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Dellorto 48s, suggestions on jets ect wanted  Rating:  Rating
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 Posted: 06-17-2007 10:54 am
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normv
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Hi all

I am chasing a starting point for a set of 48mm dellortos on a 2L 907 race motor. The engine will be going on a engine dyno but as we all know dyno time, jets and venturies are all money so I would like to have a close starting point if possible. Has anyone got experience using 48 mm Dellortos. The engine will be restricted to 8000rpm, cams are about 11mm lift, compression about 11:1 (may be slightly less if the pistons need any more relieving for valve clearance haven’t done the dummy build yet only just got my rods last week after 6 months) usual bigger valves and some porting (not huge) stock manifold just matched to head and carbs . I was thinking of 38-39 venturies as I don't want to loose all of the bottom end (not allowed to run a 6 speed). Yes I know 45 will do however the 48s give me options the 45s don’t if needed.

Thanks

Norm

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 Posted: 06-17-2007 06:02 pm
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Jensen Healey
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I think you will be close with Lotus (emission) Spec 9 to get it running and can tweak from there. I would probably start with a 7850.2 idle jet holder and a 58 or 60 idle jet. You won't have any problem with fuel atomization in 38mm chokes at high RPM.

From the Dave Andrews website: http://members.aol.com/dvandrews/dellorto.htm the Main Emulsion tube should be a 7772.5. This should keep you in the main jet circuit while your on the track.

Adjust main jets maybe up to 180?? for your preferred CO level probably around 4 to 5%. A onboard CO meter would be an immense help in tuning so you can check while on the power at speed.

good luck, Kurt

 

 

 

 

From our good friend at the Esprit S1S2S3 list at Yahoo:



Spec 9 is about right if you have a mildly warmed up 2.2 liter.
9.5:1 or 10:1 compression,  up to 104 cams,  headers.
Carb Type ......................   DHLA 45E
Choke ..............................  37 mm
Main Jet ..........................  160
Main Air Corrector Jet ...  230
Main Emulsion Tube ......  7772-8
Idle Jet .............................  55  (maybe a little lean,  try up to
58)
Idle Jet Holder .................  7850-9
Float Weight ....................  8.5 gr
Float Setting Height ........  14.5 - 15.0 mm
Float Needle Valve .........  170
Pump Jet ..........................  50H
Starter Jet .........................  95
Starter Emulsion Tube .....  7482-3
Power Jet ..........................  ---
Slow Running Speed .......  900 - 1000 rpm
Idle CO Level (hot) ...........  0.7 - 1.5%


 

Last edited on 06-20-2007 03:40 am by Jensen Healey

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 Posted: 06-18-2007 08:57 am
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Harkes
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Norm

the 45's will indeed do as they flow more cfm then your 2.0 or 2.2L head will do (even after a good porting job). What are the options the 48's have that the 45's don't?

My 2.2L engine is built by Garry Kemp and he tested the 36 venturi i already had in my 45's, and 38 venturi on the dyno. The dyno showed that the 38 venturi performed best throughout the whole powerband. Unfortunately he couldn't test 37 versus 38.

So like Kurt, i'm running spec 9 buth with 38 venturi

good luck with your engine (post pictures please)

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 Posted: 06-18-2007 02:08 pm
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normv
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Harkes

The options the 48 give me are larger chokes whilst still maintaining a good choke to body ratio. If all goes well I may later on have a set of hewland type internals made for the gearbox to allow ratio selection for different tracks, this would also allow a more high revving but shorter power band engine to chase some extra horsepower if needed. The fellow who did the head believes it can be made to produce power over 9000, he is a well respected builder of cosworth and other race engines in Aus so knows what it takes to do this, as does Gary. If I was to try for this type of engine I would need to increase the choke sizes over the limit for 45s, naturally the bottom end is the question here so it will have to prove itself at 8000 before I consider more however the rods were specked to that just in case, but I may have to look at the crank as well. I am hoping I will not need to do this but it will depend whether I can stay with those VW’s on steroids (Porsches) with the engine as it is.

I will post some photos as it nears completion, it has taken 2 years so far but I have all of the tricky parts now, just have to finish the body work and assemble.

Norm

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 Posted: 06-19-2007 04:25 pm
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Judson Manning
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Norm,

Congrats on finding a set of 48s, I heard they were NLA.

I'm not a fan of the Spec 10.  That's how DHLA 45s were/are supplied by DBE, etc. and I find they are WAY too rich.  In chasing the right jettings for my 2.0 and 2.2 engines with an EGT and O2 sensor, I find Spec 9 a MUCH better starting point.

Can I tell you the story of me 'fogging' mosquitos down the back stretch of Roebling Road at 110mph with those Spec 10 160 mains???

