Hi all,
I have a mini with the 1275 engine, and dual HS4 carbs.
We are having such a hard time getting it to run properly, and we have tried so many things:

Did the "lite" rebuild kit on the carbs, cleaned up everything. New jet, new springs, float, etc
All new gaskets, both on the carb side and heatsheild side, new exhaust manifold gasket
Took apart head, cleaned all carbon, changed the seals around the valves, new head gasket of course
Valve clearances are set to spec in haynes manual
Timing is set to spec
New plugs

Now, i followed what i read online and turned the mixture nuts all the way tight, then back down 2 turns. It also says to do this in Haynes manual.

The problem is the car won't idle, and when i hit the throttle it either does nothing, dies, or it shoots up. The idle is sporatic and goes from 2-4k over and over.

Also, something i noticed is that the pistons on the carbs don't go up equally, and that also the LEFT carb's piston is always lower than the right side, i also noticed that the left carb has far less suction.

I tried disconnecting the linkage and turning the idle screws, using the uni-syn thing but it never seems to do anything at all.


I'm really confused, have no idea what to do next... any ideas?

 

I don't currently own a classic, but I did MANY years ago. I rebuilt the SU carbs and ran into a somewhat similar problem. At the bottom of the piston there is a thin rod that goes into the jet, I managed to get one misaligned causing it to rub. That played heck with the mixture. Hopefully someone will chime in that is more experienced.

 

Make sure the pistons move freely, then you need to make sure the throttle shafts don't have play in them, if they do you'll never get it right.


Next you need to make sure the carbs are pulling equal amounts of air, using the unisyn - if the bubble is not responding you need to close down the throttle plate on the unisyn till the bubble is floating, as your engine speed changes you made need to open or close down this pate to keep the bubble centered - then get both carbs to float exactly the same - with the linkage between the carbs loose so they can move independently of each other, then do your final adjustment on the mixture.






If you have a British car club of any sort in your area, there will be someone in the club that can walk you thru this.


But check your throttle shafts for play first.

 

OH, i should have also mentioned. We already reamed out the throttle bushings and put the oversized shafts, so that is not an issue. There is zero play in the shafts now.

As far as the needle which goes into the jet, i read online that it should go down with a clunk and if not that it may be rubbing. Mine seems to go down fine and make the noise.... so i don't think it's rubbing on the side.


Now, as far as the uni-syn.... how can i even use it properly if the car won't idle? It keeps surging over and over. Sometimes though, it will stay steady at 4k rpm....

The pistons move freely, but why is the left one WAY lower than the right one?

 

If one is lower than the other when the engine is running, then that one's throttle is not opening as far or it's getting air from a downstream source like a vacuum leak - most of the air is going thru the other, which raises the piston further. If they're like that engine off you have a mechanical problem. However, one being further up than the other should not make it surge wildly. Just for grins and giggles, you do have oil in the dashpots, right?

If so I think I would disconnect and plug the line going to the brake servo and make sure you don't have a vacuum leak there....


Since I'm not there to see, hear or observe what it's doing, I'm just making the best educated guesses here that I can.....

 

When the engine is off, they are both down fully. And yea, i do have SU dashpot oil in the dashpots.

Maybe i do have a vaccum leak then but i really can't find it. All the gaskets are new too. Any particular place i should look for a leak?

I looked at the brake line one and it seemed fine although i'll plug it to be sure.

 

Judging from the responses below, most everything we can think of without seeing the car has been covered.

It is important to eliminate everything else, such as timing, making sure compression is equal in all cylinders, and the ignition system is functioning properly.

Drive Hard. Drive Safe. Keep Grinning.

 

what oil are you using in carb dashpots

 

I'm using SU dashpot oil.

I did also do compression test. They were all fine and equal. Timing is set to 10 degrees

 

Do you know what Camshaft is in your engine also how did you du the timing... here is a good way to ascertain this......first remove rocker cover (top of engine) 2 bolts, then remove spark plugs, pop in 4th gear and handbrake off now pull car forward and look at valves 1&2 rad end and watch till NO:2 valve opens and closes now look at NO:7 valve and just as it starts to move stop. now remove Distributor cap and look see if rotor arm is pointing at between NO: 1 & 2 spark plugs if so then cam is timed correctly (if not then Dizzy drive shaft is incorrect orientation) now pop a dot of white paint on block opp rotor arm now pop dizzy cap back on and NO: spark plug lead on cap should be in line with dot if not rotate dizzy by loosening clamp, and check correct lead order 1-3-4-2 in anticlockwise direction, you can now put spark plugs and rocker cover back and put hand brake on and pop in neutral and start engine.....if this does not cure then I suggest you find out what camshaft and what needles and also see if the engine has had a rebore as this will help with diagnosis

 

Sounds to me like the OP has covered all the basics pretty well, I still think he has a vacuum leak based on the symptoms.


It was running fine before, so you have to go back and look at what ever you touched - the problem is in there someplace.


I have a feeling it will be a forehead slapper when he finds it!

 

p.s. guys ... we had this same discussion in July ..... same guy

no change

 

Did he do all the engine work since his other thread or when he wrote in July?


If it has all been done since July he must really be frustrated by now......time to take it to someone who knows these cars and let hem check it over.


