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BJ8 engine sounds ashmatic

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scullion

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Hi, The BJ8 engine in my 65 austin Healey seems to run fine but I'm puzzled by the loud wheezing noise caused I think by the slow run screws (when the butterfly valves in the carbs are still closed) Do any other owners experience this and is it normal or perhaps the carbs are not properley adjusted for tick over?
Thanks
John
 
The wheezing sound I think you are referring to is the normal air sucking sound of an SU carb . Does the car idle (tick over) Im a Brit to so understand the term . It should idle at around 750rpm and be smooth . When were the carbs last rebuilt . Are the throttle shafts wobbly in the carb bodies ?
 
Hi Healey nut, yes it idles OK and is smooth. I rebuilt the carbs with a new kit 800 miles ago so I think their OK. Maybe I need to listen to a few other BJ8's for comparison. I'm in Eastleigh Hampshire.
Regards
John
 
John, I have HD8 carbs on my BJ7 and you are indeed right in that you can get a wheezing sound from the slow run screws. It is relative and depends on how you tune/adjust your carbs. If the Slow Run Screws are turned out too far they will suck air down thru the threads and bore of the screw. If you have adjusted your carb as the book explains it, then the throttle plates are closed at idle and all the mixture and there for the ability to idle is thru the slow run screws. As many have found out it is hard to get a proper tick-over speed with just the Slow Run Screws because they don't allow enough volume thru so it is very probable that in trying it this way that many will have backed the screws out too far. This allows the air to be sucked from the outside/top of the screw. The slow run screw is also suppose to have an "0" ring on it to prevent the air from entering from the top. But many times the "o" ring is missing and it still will be a problem even if it is installed and the screws are backed out alot. Many have decided to completely close the slow run screws and adjust the tick-over quality with the throttle stop screws just like on most other SU carbs. Some have decided to just crack open the throttles a wee bit and then still adjust the tick-over with the slow run screws this then allows the adjustment to be accomplished to a satisfactory degree without excessive turning out of the Slow Run Screws. So experiment with your adjustments to try to get good tick-over without turning the slow run screws out as much and see if this eliminates or at least reduces the whizzing to an acceptable level. The o-ring can be seen in Moss' HD8 Carb pic, item # 51 I believe.
 
Thanks for such a comprehensive reply, I had thought about opening the throttles a little to allow a small 'air bleed' but hesitated to do so, perhaps now I'll try
Thanks
John
 
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