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Dellorto FHC 20 13A Lean Mixture

Carb has very weak mixture. Engine runs on full choke only and hunts. Carb dismantled, cleaned and choke body blown with compressed air. Gaskets changed. No improvement. Seen many posts with similar problems. Has anyone actually found a solution? Thanks!

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Posted on Jan 02, 2017

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try removing the muffler and scraping out any carbon build up in the exhaust mouth of the block. if that doesnt help you will probably need to replace the carb.

Posted on Nov 29, 2008

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SOURCE: Coleman Powermate 6250 only runs with choke closed/air restricted

A call to Elliott Small Engine solved my problem - Oil Guard. I had checked the oil and it was just a little low but seemed well within the normal range. I was told to add more, bringing it just over the Full mark. It seems that the low oil protection system is very sensitive and shuts down the engine even when the oil is withing 1/8" of the mark. I added about 2-3 oz of oil and no more problems

Posted on Dec 16, 2008

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SOURCE: Toro String trimmer will not start; good spark; getting gas

Hi this would be the only possible solution , The flywheel may have come loose causing the keyway to sheer off this is a common problem the only way to tell is to remove the flywheel and have a look.

Posted on Aug 04, 2009

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check fuel hoses for tears as you prime make sure two screws are tight that holds the primer bulb

Posted on Aug 22, 2009

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SOURCE: I replaced the gas and air lines,cleaned the air

Hi i would recomend fitting a new diaphram kit to the carby and also replacing the filter mesh inside the carby.

Posted on Sep 10, 2009

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1 Answer

Will only idle between full and half choke after replacing fuel line and cleaning fuel filter

Hi Duane:
Sounds like it is running lean.
Are there mixture screws on the carb?
If so, back them out 1/2 turn and give it a go.
Once you don't have to use the choke you can fine tune the mixture with the engine running.

Nov 04, 2015 | Garden

2 Answers

Just had carb rebuilt. Fired it up and will not run unless choke is partially on and it back fires

then whoever rebuilt it can not have cleaned the pilot jet out properly or has fitted too small a jet in it.

May 08, 2015 | Motorcycles

1 Answer

How do i stop my Mercedes 190 engine from hunting

IF by "hunting" you mean a constantly changing speed [RPM] of the engine WITHOUT ANY change of the throttle setting, OR load, then the most probable cause of the variation is an AIR LEAK in the carburetor varying. the fuel/air mixture, AND CONFLICTING with the speed GOVERNOR of the engine.

With internal combustion engines, the RATIO of the fuel and air MIXTURE must be within certain limits depending on the fuel.

IF the mixture is TOO RICH [more fuel than necessary] then the engine will tend to run a little slower, and even raggedly and stall if the mixture is way too rich.

On the other side of the coin, when the mixture goes to TOO LEAN [less than the optimum amount of fuel] the engine RPM will tend to increase, or speed up until it gets too lean and then the engine stops.

I had this problem once with a cheap garden tractor-mower that I had used WAY beyond its intended life-span!!!!!

After MUCH observing, study, and analysis, here's what I found:

  • The steel shaft on which the carburetor butterfly valve was mounted had worn out [ENLARGED THE DIAMETER OF] the HOLES in the cheap "POT METAL" of the carb body.
  • This allowed extra air into the carb, causing the mixture to "go LEAN." which naturally caused the engine to speed up, BUT...
  • The engine speed control governor is designed to maintain a specific engine RPM, and therefore would would cut the throttle back slightly to compensate.
  • This would reduce the amount air AND FUEL,
  • and thus the engine would slow down below the governor "set-speed' causing the governor to open the throttle slightly, causing a vicious cycle of "hunting."
The "proper fix" for this problem was to install a new carburetor, but I couldn't afford it.

So I fixed it by disassembling the carb,
  • finding a short piece of Copper tubing the inside diameter of which happened to fit the steel shaft perfectly,
  • cut two short pieces off the tubing to form bushings for the shaft., and then carefully "cleaned-up" the bushings of all burrs.
  • I then had to drill-out [enlarge] the holes in the carb body to fit the outer diameter of the Copper tubing bushings. I sized the holes to provide a GENTLY-tight "force-fit" to inhibit air leakage.
  • I then greased the inside and outside of the bushings, reassembled the carb and returned it to the engine.
This cured the "hunting problem, and I used the mower for a few more years until I finally wore the chassis, and TOO many other parts completely out and beyond being worth repair!!!!!

