Carburetor trouble

[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

 

[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?

 

[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

 

[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

 

[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.

 

[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

 

[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.

 

[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

 

[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

 

[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