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Author Topic: Carburettor thread  (Read 8258 times)

Doug

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Carburettor thread
« on: August 30, 2009, 08:31:41 PM »
I have a little Chinese clone of a Keihen PZ19 carb.

I'm not particularly familiar with these carbs and never tuned anythign that had air bleed screws, jets and metering rods  ect.
I'm a Tilley carb kindof guy....

Where can I find a manual that explains the bet way to adjust this and where do you find jets?
It's a Good Life, If You Don't Weaken

SteveU.

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Re: Carburettor thread
« Reply #1 on: August 30, 2009, 09:32:03 PM »
Hello Doug
Old  gasoline carburetor  man Steve here.
The best float bowl fed carburetor information is in a Weber (Italian) carburetor manual. Hayes publishes a good one. This will not cover metering rods which are just variable orifice controlled jet openings. Rochester, some Solex, SU and Carter and Motorcraft manuals will have this info.
Basics are: Float level is Critical and will enrichen everything too the point of flooding or enlean everything to the point of stalling and backfiring.
Check/adjust this first.
Air bleeds are to introduce a metered amount of air into a fuel jet flooded mixing well to create an emulsified mix of air and fuel. Straight liquid fuel doesn't want to change speed and flow as quickly as air flow through changes take place - the lighter weight emulsified mix will have a quicker flow response speed.
A clogged air bleed will cause an enleaned condition - stall/backfire. Enlarged (BAD!) or missing air bleed can cause first a lean flat response followed by an overly rich condition.
On small governed speed engines there will be a richness idle needle adjustment AND a volume speed adjustment at the throttle plate or at a throttle plate air bypass passage screw.
Above the edge of the closed throttle plate will be a separately air/fuel supplied transition slot or series of holes. This allows additional fuel for the transition between idle circuit supplied fuel to main circuit supplied fuel.
This is subject to plugging and is very float level sensitive.
The main fuel circuit through the center fed venturi booster is usually not adjustable (except with air bleed and fuel jet change outs) and due to the larger openings gives the least problems.
Small governed speed air cooled engines I have seen almost never have an accelerator pump circuit, power enrichment circuit, altitude or economy enleanment capabilities.
Problems in order of occurrence are: air leakage at mounting, too low of float due level due to fuel absorption or pin holing of the metal, dirt/gum clogging of the air bleeds, gum/metal corrosion clogging of the fuel metering jets or into the throttle bore openings.
With no manual: carb spray all passaged for being clear. Use the same spray to check for mounting air leakage if it is run-able - should be no speed changes. After inspecting the float SET IT OBVIOUSLY TOO HIGH and try it. Keep working the float level lower until you are satisfied with the overall performance.
The fuel jet/s will be visible toward the bottom of the a casting in the float bowl, or with screw in removable upper air bleeds underneath down in the bottom of a fuel mixing well.

Let me Know
SteveU.
PS: Most anything battery start capable will have a charging circuit. This is usually used to power an electric fuel fuel shut off solenoid in the main/idle fuel well. It is the berries when you run into an solenoid with a sticky pindle, bad grounding circuit, intermittently open coil  - all of these will drive you to drinking!

« Last Edit: August 30, 2009, 10:32:10 PM by SteveU. »
Use it up. Wear it out. Make Do, or Do Without.
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Doug

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Re: Carburettor thread
« Reply #2 on: August 30, 2009, 10:00:30 PM »
Still in the evaluation stage.

The engine a Lifan Clone has a stock conventional KF 15.5mm carb clone. Its an emission carb and they don't idle very well and can't be adjusted without a kit ( better to just a Honda carb for starters )

This apears to be a 19 mm carb however it will not fit the clone without modifications

The there is the Tilley 166 and intake I already made. This is a 5/8 ventury carb that seems to work OK ( this is Jin Dong abomination that will not run right  too may odds and ends in one engine ).

http://www.youtube.com/watch?v=4T7sADPCIWE
It's a Good Life, If You Don't Weaken

mobile_bob

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Re: Carburettor thread
« Reply #3 on: August 30, 2009, 10:05:39 PM »
maybe Steve can clarify the following observation

the newer epa motors have all the adjustment screw's either plugged or never had them to start with

i notice that the little champion motor i bought a couple years back, ran with some gas and let sit since
has its orifices clogged with white powdery crap.

so now i have to remove and clean this puppy out and hope it all goes back to normal after, it will run
but only at about 3/4 choked.

guess i am lucky it has a choke, i have another engine without choke or any adjustments for air/idle
or jet/full speed,, its a real problem waiting on me to take the time to rework or replace the carb on it.

these things are even more finicky than a Quadra Jet, and i remember thinking that there would never
be anything so insanely finicky as one of those darned things

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

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Re: Carburettor thread
« Reply #4 on: August 30, 2009, 10:15:07 PM »
I wish this had Q jet I was good with those.

For clarification Bob the carb I am asking about is sort of like a Mikuni slide carb

I have a Champion generator too. If yours is like mine witha 6.5 hp clone find the head of a GX160 Honda or clone ( 5.5 hp ) this will increase the compression ratio form 7:1 to closer to 8:1. And here is a suplier for the adjustable upgrade kit for the carb.


http://www.nr-racing.com/raceparts.htm
Item - ADJJET

I have not tried this but apparently if you get some thumb drills and find the next size up for the Idle jet that should solcve most of your troubles. Here the miss in mine? all of my clones ( have 4 now ) seem to be too lean. I dont have the right combination of bits for this but don;t worry of you screw yours up trying to open it a bit I can mail you one of mine.....

The higher compression head makes a huge difference right off the bat but it made the lean condition a bit worse.

if you file .025 off the trailing edge of the flywheel key for you can advance your timing 4 deg. This also seems to make a difference right off too with the midrange and top end power. Nothing I did here hurt fuel consumption but the engine is still very new only a few hours of running
« Last Edit: August 30, 2009, 10:18:29 PM by Doug »
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SteveU.

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Re: Carburettor thread
« Reply #5 on: August 30, 2009, 10:49:48 PM »
Bob in the past I have used different brands of aluminum wheel cleaners to dissolve out the zinc and aluminum oxides. Do a small part first and watch out for plastics and brass reactions.
Having to choke tells you it is fuel starved.
Float bowl emissions carburetors are easiest richened up by raising the float level.
Diaphram/pumper carbs are my weak area Doug.

Wife has me by the ear -  i'm off

Regards
SteveU.
Use it up. Wear it out. Make Do, or Do Without.
 Electrodyne 12vdc. AC MeccAlte 8.5kw
John Deere 950 w/Yammar 3cyl IDI; Peterson 21" sawmill w/20hp Kohler v-twin; four Stilh chainsaws,  Stilh weedeaters; various Kohler, Onan, Honda, Briggs, Tecumseh singles.