Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Husqvarna => Topic started by: Cut4fun . on May 11, 2013, 11:35:30 am
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The below was posted by Shep Farmboy and thought it should be saved somewhere safe and not get lost.
Husqvarna 390 365 xt 372xp xt
While doing a little carb research I came across sonething interesting on the 390. Now uses a Walbro WJ-118 carb instead of the Tillotson HS. WJ-118 venturi size is 17.46. 365XT and 372XT RWJ-4 venturi size is 19.05mm. The RWJ-4 would be a direct swap. Larger carb may work well with MM and WPort.
Shep
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These carbs have a angled mounting bolt pattern and not horizontally straight across.
They will also adapt to the old style 372 if you use the 385 boot and 372XT filter elbow with the baffle removed but you best have some porting on a big bore.
The RWL4 was originally intended to have mainly plain air going through the top half of the throttle body above the butterfly for the strato charged setup on the XT.
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Well known info as far as I know, but it is a good idea to save it. ;D
Of course it is possible to increase the stock venturies of the different carbs as well, but you really have to know what to do, and what not to do...
Btw, I am reasonably sure that no Tilly HS carbs have a larger venturi than 17.5mm.
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Anyone have the 365xt carb model number, wanna try one on the 7900
Thk, Adam
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Anyone have the 365xt carb model number, wanna try one on the 7900
Thk, Adam
Check and make sure. Just throwing darts. http://wem.walbro.com/walbro/product.asp?CategoryName=B156&Series=RWJ&partnum=RWJ-4-1&GroupName=Chain%20Saw&FamilyName=HUSQVARNA
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RWJ 4 is correct. 19.04mm venturi IIRC.
Shep
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Thanks a lot!
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The RWJ-4 has a divider in between the choke shaft and the throttle shaft. It is difficult to see. It is made that way for the strato. So one half the carburetor is dry.
But most people say to leave the divider in there when Using on a big bore old style 372.
The carb screws have a spline around their outside. This is the same spline as the splined screw driver for the small saws.
There is a spring loaded collar sleeve under the head of the screw that works as a limiter. The splined screw driver pushes this collar out of the way so you can adjust the carb as if there was no limiter.
You can also take the carb screws out and throw away the sleeves or you can mount the sleeves on a mandrel and cut the tabs from the sleeves so the limiter function no longer works and adjust the screws with a flat screw driver.
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The last time I ordered an RWJ-4, I was informed by my distributor that Walbro no longer manufactures the RWJ-4! It is now manufactured by Tilly and is called RWJ-4-1. So I ordered one and it looks like the divider is no longer there. Perhaps I'll take it apart and post some pictures.
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660, you are correct, the divider IS still there, but it sure is hard to see. Does not look to be a big deal to remove it. Any suggestions?
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You have to pull one of the shafts to get it out. Seems to not help the carb to take it out though.
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Yes, it does not appear to be cast in. Looks to be a very thin piece of stainless, perhaps installed in a slot on either side of the carb body.
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That is my observation also.
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Just an observation/question, if because of the divider being in the carb, the top half of the carb is dry and only supplying air, then would not this air with no fuel tend to lean out the non strato saw? Carb would be supplying fuel only to half the air passing through the carb, then fuel air mix and air, mix in the carb boot after passing through the carb each on its' own path. Not saying that this could not be compensated for by adjusting the carb. So perhaps leaving the divider in is OK because its' negative effects are within the adjustment range of the carb.
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I've thought all this too but have been around several at GTG's with the plate in and out and they seem to run just fine.
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660, given your observations, perhaps there is enough available adjustment in the carb itself to be able to negate any effect the dry top might have.
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I don't think you'll see it run bad either way?
Timed cuts with the saw set up different ways would be the only way to tell a difference?
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I use that carb on alot of different saws and its works fine and I gut everything .
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Yes, it does not appear to be cast in. Looks to be a very thin piece of stainless, perhaps installed in a slot on either side of the carb body.
I've got 11-12 of those carbs all have the black plastic divider. You have to remove the throttle shaft to remove it. It fits in a machined groove. I've pulled it on 2 of mine haven't tried them tho. Am going to use one on my 372BBK when I put it back together. Solo 665/681 is getting one too.
Shep
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I wonder if this is a regoin thing , I got brandnew 365's and 372's sitting here and they all have walboro's on them
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Perhaps, I got the info about them now being made by Tilly from my distributor not HVA.
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Adam did you ever get one of these on a 7900?
