Walbro WJ-115 on a Dolmar stroker?

[S&S_Work_Saws]

Has anyone ever tried to put a Walbro WJ-115 off of a husky 395xp on a Dolmar/Makita 7910 with any luck??
I've got an OEM Walbro off of a 395xp in like new condition. It's looks like other then the bolts being clocked a little different it would be a pretty easy swap.
The saw is a Makita with a solo 681 crank assembly and a ported big bore top end. Should make it somewhere between 84cc to 90cc. So I don't think it would be touch carb.
Any thoughts??

 

[farminkarman]

Has anyone ever tried to put a Walbro WJ-115 off of a husky 395xp on a Dolmar/Makita 7910 with any luck??
I've got an OEM Walbro off of a 395xp in like new condition. It's looks like other then the bolts being clocked a little different it would be a pretty easy swap.
The saw is a Makita with a solo 681 crank assembly and a ported big bore top end. Should make it somewhere between 84cc to 90cc. So I don't think it would be touch carb.
Any thoughts??

If more peak power is the main goal, then you might want to go with the rwj-4 if you are gonna use that style of carb.

 

[S&S_Work_Saws]

If more peak power is the main goal, then you might want to go with the rwj-4 if you are gonna use that style of carb

Isn't the RWJ-4 off of a 365/372? Wouldn't that be a smaller carb then my current C3M or this possibly adaptable WJ-115 off of a 395xp?

The only reason I was asking about the WJ-115 is I already have one that's almost new sitting on my work bench. I also have a 385/390xp Intake boot I believe I can make work to install it. Just not sure if anyone has had any experience with the swap and if the juice is worth the squeeze, so to speak.

 

[farminkarman]

Isn't the RWJ-4 off of a 365/372? Wouldn't that be a smaller carb then my current C3M or this possibly adaptable WJ-115 off of a 395xp?

The only reason I was asking about the WJ-115 is I already have one that's almost new sitting on my work bench. I also have a 385/390xp Intake boot I believe I can make work to install it. Just not sure if anyone has had any experience with the swap and if the juice is worth the squeeze, so to speak.

It is the x-torque carb. It has a larger Venturi than the 390 & 395 carb. They can be a bit finicky to tune, but they can really move some air. I have a 2165 that @huskihl built for me that has the rwj. The saw dynoed 8.5hp on 65cc’s. If you want the saw to have great street manners, I would just stay with the c3m.

 

[S&S_Work_Saws]

I'm not to worried about manners with this saw. Usually I'm all about building saw for strictly work. This one is a little different though. Always wanted a stroker Dolmar. With parts disappearing rapidly I figured its now or never.
I guess I'll source an RWJ and try out the 395 carb setup also. Worst that can happen is I swap back to the other setup

 

[Ketchup]

You’ll just have to give it a try. It is possible to put too big of a carb on a saw. Wj115 may be too much fuel, then the saw will be chronically fat. The RWJ has a similar bore and venturi but a smaller jet. A 390xp carb would be the middle option, designed for 88cc.

In all cases you will find that a 390 boot will be slightly too big for the spigot and the stock 7900 boot will be restrictive. Some people add epoxy to the spigot, others just tighten the boot down with liquid gasket. You may also find that the throttle cable does not align properly with the bigger carbs and some small changes may be required.

The Big Bore jug is also restricted by the transfers. Raise the lowers and hog the tunnels as much as you dare. Keep the blowdown in the 28 degree range.

My experience with this kind of carb swap is that it’s tough to get the tune right, it’s hard to identify an air leak, and there is ample opportunity for leaks to develop. You may find a better running saw with a modded twin jet C3M.

 

[S&S_Work_Saws]

You’ll just have to give it a try. It is possible to put too big of a carb on a saw. Wj115 may be too much fuel, then the saw will be chronically fat. The RWJ has a similar bore and venturi but a smaller jet. A 390xp carb would be the middle option, designed for 88cc.

