The Lotus Grand Tourers

Hi

My hydrocarbons are way off, in order to bring them down to around 300-400ppm is to increase the CO to over 8% if I set the co to 2-3 % the hydrocarbons are 1300+.

This is on mapped ignition, the carbs were recently rebuilt by eurocarb uk and the engine was rebuilt 2-3000 miles ago the head did have a bit of polishing done. before I had the engine work and carbs done I used to get really good emissions.

I have a variety of idle jets, ie,( 55,58,60) I ve tried all 3 different sizes

So if someone could explain why richening the mixture to extreme levels reduces hydrocarbons it might lead down the right path.

Kind Regards

Hello

according to the parts list and sj sportcars the float chamber gasket is of the brown paper type on a my90 excel se powerjet carbs?

can anyone confirm this please ?

my carbs have been rebuilt by eurocarb but have the rubber type gasket and im near certain that the float levels are not 14.5 to 15mm.

Kind Regards

I'm not an expert by any means but could it be something to do with ingnition timing? If timing is unduly retarded you'll get incomplete combustion. This may improve when the mixture is richened slightly if the mixture was originally a bit weak to get reliable combustion.

Pure speculation!

Richard

Hi

At the mot, the car only just made it through by increasing the mixture to 3.50% co which brought the carbons down below 1200ppm just long enough for the analyser to print the ticket. However I went straight back home and checked the ignition timing which wasn't bang on 10 degrees btd so I adjusted it and went straight back to the mot station as I didn't have my own gas analyser, the timing adjustment knocked about 300ppm off. that was all on a dizzy with inbuilt ignition amp, I am now back on mapped ignition which I assumed would be the correct timing as it was all done on a rolling road ect, but that was before my carbs had been rebuilt too.

I picked up a snap on 5 gas handheld analyser 2 weeks ago and checked the emissions with it and it is in line with the mot station so I know it is accurate atm. Sunday I put in 4 new spark plugs and initially the readings were perfect ie about 1% co and about 150 ppm carbons but over the next few minutes the carbons started going back up to where they were before I had put the new plugs in.
My next plan is to recheck the cam timing and ignition timing and see whether they need adjusting.

I also did a compression test, actually 2 times because the 1st time I had a bit of a scare when the readings all came back at 121psi per piston, then I realised I had forgot to do it with the throttle wide open after doing it a second time properly they all came back at 198 psi. so I'm confident it isn't an internal issue.

Hi

I too dont know enough about the subject but I am following, whilst playing Google Doctor.

Here is something I read about air leaks - so will pose the question for thought

3. Lean Fuel Mixture - Any condition which will cause unmetered air to enter the intake manifold, and ultimately the combustion chambers, will cause high hydrocarbons (HC). This condition is called a lean miss-fire. Such faults as vacuum leaks and gasket leaks will cause lean fuel/air mixtures.

I had a o-ring om the intake spacers go last week, luckily I live near Christopher neil and I bought 8 new ones for £2 .
so I replaced them all and put carbs back on making sure that they were spaced as the service manual states. so im confident they don't leak. if there is nothing wrong with the timing I will look at intake gasket as that was done on the engine rebuild, there is nothing to say it is working properly

You know there was nothing wrong with car before the rebuild, hindsight says I should of left well alone

I checked cam timing today

trophy

now as you can see this is on mapped ignition, and although the original pulley marks line up the trigger wheel mark is slightly behind. if I adjust it so that the trigger wheel mark is at tdc the cams are perfectly opposite.
Moving onto ignition timing, the timing is fluctuating quite abit from 10degrees btc in both directions. so I am not happy with the timing and I am trying to get it booked in with the guy who installed the mapped ignition for him to take alook.

In my mind I am thinking that the trigger wheel mark should line up with the pulley and maybe the outfit who rebuilt the engine has fitted the trigger wheel slightly off resulting in the cams being slightly out ?

The photo of the cams looks like the marks are not opposite each other?

When checking cam position it’s not good enough to just have the marks opposite each other as they can be opposite each other and you can still be a tooth out. I know because this was how mine was when I bought it and the cambelt had last been fitted by a Lotus specialist.
To check cam timing is correct relative to each other you need to use a straight edge from center of bolt of each camshaft. The dots need to opposite each other AND in line with the straight edge.

On my car (with DTA fuel and ignition mapping) you can set in software the no. of degrees BTDC of the crank sensor. What system is installed on your car?

Richard

I have a adaptronics e420d ecu .

if you look closely at the trigger wheel, you can just about see a blue arrow about 1 tooth back from the pulley mark. the arrow has "tdc" wriiten under it. if I align that arrow with tdc the cams look perfect. I remember the guy who installed the mapped ignition cut some notches into the pulley so the trigger wheel couldn't moved independently so im thinking its all correct. the ignition timing however is fluctuating a lot, it bounces about from 10degrees btd to 0 degrees when I stick my timing probe on it.

Do you know if engine load is measured by MAP (manifold absolute pressure), TPS (throttle position sensor) or both? This effectively replaces the vacuum advance function used on the standard distributor. It could be a fault in one of these sensors, or as you originally investigated, a vacuum leak. Check where the MAP sensor is fitted. Also check that the brake servo and heater vacuum connections/pipes (if fitted to your car?) are secure and not leaking. The SE had a complex range of emission control functions built into the intake/ignition system - I'm guessing you still have these but if the engine has been removed or overhauled it could be that these have not been correctly reinstalled.

Cheers, Richard

hi

I only have a tps on my system.

anyway, today I thought I would take a look at the viton tipped needle valves,( I read somewhere else that having had there carbs rebuilt by eurocarb last year, their viton tipped needle valves were leaking).

and whilst I was at it I would check the floats were they correct ones and that they didn't have any leaks, despite being new. I have des Hamills book and set about tapping the fulcrum pin out. from the post without the split in. can anyone guess what happened ?

Float pillar snapped

it did indeed .

now I need to either buy a new top cover £100 or try and get it repaired. well I least I know the needle valve and floats are fine