Wild idling engine issue!

[Guy 600N]

Wild, oscillating idle sometimes even stalling the engine. It literally idles at 1500rpm but then if I'm in traffic or just going slowly - stop starting - the revs go so low that sometimes it can stall itself -- any ideas?! i was thinking it could be an air leak, or something along those lines.

also, random one, when the car is pulling itself along ( without me using the accelerator pedal or when the clutch isn't in) it makes a squeaking noise from the right hand side, what feels to be near the rear wheel - any ideas for this?! could it be a bearing or something (i'm making this up now)?

Many thanks in advance guys! waiting for my regulator and hopefully will see some of you at Donnington!

Guy

 

[Mr.F]

Idle fluctuations likely to be an air leak.
For rear squeak, check that none of the rear brake parts are rubbing on the inside of the drum.

 

[rhanagar]

Agree with Mr.F here on the air leak theory.

 

[Mr.G]

The air leak can be as simple as you not putting your dipstick back properly. Check dipstick is fully seated in hole, oil cap is screwed on properly and vacuum lines are not loose.

Good luck.

 

[Guy 600N]

Yeah thought it might be! i will have a look, this weekend... could it be the 'o' rings?! i've been told the carbs are on too tight and that they need replacing (the o rings)... i will try the dip-stick later today actually...

In brighter news though, regulator fitted and works BEAUTIFULLY! Many, many thanks to Mike for that.

im not sure the squeaking is from the brakes because it only happens when the clutch isn't in - so if i were driving up to traffic lights slowly (without braking) it would be squeaking until put my foot on the clutch to take it out of gear (still rolling) and it would stop whilst the clutch was down.... if that makes any sense!

 

[Mr.G]

If the squeak is dependant on you clutching in and out then it's most probably you're clutch bearing at fault.

 

[Ian Patmore]

could it be the 'o' rings?! i've been told the carbs are on too tight and that they need replacing

I presume you mean between the carb body and the inlet manifold? If so, yes, can be over tightened. This extra clamping force can over time make the rubber split, and let air in. Just want the o ring compressed enough to seal.

 

[Albrecht]

....could it be the 'o' rings?! i've been told the carbs are on too tight and that they need replacing (the o rings)... i will try the dip-stick later today actually...

One of the reasons that so many inlet manifolds have 'O' rings between the carburettor body and the manifold body is that they were designed to resist the issue of fuel 'foaming' inside the float bowls due to engine harmonics. This is ( was ) mostly a four-cylinder engine phenomenon, and Nissan's L-series sixes don't really suffer from it.

All Nissan's factory 'Sports Option' triple carburettor kits for the L6 had solid mounted carbs. They used a phenolic spacer ( with gasket material on both mating sides ) to reduce heat soak, but they were solidly mounted. There was no need for the 'soft' mounts seen on four cylinder engines, so - long term - if you wanted to delete the 'O' rings ( and make air leaks less likely, and carb linkage adjustment more constant ) you could do it without worrying about 'foaming' issues.

If anyone tells you that your carbs need to be on flexible mountings, please ignore them. It doesn't apply to the Nissan L6 engines.

 

[Alphabettispaghetti]

One of the reasons that so many inlet manifolds have 'O' rings between the carburettor body and the manifold body is that they were designed to resist the issue of fuel 'foaming' inside the float bowls due to engine harmonics. This is ( was ) mostly a four-cylinder engine phenomenon, and Nissan's L-series sixes don't really suffer from it.

All Nissan's factory 'Sports Option' triple carburettor kits for the L6 had solid mounted carbs. They used a phenolic spacer ( with gasket material on both mating sides ) to reduce heat soak, but they were solidly mounted. There was no need for the 'soft' mounts seen on four cylinder engines, so - long term - if you wanted to delete the 'O' rings ( and make air leaks less likely, and carb linkage adjustment more constant ) you could do it without worrying about 'foaming' issues.

If anyone tells you that your carbs need to be on flexible mountings, please ignore them. It doesn't apply to the Nissan L6 engines.

I guess this is because an IL6 has perfect primary balance so will just run smoother?

 

[amocrace]

The 'soft mount' for carbs were origionally used in the 50's on big 4 cylinder grand prix engines that would just about shake your teeth out. People won't believe me when i tell them the majority of engines will run quite happily with solid mountings for the carbs. The fuel frothing at it's worst used to shut the needle valve off early and could cause weak mixtures and detonation.As Alan syas not a problem on the 'l' motor and Astons always had solid carb mounts whether fitted with SU's or Webers

 

[Guy 600N]

Thanks for all of the info guys! I have noticed some fuel on top of the carbs recently - not a lot, but a noticeable amount - could this have anything to do with the lumpy, oscillating idle? I'm sure the idle gets worse as the engine warms up or/and when I'm in traffic. I am using my Datsun daily at the moment, so I'm sure that's not helping!

 

[Guy 600N]

One of the reasons that so many inlet manifolds have 'O' rings between the carburettor body and the manifold body is that they were designed to resist the issue of fuel 'foaming' inside the float bowls due to engine harmonics. This is ( was ) mostly a four-cylinder engine phenomenon, and Nissan's L-series sixes don't really suffer from it.

All Nissan's factory 'Sports Option' triple carburettor kits for the L6 had solid mounted carbs. They used a phenolic spacer ( with gasket material on both mating sides ) to reduce heat soak, but they were solidly mounted. There was no need for the 'soft' mounts seen on four cylinder engines, so - long term - if you wanted to delete the 'O' rings ( and make air leaks less likely, and carb linkage adjustment more constant ) you could do it without worrying about 'foaming' issues.

If anyone tells you that your carbs need to be on flexible mountings, please ignore them. It doesn't apply to the Nissan L6 engines.

I can't remember if he told me I needed a soft mount or not but I remember he suggested that the o rings might have deteriorated and may cause air leaks etc... (But also they're on too tight)