Need suggestions with possible twin carb issues...
- Thread starter petex19
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petex19
True Classic
I caught the 12mm suspended measurement from the diagram link but I couldn't find the full droop measurement so thank-you for that.
Now will removing the top cover plate to adjust the float levels require that gasket to be replaced or can it be re-used if fully intact?
Gaskets are cheap enough but it'll take a couple of weeks to get them
Now will removing the top cover plate to adjust the float levels require that gasket to be replaced or can it be re-used if fully intact?
Gaskets are cheap enough but it'll take a couple of weeks to get them
Dan Sarandrea (Phila)
Waitin' On Parts...
Hi Pete,
Not sure if you've been able to totally rule out valve train or intake leak issues as possible causes of your problem, but if not, try using a vacuum gauge. A vac gauge isn't going to help you much if it's a carb issue but it is particularly effective for diagnosing valve train and intake ills.
Follow this guide: http://www.secondchancegarage.com/public/186.cfm
Not sure if you've been able to totally rule out valve train or intake leak issues as possible causes of your problem, but if not, try using a vacuum gauge. A vac gauge isn't going to help you much if it's a carb issue but it is particularly effective for diagnosing valve train and intake ills.
Follow this guide: http://www.secondchancegarage.com/public/186.cfm
petex19
True Classic
Not sure exactly what you mean by valve train? The only diagnostic I've done valve related is confirm my valve clearances are all spot on. I'm very interested to try anything and read your link but wouldn't know where to connect this vacuum gauge. My DCOE's don't have a vacuum advance connection that I'm aware of and the vacuum advance capsule on my distributor isn't connected. I'm read and have been running slightly higher static timing to compensate for no vacuum advance connected. If I can learn more about this then I will certainly give it a try. May be completely unrelated but one thing I haven't tried yet is going back and re-tightening the nuts on the bottom portion of my carbs to intake manifold since the engine build. The reason being that I installed Weber heat shields on each DCOE and they make the nuts non-accessible. I've re-tightened the top mounting nuts but haven't checked the bottom ones. Wondering if nuts aren't fully tight if it's creating some form of air leak?
Dan Sarandrea (Phila)
Waitin' On Parts...
Valve train would pertain to anything to do with the valves, such as late or early valve timing, sticking valves, weak valve springs, etc. If you have an adjustable cam sprocket, the vacuum gauge might help show if it's adjusted correctly.
Intake leaks would pertain to the introduction of air anywhere below the throttle plate, as this air has not been taken into account by the carb as it provides the fuel/air mix needed to run the engine. As you posted, loose fasteners could result in an intake air leak, or what people might also call a vacuum leak. All other settings being equal, a vacuum leak is virtually always going to result in a leaner mixture.
A vac gauge is a little "old skool" but can be useful, if only to help rule out possibilities.
All that being said, if your manifold setup does not have an opening onto which you can affix the hose for the vacuum gauge, then unfortunately it's a moot point:whistle:
Intake leaks would pertain to the introduction of air anywhere below the throttle plate, as this air has not been taken into account by the carb as it provides the fuel/air mix needed to run the engine. As you posted, loose fasteners could result in an intake air leak, or what people might also call a vacuum leak. All other settings being equal, a vacuum leak is virtually always going to result in a leaner mixture.
A vac gauge is a little "old skool" but can be useful, if only to help rule out possibilities.
All that being said, if your manifold setup does not have an opening onto which you can affix the hose for the vacuum gauge, then unfortunately it's a moot point:whistle:
mx5rush
True Classic
I got no answers for your carb/running issue... but I think your mechanic is all wrong about the laser reflecting.... The laser is just to aim... my infrared thermometer can operate with the laser turned off... that wimpy laser isn't heating (or not heating) anything up when it hits it or reflects off it.
