You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Export thread
Carburetor trouble
#1
V
viperv10
V
viperv10
Hi guys. I recently picked up a 1980 R7070 model pre compliant mower with a F 100 series engine. It was hard to start, taking at least 20 pulls to get it going.
So yesterday I took the carb off and cleaned it. I checked the exhaust ports. They were clear. I took the engine off and changed both crank seals. They were the old metal ringed ones. Cleaned off the cooling fins, put in a new plug and put her back together again. After six or seven pulls it started but won't stay running. It runs a few seconds and quits. If I hit the primer bulb it will run till that gas is gone and die down then I hit the primer again and it run a little more.
So it sounds like it isn't getting good fuel flow. Does anyone have any ideas what might cause this or what I might look for when I pull the carb off again?
It is a plastic carb with really no adjustment screws. It did have a jet screw on the side but I'm pretty sure it is supposed to be screwed in snug. Here are two
other things going on with this mower. Sometimes the pull rope will fly back real hard pulling the rope out of my hands, I never really knew why mowers did that and also the crank has probably 40 to 50 thousandths play up and down. I have never had a mower that had that much play. Any help would be appreciated.
Thanks.
Jerry
So yesterday I took the carb off and cleaned it. I checked the exhaust ports. They were clear. I took the engine off and changed both crank seals. They were the old metal ringed ones. Cleaned off the cooling fins, put in a new plug and put her back together again. After six or seven pulls it started but won't stay running. It runs a few seconds and quits. If I hit the primer bulb it will run till that gas is gone and die down then I hit the primer again and it run a little more.
So it sounds like it isn't getting good fuel flow. Does anyone have any ideas what might cause this or what I might look for when I pull the carb off again?
It is a plastic carb with really no adjustment screws. It did have a jet screw on the side but I'm pretty sure it is supposed to be screwed in snug. Here are two
other things going on with this mower. Sometimes the pull rope will fly back real hard pulling the rope out of my hands, I never really knew why mowers did that and also the crank has probably 40 to 50 thousandths play up and down. I have never had a mower that had that much play. Any help would be appreciated.
Thanks.
Jerry
#2
unclelee
unclelee
Make sure your gas cap is venting probably. You may try loosening it and see if anything changes.
If not remove the main jet and make sure all the little holes in the side are clean.
Lee
If not remove the main jet and make sure all the little holes in the side are clean.
Lee
#4
Dixieboy
Dixieboy
I don't think there is much you can do about the crank end play issue unless you what break the case down and check for wear and add a thrust washer. I think it will continue to run ok regardless for a long time. Sounds like a fuel flow issue. First thing I would check is fuel flow out of the tank, pull the fuel line from the tank and see if you are getting flow when fuel valve is on. If not you can pop off the clip and clean the valve out. Next would be to remove the carb and check float operation and clean needle and seat. Like Jeff said above if you can check compression to verify good or bad would be a good idea. Carbon buildup can cause high compression making it hard to start. One more thing that came to mind is I think that model has a small filter inside the carb float bowl that could be plugged
#5
V
viperv10
V
viperv10
Thanks for your responses. I just checked the compression and it only showed 75. That's awful low. The funny thing is it ran good the couple of times I used it.
It was just hard to start. One of these days I'll look at the carb again. The Lawn boy master parts viewer does show a filter inside the carb but this one doesn't have one, I don't know any history of this mower. I got it from a guy that his wife's grandpa and dad used to have a lawn boy repair shop years ago. Taking the gas cap off didn't help any. It won't start now. Maybe I'll put it aside until mowing season is over and take it apart and see what it looks like inside. If its not too bad I might re ring it. Thanks again guys. If you have any more thoughts, shout them out.
Jerry
It was just hard to start. One of these days I'll look at the carb again. The Lawn boy master parts viewer does show a filter inside the carb but this one doesn't have one, I don't know any history of this mower. I got it from a guy that his wife's grandpa and dad used to have a lawn boy repair shop years ago. Taking the gas cap off didn't help any. It won't start now. Maybe I'll put it aside until mowing season is over and take it apart and see what it looks like inside. If its not too bad I might re ring it. Thanks again guys. If you have any more thoughts, shout them out.
Jerry
#6
L
lewb
L
lewb
I believe you need at least 90 psi to start engine. You can try and use transmission fluid to loosen up the rings, just flip motor up and fill up the spark plug hole, let sit for a day and see if you get more compression.
