vosadrian Posted June 12, 2023 Author Share Posted June 12, 2023 Hi All, We have made a little progress since a year ago. We got the engine running in our parts car some time ago, and we have now got that engine installed with a manual gearbox in our yellow car. Also have brakes and clutch systems installed and working. We are working on the fuel system currently. Previously we got the engine running off a funnel into the mechanical pump. The electric fuel pump we had in our parts car did not seem to work. We removed it and tried to run it in isolation from a head of fuel on the inlet, and nothing came out. We got a generic pump from repco, and managed to get the fuel flowing to the engine with that. But at the moment we are not running it with the fuel pressure regulator that is with the stock fuel pump. A couple of questions: * Is it necessary to run the fuel pressurre regulator? What are the effects of running the electric pump unregulated up to the inlet of the mech pump? We have this now and did not get the engine started, but could be other reasons. We got the carbys full of fuel, but I am wonder if too higher pressure caused an issue. * Is it OK to just run a generic pump with similar flow and pressure output rating to standard? We were in a rush so grabbed something we could get without ordering a stock replacement. The next step is to run a carby kit through the carbs. We have the electricals working OK at the moment and can turn key the starter. We have ignition in the right place (it kicked over with some "Start ya ba$tard". Once we get some reliable fuel into it we should be running, and then need to get a cooling system working and alternator etc. Thanks! Quote Link to comment Share on other sites More sharing options...
voslachlan Posted July 14, 2023 Share Posted July 14, 2023 (edited) Hi all, Have managed to get the fuel system working with a reasonable degree of effort, now getting a stable 2.5-3psi to the carbs. A little while ago I rebuilt our SU HIF6 carbs with a seals and gaskets kit, however we hadn't actually run them long term until very recently. When we get it running in the yellow chassis, we noticed an intermittent fuel leak through the overflow even with the pressure set correctly, so I got some new float needles and seats which seemed to fix the problem. Now with a cooling system in place we've gotten it running and up to temperature, however still fighting some idle and mixture issues. At idle it sounds a little rough (could be due to an exhaust leak at the header flange) but certainly far smoother than it ever has. However, it still has very minor stumbles and backfires every few seconds (issue #1). It was also idling very high which we only noticed once every other factor was sorted, and even with the idle screw turned all the way down and the throttle shaft touching the carb body it still sits at 1.5-2k. Obviously a vacuum leak of some sort, but the odd thing is that when I block the float overflows with my hand, the revs drop severely and the engine dies off (issues #2). Which seems to suggest suction through these overflows, but I'm not sure how that would be possible - I would expect positive pressure if anything. The only way I can see manifold vacuum getting into the float is through the jet, but surely with the floats set at the correct height there wouldn't be any way for air to get in? Would appreciate some guidance or suggestions from the SU experts before I start swapping out parts and spending money on what is ultimately an intermediate step before the RB path. Cheers, Lachlan Edited July 14, 2023 by voslachlan Quote Link to comment Share on other sites More sharing options...
RestoZ Posted July 29, 2023 Share Posted July 29, 2023 Hi Lachlan I used the reference below to get started: https://tecb.eu/onewebmedia/Tuning_SU_Carbs.pdf - Section III Tuning Multiple Carburetters Also a really good section on tuning in this: https://www.amazon.com.au/Carburettor-High-Performance-Manual/dp/1787111687 The pdf above is a good starting point, but I found the following things, which were not necessarily in the instructions, but were covered in the second manual, critical to getting things to work: 1. Fuel levels in each bowl must be at the same height. Let them fill up, take the top off and physically measure the level. I used an electronic vernier calliper to measure this accurately. 2. Height of jet below the bridge for both carbs must be the same. Again, measure with the callipers at step 17. 3. Each carby has to be adjusted individually, so critical to slacken both the clamping bolts as per step 19.What you do on one carb, adjustment wise, you have to duplicate on the other. 4. You might be able to adjust the suction using the pipe as in step 20, but you are better off getting one of these: https://www.weberperformance.com.au/product_info.php?products_id=7 which you can get off eBay as well. Good luck. It 's easy once you've done it and got it right, but getting there can be a challenge. Paul Quote Link to comment Share on other sites More sharing options...
1600dave Posted July 30, 2023 Share Posted July 30, 2023 (edited) Do your carbs have three little pipes (fuel in and overflow coming out of the carb at 90 degrees and another pipe sightly higher up at an angle) ? I worked on a friends car many years ago when he fitted HIF SU's, we traced tuning issues to the pipe that is at an angle not connecting to anything, and being open to the atmosphere. From memory, it was sort-of tucked away at the rear of the carb. Also, as well as being an overflow, he overflow is a bit of a breather / vent to allow for the ever so slight rise and fall of fuel level in the float chamber. Connecting the overflow to anything that generates vacuum or +ve pressure, no matter how slight, isn't a good idea - I once connected them up to the catch can whch also had the crankcase vent running into it, this caused all manner of issues for me that took ages to solve.... As Paul says above, they're pretty sensitive to float level. Not sure if you can on an HIF, but I set float level on the lder HS6 SU's by taking the dashpot and piston off and carefully measuring down to the level of fuel in the jet with a vernier calliper. You'd have to find what this shuold be for an HIF Disclaimer - its been a long time since I last messed with an HIF SU, I could be wrong.... Edited July 30, 2023 by 1600dave Quote Link to comment Share on other sites More sharing options...
AndBir Posted July 30, 2023 Share Posted July 30, 2023 7 hours ago, 1600dave said: Do your carbs have three little pipes (fuel in and overflow coming out of the carb at 90 degrees and another pipe sightly higher up at an angle) ? Saw a 260z with the SU HIFs fitted as shown below. Silver is fuel supply, large black is vent/overflow? and short one is blocked off. Quote Link to comment Share on other sites More sharing options...
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