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No, ended up using an HL360 I had on hand. Joe ran some velocity numbers through the stock carb venturi and it was too small for my application but I think the XT carb woukd be ideal for a hot woods port saw...
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I got 2 on the way. One for my 372 and one for the 7900.
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If you are putting one on the 372 there will be some small fitment issues, the blue choke control rod will stick out a little further than the gray one. If you run the HD filter setup on the 372 the top rear edge of the filter comes in contact with the cover and you end up with a slight crush to the filter, no big deal though.
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Yeah I don't know if it will go on it for a while. Both will probably be tested on the 7900 with the divider in and out.
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The 372 wallbro HD Has some fitment issues on then Dolmar 7900 as well. Namely, throttle shaft and cable length. Be interesting to see how the XT matches up to the 7900
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Just an observation/question, if because of the divider being in the carb, the top half of the carb is dry and only supplying air, then would not this air with no fuel tend to lean out the non strato saw? Carb would be supplying fuel only to half the air passing through the carb, then fuel air mix and air, mix in the carb boot after passing through the carb each on its' own path. Not saying that this could not be compensated for by adjusting the carb. So perhaps leaving the divider in is OK because its' negative effects are within the adjustment range of the carb.
They have to be, if it works with the devider in place.
I can't see any good reason to let it stay there anyway though. If nothing else, I assume it steals a little of the carbs venturi capasity...
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Agree.
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If you are putting one on the 372 there will be some small fitment issues, the blue choke control rod will stick out a little further than the gray one. If you run the HD filter setup on the 372 the top rear edge of the filter comes in contact with the cover and you end up with a slight crush to the filter, no big deal though.
Use everything XT from carb out shouldn't have any fitment issues. I have spares JFI.
I mounted one on my 7900 just to see what I would have to do. Have to clock intake boot for sure. Carb mounting screws will work but I would like em a little longer (385/390 w/WJ carb comes to mind for more length they should be longer). Have to fab choke lever. Didn't get to AF. Thought about a venturi w/green weenie cause I have one that would work. Might ask Randy (MM) he had a thread on SH never told what he came up with. He was using carb from 395 tho still canted like WJ. http://sawhawgz.com/showthread.php/1550-Help-me-with-my-7900-please.
Shep
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I do know the xtorq carb will fit on a 7900. I haven't swapped the throttle linkage over so it will travel right yet and pull the divider yet. Hopefully tonight I'll get that done.
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Checked on carb mounting screws 372XP w/HD carb=725-5305-55, 372XT,390 w/WJ carb=725-5309-55. Will measure in a few but pretty sure they are longer.
Shep
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The xtorq carb fits on the 7900. I used the 372 boot. I trimmed 1/4" of the plastic sleeve on the cable and then had to drill a new hole in the arm where the plastic piece goes to get full throttle without having a longer cable. I used the piece from the 7900 on it. The impulse hose isn't long enough so I had to get another one. I tried tygon fuel hose and it pulled it shut in one cut. I went and bought a few feet of 7/64" size thick walled hose and fixed it up. I pulled the divider in it and it was plastic. The saw isn't going to have a working choke so I pulled it out that side. The only thing is the air filter elbow is tilted and won't fit back into the little rubber bushing. I haven't figured out what to do with that yet. The air filter and all covers work still. The adjuster grommet is going to have to be trimmed so it can be put back in.
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Looks good! If you remove the rectangular support piece molded to the intake tube you should be able to clock it over a few more degrees?
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Looks good! If you remove the rectangular support piece molded to the intake tube you should be able to clock it over a few more degrees?
It's a 372 boot so that part is gone. I may make a plastic divider for it and something to keep the impulse hose is place better.
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Just for info. Carb mounting screw length 372XP w/HD=50mm, 372XTw/WJ=52mm, 385XP w/Tillotson HS296=70mm.
Shep
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I used the 7900 bolts but they could be a touch longer to get a little more threads past the collar.
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when using the stock carb setup on the 7900 you know you got the porting correct when it pulls the choke on at full throttle , you have to tighten the spring on the choke lever 1 more turn to stop that problem
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when using the stock carb setup on the 7900 you know you got the porting correct when it pulls the choke on at full throttle , you have to tighten the spring on the choke lever 1 more turn to stop that problem
I didn't even try the stock carb. I put the other one on at the same time I bolted the cylinder down.
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when using the stock carb setup on the 7900 you know you got the porting correct when it pulls the choke on at full throttle , you have to tighten the spring on the choke lever 1 more turn to stop that problem
+1 on that thank you for the tip!