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DHLA trouble


marcbria

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Hi All,

 

I just got of the phone with my mechanic. He is repairing the damaged cause by my engine fire last fall. I had asked him to replace the Stromberg carburetors installed on the car with Dellortos.

 

With the Dellortos installed he can't seem to get it to idle bellow 2000rpm, he was concerned that it may be something else because we replaced many parts so he put a known good pair of Strombergs on and it ran very nicely. Is there anything obvious I can suggest to him? He doesn't want to spend too much more time on them as this is an insurance claim and he has gotten the go ahead from my insurance company to install a set of Strombergs that he already has.

 

Thanks everyone,

 

Brian

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Its an air leak somewhere through the carbs.  could be leaky spindles, could be spindle twisted - e,g, butterflies not parallel or not correctly located.  maybe  problem with cold start circuit not seating properly when closed.   or a simple solution could be throttle cable too tight

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Hey Guys,

 

So basically it could be quite a few things, which is what I expected. Unfortunately I'm not with the car, so I don't have the carbs in front of me to get detailed information. I think for the moment my plan will be to get the Strombergs installed and running nicely and when I have time I'll go over the Dellorto's and see what can be done to get them running properly.

 

This might be a crazy request but is there anyone in North America I could ship them to get them setup for a Series 1? I know they would need to be tuned on the car after the fact but I suspect a lot of this may be due to the fact that the car was originally a federal spec and the Dellortos were put on after. So they likely don't have the Lotus spec jets and chokes...

 

Brian M.

Edited by marcbria
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Brian,

Another thought - I beleive Tim Engel has drafted a document detailing the different settings for Dellorto's as fitted to Lotus variants coveirng 907 through to 912.

This should be readily available via a web search (I do have a copy somewhere). It might be easier for you to get a copy and send it ot your garage, and they can check it against the jets/chokes/floats of the Dellorto's you have.

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Hi Paul,

 

This if what I found for a Lotus Spec 5, for a series 1.

 

Carb Type ...................... DHLA 45E
Choke .............................. 36 mm
Main Jet .......................... 160
Main Air Corrector Jet ... 230
Main Emulsion Tube ...... 7772-8
Idle Jet .............................50 (Too lean! Try 55-58 range)
Idle Jet Holder ................. 7850-7
Float Weight .................... 10 gr
Float Setting Height ........ 16.5 - 17.0 mm
Float Needle Valve ......... 170
Pump Jet .......................... 38V 42H
Starter Jet ......................... 70
Starter Emulsion Tube ..... 7482-1
Power Jet .......................... blank
Slow Running Speed ....... 900 - 1000 rpm
Idle CO Level (hot) ........... 2.0 - 3.0%

 

Is this what the Dellorto's were set to when they left the factory? And is it easy to read the configuration off of the various jets, I've never taken my Dellorto's apart to look at their guts.

 

Brian 

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I would suggest that this will be a good starting point, and unless you've had high lift Cams fitted, this would be fine for your engine.

I'd be interested to know if your Dellorto's are similar. If not it'll likely show you where the problem lies.

Itll be easy to check too. Good luck

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This will not be a case of wrong settings (unless they are really of).

If the idle does not settle then it is an air leak.

Most obvious, the butterfly valves are not shutting down completely.

With the airbox removed, you can check that. Don't check with the engine running or you have a burned face in case of a backfire.

however It is easier to check with the carbs out and looking into the light with the butterfly valves closed.

 

If they do not shut properly, you have your reason for not idling (80% chance It will be that....)

Then you have to search the reason , why they do not shut .

 -gas cable

 -butterflies not installed right

 - there is a small bracket attached to the pumpcover with a spring that can cause the throttle shaft to jam and not shut down completely ( I had that problem first after I overhauled mine)

 

Be sure , there is not an air leak between carbs and intakemanifold ( o rings) . This can be checked with the engine running and spraying a bit of brake cleaner around the O rings or misab spacer. The enginespeed should not alter.

 

Are those dellorthos overhauld? They should get new gaskets, diaphragm ,needle valves ( vitton tipped) and fuel filters.. ( dellortho overhaul kit), so you don't risk leaks and an engine fire

The float/fuel level should be checked and adjusted , The carbs should be syncronised.

Overhauling those carbs is a precise job but not really difficult to do yourself. Just get Des Hammill s book on weber & dellorto.

Tim Engels information is gold, you need spec 5 as described above.

 

 

Geert

Edited by gvy
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Thanks Everyone for you advice,

 

After thinking about it some more I've gone ahead and told my Mechanic to install a set of Strombergs, since he is more familiar with them. I'll still have the Dellortos and will be able to take my time figuring out whats wrong with them later. He did overhaul the Dellortos before installing them and didn't notice anything wrong although he admitted he may have missed something since he is not familiar with these carbs. So even if I had him continue working on the Dellortos there is the possibility something is warped and not easily fixed anyways especially since they are not setup to Spec 5 as far as I know. If he installs a known good pair of Strombergs my insurance will be happy and I'll have a happily running car.

 

Some time in the future I'll be able to look into installing the Dellorto's. The car still has a few annoying quirks to sort out that need time but will allow me to keep the car in running order while I fix them so I'll be able to drive it all this summer.

 

Brian

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Geert, you may well be right. My route to fault finding usually

means going back to basics. Especially when fitting new or non standard parts, so at least you can eliminate the obvious before going deeper.

This is of course more difficult in our case when we're trying to diagnose problems without seeing or even hearing the sick car.

Brian, good luck, I'd like to know how you get on.

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The comment about the idle jet..(Too lean! try 55-58 range)...very true. A 50 size jet is only just enough...and when the varnish deposits from evaporated modern petrol starts to close up the hole, you rapidly become TOO lean, and there isn't enough fuel for the upper end of the progression range...and you get a very tedious misfire. I had to use an old guitar string to get the muck out of mine, after which all was well....took a bit of finding, that did!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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