Jonsered 672 conversion. Could use some help

[huskihl]

Hi guys. I'm new to the site but I've researched here for months. Thanks in advance for your replies. I've read many posts about big bore kits on the jonsered 625 and the change overs along the way. So I figured wth. Ive rebuilt several saws, bikes, and snowmobiles. I'll give it a try. Btw, my saw is a 1988 625. Single coil.
Picked up a new AM 272xp p/c, intake block and intake bolts to attach the carb. Tore the saw apart, drilled out the impulse hole in the intake side of the carb, plugged the pulse elbow in the top of the carb, and had it running again in a couple hours. From what I've read here, the top cover problems must reside in the earlier model 625's with dual ignition. Mine fits perfectly. And looks bone stock aside from the decompression valve. :wink:
160 psi compression.
My only problem is I can't get the saw rich enough on the high side. Some guys say their original tilly 237a worked fine so I ran with it. Others have recommended going up to the 250a, but they're hard to come by on a budget. The carb bores are the same size so I'm guessing the high side needles are different. Or are there more differences that I'm missing? I may have a line on a cheap 272xp carb if it comes to that. Or maybe the high side jet needle from the 272xp carb will fit in mine?

 

[SawTroll]

A 1988 625 would be a very early one. Are you sure it isn't a 1998?

 

[huskihl]

Nope. I'm not sure. Picked up what info I have on here. Probably got the dates mixed up

 

[huskihl]

 

[wcorey]

I may have a line on a cheap 272xp carb if it comes to that.

You can get a very inexpensive chicom copy on feepay, I've used a couple on 272 conversions and they seem to work fine.
I doubt changing the h needle on yours would help, when backed out far enough the passage is pretty much as open as it can get.
I find that changing needles is more for varying the relative sensitivity of adjustment.

 

[huskihl]

Kinda what I figured. Maybe the passage is bigger on the bigger carbs. I'm running a Chinese copy on my concrete saw and it runs good.

 

[huskihl]

A 1988 625 would be a very early one. Are you sure it isn't a 1998?

This one has single coil ignition, and a wire clamp around the intake boot

 

[weimedog]

I've blended the carbs before . I retro'ed J-red controls to a 272 carb as well. That shouldn't be an issue..
You can get the choke arraignment and pulse from one to blend with the other (272 to 625)
More like you have a standard fuel restriction issue. Pulse, fuel line, fuel filter, tank vent type thing. If its idling nice probably not an air leak... a good thing.

 

[wcorey]

I believe the black tag makes it a '98, not sure though, that could be just a Husqvarna thing.
The changeover from silver to black was right around there somewhere.
I think the really early ones also had the two piece ignition.

 

[huskihl]

I've blended the carbs before . I retro'ed J-red controls to a 272 carb as well. That shouldn't be an issue..
You can get the choke arraignment and pulse from one to blend with the other (272 to 625)
More like you have a standard fuel restriction issue. Pulse, fuel line, fuel filter, tank vent type thing. If its idling nice probably not an air leak... a good thing.

When I drilled the pulse hole in the cyl side of the carb, the bit I used was a hair smaller than the existing hole. But it's larger than the pulse hole in the Chinese intake block I used so I figured it was ok. I didn't check for an air leak yet.

 

[huskihl]

I believe the black tag makes it a '98, not sure though, that could be just a Husqvarna thing.
The changeover from silver to black was right around there somewhere.
I think the really early ones also had the two piece ignition.

And from what I've read on AS, the cover on the earlier models didn't fit over the taller sparkplug angles on the 272 jug. Mine fits perfectly. Mine is weird. Has the wire intake clamp like the early ones, but the taller cover and single ignition of the later ones

 

[SawTroll]

This one has single coil ignition, and a wire clamp around the intake boot

I doubt there were any 625s with 2-piece ignitions - but I have been wrong before.

The 625 was a late entry in that family of red saws.

 

[huskihl]

I've blended the carbs before . I retro'ed J-red controls to a 272 carb as well. That shouldn't be an issue..
You can get the choke arraignment and pulse from one to blend with the other (272 to 625)
More like you have a standard fuel restriction issue. Pulse, fuel line, fuel filter, tank vent type thing. If its idling nice probably not an air leak... a good thing.

Have you ever kept the stock 237a on this setup and not been able to get the H rich enough? I'm out 3 turns and the spring won't hold the jet steady. I just rebuilt the carb a month ago, so I don't think it's dirty. Possible tho.

 

[weimedog]

Have you ever kept the stock 237a on this setup and not been able to get the H rich enough? I'm out 3 turns and the spring won't hold the jet steady. I just rebuilt the carb a month ago, so I don't think it's dirty. Possible tho.

No, never had that issue unless a supporting system was failing.... fuel lines, pulse etc.

 

[Cantdog]

Hi guys. I'm new to the site but I've researched here for months. Thanks in advance for your replies. I've read many posts about big bore kits on the jonsered 625 and the change overs along the way. So I figured wth. Ive rebuilt several saws, bikes, and snowmobiles. I'll give it a try. Btw, my saw is a 1988 625. Single coil.
Picked up a new AM 272xp p/c, intake block and intake bolts to attach the carb. Tore the saw apart, drilled out the impulse hole in the intake side of the carb, plugged the pulse elbow in the top of the carb, and had it running again in a couple hours. From what I've read here, the top cover problems must reside in the earlier model 625's with dual ignition. Mine fits perfectly. And looks bone stock aside from the decompression valve. :wink:
160 psi compression.
My only problem is I can't get the saw rich enough on the high side. Some guys say their original tilly 237a worked fine so I ran with it. Others have recommended going up to the 250a, but they're hard to come by on a budget. The carb bores are the same size so I'm guessing the high side needles are different. Or are there more differences that I'm missing? I may have a line on a cheap 272xp carb if it comes to that. Or maybe the high side jet needle from the 272xp carb will fit in mine?

When you say you can't get the carb rich enough.....is it over revving and you can't slow it down by richening it or is it not spooling up to top rpm??

 

[huskihl]

When you say you can't get the carb rich enough.....is it over revving and you can't slow it down by richening it or is it not spooling up to top rpm??

A bit of both. When I first started it, I had to keep choking it on and off or it would lean out. I went out to 2 turns out on the high side. Then 2.5. Then 3. And it won't burble yet

 

[Cantdog]

A bit of both. When I first started it, I had to keep choking it on and off or it would lean out. I went out to 2 turns out on the high side. Then 2.5. Then 3. And it won't burble yet

Hmmmm.......Ok...Now was this saw running good in it's 625 version and you just decided to upgrade it or did the 625 not run well?

 

[huskihl]

Hmmmm.......Ok...Now was this saw running good in it's 625 version and you just decided to upgrade it or did the 625 not run well?

Ran lean until a month ago. Replaced crank seals and orings (making sure the pto side didn't turn inside out) and rebuilt the carb. Fired it up, retuned, and ran like new with no lean symptoms. It was a bit low on compression at 100 psi, but still ran well. Upon disassembly yesterday I noticed about .100" ring end gap. So it just needed a ring. My goal wasn't to get it back to stock. I like tinkering on this stuff like you guys. Figured it'd be cool to try it AND get a 72cc saw out of it.

 

[huskihl]

When I drilled out the pulse chamber on the carb, I only went into the 1st chamber (about 1/8" of drilling depth). Is this correct?

 

[pioneerguy600]

Which carb gasket did you use? Did it come in a kit or did you make it, do the impulse holes line up correctly?