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Homelite UT10530A rebuild only runs idle & full throttle on full choke

#1

oldlawnguy

oldlawnguy

Bought a 2006 Homelite Ranger 16" chainsaw for $40 (looks pretty much new, came with case etc). It has a Walbro WT764-547 carb and kinda would run on idle for a bit.

I've replaced fuel filter, fuel lines & spark plug. Primer bulb is good. Also used a Walbro K20-WAT kit on carb and only replaced gaskets, fuel pump and diaphragm after cleaning out good with carb spray and drying with airgun. Carb did not look that bad at all and diaghpram was not too stiff, but rebuilt anyway.

Pulled out high & low needles and cleaned. Seated needles and then backed both out 1 1/4 turns as a baseline.

Scratching head as I can start with full choke on idle and full choke with full throttle. However, when I try and push in choke even a small bit it just dies. Playing around with needles does not do much.

With full choke and full throttle you can tell the mixture is rich, however any air just causes it to die.

Any trouble shooting tips to try? Walbro Kit came with 2 fuel pumps that matched exactly previous one which was like clear blue plastic.

I first tried the one that was a mesh yellowish plastic, then tried the one that was black similar to the black diaphragm material. Seems to run a little better, but I'm thinking it's something in the carb, just don't know what to try next. I don't think previous owner damaged needles...

Previous owner tried to adjust carb before he sold. That's why I checked high & low needles. Low needle has a more blunt tip than the high which I think is how they are supposed to be.

Could not find any aftermarkets for this carb HM-300939004

Any tips much appreciated.

Thanks!


#2

B

bertsmobile1

You got the saw cheap.
Pull the muffler & check the rings & bore.
If both look god buy a new genulne carb.
YOu will still be a long way ahead.
the L needle is longer than the H needle
If they have been put in the wrong holes then good chance the holes or the needles are now damaged
These carbs have a rubber tipped check valve that can be damaged by the use of cheap carb cleaner.
Walbro now make a safe spray cleaner but it is quite expensive.


#3

oldlawnguy

oldlawnguy

bertsmobile1 said:
You got the saw cheap.
Pull the muffler & check the rings & bore.
If both look god buy a new genulne carb.
YOu will still be a long way ahead.
the L needle is longer than the H needle
If they have been put in the wrong holes then good chance the holes or the needles are now damaged
These carbs have a rubber tipped check valve that can be damaged by the use of cheap carb cleaner.
Walbro now make a safe spray cleaner but it is quite expensive.

I did pull the muffler and piston and rings looked good for my eye. I did notice that when I pull to start it does not have quite the resistance that the Husqvarna 23 Compact that I successfully rebuilt. I"m going to do a compression test. What do you recommend is good enough compression? Could this be the issue .vs the carb? I used Gumout when cleaning carb.
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#4

B

bertsmobile1

I did pull the muffler and piston and rings looked good for my eye. I did notice that when I pull to start it does not have quite the resistance that the Husqvarna 23 Compact that I successfully rebuilt. I"m going to do a compression test. What do you recommend is good enough compression? Could this be the issue .vs the carb? I used Gumout when cleaning carb. [/QUOTE said:
Don't know about Gum out not a product I am familiar with.
The resistance of the cord to being pulled means little as it is dependent upon the diameter of the pulley.
Measuring the compression on these tiny engine without the propr gear is iffy at the best.
The right gear has a solid connector between the plug hole & the gauge with a dozen adapters to account for the volume of the combustion chamber taken up by the spark plug .
I never bother top test them but do a leak down test and a crankcase pressure test.
With my gear anything over 80 psi will usually fire , Stars gear his cut off is 100 psi this stuff is just not accurate enough for small volume 2 strokes.

If I was doing this without my regular gear I would continue opening the L jet till the engine will run without the choke on.
Some of the EPA carbs require 3 to 4 turns out because the needles are a lot finer than the old ones.
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#5

oldlawnguy

oldlawnguy

bertsmobile1 said:
OK this really helps on the compression question. I was aware that you need the expensive equipment, which I do not have, so was going to wing it. When I pulled the muffler I did not see any scoring on the piston as it looked nice and smooth with a nice coat of fuel/oil mix.

