Phil C Posted November 20, 2022 Report Share Posted November 20, 2022 I am struggling to get my newly rebuilt engine to run smoothly. It appears to be running very rich and starts to choke up at tick over. The carbs have all new internals and are adjusted to the "start settings" as per the manual. I have noticed if I remove the oil filler cap whilst running the engine speeds up and runs much smoother. I can replace the cap if the rocker cover to Emissions valve pipe is disconnected. This does not seem right but I can't quite get my head around what is happening. I have fitted an aftermarket rocker cover and a cap which is vented. I have not really done anything to the Emissions Valve apart from clean it and replace the diaphragm. It seems one or both are restricting the air intake in some way. Any thoughts from the group would be most welcome. Thanks in advance. Link to comment Share on other sites More sharing options...
johny Posted November 20, 2022 Report Share Posted November 20, 2022 It sounds like youre running too rich. The emissions valve is to keep the crankcase at a slight vacuum so when you remove the oil cap it opens more and allows extra air to be drawn into the manifold so improving the mixture. The same is also happening when you disconnect the valve pipe. If youre sure everything is correctly adjusted/working in the carbs I would try weakening their mixture... Link to comment Share on other sites More sharing options...
daverclasper Posted November 20, 2022 Report Share Posted November 20, 2022 Air filters and their gaskets are all fitted with the cut out at the top? Link to comment Share on other sites More sharing options...
Phil C Posted November 20, 2022 Author Report Share Posted November 20, 2022 48 minutes ago, johny said: If youre sure everything is correctly adjusted/working in the carbs I would try weakening their mixture... I am hopeful that the carb refurbs are all ok.....too many variables there if not! If the increase in engine speed is normal then I will try weakening the mixture. Thanks Link to comment Share on other sites More sharing options...
Phil C Posted November 20, 2022 Author Report Share Posted November 20, 2022 31 minutes ago, daverclasper said: Air filters and their gaskets are all fitted with the cut out at the top? Thanks Dave, Not fitted yet, not got that far, but I would imagine filters would make the mixture richer anyway? I was hoping to get things running 90% before final assembly and fine tuning. Link to comment Share on other sites More sharing options...
johny Posted November 20, 2022 Report Share Posted November 20, 2022 The main carb problems could be the float level too high or choke stuck on? However a weaker mixture adjustment is a good first step... Link to comment Share on other sites More sharing options...
Phil C Posted November 20, 2022 Author Report Share Posted November 20, 2022 I have re-checked float level which was ok and the choke is definitely not sticking on. I guess I was surprised how rich it was running with the jets turned down the recommended 3 rotations. Link to comment Share on other sites More sharing options...
johny Posted November 20, 2022 Report Share Posted November 20, 2022 Yes that setting is only an initial position and 2 turns down could be more like what you need... Link to comment Share on other sites More sharing options...
johny Posted November 20, 2022 Report Share Posted November 20, 2022 Did you count 3 turns from the top of jet being level with the bridge ie just touching the underside of the air piston? Link to comment Share on other sites More sharing options...
Pete Lewis Posted November 20, 2022 Report Share Posted November 20, 2022 on the rocker cover repplacement just what sort of filler cap and vent is fitted compared to the original ?? as for basic settings they are just that its a start point to get it to run i would lean it of as far as needed to increase the idle when the richness is eliminated whether thats half a turn or far more is not important Pete Link to comment Share on other sites More sharing options...
Phil C Posted November 21, 2022 Author Report Share Posted November 21, 2022 16 hours ago, johny said: 3 turns from the top of jet being level with the bridge ie just touching the underside of the air piston? I did. 13 hours ago, Pete Lewis said: on the rocker cover repplacement just what sort of filler cap and vent is fitted compared to the original ?? Its the standard alloy cover and cap available from most suppliers and the cap has a single hole through the centre. Unfortunately I can't find the original to compare....its somewhere 🙄 I was just wanting to check the increase in engine speed thing with the cap removed was normal before adjusting the mixture etc. I will now weaken the mixture and see how I get on. Thanks All Link to comment Share on other sites More sharing options...
rlubikey Posted November 21, 2022 Report Share Posted November 21, 2022 I've had problems on my PI engine with oil getting past the same filler cap as yours. I bought an original type but the bayonet fitting is completely different. I've just put a little self-tapper in the hole to see if it helps with oil on the top of my rocker cover. The situation is different with carbs as you should always have a negative pressure in the engine due to the breather tube to the manifold. (On a PI it goes to the plenum) This is why the revs go up when you take the filler cap off - it's quite normal. Do you get a detectable change in revs when you block the tiny hole on the cap? Probably not, but if it concerns you the you could block it anyway. There's no hole on the factory filler cap, so I don't know why they have one on the fancy chrome after-market type. Cheers, Richard 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted November 21, 2022 Report Share Posted November 21, 2022 the orig filler probably had a breather valve in its cap MkII 2 Litre Cylinder Head : Canley Classics the small hole has little effect but does allow the engine to breathe whilst garaged etc. Pete 1 Link to comment Share on other sites More sharing options...
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