#7
Dixieboy
Dixieboy
If you feel confident in the 75 psi reading that is too low. Since it was trying to run you may have scoring cylinder walls and rings. You know anyone with a bore scope to look and see without a teardown? Another thing is when you rock the engine by hand do you feel any slop? like rod or wrist pin bearing failure? I have seen wrist pin bearing failure and it didn't make much noise so it was hard to tell.
#8
V
viperv10
V
viperv10
Well I took the tank shroud off and I had good gas flow out of the tank. The float bowl was full. I cleaned out every little passage in the carburetor again. Then I noticed the mounting surface area of the plastic carb was warped a little bit, so I used 2 new gaskets just in case it was sucking air. Still would not start. Then I tried Lewb's idea. Turned mower up on its side and put some ATF in the spark plug hole for awhile. Every now and then I would move the blade back and forth some to move the piston up and down a little bit to try to soak the rings. The next day I checked the compression and it only showed 60 psi. That's going the wrong direction. Some of atf drained out of the carb so i'll probably clean it again and put it away for a later project.
Several years ago I noticed a Lawn Boy setting in garage across the alley from a place I mow in town. I always wanted to ask about it but there was never anybody around. Finally the other day when I went to mow there there were people there. So I went over to ask about it and they said they would let it go.
They couldn't get it started. It turned over ok so I took a chance on it for $40. It is a 1989 L21ZSNA, capstan drive, steel deck. It didn't have an air filter or cover and the carb was very dirty. The plug was fowled real bad and wasn't firing. I got good spark with a new plug. Compression showed 90 psi, but still would not start. I'm sure the carburetor is a mess. I have never had this type of shaft drive before so this will be a new experience for me. I'm going to start looking into this one in my spare time. It might work out ok or it might be a heap of scrap. Only time will. I just wanted to rescue this old mower and try to bring some new life to it. I have really enjoyed tinkering with these mowers this past year. I will probably have some more questions for you guys soon so put on your thinking caps. Thanks guys, over and out.
Jerry
Several years ago I noticed a Lawn Boy setting in garage across the alley from a place I mow in town. I always wanted to ask about it but there was never anybody around. Finally the other day when I went to mow there there were people there. So I went over to ask about it and they said they would let it go.
They couldn't get it started. It turned over ok so I took a chance on it for $40. It is a 1989 L21ZSNA, capstan drive, steel deck. It didn't have an air filter or cover and the carb was very dirty. The plug was fowled real bad and wasn't firing. I got good spark with a new plug. Compression showed 90 psi, but still would not start. I'm sure the carburetor is a mess. I have never had this type of shaft drive before so this will be a new experience for me. I'm going to start looking into this one in my spare time. It might work out ok or it might be a heap of scrap. Only time will. I just wanted to rescue this old mower and try to bring some new life to it. I have really enjoyed tinkering with these mowers this past year. I will probably have some more questions for you guys soon so put on your thinking caps. Thanks guys, over and out.
Jerry
#9
J
jp1961
J
jp1961
FWIW, G.M. top engine cleaner (available in spray cans from any G.M. dealer) removes carbon very well.
It used to be available as a liquid back when cars had carburetors.
Regards
Jeff
It used to be available as a liquid back when cars had carburetors.
Regards
Jeff
#10
L
lewb
I would say that if the compression got worse than there must be scoring or something else going on. If you could find a short block that would be the easiest fix to get the same mower running again. Good luck,
L
lewb
Well I took the tank shroud off and I had good gas flow out of the tank. The float bowl was full. I cleaned out every little passage in the carburetor again. Then I noticed the mounting surface area of the plastic carb was warped a little bit, so I used 2 new gaskets just in case it was sucking air. Still would not start. Then I tried Lewb's idea. Turned mower up on its side and put some ATF in the spark plug hole for awhile. Every now and then I would move the blade back and forth some to move the piston up and down a little bit to try to soak the rings. The next day I checked the compression and it only showed 60 psi. That's going the wrong direction. Some of atf drained out of the carb so i'll probably clean it again and put it away for a later project.
Several years ago I noticed a Lawn Boy setting in garage across the alley from a place I mow in town. I always wanted to ask about it but there was never anybody around. Finally the other day when I went to mow there there were people there. So I went over to ask about it and they said they would let it go.
