First 20 mile drive observations with a manual Stag

[sujitroy]

After 20 years of driving an auto, I got Stag no. 2 out in 50 degree weather last night here in Northern CA with top down driving and a very jacket and cap. I live about 5 mins. away from the freeway/ motorway. Observations. It a Mk1 with a Mk1 working tacho. I noticed while driving at 70 mph without OD and depending on the road's gradient, my tacho from varies between 2k and 3k? Does this sound right? I still need to get the fuel mixture right which is close and am wondering if is is causing the following issues:
If I engage the OD at 70 in 4th, the car feel very sluggish. Is this normal?
The nice this is, at this speed I don't have a diff whine, which has plague my auto since day 1.
Sujit

[trunt]

In any one gear the speed and tachometer should be in exact synch. If you are really seeing it e.g going higher when going uphill then a clutch could be slipping, but more likely is that the tachometer is not 100%

I cant remember the exact tachometer reading at 70 but it certainly should not feel sluggish so maybe some more tuning needed.

Mine is at the back of the garage at the moment so can’t get it out to look as the MG is getting a diff exchange

Terry

[richardthestag]

depends on tyre size and diff.

when I am on a motorway my tacho reads anywhere between 1500rpm and 3500rpm depending on my speed and gear selection

One thing I can help with, at 70mph I do need to flick out of 4th gear OD (J-type) should I need "Our Blessed Lady of Acceleration". however I can stay in OD 4th if I fancy a gentle acceleration up to slightly beyond the national speed limit. This is the main reason why I think the BW auto suits the stag better, always seems to be in the power band

I have a 3.45:1 diff btw, I reckon with a 3.7:1 I would have more urgency due to the slightly higher revs

[Phil S]

sounds like the taco is playing up, as its electric drive from the ignition is should give a constant result for a constant road speed, if you have a good timing light with a rpm readout this could be a way of checking up to perhaps 3000rpm this wont obviously be affected by mixture, but that would be a definite with lack of power under load with the OD engaged

[flying farmer]

Manual Stag gearing is roughly 20mph/1000 revs in 4th and 25mph/1000 in overdrive give or take a bit for diff ratio and tyre size.
Mk1 rev counters don't always like electronic ignition if you have that fitted. My Estate works fine with a MK1 rev counter, but I couldn't get my Mk1 Stag to work with electronic ignition and ended up converting it to a mk2 speedo and rev counter.
Sluggishness could be mixture related, or it could be ignition timing.
Another possibility is that there is a fault in the low tension side of the ignition. MK2 rev counters count the pulses from the coil but MK1s sense the current flowing through the coil so if the current is low it will give a weak spark and a low rpm reading.

Plug gap is another important point at high load settings. A lot of new plugs come with a far greater gap than the 25 thou specified. The engine will rev to the red line no problems at light throttle settings, but at wide throttle settings increasing cylinder pressure and a shorter charge time for the coil will result in the spark blowing out. Many years ago I suffered a coil failure and replaced it with one from the local parts store. It simply would not rev past 5000rpm on a wide open throttle.
Taking things to extremes on my high performance engines, I have to use a max of 25 thou even with a very low resistance coil and fixed dwell

Neil

[sujitroy]

Hello Neil,
I have Pertronix driving the Mk1 tacho. By mistake I left it off my original email and was meant to point that out, Timing and carbs have been checked and balanced, vacuum is new. Plug gaps were checked. I'll take it for another spin today and report back.

Sujit

[mallardstag]

You probably need to convert your tacho to mk2 spec and make minor mods to it's wiring to get it to work with the pertronix.

https://www.socforum.com/forum/forum/stag-owners-club/soc-forum/806406-mk1-tacho-not-working

[Bakdraft007]

You probably need to convert your tacho to mk2 spec and make minor mods to it's wiring to get it to work with the pertronix.

https://www.socforum.com/forum/forum/stag-owners-club/soc-forum/806406-mk1-tacho-not-working

I can comment that I have a Pertronix with a MK1 and my Tacho works perfectly. I know all systems are different, but at least I can say it is possible. I have a Pertronix Igniter and Pertronix flamethrower.

[mallardstag]

I can comment that I have a Pertronix with a MK1 and my Tacho works perfectly. I know all systems are different, but at least I can say it is possible. I have a Pertronix Igniter and Pertronix flamethrower.

It's marginal, some work, some don't. It also depends on coil, ballast, wiring, battery and tacho.

[richardthestag]

Slight thread hijack but interesting stuff that Neil writes about plug gaps. Rover v8 in Range Rover runs a 30thou gap and with LPG the recommendation is to push it to 35thou. 3.9 is no where near as revvy as the Stag v8 but on lpg it runs beautifully up to 4500rpm but no further. switch it to petrol and it goes like stink up to the red line. It doesn't happen often because the engine has acres of low down torque

Ignition on the Rover v8 is standard Lucas 35DLM8 with amplifier, Bosch coil and silicon leads. nearly a decade ago - (I know! I hang onto cars for a long time) I swapped to Bosch Super4 plugs, that set is still in there after 70k miles and still performing beautifully.

I also have pertronix and flamethrower setup in my stag and pushed the plug gap to 30thou, cannot recall what plugs I have fitted but they are standard style. No issues at all running it through the rev range.

R