JustGav Posted June 6, 2007 Author Share Posted June 6, 2007 Oh the big downfall of the twin SU. Problem with them is they need constant fettling to keep them running good. Hows about a bigger single carb? The old man is a bit of a purist, wouldn't entertain changing them unless there was a DAMN good reason (and not being able to set them up isn't good enough in his book)... If it was me, I would have ripped them off and gone fuel injection... but parents are funny things... Quote Link to comment Share on other sites More sharing options...
dangerous brain Posted June 6, 2007 Share Posted June 6, 2007 U didnt say injection just a less complicated single carb Quote Link to comment Share on other sites More sharing options...
Mike M Posted June 6, 2007 Share Posted June 6, 2007 Kind of off topic I know but does anyone know the difference between IDF's & IDA's or ICT's. All I know is Weber IDA's are rare and cost a fortune lol. Quote Link to comment Share on other sites More sharing options...
Guigsy Posted June 6, 2007 Share Posted June 6, 2007 Would you mind asking them for a rough cost on balancing dual carbs on a 1275cc a-series engine? im not going to be able to go in for at least 3 weeks m8. best phone them Quote Link to comment Share on other sites More sharing options...
dandan Posted June 6, 2007 Share Posted June 6, 2007 Oh the big downfall of the twin SU. Problem with them is they need constant fettling to keep them running good. Hows about a bigger single carb? That's just not true - that's one of the typical "myths" banded around by people. I run twin 1.5" SU's on one of my cars and have no problems with them "going out of tune" - I've never had to fiddle with them to retune once they are setup. I've been using them on the same engine for over 9 years. I have two wideband sensors installed in that car and I know 100% what the mixture should be and would definitely notice any "going out of tune". Get yourself a synchrometer and you can set them up yourself (assuming they already have the correct and identical needles and all you want to do is balance them). You have to take your time, slacken the linkages off, adjust each one till their sucking the same then tighten the linkages back up and check both are engaging at exactly the same time. You need to set something the same on both to start with - let's say the jet height at somewhere sensible and make it the same both sides. Then balance the airflow on both carbs, keep adjusting the idle speeds and readjusting the mixture screws to allow for more/less airflow. You'll probably find you can close the butterflies a fair bit from when you started by constant retrimming of the mixture to suit - if you have a vac gauge you'd see the engine pulling more vac at idle than when you started the tuning/balancing. I find the large bore A series engines idle best around 12.5-12.8:1 if they've got anything hotter than a 276 cam in - anything like stoichometric is a no no! They can obviously run much leaner once on the move/cruise etc It's not difficult - just take your time. If you need to start custom profiling your own needles then I agree to a point with DB - twins become more tricky as getting two very close needles takes time. Been there and done that more times than I care to recall Do you have a wideband in any of the manifold branches? Quote Link to comment Share on other sites More sharing options...
JustGav Posted June 6, 2007 Author Share Posted June 6, 2007 Do you have a wideband in any of the manifold branches? Cheers for that Just sent all of that over to the old man, hopefully he reads it and tries it before spending money, I bought him a carb balancer for his birthday, hopefully gives him incentive to try it. I've lent him my LM-1, so he has been using that. (Lets not even go into how much bother it was trying to explain what to do with it).... Quote Link to comment Share on other sites More sharing options...
RobSheffield Posted June 6, 2007 Share Posted June 6, 2007 My dad runs twin SUs on 3 cars, 1500 and 1800 4 cylinder and 3500 V8. All balanced by hand/ear but we are a bit far away to help Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 6, 2007 Share Posted June 6, 2007 Dandan speaks good advice Quote Link to comment Share on other sites More sharing options...
mikeyb10supra Posted June 7, 2007 Share Posted June 7, 2007 You can do it by ear with a stethascope you sure can, used to do it on my old 1.9 205Gti the 45's used to sound awesome but always needed a little tweek every couple of months, the car was running to the absolute limit of what was possible power wise, I remember someone messing with the mixture screws on mine when it went in for a service and came out running like a bag of shite, took me ages to get it back to normal Quote Link to comment Share on other sites More sharing options...
Steve Posted June 7, 2007 Share Posted June 7, 2007 You have PM Pheonix-One Quote Link to comment Share on other sites More sharing options...
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