8 replies to this topic

[Leonrjohnson]

I have a 123 distributor fitted to my 970 Mini Cooper S engine. I am running it on F curve after sessions on the Dyno. I bought the 123 from Minispares UK (their P/N C-27H7770 ) about 2 years ago, but lately I have been getting the odd Spitback(backfire) out of the carb (HIF44) at about 3000rpm and on Highway cruise mode. It doesn’t do this at full throttle operation. This may occur once an hour on a trip as a series of 1 or 2 pops, but I cannot make it happen with my input: it just happens. I can understand if the engine was cold, but this happens when it is up to operating temperature. I have a BBW needle in the carb. This was settled on after prolonged highway driving with an AFR meter in the exhaust. It almost seems like the mixture is lean when the spitback happens, but it happens so fast that I don’t have time to play with the choke to richen it up. I have renewed all intake gaskets, but no difference. I don’t have any manifold leaks, and the car is not fitted with a power brake booster or PCV valve.

The distributor doesn’t have a vacuum advance fitted to it, and I was wondering if fitting one may help my cause. New spark plugs don’t help; neither do new HT leads and distributor cap and rotor.

All compressions are 160-165 psi, and I use 97 octane unleaded fuel with valve additive. All valves were replaced with new ones about 6 months ago, along with brand new guides and double valve springs, I am using N7Y Champion spark plugs, as the N9Ys seem to be a bit too hot. I pulled them out today and they are all a nice ash brown colour. The car goes really well: this is the only bother I have at the moment.

 

Anyone else had this type of problem?

 

 

Attached Files

•  123Mini-34.pdf   46.56K   8 downloads

[mk3 Cooper S]

More than likely to be lean at in that area, Check for intake leaks and or give it a touch more fuel if possible.

What carb set up are you using?

[guywilko]

?Air leak down carb spindle 

[Leonrjohnson]

It has been suggested to me that perhaps my tacho is causing voltage spikes that cause misfire. I will try going on a long run on the weekend with the tacho disconnected. Anyone else had this problem?

[Leonrjohnson]

I took the AEG163 head off yesterday and removed all the valves. I found a crack between an exhaust and inlet valve, so this will be causing spitback !!!!  I have a 12G940 to go on when I get the combustion chamber the correct size for the 970: it is in the machine shop now.

[gazza82]

I took the AEG163 head off yesterday and removed all the valves. I found a crack between an exhaust and inlet valve, so this will be causing spitback !!!!  I have a 12G940 to go on when I get the combustion chamber the correct size for the 970: it is in the machine shop now.

 

Is the 12G940 going to fit without pocketing the block?

[dklawson]

 

Is the 12G940 going to fit without pocketing the block?

 

 

If an AEG163 was on the 970 before and worked wouldn't the 12G940 work without mods?

[carbon]

 

I took the AEG163 head off yesterday and removed all the valves. I found a crack between an exhaust and inlet valve, so this will be causing spitback !!!!  I have a 12G940 to go on when I get the combustion chamber the correct size for the 970: it is in the machine shop now.

 

Is the 12G940 going to fit without pocketing the block?

 

You won't need to pocket the block on a 970, it has the same bore diameter and spacing as the 1275.

[Leonrjohnson]

Got my modified 12G940 head on this morning. Goes like a rocket now:no more carb spit. My AEG163 is cracked between an exhaust and inlet valve; not a big crack but enough to let combustion leak into the induction , hence the spit back.

Now I am on the lookout for another 12G940 that I can modify and have ready as a spare   .