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The Nut

Dellorto Carbs Issues

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Hi to All, Car is a 1981 S2 Elite.

I have spent the last two weeks trying to get the engine to run smoothly and tick over, it sounds like a bag of nails, is lumpy and spits back through the carbs. After several goes at setting up and balancing the carbs, I finally gave up and called on a higher power in the form of Hometune. They, ( In the form of Peter ), spent 2 hrs. trying to get the thing running properly. I have read the book by Des Hammill, both edition 1 & 3, also the write up by Tim Engel and the Tuning Dellortos by The Apply Clan, I have set up the carbs on the Éclat with out any issues and I like to think I know what I'm doing. Hometune put an exhaust gas analyser on the car which told him its was running very lean almost on fresh air. lots of mucking about later, we came to the conclusion that the engine was only running on cylinders 1 & 4, 2 & 3 appear to be doing zilch. proved by taking off spark plug leads and no change to readings?,  or sound of the engine on both plugs. pull off 1 or 4 and engine responds by change of tone and lumpiness of running. There is a four port manometer fitted and columns for 1 & 2 are both high, level and stable, approx. half way up the scale. 3 & 4 do not even register and only move on the overrun if the engine is revved. We put telltales on the all plugs and they are all firing and the analyser is not seeing unburnt hydro carbons in the exhaust. The car has never run that smoothly and was a total pig to get running in the first place, the carbs have been stripped and cleaned, jets checked against the spec in the manual. The result appears to show that there is a massive air leak on the vacuum side of the inlet manifold between cylinders 2 & 3, possible head gasket was the next thought, compression test shows all cylinders at 150 or thereabouts all close enough to say all ok. there is no water in the oil or mayo under the fill cap. Mixture jets started the day at 3 1/2 turns from closed and are currently sitting at approx. 12 turns or more to try and get a richer mixture. This is totally at odds to all the books which state 2 1/2 to 3 1/3 turns.

Any one got any suggestions before I strip the carbs and manifold of. Any suggestions most welcome.

John

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Do you have O rings and spacer plates?

Gap between carbs and manifold correct? Quite hard to check the gaps on the underside but over-tightening of the carb nuts at opposite ends could result in gaps in the centre.

What about running the engine, then spraying something volatile (starting spray)where you think the leak is. If a leak is present, cylinder should fire briefly. Obviously take care if your alternator/dizzy is nearby.

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It might just be possible that the inlet valves are not fully closing, you will get some compression but not enough, take off the inlet cam cover and get the feeler gauge out. I assume that valve timing is OK and that the plug leads are in the right order. I have been there too!

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Pnce you have tried the suggestions above,Tty this link and see if it help's.

 

http://sideways-technologies.co.uk/forums/index.php?/topic/1048-setting-dhla-dellorto-dellorto-float-fuel-level/&page=2

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Hi John , I also used the book and found where the 1/2 turns are mentioned they turned out to be full turns so 

I started at 10   1/2 turns and using a colour tune increased it to about 11 , you can see the colour tune flashing as it

should but not always igniting the mixture just enrich mixture until there's no misfire , this was on an excel with 45's

hope its of some help  Ian

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Hi

Have you checked the intake manifold to the engine, I had a similar problem with

it not sealing across the bottom of the manifold as there aren't many bolts and it wasn't

sealing and sucking in loads of air.  After a while it started to suck in coolant as well

not a great design.

Hope this helps.

 

 

 

 

 

 

 

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Hi to all,

Thanks for the replies, have spent most of the day just going over every thing that I've done to the car, Duncan has helped loads, thanks Dunc. Hometune have suggested swapping over the two sets of carbs to see if the problem moves, however that might leave me with two cars with carb issues.  I have decided to take off the inlet manifold and put on a new gasket.

I have checked the spacer plates with the o rings in and they are all parallel with the correct gap, mounting bolts have also been checked and are correct. same for timing and  correct set up of the timing belt. as I was not able to balance the carbs on Thursday after numerous attempts, that's when I was convinced it was mixture I called Hometune. ( I must confess a distant memory from over 40 years ago.). on Friday Hometune & I tried all the normal fixes, reversing HT leads on  cylinders 2 & 3, with no apparent no change. checked correct orientation of the leads, etc. no issues found.

We sprayed, easy start over all the carb to manifold joints, spacer plates and mounting bolts, with no effect. then sprayed the manifold to head joint from above, with no effect, but when spraying the inlet tube on no. 2 carb, low down just above the oil pump, there was a slight reaction and the engine raced for a second, this happened a couple of times but only on number 2 port, which suggests that's a good place to start. so bit puzzled as to why it effects No. 3 cylinder and it was not constant, ie every time we sprayed. Been thinking about that and it could be that the easy start was running down the block towards the back of the engine and we just couldn't see it.

Going to have a play tomorrow and see if I can pinpoint the exact place of the leak, 

As the compression is good and constant across all four cylinders I have discounted issues with cams not closing fully, ( for now ) it was something we discussed on Friday, I did ask  if it could be one tooth out on the cam shafts, but the man from Homerune say No.

Puzzled of Caterham, John

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John, another little horror is that the keys on either the crank or cams have sheared and allowed the wheels to slip out of position however, this will upset all,cylinders not two. One other thing to look at is the vacuum outlet on the inlet manifold  for the light pop up if fitted, done manifolds had blanking plugs that can be missing.

 

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4 hours ago, The Nut said:

I did ask  if it could be one tooth out on the cam shafts, but the man from Homerune say No.

I would just have another check on the valve timing. Exhaust cam 360 degrees out gives correct firing on one and four , exhaust valves two and three open during induction (no vacuum) , but you will obtain a normal compression reading on the exhaust stroke.

 

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Are 2&3 spitting I think look  at exaust timing 

13 hours ago, Steve V8 said:

I would just have another check on the valve timing. Exhaust cam 360 degrees out gives correct firing on one and four , exhaust valves two and three open during induction (no vacuum) , but you will obtain a normal compression reading on the exhaust stroke.

 

I go with this to

13 hours ago, Steve V8 said:

I would just have another check on the valve timing. Exhaust cam 360 degrees out gives correct firing on one and four , exhaust valves two and three open during induction (no vacuum) , but you will obtain a normal compression reading on the exhaust stroke.

 

I go with this to

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17 hours ago, Steve V8 said:

I would just have another check on the valve timing. Exhaust cam 360 degrees out gives correct firing on one and four , exhaust valves two and three open during induction (no vacuum) , but you will obtain a normal compression reading on the exhaust stroke.

 

I think I may have got a little carried away with the Bacardi last night.....this is only possible on a twin coil wasted spark engine, however a few teeth out on the ehhaust cam could have a similar effect, worth a look.

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I'm surprised home tune even exists these days... When did a car with an ecu need tuning and ECU's have been around for 25 years now!

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John, I think the problem is with the fuel, if the car stands for a while, the fuel will absorb water from the atmosphere. Ethanol will take on a high proportion of water to its own weight whereas petrol will only absorb 3-3.5 percent. After that, free water will sit in the bottom of a he tank. Drain and refill the tank and try again. How do I Know This? I have just had the same happen to me. Peter

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