Jonsered 670 fuel delivery problem

[jacrawley]

I recently pulled a 670 out of my local scrap yard that had decent compression and rotten fuel lines. I replaced the fuel lines and the carb with a rebuilt one.

If I spray gas straight in the carb it starts and runs a second or two.

Attempting to start the saw it does not seem to be drawing fuel. I removed the fuel filter and tried without it and this had no effect. I've inspected that diafram hose and it appears to be free of holes.

I've screwed both the jet screws out 1 and 1/4 turns which is the recommended amount. Did I get a bum carb? Does anyone have anything else I should look at?

thanks

 

[RES]

It sounds like it is not drawing fuel. I assume that you replaced the fuel pickup/filter. You may have to pressure test the crankcase to see if there is a leak there. A leak proof crankcase is necessary in order to draw fuel.

 

[johnb]

Sound like the carb

Sounds like the carb is plugged. Disassemble, hot soapy water or a trip through the dish washer. Blow out the needle jets and main jet wholes reassemble with a new kit. Also make sure there are no blockages in your vacuum draw line for the carb. Check the needle diaprahm linkage for proper adjustment it may not be allowing enough fuel in the carb. Good luck

The Hoosier

Sharpen your chain its a jungle out there!!!!!

 

[jacrawley]

It sounds like it is not drawing fuel. I assume that you replaced the fuel pickup/filter. You may have to pressure test the crankcase to see if there is a leak there. A leak proof crankcase is necessary in order to draw fuel.

How would I go about testing the crank case for a leak?

thanks for the advice

 

[JohnL]

Agree on that. Check out the carb, did you rebuild it? If someone else did, may not have been done right. Diaphrams, gaskets, in correct order, metering lever correct height, covers not leaking, Impulse line, or passage if it is built into carb, needs to be open to crankcase, not blocked with carbon etc. Lines connected correctly. Fuel tank venting, not allowing air back in to replace fuel going out, creating a vacuum, test by trying to run with gas cap loosened. Just some ideas...

 

[RES]

To check the crankcase, you have the block all of the openings on the cylinder head and pressurize the crankcase with a mityvac or other device. You need a gauge also to determine if the crankcase can hold pressure. Do a search on this website. There is plenty of information on this subject.

 

[jacrawley]

update on 670

I checked the carb by placing it under water blocking the float open and blowing air in the fuel intake. Everything checked out with bubbles coming out the h and l jet holes and no air leaving through anywhere else. So I guess that's okay.

I then pressure tested the saw by putting some bike inner tube with the valve over the exhaust port and placing some more in between the carb and the manifold. This led to me finding a small tear in the rubber carb manifold. It's about 2mm across. after that I removed the manifold and placed rubber over the intake but I could not get an air tight seal with that manifold ring clamp. So I could no test the crank case.


Does this small of a hole sound like it would cause the fuel not to pull up?

thanks
Joseph

 

[andrethegiant70]

Does this small of a hole sound like it would cause the fuel not to pull up?

thanks
Joseph

I think its possible, but I would have guessed the saw would run, just badly. Who knows, though, under vacuum, the hole might open up more than you think. If you want to test it, put a dab of rubber cement on the hole, let it dry, then go for it. I'd look very hard at your fuel line and do a carb kit. It's reasonable to assume that if a jonsered 670 was dumped into a landfill (can you believe it?) it had been taking up space in someone's garage for a long time.

This saw is worth your trouble, the 670 is GREAT chainsaw booty. You either got very lucky or you spend all your time at the landfill.

 

[HiOctane]

It's about 2mm across.
Does this small of a hole sound like it would cause the fuel not to pull up?

thanks
Joseph

It's 2 mm too long.you CANT have air leak.Its probably the your fuel problem and could have a seal leaking too.Replace the boot because a two stroke cant run with air leak,often brings seizure.

 

[jacrawley]

update #3

I put some epoxy over the hole in the boot and this allowed me to do a new pressure test and I found a good air leak around the flywheel side of the crank.

How intense is replacing this seal? Should I replace the crankcase gasket while I'm in there? Bearings?

I should point out the carb is a rebuild that I purchased from an ebay guy. Also the cylinder/piston walls have some scouring in them. They are visible and I can feel them with the tip of my finger. New rings? piston or cylinder to?

thanks so much I don't know what I'd do without your help

Joseph

 

[jacrawley]

I think its possible, but I would have guessed the saw would run, just badly. Who knows, though, under vacuum, the hole might open up more than you think. If you want to test it, put a dab of rubber cement on the hole, let it dry, then go for it. I'd look very hard at your fuel line and do a carb kit. It's reasonable to assume that if a jonsered 670 was dumped into a landfill (can you believe it?) it had been taking up space in someone's garage for a long time.

This saw is worth your trouble, the 670 is GREAT chainsaw booty. You either got very lucky or you spend all your time at the landfill.

I'm at the scrap yard every thursday and friday. The Jonsered is one of my better finds(if I get it working) but I also have about 10 pairs of good tim snips!

 

[almondgt]

Do a compression test and go from there. Simple to do. Jonsered 670 is a great saw but can have gone array in the wrong hands.

 

[HiOctane]

How intense is replacing this seal? Should I replace the crankcase gasket while I'm in there? Bearings?
- just remove the flywheel to get the seal.No need to open the case.

I should point out the carb is a rebuild that I purchased from an ebay guy. Also the cylinder/piston walls have some scouring in them. They are visible and I can feel them with the tip of my finger. New rings? piston or cylinder to?

Depends if the scoring is deep or just"superficial".Send a pic.

Joseph

o

 

[jacrawley]

Do a compression test and go from there. Simple to do. Jonsered 670 is a great saw but can have gone array in the wrong hands.

What should the compression be?

thanks

 

[almondgt]

Compression gauges differ but if you have 150 psi on a reliable gauge you are doing very well and so is your saw.

 

[rickyrooster]

670

I would rebuild the saw and then you will know what you've got. Parts can be bought cheap on fleebay and you will have a excellent saw when you are done. You can get the parts for a basic rebuild for around 100.00. Good luck wit your project. Rick!

 

[jacrawley]

update #4

The compression is right at 100lbs.

thanks

 

[almondgt]

Saw needs to be rebuilt, compression is too low. Check the piston/cylinder with muffler removed and carb removed to confirm this. You can see how much damage there really is inside the cylinder from two points.

 

[jacrawley]

There is some cylinder/piston grooving on the exhaust side. How much damage is to much? I would say there are less than 20 groove in the the cylinder. There are more on the piston side.

thanks

 

[romeo]

This is an easy saw to do a bottom end on. I think a full gasket/seal set is under 10 bucks. The last 670 I did I used a husqvarna 272 gasket set because I could find it in town and it worked fine. I also had the same rip in the intake boot and it WAS the cause of my fuel problem, I glued it up with some epoxy a few years ago and its still working.

If you want, try running it before you dive into the lower end. If it runs weird and peaky lean, has no guts and wont adjust out you need crank seals, putting air pressure behind them cant really tell you, they aren't quite an airtight seal and are designed hold vacuum, not pressure.