Spark Plug Colour

[Terry Posma]

I have recently licenced the S3 after a very long restoration and have started to use it for longer trips where I can get the engine to full temperature for an extended period.

I have been pulling the plugs and adusting the idle mix to get all 4 plugs to approximately the same colour and condition. I know I will have a bit of trouble here as cylinder 4 will always be a bit richer than cylinder 1.

In any case here is a photo of cylinder 3 plug. It is a NGK and one step warmer than you would usually use as the car is mainly driven around the suburbs and takes a while to get up to temp.

No 3 plug

If you look carefully you can see one side is darker than the other. Looking at all sorts of photos of plugs in guides that tell you what the plug should look like I have not seen this phenomenom. Is this normal on a Lotus TC. Is it a result of the hot plugs or just that I need to get the mixture a little leaner? I also thought it may be a result of timing where fuel is still entering the cylinder as the plug has fired?

Cheers.

[elans3]

Looks a good colour to me, and probably as near excellent as dammit for a twink, in fact for any of our older cars running DCOE's / DHLA's. If you're a bit worried, just try an eighth of a turn leaner.

[bill308]

Hi Terry,
I recommend you get the air flow balanced to a fine degree, preferably with a multi column manometer measuring inlet manifold vacuum.
Once balanced, use a Colortune to set the idle mixture for each carb. This provides a common starting point for dialing in the transition range. Once all carbs are idling at the same mixture strength, switch back to normal plugs and beg or borrow an air/fuel meter reading the combined mixture in the pipe between the collector and muffler, under varying load conditions.
Bill

[alan.barker]

Terry what is the ref n° of the Plug you are using please.
NGK ref n° work the oposite way to Champion
Alan

[Terry Posma]

Thanks for the replies.

As suggested by Bill308 I had a go at balancing the carbs, not with a manometer but a piece of plastic plumbing pipe with a right angle in it. The front to rear were miles out but the front to rear of each of the carbs was ok.

It now runs smoother than ever but I do have to sort out the idle to get it to drop to set idle rpm straight away as it did at the start. I assume it has something to do with the adjuster between the two carbs.

[alan.barker]

Hi Terry,
Could you say what grade ref Plug please
Alan

[Terry Posma]

Sorry Alan.

They are NGK BP5ES. 5 is the heat range number. NGK has a heat range of 1 to 12 with 1 being the hottest and 12 the coldest.

Also just took the little car for a run again and I am now having an issue with the revs not quickly decending to idle when I take my foot off the throttle. I have done a bit of a search here as I know there is some discussion on this subject but cannot find it.

[alan.barker]

Thanks Terry,
like you say hotter than many who use BP6ES. If you want to do sme motorway maybe BP6ES would be wiser.
Have fun with the tinkering
Alan

[William2]

I recommend you invest in a Syncrometer carb balancer. Not expensive and they are so easy to use.

[SENC]

I'm no expert, but I think the lazy idle you're getting is generally caused by too much fuel through the 1st (most downstream) progression hole at idle (meaning on its idle stop, the butterflies are exposing that progression hole too much). If you can reduce idle a bit (and still have smooth idle) to allow the butterflies to close more fully, that may solve it. Others have solved lazy idle by drilling a very small hole in the lower section of the butterfly.

[Terry Posma]

Thank you, I was looking for the term lazy idle.

So I have spent a couple of hours this afternoon in the car park of the local playing field (so I could make lots of noise without upsetting the neighbours) and used the advice given plus also that from the searches I had done.

I do not have a synchoniser so just used a bit of tube. I just made the problem worse trying to find a point where one carb sounded like the other. Each of the venturies of each of the carbs were the same but the 2 carbs were just different. Anyway I reverted to backing off the idle screws completely and then figuring out when they started to move by feel rather than sight. I placed my finger on the nut on the outside of the carb and you can feel the smallest movement. This worked much better than by sight as I have poor sight at the best of times.

From that point I just added a little bit of a turn to each screw until I got to a point where the idle was about 800 rpm and then set the middle screw. After that I checked the mixture screws to see that they were not too lean or rich.

I now have no lazy idle and the car feels smooth and strong in all gears and revs. Probably famous last words.

Here are plugs 1 and 4 after a 15 minute blast.

Plugs 1 and 4.

Thanks for the assistance.

[Terry Posma]

Hello once again.

I took the car for its first big drive, a 200klm run, last Sunday. Used the back roads rather than the highway to avoid large trucks and stone damage. Nothing went wrong even though I gave it a bit of a blast and managed 10klm to the litre (28mpg).

I do have a couple of questions:

1. When cruising at constant throttle over 60kph I do feel a small stutter every so often. Can anyone suggest what this can be? There is no hesitation under acceleration, a little bit of gurgling on the overrun and the spark plugs have retained the same colour as the photos I included previously although they are a bit cleaner now.
2. When starting after a few days I get a bit of smoke after the motor catches and then it takes 20 seconds to settle down to reasonably stable idle. I do not have a choke and just give the throttle pedal a couple of jabs to start. I also have to reprime the fuel system if I leave the car for over a week. I assume I have a leak in the carb with fuel flowing from the carb float bowls into the cylinder and at the same time fuel empting back into the tank. I assume I need to clean or replace the float valves.

Suggestions would be appreciated.

[billmoore42]

I am not sure about the small stutter, but repriming the Webers after the car has been sitting for 4 days or more is normal. I believe the fuel evaporates. If I leave my S3 for a week, I generally crank it until the oil pressure comes up to 35-40, and this pumps enough fuel into the Webers to get them to start easily.

If you look on this forum, a popular upgrade is to install an electric fuel pump in the trunk, controlled by a push button so the driver can prime the car before cranking excessively.

[ericbushby]

Hi Terry,
Fuel should not be draining back to the tank as any reciprocating pump has two one way valves built in.
It is just evaporating through the air filter. The carbs are warm and the float chamber is open to the airbox or filter.
You should be able to smell it in the garage for a day or so.
Eric in Burnley
1967 S3SE DHC

[Terry Posma]

Thread resurrection.

Figured out the problem. At some point 3 of the idle trim screws had been screwed in too tight and the tips had broken off and jambed in the seats. Motor was idling on the progression holes on 3 cylinders and idle hole on the 4th. I have had to replace the carb bodies. I obtained a set of old 31's with some very strange jets. The previous carbs were 27's.

I used the same jetting as previous and found I needed to go to F55 idle jets to eliminate back firing both ways and lazy idle. With the old carbs I was using F50's and that was too rich. I guess that was as the car was idling on the progression holes.

The new carbs had 16.5 mm stroke accelerator pumps, which I kept as a experiment, (the old had 14.5 mm) and the increase in acceleration is startling.

Now all I need to do is get the final trim a bit smoother. Running is much the same as with the 27's but it does not smell of fuel after you turn off the motor.