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 Posted: 11-15-2016 01:53 am
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Bfitz241
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I'll just add this, you say you had to reset the timing...what did they have it at?
I see you have 12 initial now, did you check for max advance?
IS it possible these guys timed your cams wrong? I don't know if that'd make it run hot, but I can see how it'd make it run bad...
If it got that hot that fast and the cooling system is sound, my next stop is the distributor to map out the timing curve.

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 Posted: 11-22-2016 10:35 pm
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DonBurns
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I have received an LM-2 A/F meter, and am scheduling a local shop top weld in the bung. I will eventually get the info on all current chokes, venturis, and jets, but it may be several weeks - on my way to China for a couple of weeks. I'll update everyone on my progress when I have more info.

In the Des Hammill book he says that for Dellortos the average turns for the idle mixture screws from closed is from 3 to 5. That is incorrect, or too wide then?

Well, the answer to what thermostat is installed would be "none". I ordered a 160 deg to put in and found out when I opened it up. Last time I pay $10K to someone to do work I am capable of doing myself. I'm apparently not able to learn from past mistakes. I am curious to see if this fixes the overheating. A web search found opinions on both sides of the effect of leaving it out.

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 Posted: 11-23-2016 01:12 am
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Esprit2
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DonBurns wrote:
In the Des Hammill book he says that for Dellortos the average turns for the idle mixture screws from closed is from 3 to 5. That is incorrect, or too wide then?3 to 5 ?? Or 3.0 to 3.5? The Idle Mixture Screws don't function much beyond 4 turns out, so there would be nothing to gain by going out to 5 turns.

For Dellortos on production cars of the 70's (ie, Jensen-Healey), stretch the range to 3.75 turns out. European emissions specs forced the manufacturers to tune a bit lean. If you adjusted the mixture screws for better running without re-jetting, it would be necessary to go a little past the normal 3.5 max to compensate for the lean jetting.

If you do re-jet first, then target having the mixture screws end up 3.0-3.5 turns out.

DonBurns wrote:
I am curious to see if this fixes the overheating. A web search found opinions on both sides of the effect of leaving it out.It should. Without a thermostat, the radiator bypass circuit is open full time. Installing the thermostat closes the bypass once the engine is up to temp.

Most engines have a single cooling system circuit with a simple on-off thermostat. In a system like that, removing the T-stat does permit maximum cooling. The downside is that the engine often runs too cool.

The 907 has a dual circuit cooling system. The main loop out through the radiator and back, and another that bypasses the radiator and goes right back to the engine. In that case, the T-stat not only closes the main circuit, it opens the bypass circuit. Delete it, and the bypass is open full time. It only stands to reason that the engine will run hot with the radiator bypass open all the time.

Last edited on 11-23-2016 05:32 am by Esprit2

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 Posted: 12-27-2016 11:22 pm
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DonBurns
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All-

Thanks for the feedback. I had to step away for a few weeks due to some work travel (China!) and holiday duties. I have made a little progress, though, and thought I would provide an interim update.

First, although this belongs in a different forum, of course the overheating was not due to being out of tune. I ordered a 160F thermostat to try, and when I went to install it discovered my engine rebuilder had not bothered to put one in at all. Same shop that sent me on my way with a freshly rebuilt 4-speed with no oil, and about a dozen other issues. Anyway, the overheating seems to be taken care of with the presence of a thermostat.

I fiddled with the tuning some more, and found my best results were obtained by adjusting each cylinder by RPM. Set to 1000, and adjust the idle mixture to max RPM, reset to 1000 and repeat for the next cylinder and so on, then go through the cylinders again 1 through 4. This seemed to give me more sensitivity to adjustments than watching my CarbTune Pro, and now the JH is drivable (and not overheating in 2 miles!), but I don't think it feels perfect.

I have the week off had planed to get the bung installed for the A/F meter, but unfortunately my local exhaust shop is off this week. I'll try to get that done next week.

My Dellortos are from the JHPS site store. What I have now is-

DHLA 45
Chokes 37mm
Venturi ??

Air Correctors 230
Emulsion Tubes 7772.8
Main Jets 160

Idle Jet Housing 7850.9
Idle Jet 62

Based on recommendations above these might not be ideal.

I believe I have finally found a local shop that claims to be Dellorto gurus, which I hope means they have the magic box with all of the tubes and jets and stuff to allow trial and error testing. I plan to play with the A/F meter myself for a little while, and then probably get it over to them.

I'll update when I have more results.