Jul 13, 2014 | Garden

1 Answer

Yamaha 5200d it starts and runs 2/3 minutes and shuts down oil is full low oil lite does not light up carb is clean

This generator is equipped with an auto choke. What is likely occurring is as the engine warms up the choke is returning to the normal choke off run position leaning the mixture two lean to maintain operation of the motor.

This is occurring because the residual fuel that was left in the carburetor has evaporated and the gum residue is reducing the fuel flow through the carburetor. When the choke is applied the mixture is rich enough to support running and as the choke returns on its own to the run position the mixture leans out and the generator stalls..

Override the choke when the engine is starting to falter to confirm the problem. Continuing to attempt to run the engine possibly adding a carburetor cleaner additive to the gas will likely return the unit to normal operation.

If attempting to enrich the mixture by applying choke when the engine begins to falter does not work then a fuel flow problem to the carburetor may be the root cause. I would look for a plugged fuel filter or restricted fuel flow from the tank to the carburetor. What is happening is when the unit is at rest the carburetor is filling with gas and as it is running because of a restricted fuel flow the level lowers in the carburetor bowl resulting in a mixture to lean to run.

Jun 01, 2014 | Yamaha Ef4000dfw/5200de/6600de...

1 Answer

Choke problem

That's an indication that the idle mixture is too lean, as the choke richens up the mixture, allowing it to run.

Your carb should be similar to this:

The AIR SCREW adjusts the mixture (rich/lean), and the IDLE SCREW adjusts the idle SPEED.

Try screwing in the AIR SCREW 1/2 a turn and see if that helps.
If not, try another 1/2 turn.

Still no idle?

Turn the screw back where it was (1 full turn) and then screw it OUT 1/2 turn, then if not, another 1/2 turn.

Once you have the mixture correct, the idle speed can be set with the IDLE SCREW.

Jan 11, 2014 | 2003 ATK 125 4-stroke

1 Answer

My Weed Eater FL1500LE gas leaf blower will not run beyond the full choke setting. If I move the lever to half choke the engine will stop. Or if I move the throttle from full throttle to a lower speed...

This is a tell tale sign of a lean fuel mixture. By choking the unit you are manually creating a richer fuel mixture. I would purchase a compression tester from a local parts store and check compression. If that's ok, I'm willing to bet the problem is still carb related. Two stroke carbs are tricky to clean because of high/low ports that are one way and sometimes impossible to clean. Did you remove high and low needles when cleaning carb? Another trick is to mix seafoam with your gas, then mix two cycle oil to proper ratio. Use 2 ounces seafoam to one gallon of gas, then mix two cycle oil to proper mix. Hope this helps! Good luck and happy wrenching!

Sep 22, 2013 | Weed Eater Fl1500 Le Leaf Blowers

1 Answer

10HP Subaru/Robin gas on generator engine only runs smooth with choke half on, what can cause this? also the extra jet on the outside of carb what does it do?

Not sure about the "extra jet" on te side of the carb without a specific model, but running smoothly with half choke indicates that your mixture is lean. Choking it richens the mixture.

The extra jet may be your idle stop, or it could be the idle mixture adjustment.

Jun 29, 2010 | Coleman Electrical Supplies

2 Answers

To keep my Makita weed wacker running I have to close the choke about 3/4. I see no mixture adjustment on the carb and everything appears clean.

An IPL for a 26cc line trimmer can be found here:
BCM2610 Line Trimmer
The carburetor is pictured but not where it mounted on the engine or how you gain access.

It sounds like it is very lean. Have you cleaned the air filter? Checked for leaky fuel hoses? A loose carb or damaged boot may also be the cause. There is a reason it is running lean. HTH
Continued operation in a lean condition may cause it to cease.

Oct 02, 2009 | Makita DCS51018 18" 45cc Chain Saw 2 Cycle

2 Answers

My Stihl chainsaw starts up but then it won't stay running. Changed spark plugs and tried new gas, but didn't fix the problem.

Jets in chainsaw may have build-up. A good build-up remover is called SeaFoam. Add this by direction to the gas. When using the SeaFoam you need to run full throttle with intermittently full choke until motor runs smooth with no choke.

Double check 2-cycle mixture. Too lean mixture in the chainsaw wont stay running.

Sep 05, 2009 | Garden

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