15 replies to this topic

[mini_man96]

Hi everyone, this is my first post post so please point out if I forget to mention anything!
I have a 1996 rover mini sidewalk that has been converted to run on twin hs4's rather that the original injection system. The car has a ported head (29mm exhaust, 36mm intake) sports coil and electronic ignition. The problem I am having is that the carbs are horribly unbalanced! I know this because coving the front carburettor has no affect on the engine whereas coving the rear causes it to stall out immediately.
I also had this problem when running the efi as the rear two cylinders ran much richer than the front two. I thought this could indicate a worn out camshaft but after checking the lift with a dial indicator all the intake and exhaust rockers are moving the same amount. One other problem is that when the engine is idling the pistons in the carbs sit so high that the lifting pins do not contact them to help set the mixture. Another thing to note is that whilst the engine is running it will occasionally puff a mixture of fuel and air out of the carbs causing to stumble then idle up temporarily before returning to normal.
Any help would be greatly appreciated!
Thanks, Hal

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[Dusky]

You can balance the carbs yourself with a length of tube.
But looks to be a different problem. Maybe ignition based?

[mini_man96]

Yeah possibly, how would I check if the ignition was to blame?

[minimans]

Do a compression test first. Then move on to other things, check the mechanical linkages are set correctly on the carbs you may have one butterfly open and one closed at idle?

[mini_man96]

Okay thanks for the advice! I've ordered a compression tester so that should arrive this week and I'll check the linkages tomorrow. Hopefully it will be something simple like that!

[mini_man96]

Okay, so I've now got the engine running much better with the carbs perfectly balanced! I am still having a few issues though, I had to unwind the mixture nuts almost to the bottom of the threads to get it to run properly and it is idling fairly high even though the idle screws are backed almost fully out!
Anyone got any ideas on this?
Thanks

[Northernpower]

If the needles aren't fitted into the pistons at the correct height you'll have to make up the adjustment with the jets. You'll see there is a shoulder on the needle and the upper portion of it should be set level with the bottom of the piston. If the lower level is set level with the bottom of the piston you'll have to back the jets right off.

[mini_man96]

I've dismantled one of the carbs and this is how it looks:
I can't see any other way to fit the needle other than how it is already?

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[CityEPete]

If you're running out of adjustment the chances are you'll need different needles?

[nicklouse]

Ok back to basics. The needles are what? And they are both the same?
The springs are? And the same?

All ports on the carbs are correctly connected or blanked? Manifold likewise?

Correct number of gaskets? No air leaks?

If the jets are as low as they can go then sounds like wrong needle as you are having to allow more fuel in.

Backing idle screw off will make no difference if the cable is applying tension. Undo all cables. Or slacken them right off.

[mini_man96]

It's running ADN needles in both carbs along with red springs. Everything is blanked off apart from the vacuum take off on the rear carb which is connected to the vac advance on the distributor. Cables won't be causing any problem as it is not connected.
They could be the wrong needles but they were the ones suggested by the 'WINSU' computer program (although not sure how accurate that is).

[nicklouse]

ADN does not look to far off but I would say too lean over the whole range.

Basically a standard 1275 with a head with bigger valves but next to no work inside?

[mini_man96]

Yeah pretty much (as far as I know). Also has a LCB exhaust

[mini_man96]

Does anyone have an idea as to which needles would be best?

[nicklouse]

A single HIF44.

But if you had to have twins 1 1/4 with AH2

Sorry never been a fan of twins on any engine build unless it needs them and yours does not.



But sticking with what you have get it to someone who knows SUs and can set it up on the rollers as it sounds like you are about as close as you can without analysing the emissions.