In all cases you will find that a 390 boot will be slightly too big for the spigot and the stock 7900 boot will be restrictive. Some people add epoxy to the spigot, others just tighten the boot down with liquid gasket. You may also find that the throttle cable does not align properly with the bigger carbs and some small changes may be required.

The Big Bore jug is also restricted by the transfers. Raise the lowers and hog the tunnels as much as you dare. Keep the blowdown in the 28 degree range.

My experience with this kind of carb swap is that it’s tough to get the tune right, it’s hard to identify an air leak, and there is ample opportunity for leaks to develop. You may find a better running saw with a modded twin jet C3M.

The cylinder has been thoroughly opened.
The solo crank was a little different on the clutch side. I thought I could make it work but didn't like spacing the oil pump away from the case. So I tore it back down and chucked the crank up in the lathe and made the PTO side the same as the OEM Dolmar. Fits great now.
To make the 390xp boot fit I took a little burr bit and got rid of the little ridge on the inside of the intake boot. The little lip that sits in the groove on the intake. I actually made a little groove where it was. I then slide an o-ring onto the intake flange of the cylinder into the groove there. The intake boot slides over that o-ring now and you can kind of feel that o-ring slip into the groove inside the boot.
Waiting on a new crank seal and I'll see how it runs I guess. Worst case scenario, I switch back to the C3M and try to do the mod.

 

[S&S_Work_Saws]

I got the new crank seals installed and tried to run the C3M. I never could get enough fuel out of the high side adjustment. I went far enough out trying to get enough fuel that the High side jets completely unthreaded out of the carb body...
So now I've got the 395 carb and an RWJ off of a 372....well the red version anyway. Same carb versions I'm sure. Both carbs appear to use the same mounting with one bolt higher then the other and are the same overall external size. The 395 carb seems to run and tune out really well. Just need to figure out the air cleaner and choke lever connection.

 

[Shane¹]

Did you ever try just a regular hd-12 from a 372?

 

[S&S_Work_Saws]

Did you ever try just a regular hd-12 from a 372?

I haven't. I don't think I have one handy at the moment either. Most of my carbs are off of Stihl unfortunately. May have to try to get my hands on one.

 

[old_sir_henry]

There is a thread here in OPEforum with instructions to modify the original Zama carb for larger displacements. I don't have a link to this thread but the author was Poleman.
I did a similar setup on a PS-7900 with a Solo crank and a big bore mug resulting 87 cc displacement. I did the Poleman modifications on my carb. Runs fine.
See pics at https://opeforum.com/threads/the-of...akita-dolmar-chainsaws-thread.694/post-973025

 

[Shane¹]

Did you get the carb on this thing squared away?

 

[S&S_Work_Saws]

Did you get the carb on this thing squared away?

As of right now I'm using a modified Dolmar intake boot and the 395xp carb. I've got the c3m sitting here thinking about trying to mod it. I got my hands on a 372 Xtorq carb sitting here now also.

 

[ManiacalMark]

Being 88cc I don’t see why it wouldn’t work. Port and engine design seems to be the determining factor. Jonsered 2077/2083 run a WJ carb being on the smaller end of the spectrum. It’s worth a shot but I don’t see why an HD 12 wouldn’t do the trick

 

[Shane¹]

Lots of testing in this thread carb stuff 30+ pages in

Thread 'Stroking a Dolmar 7900'

Nov 5, 2018

Grab your popcorn boys and girls.
Hold on to your underwear, we’re headed for destruction!

• Fruecrue
• Replies: 800
• Forum: Chainsaws

• 

 

[old_sir_henry]

BTW: A friend of mine uses Walbro HD12 as bolt-on replacement for the Zama C3M DM-11 and DM-18, actually cheap aftermarket clones of it. According to him, adjustment is a little tricky but otherwise the Walbro is a perfect match.
Maybe a good starting-point if you try to modify the carb.