Bobcat 632 hard to start when hot

[slk12407]

Ok Guys when I first start the 632 when cold it starts just fine and runs great. When it gets hot or warmed up if I shut it off fora a few min it is hard to start. I have to give it full throttle and I will finally start after a lot of cranking. When it does catch and run it runs very smooth like it should. Just hard starting when hot. Any suggestions are greatly welcome.

Steve

 

[slk12407]

Does anyone know what that pump thing is on the back of the motor that the choke rod goes to from the cab and then a rod that goes to the carb off of that same pump.. The belt from to motor turns it also.

Steve

 

[Wayne440]

That "pump thing" is probably the engine governor, based on your description.

 

[foton]

yeah I was thinking the same thing governor. a good thing to keep under good Maintenace as they are tuff to find and pricy to replace.

 

[brdgbldr]

Ok Guys when I first start the 632 when cold it starts just fine and runs great. When it gets hot or warmed up if I shut it off fora a few min it is hard to start. I have to give it full throttle and I will finally start after a lot of cranking. When it does catch and run it runs very smooth like it should. Just hard starting when hot. Any suggestions are greatly welcome.

Steve

One possibility is that your fuel line is getting too hot and causing a vapor lock.

 

[cdmccul]

Hi. Did you get anywhere with this?

(Yes, I see this is an older thread.)

 

[Geo Man]

Hi. Did you get anywhere with this?

(Yes, I see this is an older thread.)

@cdmccul @slk12407 @brdgbldr @foton @Wayne440

I also agree with @cdmccul and see that this is an older thread though I don't think things got resolved to an adequate/ or granular level. I have added my 2 cents worth below:

Regarding the fuel

• Being the first issue/ question listed can as mentioned by bridge builder be due to vaporizing of the fuel (If a gas engine with a carburetor is installed and not swapped out, gather it is based on the governor question below) and it then running extremely lean.
• A second cause maybe common issue with Mitz engine is the carburetor seals having perished (easily noted by a truck load of fuel in the engine bay and wet drippy "Covid Carburetor" (my term)) (Very much a fire hazard)
• It may be a potentially combo of fuel vaporizing and carb being empty when you go to start as a combo leak and vaporization.
• Third maybe the complete opposite, the engine is flooded, the needle which stops fuel from coming into the carburetor bowl may be clog causing a failed open scenario, as the fuel tank is higher than the carb this causes a syphoning effect as fuel continues to flow unrestricted.
• Fourth is to check the Fuel Solenoid may be sticky that shuts of fuel when the ignition is turned off (round battery cylinder looking thing with wires hanging off it), that is attached to the carburetor.
• Just a few ideas to follow until you find the cause and rectify.

The "Round Pump Thingy Dodar whatya macallit" (Techo term)

• The second is the governor as the team noted above.
  • The hand throttle attached to this device. then a rod runs up to the back of the carburetor to control "Govern" the amount of fuel used.
  • on page 7-12 diagram D there is an adjustment bolt that allows you to set the amount of governing the governor will apply, remembering all the engine is doing is powering the hydraulic engine, so it doesn't need to be revving like a horde of screaming banshees.

I have included the pages from the manual that addresses both the Carburetor plus the Governor and how to adjust both.

Hope this helps

Cheers

Geo.

 

[cdmccul]

That's a nice guild to carb stuff, but is not the engine or carb on the 632.

 

[Geo Man]

I'll take your word on that @cdmccul the stuff comes from my 642b manual, for clarification and caveat.

Thanks and for the take on the guide. I guess the principles apply so if it helps all good

Cheers

Geo.

 

[Schultzy732]

One possibility is that your fuel line is getting too hot and causing a vapor lock.

I had a similar issue with my old 732. The distributer shaft wears over time. run well when it is cold and shuts down after about an hour. I replaced the timing system with a Pertronix kit that fit right on my distributor. My machine starts and runs almost like a new machine. I'm not sure if that is your issue but i chased carb and fuel issues and replaced what I could with new parts and it still came back to the timing going out as a result of the distributor shaft. I hope this helps.

