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.

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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 that might have to offer.

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PostPost by: jono » Thu Oct 12, 2017 4:12 pm


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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