slap_ed Posted October 23, 2012 Share Posted October 23, 2012 Hi all, Sigma 150 throttle bodies Does anyone know if you can balance individual intakes or is it pairs only? Cheers Link to comment Share on other sites More sharing options...
RedCat7 Posted October 24, 2012 Share Posted October 24, 2012 Yes, using the bleed screws. I followed this method. Link to comment Share on other sites More sharing options...
slap_ed Posted October 24, 2012 Author Share Posted October 24, 2012 Hi Redcat7 Maybe I'm a bit thick but I can't say I fully understand what they are saying. Do I adjust the individual intake ports by slackening off the small locknut/Allen key bolt above each body? I can balance the left or right as pairs but not individually, if you see what I mean. Appreciate your help on this. Cheers Graham Link to comment Share on other sites More sharing options...
slap_ed Posted October 25, 2012 Author Share Posted October 25, 2012 Ideas anybody? Link to comment Share on other sites More sharing options...
Molecular--Bob Posted October 26, 2012 Share Posted October 26, 2012 You need a flow meter to do this. I was told to close the air bleeds on the individual bores and then match the two bodies with the linkage balance screw, to the point where the engine will idle. Then set a reasonable idle speed with the idle screw. You then identify the runner in each body that has highest flow and then open the other bleed until you have matched the flow within that body. Do this for both bodies, then use the balance bar screw between the bodies on the linkage to set the same flow between both bodies, and finally set your required idle speed. Not had a look at how to adjust the bleeds as mine were ok, so once you have figured out how to do this you should be ok to try the above. Link to comment Share on other sites More sharing options...
Paul Deslandes Posted October 26, 2012 Share Posted October 26, 2012 As M-B says. You should end up with one or both bleed screws closed on each pair, never both open. Don't over tighten when closing, its not necessary and you can strip the thread if you're not careful. Link to comment Share on other sites More sharing options...
slap_ed Posted October 27, 2012 Author Share Posted October 27, 2012 Throttle Bodies Thanks for the replies. I have a flow meter and have managed to balance them as a left pair and a right pair. Now I want to balance the two on the left and then the two on the right. Going by the picture I've attached above, am I right in thinking that I've identified the air bleed screws correctly and are these used to balance the air intake of say the right hand pair? Does this adjusting screw allow air to bypass the butterfly or does it open the butterfly? Cheers all Edited by - slap_ed on 28 Oct 2012 17:37:50 Edited by - slap_ed on 28 Oct 2012 17:42:13 Link to comment Share on other sites More sharing options...
Paul Deslandes Posted October 27, 2012 Share Posted October 27, 2012 Can't see the pic unfortunately but the bleeds bypass the butterfly. Assuming that the bleed screws are all shut, work on the one flowing less air, adjusting so its flowing the same as its other half. You may need to reduce idle a bit as you go. Then check that you have three chokes flowing the same and adjust the remaing one. First time you may need a couple of goes at it but its easy once you realise what's going on. Edited by - Paul Deslandes on 27 Oct 2012 10:31:25 Link to comment Share on other sites More sharing options...
slap_ed Posted October 27, 2012 Author Share Posted October 27, 2012 Am I right in thinking..... The air bleed screws are/should normally be in the fully closed position. Firstly the left pair and the right pair are balanced using the central screw located between both of the throttle body pairs. If cylinders 1 and 2 intakes are out of balance then the only way to balance these is to use the appropriate air bleed screw bypass to increase the air flow into the cylinder as these two butterflies are not physically adjustable individually. The same with cylinders 3 and 4. The engine's basic tickover is controlled by the butterflies being held slightly open and nothing to do with air through the air bleed screws. Obviously they would all have to be open for this to happen. I appreciate that there are other things to set whilst doing the above ie throttle pot etc, but I'm just trying to understand how the throttle body adjustments work. Hope this makes sense. Or am I barking up the wrong tree? Cheers all Link to comment Share on other sites More sharing options...
Paul Deslandes Posted October 28, 2012 Share Posted October 28, 2012 Opening the air bleed screw has the same affect as opening that choke's butterfly a fraction, allowing more air through to match its other half. Adjusting the linkage and measuring the higher flowing choke of each pair, you balance the two pairs with all the bleed screws shut first, then use the screws to adjust the halves of each pair. Then check all four are the same at idle. Once you're off idle any slight imbalance between, say, the left pair, is too small to have a significant effect. The air bleed is a small drilling in the casting that bypasses the butterfly when closed or nearly closed. The bleed screw allows a small adjustable amount of air through the drilling. Link to comment Share on other sites More sharing options...
slap_ed Posted October 28, 2012 Author Share Posted October 28, 2012 I now understand what needs to be done so thanks to Paul, M-B and Redcat7 for your comments. Cheers Link to comment Share on other sites More sharing options...
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