SDC Carburetor

[a. palmer jr.]

I've always dipped the small chainsaw carburetors in carb cleaner and rinsed and blew them dry with compressed air but I'm wondering on these Homelite saws which use the SDC carbs whether it's a good idea to dip them, and maybe hurt the little check valve in them. I have several HDC and SDC carbs which haven't been cleaned yet but I need to re-kit them pretty soon and I hate to not clean them as good as I can.
I checked the prices on the check valve and it costs more than some of these saws are worth..

 

[scottr]

Years ago a coworker told me that quicksilver fuel system cleaner was developed at lake x by a chemical company . He used it in all his internal combustion engines and told me that it was ok to put the the whole bottle (12 ounce) in my 18 gallon boat fuel tank . The instructions are to mix 4 gallons of gas to 1 ounce of quicksilver fuel system cleaner (512:1) .

 

[Maintenance supervisor]

I bought the check valve kits for 7$ online, some guys were making their own using a 22cal. Cartrige to cut a circle out of a diaphragm.
What saws?

 

[Jasonrkba]

Those Check valves will drive you nuts if they aren't working correctly. I have rebuilt a lot of old homelites. The more of them old saws I restore the more I'm convinced to use the bare minimum when it comes to chemical cleaning. If it has the black check valve do not soak it.

 

[a. palmer jr.]

I bought the check valve kits for 7$ online, some guys were making their own using a 22cal. Cartrige to cut a circle out of a diaphragm.
What saws?

The SDC is for Homelite Super XL Automatic but I have some smaller XL saws with the HDC which also will be cleaned soon.

 

[a. palmer jr.]

Those Check valves will drive you nuts if they aren't working correctly. I have rebuilt a lot of old homelites. The more of them old saws I restore the more I'm convinced to use the bare minimum when it comes to chemical cleaning. If it has the black check valve do not soak it.

Kinda what I was thinking.

 

[ballisticdoughnut]

You can get a ultrasonic cleaner pretty reasonable these days. That’s what I use for carbs and other small parts. 70/30 mix of water and simple green works really well and it won’t damage rubber or plastic.

 

[a. palmer jr.]

As it turned out, I found something wrong with the Walbro after I installed it, wouldn't hold inlet pressure of even 5 lbs so I replaced it with a Zama from my parts saw. The fuel pump side had a hole in the top cover that matched the hole where fuel comes in and it also had the wrong gasket on it so it wouldn't pump up any fuel. I did nothing to the Zama except a little cleaning and it works great!

 

[Okie]

About your original question about dipping and thourghly cleaning carbs that may have a check valve.

Few years ago I would run most all carbs through a heated Usonic using a 50/50 mix of vinegar and water or just little bit of Dawn dish soap and water. I had some of them little carbs that did not operate properly afterwards and I got into replacing the check valves, mainly just to see if I could get a good run. I would usually get a good run after replacing a check valve if the issue was mainly a idle problem or if when I removed the check valve I could see it was distorted and bad. (one size check valve does not fit all either) Last check valve kits that I bought were in vicinity oF $10. I got into making my own using pieces of carb diaphragms.

So not caring what the outside of the carb looks like, after I manually clean and install a kit, I do not do the USonic FIRST. I just install a kit and then test.

I suspect that some of them old check valves are weak and when they are subjected to heated cleaner or even heated water they distort. You are correct about fooling around with them old carbs and saws are more than the saw itself is worth, BUT I only fool with them types for my or just to add to my collection. (or if I have old spare carbs I'll try to fix them and then label as good for when testing another saw. really nice to have a know good donor carb when working/piddling with on a chainsaw that is not running correctly)

I seem to have more issues lately with carbs kits for diaphragm type carbs not having exact fit needle and diaphragms so I have to inspect very closely before installing and trying to figure out if Bubba installed wrong parts ahead of me and maybe I do have the correct kit parts.

In answer do your question NO I do not dip them at FIRST, just clean MANUALLY and sometimes just re-install the same parts if the diaphragms are ok. But I do pay attention to the little screens, they can be clogged and not readily visible unless looked at closely.

 

[a. palmer jr.]

Now that I have the Super XL going I'm about to start on the little XL saws, maybe tomorrow. Some of them have the same carb problems I'm sure but I'm pretty sure the one just needs an ignition module since it has spark some times and sometimes not. I have three of them and a relative of mine is bringing another one so maybe I can get one or two runners out of the mess..

 

[Okie]

Now that I have the Super XL going I'm about to start on the little XL saws, maybe tomorrow. Some of them have the same carb problems I'm sure but I'm pretty sure the one just needs an ignition module since it has spark some times and sometimes not. I have three of them and a relative of mine is bringing another one so maybe I can get one or two runners out of the mess..