They couldn't get it started. It turned over ok so I took a chance on it for $40. It is a 1989 L21ZSNA, capstan drive, steel deck. It didn't have an air filter or cover and the carb was very dirty. The plug was fowled real bad and wasn't firing. I got good spark with a new plug. Compression showed 90 psi, but still would not start. I'm sure the carburetor is a mess. I have never had this type of shaft drive before so this will be a new experience for me. I'm going to start looking into this one in my spare time. It might work out ok or it might be a heap of scrap. Only time will. I just wanted to rescue this old mower and try to bring some new life to it. I have really enjoyed tinkering with these mowers this past year. I will probably have some more questions for you guys soon so put on your thinking caps. Thanks guys, over and out.
Jerry
I would say that if the compression got worse than there must be scoring or something else going on. If you could find a short block that would be the easiest fix to get the same mower running again. Good luck,
#11
V
viperv10
V
viperv10
Well I went ahead and took the case apart. I could not believe how clean the cylinder was inside. No scoring and very little carbon. Just a very little around the top end and it seems to be loose. So I ordered a new set of rings from Sohar's RCPW. They are here in Ohio and parts get here in a day or two.
The only things that I have put rings on was Stihl trimmers and blowers. They have little pins in the grooves to keep the rings in the right location. I noticed
that the lawn boy piston doesn't have the locator pins, so I took notice of the gap orientation for when I put the new ones in. I was wondering what keeps them from moving around on the piston or if it matters that much where the ring gaps go? Another question I had was have any of you put on new carburetors from newer F engines on one of these older F 100 engines? I didn't know if this would work or not, or if the CD coil would work from a newer F engine ? I was just kicking some things around in my mind to try to get this thing going again. Its kind of neat looking with the yellow shroud, wheels and hand grip. I think I will look up the on line lawn boy repair manual to gets some tips on installing the piston back into the cylinder. If anyone has any tips shout them out.
Thank you.
Jerry
The only things that I have put rings on was Stihl trimmers and blowers. They have little pins in the grooves to keep the rings in the right location. I noticed
that the lawn boy piston doesn't have the locator pins, so I took notice of the gap orientation for when I put the new ones in. I was wondering what keeps them from moving around on the piston or if it matters that much where the ring gaps go? Another question I had was have any of you put on new carburetors from newer F engines on one of these older F 100 engines? I didn't know if this would work or not, or if the CD coil would work from a newer F engine ? I was just kicking some things around in my mind to try to get this thing going again. Its kind of neat looking with the yellow shroud, wheels and hand grip. I think I will look up the on line lawn boy repair manual to gets some tips on installing the piston back into the cylinder. If anyone has any tips shout them out.
Thank you.
Jerry
#12
Dixieboy
Dixieboy
The rings are free to move. Orientate them with the gaps opposite each other. Put the gaps in the area that does not have the ports in the cylinder. The F-engine carbs have several variations but the plastic carbs will interchange. Some have a bleed hole from thru the mounting flange bored thru to the crank cavity. This is to help restarting, not sure if you see this on your carb. The piston also has a small/tiny hole thru the head, this is a compression release to make turning it over during starting easier. The hole is so small that when the engine starts and picks up rpm the flow of air thru the hole stops.
There must be reason for the low compression, how do the crank seals look?
There must be reason for the low compression, how do the crank seals look?
#13
J
jp1961
J
jp1961
Hi Jerry,
Do you plan on lightly honing the cylinder? If the factory cross hatch honing marks are gone, you may want to consider it. Before honing, I'd check the I.D. of the bore, to make sure it's within factory specs. I know, kind of hard to do with the F style jug as opposed to a Duraforce, but maybe a machine shop has I.D. bore gauges. They usually check the bore at the top middle and bottom. The rings are very brittle, don't try expanding them too much, you'll break them. I made a homemade ring compressor out of stainless steel strap stock, I have laying around. Oil the cylinder with motor oil before trying to install the piston.
Regards
Jeff
Do you plan on lightly honing the cylinder? If the factory cross hatch honing marks are gone, you may want to consider it. Before honing, I'd check the I.D. of the bore, to make sure it's within factory specs. I know, kind of hard to do with the F style jug as opposed to a Duraforce, but maybe a machine shop has I.D. bore gauges. They usually check the bore at the top middle and bottom. The rings are very brittle, don't try expanding them too much, you'll break them. I made a homemade ring compressor out of stainless steel strap stock, I have laying around. Oil the cylinder with motor oil before trying to install the piston.
