MG-Cars.com
MG MGA Synchronizing Carbs BBS discussion at MG-Cars.net
MG-Cars.net
Welcome to our resource for MG Car Information.
Recommendations
Parts
MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.
|
|
MG MGA - Synchronizing Carbs
| Hi All Just started engine after rebuild and bought a Moss synchronizing kit for the carbs. Trying to find thread about this in archives but no luck( I believe Steve Gyles had contributed?). Not clear in the instructions how the pointers fit into tubes(different diameters). Any help would be appreciated. Brian |
| Brian Paddon |
| This kit Brian? http://www.mgaroadster.co.uk/su_carburettor_tool.htm Steve |
| Steve Gyles |
| Hi Steve Yes thats the kit. Do the pointers have to be forced into the tops of the tubes? Regards Brian |
| Brian Paddon |
| Brian The thicker ends (greater diameter) of a couple of the rods are ovoid. The rods are quite a firm push in. The other end of these tubes are an interference fit inside the damper tubes. Once set up in the carbs engine off, adjust the rods so they are the same height in the tubes with the pistons fully down. Steve |
| Steve Gyles |
| Coincidentally I balanced my carbs yesterday but using the ‘trade’ method of listening with through a short length of pipe. Paul |
| Paul Dean |
| Paul I had always done that with good results until I starting using the SU equipment. It's main benefit is ease of use and valid balancing. You are able to balance them with the filters on so any oddities with airflow through each filter are balanced out. i.e. you balance them as 'road going' rather than raw 'on the bench'. Steve |
| Steve Gyles |
| My balancing kit consists of two bent pieces of welding rod which work exactly like the SU ones, cost next to nothing and are remarkably accurate. After all, whatever method is used boils down to air flow which equates to piston rise. |
| Allan Reeling |
| Allan Yes. That's all it is. I did something similar when I couldn't locate my SU kit. One additional benefit I found with the SU tubes was that because they are an interference kit I could lift each piston in turn with them very accurately for adjusting the mixture. Steve |
| Steve Gyles |
| Good point about being able to do the balance with filters on. Perhaps once filters back on i will confirm with welding rods. Paul |
| Paul Dean |
| I have used this technique - in my case with just straws in each dashpot, and agree it is a very easy technique to balance the air flow. And as has been said, its good to do it with the filters on - especially as I find the filters a real pain to remove and replace. Big bonus as far as I am concerned!
But it does assume the mixture in each carb is correct and stays correct after balancing. I've not had the benefit of using the SU kit myself, but it appears from my reading of the instructions, a benefit of using the official SU kit (rather than Allan's rods and my straws), is that the SU rods can lift the pistons for tuning. Having said that, the carbs should have lifting pins built in to them of course. Its all somewhat superfluous to me, as I tend to look at the plugs to get the mixture right - I never seem to have much luck tuning by listening when i lift the pistons |
| Graham V |
| Thanks Steve Having looked at the photos you posted I have bent the pointer ends tighter and pushed them into the tubes. Brian |
| Brian Paddon |
| Surely all the balancing act does is to get the carbs idling at the same air flow? Because all you are doing is adjusting idle screws. What happens at higher flows really depends on the similarity of the flow passages to the intake valves and the residual pressures in the cylinders as they open. Not to say that this adjustment is not important, but I think too much fuss is made of it. |
| Art Pearse |
| Art you balance them out with the interconnecting bar disconnected exactly the same as the other method. The advantage of this kit is you can leave the rods in place throughout the balancing and mixture control process. At any time you can also rev the engine and see the pistons rise in unison - or not. A tweek of the idling screws will rebalance them if they are slightly out. When all done tighten up the connecting bar, adjust the idle. Final check that pistons rise in unison throughout RPM range; remove SU rods; fill chambers with oil; replace damper rods and caps and all done. Hit the road.
Steve |
| Steve Gyles |
| Having balanced carbs by using old fashioned technique of listening to intakes through a pipe I thought I would check with rods in dashpot following this discussion.
It took about 5 minutes to make my rods with indicator arms out of welding rods. The result was my balance was perfect so the old fashioned method really works, Albeit only if you have filters off as I did and rod method is SLO very easy. By the way before starting this a quick feel of piston positions as I reved engines showed big difference so well worth doing. Paul |
| Paul Dean |
| I always balance my carbs on part throttle by adjusting the cable to give 1200rpm. If out of balance, wind up the throttle stops till just touching the body, slacken a clamp the adjust on the relevant throttle screw, just a touch more, re-tighten the clamp and slacken the stop screws. It takes a bit of fiddling. Re-introduce some free play on the cable, then set the idle balance and speed on the throttle stop screws. |
| Allan Reeling |
| If you balance once on mid speed, how can you rebalance at idle? |
| Art Pearse |
| Don't get the question Art. The balancing is done with the cable pulling the spindles. Idle is a product of the stop screws. |
| Allan Reeling |
| Allan, there is only one cable pulling both throttles, so how can the cable position affect the balance? |
| Art Pearse |
| It doesn't. There's something you're not getting here. 1. It's pointless setting balance at idle on the stop screws, as all the driving is done with the throttle operating the spindles and their discs. 2. Wind some throttle on and hold it by whatever means at say 1200rpm, then do the balancing by adjusting the linkage. 3. Put the slack back in the cable and balance again at idle, this time on the stop screws. |
| Allan Reeling |
| Allan I disagree with you. I disconnect the rod linkage then set the idle screws to balance the carbs for airflow, be it at 800, 1000, 1200 RPM etc whatever. I can wind those idle screws up to 3500rpm when I do the timing. There is massive RPM scope in those screws. Then tighten the clamp and check the balance throughout the range. When happy with the process final check that the linkage is tight and back off the idle screws for your ideal idle. Steve |
| Steve Gyles |
| I did mine at fast tickover but when I checked it with welding rods it was perfect throughout all the rev ranges. So my conclusion is it doesn’t matter what speed you do it at. I will stick with fast ‘smooth’ tickover and check at all speeds. Paul |
| Paul Dean |
| Doesn't really matter HOW, if the method works for you then that's the way to go. |
| Allan Reeling |
| i guess my point was that there is only one variable in this and that it is the relative throttle positions fixed by loosening the clamps, adjusting wherever and tightening them again |
| Art Pearse |
This thread was discussed between 28/08/2018 and 10/09/2018
MG MGA index
This thread is from the archive. The Live MG MGA BBS is active now.