MuncyBob
Platinum Member
Sounds like there is no need for the pics of my 422 carb, etc. But this is getting interesting!! That's one thing that is great about this forum...read & learn! /forums/images/graemlins/grin.gif
Vaporlock revisited
- Thread starter Phils
- Start date
- Views: 17439
- Joined
- Aug 31, 2001
- Messages
- 66,098
- Location
- South Bend, Indiana (near)
- Tractor
- Power Trac PT425 2001 Model Year
Does the carb require pressurized fuel to fill the bowl? I'm not that familiar with small gas engines that have fuel pumps. None of my lawn mowers did. Heck, I don't even know if my Kohler has one. I'll have to look, now. I think the bottom of the tank is lower than the carb, so there must be a pump somewhere to get it up to the carb? Again, I'll have to look.
That's the trouble with this Power Trac forum... it keeps making me look at stuff! /forums/images/graemlins/tongue.gif
That's the trouble with this Power Trac forum... it keeps making me look at stuff! /forums/images/graemlins/tongue.gif
SnowRidge
Elite Member
The Kohler has a pump. It is mounted on the RH valve cover.
ClintBlake
Bronze Member
I had the same symptoms on my 422. It would start and run fine for a while and then start surging and sputtering until it died. Adding 1/3 to 1/2 choke would keep it running.
I pulled the solenoid needle valve on the side of the carburetor that shuts off fuel when the key is turned off. There was a small piece of brown fiber (looked like filter paper) in where the needle goes. After cleaning that out, it ran fine.
I pulled the solenoid needle valve on the side of the carburetor that shuts off fuel when the key is turned off. There was a small piece of brown fiber (looked like filter paper) in where the needle goes. After cleaning that out, it ran fine.
- Joined
- Aug 31, 2001
- Messages
- 66,098
- Location
- South Bend, Indiana (near)
- Tractor
- Power Trac PT425 2001 Model Year
<font color="blue"> The Kohler has a pump. It is mounted on the RH valve cover. </font>
Thanks! I guess that would explain the fuel line going to my valve cover as it shows in this picture. According to the manual, I have a mechanical fuel pump. In all honesty, I thought it was part of the low oil shutoff system. Turns out, that is not how things work. There is no fuel shutoff associated with the low oil sensor. There is an electric switch under the breather. From the Kohler manual:
<font color="green"> "On stationary or unattended applications (pumps,
generators, etc.), the pressure switch can be used to
ground the ignition module to stop the engine. On
vehicular applications (lawn tractors, mowers, etc.) the
pressure switch can only be used to activate a “low oil”
warning light or signal." </font>
So apparantly it is not hooked up to do either from the factory, according to the manual. But that is for another discussion. /forums/images/graemlins/laugh.gif
The manual also states that the motor can be run without a fuel pump if the outlet of the fuel tank is higher than the inlet of the carb. I suppose as long as the level of the fuel in the tank is higher than the inlet of the carb, that would accomplish the same thing, so we could still eliminate the fuel pump from the system to see if the problem is with his carb or his fuel line.
Thanks! I guess that would explain the fuel line going to my valve cover as it shows in this picture. According to the manual, I have a mechanical fuel pump. In all honesty, I thought it was part of the low oil shutoff system. Turns out, that is not how things work. There is no fuel shutoff associated with the low oil sensor. There is an electric switch under the breather. From the Kohler manual:
<font color="green"> "On stationary or unattended applications (pumps,
generators, etc.), the pressure switch can be used to
ground the ignition module to stop the engine. On
vehicular applications (lawn tractors, mowers, etc.) the
pressure switch can only be used to activate a “low oil”
warning light or signal." </font>
So apparantly it is not hooked up to do either from the factory, according to the manual. But that is for another discussion. /forums/images/graemlins/laugh.gif
The manual also states that the motor can be run without a fuel pump if the outlet of the fuel tank is higher than the inlet of the carb. I suppose as long as the level of the fuel in the tank is higher than the inlet of the carb, that would accomplish the same thing, so we could still eliminate the fuel pump from the system to see if the problem is with his carb or his fuel line.
Keoke
Gold Member
Gravy, from the looks of Moss Road pic gravity flow to this carb is a long shot. It takes 2.3 feet of fall to generate 1 psi of pressure. In looking at the pic (a guess at best) it seems that the tank bottom is about even with carb. Most small carbs with your sized engine are happy with 2 to 4 psi at carb inlet. At high inlet psi there is a chance that the float will not put enough pressure on needle to stop fuel flow at idle. All of this depends on what is called the "wet area" of float. In short, small fuel bowls require low pressures and wide or deep bowls can take higher pressures.
