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Yep, loads of times. They're a good basic way of setting the idle mixture. You'll need a mirror to see it properly when using it on an Esprit.

Don't know where you're based, but in the UK Halfords sells them for around

Cheers,

John W

http://jonwatkins.co.uk

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Yep, loads of times. They're a good basic way of setting the  idle mixture. You'll need a mirror to see it properly when using it on an Esprit.

Don't know where you're based, but in the UK Halfords sells them for around

Im Brian and so is my wife

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...the engine seems to run fine at normal tickover with a nice blue flame pretty much consistant on both carbs, as soon as I increase the throttle theres intermittent yellow and white charges in between the normal blue power strokes, Im not sure if this is indicating air being introduced into the system somewhere or if it is being ommitted somewhere, or maybe its possibly electrical

Be careful using a Colortune. It shows you what is going on in the combustion chamber, but doesn't give you the knowledge to make appropriate changes. It's easy to go too lean and damage the engine.

A blue flame indicates a stoichiometric air/fuel ratio for gasoline... 14.7:1. That's okay if you can maintain it accurately, but it's right on the fine line between perfect and too lean. Richer (smaller number) hurts fuel economy, but is safe. Leaner (larger number) can seriously hurt the engine.

Modern engines with O2 sensors and ECU controlled fuel injection systems can maintain the mixture at the ragged edge and get away with it. They do it all the time in order to meet low emissions and CAFE regulations. But for naturally aspirated, hi-performance carb cars, the safe set-up is to stay a little rich... maybe dipping into the 12's. For turbo-carb cars, it's best to be significantly rich on boost... maybe even as far as into the 10's at high boost.

The blue flame at idle is fine. Assuming every thing else about the engine is running properly and it's not missing, then splashes of yellow indicates the mixture is getting more rich as the throttle is cracked. If you could observe the flame color under power, you would see it go very rich in the Esprit. Esprit's run rich under power. Even SE's with the GMP4 engine management system. When the local club goes for a drive, I can be 4 or 5 cars behind an SE and know it's up there. You can smell the exhaust.

Don't try to tune the mixture back to all blue on your carbed car unless you really know what you are doing, and the Carbtune directions don't include that knowledge. Follow the instructions and you'll often end up way too lean... at least too lean to run smoothly or to make good power... or to be safe under boost. Many new Colortune users run right out and adjust every thing for a consistent blue flame, then wonder why the engine runs like crap. Then they go chasing after the ignition or whatever else "is causing the problem". "I've got the carbs perfect now, so it can't be them. I'll tune up the ignition". No, it's running that bad because it's too lean.

A former acquaintance of mine had a Colortune, and being helpful, tuned other club member's cars. Invariably they ran worse after being "optimized" than they did before. I'd tune the idle mixture back to peak vacuum with a manometer and the engines ran great.

"Uhhh, bbbut... isn't it running a little rich ?!"

"Yeah, and it likes it, doesn't it?"

...Im not sure if this is indicating air being introduced into the system somewhere or if it is being ommitted somewhere, or maybe its possibly electrical

Anything that would cause the mixture to go rich (dirty filter, high float height (high float/ low numerical value) or sinking floats, high fuel pressure... etc) would result in a more yellow flame.

An air leak would cause the mixture to go lean and the flame color would tend toward blue... or beyond and toward white... too hot!

If the idle mixture gets too lean, the engine will mis-fire. That may result in flashes of yellow alternating with blue or white even though the mixture is too lean. If the engine is missing or running rough, abort any Colortune testing until you get the problem sorted. Even if that means adjusting the engine richer before carefully dialing it back down with the Colortune. The engine should have a smooth, even idle with no missing.

Use a 4-tube manometer to set the idle mixture and the engine will tell you what it likes best. That may not be an emissions friendly mixture, but at least you'll know where the engine wants to be. You can decide where you want to go from there.

Peak vacuum isn't real peaky... it will peak and then hold that level as the Idle Mixture Screw is turned for a ways. Find the peak and then note how far the screw can be turned both ways before the vacuum falls off significantly. The optimal setting for good running is usually half way between the two limits. For best economy or emissions, set the screw toward the lean end of the range, just as the vacuum falls off. That's probably still a little rich if you have to pass an emissions test, but you'll need a CO meter to optimize it better. Or you're just taking a shot in the dark.