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 Posted: 01-08-2017 11:53 pm
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Esprit2
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This is a repeat of the set-up chart I posted on 11-11-16.
Just adding the JHPS Store carb's data as provided by Don Burns on 12-27-16:

.............................. Lotus .......... Lotus .......... Per DonBurns
Engine Model: ........ 2.0 907 ....... 2.2 912LC .... JHPS Store .... Bfitz241's
Dellorto Specs: ...... Spec-5, ....... Spec-9 ......... N/A .............. Unknown
Carb Type .............. DHLA 45E .... DHLA 45E ..... DHLA 45 ....... DHLA 45 (45, or 45E ?)
Choke ................... 36 mm ........ 37 mm ......... 37 mm ......... 36 mm
Main Jet ................ 160 ............. 160 .............. 160 .............. 158
Main Air Corrector .. 230 ............. 230 .............. 230 .............. 230
Main Emulsion Tube, 7772-8 ........ 7772-8 ......... 7772.8 ......... 7772.7
Idle Jet .................. 50 .............. 55 (Esprit) .... 62 ................ 58
................................................. 58 (4-seaters)
Idle Jet Holder ....... 7850-7 ........ 7850-9 ......... 7850.9 .......... 7850.9
Float Weight ........... 10 gr .......... 8.5 gr ........... ______ ......... ______
Float Height ........... 16.5-17mm.. 14.5-15mm .... ______ ......... ______
Float Needle Valve .. 170 ............ 170 ............... ______ ......... ______
Pump Jet ............... 38V 42H ...... 50H .............. ______ .......... ______
Starter Jet ............. 70 ............... 95 ................ ______ ......... 95
Starter Emul Tube .. 7482-1 ........ 7482-3 .......... ______ .......... ______

For both the JHPS Store carbs, and Bfitz241's carbs, are they 45s with no letter suffix, 45Es, or some other suffix LETTER? The model ID should be cast into the top side of one of the barrels, inside the oval. It makes a difference... especially the desirable 'E'.

Just looking at the numbers, I suspect the idle jets are too rich for both the JHPS carbs, and Bfitz241's. The 7850.9 idle air correctors are pretty lean (emissions lean), and it appears that larger idle jets have been plugged in to enrich the mixture. It will do that. But it will also increase the idle circuit's capacity, meaning it will run beyond the 3200 rpm point at which the idle circuit should hand-off to the main circuit. The mains will still kick in on schedule, but if the idle continues beyond 3200, then it's double-fueling the engine. I suspect there will be a temporary rich spot just above 3200 rpm. I recommend reducing the idle jet size to only that required to 'just' feed the engine up to 3200 rpm without a stumble... no more. Then if the mixture is too lean, go to a richer idle air corrector (aka, idle jet holder). I get the best results with the 7850-7.

Idle Air Corrector Sizes (aka, Idle Jet Holder): (Rich/ Lean does NOT correlate to number value)
7850.5 .. LEAN, going down the list gets richer.
7850.10
7850.9 .. Spec 9, Spec 10, JHPS Store & Bfitz241 -- emissions lean
7850.4
7850.1 .. Normal -- Spec 1
7850.3 .. Normal
7850.6 .. 6 & .7 are very similar, almost interchangeable
7850.7 .. Spec 5 -- The 9XX likes 7
7850.2
7850.8 .. Richest

Regards,
Tim Engel

Last edited on 01-09-2017 06:00 pm by Esprit2

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 Posted: 01-09-2017 02:16 pm
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Bfitz241
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I believe my carbs are plain "45", but I'll check to be sure.
RE: the idle air corrector-do the leaner numbers have larger or more emulsion drillings and larger bleeds through the top or is there another difference?

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 Posted: 01-09-2017 03:00 pm
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Esprit2
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Bfitz241 wrote:
I believe my carbs are plain "45", but I'll check to be sure.
RE: the idle air corrector-do the leaner numbers have larger or more emulsion drillings and larger bleeds through the top or is there another difference?

I don't know. I've not seen them all, just the few I use. Of those, I prefer using the 7850-7.

The Main Emulsion Tubes are complicated, bordering on Black Art/ Witchcraft. The number of holes, locations, sizes and shapes vary. Then the main jet stick assembly consists of three items, main jet, emulsion tube and air corrector.

The idle jet stick assembly is only two parts, with the idle jet holder being a combination of the Idle Air Corrector Jet plus the Idle Emulsion Tube. I presume (but I don't know) some of the same 'Black Art' also creeps into the emulsion tube part of the idle jet holder.

Regardless, it's an area where you need to know what you're doing before making modifications. It's easy to drill out a jet. It's not so easy to modify an emulsion tube and get the desired result.