I've verified there is good spark after putting in new plug and ruled out bad fuel by using TruFuel 50:1 when I replaced the fuel lines. If I assume the piston/ring is good and compression after visual then I'll focus on your advice to work the L jet per your instructions.

I remember the guy who sold me the saw said he bought the pacman tool to adjust jets and just gave up. Now that I think of it I was pretty sure the L jet was turned out way more than 1 1/4 turns. Wasn't sure what he did so I did some reading where starting at 1 1/4 turns on both H & L was good starting point. However when I tried starting saw "as is" after purchase it was running full choke on idle only and would die on full choke full throttle.

So maybe I fixed somethings and gave myself some more issues :) Gumout has been around since I was a kid (I'm 60) and has been my go carb spray.

Thanks for your help and expertise to give me a plan to focus on the L jet tuning. I was thrashing as to what to do next. I'd throw another OEM carb on however the WT764 was discontinued and I can't find a substitute.

The guy who sold me the Homelite for $40 also gave me the Husqvarna Compact 23 for $20 and a Poulan 2175 for $30.

Waiting for a duckbill check valve for the Poulan after replacing primer bulb, spark plug, fuel lines/filter, then will rebuild Walbro WT324 carb. Thought the Husqvarna would be the hardest to repair and Homelite the easiest. It's been backwards. :)

Thanks again

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#6

B

bertsmobile1

Yep that Gumout is just another body cleaner.
Don't let it anywhere near the check valves or rubber tipped needles.
The formula must have changed as 5 years ago there was no problem but since then I have had way too many check vlaves stick closed after verifing them with carb cleaner
So not it is ultrasound & air at 10 psi and nothing elde.

Walbro have a carb finder hidden on their web page parts section
You might like trying that to see if they list an alternative carb.
In reality there are really only 2 cube carbs
Butterfly valve & rotary valve
After that all that is really different is the size of the venturi & jets.
So with most of them you can substitute parts as the killer is the control connections, choke catches etc.
More than once I have pulled bits off one to make a "wrong" carb fit
Only really hard bit was working out how to support the butterfly while staking the retaining bolt .
The solution was grinding down a big allan key .
That took longer than everything else added up


#7

oldlawnguy

oldlawnguy

bertsmobile1 said:
Yep that Gumout is just another body cleaner.
Don't let it anywhere near the check valves or rubber tipped needles.
The formula must have changed as 5 years ago there was no problem but since then I have had way too many check vlaves stick closed after verifing them with carb cleaner
So not it is ultrasound & air at 10 psi and nothing elde.

Walbro have a carb finder hidden on their web page parts section
You might like trying that to see if they list an alternative carb.
In reality there are really only 2 cube carbs
Butterfly valve & rotary valve
After that all that is really different is the size of the venturi & jets.
So with most of them you can substitute parts as the killer is the control connections, choke catches etc.
More than once I have pulled bits off one to make a "wrong" carb fit
Only really hard bit was working out how to support the butterfly while staking the retaining bolt .
The solution was grinding down a big allan key .
That took longer than everything else added up
Click to expand...
Thanks for all the above very useful info. Did not realize that most cubes are interchangeable and yes the mechanical hookups & orientation are the biggest headache.

I got the carb/saw running without the choke on based on your instructions!!! It was tricky. I started with both jets turned out 2 turns as that was close enough to the 1 1/4 wrong baseline that I knew would run with full choke.

It took a little practice to keep saw running and slooooowly back off jet while slooooowly opening butterfly. Lots of trial and error. Took about 20 mins, once I had the choke wide open I went to the H jet and adjusted on full throttle.

Then I put air filter and top cover on and tweaked a little more including T screw for idle. A BIG THANK YOU!!!!!! It really showed how out of tune those jets were. I did not count out turns but I think L ended around 4 turns and the H at 3 1/2.