Go too lean an the HC levels will start to climb due to poor combustion. Go so lean the engine starts to miss and the HC will spike. The Colortune will help you find max-lean (stoichiometric), but it won't tell you if the engine runs well on that mixture... either in terms of emissions, smooth running, or burning pistons.

It's not unusual for the mixture to go slightly lean as the throttle is opened more. Air is light and accelerates quickly while fuel is relatively heavy and accelerates more slowly. For subtle throttle movements, the accelerator pump may not compensate for the delay. As a result, the mixture stratifies, goes lean initially, then a little rich as the fuel catches up and finally settles down to a steady mixture.

For larger more deliberate throttle movement, the accelerator pump squirts in a shot of fuel to keep the mixture from going too lean initially. That's not a very precise action and errs heavily on the side of too rich. For large throttle changes, the mixture usually goes very rich first before settling down.

From idle, open the throttle a little, slowly enough that the pump isn't an issue. If the engine hesitates, then the Idle Air Corrector Jets (Idle Jet Holders in Dellortos) are too lean. Not unusual in emissions engines... certainly emissions 9XX engines on Dellortos.

If the engine hesitates or stumbles with large off-idle throttle openings, then the accelerator pump is too lean. It's stroke determines the total volume of fuel delivered, the Pump Jet determines how quickly it's delivered, and the spring tension/ pre-load determines over what period of time it's delivered. It get's complicated. Play with the jet size first... that's easier.

The Idle Circuit feeds the engine up to around 3500+ rpm, then the Main Circuit takes over. If the engine does a lean-stumble at around 3200-3500 rpm, then the Idle Jets are too small. The circuit runs out of capacity just before the mains take over and the engine stumbles.

If it goes lean above 4000 or so, then you play with the Main Jets and Air Correctors.

Good luck with your new toy,

Tim Engel

Lotus Owners Oftha North

Edited by Esprit2
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If the engine hesitates or stumbles with large off-idle throttle openings, then the accelerator pump is too lean. It's stroke determines the total volume of fuel delivered, the Pump Jet determines how quickly it's delivered, and the spring tension/ pre-load determines over what period of time it's delivered. It get's complicated. Play with the jet size first... that's easier

This is looking the likely culprit.. I noticed today I forgot to let my choke off and the car didnt splutter anywhere near as bad, even when warm Im assuming this is due to the extra fuel helping out on the initial pull away as Id imagine the car would just stall with choke on when warmed up if the carbs were set up.right.. :)

Ian

Im Brian and so is my wife

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This is looking the likely culprit.. I noticed today I forgot to let my choke off and the car didnt splutter anywhere near as bad, even when warm Im assuming this is due to the extra fuel helping out on the initial pull away as Id imagine the car would just stall with choke on when warmed up if the carbs were set up.  right..

Ian,

Maybe. It's hard to judge from a distance what's going on with a set of carbs. There's nothing like a little "laying on of the hands" to get a feel for what's going on. Without that, I'm guessing...

Myself, I think the engine is running lean overall. The fact that the engine runs better with the choke on a little supports that theory. Pre-1988 DOM / ROW DHLA45 carb turbos had the idle circuit jetted pretty lean. Then from 1988 onward they leaned it out some more. It must have been in response to tighter emissions requirements since I don't think the engine was any happier for the change.

Esprit Carb Turbo ....... 1988 onward ... pre-1988 ........ 1983-86

Market ....................... DOM / ROW .... DOM / ROW ... US-Federal

Carb Type .................. DHLA 45M ...... DHLA 45M ...... DHLA 45M

Choke ........................ 35 mm ........... 35 mm ............ 37 mm

Idle Jet ....................... 58 .................. 58 .................. 52

Idle Jet Holder ............. 7850-10 ........ 7850-9 ............. 7850-7

Accelerator Pump...

Pump Jet ..................... 35 (Special) .... 35 (Special) ..... 38H

Pump Delivery ............. 8cc/ 20 strokes 8cc/ 20 strokes 8cc/ 20 strokes

Pump Lever Clearance .. 0.1 +/-0.05 mm

Idle Speed, rpm .......... 900 - 1000 ....... 850 - 950 ........ 900 - 1000

Main Circuit, FYI...

