SU Tuning and Timing

[mibazza]

Well it's away for it's MOT and hopefully when it passes I want to tune my SU and set my ignition timing. I've put a timing light on the flywheel and noticed that its not at 8deg BTDC which I believe it should be (8v vitara engine in my Samurai). When I adjust the mixture screw on my SU I notice I can get it to 8deg but it's running really rich and unburnt fuel dripping out of the exhaust. I've got it running really lean at the moment for MOT so once it comes back I want to tune it. My question is, should I tune the SU first using the procedure in the Haynes SU manual then adjust the dizzy to get the correct timing or the other way round?

[Twiss]

You should really get the engine up to temperature and then do the timing first...
Disconnect the vacuum advance temporarily, as that will advance the timing if the engine is revving, then set the timing to the mark on the flywheel.

Then do the SU mixture afterwards... thats how I usually do it anyway

Also its worth checking that your vacuum advance port on the SU comes out on the air filter side of the throttle disc, rather than the engine side.

If its coming out on the engine side you will have full advance at idle, and no advance at thottle... This will make it run rich as hell probably!

If you touch the end of the tube to your skin with the engine running on idle, there should be little or no suction. if there is suction at idle, disconnect the vac advance and leave it disconnected. If thats the case you will probably have to redrill it to the other side of the throttle disc

[mibazza]

Cheers twiss, I know about the vacuum advance thing and mines it blocked off so it doesn't get any advance at the moment. I want to move the port to the filter side of the butterfly but I've been told that you can pull it out of the carb and so far I've not managed this and don't want to be too rough with it as it's only a few mill width, do you know if this is correct that the vacuum advance port can be pulled out of the carb body? I've tried twisting force (gently) on it too to try and free it but nothing so far. As for tuning I'll do the timing first as you say then the carb, once the carb is tuned and if the timing is out again will I just re-adjust the timing again? Been called offshore for a few days so it'll have to wait till next week now. Bloody garage failed it at it's MOT again, back brakes are good now apparently but still failing it on the handbrake. Guy told my missus that he thinks theres water in the cable linings? Never heard so much BS in my life.

[Twiss]

The timing shouldn't change when you do the carb... especially if you are running it static timing with no vac advance...

As for the rear brakes, if they are working OK and even on the brake tester and the handbrake still doesn't work, it might actually be the handbrake cables! I would probably whip them off and have a feel and see how smoothly they move

If they have had water in them the inside of the handbrake cable could be rusty...

[RichardD]

I took mine to a local classic mini garage to set up. SU's respond best to black magic and voodoo in my experience!

[ScottieJ]

http://sucarb.co.uk/technical-hif-type-carburetter-tuning-general

http://sucarb.co.uk/technical-hif-type-carburetter-tuning-single

When adjusting the carb blip the throttle and let is settle between every adjustment.

Don't forget to make sure your dash pot is full to the correct level and preferably the correct grade oil, straight sae 20 weight oil is best and what you'll find in a bottle of SU carb oil.

This is a quick guide to the black magic and voodoo of SU carbs i.e. how to tell that your mixture is right when tuning by ear. Once the engine is up to temperature remove the air filter and use a screw driver to slowly lift the piston 1-2mm while it's idling and listen to what the engine does......

If it stumbles and the revs drop you are too lean so enrichen the mixture. (don't forget to blip the throttle and let it settle)

If the rpm picks up slightly (50rpm or so) peaks and then drops back to idle you are about spot on.

If the rpm picks up and continues to rise then you are running too rich.

[Joe b]

why was i never informed of this awesome method

[mibazza]

Sounds good guys I'll give this a go whenever I eventually get home from this offshore prison! I do have proper dash pot oil in the carb from Burlen so thats ok. And I am running static advance (pipe on carb and pipe on dizzy blocked seperately) I'm running a BDL needle and yellow or red spring whichever is the stronger one, I can't remember.I do have a BFM needle as well so I'll see how I get on with the BDL first and change it out and re-tune if necessary. Timing definately changed tho when I adjusted the carb last time, although I was changing the carb screw a LOT not a little. Changed the spark plug leads for new recently too but I haven't cleaned the plugs or dizzy yet so I'll do them too before I start.

[ScottieJ]

Timing won't change when you adjust the carb, the rpm of the engine will though

[mibazza]

Had a timing gun on the flywheel when I was adjusting the carb and it defo changed the timing, I was able to set exactly 8deg btdc using the carb adjustment but that made the carb run incredibly rich so had to lean it right down for MOT. I'll double check this when I get home, but I'd just got the timing gun and wondered what effect the carb mixture had on timing so I tried it.

[ScottieJ]

If the RPM changes while adjusting the carb this can effect the timing the mechanical advance mechanism in the dizzy, but that is not adjusting the timing.

Once the engine is up to temp the timing needs to be set at idle 800 +/-50rpm and by adjusting the dizzy, Most of the people I know run 10degrees BTDC as long as there's no signs of pre-ignition then you'll get a bit more power.

Then once the timing is set move onto tuning the Carb.

[mibazza]

Ah well my rev counter is U/S so that won't help. Bought a cheap one off fleabay that I'll use for checking the revs when tuning then I'll probably mount it somewhere for good, save takng the dash apart and fixing the old one. Still stuck on my offshore prison till next week now so I'll have to wait a bit longer to get this done. So you reckon about 10deg BTDC then, that same for an 8v vit engine as that's what I've got in the sammy.

[mibazza]

Well I'm finally home so I've checked timing and it's 8deg BTDC at 850rpm. Took a long time to figure out why I couldn't get the revs lower than 1000rpm but turned out that the throttle cable was slightly tight and preventing the throttle lever on the SU getting to idle position. Tuned the carb as per the SU manual and it seems to be running reasonably well. Should I adjust the timing to get to 10deg BTDC? Would this be of any benefit driving on the road as I don't use it offroad yet.

[Joe b]

in my opinion if its running ok now, just leave it at that, its only a little zuk at the end of the day

[ScottieJ]

My 1.6 had no torque at 8* btdc pulls loads better at 10*

[mibazza]

OK well I'll give it a tweak at the dizzy tommorow to set 10deg and see what it's like, will I need to retune the carb after doing this?

[cookie1978]

From my experience it will never run as good as u can get it to run without doing the van pipe mod. Its so easy to do it isn't worth the time spent trying to get it to run right without doing the mod.
Try twisting the nipple gently with a small pair of mole grips being careful not to crush the nipple, that's how i got it out.

[geoffw]

cookie..