No lower carb adjustment

[fluidjuice]

Mercury 40hp 1991 4 cylinder 2 stroke.

Problem pressure test good
spark good
now runs on 4 cylinders
carbs have been cleaned
Both carbs suck well

But i have no adjustment on bottom carb at all.
If i spray fuel/oil mix into top carb it stalls
if i spray fuel/oil into bottom carb it picks up same if i squeeze primber bulb.

This must be why it dies under load when trying to accelerate. But Why????

Any ideas would be great

 

[Laddies]

Re: No lower carb adjustment

Is the plastic venturi in the bottom carb. The low speed pickup tube that goes to the float chamber behind the high speed jet is probably plugged.

 

[fluidjuice]

Re: No lower carb adjustment

Thanks for the speedy reply,Yes the venturi is in the bot carb ,Do you mean the tube that goes to the bottom of the float bowl on the top carb ????I think this is the fuel enricher tube which flows to the fuel switch. As bottom carb just has nut and no tube.
just one question , if this was the problem would i still get fuel in bottom carb when i use the fuel enricher prior to starting, as i do get fuel in bot carb then.

 

[Laddies]

Re: No lower carb adjustment

The idle pickup tube only effects the carb that is in, the tube is item 17 but on some carbs the tube is not removable and is 2 pieces a slotted cap and the tube is cast in the carb body, if your is one of them you need to run a piece of tag wire through it and some carb cleaner

 

[fluidjuice]

Re: No lower carb adjustment

Here is an exploded diagram of my carbs, could you please point out the idle pick up tube on here for me .
Thank you.

 

[Laddies]

Re: No lower carb adjustment

It does not show one but there still has to be a passage of some type from the float chamber to the idle adjustment screw and thats where I believe the trouble is.

 

[fluidjuice]

Re: No lower carb adjustment

Well stripped down carbs and cleaned thoughly, still will not adjust when mixture idle screw is turned.when stripping down there was a slotted brass screw which i could not get out without fear of breaking it located on top right of carb ,i think this might have been like a welch plug of some kind to block manufactoring holes, i just hope that there is not something behind that screw that is my problem???? The only passage i could find from the idle mixture screw hole when screw and spring was removed was a passage that went from the idle mixture hole in to the center chamber where the venturi is located ( not the float chamber) and this was clear,

 

[Laddies]

Re: No lower carb adjustment

It's under that brass plug.

 

[fluidjuice]

Re: No lower carb adjustment

Laddies thanks for all your input so far.
befor i try to remove/break screw i would just like to confirm something, when i had the bottom carb apart and the bowl, baffle and float removed ,i only saw main jet holes and no other ssigns of passages that could have led to the idle mixture passage,

 

[Laddies]

Re: No lower carb adjustment

If you look up the center of the casting you should be able to see just the tip of the tube next to the main noozle.

 

[fluidjuice]

Re: No lower carb adjustment

ok got screw out and cleaned all airways out put back together , replaced all fuel lines and new inline filter,starts first time but no adjustment on bottom carb, so this time i squirted fuel oil mix through bottom carb and engine pics up so it must be firing ok but the bottom two cylinders dont appear (again) to be running(makes no diffrence to the sound of the engine and it doesnt stumble.) so am at a loss at what could be the problem it must be fuel related as when i take the bottom two plugs off it still sparks against engine strongly,engine also picks up if i squeeze the primer bulb, ??????????????????????????????????????????????????????/

 

[fluidjuice]

Re: No lower carb adjustment

I have used a strobe light to analize spray pattern in carbs, and what i see is in the top carb i can see fuel coming out of jet and spraying (albut not a fine spray) in to engine.
But bottom carb no fuel coming from jet untill you revv engine and then i can only see fuel coming to the top of the jet but not spraying into engine.
Is this fuel pump ???