IDA idle mixture screws

[Peter]

Dear all,
a question...
when i bought a new mixture screw for my ida's (the old one was bent from previous owner)
i noticed that the tip was not as sharp as the original one...
I have some surging when cruising recently and i can not get rid of this hesitation..
I tried many different settings of the idle screws, but cant get it right...
i tried with 60 and 65 idle jets and with the 65 its better.
I just thought it might be false air, but have to check on that still..
I tried maybe 1.5 turns out, so its rich idling, but doesnt seem to cure the surging.
Other ideas?

Peter

[Peter]

Oh yeah,
so i guess its better to put all new mixture screws i guess or get one other original one?

[kb]

If they are not 100% identical I'd guess that the one that's different would need a different amount of "turns".. Just my thought.

[Peter]

So I replaced the new screws with the old ones again so both carbs are the same..
hesitation is still there no matter what i do.
it feels like enriching makes the surging in cruising less,
but when its idling it smells so rich, and the plugs are sooted.
could it be, due to the locked ignition being at 30btc, that the engine needs more fuel in cruising mode and thats why it runs a bit better?
I am at about a full turn on the mixture screws now with 65 idles..
could it be that i need to unscrew them even more to be able to cruise properly?
but the plugs tell me otherwise??

hoping for your help
Peter

[Peter]

Hello,
tried some more today and found out the following:

screwed in the mixture screws to lean out one by one.
left hand carb responded like normal (very rough running when completely closing the screw)
right hand carb almost didnt respond to screwing in (it kept just running with the two right hand screws completely in!)
I am puzzled by this... somebody knows whats happening?

[BeetleBug]

Hello,
tried some more today and found out the following:

screwed in the mixture screws to lean out one by one.
left hand carb responded like normal (very rough running when completely closing the screw)
right hand carb almost didnt respond to screwing in (it kept just running with the two right hand screws completely in!)
I am puzzled by this... somebody knows whats happening?

Do you have a IR termometer and/or a AF meter? If you find that one or several exhausts are hotter than the other it usually means it is running lean. Its been a while since I messed around with IDA but if they do not respond well on tuning it usually means they are running fat.

[Peter]

thanks BB,
i have an af meter, but its not working for the moment..
yesterday when idling for some time, the engine was colder at the side of the non responding carb,
so yeah its probably too fat on the right bank.
but how could this be? idle jets are the same but I will double check.
something damaged in the carb body where the mixture screw seals off?
It seems i cannot close off the fuel on that side.
Or maybe something is wrong with the engine?
swapping the carbs over side to side would tell me this i think..

[BeetleBug]

thanks BB,
i have an af meter, but its not working for the moment..
yesterday when idling for some time, the engine was colder at the side of the non responding carb,
so yeah its probably too fat on the right bank.
but how could this be? idle jets are the same but I will double check.
something damaged in the carb body where the mixture screw seals off?
It seems i cannot close off the fuel on that side.
Or maybe something is wrong with the engine?
swapping the carbs over side to side would tell me this i think..

Lots of things can cause one side to run hotter compared to the other side. Dirt, jets, carb issues, fuel pressure causing it to leak... a cheap IR termometer will give you a lot of info.

-BB-

[richie]

Usually that is when the carbs are not synched correctly, the other side is doing all the work.

I would diss-connect the linkage and see what difference the idle screws make, get it so each side changes engine rpm when you turn 1/4 turn in or out then you know its close, the cold side is probably not open enough and the other side too much right now


Also check that on the cold side the accelerator pump squirter is not dribbling at all when idling


cheers Richie

[Peter]

Thanks guys,
I did sync them yesterday to be sure that was ok,
but i can try again..
what i found really strange is that the engine just keeps running with both screws completely in on the right hand side!?)
and pretty good too.. definately not lilke running on two cylinders...
I guess some fuel must still be going in even with both of them bottomed out?
maybe change the screws from side to side will help me tell anything

[BeetleBug]

Richie is of course right. I took it for granted that you have checked for vacum leaks, synched the carbs.. all the basic stuff.

[JS]

thanks BB,
i have an af meter, but its not working for the moment..
yesterday when idling for some time, the engine was colder at the side of the non responding carb,
so yeah its probably too fat on the right bank.
but how could this be? idle jets are the same but I will double check.
something damaged in the carb body where the mixture screw seals off?
It seems i cannot close off the fuel on that side.
Or maybe something is wrong with the engine?
swapping the carbs over side to side would tell me this i think..

Lots of things can cause one side to run hotter compared to the other side. Dirt, jets, carb issues, fuel pressure causing it to leak... a cheap IR termometer will give you a lot of info.

-BB-

I´ve had lots of help from the IR thermometer mentioned, wish I bought one years ago.

[Jim Ratto]

if one throat isn't reacting to mixture screw the same as other 3 throats you might check from easiest to most difficult:

- valve lash on that cylinder
- vacuum leak at any joint between carb/manifold & manifold/head
- plug condition (gap, electrode condition?)
- plug wire
- throttle shaft.... are you synchronizing that carbs and check all 4 throats? If that throat is pulling more or less air than other 3, then mixture will be off too. maybe shafts are twisted?
- leakdown test (is that one cylinder healthy?)
- guide tight in head/spring bump in intake port not chiseled through (sucking oil from rocker area)

[Jim Ratto]

if one throat isn't reacting to mixture screw the same as other 3 throats you might check from easiest to most difficult:

- valve lash on that cylinder
- vacuum leak at any joint between carb/manifold & manifold/head
- plug condition (gap, electrode condition?)
- plug wire
- throttle shaft.... are you synchronizing that carbs and check all 4 throats? If that throat is pulling more or less air than other 3, then mixture will be off too. maybe shafts are twisted?
- leakdown test (is that one cylinder healthy?)
- guide tight in head/spring bump in intake port not chiseled through (sucking oil from rocker area)

sorry all idle air / jet holders are same size and not soldered/re-drilled?.

[Peter]

Thanks Jim,
I m pretty sure they are still original, will check this.
Is there a way that the engine can keep running with the 2 RH screws fully turned in?
I mean like running on 4 not on 2 cyls... I dont get it

[Jim Ratto]

yeah I think what may be happening is the throttle plates are not closed all the way on the 2 cylinders that run with mixture screwed in all the way. Or the accelerator pump nozzles are being triggered and are supplying the fuel the engine needs to "run" at idle
I've read sometimes the idle mixture will "back feed" through progression holes (above butterfly) instead of idle mixture holes (below butterfly). The throttle plates would have to be in the wrong position @ idle for that to happen. I know you said you synced the carbs, but they may flow same air into carbs @ idle but the butterflies may not all be in same position. I've seen where there is clearance between edge of butterfly and ID of carb. Makes the idle climb and will pull mixture from progression ports too.
Are you running a lot of initial ignition advance?

[Peter]

Hello Guys,
thanks for the advice..
Jim, I am using a locked magneto set at about 30 degrees.
I ended up with synchronising them again and resetting the screws to 3/4 turn.
then i turned the screws in and tried to feel and hear the vibrations as i changed.
tried to keep the motor at 2000 or so with light throttle and reset screws until it was running the smoothest..
So did a testdrive again, and hey... It runs pretty good right now
It feels good to be able to cruise again

[Jim Ratto]

good to hear. Nice when they run good and don't give you fits. 

[Fritter]

48's (and any carbs for that matter) do not like vaccuum leaks.  Check that first.