The poppet valves for emission control. The normal problem with those is the engine won't return to idle speed because the vacuum holds the poppet valves open when the spring should be strong enough to keep them closed. Switch off and restart without touching the throttle and the idle speed returns to normal. The OPs problem is not revving over 3000rpm and weak mixture, and I can't see how the poppet valves could cause these problems as the butterflies will be open and there will be a lack of vacuum to pull the poppet valves open as well, and even if they were I can't see it causing it. I'd still throw them in the scrap or solder them up though.
SU HIF6 carb problems
- Thread starter RobertM
- Start date
The poppet valves for emission control. The normal problem with those is the engine won't return to idle speed because the vacuum holds the poppet valves open when the spring should be strong enough to keep them closed. Switch off and restart without touching the throttle and the idle speed returns to normal. The OPs problem is not revving over 3000rpm and weak mixture, and I can't see how the poppet valves could cause these problems as the butterflies will be open and there will be a lack of vacuum to pull the poppet valves open as well, and even if they were I can't see it causing it. I'd still throw them in the scrap or solder them up though.
I have removed the rocker covers today as per the earlier post and turned the engine over by hand and I'm getting good movement on all the valves suggesting that the camshaft is okay? Afterwards I started the engine and just as a test I removed/replaced spark plug leads individually which created a slight misfire but engine revs held steady. However when I removed the plug lead on cylinder No 6 the engine revs increased immediately by about 500 rpm. I replaced the plug lead and the engine revs remained the same. Any thoughts on why this should happen please?
Hi Neil, a couple of questions for you if you don't mind to help me with my diagnostics: Did you observe the operation of the rockers and valve travel with your worn camshaft? (I'm getting good length of travel on mine). Did your engine rev freely when not driven with the problem only occurring with the engine under load? (my engine revs freely when not being driven).
Rob.
Rob.
Neilr
Member
Hi Rob I was unable to drive mine. It would only run on choke and was difficult to rev it would rev to about 4000 rpm. I did not look at travel of valves though. I decided to remove cam after advice on here that worn camshaft could cause symptons I had. I had replaced everything on fuel and induction side and also all of the ignition side. There was nowhere else to go so I removed camshaft as a last resort. The last time I drove it started to surge and appeared to misfire under load and had not done this before.
Neil.
Neil.