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Dellorto DHLA 45  Rating:  Rating
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 Posted: 11-27-2015 08:10 pm
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Koit
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Hey

I'm new for this forum, but I registrated for a reason, namely I purchased an old volvo 164 and it has been converted from bosh mechanical injection to carburettors, three Dellorto DHLA 45 C's.
So its a B30 engine strait 6 with displacement of 2978 cc, with quite high compression ratio of 10:1. Because the car didn't run great at all and the carburettors were really dirty on the outside the first thing I did was cleaned up the carburettors.

 The insides

So it had:
Choke: 36
Aux. Venturi: 8011.1
Main Jet: 150
Emulsion Tube: 7772.7
Air corrector: 160
Idle jet holder: 7850.9
Idle Jet: 60
Cold start  emulsion tube: 7482.3
Cold start jet: 95
Pump Jet:40

So I read the SpeedPro series booklet How to build and powertune weber and dellorto carburettors and it gave some suggestions on what the parts should be for particular dispacement, I belive my engine is rather stock. So for the reference some parts are off.

Idle jet 50 or 55 with emulsion tube 7850.6
Emulsion tube 7772.4 with air corrector 180
One smaller aux. venturi 8011.2

So after the clean in ultrasound bath, carb cleaner and compressed air it seems I have more less got the engine to idle, but it's still bit rough. Slow acceleration works good and from over 2500 rpm it runs good. The problem is quick acceleration completely fails the engine chokes and looses rpm and wants to die out. So there's something fishy with the jet pumps I assume but its my first contact with dellorto carburettors and I saw this forum seems to have lot of knowledgeable users in theese matters.
The previous owner said that when he was driving the car it didn't have symptoms like this. I have checked the jetpump holes are clean however I haven't jet tied if they squirt when taken of the engine.
I checked the timing on the engine with strobe and it seems to be 10 degrees BTDC as it should on 1000rpm.
One other question, it seems theese carbs don't have air bypass valves for balancing, so how should I balance them?
,

I haven't measured the exhaust yet with wideband lambda but It seems the mixture is a bit rich, the spark blugs where carbon fouled. So what do you guys think?

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 Posted: 11-27-2015 10:40 pm
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Jensen Healey
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90% of carburetor issues are ignition. If the car ran great before, replace the plugs, wires, points, etc.

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 Posted: 11-28-2015 01:29 am
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Esprit2
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In the engine's stock configuration, at what rpm did peak power occur?

Regards,
Tim Engel

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 Posted: 11-28-2015 05:33 am
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Esprit2
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Carbs require a little black art to tune them. They are not ECU controlled with sensors and feedback loops, so it's not a simple matter of working out some ideal settings, plugging them in, and it runs perfectly. All the generic formulas, as in the Speedpro book, will get you close, but plan on doing some tuning afterwards. Also, carbs don't have the flexibility of an ECU controlled fuel injection systems, so you can tune for peak power, or best driveabililty, or best economy, but not for all at once. You need to choose what you want, and "both/ all" isn't a choice.

The best way to approach jetting of a custom installation is to take it to a shop with a rolling road dynamometer, an exhaust gas analyzer, and (hopefully) a comprehensive supply of Dellorto jets and parts. I'm fortunate to have one near me.

It's also important to keep the three-Cs in balance... Carbs, Compression & Cams. If a big set of carbs are just bolted onto a mostly stock sedan engine, then the resulting gain will probably be be less than hoped for with the stock compression and cams. For best results, the 3-C's need to be optimized together. The B30's 10:1 compression is higher than I would have guessed, but it's not "hi-performance" high. I know nothing about the cam, but expect that it's fairly mild.

I'm not familiar with Volvo 164/ B30, but I'm thinking a pair of 45mm DHLAs is a lot of carb for the existing compression & cams in a 496cc/ cylinder engine. Then add in the 36mm chokes, and I think the engine is a little over-carbureted. Now, maybe the 164 is a hotrod Volvo, and loves the carbs; but without knowing more, I'm betting that's not the case.

