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Overheating troubles, fuel mixture help
https://www.ausmini.com/forums/viewtopic.php?f=2&t=42526		 Page 1 of 2
Author:  EAB [ Fri May 30, 2008 12:49 pm ]
Post subject:  Overheating troubles, fuel mixture help
ok so i put a bigger carb on my engine the other day, what i thought was a HS4, founf the fuel mixture to be inconsistent through the revs so i took the needle out and found it to be a KU needle

rang up the guys at link to get an idea of what i need and they told me that my carb was a HI44? and gave me a TW needle to try out.

put it in and set everything at 1500rpm, timing, mixture, everything went to take it for a spin and it had no power at all and temp was reading 105 by the time i'd gone 50m, engine was warmed up before hand but i didnt notice any problems.

car has a 998 engine with a ported head and ectractors, was running the standard 1.25 inch carb with the AN needle with no problems,

new radiator and fan so i know thats working,
any ideas!
Author:  sgc [ Fri May 30, 2008 12:54 pm ]
Post subject:  Re: Overheating troubles, fuel mixture help
EAB wrote:
went to take it for a spin and it had no power at all and temp was reading 105 by the time i'd gone 50m, engine was warmed up before hand but i didnt notice any problems.


DON'T DRIVE IT LIKE THAT!

Sounds like the mixture is waay too lean, if you drive it in that condition you're going to melt a piston.

If I were you, I'd find out exactly what carb you have, and start with the standard needle for that carb and work from there. Really, it sounds like you're going to need a dyno and an operator who knows his way around an SU.
Author:  BALLISTIC [ Fri May 30, 2008 1:21 pm ]
Post subject: 
Mixture may be right for the idle circuit but once you open the throttle it ay lean out to much due to the increased air speed through the carb......
HIF44 probably to big for the 998 even though its a slightly "warmed engine". best you find yourself an 1.5" carb.......Hmmmm i wonder who might have one lying around??

:? Why did you set your idle so high?
should be ticking over at idle max 1000rpm (my preference)and thats only if it has a large lobe spec cam very well ported head 60+ over sized bores etc etc..... then i'd run an 1.75 carb.

My 5 cents worth......but what would I know :wink: :P hey Poeee :P :lol:
Author:  simon k [ Fri May 30, 2008 1:42 pm ]
Post subject: 
BALLISTIC wrote:
:? Why did you set your idle so high?
should be ticking over at idle max 1000rpm and thats only if it has a massive race spec cam very well ported head 60+ over sized bores etc etc..... then i'd run an 1.75 carb.



slight hijack... what's the reason behind idling at 800 or 1000rpm? is it just 'the done thing', or is there an actual reason for it - other than personal preference of it not roaring away at 2000rpm when you're sitting at the lights

just curious

but I agree with the other 2 anyway... dodgy setup, put it all back how it was with the 1.25" and start again
Author:  drmini in aust [ Fri May 30, 2008 1:54 pm ]
Post subject: 
Idling too slow with a reground sports cam is worse than idling too fast- you can starve the cam lobes of oil and scuff the lobes and lifters.

Ours both idle at 1000-1100, neither are stock.
Author:  EAB [ Fri May 30, 2008 5:07 pm ]
Post subject: 
i wqas under the impression i'm supposed to set the mixture at about 1500rpm then drop it back to idle once thats done?

will trying setting the mixture at 850rpm (matches the car :P) and see how it goes, otherwise the 1.25 will go back in,

apart from the obvious rise/fall of rpm when setting the mixture what other ways can i tell how its running, eg smoke colour from the back of the car, i've gotten ok at reading plugs but need to take it for a spin to do that properly i think.

as for a 1.5inch carb ballistic, i have a collection of about 8 carbies in various conditions, one of thems got to be at least a two inch no idea what it is,

thanks for the info people, will get back to you with the result on sunday.
Author:  Mister White Keys [ Fri May 30, 2008 6:02 pm ]
Post subject: 
A 998 will run fine on a 1.5" HS4 but if you want that bit extra, see if you can find yourself a set of twin 1.25" HS2's. With an M needle they seem to give a small bore much more low down power while keeping a great strong high end as well.
With 8 carbies lying around you've probably got a 1.5", as far as I know they were on most of the 998 clubmans so there should be a fair few around.
Otherwise I'm sure you could do a great deal with BALLISTIC :wink:

