2.0cu ignition timing - not enough adv adjustmentavailable?

[T25rc]

2.0cu ignition timing help request!

I've just attempted timing my van - somebody in the past has removed the timing scale however they have marked the engine with a tdc mark and also the pulley. I've checked against pictures and they look as accurate as is possible to tell in that manner.

With the engine at 900rpm and all pipes connected I understand I should be aiming for 5 BTDC.

My issue is that my distributor is at its most advanced position and I'm still not apparently advanced enough. (I'm setting 5 degrees on my timing light and see to line up tdcs)

[sarran1955]

Hello,

This may help..

I hope you are not trying to use the remains of the 2 spigot dizzy with the amp and idle control..

https://www.youtube.com/watch?v=KkyBAMMHpa4" onclick="window.open(this.href);return false;

Cordialement,

[T25rc]

I am using what appears to be the original setup however has the idle stabiliser removed and wires joined, I'm not sure what you mean when you say you hope not?

That video should help me make some new timing marks, thank you. However I fear they will line up with the other people's and it will still show up as it does at the moment.

[bigherb]

Why not just fit a new timing scale then you will be able check everything properly.

[mr_nunn]

I think you should aim for 5deg after tdc, not 5deg before, no? Assuming everything original...

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[T25rc]

Oops, yes I should be! What should I time to at idle with the retard vac removed and blocked? 7btdc, is that correct?

[mr_nunn]

Yes i think without retard it will be 7deg btdc, but the manuals i think say to time with both vac pipes connected..

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[T25rc]

Well i've driven it today after getting it as advances as it would allow and then setting the carbs a little at 900rpm. The van is completely different, loads of torque and much smoother. A good start!

[T25rc]

Problem solved:

I bought a timing scale from brickwerks and fitted. The mark someone had put on the engine was way out. I checked what i had been running the last few days and it was 0 degrees with everything connected, so 5 degrees advanced. It pulled very well up hills in 3rd and 4th - hopefully i'll be so lucky now its reset to 5 deg ATDC.

I'll reset the carbs base level as i imagine it'll be a tad rich now with less time for the fuel to burn.

I've been balancing them at idle by setting at 900rpm and then disconnecting each fuel cut off in turn to get the idle speed the same running on just one carb ( as advised in some guides). Does anyone know what speed i should aim at while running on one carb? I've been hovering around 550-600 and that seems to be ok, but i have no gas analyser to check if thats lean/rich when both connected up.

[mr_nunn]

Hello,

I have struggled with getting info on the procedure for DIY tuning. The video by sarran1955 is great for getting the base setting, but then if I remember rightly it cuts to everything on the van and already adjusted right. So I haven't yet found a good vid of doing the balancing/mixture/idle/screws from the point where you first put the carbs on the van and start the engine (and using DIY equipment only, i.e. only a basic analyser or none at all). If anyone who is good with tuning these fancies making a video to demonstrate this it would be hugely useful and appreciated!

When I was looking into this I amassed various bits of guides (from Bentley, Haynes, and various websites such as Itinerant Air Cooled and ratwell); my notes were as follows - but be great to hear comments on this from people who know what they are doing with these carbs (e.g. bigherb? sarran1955? ajsimmo? - do you agree with the procedure below?). Some of it comes from info that was written for Bay vans with the same carbs and I don't know whether it carries over to the T25 CU setup.

0) warm engine

1) synch at 2-3000 rpm using using synchrometer (or the cheap Gunson carbalancer) and adjusting RH linkage rod length to get equal readings

2) adjust L and R mixture
- undo RH linkage rod
- pull off retard hose
- disconnect central idle cutoff
- starting point is 2.5 turns out on each of the bottom mix screws
- idle should be 500-700
[if too rough, use dashpot to raise rpm a little]

- with a gas analyser, adjust CO to 3-5% by turning bottom two mixture screws uniformly in/out
OR
- without an analyser, the Itinerant Air Cooled website says you can use the "mixture reference hose" trick here as follows:
- take left hand vac hose off air cleaner
- if finger on hose vs finger off hose gives the same rpm, mixture is ok
- if finger off increases idle then you are rich (so turn in both screws, 1/4 turn at a time)
- if finger off decreases idle then you are lean (so turn out both screws, 1/4 turn at a time )
- however, this was written based on a Bay set up so not sure if it applies to the T25 CU...!

3) fine tune L and R mixture
- disconnect one idling cutoff solenoid- read drop in rpm
- disconnect other - read drop in rpm
- less drop means that side is leaner/weaker - screw out to richen (1/8 to 1/4 turn)
- more drop means that side is richer/stronger - screw in to lean (1/8 to 1/4 turn)
- adjust in opposite directions to equalise

- reconnect retard hose/central idle cutoff

[4) RATWELL SAYS RECONNECT AND SET DASHPOT HERE:
- start so doesn't contact plunger
- turn to left till rpms begin to rise
- back off by 1 full turn
- rev and look for smooth return to idle
]

5) adjust idle to 800-900 (idle speed screw)

6) with a gas anlayser, adjust top idle mixture screw to 3 +/- 1% CO (from the Bentley Bay manual, but iirc I think Haynes T25 specifies a lower CO reading of 0.3-0.9% here, so ???)
OR
- without a gas analyser, turn top idle mix screw IN till idle drops noticably
- then out till fastest idle speed reached
- then in till drops by 30-50
- then out by 1/4 turn

7) re-adjust idle to 800-900

[T25rc]

Thanks for that - by the looks of it that will give a reasonable tune at home.

[mr_nunn]

If one or more of the Aircooled gurus/pro mechanics would be willing to review/E D I T/refine the procedure above then it might be a useful addition to the wiki?

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