Main Jet ....................... 160 ................. 160 ................ 165

Main Air Corrector Jet ... 180 ................. 180 ................. 230

Main Emulsion Tube ...... 7772-14 .......... 7772-12 .......... 7772-13

The US-Federal numbers are potentially confusing, but I threw them in since the carbs were also DHLA45M's. The Fed carbs are running larger chokes which means lower gas velocities and potentially a weaker low rpm response. They probably need a little richer idle since the vacuum to pull fuel over is weaker with the larger chokes.

The -9 Idle Jet Holder (Idle Air Corrector Jet) used in the pre-88 DOM / ROW 910's is pretty darned lean (3rd leanest available). Granted, the carbs had smallish 35mm chokes for higher gas velocities, but -9 still seems pretty lean to me. Then from 1988 onward they went another step leaner to -10. If I had a carb turbo running a little lean as you describe, I'd probably start by going several steps richer on the Idle Jet Holders... like a -1.

If the car doesn't stumble at around 3200-3500 rpm under hard acceleration, then the Idle Jet itself if probably about right. If it does stumble, then you may end up needing larger Idle Jets as well. But wait with that. One change at a time. Optimize the Idle Jet Holders first, then follow up with the Idle Jets if required.

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

Weaker ........................ Normal ....................... Richer

7850.5, .10, .9, .4, .1, .3, .6, .7, .2, .8

.6 and .7 are very close... virtually the same.

7850.1, 7850.6, 7850.2, 7850.8 are more commonly used and readily available.

Good luck,

Tim Engel

Lotus Owners Oftha North

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Ian,

Maybe. It's hard to judge from a distance what's going on with a set of carbs. There's nothing like a little "laying on of the hands" to get a feel for what's going on. Without that,  I'm guessing...

Myself,  I think the engine is running lean overall. The fact that the engine runs better with the choke on a little supports that theory.    Pre-1988 DOM / ROW DHLA45 carb turbos had the idle circuit jetted pretty lean. Then from 1988 onward they leaned it out some more. It must have been in response to tighter emissions requirements since I don't think the engine was any happier for the change.

Esprit Carb Turbo ....... 1988 onward ...  pre-1988 ........ 1983-86

Market ....................... DOM / ROW ....  DOM / ROW ...  US-Federal

Carb Type .................. DHLA 45M ......  DHLA 45M ......  DHLA 45M

Choke ........................ 35 mm ........... 35 mm ............ 37 mm

Idle Jet ....................... 58 .................. 58 .................. 52

Idle Jet Holder ............. 7850-10 ........ 7850-9 ............. 7850-7

Accelerator Pump...

Pump Jet ..................... 35 (Special) .... 35 (Special) ..... 38H

Pump Delivery ............. 8cc/ 20 strokes  8cc/ 20 strokes  8cc/ 20 strokes

Pump Lever Clearance .. 0.1 +/-0.05 mm

Idle Speed,  rpm .......... 900 - 1000 ....... 850 - 950 ........ 900 - 1000

Main Circuit,  FYI...

Main Jet ....................... 160 ................. 160 ................ 165

Main Air Corrector Jet ... 180 ................. 180 ................. 230

Main Emulsion Tube ...... 7772-14 .......... 7772-12 .......... 7772-13

The US-Federal numbers are potentially confusing, but I threw them in since the carbs were also DHLA45M's. The Fed carbs are running larger chokes which means lower gas velocities and potentially a weaker low rpm response. They probably need a little richer idle since the vacuum to pull fuel over is weaker with the larger chokes.

The  -9 Idle Jet Holder  (Idle Air Corrector Jet) used in the pre-88 DOM / ROW 910's is pretty darned lean (3rd leanest available).  Granted,  the carbs had smallish 35mm chokes for higher gas velocities,  but -9 still seems pretty lean to me. Then from 1988 onward they went another step leaner to -10. If I had a carb turbo running a little lean as you describe,  I'd probably start by going several steps richer on the Idle Jet Holders...  like a -1.

If the car doesn't stumble at around 3200-3500 rpm under hard acceleration,  then the Idle Jet itself if probably about right. If it does stumble,  then you may end up needing larger Idle Jets as well. But wait with that. One change at a time. Optimize the Idle Jet Holders first,  then follow up with the Idle Jets if required.

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

Weaker ........................ Normal ....................... Richer

7850.5,    .10,    .9,    .4,    .1,    .3,    .6,    .7,    .2,    .8

    .6  and  .7  are very close... virtually the same.

