Lotus Elan

Using Leaner Idle Jet Holder on Dellortos

PostPost by: UAB807F » Wed Oct 11, 2017 7:45 am

I have nothing useful to add to this thread other than to thank those who are contributing. I'm debating the 360 cams vs standard sprint ones for the Europa so I'm very interested in how this pans out.

Thanks to all for the info.

Brian
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PostPost by: Esprit2 » Wed Oct 11, 2017 3:46 pm

The "Three Cs", Compression, Cams & Carbs, must always be kept in balance in order to get the best results. If you just hang larger carbs on an otherwise stock engine, you won't achieve the power level those carbs might be capable of. The same for installing a 'hot' cam. Each one alone isn't as great as it could be if it's companions were optimized to support it.

I have no experience with the Q360 cam, but I like the published specs. It looks like it might be a nice street cam. But there's no direct "carb data chart" that says with this much duration and lift, use this carb set-up. It's something you must tune your way into, and that's best done on a dyno. If someone else has successfully installed a Q360 cam on an otherwise similar engine (like a Twin Cam with the same other mods yours has), then sharing their carb set-up would give others a head-start on tuning their carbs. But even then, don't expect plug-n-play jetting. Carbs aren't that repeatable, and they are sensitive to the specifics of the engine they're on, and sensitive to environmental differences (including altitude above sea level). In the end, you're going to have to do some dedicated tuning.

The cam manufactures don't develop cams in a vacuum. Well, good ones don't. QED provides some jetting specs for their Q360 cam, so they've put some thought into it. I strongly recommend that anyone installing that cam should contact QED and ask for the missing Idle Air Corrector spec, and for any other set-up wisdom they might have to offer.

Regards,
Tim Engel
Last edited by Esprit2 on Wed Nov 18, 2020 8:58 pm, edited 1 time in total.
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PostPost by: jono » Thu Oct 12, 2017 4:12 pm

Tim,

My DHLA 40's have been upgraded to QED 360 recommendations, thus:

Chokes - 33
Main jets - 135
Air correctors - 150
Emulsion tubes - 7772.5
Idle jets - 50

The idle air correctors are 7850.1. I tried 7850.3 simply because I have some but they did not appear to make much difference. I also tried 52 idle jets but this seemed to make matters worse.

My float heights (10g floats) are set to 14.5mm

I will ask QED for recommendations on idle air correctors but of you have any observations on the above I would. as always, be interested to hear them!
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PostPost by: jono » Tue Apr 02, 2019 12:25 pm

Just to resurect this thread, I tried the richest idle jet holders and saw a noticeable improvement but the stumble persisted. Going up a jet size to 52's made no difference.

And what finally resolved it?....dropping down a choke size to 32mm - stumble now gone and the engine feels much more responsive.

I also found I had non functioning pump jet on one carb where I think the ball in the non return valve was sticking - this was causing a 'bog' on hitting the throttle (also now gone).

So the next step is to get everything properly set up on a RR and I've booked in with Peter Burgess on the recommendations of another poster on here.

So, we are almost there after some 13,500 miles!
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PostPost by: jeff jackson » Tue Nov 17, 2020 7:54 pm

Hi All,
I'm sorry this is an old thread, but just to save starting a new one on the same subject....
I have struggled to get my 72+2 to run lean.
I always have black sooty plugs and if the car has not been run for a while, I alwys have to take th plugs out clean them and replace and then start.
I have had bothe D'ellortos re built and cleaned, this was a while back.
I have a morgan carb balancer ands a colourtune.
When the car runs, it smells rich, if I had a pound for every smart Alec who told me that my car is running rich, I would be rich. I have also checked and double checked the float height and they are correct.
So reading this thread I thought I would pull the emulsion tube and the idle jets out and check the numbers.
I have two references, Miles Wilkins Twin Cam Engine book and the Speedpro How to build Weber and Dellorto carburettors book. The Lotus workshop manual does not mention jets.
I have exactly the same jet numbers as quoted in Miles Wilkins book for UK spec big valve engine.
120 Main Jet, 130 Air corrector and 7772.5 Emulsion Tube.
Idle jet holder 7850.2 and a 50 idle Jet.

From the Speedpro book, they suggest loads of combinations, so it's a question of what do I change for a leaner mixture?
There has been a new thread on a you tube video showing a series of carb setups for Webers, and here it suggests the idle jet should be for a 1558cc engine, i.e. 389.5cc per cylinder a 45 idle jet not a 50.
However I realise it's not just a matter of changing that one jet.
Any suggestions what to try to get my engine to run lean?
Kind regards
Jeff
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PostPost by: Grizzly » Wed Nov 18, 2020 8:10 pm

I don't know anything about Dellortos but before adjusting anything put some warmer running plugs in it..... it is always going to run rich on idle (i found mine would develop a big lean spot just off idle if i went leaner than 12.5afr) i found with mine after a couple of minutes idling the plugs would soot up and although the afr said it was running about right it would make your eyes sting.

I was advised to put Bp6es's in but the shop i buy my parts from had sold out that weekend so i ended up putting NGK Bp5Es's in, although they still went black if left to idle for long periods they never go sooty, it drives much smoother and upto now have lasted twice as long as the 7's they replaced.
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PostPost by: mbell » Wed Nov 18, 2020 8:26 pm

My limited experience is in webber but...

I agree with checking the plug temp range and maybe going to hotter plugs.

After that I think you need to decide what approach you want to take:
1) Live with it as is
2) Buy a range of jets/holders etc and test them out based on feel
3) Buy+Fit a AFR gauge, use AFR gauge to see where mixture is and buy more targeted range of jets to test. With ability to see the impact and judge where to go next.
4) Take it too a rolling road with experience with the carbs and a selection jets to tune the car with.

Which approach really depends on how much money and effort you want to spend, what skills you have and availability of suitable rolling road.

Personally I am going 3) route, as it interesting and not aware of rolling road around here I'd trust to do it.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: jeff jackson » Thu Nov 19, 2020 8:29 pm

Hi All,
Thanks for the replies.
It was suggested to me some time back to run hotter plugs, I did just that, but I am still running rich.
I have also checked for air leaks and have replaced the o-rings on the fexible mounts, new thackary washers and gapped them.
As for an AFR thats an idea I had not thought of. However, id installing an AFR guage still tells me I'm running rich it doesnt really help getting to "the why".
True, I could then start fiddling with jets to see if it gets better using the AFR as a guide.
I might just go that route. Something to buy as a Christmas present!
Regards
Jeff 72+2
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PostPost by: mbell » Thu Nov 19, 2020 9:23 pm

Here in the US you can pick up a AEM AFR gauge and setup for ~$150, so not particularity expensive. This can output via serial connection so you can log the data.

Its no magic bullet but at least you see where it is now and what impact changes have. So can at least see if a change is positive or negative. With some careful driving logging you can focus in on certain rev ranges to try tune the different jets.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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