In looking at the pic I feel for you guys. Having the carb so close to that muffler was not smart. With the muffler so close to carb there is a possibilty that fuel in the bowl it's self is boiling and causing starvation problems.
The fuel pump on the rocker cover may be of the "crankcase pulse" design. These pumps use crankcase pulses caused by the pistons going up and down to work a diaphragm to move the fuel along. Or it's possible that it is conventional pump running off the rocker arm or cam if it's an overhead cam engine.
If it is the crankcase pluse type then you would be better off going to a pluse type (self priming) elec pump. Watch the pressure thing when choosing the pump. You can also buy pressure regulators if needed to control a high pressure pump. Try without regulator first, if float needle holds at idle then you are ok if not use regulator.
The material used on cars as an insulator between carb and manifold is called a "phenolic" insulator and is made from phenol. However, in looking at you pic, the more you space the carb out the closer you get to the muffler. Thats a **** of a choice, none the less, there should be at least an insulator gskt between carb and manifold to reduce engine heat conductivity between carb and manifold.
One more thing, before screwing new elbow into tank bottom,
I would add a short standpipe (1/2" above tank floor) to keep the bottom junk out of your gas line.
lots of luck,
In looking at the pic I feel for you guys. Having the carb so close to that muffler was not smart. With the muffler so close to carb there is a possibilty that fuel in the bowl it's self is boiling and causing starvation problems.
The fuel pump on the rocker cover may be of the "crankcase pulse" design. These pumps use crankcase pulses caused by the pistons going up and down to work a diaphragm to move the fuel along. Or it's possible that it is conventional pump running off the rocker arm or cam if it's an overhead cam engine.
If it is the crankcase pluse type then you would be better off going to a pluse type (self priming) elec pump. Watch the pressure thing when choosing the pump. You can also buy pressure regulators if needed to control a high pressure pump. Try without regulator first, if float needle holds at idle then you are ok if not use regulator.
The material used on cars as an insulator between carb and manifold is called a "phenolic" insulator and is made from phenol. However, in looking at you pic, the more you space the carb out the closer you get to the muffler. Thats a **** of a choice, none the less, there should be at least an insulator gskt between carb and manifold to reduce engine heat conductivity between carb and manifold.
One more thing, before screwing new elbow into tank bottom,
I would add a short standpipe (1/2" above tank floor) to keep the bottom junk out of your gas line.
lots of luck,
- Joined
- Aug 31, 2001
- Messages
- 66,098
- Location
- South Bend, Indiana (near)
- Tractor
- Power Trac PT425 2001 Model Year
Remember, I have a Kohler engine and he has a Robbin. There is probably a difference in the setup.
OP
Phils
Platinum Member
There is DEFINITELY a difference in the setup between engine brands!
The Kohler exhausts out the back, the Robin out the front then to the side then toward the back then down. It's that transit down the side that parallels the fuel line. The tub gets hot, and the fuel hose an inch or less from the tub then gets hot too. I'm convinced that is where the problem is rather than in the carb bowl. I also didn't notice an electric fuel cutoff solenoid at the carb inlet on mine, although it may be elsewhere on the carb and just not at the inlet.
Phil
The Kohler exhausts out the back, the Robin out the front then to the side then toward the back then down. It's that transit down the side that parallels the fuel line. The tub gets hot, and the fuel hose an inch or less from the tub then gets hot too. I'm convinced that is where the problem is rather than in the carb bowl. I also didn't notice an electric fuel cutoff solenoid at the carb inlet on mine, although it may be elsewhere on the carb and just not at the inlet.
Phil
SnowRidge
Elite Member
Gravity fed high powered motorcycles have been running fine for years with a foot or less of head, so I doubt that even 1 PSI is really needed.
No need to substitute **** for the word Hobsons, which is what I'm sure you meant. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
No need to substitute **** for the word Hobsons, which is what I'm sure you meant. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
SnowRidge
Elite Member
Some Kohlers exhaust out the right side. I got rid of my PT built right side 'tank' muffler and replaced it with a rear exhaust Kohler muffler, just like the one that came on Moss's PT.
Keoke
Gold Member
Snowridge, you are right that mortorcycles and almost all small engines run on less then 1 psi at carb inlet. Also, there is no need to over design a system if it's not needed.
However, the higher the pressure in the fuel line the less likely it is to vapor lock. One psi raises the boiling point of water almost 3 degrees but it raises the boiling point of gasoline at lot higher depending on it's volatility.