7850.1,    7850.6,    7850.2,    7850.8  are more commonly used and readily available.

Good luck,

Tim Engel

Lotus Owners Oftha North

<{POST_SNAPBACK}>

Thanks Tim

This really is way over my head, I will print it all off and give it to the guy who is doing the carbs for me.

Many Thanks

Ian

Im Brian and so is my wife

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  • 3 weeks later...

Tim

Not sure when you will get this .. heres an update, Ive replaced my carbs with the original carbs from my old engine, my new carbs caught fire.. and are history. The car is running lovely in every respect Except... I cant get the idle speed down below 1500 revs no matter what I do, Ive even took the idle control screw right out and disconnected the throttle cable off the car completely, it still wont go under 1500 revs, when the car is cold it ticks over at 1100 revs then when the car warms up it goes up to 15000 to 1800 and wont come down no matter what, I can dip the clutch and select a gear and get a biting point this brings it down to a reasonable level but as soon as I dissengage it shoots back up to 1500 to 1800, also the in car heaters are not working as they should be.. Ive got a feeling its all linked.

Many Thanks

Ian :rolleyes:

Im Brian and so is my wife

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Ian,

I'm in the USA and have never had the opportunity to work on a DOM spec Esprit (UK). Especially a late carb model like yours since US Esprits ran with Bosch fuel injection beginning in 1986. So I'm going to approach this like I would a US carb car (through 1985) and you'll have to see if you can find any parallels in your car.

The problem could be related to something with the carbs themselves

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Ian,

Try the throttle jack mounting. It's made of alloy and you can move it with your hands. I reckon it's one of three things.

1. Firstly disconnect one of the wires from the throttle jack, does the revs comes down now?

2. Try bending the mounting upwards, does this have any affect on the revs.

3. The thermal inigition valve and your cold start vacuum system is charging the throttle jack. It's basically an solenoid button the raises the idle when an electrical charge is put through it.

The problem I had when the thermal ignition valve went was the idle was raising exactly how you describe. I had to disconnect the throttle jack and it was fine. When I had a new thermal ignition valve fitted and put back the vacuum pipes, I reconnected the throttle jack and it worked fine. I think you'll find you have the same problem somewhere. Don't buy a new throttle jack until you get to the bottom of the problem. Try adjusting the mounting by simply bending the bracket. Sounds harse but it does work.

Let me know if this helps.

Dave Walters

Tim

Not sure when you will get this .. heres an update, Ive replaced my carbs with the original carbs from my old engine, my new carbs caught fire.. and are history. The car is running lovely in every respect Except... I cant get the idle speed down below 1500 revs no matter what I do, Ive even took the idle control screw right out and disconnected the throttle cable off the car completely, it still wont go under 1500 revs, when the car is cold it ticks over at 1100 revs then when the car warms up it goes up to 15000 to 1800 and wont come down no matter what, I can dip the clutch and select a gear and get a biting point this brings it down to a reasonable level but as soon as I dissengage it shoots back up to 1500 to 1800, also the in car heaters are not working as they should be.. Ive got a feeling its all linked.

Many Thanks

Ian

Edited by superdavelotus
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Thanks Dave

Yes your spot on when I bend it it seems to behave itself, Ive got it dissconnected from the electric altogether and seems to be fine without it up to now, still having trouble with the heaters but might leave it till Ive lost a couple of stone.. :rolleyes: have bought a cheap in car heater which is more than adaquate keeping the cab warm and windscreen clear.

Cheers

Ian

Im Brian and so is my wife

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Have you checked the heater cable like I did on mine? It's a relatively easy job and doesn't require you to crawl under the dash.

Mine snapped and I was getting cold air coming through. Also on Esprit, you have to close off the face vents as they only ever blow cold air whatever the heater temperature is.

Give me a ring sometimes and I'll run things with you.

Thanks Dave

Yes your spot on when I bend it it seems to behave itself, Ive got it dissconnected from the electric altogether and seems to be fine without it up to now, still having trouble with the heaters but might leave it till Ive lost a couple of stone.. :rolleyes: have bought a cheap in car heater which is more than adaquate keeping the cab warm and windscreen clear.

Cheers

Ian

<{POST_SNAPBACK}>

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