I suspect the Lotus 907 (493cc/ cylinder Vs B30's 496cc/cyl) is a bit more of a hotrod than the B30, and the Jensen-Healey version of that engine uses 40mm DHLAs with 35mm chokes. The Lotus version of the same basic 907 engine uses 45mm DHLAs with 36mm chokes, but Lotus also targets a more boy-racer clientelle. Flog the engine and it goes, but it's not meant for casual driving. Many J-H owners criticise the Lotus-spec 907 for having too little torque at low rpm, and not being easy to drive in commuter traffic. Big carbs just aggravate that condition.

So what are your goals for the Volvo B30 engine?

Searching the internet, I find:
2980 cc 6-cylinder (496 cc/cyl)
88.9 mm x 80.0 mm bore/stroke
145 bhp (SAE) at 5500 rpm
163 lbs-ft at 3000 rpm.

Using some standard formulas and assumptions, I get the first two columns:
............................... Generic ......... Generic .......... Stock
Engine .................... Volvo B30 ...... Volvo B30 ....... J-H 907 ........ Yours
Displacement (cc/cyl) 496 ............... 496 ................ 493 .............. 496
Power Peak RPM ...... 5500 .............. 5500 .............. 6500 ............ 5500
Tuned for: ............... Power ............ Flexibility ........ J-H Stock
Carb Type ............... DHLA 40 / 45 .. DHLA 40 ......... DHLA 40 ...... DHLA 45
Choke ..................... 36 mm ........... 34 mm ........... 35 mm ......... 36 mm
Venturi Reduction %.. 0.90 / 0.80 ..... 0.85 ............... 0.875 ........... 0.80

Main Jet ................... 145 ................ 140 ................ 130 .............. 150
Main Air Corrector .... 180 ................ 180 ................ 160 .............. 160
Ratio, Air Corr/ Jet ... 1.241 .............. 1.286 ............. 1.231 ........... 1.067
................................................................................................... 180 SpeedPro
Ratio, Air Corr/ Jet ....................................................................... 1.200

Main Emulsion Tube.. 7772-6 or -5 for both ................ 7772-5 ......... 7772.7
.................................................................................................... 7772.4 SpeedPro

Idle Jet ..................... 50 ................... 50 ................. 50 ................ 60
.................................................................... I prefer 55 ................ 50-55 SpeedPro
Idle Air Corrector ...... 7850-2 ............ 7850-2 ........... 7850-1 .......... 7850.9
................................................................... I prefer 7850-7 .......... 7850.6 SpeedPro
................................. 2nd richest ...... 2nd richest ... "normal" ......... 3rd leanest

Pump Jet .................. 40 ................... 40 ................. 45 ................. 40
Auxiliary Venturis ...... 7848.2 ............ 7848.2 ........... 7848.1 ........... 8011.1
Aux Vent sized for ... <550 cc/ cyl .... <550 cc/ cyl ... >550 cc/ cyl ... >550 cc/ cyl
Aux Venturi should be ............................................... Lotus uses ..... 8011.2 SpeedPro
........................................................................ large Aux Venturi.... a size too big
Pump Delivery in 20 Strokes ...................................... 8.0cc
Pump Lever Clearance (mm) ...................................... 0.1 +/- 0.05
Fuel Delivery Pressure (psi) ....................................... 1.5-2.5 at carb inlet

Idle Air Corrector Jets (aka, Idle Jet Holders) are not numbered sequentially, but totally randomly. Don't get caught making any assumptions about which one is the next size richer or leaner. Go by the following chart:

7850.5 .. Leaner, going down the list gets richer.
7850.10
7850.9 .. In your Volvo B30, pretty lean.
7850.4
7850.1 .. Normal
7850.3 .. Normal
7850.6 .. Normal, 6 & .7 are very similar, almost interchangeable
7850.7
7850.2
7850.8 .. Richest

That's a lot of writing to not come up with a specific recommendation, but I'll fall back on the earlier statement that you can't calculate a correct setting for carbs, and then have it work first time when you plug it in. But having looked at all the above...

