My john deere cs40 was hard to start, wouldn't idle, and didnt run well at all. I put new fuel filter and fuel line on this spring because of crack in line, rebuilt the carb while it was off took off muffler and looked at cylinder, it was scored pretty good, so I decided to try to rebuild it. It is my first time rebuilding a carb or piston and rings. It has a walbro wa carb and I read on online pdf about it first and think I got it right, only question is if on the pump side the gasket goes on then the diaphram against the carb body? Thats how I put it. Before I took it down I had about 95-100 psi compression. I cleaned the cylinder up with a little acid and some scotch brite pad, as well as 320 grit wet/dry paper. I couldnt get all the vertical score lines off the exhaust side the intake side looked good to me but im no professional. I actually just stopped because I didnt want to sand too much in the bore. Put it all back together with new piston and rings, it had no base gasket so I used red rtv sealant. Looks like what it had when I took it apart the first time. Pulled on it to start it noticed a big difference in felt pulling compression. But no fuel will pull in from the tank the line is dry. I checked that the line is clear I can blow into tank, tank vent is clean, pulse port from cylinder into carb is clean. I sprayed carb cleaner into throat of carb, wont hit on it, I sprayed it into spark plug hole on top of piston still wont hit at all. New spark plug and I have spark when I pull it over. Why would it not hit on carb cleaner? I did not remove flywheel from crank or disturb the distance to the ignition module. I also rechecked compression and only getting 90 psi, I would think it would be more on new rings as the pull rope pulls harder now. any help appreciated thanks
need advice john deere cs40 wont start after carb rebuild and new piston and rings
- Thread starter tmock84
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fearofpavement
Trying them all
Don't use carb cleaner to try to get the saw to start on. NO NO NO!
Use a bit of gas/oil mix. I use an eye dropper.
1. Double check the carb assembly as it is easy to get the gasket diaphragm order mixed up.
2. Try a different spark plug
3. If the saw won't "pop" on the mix you put into the carb then either you're not getting spark (at the correct time) or it is flooded.
So, if you have compression and spark it should at least pop even if you have the carb off the saw. So if it won't pop you have problems other than the carb. If it pops but doesn't run more than a few seconds, then look to the carb, fuel lines and air leaks.
Make sure the switch is turned on. lol
Use a bit of gas/oil mix. I use an eye dropper.
1. Double check the carb assembly as it is easy to get the gasket diaphragm order mixed up.
2. Try a different spark plug
3. If the saw won't "pop" on the mix you put into the carb then either you're not getting spark (at the correct time) or it is flooded.
So, if you have compression and spark it should at least pop even if you have the carb off the saw. So if it won't pop you have problems other than the carb. If it pops but doesn't run more than a few seconds, then look to the carb, fuel lines and air leaks.
Make sure the switch is turned on. lol
ok i got it to hit or pop on fuel oil mix dropped into carb opening. But still not pulling fuel from tank, so I will go over the carb and lines again tomorrow. If the crankcase wont hold proper pressure could it be causing it to not get fuel into the line and carb? Also do I need more than 90 psi compression?
Metering side; Gasket goes against the carb body followed by the diaphragm and then the cover with 4 screws.
Pump side; Diaphragm goes against the carb body followed by the gasket and then the cover with one screw.
Pump side; Diaphragm goes against the carb body followed by the gasket and then the cover with one screw.
o8f150
Tree Freak
90 psi is real low for that saw
gmax
Addicted to ArboristSite
Only 90 psi with a new piston/rings? that cylinder must be bad.
fearofpavement
Trying them all
Or it could be the gauge. Check a different saw to see what kind of compression reading you get on that. If it is actually 90psi, that's not enough.
new info on john deere cs40 rebuild
I checked my compression gauge on another saw it has good compression (160 psi If i remember right) I took motor off again and pressure and vac checked my bottom end it seem to hold alright for a couple min. It was dropping but I had a small leak around intake didn't get sealed perfectly. Bottom end showed no bubbles with water. So I checked carb again, and pressure checked it for pop off and seat pressure, It seem to act fine. I made sure that the impulse hole was clear all the way from cylinder into carb. Put the saw back together and got 120 psi compression this time, not sure what changed unless rings are setting better. So I put a vacuum gauge on the end of the fuel line in the tank to see if the needle would move when I cranked on it, and got nothing. It acts like it has no impulse at all no needle movement what so ever? I am stumped. I must be missing something or don't fully understand something, anyone see anything wrong with what I'm doing or do you think this is a valid test for impulse? Also why am I not getting any pull from tank?
I checked my compression gauge on another saw it has good compression (160 psi If i remember right) I took motor off again and pressure and vac checked my bottom end it seem to hold alright for a couple min. It was dropping but I had a small leak around intake didn't get sealed perfectly. Bottom end showed no bubbles with water. So I checked carb again, and pressure checked it for pop off and seat pressure, It seem to act fine. I made sure that the impulse hole was clear all the way from cylinder into carb. Put the saw back together and got 120 psi compression this time, not sure what changed unless rings are setting better. So I put a vacuum gauge on the end of the fuel line in the tank to see if the needle would move when I cranked on it, and got nothing. It acts like it has no impulse at all no needle movement what so ever? I am stumped. I must be missing something or don't fully understand something, anyone see anything wrong with what I'm doing or do you think this is a valid test for impulse? Also why am I not getting any pull from tank?
Well I went back and checked, found that I didn't put the carb nuts back on when I put it on so I guess it was leaking around the intake seal. I got it to hold a small vacuum at the fuel line this time, filled it up with fresh gas, pulled it a few times and it started. I guess just getting this all typed out helped me think it through and I got it.
Good job so far
Did you replace the pump side of the carb correctly like "rmh3481" said?
How does this saw do now?
Do you still use it sir?
This saw is running fine last time I started it which was before winter. It has been sitting (empty) in the shed I have not used it in a while, or plan on it.Good job so far
Did you replace the pump side of the carb correctly like "rmh3481" said?
How does this saw do now?
Do you still use it sir?
well..
if it happens that you don't need / want it, or that you've found a replacement, will you remember me?
if it happens that you don't need / want it, or that you've found a replacement, will you remember me?
RSD
ArboristSite Lurker
This thread could inspire me to work on mine...although this was thread was from 5 years ago....wonder if carb parts are even available anymore.
Carb kits are easily found for almost all carbs made since the early 50`s you just have to know which company made them, like Tillotson, Walbro or Zama and then the model number off the carb body. If this info is known then a carb rebuild kit is still available either online or at a small engine shop.
