Automatic transmission hesitation

[fairline38]

So...it's been almost three years since I visited this topic.

Ultimately, the hesitation problem (fade out at start-off - low speed acceleration) returned.

In late 2019, I took the car down to a carburettor specialist near Winchester on the recommendation of another owner.

These guys definitely know what they are doing.

They first tested the SA on their rolling road and she was putting out just under 125hp at the rear wheels.

After about an hour of intense testing, they changed the jets, retuned the carbs, and retested her. The changes raised the hp to 166! I wouldn't have believe it unless I had stood there and watched the process.

It was a bit disappointing that they would not road test the car themselves. Also, I paid over £ 300 for less than two hours time, which I felt was excessive, although they did have all the equipment. For that money I thought they were going to remove and rebuild the carbs. (In all fairness, their website did state exactly what the process was and that they do not test drive owner's vehicles).

One observation is that upon warm-up, the volt meter flutters with the rough idle. This has led me to believe that this may be an electrical problem.

My next step is to have a local specialist retune the carbs.

[richardw]

I don’t think that £300 is bad at all for what they did, which is fix your problem and give you a lot more power. Great result!

Richard

[Lotus-e-Clan]

So...it's been almost three years since I visited this topic.

Ultimately, the hesitation problem (fade out at start-off - low speed acceleration) returned.

In late 2019, I took the car down to a carburettor specialist near Winchester on the recommendation of another owner.

These guys definitely know what they are doing.

They first tested the SA on their rolling road and she was putting out just under 125hp at the rear wheels.

After about an hour of intense testing, they changed the jets, retuned the carbs, and retested her. The changes raised the hp to 166! I wouldn't have believe it unless I had stood there and watched the process.

It was a bit disappointing that they would not road test the car themselves. Also, I paid over £ 300 for less than two hours time, which I felt was excessive, although they did have all the equipment. For that money I thought they were going to remove and rebuild the carbs. (In all fairness, their website did state exactly what the process was and that they do not test drive owner's vehicles).

One observation is that upon warm-up, the volt meter flutters with the rough idle. This has led me to believe that this may be an electrical problem.

My next step is to have a local specialist retune the carbs.

They could have made 3 or 4 adjustments to increase the max power at the wheels from 125 to 166 bhp - unrelated to changing jets.

• • 1) rebalanced the throttle plates physically
    2) adjusted the throttle cable to fully open the throttles
    3) reset the float levels
    4) reset the maximum mechanical ignition advance to spec.

It's VERY unlikely that the factory spec jets (Mains, Airs, emulsion tubes, idle jets or the Lotus-specific power jet) were wrong and causing reduced maximum power.

You now have a rough idle, which has many causes and cures, and doesn't exclude the possibility of inappropriate jet changes or other adjustments made during the 2019 session.
Maximising power is the easiest and most profitable adjustment to make on a rolling road. Optimising driveabilty is much harder.
So jury's out on whether it was £300 well spent.

[fairline38]

Here is an update on the SA auto box hesitation from start-off...turns out that the idle balance lever had been jimmied by someone in the past. I was able to source a new carb balance lever for the Dellorto 45 carb with both balance barrels attached. It is part number 11129 - Lotus Turbo Balance Lever from Eurocarb. Speak to Travin. He was incredibly helpful. You can fine turn the balance lever to remove the engine low rpm hesitation. The engine idle is perfectly smooth now and acceleration and kickdown is perfect.

[Hawaiis0]

Very interesting report.

How long have you been running 'fixed', as after a earlier attempt the symptom came back?

My similar hesitation would come and go with out warning. Cant try your fix as now the engine and Gearbox are up for refurb.

Stu

[Pete Boole]

Yes - a very interesting thread. I'm in the process of fitting a ZF into my Elite, but with fuel injection etc. It will be interesting to see how it runs!

Pete

[Zaphod]

Am I right in thinking the autobox used in the SA is a ZF HP422? If so did lotus use the fix that Jaguar and later Land Rover did to stop premature wear in the 1st gear clutch pack? This was a fault that plagued BMWs and Volvos that used this gearbox and the earlier 4 speed auto range rovers. There is a condition that occours when the gearbox has a slight wear on one of the seals which means there is always some drag on the first gear clutch pack. Initially it manifests as a reluctance to change gear till warm, sometimes the gearbox will stick in first when driving off then when warmed up normall operation is resumed. In later stages it will either loose all forward gears or reverse. The fix was simple, a hole was drilled to relive the unwanted pressure, this was applied to all jaguars using the gearbox which would normally outlast the car, the same can’t be said of the BMWs that used it. The problem was so bad California exempted cars using it from the high RPM part of their smog tests as cars had failed at the testing stations!

[Hawaiis0]

Am I right in thinking the autobox used in the SA is a ZF HP422?

Yes the 4HP22 is the box used. I'm not sure if that fix is built in. I will enquire with Ashcroft's when i send mine in for overhaul.

[Pete Boole]

I'm not sure if that fix is built in. I will enquire with Ashcroft's when i send mine in for overhaul.

Thanks Stu - let us know what comments they make about that.

Pete