problems setting idle.

[nicolas]

i have been cleaning and trying to set up my carbs again. and i have found that one carb is causing me a bit off trouble.
i try to adjust the carbs with a unisync gauge and it wont work on one carb. i have unscrewed the idlescrew all the way out and it still pulls in too much air. idle is now at 1100 rpms insted off 850 as it was before. what am i missing here?
i have unbolted eveything and i must have missed something when i assembled them again. the carbs respond good and i have no flatspots or problems, other then the one carb not being adjusted the way they should.

[Lee.C]

maybe a small air leak  torn/ripped gasket 

[Fasterbrit]

Sound like a blocked idle jet for sure

[Fastbrit]

First thing to do is check your valve clearances before attempting to adjust your carbs, then go from there.

[LGK]

Nicolas,

Why did you take the carbs off please?the car ran smoothles when you left the shop???

Steve

[nicolas]

Nicolas,

Why did you take the carbs off please?the car ran smoothles when you left the shop???

Steve

yes it did, but i have got my DCNFs and they were cleaned and fitted. i was getting too much fuelgasses inside the car, so i had to find a solution to fit them under the lid again. the carbs work as good as the IDF's, but they were not adjusted correctly. they even cured the flatspot off the IDF's. no worries i run the engine carefully.

[Jim Ratto]

Hi nicolas,
first I would make sure the carb is actually snapping completely closed. Back idle speed screw all the way out so it no longer touches carb arm on end of shaft. Take carb off manifold and see if butterflies snap closed completely. You can shine a flashlight down the intake rams of carb and look at bottom of carb. Do you see a big crescent of light coming through? Just one barrel or both? Or are butterflies closed? If they snap closed, screw idle speed screw in until it just contacts the arm. Give it one more turn and see if carb still snaps closed against screw. If it doesn't you may have a twisted throttle shaft or the arm is binding against end washer. Try loosening nut at end of shaft and see if that frees it up?
Maybe (I don't knwo much about DCNFs, but isn't there a ramp that operates accelerator pump?) the accelerator pump cam and ramp is hanging up?
Do the butterflies interfere with the ID of the intake manifold passageways? Maybe they are sticking against ID wall as they close? See any shiny marks on ID of wall?

Obvious stuff, linkage holding carb open (never synch carbs with linkage attached, until carbs are balanced 100%), air leak, timing advance too advanced at idle...

hope this helps dude,
Jim

[nicolas]

well i was hoping this would not have been posted:

First thing to do is check your valve clearances before attempting to adjust your carbs, then go from there.

as i was worried it would be something involving to take off the carbs...

but i did. so i have looked at them and they did have one problem. the shaft was pushed to one side on opening. that is because the accelerator pump is directly on the shaft (sideways) and pushes on the shaft. so i fixed that now it opens up straight and closes completely. well except for the part were the butterfly is going through the shaft. that is were it had some play...
so i used a flashlight and couldn't see much light going through.

i bolted them back on and took it for a drive and it reacted differently, it bogged now just off idle. like a plugged idlejet. but i now suspect there must be something in the galleries and not in the jet itself as that one is clean.
i cleaned it in a supersonic bath and something must have come lose and clogged up the carb circuit.
i haven't been able to check it all today as i found out the problem yesterday, but i will take it all apart again and see if there is any dirt in it.

if not i suspect the valve / butterfly not closing off completely and that means i need replacement butterflies for 42 DCNF's... but i don't know if those are still available or not??? i hope someone can help me with those if necessary.

thanks for all the advice allready.

[Jim Ratto]

bog off idle could be from accelerator pump not doing its job like it should. Not real sure what is going on from your above post though.... is the pump working?