 

[cdmccul]

I think I'm having the distributor issue, but mine is opposite. Mine won't be in time till it's up and spinning fast enough. Once it's running, it runs like a top!

 

[Geo Man]

Wow all these old issues and challenges I had forgotten about since EFI and chips. Great points guys. I guess it's getting back to basics of fuel, spark or air.

 

[cdmccul]

Got points, or electronic ignition?

 

[Schifference]

If original gas engine I suggest the following:
Replace coil
Points
Condesnor
Cap
Rotor
Remove carburetor. There is a solenoid on it I think they call it anti backfire. Take it out and cut off the metal tit.
I would put electric fuel pump on it and wire that from the disconnected anti-backfire wire.
All in probably $200 and less than 2 hours.
Save all the parts you removed.
In my opinion it is not worth trouble shooting each item.

 

[Geo Man]

@Schifference , quick question does the electronic fuel pump have a cut off? I am not familiar, but I do know with the mechanical one fuel flows through due to gravity. The solenoid also shuts off the fuel flow to the carburetor's venturi, as the fuel tank is higher plugging fuel from being pulled down, which if not working correctly causes flooding??

Appreciate your advice/ insight on this.

Cheers

Geo.

 

[oiu789]

I had a similar issue with my old 732. The distributer shaft wears over time. run well when it is cold and shuts down after about an hour. I replaced the timing system with a Pertronix kit that fit right on my distributor. My machine starts and runs almost like a new machine. I'm not sure if that is your issue but i chased carb and fuel issues and replaced what I could with new parts and it still came back to the timing going out as a result of the distributor shaft. I hope this helps.

DIDO Check the side to side play in the distributor shaft. I had the same issue. When it warms up the points gap changes. My would run ok if it would start when warm but was very hard to start. Also check the spark plugs. My snapper mower was acting like this and a new plug fixed it.

 

[Schifference]

@Schifference , quick question does the electronic fuel pump have a cut off? I am not familiar, but I do know with the mechanical one fuel flows through due to gravity. The solenoid also shuts off the fuel flow to the carburetor's venturi, as the fuel tank is higher plugging fuel from being pulled down, which if not working correctly causes flooding??

Appreciate your advice/ insight on this.

Cheers

Geo.

All I know is that I did that to a 642 that I own. If that antibackfire solenoid is faulty you will have a no fuel. Without a fuel pump mine will not run. When I turn off the key my coil has no voltage and my fuel pump shuts off.

 

[cdmccul]

Electric fuel pumps, (Chugger pumps) do not have a cut off.... But they have a low enough fuel pressure that the needle and seat should hold back the fuel.

Yes! That means that if you have a faulty carb (bad bowl gasket, bad float, bad needle, etc) you may very well empty your fuel tank into your engine compartment.

If functioning properly, it won't have a problem. The anti backfire solenoid was removed from later models, it must have been found to be unneeded. I have cut mine and have no problems. I do not even turn off the fuel valve under the tank by the filter.

And you're right, you have to have a pump... It won't gravity feed (enough) to run the engine.

I have a pertronix electronic module in an old points distributor. Mine will NOT start cold without a LOT of fusing. Once warm, it generally starts like a dream. I think my timing is too far off to start due to the bad distributor shaft.

 

[Cary E Sip Sr]

Starting cold , not when warm reminds me of of a couple jobs that a new coil fixed. Coil was on its way out but worked cold. Could prove that by checking spark when it won't start.
Another amateur fix was clean carb and float. Use carb cleaner to shine float .Make sure the float pin is shiny as a mirror. I also lowered the float to less than level . That spring that goes on float pin - kinda puts a snake bite on pin , Does anyone know what it's for ? It's difficult getting it on right so I left it off . Works for Me .

 

[cdmccul]

The spring kinda keeps the float from bouncing so much. It doesn't really add and real adjustment to float height.