Lotus Elan

Some progress

PostPost by: Robbie693 » Thu Jul 01, 2010 9:13 am

Still trying to chase down a hesitation problem I have when coming back on the throttle and I think I've found a possible explanation.

I have had the carbs set up and a service kit installed by a tuning man. When I got the car back the problem was improved but still slightly there. I noticed that he'd done up the mounts slightly tighter than the 40 thou that is recommended so decided to slacken them off a bit. This has caused the problem to return (I know, should have left it alone :roll: ). I also noticed that a couple of the o-ring carriers are not central in the gap between the carbs and manifold so I have the theory that they are letting in air.

This would correlate with the fact that, a while ago, I discovered the hose had come off the air cleaner and this had caused the hesitation to get worse.

I am thinking of setting up the thackary washers by gapping the actual space between the flanges/o-ring carriers rather than the washer coils. Does this sound like a good idea and does anyone know what this gap should be?

Thanks

Robbie
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PostPost by: types26/36 » Thu Jul 01, 2010 9:26 am

Robbie693 wrote: I also noticed that a couple of the o-ring carriers are not central in the gap between the carbs and manifold so I have the theory that they are letting in air.


Robbie, why don't you spray some "cold start" around the joints with the engine idling, if it speeds up then you have an air leak....even better if you have access to a exhaust analyzer spray and see if the readings change.
Last edited by types26/36 on Thu Jul 01, 2010 10:11 am, edited 1 time in total.
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PostPost by: Robbie693 » Thu Jul 01, 2010 9:38 am

Thanks Brian,

I'll have to get some of that, or can I use WD-40?

Cheers

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PostPost by: types26/36 » Thu Jul 01, 2010 10:10 am

Not sure about that as I think cold start contains either and don't know if WD40 is combustible, you can always give it a go and at least your carbs will be lubricated :lol:
You can get Cold Start of ebay and Halfords I think.
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PostPost by: 512BB » Fri Jul 02, 2010 8:00 am

Hi Robbie,

Measuring the gap between the flanges and misab plates is not the way to go, as different suppliers O rings will vary in thickness and therefore, there will not be a universal gap. The measurement of the thickness between coils of the thackarys is also not critical. I like to leave the gap on the generous side of 40 thou, specially when using new thackarys, which you should always do when carbs have been taken off, along with new O rings, as otherwise they compress in use, and if used agen, the said 40 thou gap does not hold the carbs tight enough.

If you think that you have a problem with a couple of your misab plates not lining up, let me know and I will send you some. Occasionally you have to fettle the holes at the top and bottom to slide them onto the carb mounting studs, but nowhere near enough to make them not line up with the inlet tracts.

All the best,

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PostPost by: Robbie693 » Fri Jul 02, 2010 8:56 am

Thanks Leslie, that's very kind of you.

I didn't think about the washers and o-rings compressing, They are only about 18 months old but the carbs have been on and off about 5 times in that period so I think I should get some new ones and see what the effect is.

When I said the Misabs were not central between the flanges, I meant that the gap seems tighter from the manifold to misab than misab to carb, if that makes any sense. As if they were bent slightly. This could be the o-rings compressing too I guess.

I'll also get some Easy Start (thanks Brian) to see what's going on.

Cheers all,

Robbie
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PostPost by: worzel » Fri Jul 02, 2010 10:26 am

Hi Robbie

If you've understanding neighbours try trickling brake fluid around the O rings- if there is a leak the exhaust will soon let you know!

Regards

John
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PostPost by: Robbie693 » Fri Jul 02, 2010 1:36 pm

Hi John,

Yes I imagine it would be quite dramatic! The garage neighbours are not known to me (I live a few streets away) so I don't know if they're understanding or not :shock:

Cheers

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PostPost by: Robbie693 » Wed Jul 07, 2010 12:35 pm

So I fitted new Thackary washers and there was no change. Squirted some Easy Start around every joint I could find (vacuum connections also) and no sign of a leak.

Then discovered that the ignition timming had slipped to about 8deg so I reset that and there is an improvement (hurrah!).

I am still getting some hesitation and stumbling from when I first touch the throttle. It kind of takes a breath before accelerating. More with small throttle openings than large ones..

I need more suggestions :? - please help

Cheers

Robbie
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PostPost by: kstrutt11 » Thu Jul 08, 2010 9:14 am

Mine has behaved like this a couple of times, it seems to be debris blocking the progression holes, in my case I have cleared it each time by revving the engine and holding a balled rag over the carb inlet (if the debris is small or soft the high depression sucks the jets clean). I must get round to removing the carb and cleaning it out one day...

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PostPost by: collins_dan » Thu Jul 08, 2010 2:05 pm

I had a similar hesitation with my S4 with strombergs, I rebuilt the carbs and found a number of sources of air getting in. I also replaced the stock needle with a new adjustable needle that others had good luck with and the problem is completely gone. What kind of carbs do you have? Dan
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PostPost by: Robbie693 » Thu Jul 08, 2010 7:45 pm

Thanks Kevin, I think the carbs are clean, I just had them stripped and new gaskets etc and the man that did it said there wasn't particularly much cleaning to be done. The problem is better since then but not entirely sorted.

Dan - the car has Dellorto's. I did suspect an air leak but can't find one. I sprayed that ether stuff that helps start cars on cold mornings (Easy Start) everywhere but this caused no increase in revs so I surmised no leaks are present..

I read on here that when new Viton tipped float valves are fitted they can compress slightly and then require the float level to be reset. Has anyone ever experienced this?

Link to that information:

http://www.lotuselan.net/forums/elan-f15/dellorto-carbs-spark-plugs-t20419-15.html

Thanks for the replys

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PostPost by: billwill » Thu Jul 08, 2010 11:33 pm

It may be your accelerator pump setting.


This is the tiny screwed rod on the engine side of the dellorto carbs.

You probably need to get the carbs out to adjust it, so it will be a long slow trial & error process.

Make sure the pump diaphragm is OK and that it does squirt the fuel into the manifold. In free air, working the pump, you should see a fine jet of fuel 4 to six feet long.

The tiny ball valve inside the pump is in the habit of sticking due to getting gummed up, So clean everything properly blast air threough all the holes and fit a new daphragm and gaskets, before you muck about with changing the settings on the pump adjustment rod.
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PostPost by: Tonyw » Fri Jul 09, 2010 1:29 am

Robbie,

I think Bill is on the money, sounds like a classic "flat" spot usually caused by insufficient fuel from the accelerator pumps, although it can be cause be excessive fuel from that source as well. Sounds like you almost have your problem solved.

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PostPost by: Robbie693 » Fri Jul 09, 2010 8:26 am

Bill, Tony - thanks .

The pump diaphragms were replaced during the overhall and were checked for operation.

How do I adjust the pump settings? In other words what happens when I turn the nut and do I tighten it or loosen?

Cheers

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