1310 Running/tuning question

[Coalhod]

Hello;

Any tuners out there - need help with the beast!

Ignition is a Pertronix II module on a rebuilt 25D distributor with their recommended 0.6 ohm coil.  Carburetion is 2 X HS4 SU's using MME needles and red springs, 20w-50 synthetic oil in the dashpots.

AFR gauge installed with oxygen sensor mounted on an LCB manifold just downstream of the exhaust collector with an RC-40 2 box system.

At idle I'm reading 12.5-13 AFR and climbs to 14.5-15 AFR on acceleration.  Car pulls like a train.  On deceleration and at low rpm or when coming to a stop the AFR goes to 16-17 almost off scale and the engine wants to stall.

I'm thinking ignition problem and may have to go back to contact breaker points and that may be the way to tell if any change happens with the way the car is running.

The lean condition on deceleration has me puzzled all I can reckon is that as the car decelerates it causes higher vacuum and the dashpots are being lifted too quickly causing it to go lean.  Maybe go to a heavier yellow spring?

Will also go back to square one to check compression, valves, air leaks etc.

Thanks  Andrew

[94touring]

You can try a heavier spring or just add a little weight (as in a big washer from the hardware store).  What's your cruise light throttle air fuel ratio?  14-15 air fuel at wide open throttle is too lean also. Shoot for 13:1 at full throttle.

[MiniDave]

Pertronix wants a 3 ohm coil on a Mini I believe. All the points eliminator set ups I've ever used want 3 0hm coils. Make sure you don't have a ballast resistor wire anywhere in the system. Electronics want a full 12V at the coil.....

Dashpots shouldn't lift till you open the throttles again, not sure if your description matches what's actually happening? Seems normal for the exhaust to go very lean on decell, but Dan can chime in on that better - he spent a lot of time fussing with the twins on his Mini.

[94touring]

Decel 19:1 or so is perfectly normal, but as you come to a stop it should richen back up and keep running without stalling.      You could check to see if the return springs are pulling the throttles too far closed after letting up off the throttle, causing a drop in rpms and a lean mixture you see. 

[Coalhod]

I did a wholesale change and removed all of the Pertronix items and went back to contact breaker points with corresponding Bosch 3.0 ohm "Blue" coil.  All of the above running symptoms have disappeared.  It does not rev to 6500 rpm quite as freely, however I may experiment with a 23D Cooper S baseplate and 32 oz. points over the winter.  Still pulls like a train.  My only concern is the AFR is around 11.0 at idle.  A flat or 2 leaner might rectify that.

Maybe the original Pertonix (not II) is better for these engines?  Can still use the 3 ohm coil whereas Pertonix recommended their 0.6 ohm coil with the Pertronix II module.

[94touring]

Well that's good if the ignition is the only thing causing the issue. I've only ever ran 3ohm coils.

[MiniDave]

Normally you run a 3 ohm coil with electronics, 1 ohm coil with points.

[Coalhod]

Well it's back to square one.  This dizzy was rebuilt by Advanced Distributors years ago and I stand by his work.  I  did not build this motor so I do not know its contents.  Anyway, put the timing light on it and it was too far advanced which would explain all the lean conditions.  I tried to take it back to spec with a dial back timing light and the odd thing is when I turned the dial to the number I wanted for advance it did not go to tdc on the pulley but showed the same amount as was required i.e. 18-20 degrees at idle.  I tried moving the diz counter clockwise and it wanted to stall.  All ports plugged and capped.  Also, vacuum gauge hovered around 10 so probably not a stock camshaft.  Sprayed carb cleaner on all intake areas no change in engine speed.  It's possible timing chain jumped a tooth - it's an old S motor with duplex chain which was replaced recently, cam sprockets lined up dot to dot.  AFR still reading around 14 at idle.  Static timed it using marks on the flywheel, will go from there.

[94touring]

Timing doesn't effect air fuel ratios.

Secondly, timing at idle shouldn't be 18-20 unless you didn't disconnect the vacuum hose. To check timing, disconnect the hose and rev the motor past 3k rpms and set it to 30-32 degrees.  Then reconnect the vacuum line and you're done.  If air fuel is still 14:1 at wide open throttle you need a richer needle if adjusting the mixture screw doesn't get you into the 13s at full throttle.

[Coalhod]

Thanks!  It turns out after more diligent carb cleaner spraying around the intake, the HS4 gaskets have an air leak.  I purchased them from Moss which I thought were a little thin and sealed with grease.  I have used FELPRO before with good results although hard to find now.  Also tried Mania, out of stock backorder 3-4 weeks!

Anybody ever try a gasketless sealant on the intake manifold/carburetor connection?  I suppose I could make some with gasket material, might be a little tricky.

[MPlayle]

Mini Spares has all of the carb gaskets in stock.

[Tim]

What

Timing doesn't effect air fuel ratios.

Secondly, timing at idle shouldn't be 18-20 unless you didn't disconnect the vacuum hose. To check timing, disconnect the hose and rev the motor past 3k rpms and set it to 30-32 degrees.  Then reconnect the vacuum line and you're done.  If air fuel is still 14:1 at wide open throttle you need a richer needle if adjusting the mixture screw doesn't get you into the 13s at full throttle.

What tool do you use to set the timing in this way?  I definitely cannot get that accurate looking through to the timing marks.

Tim.

[94touring]

I use a gun that you set to what you're wanting and it pulls your timing light on the pulley to 0 once you get the desired distributor position.  Otherwise you'd need to measure and mark a new spot on the pulley for say 30 if that's the target.

[Tim]

Can you provide a make and model?  Do you have a special timing sprocket as well, or just the standard marks on the damper pulley?

[94touring]

I believe this is the one: Innova Digital Timing Lights 3568.

Standard marks for me on the minis. The bus has a pulley with 360 degrees marked out for very easy timing.

[94touring]

If you need a visual explanation, this video should help you.  Around the 4:45 mark he gets into the meat and potatoes of it. 

[MiniDave]

I got mine at Harbor Freight, it has a dial on the back with numbers 0-60. Set it to 30* for example and rev the motor and when you look for the marks, if it's at TDC you're spot on. If not you move the dizzy till the marks line up - then you're set. Pretty easy actually.

[Tim]

I got mine at Harbor Freight, it has a dial on the back with numbers 0-60. Set it to 30* for example and rev the motor and when you look for the marks, if it's at TDC you're spot on. If not you move the dizzy till the marks line up - then you're set. Pretty easy actually.

. Excellent!  That should make things much easier.  Thanks for the help guys.