Jonsered 625 help

[JesseR372xp]

I’ve been putting this post off for a while because I’ve been trying to sort it out on my I’ve searched this forum and all the other forums about my issue but haven’t found anything new. I apologize in advance because this is gonna be long winded.

what I have is a Jonsered 625 that I picked up with the two piece ignition. I was told it would just need a new coil and be all good well once I dug into I found it needed a new jug and piston. Stock top end is less than ideal and My buddy had a complete 268 top end except the carburetor so I took it put it on. Converted the original carburetor off the 625 over from the external pulse line by drilling out the hole on the carburetor to run off internal pulse through the intake block and all that. I figured while I was at it I would put new seals and new orings on the oil pump and the flywheel side seal holder as well as all new intake gaskets new fuel line and filter and a carb kit New tank vent.


So after all that I fire it up tune it up and the thing idles Perfectly but when I grab the throttle the best way I can describe what happens is that it surges aggressively at half to full throttle. No matter what I do with the carb adjustment I can’t get it to rev up but it will always idle perfectly.
Has anyone every experienced this before? Cause I’m stumped and don’t want to give up on the old saw. I do not have a pressure tester or vacuum tester but It feels like it has tons of compression and I’ve tried spraying break cleaner around the seals and other common spots that could leak and the saw just keeps running. I’ve tried it with it without the air filter on no change.

 

[Cantdog]

I’ve been putting this post off for a while because I’ve been trying to sort it out on my I’ve searched this forum and all the other forums about my issue but haven’t found anything new. I apologize in advance because this is gonna be long winded.

what I have is a Jonsered 625 that I picked up with the two piece ignition. I was told it would just need a new coil and be all good well once I dug into I found it needed a new jug and piston. Stock top end is less than ideal and My buddy had a complete 268 top end except the carburetor so I took it put it on. Converted the original carburetor off the 625 over from the external pulse line by drilling out the hole on the carburetor to run off internal pulse through the intake block and all that. I figured while I was at it I would put new seals and new orings on the oil pump and the flywheel side seal holder as well as all new intake gaskets new fuel line and filter and a carb kit New tank vent.


So after all that I fire it up tune it up and the thing idles Perfectly but when I grab the throttle the best way I can describe what happens is that it surges aggressively at half to full throttle. No matter what I do with the carb adjustment I can’t get it to rev up but it will always idle perfectly.
Has anyone every experienced this before? Cause I’m stumped and don’t want to give up on the old saw. I do not have a pressure tester or vacuum tester but It feels like it has tons of compression and I’ve tried spraying break cleaner around the seals and other common spots that could leak and the saw just keeps running. I’ve tried it with it without the air filter on no change.

Welcome to the site!
Couple questions......was the 268 top end the closed port Mahle or the open port Gilardoni? Did you use any sealer on the cyl base gasket or intake gskets? If so what did you use?

 

[JesseR372xp]

Welcome to the site!
Couple questions......was the 268 top end the closed port Mahle or the open port Gilardoni? Did you use any sealer on the cyl base gasket or intake gskets? If so what did you use?

Thank you it’s helped me with a lot of since I joined. And It’s a hyway cylinder and piston I wanna say it was closed port but I can’t remember. I try to use OEM as much as possible but it was just convenient to use the hyway topend. And I use the grey motoseal (it escapes me who it’s made by but I know that’s what it’s called) used it on all the intake gaskets but I didn’t use a base gasket. Squish was 25 thousands

 

[huskihl]

Chain brake on?

 

[JesseR372xp]

Chain brake on?

Fair question but no, i ran it without the clutch even it on it this afternoon and it acts the same

 

[Cantdog]

I'm not much on sealers because I've seen them clog to many impulse passages......with out a gasket you don't have much choice on the cyl base. First thing I'd make sure your impulse passage from the carb to the crankcase is not plugged or otherwise obstructed. I picked up a pretty nice 266XP from a member a couple years ago. He had been fussing with it endlessly and it was doing just about the same thing....would idle ok but just wouldn't run out. He practically gave it to me he was so fed up with it. I had it a couple months pondering what he said the had tried and changed and how I should proceed......finally it boiled down to the cyl base and knowing he's gasket goober I figured he had plugged the impulse passage but when I took it apart I found he had not been in there but the previous owner had.....the base gasket was flipped over covering the impulse passage completely. I have no idea how it even ran at all. I put a new ring in it while I had it apart...started first pull and ran great!!!

 

[JesseR372xp]

I'm not much on sealers because I've seen them clog to many impulse passages......with out a gasket you don't have much choice on the cyl base. First thing I'd make sure your impulse passage from the carb to the crankcase is not plugged or otherwise obstructed. I picked up a pretty nice 266XP from a member a couple years ago. He had been fussing with it endlessly and it was doing just about the same thing....would idle ok but just wouldn't run out. He practically gave it to me he was so fed up with it. I had it a couple months pondering what he said the had tried and changed and how I should proceed......finally it boiled down to the cyl base and knowing he's gasket goober I figured he had plugged the impulse passage but when I took it apart I found he had not been in there but the previous owner had.....the base gasket was flipped over covering the impulse passage completely. I have no idea how it even ran at all. I put a new ring in it while I had it apart...started first pull and ran great!!!