The color/reflectivity of the header could make some difference, but I'm betting not in your situation. As mentioned earlier, thickness of the coating can vary too and possibly make a difference.
http://www.thermoworks.com/blog/2012/03/infrared-thermometry/
petex19
True Classic
I wanted to check my float settings today which unfortunately meant removing my dcoe's from the car. I was able to do it with intake manifold still attached so as to not mess with the balance of the carbs.
Anyways hoping someone can post a link to literature mentioning the float settings for Weber DCOE 152's which are the newest models with the plastic floats.
Mine were set at 12mm suspended and at 18mm at full droop which is inline with the brass floats of older models. A fellow member stated that the measurements are supposed to be 12mm suspended but 25mm at full droop. I'm not sure where he found this info. but I found info. on another forum stating 12mm and 26mm at full droop but then as much as 12mm and 32mm at full droop on an MG forum. All these other forums stated that these float settings are for the 152 series 45DCOE carbs.
Even my Weber tuning manual only states float settings for all the older DCOE models such as 9,13, etc.....
What effect would incorrect float settings have on performance? Specifically the full droop setting. I'm curious because this may explain a lot.
Anyways hoping someone can post a link to literature mentioning the float settings for Weber DCOE 152's which are the newest models with the plastic floats.
Mine were set at 12mm suspended and at 18mm at full droop which is inline with the brass floats of older models. A fellow member stated that the measurements are supposed to be 12mm suspended but 25mm at full droop. I'm not sure where he found this info. but I found info. on another forum stating 12mm and 26mm at full droop but then as much as 12mm and 32mm at full droop on an MG forum. All these other forums stated that these float settings are for the 152 series 45DCOE carbs.
Even my Weber tuning manual only states float settings for all the older DCOE models such as 9,13, etc.....
What effect would incorrect float settings have on performance? Specifically the full droop setting. I'm curious because this may explain a lot.
rjplenter
True Classic
I found this
From this website:
http://www.lotuselan.net/forums/lotus-carbs-f40/weber-carb-question-t23346.html
Plastic (Black, new -151 & -152 models)
Float Height ... 12.5 mm
Float Drop ...... 25.0 mm
Some applications took liberties with the float height to promote overall rich or lean conditions; but if you don't know the specific float height, use the standard Weber height. Since Lotus never used the 151 model or the plastic floats, you're kinda on your own. I'd default to the 12.5 / 25.0 mm numbers and tune from there.
The float height measurement is made with the carb cover held vertically, float hinge upper most, the floats hanging down and just lightly resting against the inlet valve. With the cover gasket in place, measure from the float to the gasket face, not from the float to the metal cover face.
In the Alfa site referenced previously, one writer posted marked up photos and said to measure from the top of the float as it hangs vertically (see the photo). That's the first time I've seen that measuring point called out, and most manuals show the measuring point as being the bottom of the float (as shown in that photo).
It's my opinion that the difference is in the Alfa guy’s interpretation of “top”. Manuals typically refer to the side of the float that faces up when the cover is in the horizontal/ as-installed position as the "top". Then they specify measuring from float “top” to gasket face… but “top” doesn’t change just because the cover has been rotated to vertical (ie, your right hand is still your right hand even if you turn around). IMHO, the Alfa guy’s version of measuring from the "top" of the float is unique and a little off the norm.
Regards,
Tim Engel
I also found several mentions of the fact that the 152s only have 3 progression holes and how that produces a flat spot. Modifications to fix this are described here:
http://www.alfabb.com/bb/forums/car...-45dcoe-progression-circuit-modification.html
Cheers,
Rob
From this website:
http://www.lotuselan.net/forums/lotus-carbs-f40/weber-carb-question-t23346.html
Plastic (Black, new -151 & -152 models)
Float Height ... 12.5 mm
Float Drop ...... 25.0 mm
Some applications took liberties with the float height to promote overall rich or lean conditions; but if you don't know the specific float height, use the standard Weber height. Since Lotus never used the 151 model or the plastic floats, you're kinda on your own. I'd default to the 12.5 / 25.0 mm numbers and tune from there.
