Fred is correct about the YF carb.
The best thing you can do is take the tag off the carb and get yourself a rebuild kit...
Once the carb has good everything inside, and it's working properly, you CAN adjust the carb in a number of ways...
But the most important thing is to get the carb working with the ignition!
If you aren't burning the fuel the carb is pumping in, you won't have power and you won't have fuel economy...
FIRST AND FOREMOST!
WEAR SAFETY GLASSES WITH LOTS OF PROTECTION!
YOU WILL get carb cleaner blown back in your face,
AND CARB CLEANER WILL TAKE YOUR EYES IN A HEARTBEAT!
There is no excuse for stupidity like that, so get yourself some COMPREHENSIVE SAFETY GLASSES!
Beg, borrow or STEAL a digital camera with resolution and take images from all angles!
These things can be a nightmare to get the linkages, hoses, ect. back on correctly, so LOTS OF PICTURES both before, and WHILE you are taking the carb off and cleaning it!
Lay out a CLEAN WORKING SPACE THAT IS NOT GOING TO BE DISTURBED!
Lay the parts out in ORDER as you take them out!
This will give you a record of what/how things come apart, and it will keep you from 'Forgetting' to get things back in the order they came out!
KNOW THE DIFFERENCE BETWEEN CARB CLEANER AND BRAKE CLEANER!
Carb cleaner is designed to hang around a while, soften up shellac and varnish left by fuel, and you shoot things down, then go back in a few minutes and spray them clean.
Brake cleaner is designed to dislodge oil/crud and evaporate cleanly.
Once the carb passages are clean (AND DON"T MISS ANY!, BLOW THROUGH FROM BOTH DIRECTIONS WITH THE 'STRAW'!
Then use brake cleaner to clean out the moisture/carb cleaner...
Then used DRY air (Canned air works well) to evaporate the brake cleaner.
DO NOT USE BRAKE CLEANER ON THE PLASTIC/RUBBER PARTS, it will attack them!
Most of the YF carbs I run into (not many!) are just gummed up inside, usually full of crap and crud and need to be cleaned out.
YF carbs are VERY SIMPLE to work on, and you won't have to do a bunch of disassembly,
Just separate the top plate from the main body,
And the main body from the base plate (Throttle valve 'butterfly')
And clean out all the passages.
The #1 problem I run into is the seat for the accelerator pump check ball SEAT is corroded letting the carb draw fuel into the venturi body all the time and waisting fuel.
(I just did one last week that had a corroded check ball, and as soon as you 'Tipped' into the throttle, the accelerator pump 'Shooter' nozzle starting dripping raw fuel into the carb!)
The second biggest problem I run into is the Phenolic Spacer between carb and intake is WARPED,
Giving a HUGE vacuum leak at the baseplate of the carb...
(This particular one had 5 gaskets stacked up trying to get rid of the leak! and failing!)
That is EASY to fix...
First off, make sure your Intake Mounting Studs don't have any rust, gasket/sealer residue collected around the base of them at the intake...
This will keep the gasket/spacer from seating on the intake!
Lay a sheet of plate glass down, tape a piece of finer grain sand paper to it.
Sand BOTH SIDES of the phenolic spacer until the surfaces are FLAT.
Sand in a figure '8' pattern so you don't get sand lines or low spots.
You will be able to tell when it's flat because all areas will be sanded...
Use a VERY THIN coat of FUEL SAFE gasket sealer on the intake, bottom and top of the spacer when you put the thing back together.
If you use too much sealer, it will get into the vacuum passages of the baseplate of the carb, so DO NOT use sealer on the base of the carb, just a VERY LIGHT coat of sealer on the top of the baseplate gasket...
And I mean VERY LIGHT, just a whisper of sealer there!
That will stop the baseplate/spacer leaks.
DO NOT take the linkages apart!
You DO NOT have to remove the throttle linkage from the bores or take the throttle blades off!
Just clean that external linkage with carb cleaner and use a little light lubricant on it.
You need to remove the accelerator pump from the carb,
and replace the rod and diaphragm assembly,
Remove the check balls and check the seats.
Using the old ball (if it's not rusted/corroded) and a punch to 'Tap' the CLEANED seat flush again is a very good way to get the seats working again.
Some things you need to know...
1. Make sure the SEAT & Ball is clean!
You don't want to stamp in the imprint of dirt, corrosion, ect into the carb body!
That will cause another leak that will be VERY HARD to fix!
2. Make sure the kit has a NEW ball before you hammer on the old one!
3. Make sure you have the 'Check Ball' and NOT the aluminum slug they give you to seal up passages!
If you DO NOT have a new check ball in your kit, then DO NOT hammer on the old one!
4. Make sure your float is still good!
Most floats have weight limits, so weight your float on a small Mail scale and compare to the chart.
A leaking/saturated float will be heavier than the specifications and/or if you have a brass float, you will be able to hear fuel sloshing around inside of it if it's failed.
5. YF's usually have a spring loaded inlet valve (needle & seat type), so make sure you get a float level reading with the valve CLOSED, then one with the valve spring COMPRESSED...
And do this BEFORE you take the old float off of the carb top plate...
The spring is in the linkage to keep the float from bouncing open or bending float arm when you hit washboard ruts or pot holes, and you need BOTH readings written down before you take the old float off.
Otherwise, the internals are VERY EASY to take apart, clean and reassemble.
Make sure you take the idle mixture emulsion tube out (Looks like a 'Jet' in the top of the main body) and clean it!
They LOVE to get plugged if you have had unfiltered fuel through it anytime in it's life (VERY LIKELY!)...
Once you get that done and the carb reinstalled,
Then set the idle mixture for a reasonable amount of fuel when you idle...
The 'Proper' way in the manual is to turn the screw 'IN' until it bottoms out on the seat LIGHTLY,
Then back out about 4 turns.
Then screw the idle mixture screw back 'IN' until the RPM drops about 500 RPM and you are done.
You can also set the idle mixture with a vacuum gauge...
Make sure the 'High Idle' isn't set and holding the throttle open when you are doing this.
It should be done on a 'Warm' engine with the choke/high idle pulled 'Off'.
The 'Idle Mixture' screw is located just under the float bowl in the front of the carb.
The CURB IDLE screw is accessible from the PASSENGER SIDE of the engine, and you will find it in back of the carb on the throttle blade shaft just outside the base plate.
Once your idle mixture is set, then adjust the 'Curb Idle' screw for proper engine idle speed...
YOU WILL NOT get proper 'Idle' mixture with the timing set way off!
Check your timing and make sure the timing is set to factory specifications BEFORE you set the idle mixture!
Timing will effect the IDLE SPEED, so make sure you timing is set correctly before you try and set the curb idle, or you will have to do that particular chore again once the timing is correct.
Have you considered an ignition upgrade away from the Prestolite ignition to something a little more reliable and powerful?
If you are interested in getting that done, let me know and I can walk you through that also...
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