Hey Snowridge, the word that got beeped out of my post is the one that describes where the fires burn down below and most likely where I will end up. Minus the virgins of course.
Next time I will use the word "HECK".
take care and have a good one!!!
However, the higher the pressure in the fuel line the less likely it is to vapor lock. One psi raises the boiling point of water almost 3 degrees but it raises the boiling point of gasoline at lot higher depending on it's volatility.
Hey Snowridge, the word that got beeped out of my post is the one that describes where the fires burn down below and most likely where I will end up. Minus the virgins of course.
Next time I will use the word "HECK".
take care and have a good one!!!
- Joined
- Aug 31, 2001
- Messages
- 66,098
- Location
- South Bend, Indiana (near)
- Tractor
- Power Trac PT425 2001 Model Year
I have heard that folks will be visited by the spector of dimness before they are sent to heck. Gosh! /forums/images/graemlins/tongue.gif /forums/images/graemlins/wink.gif
Gravy
Platinum Member
Keoke,
First, let me welcome you to the forum. You're already contributing useful stuff. Based on my experience of 20+years as an auto mechanic specializing in driveability and electrical/electronic diagnosis, I agree with all the points you make.
Cutting to the chase, I have verified that the problem with my 425 was simple fuel starvation. After cleaning the tank and lines, replacing the restrictive factory tank outlet elbow with a straight brass hose nipple, and relocating the pulse fuel pump to the fuel tank supports (well away from the exhaust), I still had the problem. I then disconnected the fuel hose from the carb and cranked the engine. Virtually no flow I tried MR's suggestion of straight gravity feed with the same results. Since the bottom of the tank is below the carb inlet, I wasn't very surprised.
I then installed an elecrtic fuel pump that I had laying around, bypassing the original pump. I have no idea what the pressure and flow specs are. I had no way to test the pressure today at the job site I jumpered it straight to the battery and got enough flow to run a Chevy 350. I connected the hose to the carb and started up. Problem solved! I ran for an hour or more at full throttle with no problems.
Before I commit to properly installing the electric fuel pump with the attendant relay, fuse, and bracketry, I plan to disassemble and inspect the OE pump. It's possible that it just needs to be cleaned. I will also test the fuel pressure. I had no signs of flooding, but if I find much over 5-7psi, I'll take appropriate measures.
That's where I'm at for now. I'll be working on it further this weekend. If I find anything new, I'll pass it on.
Gravy
First, let me welcome you to the forum. You're already contributing useful stuff. Based on my experience of 20+years as an auto mechanic specializing in driveability and electrical/electronic diagnosis, I agree with all the points you make.
Cutting to the chase, I have verified that the problem with my 425 was simple fuel starvation. After cleaning the tank and lines, replacing the restrictive factory tank outlet elbow with a straight brass hose nipple, and relocating the pulse fuel pump to the fuel tank supports (well away from the exhaust), I still had the problem. I then disconnected the fuel hose from the carb and cranked the engine. Virtually no flow I tried MR's suggestion of straight gravity feed with the same results. Since the bottom of the tank is below the carb inlet, I wasn't very surprised.
I then installed an elecrtic fuel pump that I had laying around, bypassing the original pump. I have no idea what the pressure and flow specs are. I had no way to test the pressure today at the job site I jumpered it straight to the battery and got enough flow to run a Chevy 350. I connected the hose to the carb and started up. Problem solved! I ran for an hour or more at full throttle with no problems.
Before I commit to properly installing the electric fuel pump with the attendant relay, fuse, and bracketry, I plan to disassemble and inspect the OE pump. It's possible that it just needs to be cleaned. I will also test the fuel pressure. I had no signs of flooding, but if I find much over 5-7psi, I'll take appropriate measures.
That's where I'm at for now. I'll be working on it further this weekend. If I find anything new, I'll pass it on.
Gravy
- Joined
- Aug 31, 2001
- Messages
- 66,098
- Location
- South Bend, Indiana (near)
- Tractor
- Power Trac PT425 2001 Model Year
Good job of sticking with it! /forums/images/graemlins/laugh.gif
Keoke
Gold Member
( quote) Keoke,
First, let me welcome you to the forum. You're already contributing useful stuff. Based on my experience of 20+years as an auto mechanic specializing in driveability and electrical/electronic diagnosis, I agree with all the points you make. (end quote)
Gravy, based on my 34 yrs of full time teaching auto tech at a Junior College; let me say that you look like a super wrench to me.
