I'm hesitating!!!

[Elanconvert]

hell guys! I'm a newby! I'm putting this query on here first although it might have to go on elec. one?
Dellortoes on big valve head
Symptoms:
1. backfire...popping and barking on trailing throttle
2. hesitation when accellerating from low revs, i.e. either stationary or poodling along at 30mph, followed by running on three cylinders for a few seconds, then fine.
idle smooth at 800rpm, accellerating smooth and even from 60 - 90mph [honestly, officer, I was clearing the carbs........you wouldn't want me to break down and cause a traffic jam on this busy road, would you?]

Okay, I've ordered Des Hammill's book, and I'm prepared to be politely nudged towards the archives, but there may be an experienced and knowledgeable guru out there who could save me a lot of time and effort...

my initial thoughts are; lazy plug/plug lead?
unbalanced carb/one choke either too rich or too weak [note ; previous owner disconnected choke cable]

any advice appreciated!!
fred

[billwill]

Some popping & barking, when you close the throttle after a fast run section almost always seems to happen with our twin-cam engines and unless excessive can be ignored.

When you get the book, get yourself a pair of servicing kits for the Dellortos and give them a thorough clean out. Using an air blast down the passages. Buy some airblast aerosols if you don't have any other source of compressed air.

Hammil doesn't really cover the accellerator pump, but I suspect yours needs thorough cleaning, including the tiny tiny ball valve in there. and you may need to check that you can get a long squirt from them.

Then get a transparent Colortune plug to set the idle mixtures and a airflow meter to balane the carbs. See my experiences in my topic from this address onwards:

lotus-elan-f19/getting-ogu-roadworthy-again-t26101-105.html#p191111

[Galwaylotus]

Vacuum leak? Check all your Thackery washers to make sure none has broken and all the gaps are per spec.

[Elanconvert]

thanks for the advice chaps...I will assemble the required equipment...as with medicine, correct diagnosis is 90% of the cure...........
the carbs were apparently set up on a rolling road not so long ago, so as you say maybe just a good clean...
on the subject of which, I note that my car does not have an in-line fuel filter fitted...I would have thought that would be sensible, and this will be "rectified"....I presume there are no reasons why not?
fred

[Galwaylotus]

thanks for the advice chaps...I will assemble the required equipment...as with medicine, correct diagnosis is 90% of the cure...........
the carbs were apparently set up on a rolling road not so long ago, so as you say maybe just a good clean...
on the subject of which, I note that my car does not have an in-line fuel filter fitted...I would have thought that would be sensible, and this will be "rectified"....I presume there are no reasons why not?
fred

None whatsoever! It should be a given. My S3 SE came with an in-line filter installed between the tank and the inlet of the electric fuel pump. Easy to check and to replace if necessary and it protects the pump as well as the carbs. On that subject, I am overhauling my DCOEs and when I replaced the filters in the covers I found them very clean. The in-line filter is obvoiusly doing its job!

[Elanconvert]

right, then.....while waiting for des hammill book, gunsons colortune, air flow balancer.....had a quick look at the thackeray washers as suggested by galwaylotus...none of the top ones are broken as far as I can tell... HOWEVER, I noticed that the washer for no1 cylinder [at the front] is tightened right up, while no4 has a gap of about 2-3mm. the in-betweens somewhere in-between. I would assume they should all be equal? unless the head is twisted slightly? or manifold/surfaces not square/flat?
Left like this, should I anticipate maybe an air leak at no4?

[Galwaylotus]

Gap between coils of each Thackery washer should be 0.04 inches (1.02mm) per Lotus Elan Workshop Manual. The purpose of the mounting system, o-rings and spring washers, is to provide a seal while still isolating the carburettors from engine vibrations which can cause fuel frothing.

[billwill]

thanks for the advice chaps...I will assemble the required equipment...as with medicine, correct diagnosis is 90% of the cure...........
the carbs were apparently set up on a rolling road not so long ago, so as you say maybe just a good clean...
on the subject of which, I note that my car does not have an in-line fuel filter fitted...I would have thought that would be sensible, and this will be "rectified"....I presume there are no reasons why not?
fred

I think the dellortos have a smaill fuel filter mesh, just inside the fuel inlet fitting. As mentioned by GalwayLotus above.


Next time you have the carbs off, check that the o-rings or combined O-ring seals between the carb and the head are in good condirion, with no nickes or dents in the rubber and that the flat surfaces of the head and the carburettors do not have any pits in them.



http://www.burtonpower.com/parts-by-cat ... ories.html

[Galwaylotus]

I think the dellortos have a smaill fuel filter mesh, just inside the fuel inlet fitting. As mentioned by GalwayLotus above.

Oops! I forgot that we were discussing a Dellorto setup here. My Elan has Weber 40DCOEs.

[Elanconvert]

a little query on the 'O' ring plates....the burton ones [and others I've seen advertised] seem to be made out of thin steel plate maybe 2mm thick, whereas the ones fitted to my car appear to be die-cast metal 5mm thick....I presume they are interchangeable?
fred

[Galwaylotus]

The Misab plates pictured on the left above in Bill Williams' post are not steel but probably aluminium, 1mm thick, with a moulded o-ring - all one piece. They are an alternative to the 3-piece o-ring - spacer - o-ring setup originally on the Elan. Either setup will do the job as long as the preload is correct (gap in Thackeray washers as above).

[Elanconvert]

yes thanks....I've just spotted the 3 piece jobs on dem*n twe*ks......so answered my own question .think I might use those just in case there's a problem with the stud length .....
fred

[Elanconvert]

ok I'm being picky now......
the workshop manual that I have just consulted [1970 ed] states that the carbs should be mounted so that the gap between flange - spacer - flange i.e. the space taken up by the 'O' rings when compressed, should be 0.040" [1mm approx]
this seems more sensible and accurate than measuring the gap in the thackery washer coils, which I suppose could vary in compressive strength?
what do you reckon?

[holywood3645]

Before you go start changing O Rings on the carbs, Do a little squirt test using engine start fluid (sparlingly) around each carb O ring/manifold when engine its at idle. If rpm pick up you have a Vac leak, and O-rings need replacing. The other things I check on a regular basis is the cylinder air flow, carb balance, mixture adjustment and timing. I check spark plug color after adjustments and a long run. Even get a new set of spark plugs and HT leads. (always good to have spare)

Good luck

James

[billwill]

a little query on the 'O' ring plates....the burton ones [and others I've seen advertised] seem to be made out of thin steel plate maybe 2mm thick, whereas the ones fitted to my car appear to be die-cast metal 5mm thick....I presume they are interchangeable?
fred

The right hand picture above is the three piece system. They seem to have the spacer available as alloy or as plastic nowadays.