carb mixture screws dont do anything!

[b.gagnon]

1979 Chrysler 70hp...
I rebuilt the carbs and changed the fuel pump.....Now when I try to adjust the carb it has no effect on the motor!
The best part of all is that the motor is running Great! In the water It is idling @650rpm in gear and smooth as can be. Top end is great too. The only problem is it is hard to get started (not sure if it had to do with some bad fuel that was left in the lines). Once it is started it will start right back up.
I set the needles to 1 turn out, and the choke is working.
What did I mess up!

 

[cambosoup99]

Re: carb mixture screws dont do anything!

mixture screw only adjust fuel air mixture.

there's another screw for idle.


not sure what your question is.

 

[b.gagnon]

Re: carb mixture screws dont do anything!

It is the idle mixture screw in the fron of the carb....The motor should either race of die by turning them. But mine do nothing!

 

[b.gagnon]

Re: carb mixture screws dont do anything!

I am typing in the dark! can't see the keys very well......Sorry!

 

[cambosoup99]

Re: carb mixture screws dont do anything!

you know i noticed that today on mine. when i went to try to adjust the mixture. so i just left it at 3/4. must be a problem somewhere else.


for the hard starting check your choke. when engaged do all valve close all the way. mine was out of adjustment.

 

[b.gagnon]

Re: carb mixture screws dont do anything!

I know that they did work in the past! I just want to make sure it is not running too lean.

 

[DavidW2009]

Re: carb mixture screws dont do anything!

Did you remove the idle air/fuel screws when cleaning? Then blow out the passages with compressed air and test the passages?

I haven't rebuilt the carbs on mine (90 HP 907HA, 1974) but I did thoroughly clean them and test the passages. When running, those screws do make a difference. I've got them set at about 1 turn out for now.

 

[b.gagnon]

Re: carb mixture screws dont do anything!

I took them out and used carb clean...not air. I just went out to start it and I ended up having to use a spray can of gas oil mix to get it going.. Once it starts it runs fine?

 

[cambosoup99]

Re: carb mixture screws dont do anything!

yeah i did the same thing on mine.. used cleaner and compressed air. so what gives with these idle mixture screws.

 

[DavidW2009]

Re: carb mixture screws dont do anything!

The air/fuel passages may be clogged with trash.

I placed the nozzle of a blow gun on the idle mixture orifice in the venturi and blew back thru the passage with the screw out and felt for air coming out where the screw goes.

What is your idle speed (RPM)? The idle mixture function (I'm reasonably sure) drops out once the RPM's get to a certain level. In other words, if you throttle plates are open, the idle screws won't do any thing. The main jetting takes over.

 

[cambosoup99]

Re: carb mixture screws dont do anything!

mine idle around 1k to 2k. but then start slowly droping to 1.5k

 

[DavidW2009]

Re: carb mixture screws dont do anything!

That idle speed is too high. It should be around 600-700 RPM.

 

[cambosoup99]

Re: carb mixture screws dont do anything!

I got it in the water, and the idle seems to be good but its still high around 1k-2k. but when i put it in gear it drops to around 700 - 800. My question is...

Idle supposed to be high in neutral? If i adjust it in neutral will it affect my idle in gear? Because in gear its sits around 700-800 rpm.

Took it out wot and it doesnt seem to get to the full rpms like before i did the carb rebuild. it would go up to 3k rpm and not any further.

could this be a timing issue now?


by the way.. the carb overhaul did fix my stalling issue i was having before. it doesn't shut off anymore when i go to put it in gear. but now i have a new issue. dang... maybe i should start looking for a new motor.

 

[DavidW2009]

Re: carb mixture screws dont do anything!

No, the neutral idle should not be that high. That's why your idle screws don't respond.

Did you put the proper torque on the carb nuts and use new gaskets? It sounds like there's a bad vacuum leak(s) or the float levels are too low.

Is the carb linkage adjusted properly and does it move full stroke without a bind? Do the throttle plates close when the throttle is returned to idle position?

If you didn't change the timing, I don't see how that would be affected. Is the tower shaft linkage okay? Do you have an ignition points distributor?

 

[cambosoup99]

Re: carb mixture screws dont do anything!

i'll adjust the neutral idle then see if that works.

nuts are torqued to spec. new gasket installed
and the floats are parallel to the carb.
at wot the butterfly valve is fully horzontal.
throttle plates do close when returned to neutral
i have cdi ignition

http://forums.iboats.com/showthread.php?t=383169

 

[b.gagnon]

Re: carb mixture screws dont do anything!

Any Ideas? Anyone.....

 

[cambosoup99]

Re: carb mixture screws dont do anything!

ok i adjusted my idle in neutral when i was in the water today.

I got the idle down to 700-800 range. I notice there was some play in the linkage. on the tower shaft. i could move it maybe 1/4" forward and back. so it was a lil difficult to get adjusted and when i got it adjusted it would somehow still rev up and down by itself.

then i tried to turn the idle mix screws but still no effect on the motor. so i left it at 3/4.

from 700-800 rpm range it would cut out when i go to put it in gear. i'm thinking my controls need adjusting too. it also was a little more hesitate to start and idle properly

it seem to run better at 1k rpms then lower. i dunno.

i'll do somemore adjusting later.

when i did lower the idle rpm it did seem to have better wot but it was not consistent. it would go full then trottle down then full. it seemed more noticeable also when i hit bigger waves.

 

[allhrt]

1986 Classic 50 with dual carbs. Unable to loosen brass reset screw next to plug. Both plug and screw have red markings as if to designate them for some reason. What's their purpose please.

 

[GA_Boater]

1986 Classic 50 with dual carbs. Unable to loosen brass reset screw next to plug. Both plug and screw have red markings as if to designate them for some reason. What's their purpose please.

Start a new thread.

Closed.