763C occasionally losing prime

Hi all, new to forum. I have a 763C with 4400 hours. Occasionally when it has sat overnight or longer it acts like it's lost prime. Not always, only about 25% of the time. When I go to start, it will start to fire for about a half second, then I'll have to crank and crank, and it will eventually start. Once started, it will run fine, and if shut down will re-start fine if it hasn't sat for more than a few hours. I occasionally see a bit of fuel seepage from the top of the injection pump where the injector lines attach, but not a lot, and not often, and not necessarily when it has the starting problem. I understand there are some o-rings in there I need to change? I've seen no other fuel leakage. Thanks in advance for any insight!

Well, I think I found the problem. I pulled the hose from the filter to the IP and got a good stream of fuel by squeezing the bulb, but then I cranked the motor and I barely got a small trickle. Looks like it's time for a lift pump. Usually when a lift pump goes, it can pump fuel into the crankcase, correct?

Phydeaux said:

Well, I think I found the problem. I pulled the hose from the filter to the IP and got a good stream of fuel by squeezing the bulb, but then I cranked the motor and I barely got a small trickle. Looks like it's time for a lift pump. Usually when a lift pump goes, it can pump fuel into the crankcase, correct?

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could be the pickup tube in the tank

[email protected] said:

could be the pickup tube in the tank

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It could indeed be a cracked pickup tube.
The fuel around the injector pump, there are O rings around the delivery nozzles. Just be very careful when removing them that you only take the top part with you, go no deeper. If you manage to pull out anything further than the spring and non return valve, you can mess up your fuel delivery that will make one get more fuel than the others.
The job of replacing the O rings isn't too hard, un-screw and put new ones on, screw them back in. Take the old ones to your friendly seal shop to get matched.

Tazza said:

It could indeed be a cracked pickup tube.
The fuel around the injector pump, there are O rings around the delivery nozzles. Just be very careful when removing them that you only take the top part with you, go no deeper. If you manage to pull out anything further than the spring and non return valve, you can mess up your fuel delivery that will make one get more fuel than the others.
The job of replacing the O rings isn't too hard, un-screw and put new ones on, screw them back in. Take the old ones to your friendly seal shop to get matched.

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Thanks for the replies! Wouldn't a cracked pickup tube suck air and cause rough running during use? Mine runs fine, just seems to lose prime when sitting... I thought I had found the problem when I saw how little fuel the lift pump put out. I replaced it, and the new one doesn't seem to put out any more. I guess they don't put out much volume, especially at cranking speed. It started fine this morning, so I guess I'll see if the problem continues... BTW- sorry for the run-on paragraph. I set it to use the HTML editor in my profile, but it won't let me type in the message box, so I had to set it back. What am I doing wrong? Thanks!

Phydeaux said:

Thanks for the replies! Wouldn't a cracked pickup tube suck air and cause rough running during use? Mine runs fine, just seems to lose prime when sitting... I thought I had found the problem when I saw how little fuel the lift pump put out. I replaced it, and the new one doesn't seem to put out any more. I guess they don't put out much volume, especially at cranking speed. It started fine this morning, so I guess I'll see if the problem continues... BTW- sorry for the run-on paragraph. I set it to use the HTML editor in my profile, but it won't let me type in the message box, so I had to set it back. What am I doing wrong? Thanks!

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Isn't there a check valve in the primer bulb? I wonder if it has deteriorated a bit or has some debris that allows it to bleed off pressure. Agree that if the pickup tube was at fault it would show up while running, acting like an empty tank.

Phydeaux said:

Thanks for the replies! Wouldn't a cracked pickup tube suck air and cause rough running during use? Mine runs fine, just seems to lose prime when sitting... I thought I had found the problem when I saw how little fuel the lift pump put out. I replaced it, and the new one doesn't seem to put out any more. I guess they don't put out much volume, especially at cranking speed. It started fine this morning, so I guess I'll see if the problem continues... BTW- sorry for the run-on paragraph. I set it to use the HTML editor in my profile, but it won't let me type in the message box, so I had to set it back. What am I doing wrong? Thanks!

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As the HTML goes, this board seems to prefer Internet Explorer. I have the same problem you do because I use Chrome. The same for posting pics, IE, no trouble. Chrome wont let me post pics.

reaperman said:

As the HTML goes, this board seems to prefer Internet Explorer. I have the same problem you do because I use Chrome. The same for posting pics, IE, no trouble. Chrome wont let me post pics.

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Yup, I'm using Chrome... As for my original problem, changing the delivery valve o-rings fixed it. No more losing prime. I guess if fuel can leak out, air can leak in... Thanks for the help!