I’ll have to take it apart again and check it out, it’s possible it could be blocked slightly and That would cause me the grief I’m having. I’m pretty confident even without a pressure tester I shouldn’t have any air leaks I’m was very diligent replacing the seals and the orings. And the brake clean test is encouraging. What your saying makes the most sense really. I’ve been told different things about using sealers on the gaskets some like you say it cause problems others have told the never put a intake back together without it. And I always lean to the side where a little bit shouldn’t hurt anything. I’ll try it with fresh gaskets and no sealer when I re assembly this time

 

[Cantdog]

About the only sealer I use on saws is HyloMar Blue. You can put it on very thin with your finger, it doesn't harden ever, is impervious to gas and oil and cleans up easily if you have to take it apart in the future. It's pricy but a little goes a long way. Even then I don't use it on intake gaskets unless I'm reusing them or need to hold a gasket in place while assembling. Good luck!

 

[rupedoggy]

Did you plug the original hole for the pulse line?

 

[JesseR372xp]

Did you plug the original hole for the pulse line?

Not sure what you mean. The original hole for the impulse was in the old cylinder which fed into the top of the carburetor through a little brass 90 degree fitting. so I just swapped the top with the top off an old carburetor that didn’t have the fitting on the top

 

[rupedoggy]

OK that should do.

 

[JesseR372xp]

Update, so after checking all the impulse passages on cylinder and intake block (even went as far as running a drill bit through) and checking that the case was blocking part of the impulse hole in the cylinder. I started checking crazy things and I found that the intake block was not perfectly flat and true on the side that mates up to the cylinder. I believe it would seal at idle or it wasn’t a big enough leak that I could just adjust it out with the carb but would leak at mid to full throttle.

doesn’t explain why it passed the break clean check but sounds plausible to me.

 

[Cantdog]

Update, so after checking all the impulse passages on cylinder and intake block (even went as far as running a drill bit through) and checking that the case was blocking part of the impulse hole in the cylinder. I started checking crazy things and I found that the intake block was not perfectly flat and true on the side that mates up to the cylinder. I believe it would seal at idle or it wasn’t a big enough leak that I could just adjust it out with the carb but would leak at mid to full throttle.

doesn’t explain why it passed the break clean check but sounds plausible to me.

Well we've eliminated the first possibility. How is your fuel line? Is it the type with a grommet made into the line or the type that just uses a straight piece of hose? Either way you need to check the line over very closely for cracks when bent or pinholes.....if that checks out it's onto the carb. .That is a pretty anemic carb for a 268XP top end but should run it just not at full performance. It should be able to rev up no problem. Did you rebuild it with a new kit? If so, did you make certain the metering lever was set perfectly flush with the carb floor? And if you did or did not rebuild it did you notice any crap in the final fuel filter located in the carb body under the cover you changed out? Sorry for all these questions but just trying to get a feel for what's going on with your saw. One other thing.....you said earlier it needed a coil.....what did you replace it with? And did you replace just the coil or the module too?

 

[JesseR372xp]

Well we've eliminated the first possibility. How is your fuel line? Is it the type with a grommet made into the line or the type that just uses a straight piece of hose? Either way you need to check the line over very closely for cracks when bent or pinholes.....if that checks out it's onto the carb. .That is a pretty anemic carb for a 268XP top end but should run it just not at full performance. It should be able to rev up no problem. Did you rebuild it with a new kit? If so, did you make certain the metering lever was set perfectly flush with the carb floor? And if you did or did not rebuild it did you notice any crap in the final fuel filter located in the carb body under the cover you changed out? Sorry for all these questions but just trying to get a feel for what's going on with your saw. One other thing.....you said earlier it needed a coil.....what did you replace it with? And did you replace just the coil or the module too?

Brand new fuel line (grommet type) new tank vent, new fuel filter, rebuilt carburetor with OEM kit, never put much thought into the meter lever being flush but a new needle valve came in the kit and it looked right to me. Replaced both the coil and module with known good used ones. I have to wait until Monday to get new gaskets and a new intake block to try it But I’m fairly convinced it was the intake block not being true to the intake port on the cylinder. When I held it up to the intake port it would rock back and fourth more than one would expect.

 

[Cantdog]

Brand new fuel line (grommet type) new tank vent, new fuel filter, rebuilt carburetor with OEM kit, never put much thought into the meter lever being flush but a new needle valve came in the kit and it looked right to me. Replaced both the coil and module with known good used ones. I have to wait until Monday to get new gaskets and a new intake block to try it But I’m fairly convinced it was the intake block not being true to the intake port on the cylinder. When I held it up to the intake port it would rock back and fourth more than one would expect.

Well if that fixes it great. Seems like the sealed gasket would absorb the difference. But on these Tilly HS carbs the metering lever must be set flush with the surrounding floor of the carb body. This is accomplished by bending the lever carefully until it is.

 

[JesseR372xp]

Well if that fixes it great. Seems like the sealed gasket would absorb the difference. But on these Tilly HS carbs the metering lever must be set flush with the surrounding floor of the carb body. This is accomplished by bending the lever carefully until it is.

I’ll take it apart and have a look at it tomorrow. And will try the carb on another saw to rule that out as well. I tried to get a picture how flush the intake block was but pictures just wouldn’t do it justice. I’m I’d be willing to say that it was out the almost the thickness of the gasket on the one corner.

 

[JesseR372xp]

Well if that fixes it great. Seems like the sealed gasket would absorb the difference. But on these Tilly HS carbs the metering lever must be set flush with the surrounding floor of the carb body. This is accomplished by bending the lever carefully until it is.

Also just wanna say i appreciate all the advice. Usually I can sort things out pretty good this saw has thrown me for a loop.

 

[Cantdog]

I’ll take it apart and have a look at it tomorrow. And will try the carb on another saw to rule that out as well. I tried to get a picture how flush the intake block was but pictures just wouldn’t do it justice. I’m I’d be willing to say that it was out the almost the thickness of the gasket on the one corner.

Wow!! That's quite a bit out!!! Yeah if you try the carb on a different saw that will tell a lot!