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Running lumpy - have I given myself another prob?


Mashby
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About a month ago I posted that I had a fuel leak on the exit side of the pump. Got some good advice on the forum on how to fix it and so I ended up cutting the flared pipe end off and finding a screw fitment to go into the pump secured to the rest of the copper by rubber pipe and two jubilee clips. So far so good. However, I now seem to have a problem with the car between 40 and 50 mph when it runs spasmodically lumpy it really does judder as though it is threatening to cut out. This only seems to happen at this speed, it ticks over beautifully and can run around at lower speed quite happily.

 

Has my fix given me another problem? Is the nozzle I fitted to the pump too small an aperture? I am scratching my head so any advice really appreciated

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Disturbing the fuel lines is most likely you have rubber sliver syndrome

 

there will be particles of rubber sliced off when inserting metal pipes these flat about and block the back of the float needle valves

 

can make spasmodic power outages

 

also check ht terminal in the coil head and the brush in the dizzy cap is in contact with the rotor

 

what dia is the hole in the replacement fitting ?

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Thanks I will check. I didn't think I had disturbed the line too much and there is only about four inches of rubber in total.

 

I did check the diameter tonight as I thought it may be too small but if anything it's slightly larger than the copper pipe end

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  • 4 months later...

Just reviewed this after four months. To finish off, I did check for bits of rubber but there were none. Eventually after running the engine for a while I noticed a fuel puddle at the BACK of the car. Turns out I had another braided pipe Union from the fuel tank above the rear wheel that had failed and air was getting into the system that way. Moral is it always pays to check all the way along the system end to end.

Now in December I am going to replace the fuel pump as the gasket has failed and it’s oozing fuel. What I need is the brass connectors to join the rubber to the pump on both sides (carb and fuel tank). I have looked everywhere but can’t seem to find them, any suggestions really welcome 

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  • 1 month later...

I really need some help as this is messing with my brain! 

I now have a shiney new pump (see pic) and as per the thread want to change the copper feed to rubber. To that end I have purchased some brass (and steel) connectors (see pic). The trouble is they go in half a turn then quickly tighten up. I have kept the old  copper pipe connector  (see last pic) which goes in pretty freely. I can only think the new thread must be different (metric compared to AF, BSF, or whatever imperial thread was on the original??) Can anyone let me know where I can get the right connector and indeed what to order?

Many thanks in advance

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Well I have been a bit cheeky and borrowed this from the classic rover forum

"Well I have done some investigating and have found the following.

The AC valve chamber inlet and outlet ports are not BSP threads,...tapered or straight. So what might they be? I took the valve chamber to Pirtek, the fellow looked at it, scanned the wall of containers before him and then reached into one, pulled out a brass fitting and voila...perfect fit. So what was it? The fellow said it was an SAE thread.

I thought.."fair enough" but....behind the threads leading into the pump there is a taper which provides the seal. On the brass fitting there is an extension behind the threads and then the taper which seals against the port taper.

So I did some reading and suitable SAE fittings typically have a 45 degree taper, where as the fitting that I had provided a 30 degree taper,..corresponding with the taper within the port. That means that it had to be something else. As best I can tell it is a NPT fitting,...in this case a NPSM which is a National Pipe Straight Mechanical fitting. Both NPT and SAE are American threads and both have the same thread profile.

AC Delco..being an American company, it would seem logical that the fittings within would also be American in profile. The same applies to the AC fuel filter, the thread on the swivel nuts and their fitting arrangment with the olives and accompaning pipes being NPSM.

As for the size thread size of the fittings,...still not 100% sure but 1/4" seems likely with 5/16" barbs. The fuel delivery lines are all 5/16".

Ron. "

Im sure Ron won't mind if it helps!!

However another post suggests that they are BSP (British Standard Pipe thread) which was my original thought. Cant you clean up the original fitting and pipe and use that?

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Thanks Ben (and Ron for that matter). This is a really comprehensive answer.

I could clean the original and cut it down, but this was the part that was weeping in the first place so I would have to find a way to seal the copper pipe/brass nut interface properly

I think I would still like to get a replacement part if possible

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I'd keep the old nut, and use new copper pipe - long enough to attach a rubber hose to - and a new olive. That should seal any leaks around the pipe where it goes through the nut whilst being a lot easier than having to source the correct threaded nut. You might want to flare the pipe slightly or add a flange to make the rubber connection more secure.

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Your old fuel fixing appears to have a parallel thread, if so it cannot be NPT or BSPT - the T standing for taper.

It is most likely a BSPP fitting (British Standard Parallel Pipe) and the fact that is has an olive suggest this even more so; as such you would not require a sealant for obvious reasons.

The BSPP thread is commonly used for fuel pipe fixings and I have attached photos of such a fuel pipe fixing from another car - fuel pipe in to a balancer pipe. In addition the compression joint exploded.

Size wise you are probably looking at 1/4" BSSP which will accommodate a 5/16" (8mm) pipe.

The quickest way to confirm the thread is to pop in to a plumbers merchant and ask if they have a 1/4" BSSP male fixing; if it screws in properly in to your pump then problem solved.

When I first looked at your photo I thought it may be metric as the thread gap is quite wide, but I think it unlikely. 

Regards.

Richard.

 

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Hello Pete.

Interesting you say that, because there is little difference between  1/2" UNF (20 tpi OD 0.5") and 1/4" BSSP (19 tpi OD 0.51") plus on the photo I have flagged of the balancer pipe my initial thought was UNF, but BSSP fitted perfectly.

Regards.

Richard.

 

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On ‎25‎/‎02‎/‎2018 at 7:20 PM, classiclife said:

1/2" UNF (20 tpi OD 0.5") and 1/4" BSSP (19 tpi OD 0.51")

That's useful Pete and confirms the above.

Am I right in thinking that 1/8" NPTF will also be the equivalent to the above as well ??

Regards.

Richard.

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