Fuel pressure is important. The Dellortos like 1.5 to 2.5 psi at the carb inlet. Higher fuel pressure can over-power the inlet shut-off valve, and result in an overall rich condition. If the inlet pressure is too high, then install an inline adjustable fuel pressure regulator, and set it for 2.0 psi.

Next, the fuel level in the float bowl is critical to correct mixture control. There are three or four Float Weights available, and each has a different required Float Height setting. If you use the wrong height for the weight that's installed, then the fuel level will be wrong, and everything goes to heck from there.

The Dellorto part number for the floats is 7298-99-_ _ with two final digits for each weight:

01 = 10 gr, 16.5 - 17.0 mm Float Height.
02 = 8.5 gr, 14.5 - 15.0 mm Float Height.
03 = 7.0 gr, 16.5 - 17.0 mm Float Height.
(01 = 10 gr, 14.5 - 15.0 mm, Non-standard, Lotus sometimes used a higher fuel level to create an overall richer mixture)

Remove the carb's top cover. Use a small scoup, or an eye dropper/ turkey baster to remove a little fuel to create a low condition. Re-install the top cover. Switch on and run the electric fuel pump until it's tone changes, indicating the float bowl is full. If the pump is mechanical, then remove the coil wire, and crank the engine over (without starting it) long enough to ensure that the float bowl is full and the float has closed the inlet valve.

Switch off. Promptly remove the top cover. Using the depth gauge feature of a vernier or dial caliper, measure down from the top of the jet pedestal in the float bowl, near the middle between the two Idle Jet assemblies, down to the fuel surface. The correct level is 27mm / 1.063”. Adjust the Float Height and repeat the procedure as required to achieve that level in both carbs. If each available weight float is set to it's specific correct height, then all float weights will result in the same standard 27mm fuel level in the float bowl. Setting the Float Height is an easy expedient, but correctly setting the fuel level is the real goal.

Don't try to do any tuning until the fuel pressure and Float Height (fuel level) are correct !

IMHO, the 45mm DHLAs and 36mm chokes are on the large side for a Volvo 164/ B30 (while admitting that I know nothing about them). But given that is what you have, and that changing the sizes will be expensive, lets just roll with it for now.

The Main Jet and the Main Idle Air Corrector are both too rich. If you stay with the rich 150 Main Jet, then I think the Main Air Corrector number you got reading the SpeedPro book is going in the right direction, but maybe even 185-190. But if you reduce the Main Jet a size or two, to a more reasonable 145 or 140, then a 180 Air Corrector is about right.

I don't know what to say about the Main Emulsion Tube... that's more black magic than I can stir in my kettle.

The Idle Jet also seems too rich to me. I'd expect to go 55, 58 max, but 60 just seems like too much. And the Idle Air Corrector is the third leanest one available. The number you got from SpeedPro, 7850.6, is about right, but my favorite is 7850.7. The .6 and .7 are very close, and almost interchangeable, but the .7 is a wee bit richer. If the engine doesn't have to pass an emissions test, then a little richer is good.

The transition point between the Idle and Main circuits occurs at about 3200 rpm. The Idle Jet must be just large enough to have the flow capacity to feed the engine up to 3200 rpm, but be no larger than required. Then the Idle Air Corrector is sized to add the right amount of air for the best A/F ratio. The best way to set the Idle Jet and Idle Air Corrector sizes is to...

1) Give the ignition a tune-up.
2) Accurately balance the carbs (that's critical).
3) Set the Idle Mixture screws for peak manifold vacuum.
4) Set the Idle Speed as slow as possible consistent with smooth running. Then...