[nicolas]

i have a hard time getting my words lined up in sentences today...

what i mean is that the pump is mounted on the side off the carb and is activated by a wedge/ramp that opens the pump when the butterflies are opened. (look at number 34, that is the wedge) so too much pressure was put on the wedge by the pump spring and it pushes the whole shaft to the other side for 0.2 mm or something like that. not much but noticeable.
so i fixed that, but if the shaft moved the butterfly must be somewhat oversize on the sides as well if i am correct... that is what worries me now. could it be that due to the use over the years the butterfly was scraped off because off the sideway movement and that making the gap? and after cleaning them and getting some dirt out there and opening up the gap a bit more so the airspeed is up?
again this is what i THINK it is, but i will try and look at it some more and make out what is failing.
the pumps work OK and dispense a nice straight squirt on both sides.

i will go through the carbs again and set them up correctly and go from there. and check the gaskets for leaks as well. it is most likely something i have overlooked at the setup and that is why i can now dig in again and find it.

btw i always balance carbs with the linkage off as it is indeed a subtle difference that can make a carb work or not.

[Jim Ratto]

i have a hard time getting my words lined up in sentences today...

what i mean is that the pump is mounted on the side off the carb and is activated by a wedge/ramp that opens the pump when the butterflies are opened. (look at number 34, that is the wedge) so too much pressure was put on the wedge by the pump spring and it pushes the whole shaft to the other side for 0.2 mm or something like that. not much but noticeable.
so i fixed that, but if the shaft moved the butterfly must be somewhat oversize on the sides as well if i am correct... that is what worries me now. could it be that due to the use over the years the butterfly was scraped off because off the sideway movement and that making the gap? and after cleaning them and getting some dirt out there and opening up the gap a bit more so the airspeed is up?
again this is what i THINK it is, but i will try and look at it some more and make out what is failing.
the pumps work OK and dispense a nice straight squirt on both sides.

i will go through the carbs again and set them up correctly and go from there. and check the gaskets for leaks as well. it is most likely something i have overlooked at the setup and that is why i can now dig in again and find it.

btw i always balance carbs with the linkage off as it is indeed a subtle difference that can make a carb work or not.

that's ok buddy I have been away since 3:00am.... zzzz

I get what you're saying now. So maybe edge of butterfly has worn away? Or ID of carb has been worn away? Can you slip feeler gauge blade up between the butterfly and barrel ID and compare all 4? If butterfly wore away, I would think it would leave a lip on surface of butterfly, or show a polished witness mark? can you remove from shaft and compare to others to see if it is oblonged or deformed? Now it makes sense yes the air bypassing butterfly would change idle and you'd have to set mixture screw different for that hole too.

[Lee.C]

Just a thought but you might have the wrong sring fitted INSIDE the pump they normally have a VERY soft and short spring - just a thought but I have mixed them up before  Also add plenty of grease to this whole mechanism trust me it needs it 

[nicolas]

thanks, i thought it was a light one in the pump, but i will open it up all again and see what is causing what. i just will measure everything and let you know. and yes white grease is my friend. 

hopefully i have some time this evening

[Fasterbrit]

Nicolas, I had a problem with my DCNFs that I just couldn't work out for ages. It turned out to be a slight side play in the throttle shaft that allowed the accelerator pump to function all on its own at idle! Because of the flat four arrangement DCNFs sit 90 degrees out to how they were designed (for V engines). Any play in the throttle shaft allows the cam on the accelerator pump to flutter back and forth squirting neat fuel down your carbs at idle. On my carbs as soon as you brought the revs up the harmonics balanced out and the problem no longer occurred. But it had me scratching my head for ages before I worked out what was happening.

At idle, shine a torch down the carbs and watch the pump jets. If any of them are squirting fuel, then you have the same problem. I cured the problem by setting up the throttle shaft with no play as per the Weber manual.

Matt

[nicolas]

i have set up all the carbs and they still do the same thing. the small bog is gone and all works nicely, but the idle is still high.

the problem is the butterflies, they are worn a bit and leave a small gap, but big enough to get the RPMs up to 1100. so i'll be looking for a set of replacement butterflies i can have fitted.

again thanks for all the help.