The float height measurement is made with the carb cover held vertically, float hinge upper most, the floats hanging down and just lightly resting against the inlet valve. With the cover gasket in place, measure from the float to the gasket face, not from the float to the metal cover face.
In the Alfa site referenced previously, one writer posted marked up photos and said to measure from the top of the float as it hangs vertically (see the photo). That's the first time I've seen that measuring point called out, and most manuals show the measuring point as being the bottom of the float (as shown in that photo).
It's my opinion that the difference is in the Alfa guy’s interpretation of “top”. Manuals typically refer to the side of the float that faces up when the cover is in the horizontal/ as-installed position as the "top". Then they specify measuring from float “top” to gasket face… but “top” doesn’t change just because the cover has been rotated to vertical (ie, your right hand is still your right hand even if you turn around). IMHO, the Alfa guy’s version of measuring from the "top" of the float is unique and a little off the norm.
Regards,
Tim Engel
I also found several mentions of the fact that the 152s only have 3 progression holes and how that produces a flat spot. Modifications to fix this are described here:
http://www.alfabb.com/bb/forums/car...-45dcoe-progression-circuit-modification.html
Cheers,
Rob
Last edited:
petex19
True Classic
Wow thanks a lot for finding all that very useful info. That progression hole problem would explain why I could only get the car to run properly using my F855 idle jets which resulted in AFR's in the 11's at idle. Reducing the idle jets put the idle in the perfect 14's but made the car undriveable even at low rpm's. I'll set my floats correctly and hopefully this may help the 3000rpm flat spot.
rjplenter
True Classic
Glad to help
Having the floats adjusted correctly is crucial. The level of fuel in the bowls governs the level of fuel in the emulsion tubes and that is where the air and fuel are mixed! Jet sizes are important and so are the emulsion tubes. These tubes can only work properly with the fuel level within a certain range. Also with a capacity increase to 1600cc you may need to review your needle and seat size, but don't be tempted to go too big.
I think the extra progression hole would help too. Progression is an area of carb tuning we often overlook and it really makes a big difference for smooth acceleration.
Another area we tend to "ignore" is adjusting the accelerator pump linkages. I had adjusted mine according to my manuals and they seemed to be fine. But I had a stumble accelerating out of corners so when I had them off a couple of months ago I shortened the rod nuts a little (half a turn from memory) and that stumble went away!
I haven't had a chance to send you the Des Hammill book yet but will get it in the mail this week.
Cheers,
Rob
Having the floats adjusted correctly is crucial. The level of fuel in the bowls governs the level of fuel in the emulsion tubes and that is where the air and fuel are mixed! Jet sizes are important and so are the emulsion tubes. These tubes can only work properly with the fuel level within a certain range. Also with a capacity increase to 1600cc you may need to review your needle and seat size, but don't be tempted to go too big.
I think the extra progression hole would help too. Progression is an area of carb tuning we often overlook and it really makes a big difference for smooth acceleration.
Another area we tend to "ignore" is adjusting the accelerator pump linkages. I had adjusted mine according to my manuals and they seemed to be fine. But I had a stumble accelerating out of corners so when I had them off a couple of months ago I shortened the rod nuts a little (half a turn from memory) and that stumble went away!
I haven't had a chance to send you the Des Hammill book yet but will get it in the mail this week.
Cheers,
Rob
Black-Tooth
Tony Natoli
As Mr. GTO says above...
Usually engines running multiple carbs and hot cams do not develop the vacuum needed for the vacuum operated advance to work properly, or work properly relative to time, or even work at all.
Most RACERS use a purely mechanical advance and this is done by trimming weights, adding "stops" and messing with the return springs... to bring the advance in faster or at a certain RPM, or further.
This is a lot of trial and error but EXPERIENCE and a Sun Distributor Testing Machine really helps here.
I believe I said earlier that when you go to multiple carbs your entire life changes. HA!