5) Open the throttle slowly enough that the accelerator pump isn't much of a factor. If the engine hesitates off-idle, then go a step or two richer on the Idle Air Corrector. If the engine does not hesitate, then go a step or two leaner until it does 'just' hesitate, then go back one step richer until the hesitation just disappears. The result will be fine sitting in the driveway, but in real world driving, you may find that the hesitation becomes noticable. If so, go a step richer with the air corrector until the hesitation just goes away.

6) Next, set the Idle Speed to normal (~900 rpm) and go for a drive. Short-shift into a middle gear, then accelerate at full throttle to well past 3200 rpm. If the engine stumbles at around 3200 rpm, then the Idle Jet is too lean, and the circuit is running out of capacity before the Main Circuit kicks in. Go a step or two larger/ richer with the Idle Jet until the stumble just goes away. If the engine does not stumble, then go a step or two leaner until a stumble just develops, then go back richer one step until it just disappears. Do not go richer than is required to eliminate the stumble.

The current Pump Jet size is close to right, but could go a step larger to 45 or so. I don't think it's the root cause of any running problems. The pump's stroke should be adjusted to deliver 8cc of fuel in 20 strokes. That sets the total volume of fuel that can be delivered. The linkage is spring loaded, so fully opening the throttle spring-pressurizes that volume of fuel, then the size of the Pump Jet determines how quickly that volume will be delivered. A fat stream that's gone in an instant, or a skinny stream that lasts a long time. If the pump linkage isn't correctly adjusted to deliver enough fuel, then changing the Pump Jet larger isn't going to cause more fuel to flow.

The only way to correctly adjust the linkage is to use two graduated cylinders (chemistry lab bits), one in each throat, then fully stroke the throttle 20 times. Measure the fuel dispensed, and adjust the linage accordingly until 8cc is achieved.

Koit wrote:
One other question, it seems these carbs don't have air bypass valves for balancing, so how should I balance them?The manometer vacuum ports appear to be present, but the Air Bleed Screws are covered with anti-tamper plugs. Those aluminum domes in the bosses. Pry out the anti-tamper plugs, and you'll probably find the Air Bleed Screws.

Failing that, an airflow meter, like a Synchrometer, will work. The problem with any instrument that is placed over the carb's inlet is that it disturbs the very airflow it's trying to measure. A manometer is best, but an airflow meter will work. A Uni-Syn is another type of airflow meter, but it's best used as wall art.

Koit wrote:
I haven't measured the exhaust yet with wideband lambda but It seems the mixture is a bit rich, the spark blugs where carbon fouled. So what do you guys think?
I think both the Idle and Main circuits are currently too rich, and the carbon fouled plugs confirm that.

Good luck,
Tim Engel

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 Posted: 11-28-2015 11:57 am
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Koit
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Thank you all for the quick responses. This is how my floats are set, as I did it by the book I had. The car has mechanical fuel pump from the crank so I don't think thas going to be an issue. So I can check the fuel levels again in the carb bodies. I will also not that I changed the needle valves one seemd to have leaked so I changed them for all the carbs.

I changed the spark plugs and the carbon fouling was present in the beginning but I leaned the idle mixture from the screw and it seemed to have gone better. Also previous owner has changed the original ignition coil for some aftermarket one.

Yes I know the numbers on the parts are for some parts random.
I wanted to know what you guys think would be the "generic" ballpark parts to start with. The car itself is an old one and  ment to be driven around for fun,  plus its not sporty like Jensen Healys, so I could probably live with the carbs not ultimately fine tuned.

Also I only have a word from the previous owner for the car running good but he was quoting on times more-less 10 years ago.

So I will start with:
Emulsion tube 7772.5
7484 main jet size 145
7485 air corrector jet size 180
Emulsion tube 7850.7



Last edited on 11-28-2015 12:00 pm by Koit

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 Posted: 12-01-2015 05:52 pm
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Esprit2
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Koit,

If you were talking about a Lotus 907/ 912 engine, there's enough Dellorto history with those engines, both Jensen-Healey and Lotus versions, that we could tell you what set-up will work. And there may be a Volvo forum with similar Dellorto history for the B30; but on this forum, the B30 is just not something we talk about.