Regards
Jeff
#14
V
viperv10
V
viperv10
Hey Dixieboy, thanks for your reply. I just put brand new crank seals in. They were Sten's and not OEM but I have used them before and they seemed to work ok. Maybe my compression tester is faulty. It is just a cheap one from China, I don;t know. I just recently got the mower for free and I used it 2 or 3 to do a little trim mowing. It ran good but it wore my arm out trying to start it.
Hey Jeff, thanks for chiming in. The bottom part of the cylinder still has the honing marks up almost up to the port holes then it seems to be just smooth. I don't have a cylinder hone so I wasn't really thinking about doing that. I have another F engine torn apart and it has a little bit of aluminum from the piston on the cylinder wall. A guy at a repair shop said it looked like it would be fine if I honed it out some and got a new piston. I might try some day but it is just a donor mower anyway. I think I will just try putting the new rings on and see if I can get the piston back in ok. If it runs that will be great, but if doesn't, it won't be the end of the world. Thanks again.
Jerry
Hey Jeff, thanks for chiming in. The bottom part of the cylinder still has the honing marks up almost up to the port holes then it seems to be just smooth. I don't have a cylinder hone so I wasn't really thinking about doing that. I have another F engine torn apart and it has a little bit of aluminum from the piston on the cylinder wall. A guy at a repair shop said it looked like it would be fine if I honed it out some and got a new piston. I might try some day but it is just a donor mower anyway. I think I will just try putting the new rings on and see if I can get the piston back in ok. If it runs that will be great, but if doesn't, it won't be the end of the world. Thanks again.
Jerry
#15
P
Phototone
P
Phototone
If your plastic or metal carb has a screw on the outside, and you screw it all the way in, of course you aren't going to get it to run. You are cutting off the fuel flow either partially (altitude adjustment screw) or completely. You need to open this screw up 1 to 2 turns and see how it runs, and you may need to make adjustments after that, closing it in a bit, if it runs too rich. 75 psi is not too low to start.
#16
V
viperv10
V
viperv10
Well Phototone you might be on to something. I thought it was screwed in tight when I took it out but I might be wrong. It didn't have spring to hold tension on it like most adjustment screws have. I just figured it was like the screw on the side of a Duraforce carburetor that gets turned in snug. On the Lawn Boy master parts look up page it is called a F screw carb, just a short little thing. When I get it put back together, I will back it out some and try that. Thanks for the tip.
Jerry
Jerry
#17
Dixieboy
Dixieboy
Just thinking out loud but I didn't see you mention the seal for the driveshaft. And also basics like reeds, crank key/flywheel, etc.
#18
V
viperv10
V
viperv10
Well I put the new rings on and got the piston in and had to go to work. At work I asked a guy who took small engine repair in high school about the purpose of honing and its advantages as to not honing. So today I went to Auto Zone and bought a $ 32 cylinder hone. I watched a couple videos on honing small engines
and went to work. I also noticed the the flywheel key was skewed a little bit. I remember reading that if the timing was off a little that could make the pull rope
jerk out of your hand. This mower would sure do that. So I ran into my local Toro dealer and got a new key. I cleaned out the cylinder, then oiled everything up
and put piston back in, cleaned off the mating surface and sealed her up with some Permatex anaerobic gasket maker. Now I will wait a few days to let the gasket material to set up before I try to start it.
Thanks for checking in Dixieboy. It is a straight push mower with no drive shaft, but I believe the flywheel key could have been part of the problem. We will see in a few days. Thanks guys.
Jerry
and went to work. I also noticed the the flywheel key was skewed a little bit. I remember reading that if the timing was off a little that could make the pull rope
jerk out of your hand. This mower would sure do that. So I ran into my local Toro dealer and got a new key. I cleaned out the cylinder, then oiled everything up
and put piston back in, cleaned off the mating surface and sealed her up with some Permatex anaerobic gasket maker. Now I will wait a few days to let the gasket material to set up before I try to start it.
Thanks for checking in Dixieboy. It is a straight push mower with no drive shaft, but I believe the flywheel key could have been part of the problem. We will see in a few days. Thanks guys.
Jerry
#19
J
jp1961
J
jp1961
Hi Jerry,
What type hone did you use? The 3 arm type or ball end hone? Let us know what the compression reading is.
Regards
Jeff
What type hone did you use? The 3 arm type or ball end hone? Let us know what the compression reading is.
