82 replies to this topic

[Cooperman]

Now, that is interesting. Nos 1 & 4 each have their own exhaust whilst 2 & 3 share a single one between them. a 1" bore for the end LCB pipes does sound a little small and although I've not measured it, a maniflow big-bore LCB is more than that.
Perhaps an original Cooper 3-into-1 type of manifold would work better on that engine spec as all 3 pipes converge at the same point.
Is the diameter of the single initial exhaust from 2 & 3 the same size or is it larger? Twice as much mixture goes down from 2 & 3, so if the pipes are the same diameter, the gas velocity will be twice as much on 2 & 3 as on 1 & 4 until the Y-piece is passed. It could be an issue, although never heard of it before.

[bmcecosse]

The centre port and shared pipe is not a huge problem - especially at idle speed! The firing order is 1342 -so the centre port (and pipe) gets a little rest between uses - while #1 and then # 4 do the firing.... You are over worrying this idling problem - the idle will never be smooth with a set-up like this - it's the RUNNING that matters! Just stop worrying about the idle, However if your pipes are really only 1" internal diameter - that does sound on the small size for a decent engine. And -you can't expect to take a Weber from a completely different engine and stick it on a Mini engine....... A big single SU on a decent manifold is by far the better route...

[bigmatt4]

i re jetted the other carb to suit the mini engine i have a full range of weber and delorto jets and tubes been stuffing with them 4 years. The idle mixture is out 3 turns at the moment but i have started lean at this time to stop fouling the plugs.
I have only 45 idle jets when it should be 50 at least but it idles ok just has a small flatspot off idle.
The rough idle wasnt my concern it was the oil beeing sucked down the exhaust guides at idle i have fitted guide seals to help pevent that and also if you have lazy cylinders you are more likely to foul plugs at idle.
The exractors have seen better days look like a cheep set think they must have been from an 850 or 1000 because they are very short and very close to the floor on the bend also noticed when sticking a large piece of trailer cable down the pipes there are alot or edges that the cable gets stuck on on the way down it is very difficult to get right through and they have had a big butcher weld on the bottom of them to fix all the cracks they had (not my welding) . Yeaterday i spent 10 hours trying to find this idle fault i had moved the cam from 6 deg retarded to 6 deg advanced trying to locate fault until i spoke to someone said cut off the exhaust and check it did that and we have a lumpy idle and plugs run clean and dry still have to refit the other head and try it . after spending thousands of dollars on a full rebuild of an engine you would expect it to idle though used all top quality gear from rover and minispares only thing that is from New Zealand is the camshaft we imported all the rest from england. will keep you updated till shes driving again.




sorry cutting off exhaust has fixed idle problem:)

Edited by bigmatt4, 29 August 2011 - 07:23 AM.

[bigmatt4]

The idle mixture is out 3 turns at the moment but i have started lean at this time to stop fouling the plugs.
I have only 45 idle jets when it should be 50 at least but it idles ok just has a small flatspot off idle.

Easiest way to sort the idle jet's, is drill 'em out.
The trouble with only adjusting the screw is, it can only weaken of the idle jet. ie. increase the amount of fuel, that size of jet can supply.

I have the jets and they work fine just bit touchy on idle mixtures.
ive found 45s have more adjustment for idle only conditions 50s get rid of most of that off idle flatspot but a finer idle mixture adjustment may go to 55s if i can get idle ok on 50s or change the pump jets to help

[b34k3r]

Not really, it was dropping cylinders under 1700 rpm.. which is too high for a idle, you pull up to the lights and sound like a ******* with his choke stuck on.

[AndyMiniMad.]

What exhaust manifold are you useing? You have spent a lot of ££ on your engine so I assume you have a decent exhaust as well..your not useing the thing you described above are you....

[bigmatt4]

What exhaust manifold are you useing? You have spent a lot of ££ on your engine so I assume you have a decent exhaust as well..your not useing the thing you described above are you....

nope not now new ones comming has 1-7/8 pipe to the rear strait muffler

[bigmatt4]

I have the jets and they work fine just bit touchy on idle mixtures.
ive found 45s have more adjustment for idle only conditions 50s get rid of most of that off idle flatspot but a finer idle mixture adjustment may go to 55s if i can get idle ok on 50s or change the pump jets to help

Goal posts seem to be moving around a lot, because earlier you only had 45's

I have only 45 idle jets when it should be 50 at least but it idles ok just has a small flatspot off idle.

What have you got the idle speed set to ? Starting to sound like it's to low.......

sorry mate ment to say i only have 45 idle jets in it at the moment because the car is un driveable at the moment and it only does start and run no drive . engine runs very well on the road smooth clean power lots of go just has this idle issue normally run 50 idle jets to get rid of flatspot but idle mixture is a finer adjustment . I am welding a o2 sensor in the collector of the new headers so we can put a digital lambda meter in and road tune it. removing the exhaust has made it idle nice at 1100rpm still have to refit ported 12g 295 head and electronic dizzy

[bigmatt4]

Now, that is interesting. Nos 1 & 4 each have their own exhaust whilst 2 & 3 share a single one between them. a 1" bore for the end LCB pipes does sound a little small and although I've not measured it, a maniflow big-bore LCB is more than that.
Perhaps an original Cooper 3-into-1 type of manifold would work better on that engine spec as all 3 pipes converge at the same point.
Is the diameter of the single initial exhaust from 2 & 3 the same size or is it larger? Twice as much mixture goes down from 2 & 3, so if the pipes are the same diameter, the gas velocity will be twice as much on 2 & 3 as on 1 & 4 until the Y-piece is passed. It could be an issue, although never heard of it before.

measured the pipes today on old extractors 28mm id 1-1/8

[Yoda]

One thing that has been bugging me for a while!

Why are you using small bore cylinder heads? could be the main cause of your problems.

1330cc is obviously a big bore block and using a small bore head can cause more issues than you would believe! get a 12G940 head and try that!

EDIT.

Just reread your original post and it looks like you started out with a 12G940. now that you are progressing, put it back on and see where you are with that. first though, get it checked for warpage and cracks!

Edited by Yoda, 29 August 2011 - 08:30 AM.

[b34k3r]

It has a ported 12G940 head, he simply put a 850 head on it for testing purposes, and it improved the idle quality, has not been road driven with the 850 head. It will go back to the ported 12G940 this weekend with a new set of headers with larger pipe diameter for further testing.

Edited by b34k3r, 29 August 2011 - 08:37 AM.

[Yoda]

still have to refit ported 12g 295 head and electronic dizzy

So whats this then?




Hopefully if you say you now have the correct head and are fitting the correct size exhaust system, you will find a vast improvement. an exhaust exit of 1 1/8 inch as stated recently is most likely not helping at all.

[jaydee]

Matt, with the 1330 you need a ported 940 head (or a leaded MG head which has bigger valves) and a 1,75" exhaust system or the engine will be very restricted in breathing.

[bigmatt4]

Matt, with the 1330 you need a ported 940 head (or a leaded MG head which has bigger valves) and a 1,75" exhaust system or the engine will be very restricted in breathing.

sorry again mate been long day it is a 940 head to go on. ive been doin so much research lately to find this fault my head is screwed with all sorts of numbers havin a brake away from it this week need a brain rest til weekend

[b34k3r]

It only has the standard size valves for the 12G940 with hardened valve seats, I was warned against going oversize due to the proneness to cracking. Im hoping investing in some 1.5 rockers in the long term will compensate for this. Im guessing Matt made a typo quoting the 12G295, it will be going back to the 12G940.