Lotus Elan

Bought a wide-band lamda meter.

PostPost by: 65 Lotus » Fri Jun 08, 2012 9:44 pm

I can't take it anymore. I'm starting to not want to drive the Lotus because of the bumping and thumping I get at 60 mph ± 10 mph when cruising. Running around town is fine, but I can't take it anywhere of any distance; it just won't cruise.

Runs great there when not fully warmed up (<45 minutes) but once it gets good and warm, the thumping starts which in my mind says it's going rich. Tried all manner of air correctors and just can't seem to fix it. Runs great every other way though.

I'm going to fix this though if it's the last thing I do. Been fighting it every season for years now.

I've had enough. :( :evil:
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PostPost by: twincamman » Fri Jun 08, 2012 10:13 pm

Scott---- I had a plug miss, fouling and various starting woes for 2 years,, the problem was a bad battery and ground and a loose fan belt [Im paranoid about loading the water pump up ] I so concentrated on carbs that I bought new ones . After the electrical problems were solved the thing is magic , starts runs accelerates smoothly and is a joy to drive last time I drove it last month .you need lots of spark to keep the plugs clean ..try looking there ----ed
dont close your eyes --you will miss the crash
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PostPost by: EdHolly » Fri Jun 08, 2012 10:46 pm

What size bleeds do you have in the float chambers - mine were way too small .5 and by playing around with them have got it almost perfect drilled to .85. Also pump stroke length has a bearing obviously. Sometimes the bleeds are called drains. Of course all this in conjuction with all the other variables !

Not much is written about pump bleeds but I have found them a critical part of a road cars tuning, even my Eleven has benefitted on the road by going the other way, ie now 0's in lieu of .5's

After buying my Series 1 Elan I played around with the Webers for yonks before being happy with them. Never had a problem with a race car - but they never use the low speed circuit as a road car does. Even drilled the butterfly hole larger as per various advice on the web for type 31's.

In retrospect I suspect a lot of the trouble was caused by a longer pump stroke length than the original -18's had and getting rid of that extra fuel was my main problem - along with the progression hole problem that the -31's seem to have.

Ed
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PostPost by: john.p.clegg » Sat Jun 09, 2012 7:55 am

Scott

The title says "BOUGHT A WIDE-BAND LAMDA METER.",what does that tell you,or is it just a wish?

John :wink:
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PostPost by: simonknee » Sat Jun 09, 2012 10:57 am

On Webers? Head to Keith's group. What rpm does this happen at? Sounds like it could be when the main jets tip in. Get the white paper @ Yahoo Groups, Sidedraft_Central. Set the float level by Keith's method it does wonders with stock jetting.

If you are using a Widband make sure there are no leaks what so ever in your exhaust system or you'll be taking junk readings.
Remember sort everything else before you even think about starting on the carbs. Then start on the carbs!

Simon
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PostPost by: fatboyoz » Sat Jun 09, 2012 1:29 pm

Ed,
I have fitted one of these kits, and run the toothed belt quite loose. May eleviate your paranoia.
http://www.burtonpower.com/parts-by-cat ... 1&cat=2424
Colin.
PS. I second Simon's advice on Keith Franck's Yahoo site.

[quote="twincamman"]Scott---- I had a plug miss, fouling and various starting woes for 2 years,, the problem was a bad battery and ground and a loose fan belt [Im paranoid about loading the water pump up ]
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PostPost by: 65 Lotus » Sun Jun 10, 2012 1:26 am

You guys got me thinking, so I spent all day double checking a lot of possible problem areas. Optically checked the float heights (again), perfect at 25mm.

Running a generator, but I get solid 13.3 VDC charge so I don't see that as a problem. If I check between a spark plug base (BP6ES with a .030 gap) and the battery ground lead/chassis, I get 3.0 ohms. Too much?

In all, I think I may have an ignition problem. I'm running 20 degrees advance at 1500 rpm using a Pertronix Ignitor kit with a 3.2 ohm coil, but I have solid core wires which apparently can be a problem due to RFI. The timing is very erratic, so RFI interference could certainly be the issue. I ordered a new set of non-solid core wires.

Also, I'm still using a cutout rotor (which works as advertised). Is anyone still using these, or should I go to a solid rotor?

Thanks everyone.
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PostPost by: StressCraxx » Sun Jun 10, 2012 4:18 am

3 Ohms seems high. Remove, clean and remake your chassis ground to engine block and battery cable to chassis ground. Then check resistance again.

I believe Roger Sieling is near you. He is a long time, multiple Elan owner.

Regards,
Dan Wise
There is no cure for Lotus, only treatment.
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PostPost by: Chancer » Sun Jun 10, 2012 9:42 am

Check the resistance reading when you short out the meter probes and subtract that from the measured reading for the true resistance.

Since the advent of digital multimeters we seem to have lost the "zero ohms" facility, some of my meters on certain days can indicate close to 3 ohms with the probes shorted.

3 ohms might be significant in terms of the starter motor resistance and cold cranking but it is relatively insignificant in terms of the coil impedance and resistance of the ignition module.

To me an engine that will fire up when cranking does not have a resistance problem on the ignition circuit but others have attested to exactly this, I wonder if they all had electronic ignition?
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PostPost by: simonknee » Sun Jun 10, 2012 10:39 am

65 Lotus wrote: I'm running 20 degrees advance at 1500 rpm using a Pertronix Ignitor kit with a 3.2 ohm coil,


A 3.2 ohm coil is fine and correct for a Pertronix http://www.pertronix.com/prod/ig/flame/ ... _volt.aspx

3ohms to the battery might be a little high - work your way closer and closer to the battery to find out where the resistance is.
(buy Fluke, not a Maplin special, Chancer :D)

20 degrees advance at 1500rpm seems a bit much - however what model dizzy do you have?
Why not stick in a solid rotor just to eliminate this from your enquires.
Have you made sure your advance weights are all OK.

It is interesting that the problem only exhibits when you are up to temp.
Plenty of electrical bits can have heat related failure modes.
It is possible that whatever is giving you 3 ohms now goes much higher when warm.
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PostPost by: terryp » Sun Jun 10, 2012 12:10 pm

65 Lotus wrote:Runs great there when not fully warmed up (<45 minutes)


What theromostat are you running?
I put a 71 degree in my old +2 with a Kenlowe fan coming on at approx 78 (via revotec switch). Temperature never rose above 85 degrees
Car then ran superb. Before the thermostat change it ran like yours.

TT reckons that optimum temperature for a Twincam is just above 70 degrees

Terry
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