mailman Posted September 10, 2013 Author Share Posted September 10, 2013 I'm concerned with the issues of setting up one carb, that trying to sort twins would be a step too far. I prefer the HIF series carbs, if I can track down a 38 I'm feeling like that may be worth a go. Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 10, 2013 Share Posted September 10, 2013 You know you can buy the needles you need rather than trying to guesstimate your own profile? There is an SU needle book that lists all the profiles you need and I think an online calculator available too (which costs some $$$) Quote Link to comment Share on other sites More sharing options...
mailman Posted September 10, 2013 Author Share Posted September 10, 2013 I've got the paid for version of WinSU which suggested BDL. I'll go back and have another look. 1 Quote Link to comment Share on other sites More sharing options...
Ghostchips Posted September 10, 2013 Share Posted September 10, 2013 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 think i had one of those carb's it has been a while so i am not sure of the numbers. i got it to work but went smaller because high revs were fine but the low range was terrible? (not enough airflow? i might be way off here) Quote Link to comment Share on other sites More sharing options...
Llama Posted September 10, 2013 Share Posted September 10, 2013 EFI can be done, if you can set up your sequential injection to compensate for the siamesed ports, but it's not reaaaaly worth the effort unless you are into that kind of thing. A too large carb will give you a poor low end as the air velocity is not fast enough to give you enough difference in the pressure to draw fuel out. Quote Link to comment Share on other sites More sharing options...
mailman Posted September 10, 2013 Author Share Posted September 10, 2013 Hmm, I see the potential in EFI with the tuneability. But I am not 100% convinced on the benefits vs cost/effort. In saying that though, getting a HIF38 in from the UK is looking like it's going to be around the $500-600 mark after shipping and GST. I've just been to see the mini guru here in Christchurch and he has given me a yellow (8oz I believe) spring, if I understand him right, this should be similar-ish in principle to having a smaller card as the piston will be open a smaller amount. I may have completely and utterly misunderstood/misquoted him there, but he definitely knew what he was talking about. 1 Quote Link to comment Share on other sites More sharing options...
mailman Posted September 12, 2013 Author Share Posted September 12, 2013 Ok, I've spent the afternoon mucking around with the mini. I tried the yellow spring that Larry gave me, that seemed to help initially but meant that it was running quite lean at cruise. I removed the carb and stripped it down to make sure that the everything was working as it should. It all appeared to be in good nick. I am now debating whether I need to try a new needle with the new spring, or go back to the lighter spring. Does anyone know, does the piston go up (and the needle stages effect the fuelling) with throttle position or engine speed? i.e. if I am trying to get extra fuel in to prevent the excessive lean conditions at 5000rpm and up, does that use the same part of the needle as going full throttle lower in the rev range? Quote Link to comment Share on other sites More sharing options...
mjrstar Posted September 12, 2013 Share Posted September 12, 2013 It moves with airflow. Which is a resultant of rpm and throttle. If you are at light throttle at 5000rpm you may be using a similar area of the needle as lower rpm with more throttle %. Oil thickness will control rate of opening( dampening effect) and spring dictating max opening amount depending on airflow. A larger bore motor (or more efficient air pump )will require a heavier spring. Hence why I suggested you try running a lighter or no spring to understand how low flow affects the big carb.. You will find a lighter spring will open the piston more and reducing vacuum across the needle reducing suck capability to draw fuel out of the jet. not just as simple as raising needle to hose in more fuel. I assume you went heavier- if so you will be running in the fatter/ leaner part of the needle.. Maybe a super fat needle at idle and lowering the jet would mask the problem.. Personally I would try for a smaller carb (s) which will meter fuel with greater accuracy. Tl:dr Quote Link to comment Share on other sites More sharing options...
mailman Posted September 12, 2013 Author Share Posted September 12, 2013 Thanks, yea I am very strongly considering ordering a HIF38 as you say. My only concern is that WinSU recommends HIF44 and says that with HIF38 I'll be too lean. So hard to work out. I think that the reason for the heavier spring is as you say to reduce the max opening (similar effect to using a smaller choked carb?). I may need completely different needles with the lower opening. I may have to try and actually see how much the piston is lifting for different loads... Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 12, 2013 Share Posted September 12, 2013 HiF44's are for higher compression 1275's or fairly warm 1000's How modified/radical is your 1000cc? Also these carbs came off a 1100cc motor so would not be too far from what you want. //oldschool.co.nz/index.php?/topic/39048-fs-twin-hs2-su-carbs-linkages-and-more-akl/ Quote Link to comment Share on other sites More sharing options...