Regards
Jeff
#20
V
viperv10
V
viperv10
Well its been a busy week, lots of overtime and no time to work in the garage. I finally got the engine all put together again and it won't fire up.
Jeff I got a three arm hone with medium grit stones. It is testing in the low 80's. The spark checker shows a little spark but it must not be enough. It won't even fire on starting fluid. I'm a little disappointed. I was going to try a new cd coil but I didn't have the right one for this mower. I was reading that the 78 to 82 F series engines take a different coil than the newer ones. So I ordered one and it should be here by the weekend. Hope this does the trick. I'm about out of ideas. I have a brand new cj 14 plug waiting to go in too. Well fellows its bed time and the sand man is calling me. Over and out.
Jerry
Jeff I got a three arm hone with medium grit stones. It is testing in the low 80's. The spark checker shows a little spark but it must not be enough. It won't even fire on starting fluid. I'm a little disappointed. I was going to try a new cd coil but I didn't have the right one for this mower. I was reading that the 78 to 82 F series engines take a different coil than the newer ones. So I ordered one and it should be here by the weekend. Hope this does the trick. I'm about out of ideas. I have a brand new cj 14 plug waiting to go in too. Well fellows its bed time and the sand man is calling me. Over and out.
Jerry
#21
J
jp1961
J
jp1961
Hi Jerry,
You're testing the compression with the choke open, right? You have 20 more PSI than before, I wouldn't be too disappointed. You'll get her running.
The only top end restore I've done was on a 3hp Tanaka outboard. I replaced the piston and rings, but the cylinder jug is no longer available. I did lightly hone the cylinder with a 3 arm hone purchased at NAPA, actually designed for brake cylinders. It has about 103 PSI after the new piston and ring, but Mr. Brainiack here didn't do a compression test before, so I'm not sure how much (if anything) I helped the compression.
Regards
Jeff
You're testing the compression with the choke open, right? You have 20 more PSI than before, I wouldn't be too disappointed. You'll get her running.
The only top end restore I've done was on a 3hp Tanaka outboard. I replaced the piston and rings, but the cylinder jug is no longer available. I did lightly hone the cylinder with a 3 arm hone purchased at NAPA, actually designed for brake cylinders. It has about 103 PSI after the new piston and ring, but Mr. Brainiack here didn't do a compression test before, so I'm not sure how much (if anything) I helped the compression.
Regards
Jeff
#22
V
viperv10
V
viperv10
Oh the sweet smell of success and 2 stroke exhaust. Saturday evening after work I got back to it and put a new coil and spark plug in the old R7070.
After about 5 pulls it came back to life. I didn't let it run too long at 10:00 P.M. to upset the neighbors, but I shut it off and restarted it with one or two pulls.
That's a good sign. I also backed the little screw out a couple turns on the carburetor. I'll try to fine tune it tomorrow.
Jeff I don't think this carb really has a choke. It has a primer bulb and the throttle lever just above the air cleaner for low or high speed. No cables. A very simple engine. Thanks for you input.
Jerry
After about 5 pulls it came back to life. I didn't let it run too long at 10:00 P.M. to upset the neighbors, but I shut it off and restarted it with one or two pulls.
That's a good sign. I also backed the little screw out a couple turns on the carburetor. I'll try to fine tune it tomorrow.
Jeff I don't think this carb really has a choke. It has a primer bulb and the throttle lever just above the air cleaner for low or high speed. No cables. A very simple engine. Thanks for you input.
Jerry
#23
V
viperv10
V
viperv10
Hey guys , here is an interesting story I forgot to tell you. Last week I was talking to the guy I got this R7070 from. He said that when he first got it, it would run wide open and way too fast. He told me that he looked at the carburetor and said that there was no butterfly disc in it. He told me he had a different plastic carb and put it on. Well I told him that I know where that little disc went to. When I cracked the engine apart the other day, I found a piece of what looked to be a little brass tag or something inside the intake of the engine. I thought to myself, how did this get in here? So I told Darin that it must have come loose and got sucked into the engine. It was folded and bent up but now I can tell that that was what it is. It is hard to believe something that big could go through the reed valves and not damage them but they looked perfect. We both had a good laugh about it. I have noticed that some are held in with a little screw and some just slide into a little slot on the shaft held in with little notches. I could make out the little notches on the damaged throttle disc. Well I just wanted to share this odd story with you.
Jerry
Jerry
#24
Dixieboy
Dixieboy
Love that little story, and yes the plastic carb throttle plates just clicked into place.