I let it run on idle for about 15 minutes and notice that every few minutes the RPM would drop like for 1/2 sec before picking back up. Any tip for tweaking or leave as is? I know the saw should just run all day on idle if set correctly. :)

THANKS AGAIN!!! :)

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#8

B

bertsmobile1

Most of the on line free information is for older pre-EPA carbs.
The new compliant carbs have finner threads and longer tapers on the needles so you can make finner adjustments.
You can continue to tweak the balance between the F & H jets.
What people fail to understand is the L jet flows fuel all of the time but because it is smaller than the H jet it affect is reduced progressively the faster the engine spins
Weather the H jets works or not is dependent upon the volume of air that is passing over the venturi so if the throttle stop is open too far then you can be starting on 90% L + 10 % H which progrssively changes to 10% L + 90% H at WFO
An occasional faulter at WFO could be a stiff metering diaphragm , a sticky check valve , a slightly restricted exhaust outlet , whiskers forming on the spark plug , shorting of the kill wire, faulty kill switch and a truck load of other things.
By now your ear should be able to determine the difference between rich missing , lean missing & ignition missing so that will be your key.

Getting old gear to work 100% is always a problem because of wear .


#9

oldlawnguy

oldlawnguy

Yes this is where I went wrong. Anything before 1995 was pre-EPA carbs. I'm working on "old" stuff (1997, 2001, etc.), however they have EPA carbs and I did not realize how sensitive they are on adjustment.

I knew that when running on full choke the mixture was enough to fire, but when you backed off even a hair, more air got sucked into the vacuum and it would die.

Prior to getting it working yesterday I had a plan B on swapping a carb and jimmying the mechanicals. I got a $10 Homelite Pro 46cc saw. Owner said up front it had no compression and I told him you may have bad piston. I picked it up yesterday, this thing has been used probably 5 times. Its a 2010 model with everything (case, docs, original packaging)

Popped off the cover & spark plug was loose (said you kidding me) but then no spark (ignition?), pulled plug and cylinder bone dry and whitish :(
Pulled muffler and piston has vertical scars across exhaust side and bone dry. Air filter was clean, fuel filter broken in tank. Regular gas (no mix) or maybe cold seize?

Is it worth trying to replace piston, ring etc? Will boring be required? I don't have all the professional tools. If it a parts saw then so be it, but this thing is basically brand new. P.S. carb retrofit would have been a nitemare. :)


#10

Hammermechanicman

Hammermechanicman

Almost all chainsaw cylinders are plated and can't be overbored. Probably the cost to fix the saw will excede the cost of a new similar saw. That is what is called a clamshell saw. The cylinder is part of the crankcase. You must pretty much disassemble the entire saw to change the cylinder. By the time you buy a cylinder, piston, bearings and seals you could buy the saw new.


#11

oldlawnguy

oldlawnguy

Hammermechanicman said:
Almost all chainsaw cylinders are plated and can't be overbored. Probably the cost to fix the saw will excede the cost of a new similar saw. That is what is called a clamshell saw. The cylinder is part of the crankcase. You must pretty much disassemble the entire saw to change the cylinder. By the time you buy a cylinder, piston, bearings and seals you could buy the saw new.
Click to expand...
Thats what this here grasshopper was guessing... wanted some validation from the pro's out there. Will part it out to my other saws. Thanks.


#12

oldlawnguy

oldlawnguy

Hammermechanicman said:
Almost all chainsaw cylinders are plated and can't be overbored. Probably the cost to fix the saw will excede the cost of a new similar saw. That is what is called a clamshell saw. The cylinder is part of the crankcase. You must pretty much disassemble the entire saw to change the cylinder. By the time you buy a cylinder, piston, bearings and seals you could buy the saw new.
Click to expand...
I bit the bullet and took on the 2010 Homelite UT10519 46cc full rebuild. The new stuff for $120-$150 in box stores is disposable and less quality than the older stuff I have found. It cost me $80 in parts (cylinder, piston, piston ring, ignition coil, spark plug, broken muffler bolt and a missing screw. Was fun doing the full rebuild and this saw is still basically brand new (came with case & original packaging).

Piston and cylinder was shot and the heat probably fried and cracked the coil and spark plug (ohm readings out of spec).

While apart I replaced the brittle fuel lines/filter and took apart & cleaned the ZAMA carb. Carb was in good shape. Got it all put together again and it fired right up. Was running, but way out of tune. The guy whole sold me the saw for $10 said he was playing with the jets, so I seated and then backed off 3 turns, fine tuned, sharpened chain and she's humming.

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#13

Hammermechanicman

Hammermechanicman

Nice job!?


#14

oldlawnguy

oldlawnguy

Hammermechanicman said:
Nice job!?
Click to expand...
Thanks for the help! :)


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