Going richer means less air, which will require reducing hole sizes/ quantities. That's not as easy as just getting busy with a drill.

Last edited on 01-09-2017 03:02 pm by Esprit2

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 Posted: 01-09-2017 03:55 pm
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Esprit2
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Bfitz241 wrote:
I believe my carbs are plain "45", but I'll check to be sure.All Dellorto DHLA models are arguably better than the corresponding Weber DCOEs, so a plain "45" isn't a lesser carb. The "45E" was developed for Lotus first, and then saw wider use. It has a number of detail differences that give it finer resolution for sneaking up on precise emissions settings. Things like 5 or 6 idle progression holes in a unique Lotus pattern, verses as few as two in some Weber DCOEs. And Idle Mixture screws with a finer thread and a longer, more finely tapered needle.

All the Lotus set-ups, like "Spec 5", are based upon the 45E model with it's finer resolution. If those set-ups are used in the 45, or other letter-suffix models, the results 'may' not be exactly the same. But the Lotus "Spec _" is still a better starting point for a non-E carb on a 907 than some generic formula or Des Hammill recommendation. Just expect that you may not get exactly the same results that someone else talks about getting without first doing a little tuning of your own.

For instance, a plain 45 with fewer/ larger idle progression holes than in a 45E 'may' require a slightly richer idle mixture to avoid hesitation. And the number of turns required to tune the Idle Mixture Screws will be less.

Details, and you may have to work out a few of them on your own. But once you have it tuned up, the 45 is still a great carb, and better than the comparable Weber DCOE.

Also keep in mind that Lotus had to meet European Emissions Standards, so the factory set-up is on the lean side. And it got progressively emissions-leaner from Spec 1 to 3 to 5 to 9. You can make any Spec 907 run better than stock if you tweak the jetting a bit richer than stock.

I have three 907s with 45Es, and I work on a number of local club member's Lotus & JH cars with DHLAs, including 910 Turbos. Then I have one Europa S2 with a single Weber DCOE 45. That one DCOE causes me more constant fiddling to keep it in tune than all the other DHLAs I work on, combined.

Love your Dellortos, they're great carbs. It's just that if you aren't running 45Es, or if you want better than factory emissions lean, you may have to make a few creative adjustments from the Lotus or JH spec to dial them in.

Regards,
Tim Engel

Last edited on 01-10-2017 12:57 am by Esprit2

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 Posted: 01-09-2017 06:26 pm
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DonBurns
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Tim-

The identification on my carbs is just DLHA 45, no letter.

I finally got the bung welded in for the A/F meter, and some initial readings are below - confirming that I am running rich assuming the meter is reading correctly. I followed the calibration and set up instructions very carefully, so I have to assume so. The results below are static. The weather here is not conducive to road testing at the moment.

RPM A:F
1000 11.8:1
2000 13.5:1
2500 13.0:1
3000 12.8:1
3200 12.8:1
4000 12.1:1

Rather than ordering various tubes and jets, I am on the waiting list to have a carb shop that is reportedly good with Dellortos, and has a selection of parts on hand to try (not a complete set, however) and I plan to let them take a shot at it first. Should be in about 3 weeks.

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 Posted: 01-12-2017 08:20 pm
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Bfitz241
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checked, DHLA 45, no letter

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 Posted: 01-19-2017 03:11 pm
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Bfitz241
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while I'm aware of the accelerator pump jet, is there an adjustment for the accelerator pump stroke? Any way to alter its performance through its range of motion? Like a cam?

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 Posted: 01-19-2017 04:22 pm
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Esprit2
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The accelerator pump's external linkage is stroke-adjustable. A longer/ shorter stroke controls the total amount of fuel dispensed by the pump per stroke. The pump jet controls the rate at which it's dumped into the throat and the duration of the stream. The linkage is spring loaded, so stepping on the throttle applies spring pressure to the diaphragm without necessarily forcing it to instantly move full stroke. Then a small jet will result in a tiny stream that lasts a relatively long time, while a larger jet produces a larger stream that ends more quickly. In the end, the total volume is set by stroke length, then jetting controls how fast & long it's dumped.

To check the current setting, put a slender graduated cylinder (chemistry set) into each throat to catch the pump jet's output. Then fully stroke the throttle 20 times, holding each stroke long enough for the flow to cease before stroking again.

7cc to 8cc in 20 strokes is in the normal range. 7cc is about right for a 2.0 907 with the idle circuit's mixture properly set. If the idle is a little lean, then the engine may need a little more help from the accel pump... but don't exceed 8cc.

