel which has enormous low down torque and well over 100bhp!!

Ian F

[Paul Hollingworth]

Those who have read my previous comments on the 45D distributor will know I'm not a fan. Neither is Peter Burgess if you read his book. The 45 disi generally goes with the HIF carbs with the vacuum advance taken from the manifold. In total the 41610 curve has too much advance meaning that you start off too retarded. According to Paul Hunts Bee and Vee website the static timing is 7 deg BTDC and 9 deg at 1000rpm (vacuum disconnected). I do hope you have a 25D disi with the Vernier adjustment. All the curves are available on Pauls site just look up your particular one.
http://www.mgb-stuff.org.uk/ignitiontext.htm