Re: SU HiF6 weird problem on a 3.5 Rover.
Posted: Wed Jul 10, 2019 12:25 pm
After a slight break I have returned.Sorry the video for the broken engine has gone missing as I shut down my channel hosting it.
The slight break was caused by me building an engine to put under the carbs.Vitesse bottom end with some stock carb heads and the usual 3.9 grind replacement cam.It's all run in and working nicely.Except that when ..............
Yup.The carbs are still playing up. It seemed to work ok for a bit on book settings (for a carb rebuild) as I got the timing sorted after running in the cam and it drove rather nicely with gobs of grunt up to that 3000 mark. And then I tried to tune the carbs into the new engine. Drivers side no problem. Mixture screw lean too much and the revs drop,richen it too much and ditto. But on the other side the moment I screw the mixture screw clockwise from the 1.5 turns starting point the revs rise.And keep rising as I turn the screw.Adjusting the tickover screww until it's off of the cam has no effect lowering the revs and they can hit 3000 before I crack and kill the experiment.It will stall if I weaken the jet.I have been able to set a steady tickover but only before the motor warms up fully.Once warm it will rev away from the tickover set up to it's favourite 1800-2000 point and sit there until it just drops back to tickover.This is with the throttle cable disconnected and the interconnect between carbs off as well.Fast idle adjusted properly,or a bit slack if anything).Just a pair of carbs operating independantly on tickover with zero physical inputs one of which revs the engine seemingly at will,or randomly at least.
I've got a logic block somewhere. The throttle disk isn't a gas tight seal with the stop screw all the way out.There are a few points of light that squeeze around the edges but it's the same on both carbs and the disks were out of the packet.This should restrict the airflow so much the engine will stall and it needs to be opened a turn or so on the idle screw to tickover. So where's it getting the air from to suck that fuel inside when I richen the jet with the butterfly closed ? I can't work that one out.I'm told that the air draws the fuel out of the jet as the air pressure drops above it but not much air is getting by the throttle disk when it's revving up.But somehow by enrichening that carb I can get the revs up way past the point of comfort.Spraying WD40 all over during the revving makes everything stink of WD40 and nothing else.
I am at the point of junking this set of carbs and maybe the manifold (I could do a manifold swap I suppose but I can't see where the problem might be).I'm looking at a complete replacement Weber kit from RPi for a bit of mental relief.I've looked at the birdsnest of wiring on the EFi set I have on the shelf and really don't fancy that much despite the benefits of fitting it.It would mean ripping the exhaust off for welding and experimental wiring stuff, which I normally do in the winter.I would much rather drop something on that works properly on it from the start and go bloody driving for a bit rather than fault finding without finding the fault.
Last ditch attempt this morning was to replace the copper washers on the manifold take-offs and blanking plug.It didn't work.I'm stumped.
The slight break was caused by me building an engine to put under the carbs.Vitesse bottom end with some stock carb heads and the usual 3.9 grind replacement cam.It's all run in and working nicely.Except that when ..............
Yup.The carbs are still playing up. It seemed to work ok for a bit on book settings (for a carb rebuild) as I got the timing sorted after running in the cam and it drove rather nicely with gobs of grunt up to that 3000 mark. And then I tried to tune the carbs into the new engine. Drivers side no problem. Mixture screw lean too much and the revs drop,richen it too much and ditto. But on the other side the moment I screw the mixture screw clockwise from the 1.5 turns starting point the revs rise.And keep rising as I turn the screw.Adjusting the tickover screww until it's off of the cam has no effect lowering the revs and they can hit 3000 before I crack and kill the experiment.It will stall if I weaken the jet.I have been able to set a steady tickover but only before the motor warms up fully.Once warm it will rev away from the tickover set up to it's favourite 1800-2000 point and sit there until it just drops back to tickover.This is with the throttle cable disconnected and the interconnect between carbs off as well.Fast idle adjusted properly,or a bit slack if anything).Just a pair of carbs operating independantly on tickover with zero physical inputs one of which revs the engine seemingly at will,or randomly at least.
I've got a logic block somewhere. The throttle disk isn't a gas tight seal with the stop screw all the way out.There are a few points of light that squeeze around the edges but it's the same on both carbs and the disks were out of the packet.This should restrict the airflow so much the engine will stall and it needs to be opened a turn or so on the idle screw to tickover. So where's it getting the air from to suck that fuel inside when I richen the jet with the butterfly closed ? I can't work that one out.I'm told that the air draws the fuel out of the jet as the air pressure drops above it but not much air is getting by the throttle disk when it's revving up.But somehow by enrichening that carb I can get the revs up way past the point of comfort.Spraying WD40 all over during the revving makes everything stink of WD40 and nothing else.
I am at the point of junking this set of carbs and maybe the manifold (I could do a manifold swap I suppose but I can't see where the problem might be).I'm looking at a complete replacement Weber kit from RPi for a bit of mental relief.I've looked at the birdsnest of wiring on the EFi set I have on the shelf and really don't fancy that much despite the benefits of fitting it.It would mean ripping the exhaust off for welding and experimental wiring stuff, which I normally do in the winter.I would much rather drop something on that works properly on it from the start and go bloody driving for a bit rather than fault finding without finding the fault.
Last ditch attempt this morning was to replace the copper washers on the manifold take-offs and blanking plug.It didn't work.I'm stumped.