In the jetting table in message #4 above, the first two generic columns are what the standard formulas indicate for an engine with 496cc per cylinder that delivers peak power at 5500 rpm... in the broadest of terms. Since your carbs are already 45C's with 36 chokes, try something based on the first column... which seems to be what you're doing...
So I will start with:
Emulsion tube 7772.5
7484 main jet size 145
7485 air corrector jet size 180
Emulsion tube 7850.7
By the book, the 7772.5 Emulsion Tube is about right for an engine with a one-cylinder displacement of 450-575cc, which covers the B30's 496 cc/cyl. However, the 45C / 36 Choke combination is large for a "near-stock' sedan engine of that size, so flow velocities will be slow, which will create a weak vacuum. That could lead to an overall lean condition. I'm not suggesting you start with a richer Emulsion Tube. I'm just saying that if you end up fighting an overall lean condition in the future, that it might help to go richer on the Emulsion Tube.

The J-H version of the 907 used DHLA 40s with 35 chokes. However, for Lotus own version of the 907, they used a 45E/ 36 Choke that's similar to your carbs. The 907 & B30 are very close to the same cylinder displacement (493 Vs 496 cc/cyl), but very different in tuning (peak power at 6900 rpm Vs 5500). While I expect the final jetting set-ups to be different, I will point out that Lotus used a richer 7772-8 Main Emulsion Tube.

In the chart below, the first column is the generic 'Power' set-up from message #4, and the second column is Lotus' 45E / 36 Choke set-up. Just keep in mind that much of the J-H community shuns the 'Lotus' set-up as over-carbureted, and the J-H factory used DHLA 40 carbs with 35 chokes. In the end, I suspect you'll find the 45C's with 36 chokes are a bit much for a near-stock B30. If it has been hotrodded, then they might be about right, but you haven't indicated that's the case.

Since your 45C carbs currently have 7772-7 Emulsion Tubes (?), it might be worth saving the initial expense and trying the first round with the existing tubes. If the mixture is still too rich (the plugs are now black and carbon fouled), then you can spend the money and go with a little leaner tube on your second try.

Your current Main Jet isn't far off the generic 'Power' value, but the Idle Air Corrector is small. Small means less air and a richer mixture. If you don't mind chipping away in small steps, installing larger Main Air Correctors with the current Emulsion Tubes might be a good first step.

The Lotus 45E / 36 Choke's Main Jet is larger than the generic B30 'Power' recommendation, but the Idle Air Corrector is also much larger... much more air to keep the Air/Fuel ratio in check. The Lotus Air Corrector might actually be larger than optimal, since by that point in time they were running into more strict emissions standards, and mixtures were a little lean to meet mandated standards rather than give best running or power.

............................... Generic ......... LOTUS (not JH)
Engine .................... Volvo B30 ...... 907 ................ Your B30
Displacement (cc/cyl) 496 ............... 493 ................ 496
Power Peak RPM ...... 5500 .............. 6900 .............. 5500
Tuned for: ............... Power ............ Power
Carb Type ............... DHLA 40 / 45 .. DHLA 45 ......... DHLA 45
Choke ..................... 36 mm ........... 36 mm ........... 36 mm
Venturi Reduction %.. 0.90 / 0.80 ..... 0.80 ............... 0.80

Main Jet ................... 145 ................ 135 (160) ....... 150
Main Air Corrector .... 180 ................ 150 (230) ....... 160
Ratio, Air Corr/ Jet ... 1.241 .............. 1.11 (1.44) ..... 1.067
.............................................................................. 180 SpeedPro
Ratio, Air Corr/ Jet .................................................. 1.200

Main Emulsion Tube.. 7772-6/ -5 ....... 7772-8 ........... 7772.7
.............................................................................. 7772.4 SpeedPro

