M-700 carb question

[AutoScott]

I have a 1975 M-700 with a VH4D gas engine. I've gone through it thoroughly by doing a tune up and carb rebuild. Also flushing out the fuel tank and installing an electric pump (3-5 psi). It pulls great vacuum at idle (21"). My problem is that when I'm really bouncing around working, it will stumble badly but then pick back up like its flooding. I set the floats to specs when I rebuilt the carb. It has the updraft Zenith carb. Is this just the norm for carb engines or is there a solution out there? Thanks guys!

 

[Tazza]

Could it be a govenor adjustment?
If it's not adjusted right, it could cause it to bog down. Not sure how it's adjusted on the model engine you have though.

 

[flyerdan]

Could it be a govenor adjustment?
If it's not adjusted right, it could cause it to bog down. Not sure how it's adjusted on the model engine you have though.

They are very particular about fuel pressure, try putting a regulator before the carb and set it for 1.5 psi. Somehow this carb has a tendency to flood at relatively low pressures.

 

[AutoScott]

They are very particular about fuel pressure, try putting a regulator before the carb and set it for 1.5 psi. Somehow this carb has a tendency to flood at relatively low pressures.

Well I've been trying the things you guys brought up, but no closer to a solution. The odd thing is that when I first start working with the bobcat, I can bounce around without a problem. But after I've been working it for over 30 minutes if I bounce around it acts like its flooding. It seems to be worse when I'm at a low load on the engine. If I'm really pulling a load on her it doesn't seem to effect her as bad.

 

[Tazza]

Well I've been trying the things you guys brought up, but no closer to a solution. The odd thing is that when I first start working with the bobcat, I can bounce around without a problem. But after I've been working it for over 30 minutes if I bounce around it acts like its flooding. It seems to be worse when I'm at a low load on the engine. If I'm really pulling a load on her it doesn't seem to effect her as bad.

It still sounds like it's a float issue. The lower the load, the less fuel it needs, so it may be over filling and getting sucked in, flooding it.
How is the air filter? I have found that when the filter is restricted, it sort of acts like having the choke on. The extra vacuum pulls more fuel in through the jets and into the engine.

 

[6brnorma]

It still sounds like it's a float issue. The lower the load, the less fuel it needs, so it may be over filling and getting sucked in, flooding it.
How is the air filter? I have found that when the filter is restricted, it sort of acts like having the choke on. The extra vacuum pulls more fuel in through the jets and into the engine.

My opinion……I deal with this engine a lot. I think it is one of two things…….I do not think it needs a pressure regulator. The carb calls for 2 to 3 PSI…..you say you have put an electric fuel pump on which I believe is the only route to go, however, not all electric fuel pumps are created equal. The only pump I will use(and I have used several) is the NAPA pt#P60504 (which if I recall correctly is a Carter with the same part number)……..or………like Tazza has said, probably float issue. You said you used the "recommended" setting……I have seen a couple of different "recommended" settings depending on the kit. I always go with the 1 5/32 setting on all of my rebuilds and never have a problem. Hope this helps.

 

[6brnorma]

My opinion……I deal with this engine a lot. I think it is one of two things…….I do not think it needs a pressure regulator. The carb calls for 2 to 3 PSI…..you say you have put an electric fuel pump on which I believe is the only route to go, however, not all electric fuel pumps are created equal. The only pump I will use(and I have used several) is the NAPA pt#P60504 (which if I recall correctly is a Carter with the same part number)……..or………like Tazza has said, probably float issue. You said you used the "recommended" setting……I have seen a couple of different "recommended" settings depending on the kit. I always go with the 1 5/32 setting on all of my rebuilds and never have a problem. Hope this helps.

"IF" I was a betting man and you did not use the Carter fuel pump……….That would be my first $35.00 amazon purchase. Again……….JMHO

 

[AutoScott]

"IF" I was a betting man and you did not use the Carter fuel pump……….That would be my first $35.00 amazon purchase. Again……….JMHO

I'm almost positive that's the NAPA pump I got. I got the part number a while back from this forum. I will definitely check the floats again. What is the measurement you referred to? This is my first updraft carb that I've messed with, but I didn't think they could flood from bouncing around. But I really appreciate all your guys great advice!!

 

[AutoScott]

I'm almost positive that's the NAPA pump I got. I got the part number a while back from this forum. I will definitely check the floats again. What is the measurement you referred to? This is my first updraft carb that I've messed with, but I didn't think they could flood from bouncing around. But I really appreciate all your guys great advice!!

The measurement I was reffering to was the 1 5/32. Also where could I get the pressure regulator you mentioned?