Have a nice weekend,
First, let me welcome you to the forum. You're already contributing useful stuff. Based on my experience of 20+years as an auto mechanic specializing in driveability and electrical/electronic diagnosis, I agree with all the points you make. (end quote)
Gravy, based on my 34 yrs of full time teaching auto tech at a Junior College; let me say that you look like a super wrench to me.
Have a nice weekend,
J_J
Super Star Member
- Joined
- Sep 6, 2003
- Messages
- 18,973
- Location
- JACKSONVILLE, FL
- Tractor
- Power-Trac 1445, KUBOTA B-9200HST
You must have overlooked my earlier post about a fuel gage at the carb. It's hind site now but it could have saved you a lot of frustration. Just don't let that electric fuel pump overpower the float in the carb, and flood the engine. Your original fuel pump might only need a new diaphragm, or replace the factory unit.
Gravy
Platinum Member
JJ,
I didn't overlook your post. You had a good idea - I just forgot to bring a pressure gauge with me to the jobsite yesterday, so I couldn't take your advice then. Now that I've got the machine back home, I plan to check the pressure, and disassemble & inspect the OE pump. Since it ran well for over an hour with the electric pump, I'm pretty confident that the pressure isn't excessive, but I'd prefer to run the stock pump and save the electrons for the battery.
Thanks,
Dave
I didn't overlook your post. You had a good idea - I just forgot to bring a pressure gauge with me to the jobsite yesterday, so I couldn't take your advice then. Now that I've got the machine back home, I plan to check the pressure, and disassemble & inspect the OE pump. Since it ran well for over an hour with the electric pump, I'm pretty confident that the pressure isn't excessive, but I'd prefer to run the stock pump and save the electrons for the battery.
Thanks,
Dave
Keoke
Gold Member
Gravy, here is a site with a low pressure pump at a decent price.
Click here for link.
cheers,
EDIT: Shortened long link.
Click here for link.
cheers,
EDIT: Shortened long link.
Gravy
Platinum Member
Latest update:
I disassembled the OE pump and found oil behind the diaphragm. IIRC, JackRobin has said this results from a high oil level and/or operating a lot on steep slopes. Since much of my work is on fairly steep slopes, I don't have much confidence that it won't happen again.
I tested the fuel pressure from the electric pump I used for testing. It puts out 4psi, and pulls 1.1 amps, so I feel comfortable using it in a permanent installation. I am leaving the OE pump in place so I can switch back and forth just by swapping hoses. That way, I should always have a backup.
I still don't have a good explanation as to why the OE fuel pump worked fine for the first 20 minutes or so, then, lost virtually all flow (I did test that by pulling the fuel hose at the carb and cranking the engine - virtually zero flow when hot, so I knew it didn't really matter that I'd forgotten my pressure gauge).
Thanks to all for all the suggestions. Now I need to fix my leaking quick-attach cylinder /forums/images/graemlins/mad.gif
Gravy
I disassembled the OE pump and found oil behind the diaphragm. IIRC, JackRobin has said this results from a high oil level and/or operating a lot on steep slopes. Since much of my work is on fairly steep slopes, I don't have much confidence that it won't happen again.
I tested the fuel pressure from the electric pump I used for testing. It puts out 4psi, and pulls 1.1 amps, so I feel comfortable using it in a permanent installation. I am leaving the OE pump in place so I can switch back and forth just by swapping hoses. That way, I should always have a backup.
I still don't have a good explanation as to why the OE fuel pump worked fine for the first 20 minutes or so, then, lost virtually all flow (I did test that by pulling the fuel hose at the carb and cranking the engine - virtually zero flow when hot, so I knew it didn't really matter that I'd forgotten my pressure gauge).
Thanks to all for all the suggestions. Now I need to fix my leaking quick-attach cylinder /forums/images/graemlins/mad.gif
Gravy
Keoke
Gold Member
Gravy, if OEM pump is of the crankcase type (only a guess) then don't expect much from this pump while turning engine over with the starter. These guys need rapid pulses on the back side of the diaphragm to move the front side of the diaphragm and get the fuel moving.
Bottom line, it looks like the electric pump is the sure way to go for a once and for all repair.
Sometimes the OEM design simply cannot be repaired and a design change, such as you did, is in order.
Unfortunately, this happens often when a machine comes with various OEM engines, not all of which went through hard field testing in their individual configurations.
take care,
Bottom line, it looks like the electric pump is the sure way to go for a once and for all repair.
Sometimes the OEM design simply cannot be repaired and a design change, such as you did, is in order.
Unfortunately, this happens often when a machine comes with various OEM engines, not all of which went through hard field testing in their individual configurations.
take care,
