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Discussion in 'Technical Q&A' started by ham308, Nov 26, 2003.
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The Haynes manual or the Pat Braden book ?
Christmas is coming and I can't understand the F manual
Don't know the Braden book.
Haynes is good for the basics.
Pierce is also selling an updated book originally produced by Weber (v cheap - less than $15 if I recall correctly) with tuning procedure and specs on all the emulsion tubes, for example. I'd recommend it.
I've got the Haynes manual which is nice,
but would like to see the others as well.
I have the Haynes book also. It gives very good basic info. You can check the internet, try typing some direct questions, see if anything pops up on google. What are you looing to do? rebuild, re jet, set correctly.
Weber had there own tuning books a small tuning guide part #99001.700 and a larger version which is great for anything you would want to do part #95.0000.54 tuning manual.
Ferrari guide to Performance by Allen Bishop if you can find it has a great section on tuning the DCNF
Thanks for all the replies.
I'm not planning on doing anything drastic. The carbs were apparently set up by an expert and they seem just fine most of the time. Only problem is the engine doesn't want to idle when its very hot. Especially on a down-hill facing junction, it just dies.
Anybody got an idea what it could be ?
At what revs does the engine idle when hot and on the level?
Easy enough to open up the throttle plate screws by 1/8 to 1/4 of a turn on F, R banks to open the idle
Normal temperatures - spot on at ~1000 rpm, very steady.
Hot conditions - not quite so happy, ~900 rpm and will eventually die say after a minute.
Very hot conditions - not at all good. It will die fairly quickly and approaching a downwards facing junction I'm practicing my heeling and toeing the whole way, my wife is rocking about like a nodding dog, and she's not happy
I have both books, and altho I'd lean toward the Haynes book, I've found both to be essential.
I'll have to look into the Pierce Manifold book, tho.
BTW, as to your problem: Do you have the return fuel line from the last carb in the series? Or is it plugged? It keeps cool gas circulating, reducing vapor lock, as well as having an effect on keeping fuel pressure stable.
The problem could also be the level of fuel in the bowl (regardless of float height). Keep in mind that as the car points downwards, I've figured the fuel tilts up at the leading side of the bowl, but with the emulsion tubes at the back, the level will be down because of this and the mixture will therefore lean out. Its probably leaning out so much it'll get to the point where it'll die.
My car has problems with the opposite, if I stop facing up on a severe slope, it'll flood and die (fuel tilts back and goes way up the emulsion tube).
Haven't firgured a solution to fix it, I just try not to stop on a hill!
I have all the books by the way, Haynes, Braden, Pierce, Passini, Bishop. They're all informative and useful (the Passini book is a heavy read. More theoretical than maintenance).
One of the things I found out with the Hynes manual is that the set up proceedures do not work for the 308 webers. For example if you do the A/F mixture it says to close them up and turn them out 2 turns. Well unless you have something different from my 77 you need to turn them out 6-7 turns to get it to run. Also it does not speak to the linkage on the front right and rear right carbs.This spring loaded device is a mild PITA to set and would have been better if they sed the direct coupling similar to the earlier jag multi carb setups. That way you could adjust all of the throttle screws independly which simplifies the set up. I have also found that the set up of the air bypass screws leaves something to be desired. Other than that it is good for the internal details. My 2 c here
Ham if you are facing down and the idle drops really low or stalls you are not on all 8 cylinders or if you are some are weak.
thanks for the feedback on the books, I'll get the Haynes manual.
In case the book doesn't help, I'll ask a question here anyway.
Each choke seems to have a air/fuel idle mixture screw and a metering screw at the bottom. Is the idea that these are used to set the idle up perfectly with the butterflies completely closed? So the car should be idling with the butterflies closed right?
I'm thinking mine's been set up using the butterflies so that it's not so stable when things get hot. Or am I barking up the wrong alley
Maybe better said "with the throttle plate linkages resting on their appropriate mechanical stops" rather than "completely closed" to describe the condition where you use the mixture screw to (mainly) set the idle A/F ratio for that barrel.
308 carbed idle set-up is a balance between 1) idle ignition timing and 2) carb mass airflow rate to get the 3) idle RPM you want (and then at that airflow rate you set the idle mixture for each barrel) -- I really don't see how you can tweak one without at least measuring (if not tweaking) the others.
JMO -- but you're groping if you can't measure all three of those parameters while you're trying to do the set-up.
[Depending on your idle ignition advance setting(s), the mass air flow rate per barrel at 1000 RPM will be slightly different but should be in the 3~4 Kg/hr per barrel ballpark]
thanks for taking the time to explain it to a non specialist. (I think you've answered my queries in the past as well)
Just to be sure though, are the throttle plates (butterflies) shut during idle, or resting against screw stops ??
Throttle plates are not totally shut during idle, so the screws rest against the rest stop.
While I won't deny what Peter and others are saying about float level, what strikes me about your complaint is that it is heat related. I'd sure check that fuel return hose.
FWIW, the tops of my carbs feel almost icy cold, even in the summer. There seems to be quite a bit of fuel circulating thru the system - ie thru the return hose. Also, there seems to be a bit of disagreement in the various books as to float level. I used the highest of all the specs (lowest #, as it's measured). Unfortunately, I don't have the number right at hand. But, absolutely no problems on steep grades, up or down. (Other than the fact that the damn car doesn't have enough torque to start out on a hill w/o an extreme amount of clutch slippage!)
thanks one and all for the carb advice.
4re GT4, yep the fuel return hose is there but it may be blocked.
I'll have read of the Haynes manual which I ordered today. Strangely enough they've sold out on Amazon UK...