630 VH4D won't stay running

Fabricator said:

Ok, rather than pull everything back apart again, I was able to reach under the carb and remove the access plug for the main jet. No fuel came out. The plug sits at the bottom of the bowl, so I was expecting at least something...

So it looks like ordering a new fuel pump Monday morning is the next step in this story.

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Fabricator said:

Ok, I think that I finally have this problem licked. I had to let it sit for awhile to get some other things done and can't believe that it has been over a month since I was last working on this. August just disappeared!

Anyway... I was about to the point of selling it, taking it to the dealer, or just burning it to the ground - depending on the day and my mood. Finally had some time yesterday to really spend some time with it.

It obviously wasn't getting fuel, so I wanted to be systematic about things. Took the fuel line off after the filter and got good fuel through the filter. Took the line off the fuel pump and turned the key - fuel solenoid opened and I got good fuel. Took the line off after the fuel pump and got good solid squirts from the pump. Again took the access plug off the carb for the main jet - fuel bowl was empty...

Took everything off to remove the carb thinking the float was jammed. Shook the carb before I took it all apart and could hear the float shaking back and forth inside. Ok...?

Took the bowl off and sure enough, the float moved freely. But then noticed that although the float was moving, the needle was staying put... Got my pocketknife blade in and pulled the needle down to free it. Pushed on the float and the needle moved back up - but fell back down when the float was released. Did this several times to make sure it was moving freely.

Put everything back together and after some cranking, got it to fire up for the first time in over a month. Wrapped everything up before dark last night. Have to go out today to see how she runs.

But isn't it always the littlest of things that really stump you? I guess the new rubber grommet that the needle passes through had just enough friction to not let the needle slide freely. Maybe a drop of gas or oil on it during assembly would have solved all my nightmares and hair pulling.

But the good news is that with a rebuilt carb, new fuel solenoid, new fuel pump, and cleaning a couple decades of crap out of everything it ran last night better than it ever has.

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Fabricator said:

Ok, spoke too soon...

Ran it for a bit today and I'm right back to the same issue as before. Will run very strong at first and then it just starts running slower and slower until it dies out.

Going to pull the carb back apart to see if the needle is sticking. I had thought that with the fuel running through it now that it would react more favorably and not stick. The rubber seat is new, as is the needle - from the carb rebuild kit. But at least now I sort of know what I'm looking for - provided it is the same problem.

Any suggestions? There's a temptation to open up the rubber seat a bit more but I can see that going too far in the other direction and not sealing up the flow of gas and flooding things...

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Fabricator said:

Pulled the carb back off and this time the bowl definitely had gas in it and the needle valve at the float wasn't sticking.

Now I'm really at a loss as to what to try next...

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jerry said:

Isn't the needle held to the float by a fine wire spring clip? Most I have seen are so when the float drops it pulls the needle down from the seat. If you have rubber tube from the fuel pump to the carb maybe you can put a outboard motor type primer bulb between and then when it begins to die squeeze it a little to see if that helps, it may be the fuel pump. You may have to use a long hose temporarily for this. I put a primer bulb on the 610 I had just to make sure the carb was full before trying to start it as those fuel pumps on the wisconsin engines just don't deliver much especially if the machine had been sitting for a few days.

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Fabricator said:

Nope, no clip. I had thought I remembered the needle seating into a rubber grommet, but when I pulled it apart tonight there is just the metal needle and the metal seat. So I'm not sure why it was sticking before.

Also, when I took it apart, the bowl was full of fuel so it wasn't a fuel starvation problem. And with the new pump, the fuel supply when disconnected from the carb is strong.

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Fabricator said:

Stopped by the local dealer on my errands today and told them my tail of woe. Their head mechanic wasn't in, but the service manager said he had a similar problem with an old Farmall.

It would run like a "raped ape" when you first started it but then slowly wind down and stop running - pretty much the experience I've been having.

He said the solution was a valve job. That as the engine warmed up the valves wouldn't seat properly, lose compression, and the engine would stop running.

Not the answer that I wanted to hear, but at least an answer that seems to explain the symptoms. He's going to run it past the head mechanic tomorrow and let me know what the mechanic thinks.

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jerry said:

Is it warm weather where you are? On the 610 I had with the wisconsin there was a overheat sensor on one cylinder head and it hot weather when you worked it sometimes it would just begin to cut out and then stop. After cooling off it would go again. as soon as it stops again check for spark as that sensor cut the power supply to the coil and thus the spark. I don't see it in the book for the 630 but the book for the 610 said the wisconsin was prone to building up deposits on the valves and head. The sensor was just a little button thermostat with one wire going to it.

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Fabricator said:

It is warm, but not too bad lately - about high 70°Fs to low 80°Fs.

No signs of a overheat sensor. Only wiring to the engine is the rectifier, regulator, spark plugs, and oil pressure switch.

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jerry said:

Do you have a good strong spark if you check it immediately after it dies? If you have good fuel supply it may be coil or condenser, both will act like that when they get tired although the condensers I have had go bad stopped all at once whereas sometimes a coil is more gradual. However if you have spark next check compression while it is warm. Some problems like this have a simple solution such as a wire shorting out only at times. If all else fails run a wire directly from the battery to the coil , distributer and bypass everything as a test.

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Fabricator said:

Ok, I think that we're back in business now!

The two problems that I've been having are the fact that it runs so well when it is running and also that life intervenes and usually several days (at least) pass between the times I have to sit down and work on the machine.

Although it seemed like I was getting a decent spark, in the interest of eliminating things today I swapped in the coil for my pickup truck. Fired right up (usually, it has to crank for a moment before firing) and ran strong. Didn't really have too much to do with it today, but it definitely ran long enough to verify that was the final problem in the mix.

Just in the interest of tying up loose ends, I'm going to put a new coil, spark plug wires, and spark plugs into it and call it a day.

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jerry said:

Good to hear you have the problem solved.

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Fabricator said:

I've got to say, it feels exceptionally good to have it running again!

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