TheSamba.com :: View topic

Fri Dec 22, 2023 10:00 am

Hi everyone,

Looking into servicing the engine in a 77 Bay with a 2 litre dual carbs for the first time and I have seen carb tuning mentioned a couple times. What are your thoughts on getting the carbs tuned professionally on a rolling road? Is it worth the high costs (~£350 for www.aireytuning.com !!) in the long run, or will DIY do it well enough?

Many thanks in advance,

Tom

Fri Dec 22, 2023 10:23 am

Do it yourself and learn, save the dollars.

Fri Dec 22, 2023 10:46 am

What kind of carbs (stock, afrtermarket)?, who's been working on it in the past?

Fri Dec 22, 2023 1:10 pm

busman78 wrote: Do it yourself and learn, save the dollars.

Yes, these need periodic adjustments, so it will need re-tuning anyway. Proper jetting, balancing, adjusting idle mixture and speed are all do-able at home.

Learning how to take it from start to finish yourself will be valuable down the road, either to tune it again later, or save it on the side of the road.

Fri Dec 22, 2023 2:08 pm

Buy and fit an Air Fuel Ratio meter, and get a carburettor synchroniser tool.
Cheaper and any day can be a tuning day if you wish.

Fri Dec 22, 2023 5:07 pm

do you know how to tune and sync the two carbs other than main jets?

Fri Dec 22, 2023 9:54 pm

Having your vehicle tuned for the proper air-fuel ratios and ignition timing (using a wideband and a dyno) is the best thing you can do to a running engine keeping it "as-is"

most particularly, an air-cooled one

water cooled engines have extra capacity for cooling with large radiators and lots of coolants buffering temperatures, and a thermostat always working to apply the cooling system only as much as needed .. the state of tune on these engiens can change quite a bit without really having a dramatic impact on cylinder head temperatures in normal operating conditions

An air-cooled Bus engine cruising the highway, however, is just blowing a fixed amount of air onto itself from the engine fan based on RPM, and the cylinder head temperature is basically whatever you get based on how hot its running vs what RPM the fan is at.. the thermostat is is not in play under those conditions....

small tuning changes can have pretty dramatic impacts on engine temperatures with a Bus, as tuning is the part of the formula for real life cylinder head temperatures that you can actually have the most control over

the difference in drivability and efficiency can be pretty dramatic, too

don't listen to people say that you tune it by ear, DIY, at home driving around the block and reading spark plugs
that isn't the same thing at all

no substitute for...

ROLLING ROAD
WIDEBAND
DATA LOGGING,
tuning BY the NUMBERS. as inrejetting..not just setting idle/mixture screws and acting like that's what "tuning" a carb means.

that will definitely produce results !!!

As a general rule, target 0.80 - 0.89 Lambda values for fuel and you will be solid

Once your carb is feeding the correct fuel ratios across all loads
then you can do your ignition, using "MBT" (look it up)

if you have a 123 distributor then you can do a totally custom map to follow MBT exactly
if you have an OEM distributor you can just spin it and advance until you find the absolute minimum amount of static advance where you have basically the max torque value
you can futz with weights and springs to really customize the map, but at that point the 123 is a much better choice

the ignition timing isn't usually that serious, though .. it's the carb tuning that can vary greatly. a stock distributor at stock specs is always fine but get those air-fuel ratios PERFECT...and it will be great.

if someone else it doing it all, and knows your carbs, then great

in the UK, this seems to be a a much more common practice, and there seem to be a lot of people doing that sort of work..

Sun Dec 24, 2023 11:34 am

Thanks for the responses everyone. I have twin Dellorto DRLA 40s and we recently bought the bus so this is the first time I am doing this. My current plan is to install a wideband sensor and log the readings whilst driving a set bit of road. Do you think this will suffice or is a rolling road much better?
Thanks again and have a good Christmas!
Tom

Sun Dec 24, 2023 1:00 pm

I agree with going with an AFR gauge and maybe dyno tuning…at a certain point.

Lots of bus engines don’t run as well as they could because of tuneup and maintenance 101 kinds of issues; timing, vacuum leaks, missing tin, improperly adjusted valves. You would want to make sure all of these are put right as well as having healthy compression on all 4 cylinders.

I would want to have all these things sorted out with the bus running the best I could get it before spending the money on a dyno tune. Since your bus is new to you, you are likely to have some of the issues mentioned above. At the very least, these skills are a requirement if you want to drive your bus any distance.

Sun Dec 24, 2023 3:46 pm

Depends on where your wideband bung is. Tailpipe clamps get less accurate the faster you go, but an O2 sensor at a header collector or pre-cat/muffler would be great.

Robbie