View single post by Esprit2
 Posted: 02-27-2017 07:21 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 337
DonBurns wrote:My engine is 2.2 and I can tell you this combination did not work at all, could barely keep is running. Also noticed that my Carbtune Pro columns were barely moving no mater how I adjusted the idle screw.
According to an earlier post, your carbs have 37mm chokes, as would be correct for a 2.2 912LC. The 2.0 907 uses 36mm chokes. Choke size has a big impact on what goes on inside the carbs (it's a foundational setting), mixing-n-matching jetting from 36mm & 37mm choke carbs isn't likely to produce an optimal result.

I suspect that the 50 idle jet is too small for your 2.2. However, the engine should have started and idled reasonably well, there just would have been a stumble at full throttle around 3200 rpm when the too-small idle jet ran out of capacity before the main circuit kicked in.

Good, you have a Carbtune. When you hook it up, does it indicate the carbs are balanced?... ie, all throats has the same vacuum reading? Four columns all the same height, forming a level, horizontal line across the Carbtune? Incorrect balance is a big deal, and a small mis-adjustment will cause the engine to run like crap... if it runs at all. Your "could barely keep it running" comment makes me question whether the carbs are properly balanced. The first thing to check & adjust after installing carbs, even if it was just a quick remove & replace, is balance.

Ideally, when the carbs are balanced, all the air bleed screws should be turned all the way in and seated. If you do need to open an air bleed to balance a throat, then it should be by only some fraction of a turn... not multiple turns. Air bleed screws are a finesse adjustment, not a gross setting. In the end, when the carbs are balanced, no more than one air bleed per carb body should be open. It's mate on a single carb should be closed and tightly seated.

If there's a big difference in vacuum between the throats of a single carb, then that indicates the throttle shaft is twisted. If so, then that has to be fixed before the throats can be balanced, and before playing with jetting. The book-fix is to replace the twisted throttle shaft. In the real world, with care, the shaft can be twisted back straight.

DonBurns wrote:Tim - could you suggest a starting point idle jet for use with the 7850.7 on an engine built to Esprit S3 specs (plus big valves)?
Carbs aren't 'repeatable' like electronic fuel injection. Each has it's own personality, and has to be tuned individually if you want an optimal set-up. Throwing out one canned number as a cure-all isn't going to work. And you're big valves are also going to affect the final jetting. Having said all that, I suspect the Idle Jet will end up somewhere around 55 by the time you're done tuning. But don't even go there until the balance is perfect.

DonBurns wrote:
Does someone have a Dellorto parts source in US? I sent away to the Netherlands for parts, but that means over a month between adjustments.'The Dellorto Shop' in the Netherlands is a good source, but IMHO, the best source for Dellorto parts is Eurocarb Ltd in the UK. Matthew Cooper worked with Lotus back in the day, helping to tune Dellortos for Lotus engines. He not only knows Dellortos, he knows the Lotus applications. Other sources can sell parts to you, but no others can dispense Lotus-specific knowledge like Matt.

If you insist upon a North American parts source, then try some dune buggy and Harley Davidson specialists. I don't run in those circles, but I have stumbled across a couple.

CB Performance (they're more into old VWs & Dune Buggies), Inc

Both of them stock 'some' Dellorto parts that apply to their narrow markets, and neither are Dellorto generalists. If you know what you want and can specify it by part number, then they may be able to sell parts to you. But don't expect any help debugging the hotrod 907 in your Jensen-Healey... you're outside their scope.

DonBurns wrote:
I checked my pump jets and they are 50's. In the Des Hammill book the diagram (looks like official Dellorto diagram) shows a spring between the pump jet and holder. Mine have no spring, and pictures of actual pump jet assembly in the book don't seem to show a spring. Was that a later modification?Spring? I don't think so. How about item #53, DHLA Pump Jet Filter, part number 10748. That may or may not be there, depending upon vintage. Each of your carbs should have a small aluminum tag with a number stamped in it, secured under one of the top cover screws. Contact Matt Cooper at Eurocarb, give him the tag numbers, and he can tell you more specifically what should be there. But if the filter is missing, it won't cause a problem if you have a good inline filter before the carbs.