mailman Posted August 21, 2013 Share Posted August 21, 2013 Hi Guys, So I've been spending the last few months trying to get my mini running sweetly. It seems like it's just about there and ready for the roads, but I have final issue that I can't quite make sense of. I searched the forum and couldn't find anything specific, but I've been reading the forum for a while now and there is definitely a heap of clued up people around, so I figured someone may be able to see the simple thing I'm missing. I have an HIF44 SU carb on my 998cc mini and have it running pretty well now on a BBB needle. My problem is at about 5-6000rpm it leans right out, and it seems to do this under both full and 3/4 throttle. It doesn't appear to be lean at full throttle below those higher revs. Does this sound like a needle modification type situation? Or something else? Has anyone modified SU needles themselves? I have bought a spare BBB needle, though I do wonder if there is a better profile. I have also got a sheet that shows the 16 stages on the needle. The big question there is, which stages to modify? Alternatively, what's the cheapest and most effective way of fuel injecting a mini? Thanks heaps. Quote Link to comment Share on other sites More sharing options...
Ghostchips Posted August 21, 2013 Share Posted August 21, 2013 Dad files a little off the needle at a time until it is right, patience needed. i stuffed needles messing with them so i no longer do that. Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted August 21, 2013 Share Posted August 21, 2013 http://www.mintylamb.co.uk/suneedle/ http://www.terryhunt.co.uk/mini/pics/tech/picsb/pics.htm i have just finished tuning a mini with a hif 44 have a look at these sites they helped me heaps ive got a 1360 fitted with a hif44 and a self modified bbw needle i used a innovate oxy sensor and got the needle perfect in about 3 hours of sanding fittng and testing http://www.sw-em.com/su%20needle%20dimensions.JPG also bdl is the most common hif 44 needle Quote Link to comment Share on other sites More sharing options...
Llama Posted August 21, 2013 Share Posted August 21, 2013 There is a very good book called The SU carburettor high-performance manual / Des Hammill The Auckland libraries has a copy, not sure about chch. It takes you through all the tuning, needle profiles, how to modify, etc etc Quote Link to comment Share on other sites More sharing options...
mailman Posted August 21, 2013 Author Share Posted August 21, 2013 Thanks, I have that book on hold at the ChCh Library actually. Still waiting on them to get it back though! Quote Link to comment Share on other sites More sharing options...
sheep Posted August 21, 2013 Share Posted August 21, 2013 Looking on that Mintylamb SU website, when looking at your BBB needle in comparison to say the BDL or BDP (what Minisport supplies in their "Stage One" kit) your BBB needle is quite a lot richer in the mid range, but towards the top end it flattens right off into leaner mixture territory. Ive also downloaded a free trail programme called WinSU which gives you a bit of an idea, but doesn't tell you the correct needle until you pay for the full version! Have you also tried hitting up Larry at Swift Auto for his advice? You might need to call in & see him as he is much better face to face rather than over the phone. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted August 21, 2013 Share Posted August 21, 2013 Needle profiling assumes knowledge of dash pot height. My guess is that the little 998 will be struggling to get the dashpot drawn open far enough to get good gains from needle mods... Quote Link to comment Share on other sites More sharing options...
mailman Posted August 21, 2013 Author Share Posted August 21, 2013 I have got the paid for version of WinSU and it suggests BDL as the start point. Using that needle it was definitely too lean through the mid-range, and too rich up the top end. I used the mintylamb comparorama tool and found that BBB and a few others provided a richer and leaner top end. I am wondering whether a different profile may be the answer. I am considering BBZ at this stage. Larry has been quite helpful with this needle stuff, and he has stacks of needles, but he wasn't prepared to guess which needle would be right (and fair enough too!). Needle profiling assumes knowledge of dash pot height. My guess is that the little 998 will be struggling to get the dashpot drawn open far enough to get good gains from needle mods... You could well be right there! Are you implying that it'll be too big? I should also add that I'm running a 998(+060) with 12G940 head, 9.75:1 Comp Ratio, Kent 266 Camshaft grind. Would that make a difference? Quote Link to comment Share on other sites More sharing options...
mjrstar Posted August 21, 2013 Share Posted August 21, 2013 Those mods would help with breathing but I cant help but think a 38mm may be a better option... There are ways to try the theory such as reducing dashpot spring pressure. Quote Link to comment Share on other sites More sharing options...