Edit: went back and reread the previous thread, the headwork and cark work has been done since then, and the car is doing the same thing......some question I asked earlier wee not answered, so....it's hard to get a handle on this remotely.


I still think he has a severe vacuum/intake leak.

 

just read the old thread.......you still have not clarified what cc your engine is at a guess its a +20 rebore with 11 stud head conversion, have you any paper work on the engine regarding tuning mods done......there are many types of camshaft that can be fitted......giving different power curves in turn need different carb needles

 

Yes all the carb / head stuff was done after the other thread. And yes i am horribly frustrated at this point.

My engine is a 1275 CC as far as I can tell.

I measured the bore at 70.6mm when i had the head off. I don't know the camshaft in it.

Another thing, the original owner thought it was a 1380 OR 1275, and he wasn't sure. There are no paperwork / documents to show anything about the engine either...

It's important to note that it was NEVER running right. I bought the car as a non-runner. Sitting in somebodies garage for 13 years untouched. He parked it all those years ago because "it stopped starting"... well that turned out to only be bad wiring and bad relays, which i quickly fixed. But now i'm stuck on this problem.

I also think that it's a vaccum leak although I am totally stuck on trying to find it. The exhaust manifold and carb gaskets are all brand new, the throttle shafts are bored out and new oversized shafts installed (we thought for sure that was the problem....)


i'm gonna try taking off the brake servo line / plugging this weekend like you suggested. Maybe that's it.


Yeah, at this point I really just want to be able to drive it and i'd rather just take it to a shop and have a pro do it... but I'm working on this car with my dad and he INSISTS that we figure it out ourselves without "giving up" and going to the shop!!

 

IMO ignition issues have not been ruled out

and ignition should always be futzed with b4 fuel system ....

mine ran like crud when the wrong pertronix insert was used .... idle wouldn't hold .... surging .... sometimes nothing. Turns out an 'expert' had incorrrectly identified the dizzy model and curiously the wrong points fit perfectly ... they just didn't work right ...

finally found this, took 5 minutes to swap in the correct pertronix part and it runs like a sewing machine ever since.

But I have ONE carb .... no balance issues to worry about. If the two carbs don't seem to 'operate' the same, sounds to this guy like one must be wrong ....

 

Even if they were different sizes, it should run smoothly on just one...not surge like he's describing.


Weird situation.......but again it sounds to me like it's getting air from someplace it shouldn't and that servo is about the only place left, assuming the intake is installed correctly and so on.


You did use the fat washers between the intake and exhaust manifolds? I used the flat washers but weld a short bead on one side, then grind it down so the washer can apply even pressure to both the intake and exhaust, as I find a lot of aluminum intakes have thicker bosses at the head than the flange on the exhaust header.


One other thing I noticed, there don't seem to be any spacers between the carbs and intake,, I've never seen one run without them.....I'm not sure why they would matter to this situation but make sure the throttle plates aren't getting caught on the edges of the bores in the manifold.

 

sounds to me like it's getting air from someplace it shouldn't

and sounds to me as ignition .....

 

SO update after a long time of struggling... I gave up finally, called a few pros and most of them suggested i bring the car to them and they do a single carb swap on the thing... so i thought... I can just do that myself.


I got the HIF44 swap kit online, installed it today and the car runs AMAZING!! idles smooth and NO surging, starts up everytime, pulls hard. Best it's ever ran.


So clearly something was wrong with the old carb setup. leaking manifold? broken carb? I don't really know. I had previously taken them totally apart and reassembled with all the new parts so I just don't get it. Anyways, dosen't matter now.
The only thing now is there a little bit of white smoke for a while after starting. I don't know if that is normal or what.
The gas in the car is also a few months old at this point so i'll get some fresh gas in it tomorrow along with changing the oil.

 

I posted early in this thread, forgot to mention I did the same thing. After getting tired of messing with the dual SU, finally bought a single Weber swap out kit. Eliminated all my carb problems.

 

71 Mini, good news that you got it sorted, if you don't want those old carbs I'll take them off your hands for you.....

 

^ I do want to sell the old carbs and manifold and stuff. I was thinking of putting it up on the for sell section or on eBay or something. If you want to buy it shoot me a PM

 

I'm guessing a 44 and a cone filter?

Do you know what needle is in the carb?

btw, this is the same fix that often gets recommended when folks with newer injected Minis (grey market revins) find they can't straighten out the injection system .....

 

Yes hif44 and KN cone filter. Its this exact kit: http://www.7ent.com/products/hif6-hi...-sevr0001.html

I don't know the needle, but when i called them up it said it'd be fine for my engine. It runs very well now.

Changed the oil and got fresh gas. I used the VR1 stuff with high zinc. There is still a little white smoke for the first few minutes on startup. I dunno what that's about. After a while it goes away though. There also seems to be a lot of vibrations in the cabin, but i dunno how much is normal as this is my first classic. Also my wheels are currently not balanced so i'm sure that's part of it.

Some guys at a show i went too recommended me to use 93 octane gas and zinc additive... what do you guys use?

 

I do use the high octane, but the ZR1 has zinc in it, so you don't need to add any more.


Watch your brake fluid and coolant, see if one or the other goes down, then you'll know the source of the white smoke.