Similar to Spec 9, I'm running 55 idle, 135-138mains, 170-180A/C with 11:1 on my 2.2 w/ .388" lift in/ex, 36mm chokes, mild port-matching.

Judson

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 Posted: 06-20-2007 03:39 am
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Jensen Healey
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Hi Judson, I thought spec 9 had the big jets.


 

Spec 10 ...  10.9:1 or 11:1 compression,  104 or DS2 cam,  2.2 liter.
Carb Type ......................   DHLA 45E
Choke ..............................  37 mm
Main Jet ...........................  135
Main Air Corrector Jet ...  150
Main Emulsion Tube ......  7772-8
Idle Jet .............................  56  (maybe a little lean,  try up to
58)
Idle Jet Holder .................  7850-9
Float Weight ....................  8.5 gr
Float Setting Height ........  14.5 - 15.0 mm
Float Needle Valve .........  170
Pump Jet ..........................  45H
Starter Jet .........................  80
Starter Emulsion Tube .....  7482-3
Power Jet ..........................  70
Slow Running Speed .......  900 - 1000 rpm
Idle CO Level (hot) ...........  0.5 - 1.5%

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 Posted: 06-20-2007 08:20 am
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Harkes
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according to my data spec 9 indeed has the big jets with 160 mains and 230 main A/C.  Judson's engine is similar/close to spec 10 with 135 mains, main A/C 135

i have an overview of all specs if anyone is interested.

Erik

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 Posted: 06-20-2007 02:35 pm
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Judson Manning
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Pardon my dyslexia!

Spec 5 thru 9 has the 160 main jet.  On a 2.0 engine I found this jetting way too rich with EGT readings barely above 1,200^F at WOT.  I dropped down to 130-140mains to get a more preferred 1,500^F. 

Even with 135 mains I have O2 readings 12.5:1 at WOT (preferred) and 13:1 (too rich) at cruise.  The challenge with going lean on the mains is drivability.  As you drop the main size for an efficient cruise, you have to compensate with fatter A/C jets or the engine flat-spots on acceleration.  I never had the chance to experiment with a set of -5 emulsion tubes.

That's not to say I like the 'drivability' of the Spec 9.  I found my car to be unresponsive and sluggish below 4,000rpm with the 160 mains.  Plugs were always fouled, oil was always too black, tailpipe and head had too much soot, plus the previously mentioned cloud of black smoke following me.

Bottom line, I wouldn't start with 160 or 130 mains.  Our buddy Dave Andrews at the Pinto DHLA site shows a 'real world example' of a race modified 2000/2100 at:  38 chokes, 150 mains, 190 a/c, and 45 pump. 

My suggestion is to start with the 150s, but be take along several sets of mains ranging from 145-160 and a/c jets in the 160-180 range.

Judson

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 Posted: 06-21-2007 02:06 pm
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normv
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Thank you for all of your input, I will make a collection based on your advice as a good starting point and get a few spare mains to drill if needed, I also have a set of 39 mm chokes currently in the carbs so I will give them a quick try as well to se e what sort of difference it makes, if it is a improvement I will report back. Looks like it is time to contact alfa 175 on the ebay and place a order( I have found them to be excelant in the past).

Judson in relation to the 48 being NLA I believe you are correct, These were second hand and even they were hard to find and as such lot more than I could have got 48 Weber’s for. The rules here only allow the original manufacture and type (but size is free) so they had to be Dellorto DHLA’s.

Thanks

Norm

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 Posted: 12-09-2007 01:13 am
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timeforwalkies
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I don't know if this is usefull or not.
I contacted Eurocarb Ltd to find out if my carbs were correct for the 2.2 and received the following.
 
R5326 carbs. had the following jetting originally:
 
36mm chokes
158 mains
58 idles
60 pumps
7772.8 emulsions
230 airs
7850.9 idle emulsions
They were O.E. on Lotus Talbot 2.2 engines.
 
The E signifies that it has 6 progression holes, exclusive to Lotus.
 
eurocarb ltd.
 
However now there seems to be a little trouble with the engine running to lean.  The solution seems to be at the fuel tank where when you plug off the excess return everything seems to straighten itself out.
I am using the stock origional pump and 45's.
Anybody have any comments about this.
Thanks a bunch,
timeforwalkies

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 Posted: 12-09-2007 04:09 am
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Jim Ketcham
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Excess fuel return?

Are you refering to the line that tees off after the pump back to the filler neck ?  If so, that line should have a check valve in it to stop flow from the pump back to the tank.  It is strictly an anti-syphon line to break a potential syphon when the tank is higher than the carbs.  The check valve allows air to be sucked into the line when there is no pressure in the fuel line.  The check valve is small and inserted into the original hose.  Unfortunately, many were lost when owners replaced the hose and were not aware of the valve in the old hose.

Jim

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