mjrstar Posted September 12, 2013 Share Posted September 12, 2013 I had another thought, how about upping the idle to say 1400-1500 rpm (or more if it needs it) (so it doesn't run too rich and foul at idle) then drop the jet 3 or 4 turns. then see if your lean top end improves.. this would give you an opportunity to see if a needle with a comparatively lean idle could be an option for you.. before forking out big bucks on a new HIF38. come to think of it the problem you are having is pretty much the same as I had on my 1330 with 296 cam and stage 3 head plus high compression.(also running Hif44) 1 Quote Link to comment Share on other sites More sharing options...
mailman Posted September 12, 2013 Author Share Posted September 12, 2013 K-trips, I have a 266 cam, 12G940 head, +060 over bore, alloy inlet and maniflow exhaust. 9.75:1 comp ratio. It's quite nice but I'm not getting the most out of it with the leaning issues. I would rather stick with a single carb and with the HIF44 if it's feasible. Cost is the major thing right now. I don't really have any money left to tie up in it. Mjrstar, that sounds like a good plan. Would you recommend trying that with the light or heavier spring? Also, which needle should I try it with? The BBB I am getting close with, or the BDL that WinSU suggests? What was the solution for your 1300? Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 12, 2013 Share Posted September 12, 2013 Why do you think you are running lean? Are you running an AFR gauge? Quote Link to comment Share on other sites More sharing options...
mailman Posted September 12, 2013 Author Share Posted September 12, 2013 I have been testing with an AFR readout with the sensor up the tailpipe. It doesn't read accurately at idle, but with the BBB needle I get around 14-15 at cruise, and about 13-14 at full throttle until about 4500rpm. At that point it's about 15 and climbs to 16+ as the revs increase Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 12, 2013 Share Posted September 12, 2013 Wind the jet down 3-4 flats and fatten the whole range IMO. You would be fine to get away with 13:1 at cruise. and 12:1 at full throttle. How high do you rev? Quote Link to comment Share on other sites More sharing options...
mailman Posted September 12, 2013 Author Share Posted September 12, 2013 What do you mean flatten it sorry? Just flstten the profile of the needle? I don't plan on revving it really high all the time, I'm just trying to get the tune right for the full range as it should rev to about 6000rpm I believe. Though I could be wrong, and perhaps I'm being abusive? Quote Link to comment Share on other sites More sharing options...
mjrstar Posted September 12, 2013 Share Posted September 12, 2013 ^^ HIF has turns not flats but yeah... jet height adjustment is via a screw on the side. By "fatten" he means richen up. My suggestion is to use whichever needle has the greatest amount of taper to maintain some form of idle (it sucks when you have plug fouling). I can't really say which spring is likely to net best results but it will define your problem, if the lighter spring gives a leaner a/f you don't have enough suck. if the heavy spring is lean you need to keep dropping the jet (if it will still idle) or start trimming down the lower section of a needle. bearing in mind the heavy spring will be harder to get the tune right as you won't be using the very bottom point on the needle. Have you tried gently giving it a bit of choke when it gets into it's lean rev range? plan C would be to grab an old HS4 for cheaps and give it a go? How did i fix mine - well it's still not 100% but i went to twin motorbike carbs. - in my mini project thread. did a pile of research and tuning and the best i got it was (needed 1400 rpm as a minimum to idle OK) and was a dog below 3500rpm but pulled like a deamon tope end. the other way i could tune it was to raise the jet and run an ok idle but lack fuel in the top end. 1 Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 12, 2013 Share Posted September 12, 2013 The jet is adjusted by a 6 sided nut - if you turn it one flat you are turning it 1/6th of a turn - 3 flats is a half turn of the nut. If you wind the jet down it richens it (fattens it) - if you wind it up you lean it out. Quote Link to comment Share on other sites More sharing options...
KKtrips Posted September 12, 2013 Share Posted September 12, 2013 Sorry yeah that's right - HIF is different from HS. HS has a nut that adjusts the jet where HIF has a screw - I would turn the screw a half turn and see if it makes it any better through the rev range. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted September 12, 2013 Share Posted September 12, 2013 On a side not with the motorbike carbs the idle is super smooth and bottom end torque is much improved. You'd hardly know it had a reasonably sizable cam in it. This situation is way better suited to the long 1st gear my car has now with the straight cut close ratio box. / enough about my rubbish cars Quote Link to comment Share on other sites More sharing options...
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