My two cents anyway
Author:  BALLISTIC [ Sat May 31, 2008 4:00 am ]
Post subject: 
simon k wrote:
BALLISTIC wrote:
:? Why did you set your idle so high?
should be ticking over at idle max 1000rpm and thats only if it has a massive race spec cam very well ported head 60+ over sized bores etc etc..... then i'd run an 1.75 carb.



slight hijack... what's the reason behind idling at 800 or 1000rpm? is it just 'the done thing', or is there an actual reason for it - other than personal preference of it not roaring away at 2000rpm when you're sitting at the lights
just curious

but I agree with the other 2 anyway... dodgy setup, put it all back how it was with the 1.25" and start again


Stock ones are set @ around 850-900 rpm and ive always set them to 1000 rpm so they dont sound like they are reving thier heads off, still got good oil pressure, not chewing through the fuel.

One or 2 race type motors ive set up running up to 1300 rpm to try and smooth out the idle and reduce carboning up the pistons, plugs, valves at the same time but do not like doing that.
Author:  BALLISTIC [ Sat May 31, 2008 4:36 am ]
Post subject: 
drmini in aust wrote:
Idling too slow with a reground sports cam is worse than idling too fast- you can starve the cam lobes of oil and scuff the lobes and lifters.

Ours both idle at 1000-1100, neither are stock.


I dont mean to step on your toes and or p1$$ you off. Im quite sure your knowledge is greater than mine on this subject but if the engine (when hot/normal operating temp) hasnt got at least the minimum pressure at idle (about 25psi from memory) you know there is something wrong due to the cam (which runs the oil pump) doing twice the crankshaft revolutions so therfore it should be pumping plenty of oil around the engine so no harm can happen to said engine. Anyways enough from me now.......so what does that make it.....another 5cents.......so we are up to 10 cents now :lol:
Author:  drmini in aust [ Sat May 31, 2008 8:55 am ]
Post subject: 
When I say don't idle too slow, I mean ticking over at 600rpm or so with hi-lift cams. There is no direct oil feed to the cam lobes, and many lifters have no oil hole to let rockers return oil drain out, so all the lobes get at idle is splash from the crank and rods. Not much, at 600 rpm. :wink:
Author:  tinymorris1969 [ Sat May 31, 2008 10:12 am ]
Post subject: 
twins are awsome i reckon the car runs 10x better with them even though ive had nothing but trouble with mine so far. but if your not interested in tuning all the time stick to a hs4 1.5" it will provide more then enough power. mine use to
Author:  d1ck0 [ Sat May 31, 2008 10:23 am ]
Post subject: 
tinymorris1969 wrote:
twins are awsome i reckon the car runs 10x better with them even though ive had nothing but trouble with mine so far. but if your not interested in tuning all the time stick to a hs4 1.5" it will provide more then enough power. mine use to
Umm, why would you have to tune all the time?

My twins, once set up, have needed no further tuning. Obviously when doing a tune up I check balance (with a hose) and mixtures, but thats a 10 minute job and very rarely needs adjusting.

Dicko
Author:  tinymorris1969 [ Sat May 31, 2008 10:24 am ]
Post subject: 
how often do you drive it? and plus im passing on what everyones be tell me about them. trying to convince me to stay with my single 1.5"
Author:  d1ck0 [ Sat May 31, 2008 10:39 am ]
Post subject: 
It's usually a daily driver....

But recently broke 2 wheel studs on the RHF wheel (but that's another issue) and is about to have Cooper S Disks fitted (I'll post about all of this soon).

I suppose your ability to keep twins running nicely comes from your experiences. I've had:

    An Austin A30 with sprite twins on it (paddock basher when 13).
    A 78 Mini with twin 1.25's.
    A 76 LA Lancer built to GSR specs with Twin Solex 2bbls.
    A Jaguar XJ6.
    A 78 Skyline with 240z carbies.
    And now my 1100 Clubman with twins


So lots of experience and can do it all very quickly. But back to my original comment. I check it all when doing a tune up, but, they very rarely need changing.

Dicko.
Author:  tinymorris1969 [ Sat May 31, 2008 10:43 am ]
Post subject: 
ahh see experience is on your side. how did you manage to break 2 wheel studs? and im guessing you got drums? wait till those disks go in
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