Replaced Fuel Pump - Question about driving after install

[777Gage]

Hello All,
I may have solved this, but wanted to run it by a few of you please.

A few weeks ago I smelled gas when I went out to the 40, noticed a small drip on the ground coming from the fuel pump. I ordered the OEM pump
(part # 23100-61030) and installed it yesterday. (super simple R/R)

Today, I went for a drive - started right up, idled great, drove well except for a few times it briefly shuddered and felt fuel starved. I put it in neutral and it idled back up and I drove home. Re-checked the hose connections and made sure the 2 bolts holding it to the block were correctly tightened. Took it back out and the motor stumbled again, came back and went over everything again.
Then went for a 12-15 mile trip and stumbled mildly and all went well back to home

Yes, I have fuel
Yes, I have a new fuel filter, after the tank, and before the new pump
Yes, I checked all the vacuum lines - didn't disconnect anything other than the fuel pump lines
Yes, I check the oil and it's clean - no fuel in the oil (I haven't driven it in a few weeks)

My .02 is, there were a couple of air bubbles in the fuel line from removing the old pump, and they just had to work through the system?
Anyone else have this experience or possible direction to check if it comes back?

Thank You

 

[charliemeyer007]

Maybe you loosened some crud in the lines. Get it running then, shut it off. Take the fitting loose at the carb - have a cup to let the gas squirt in while someone starts it for you. Idle up and let it run until it dies, hopefully that will flush the line.

 

[DeskJock]

I don’t think air bubbles would matter if there is fuel in the carburetor float chamber.

If it were me. I would remove the air box. And full throttle back to back several times while watching the float chamber to see if it stay close the the half way mark.

 

[Living in the Past]

Did you check to be sure there was no gas in the oil? The fuel pump is driven off the cam shaft. When the diaphragm fails not common to leak in to the oil sump. Just for safety I would check for a gas smell on the oil dip stick.

 

[Pighead]

Sometimes (just sometimes) there is a small screen "sock" just under the fuel inlet to the carb, before the needle valve. Not hard to get to. Perhaps you have one and it's dirty?

 

[65swb45]

Did you check to be sure there was no gas in the oil? The fuel pump is driven off the cam shaft. When the diaphragm fails not common to leak in to the oil sump. Just for safety I would check for a gas smell on the oil dip stick.

/this\

 

[777Gage]

Did you check to be sure there was no gas in the oil? The fuel pump is driven off the cam shaft. When the diaphragm fails not common to leak in to the oil sump. Just for safety I would check for a gas smell on the oil dip stick.

Yes Sir,
I searched the forum for about 2 hours prior to starting the work so I'd have an idea of what to expect and look for. I saw a few comments regarding the fuel mixing with oil.
My oil and dipstick has no smell of gas. I also just changed it about 100 miles ago, the oil is still as clear as when I poured it in. The 40 had been sitting for about 3 weeks after the oil change, and the fuel leakage only lasted about a day.

Please let me know if you guys have seen something different, I'll check anything suggested.

THANKS for the reminder - I appreciate it!

 

[DeskJock]

So - what I’m hearing here is - if it leaked to the exterior of the mechanical pump- it likely leaked into the interior- so - the safe thing to do would be to change the oil.

 

[charliemeyer007]

If you can't smell gas on the dipstick oil you are fine.

Somewhere on the winter western front when the Stuka's were frozen to the 40 below zero ground, a Rusky was shot down while strafing. He was polity ask how could they get their engines started in the bitter cold. They would thin the oil with gasoline 33%, fire it up and wait like 1/2 an hour to evaporite the gas, top off the oil and then go harass the Kraut's.

 

[DeskJock]

Interesting.

 

[777Gage]

I swear this is the best forum I've ever been a part of! (my old Ducati forum was also great)

It's easy enough to switch the oil out, I ordered a few OEM oil filters when I ordered the fuel pump so I'm good to go.

Would gas in the oil cause the shuddering? (still haven't found any traces in the oil)

I'm pulling the fuel line to the carb tomorrow as suggested above, look for debris and give a few pumps to make sure we are clear.

I appreciate it!

 

[Mark W]

.

 

[pb4ugo]

Make sure your fuel line connections are tight so they aren't sucking air.

 

[DeskJock]

the oil change doesn’t seem to be a pressing need at this point. Determining if you have a fuel supply issue would be at the top of my list. That’s assuming the rig was running great to begin with.

Vacuum hoses all in place? (Distributor in particular).

On my rig - I would also check dwell angle and timing advance to knock them off the list. Probably eye ball my points to see if there is any damage to the points.

 

[peesalot]

Why are we all assuming the intermitant stumble is from fuel issue ? just curious ? I would look at the carb, crap in the bowl, bowl level, etc.. , then the plugs and wires, dist.

 

[777Gage]

Why are we all assuming the intermitant stumble is from fuel issue ? just curious ? I would look at the carb, crap in the bowl, bowl level, etc.. , then the plugs and wires, dist.

That was my initial question about fuel, because I only touched the fuel pump. (and pulled the battery for easier access) Ran perfectly fine prior to the new pump. And it only stumbled randomly, would run fine for a few miles then stumble and resume driving normal. Acted almost like an air bubble in the line.

 

[777Gage]

So to wrap this up - I like when people wrap up their inquiries after fixing the issue!

Today I pulled the air cleaner, fuel lines at the carb, and traced all the vacuum lines. Turned the motor over and pumped the fuel into a bottle, cleaned/sprayed out the carb fuel inlet and the screen (weird sock/screen looking thing in the carb fuel inlet) Checked the fuel pump bolts and fittings, all good.

I did notice a vacuum line that started at the distributor, and went to the driver's side vacuum bank, wasn't fitting as tight as it should be, replaced that with new tighter hose. But that's all that I noticed and changed.

Put it all back together, fired right up. Drove it approximately 20+ miles of stop and go traffic, with a few 50mph runs, no sign of the stumble any more.

I'll report back if it returns.

Thanks for all your assistance and follow-up

 

[John Smith]

Your distributor should be vented to the air cleaner. If you have it plumbed into the intake manifold, that is a massive vacuum leak.

 

[777Gage]

Your distributor should be vented to the air cleaner. If you have it plumbed into the intake manifold, that is a massive vacuum leak.

Thanks John,
You are correct about that. I should have been more specific "the hose from the vacuum advance" on the distributor was the loose one I replaced.

The hose in the top of distributor cap is vented to the air cleaner