 

[6brnorma]

The measurement I was reffering to was the 1 5/32. Also where could I get the pressure regulator you mentioned?

Fuel pump #60504 provides about 3 PSI…….that Zenith carburetor requires 2-3 PSI……I have never used, nor do I believe you need a regulator (My opinion) The 1 5/32 is the measurement/setting for the floats……I have bought a number of different 'rebuild kits' through the years and have found three different "recommended" settings in those kits. When I use anything but the 1 5/32 measurement I have had symptoms similar to what you are currently experiencing. I will say that when the setting was wrong in the float, the symptoms were immediately noticeable, not later when bouncing around. That is why I felt it was in your pump as those are classic symptoms for the fuel pump. Carter makes two pumps that look identical but one produces about 10 PSI (IIRC) and will cause the same symptoms.

 

[stroklund]

Fuel pump #60504 provides about 3 PSI…….that Zenith carburetor requires 2-3 PSI……I have never used, nor do I believe you need a regulator (My opinion) The 1 5/32 is the measurement/setting for the floats……I have bought a number of different 'rebuild kits' through the years and have found three different "recommended" settings in those kits. When I use anything but the 1 5/32 measurement I have had symptoms similar to what you are currently experiencing. I will say that when the setting was wrong in the float, the symptoms were immediately noticeable, not later when bouncing around. That is why I felt it was in your pump as those are classic symptoms for the fuel pump. Carter makes two pumps that look identical but one produces about 10 PSI (IIRC) and will cause the same symptoms.

my 700 does this also im on fuel pump #4 now. I mounted it on the bolt that sticks out on the right hand side about even with the top of the engine and now when I bounce the machine or go up an incline it wants to bog down and stall. it never did this before with the other pumps and I had them mounted to the side of the engine but im thinking those ones died due to heat and vibration.

 

[6brnorma]

my 700 does this also im on fuel pump #4 now. I mounted it on the bolt that sticks out on the right hand side about even with the top of the engine and now when I bounce the machine or go up an incline it wants to bog down and stall. it never did this before with the other pumps and I had them mounted to the side of the engine but im thinking those ones died due to heat and vibration.

I mount my pumps to the side of the machine with rubber (not metal) fuel line leading to the carb…….there is no way those pumps will hold up to the heat generated by the Wisconsin air-cooled engine mounted directly to the engine. Especially in the desert where we work.

 

[6brnorma]

I mount my pumps to the side of the machine with rubber (not metal) fuel line leading to the carb…….there is no way those pumps will hold up to the heat generated by the Wisconsin air-cooled engine mounted directly to the engine. Especially in the desert where we work.

Is that the Carter pump?

 

[stroklund]

Is that the Carter pump?

I put one on from CARQUEST part number E8012S some current research has provide me with information its Brand: Airtex Manufacturer's Part Number: E8012S Free Flow Rate: 30 gph Maximum Pressure (psi): 9 psi Inlet Size: 5/16 in. Inlet Quantity: One Inlet Attachment: Hose barb Outlet Size: 5/16 in. Outlet Quantity: One Outlet Attachment: Hose barb Notes: Designed for 12 volt carbureted applications. not sure how to add photos to this post I have a picture of where I have it mounted at

 

[6brnorma]

I put one on from CARQUEST part number E8012S some current research has provide me with information its Brand: Airtex Manufacturer's Part Number: E8012S Free Flow Rate: 30 gph Maximum Pressure (psi): 9 psi Inlet Size: 5/16 in. Inlet Quantity: One Inlet Attachment: Hose barb Outlet Size: 5/16 in. Outlet Quantity: One Outlet Attachment: Hose barb Notes: Designed for 12 volt carbureted applications. not sure how to add photos to this post I have a picture of where I have it mounted at

Flow rate is fine, however I believe the PSI is about 2 1/2 times what that carb can handle. Carter has two carbs that look identical and I once accidentally put the 9 PSI Carter on and had the same issues you are experiencing.
As a side note……I have used several brands and not had much luck with them as they simply couldn't handle the heat generated in the engine compartment by the Wisconsin engine.

 

[stroklund]

Flow rate is fine, however I believe the PSI is about 2 1/2 times what that carb can handle. Carter has two carbs that look identical and I once accidentally put the 9 PSI Carter on and had the same issues you are experiencing.
As a side note……I have used several brands and not had much luck with them as they simply couldn't handle the heat generated in the engine compartment by the Wisconsin engine.

thinking ill just get a psi regulator and dial it down a bit.

 

[6brnorma]

thinking ill just get a psi regulator and dial it down a bit.

I meant to say "Carter has two pumps"……..not carbs.