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| Needle selections, twin SUs on a overbored 998. https://www.ausmini.com/forums/viewtopic.php?f=2&t=67712 |
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| Author: | Mick [ Sat Dec 18, 2010 6:00 pm ] |
| Post subject: | Needle selections, twin SUs on a overbored 998. |
I've got to pick up a pair of needles for my twin 1.25 SUs on stock MOWOG twin manifold. Can I please have some opinions on starter needles to set my new engine up with. I've got a 998 at 100 thou over for a displacement of 1075. The camshaft is GR's RE83. The head is a 295 set at about 9.5:1 and 3:1 extractors. Can anyone give me a few selections to try out? |
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| Author: | 74snail [ Sat Dec 18, 2010 6:06 pm ] |
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CP4 or MME would be the preferred needles to start with . |
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| Author: | TheMiniMan [ Sat Dec 18, 2010 6:31 pm ] |
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i`d stick a pair of "M"`s in them first & see how they run CP4`s & MME`s are more suited to a mild/hot-ish 1275 on twin 1.5 carbs |
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| Author: | 74snail [ Sat Dec 18, 2010 7:03 pm ] |
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Engine Size Needle Std Needle Rich Needle Lean Spring Type 850 comp 1071 S Comp MME - - Blue 997 Cooper thermo jets MME - - Blue 998 Cooper modified head AO - - Blue 970 Cooper S comp CP4 - - Blue Thats from a BMC Tuning page I found ages ago , they have same details on Seven Enterprises ( it looks strange as I cant make it line up properly  )
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| Author: | Mick [ Sat Dec 18, 2010 7:09 pm ] |
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TheMiniMan wrote: i`d stick a pair of "M"`s in them first & see how they run
M's I would not have picked as a choice, I have always thought the selections were based on capacity first..shows I have a lot to learn still....I have a pair here as it is however, so it won't hurt. |
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| Author: | drmini in aust [ Sat Dec 18, 2010 7:53 pm ] |
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Ms seem to work well in tuned 1098s so should in yours too. AH2 is a bit richer than M, if you need this. |
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| Author: | Mick [ Sat Dec 18, 2010 10:13 pm ] |
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drmini in aust wrote: Ms seem to work well in tuned 1098s so should in yours too.
AH2 is a bit richer than M, if you need this. I even happen to have a pair of those too.. 
I'm set it seems! |
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| Author: | Goldbrocade_62 [ Sat Dec 18, 2010 11:09 pm ] |
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I'm using M needles in my cooper I bought new ones 3 & 4 cylinder and not firing plugs very wet the needle measured up at 75 thou at the idle end instead of 87 thou like the other one on cylinder 1&2 |
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| Author: | GT mowog [ Sun Dec 19, 2010 8:31 am ] |
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Mick wrote: ......... I have always thought the selections were based on capacity first...
Actually Torque / HP. Find an engine with a similar torque / HP curve to what you expect yours will have. That will be a very good starting point. And don't overlook the springs. |
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| Author: | TheMiniMan [ Sun Dec 19, 2010 9:14 am ] |
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GT mowog wrote: Mick wrote: ......... I have always thought the selections were based on capacity first... Actually Torque / HP. Find an engine with a similar torque / HP curve to what you expect yours will have. That will be a very good starting point. And don't overlook the springs. yeah pretty right I will add tho, that it`s more about "air speed" through the carb a really big carb on a small , low reving, engine will need a much richer needle profile than a smaller carb on the same engine... the smaller carb will pull up the fuel from the jet far better with the higher air speed & with a small carb on a very big high reving engine will only need a fairly lean needle profile,,, etc etc etc,,, that`s the part where GT mentions how the spring rate affects things i recently sent a single 1&3/4 carb to a guy (way out west somewhere) to fit onto a massive 4.5litre straight 8 (of some sort) & i set it up with the same old OA6 needle & Red spring ,,, the very same "base-setting" that i do with every thing to start with he rang me back telling me how he couldn`t believe how good it was & no need for any tune work,,, (his actual words were "It`s spot on" ) Now i`m sure we could have improved it a tad more with some time playing, but he was more than satisfied however, if it were a race engine (higher revs & obviously much higher air speed through the carb) well i guarantee it would have needed much more than a play with to get it right (maybe add a few more carbs to be honest) but still,,, as big as the engine is , it still had fairly low revs, so air speed wasn`t too fast to cause any issue & my faithful old "std" base setting was sweet so,,, there you go,,, think "air speed" more than anything & you`ll be on the right track |
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| Author: | BALLISTIC [ Sun Dec 19, 2010 9:28 am ] |
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Mick wrote: drmini in aust wrote: Ms seem to work well in tuned 1098s so should in yours too. AH2 is a bit richer than M, if you need this. I even happen to have a pair of those too.. I'm set it seems! Mick the "M" needles should be all you will need for this size engine (Im not 100% sure of specs of your cam but I dare say its "nice"  ) but as the good Doc said if you need slightly richer AH2's will do the job.
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