mailman Posted August 21, 2013 Author Share Posted August 21, 2013 I have the standard carb spring in there at the moment, I assume that is the lightest? I do wonder if a thinner dashpot oil might help, but I would be concerned that might cause the carb to dump too much fuel in too quickly when first getting on the throttle. Would that be the case? I did wonder about an HIF38 but the HIF44 seemed a good fit based on what WinSU suggested and what I was hoping for power-wise. I would possibly have had a more responsive engine, but who knows, the HIF44 is close now I think/hope. Hopefully BBZ needle or a modified BBB will help. I definitely need to get my hands on Des Hammels book. For the guys who have flirted with needle modification, did your experiences line up with the guy from the website linked above regarding needle stage and throttle position etc? Quote Link to comment Share on other sites More sharing options...
mjrstar Posted August 21, 2013 Share Posted August 21, 2013 I wouldn't mess with oil weight if the throttle response is good at the moment. I would think taking it for a quick hoon without the spring would be an interesting trial to do. Are you running a wide band to measure a/f ratio? Quote Link to comment Share on other sites More sharing options...
mailman Posted August 21, 2013 Author Share Posted August 21, 2013 Yea, using a wideband. Only a temporary install though, it's not a weld in kpb or anything. Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted August 21, 2013 Share Posted August 21, 2013 yea i done it the way he said my problem was leaning up top too fluked it with the third run my ratios were 14.7 idle 14.2 cruse up to about 80km/h in top then started leaning out to about 16.3 WOT from 100km/h up. managed to get 12.3 at WOT with his method has a cruse ratio 100kmh at 14.6 very light throttle spikes down to 11.9 if you snap the throttle very briefly i only played with station 6 to 10 to achieve this Quote Link to comment Share on other sites More sharing options...
mailman Posted August 24, 2013 Author Share Posted August 24, 2013 yea i done it the way he said my problem was leaning up top too fluked it with the third run my ratios were 14.7 idle 14.2 cruse up to about 80km/h in top then started leaning out to about 16.3 WOT from 100km/h up. managed to get 12.3 at WOT with his method has a cruse ratio 100kmh at 14.6 very light throttle spikes down to 11.9 if you snap the throttle very briefly i only played with station 6 to 10 to achieve this Thanks for this info!! I have been thinking over the last few days about what you've all said. I've got my BBB needle and am going to have go when I get some decent emery tape. Question for BigMatt though, did you make alterations to single stages between 6 and 10? Or make tiny changes to 6-10 at the same time? I.e. Taking 0.01mm off of each stage so that the profile remains the same but at a "richer" point? Thanks. Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted August 24, 2013 Share Posted August 24, 2013 just worked the whole area between 6 and 10 i use 240 grit wet an dry sand paper emery takes off too much at a time 1 Quote Link to comment Share on other sites More sharing options...
mailman Posted August 24, 2013 Author Share Posted August 24, 2013 Sweet, thanks. Did you find the 240 left a sufficiently polished finish? Or did you use some 1000 or 1200 grit to polish it up after? Quote Link to comment Share on other sites More sharing options...
bigmatt4 Posted August 24, 2013 Share Posted August 24, 2013 use 1000 to polish when it was close be aware it dosnt take much to sand like 5 seconds at a time is all i done follow that terry hunt guide it is almost spot on to wot i understood Quote Link to comment Share on other sites More sharing options...
mailman Posted August 24, 2013 Author Share Posted August 24, 2013 Sweet thanks. A task for Monday. Quote Link to comment Share on other sites More sharing options...
mailman Posted September 10, 2013 Author Share Posted September 10, 2013 Ok, so I had a go at altering the BBB needle today. I didn't get it right and it ended up too rich in the mid range and at pick up without any huge improvement at high revs. I also tried a BBZ needle which seemed like it had a lot of potential but also provided too much fuel. I had kind of been hoping that I could use BBZ and just raise the jet to bring the thicknesses in the upper stages between BDL and BBB. No real luck though. One thing that came up again (among the idea of just going to EFI $$$) was that the HIF44 may be too big and that the 1000cc motor may not be able to suck enough air to get it to perform properly at those higher rev numbers. I find this a little bit hard to understand, has anyone had this experience, or success with using the HIF44 on a 1000? I am very tempted to order a HIF38 if it is likely to be a much better (and not reduce power) fit to my build. I just don't want to go melting things. I haven't given up yet, but it's a bit of a PITA. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted September 10, 2013 Share Posted September 10, 2013 I researched efi and did not find enough evidence of good results to continue chasing down the required bits... ( due to dramas with siamese ports) How about the twin 1 1/4's advertised on here? Quote Link to comment Share on other sites More sharing options...
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