Don't use the accelerator pump as a crutch, or a reason not to address the idle circuit. The correct approach is to get the idle mixture right first, with no off-idle hesitation, just sitting in the driveway/ on the dyno!! Then use only as much pump as the engine needs to help the car off the line.. a heavier car needs more help than a light one. The pump is the last tuning priority, not the first.

Regards,
Tim Engel

Last edited on 01-19-2017 09:49 pm by Esprit2

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 Posted: 01-30-2017 02:24 pm
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Bfitz241
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for those following, I hooked up my AEM air fuel gauge yesterday...still didn't drive the car, but got some idle/cold start/ no load info.
FIrst cold start: the cold start valve leans the mixture out drastically, I mean the gauge stops reading, over 22:1 afr. A rich misfire could also cause this but judging how the engine ran, it's not rich.
Idle: very well, readings between 13.9 and 14.1, a little bit of oscillation but not horrible, idle is smooth enough and right around 850 rpm.
No load acceleration to 2500rpm: engine shows a leaning trend as rpm increases. This really doesn't mean much to me as there is no load on the engine and very little throttle opening. I will give more weight to testing done with the car in gear and moving.

All of this info is really for amusement at this point...the engine has to be hot and under load for any meaningful readings....but it's fun to watch the gauge

Last edited on 01-30-2017 02:26 pm by Bfitz241

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 Posted: 02-14-2017 08:54 pm
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Bfitz241
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Tim,
I curious to know what the step up for idle air correctors is. Do you go up one step or two as a tuning method? I ask because I've been driving the car and it has an almost imperceptible misfire at the top of the idle circuit. I have a 55 idle jet and would rather restrict the air at this point than increase the fuel.
Any thoughts are appreciated.

Car runs great otherwise, starts right up runs and drives. Plugs are clean.

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 Posted: 02-14-2017 11:55 pm
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Esprit2
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Bfitz241 wrote:
(Snip)... I've been driving the car and it has an almost imperceptible misfire at the top of the idle circuit.I'm not totally clear on what you're saying. It has a slight miss/ stumble at around 3200 rpm? If so, that's the idle circuit running out of fuel capacity before the mains take over, and usually, playing with the idle air corrector will not fix that. It needs more fuel, and that's done with the idle jets.

If you're bent on tweaking the idle air corrector, then note that they are not listed in any logical order... purely random. The order is as follows:

Idle Air Corrector Jet Sizes:
7850.5 .. Leaner, going down the list gets richer.
7850.10
7850.9
7850.4
7850.1 .. Normal
7850.3 .. Normal
7850.6 .. 6 & .7 are very similar, almost interchangeable
7850.7 .. The 9XX likes 7
7850.2
7850.8 .. Richest

Changes to the idle jet and idle air corrector do influence one another, so it's possible that going richer on the air corrector will solve a marginal stumble at around 3200 rpm, but don't count on it. Try playing with the air correctors if you wish, but don't be surprised if, in the end, it's a jet change that eliminates the stumble.

Regards, and good luck,
Tim Engel

Last edited on 02-15-2017 09:41 pm by Esprit2

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 Posted: 02-14-2017 11:59 pm
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Bfitz241
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thanks

Last edited on 02-15-2017 01:43 am by Bfitz241

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 Posted: 02-26-2017 05:01 pm
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DonBurns
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Have not made much progress. I sent away for some jets to play with, including a set of 7850.7 corrector jets and 50 idle jets which is listed above under Lotus 2.0. 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. 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)?

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.

I finally realized I have DLHA 45 E carbs. I thought the letter was cast after the 45 so I thought mine was "no letter", but I finally noticed a very faint, as in it's not even complete, E stamped under the DLHA 45 casting, and I have 5 progression holes.

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?

This might be a really basic question that I probably should have understood before I started fiddling, but what is the goal for A:F mixture? I mean for optimizing for set-up and a different A:F ratio might turn out to be different for fine-tuning power and drivability. When changing jets and seeing effects is there a A:F curve we are trying to match? 13.5 at Idle and 12.5 full power? Currently I think I am rich at idle (11.8) OK during progression (13.5 - 13.0) and then maybe slightly rich at 4000. If rich at idle but good during progression, is that the reason to move from one progression tube to another?

Trying to get my head around all this - thanks for any help.

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 Posted: 02-27-2017 06:21 pm
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Esprit2
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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)
http://www.cbperformance.com/Dellorto-Parts-Locators-s/337.htm

Motorcyclecarbs.com, Inc
http://www.motorcyclecarbs.com/Dellorto-65

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.

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