Idle Jet ..................... 50 ................... 50 ................ 60
............................................. I prefer 55 ................ 50-55 SpeedPro
Idle Air Corrector ...... 7850-2 ............ 7850-2 .......... 7850.9
............................................. I Prefer 7850-7 ......... 7850.6 SpeedPro
................................ 2nd richest ....... 3rd richest .... 3rd leanest
Idle Jet Holder ................................... 7850-7

Float Wgt (gram) .............................. 10.0 ............... ??.?
Float Hgt (mm) ................................. 16.5-17.0 ........ 14.5-15.0 ??
Float Valve ....................................... 170 ................ 170
Pump Jet .................. 40 .................. 38V 42H .......... 40

Auxiliary Venturis ...... 7848.2 ............ 8011.1 ........... 8011.1
Aux Vent sized for ... <550 cc/ cyl .... >550 cc/ cyl ... >550 cc/ cyl
............................................................................... a size too big
Aux Venturi should be ............................................... 8011.2 SpeedPro

Pump Delivery in 20 Strokes .............. 8.0cc
Pump Lever Clearance (mm) .............. 0.1 +/- 0.05
Fuel Delivery Pressure (psi) ............... 1.5-2.5

*~*~*
This is how my floats are set, as I did it by the book I had. The car has mechanical fuel pump from the crank so I don't think thas going to be an issue. So I can check the fuel levels again in the carb bodies. I will also not that I changed the needle valves one seemd to have leaked so I changed them for all the carbs.
In the fuel inlet valve, which needle style did you use? Stock Dellorto valves are all brass, while aftermarket valves have a Viton rubber tip. Both work. But the rubber tip takes a compression set after a short while, which allows the float and the fuel level to rise a bit. If you used a rubber tipped needle, then it's best to re-set the float/ fuel height after they've been in service a few days to a couple of weeks.

Your photo shows the cover in the correct position, with the cover gasket in place, for setting the float height. And as far as I can tell in the photo, that one is set to 14.5-15.0 mm. That's all good as far as it goes. However, as I mentioned above, Dellorto floats were available in several weights (Weber uses only one), and each weight requires a different height. You have not stated what your float weights are, so I can't say if 15.0 mm is correct.
10 g = 16.5 - 17.0 mm Float Height
8.5g = 15.5 - 16.0 mm Float Height
7.0g = 14.5 - 15.0 mm Float Height
25.0 mm = Float Drop, common for all.

Des Hammill's book is probably the best amateur guide on the market for Dellortos; however, it's not perfect. One flaw is that he states an over-simplified one float height, like it's singular and gospel. It's not. It varies according to float weight. So, what is the weight of the floats that are installed?

Or, as I wrote in message #4 above, the best approach is to simply set the fuel level to 27mm/ 1.063” down from the top of the jet pedestal in the float bowl.

Good luck,
Tim Engel

Last edited on 12-01-2015 07:08 pm by Esprit2

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 Posted: 12-01-2015 06:37 pm
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Koit
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Well I ordered below parts:

main jet size 145 Air corrector jet
air corrector  180
emulsion tube 7850.2
emulsion tube 7850.6
 idle jet size 50
 idle jet size 55

So I ordered couple of idle jet holders (emulsion tubes) and different sized jets for the idle, 145 sized main jets and 180 size air corrector to start with. I didn't add the main emulsion tubes to the list cause eurocarb said  7772.5 is alternative to 7772.7 so, I guessed there is no point of spending extra credits for the thing I all ready have.
I'm sorry if I pressed the Volvo and the B30 into your forums, just the B30 is quite unique to the volvo cars (it was only 164 and C303 that were released with this engine) and dellortos were never officially fitted to the engine, it had zenith-strombergs. Your forum was the place where I found most info on the dellortos.

The fuel needles were full brass type:



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 Posted: 12-01-2015 07:12 pm
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Esprit2
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Matthew Cooper (Matt) at Eurocarb Ltd is a great tech resource for Dellortos (and Webers). He knows it all, and is willing to work with you.

Regards,
Tim Engel

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