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PostPosted: Mon Jun 19, 2017 4:29 pm 
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As I just began to tune my carbs, I started playing with the air mixture knobs on the right carb. I screwed them all the way in, then back out 1 & 1/2 turns. Car started up faster than usual, but then started running badly, then not at all. Wouldn't fire at all, seemed starved for fuel. No gas coming out squirters.

I removed the cover to the fuel pump, and there was a very fine semi-circle of metal caught in the screen, and a very fragile spring loose down in the bowl. See attached pic. So this is obviously the problem, though badly coincidental that it happens while I'm tuning the carbs.

I have my rebuild kit now and will try to rebuild the pump. I've never rebuilt a fuel pump... any tips, tricks, traps that I should be aware of?


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fuel pump spring b.jpg
fuel pump spring b.jpg [ 143.49 KiB | Viewed 442 times ]

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PostPosted: Mon Jun 19, 2017 4:44 pm 
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Hi Mitch,
If you already removed the top dome piece, be very careful torqueing the bolt back down. If you haven't removed it yet (looks like you have, though) and it's not leaking, DON'T touch it. Don't ask me how I know. Good luck.


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PostPosted: Mon Jun 19, 2017 4:51 pm 
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Follow the instructions in the factory manual but make sure you pretension the diaphragm as you tighten the screws around the periphery. If you do not pretension the diaphragm the pump will not work. Page F23 paragraph 8 refers.

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PostPosted: Mon Jun 19, 2017 9:04 pm 
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Jon Schmid wrote:
Hi Mitch,
If you already removed the top dome piece, be very careful torqueing the bolt back down. If you haven't removed it yet (looks like you have, though) and it's not leaking, DON'T touch it. Don't ask me how I know. Good luck.


OK, I won't ask you how you know, but now you have my curiosity up... what happened when you removed the dome cover?

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PostPosted: Mon Jun 19, 2017 9:12 pm 
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Getting it to seal again can be a bitch Mitch. (that rhymes, how cool) if you tighten down on the top bolt too much it distorts the cover and the bottom seal can also be difficult unless it is spotlessly clean.

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PostPosted: Mon Jun 19, 2017 9:32 pm 
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Was just reading on Bruce Smith's web site about fuel pumps about how easy they are to crush. Must be a common problem. I don't think I torqued mine down too much since i thought I'd right back in it soon without running my engine. Bruce seems to have relatively good prices on fuel pumps.

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PostPosted: Mon Jun 19, 2017 11:28 pm 
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Mitch,

It looks like your valve seat is probably shot. I'm surprised that the pump worked as long as it did and continue to wear down the phenolic valve and let the spring through. If you take a look on the third page of 2nd fuel pump article from the registry magazine (below), you'll see a picture of a replacement valve seat that we've made for such a repair. Without a repair like this, you might never get the valve to seal. As far as the dome cover, Dave's advice is good. Overtightening reaches the point of no return once the surface sealing with the cover bolt is no longer flat. But it does take a lot of pressure to destroy one.

http://www.sparkingplugs.com/resources/ ... p+39-2.pdf
http://www.sparkingplugs.com/resources/ ... +pumps.pdf

- Bruce

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PostPosted: Tue Jun 20, 2017 12:03 am 
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Very nice articles! They certainly help to understand fuel pumps. They're much more complicated than I imagined, especially having just rebuilt my carbs -- relatively simple. Now.. if I could just find an already built fuel pump to buy off the shelf... Know where I can find one? :)

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PostPosted: Tue Jun 20, 2017 7:54 am 
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Mitch Covington wrote:
Jon Schmid wrote:
Hi Mitch,
If you already removed the top dome piece, be very careful torqueing the bolt back down. If you haven't removed it yet (looks like you have, though) and it's not leaking, DON'T touch it. Don't ask me how I know. Good luck.


OK, I won't ask you how you know, but now you have my curiosity up... what happened when you removed the dome cover?


Nothing. It was when we put it back on. Let's just say that the metal used for both the upper body and the dome are made of butter, not guns. :!:


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PostPosted: Tue Jun 20, 2017 8:05 am 
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Mitch Covington wrote:
Very nice articles! They certainly help to understand fuel pumps. They're much more complicated than I imagined, especially having just rebuilt my carbs -- relatively simple. Now.. if I could just find an already built fuel pump to buy off the shelf... Know where I can find one? :)


Hey Mitch - I've got a few, I replied to your email. - Bruce

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'67 MGB GT (Grampian Grey)
'68 912 (Golden Green)
'70 911T (CDI, Marelli, & Zeniths)
'80 Chevy C10 (Stepside)
'14 911-50 (GTS)


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PostPosted: Tue Jun 20, 2017 3:41 pm 
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Bruce Smith wrote:
Mitch,

It looks like your valve seat is probably shot. I'm surprised that the pump worked as long as it did and continue to wear down the phenolic valve and let the spring through. If you take a look on the third page of 2nd fuel pump article from the registry magazine (below), you'll see a picture of a replacement valve seat that we've made for such a repair. Without a repair like this, you might never get the valve to seal. As far as the dome cover, Dave's advice is good. Overtightening reaches the point of no return once the surface sealing with the cover bolt is no longer flat. But it does take a lot of pressure to destroy one.

http://www.sparkingplugs.com/resources/ ... p+39-2.pdf
http://www.sparkingplugs.com/resources/ ... +pumps.pdf

- Bruce

Bruce, can you help me with a related fuel pump question? After spring start up from winter storage my pump had a bit of fuel coming from under the dome top. When I went to tighten the top hex bolt, the bolt just spun. The more I "tightened" it, the more fuel leaked. What do you think is up with this? Thanks, Mike.

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PostPosted: Tue Jun 20, 2017 4:17 pm 
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Mike - It sounds like you've stripped out some threads. The cover bolt is M6x12 but there are a few threads deeper than that in the top that can take a longer M6x16 bolt. If that can pick up a few more threads, it's a simple solution available at your local hdwr store. Otherwise you'll need to do a 6mm Helicoil. If so, let me know.

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'67 MGB GT (Grampian Grey)
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PostPosted: Tue Jun 20, 2017 4:56 pm 
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Thanks Bruce I'll try that.

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PostPosted: Tue Jun 20, 2017 5:41 pm 
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Bruce Smith wrote:
Mike - It sounds like you've stripped out some threads. The cover bolt is M6x12 but there are a few threads deeper than that in the top that can take a longer M6x16 bolt. If that can pick up a few more threads, it's a simple solution available at your local hdwr store. Otherwise you'll need to do a 6mm Helicoil. If so, let me know.


Or carefully tap the body to accept an M7 bolt. You'll also have to open the dome hole a tad. That's what we ended up doing--I got a fat o-ring whose ID was just larger than the bolt' major thread, and then a big flat washer whose ID was snug to the threads. It might not be concours stock but by God it doesn't leak anymore. It was that or shell out for another used body which came with--yep, a cracked dome. Or shell out more and wait 2 months for Carburetor Rescue to fix it to stock specs. Good luck.


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PostPosted: Tue Jun 20, 2017 6:43 pm 
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Bruce's suggestion worked like a charm, and I even had the right, longer bolt in my basement. Thanks a million Bruce and Jon.

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