That is what I shoot for also.
Taking a pile of the old Homies and Poulans, especially Poulans and try to take several and make one or two.
Was given a really nice new looking Poulan Pro, (surprised it sold for over $300 when new) with no clutch side cover no chain and a bar just hanging by one bar nut and the bar did not match the saw for roller tip pitch and oiler holes, It would normally have went into my salvage as a donor if no spare parts available. (some of the later model plastic Mac's parts will fit the Poulans)
Installed new fuel line and got a good run on the power head, dug up a chain and bar from Poulan donor parts salvage and with help from a member on here converted the normally wimpy knob adjust plastic knob chain tension adjuster to manual screwdriver adjust. (wimpy costly plastic knob chain adjust is why the saw got a reject by previous owner.
When piddling with old Homies and Poulans it's a good thing to have lots of donor saws so as to come up with a Frankenstein good runner without getting pocket book emptied installing new parts just to get a test run.

 

[a. palmer jr.]

That is what I shoot for also.
Taking a pile of the old Homies and Poulans, especially Poulans and try to take several and make one or two.
Was given a really nice new looking Poulan Pro, (surprised it sold for over $300 when new) with no clutch side cover no chain and a bar just hanging by one bar nut and the bar did not match the saw for roller tip pitch and oiler holes, It would normally have went into my salvage as a donor if no spare parts available. (some of the later model plastic Mac's parts will fit the Poulans)
Installed new fuel line and got a good run on the power head, dug up a chain and bar from Poulan donor parts salvage and with help from a member on here converted the normally wimpy knob adjust plastic knob chain tension adjuster to manual screwdriver adjust. (wimpy costly plastic knob chain adjust is why the saw got a reject by previous owner.
When piddling with old Homies and Poulans it's a good thing to have lots of donor saws so as to come up with a Frankenstein good runner without getting pocket book emptied installing new parts just to get a test run.

I've kinda cooled it on the small Poulan saws, just the 2000 version, mainly because I have trouble getting the oilers working. That one way valve thing I think is discontinued and I tried making one with little success. I'm sure someone on here knows how to fix that..

 

[a. palmer jr.]

Yesterday I disassembled another Homelite XL with the intention of replacing the module only to find that it has points that weren't making contact. I cleaned them, put the saw back together, has lots of spark now but the saw still won't run. It has 150 psi compression so I'm guessing this one has carb problems also. It will hit when fuel is squirted into the spark plug hole but it seems it won't pull fuel into the carb. This carb only has the one adjustment screw also besides the idle speed screw.

 

[heimannm]

The fixed H jet carburetors on the XL models are notoriously rich in my experience, but that should not prevent it from at least firing with a bit of prime in the carburetor. It is possible that the reed valves are somehow buggered and that could prevent a charge from getting from the crankcase into the cylinder. A shot of fuel directly in the cylinder would still fire once or twice.

Mark

 

[Jasonrkba]

Those old reeds can drive you nuts also. Take them out and inspect them. Sometimes you can flip them if needed. If they are nla supposedly you can cut new carbon fiber ones. Those old Homelite ones should be easy to find. (Leonschainsawpartsandrepair)

 

[a. palmer jr.]

The fixed H jet carburetors on the XL models are notoriously rich in my experience, but that should not prevent it from at least firing with a bit of prime in the carburetor. It is possible that the reed valves are somehow buggered and that could prevent a charge from getting from the crankcase into the cylinder. A shot of fuel directly in the cylinder would still fire once or twice.

Mark

It will fire with fuel in the cylinder, I may have put too much in it last time and flooded it. One thing I forgot to mention, the XL I'm working on presently was one brought to me and no history on the saw offered so I don't know how long it has sat. I didn't do much to the carb but I put it back on my bench. Maybe tomorrow I'll tear it back down and go through the fuel system. I learned by watching Leon how to test the check valve in those carbs so I'll do that when I go through the carb on this one..

 

[a. palmer jr.]

Those old reeds can drive you nuts also. Take them out and inspect them. Sometimes you can flip them if needed. If they are nla supposedly you can cut new carbon fiber ones. Those old Homelite ones should be easy to find. (Leonschainsawpartsandrepair)

I have a good supply of reed valves for this model.

 

[a. palmer jr.]

Okay, I went out to the rather warm garage this morning and disassembled the previously disassembled XL. I removed the carb, checked the inlet pressure and it held 7 psi as long as I wanted. I disassembled the carb further and found some rather old gaskets so I replaced them. I did the blow/suck test to the check valve and I could hear the little valve inside going back and forth but it didn't resist pressure fully when the valve was closed. I thought it might not matter since the valve did open and close so I put the saw back together. I now realize that it did matter that the valve didn't resist the sucking since the saw ran like crap when I started it...It starts, runs a little hit and miss and eventually dies. It does seem to run very rich also. Eventually I may come up with a good carb for this saw but I don't have any good ones right now. I may also change the engine over to one without points.

 

[a. palmer jr.]

As it turns out I did find another carb, this one with both H and L screws so I installed it after pressure testing the inlet which was okay. It ran terribly with this carb also so I took it apart again and found the carb had the wrong metering plate gasket. Everything else seems to check out so I'll try to see if it runs tomorrow. I finally got my buddy's XL2 running okay by changing the round metering plate gasket in it. Whoever took the carb apart before must have guessed at what gaskets should be used. Leon says in his video that if the metering plate has only one hole in it (other than mounting screw holes) then it should use the gasket with the Z shaped passage cut in it. If it has 2 holes then the Z shaped passage is not needed so use the other gasket in the kit..