Secondly... Allison's "distributor-less" ignition system is something I don't know that much about. Page or call Mark or Bob Brown for some details. I'm sure there is an electronic advance of sorts but am not aware if it is re-programmable. To the best of my knowledge it does not have a rev limiter as well.
There are other forms of electronic ignitions, specifically MSD and several knock-offs that have fully programmable advances, as well as soft and staged forms of rev limiters. Many prices out there also... but all will require modifications to the distributor or a crank-trigger added. But hey... ya gotta do something during those long winters!
Continue having fun Pete... and send PHOTOS!
Usually engines running multiple carbs and hot cams do not develop the vacuum needed for the vacuum operated advance to work properly, or work properly relative to time, or even work at all.
Most RACERS use a purely mechanical advance and this is done by trimming weights, adding "stops" and messing with the return springs... to bring the advance in faster or at a certain RPM, or further.
This is a lot of trial and error but EXPERIENCE and a Sun Distributor Testing Machine really helps here.
I believe I said earlier that when you go to multiple carbs your entire life changes. HA!
Secondly... Allison's "distributor-less" ignition system is something I don't know that much about. Page or call Mark or Bob Brown for some details. I'm sure there is an electronic advance of sorts but am not aware if it is re-programmable. To the best of my knowledge it does not have a rev limiter as well.
There are other forms of electronic ignitions, specifically MSD and several knock-offs that have fully programmable advances, as well as soft and staged forms of rev limiters. Many prices out there also... but all will require modifications to the distributor or a crank-trigger added. But hey... ya gotta do something during those long winters!
Continue having fun Pete... and send PHOTOS!
rjplenter
True Classic
You said it Papa!
For one thing you acquire a dedicated draw in the workshop containing various choke sizes, idle fuel jets, idle air jets, main fuel jets, main air jets, emulsion tubes, and accelerator pump jets! :confuse2:
For one thing you acquire a dedicated draw in the workshop containing various choke sizes, idle fuel jets, idle air jets, main fuel jets, main air jets, emulsion tubes, and accelerator pump jets! :confuse2:
DCOE 45 float levels
I doubt dropped level is as important as the suspended level but float level is definitely the first thing to check.
Here's a little reading material on basic setup - you must get the idle circuit setup before you go on:
http://www.piercemanifolds.com/category_s/311.htm
http://www.piercemanifolds.com/category_s/313.htm
http://www.piercemanifolds.com/category_s/312.htm
The progression circuit is controlled by holes drilled into the body of the carb by Weber. I believe I would treat this circuit as though it is not adjustable for time being. Weber guys are quick to point out that Weber never made an after-market carburetor; all of these carbs were originally intended for a specific model car. That's why you need a matched set that were from a car with an engine similar to yours.
Your carbs probably come on the main circuit at about 3000-3500 RPMs - how about that - that's right about where your flat spot lives. Can you tell us what your AFRs are doing when you are in that spot? You can adjust where in the RPM range where the main circuit kicks-in by changing the emulsion tubes and/or float levels.
I doubt dropped level is as important as the suspended level but float level is definitely the first thing to check.
Here's a little reading material on basic setup - you must get the idle circuit setup before you go on:
http://www.piercemanifolds.com/category_s/311.htm
http://www.piercemanifolds.com/category_s/313.htm
http://www.piercemanifolds.com/category_s/312.htm
The progression circuit is controlled by holes drilled into the body of the carb by Weber. I believe I would treat this circuit as though it is not adjustable for time being. Weber guys are quick to point out that Weber never made an after-market carburetor; all of these carbs were originally intended for a specific model car. That's why you need a matched set that were from a car with an engine similar to yours.
Your carbs probably come on the main circuit at about 3000-3500 RPMs - how about that - that's right about where your flat spot lives. Can you tell us what your AFRs are doing when you are in that spot? You can adjust where in the RPM range where the main circuit kicks-in by changing the emulsion tubes and/or float levels.