Could my leaking fuel pump be causing awful mpg?

Hi Warren,

From what you had described with regards to the vacuum module, sounds fine, so no problem there.

Ideally, if you wish to compare the air flow into each carburettor, you should use a flow meter. That will provide a far more accurate measure compared to using a screwdriver or listening to the hiss.

As far as the mixture settings on each carburettor are concerned, the one idling slightly rich you could lean out just a twizzle, keeping an eye on the engine rpm which will likely increase ever so slightly. Again the ideal method would be to remove both dashpots and pistons, then measure the distance that each jet sits below the bridge. Adjust as necessary via the mixture screw so that both are identical.

Another area which can have a negative impact on fuel consumption is ignition timing. At 600rpm, what is your engine timed at Warren?

Ron.

P.S : Sounds as if something isn't right reading your latest post. Winding the screw right in should significantly richen the mixture, all the way the opposite, and the latter will see the engine lose revs and idle very roughly. As you don't feel happy doing it, best to let (hopefully) someone who can do it properly take a look.
 
6 degrees BTDC, Ron, or at least it was when last set. Went to check it just before, but the bloody timing light appears to have crapped out. Oh well, I've had 20 years out of it!

The port carburettor is responding to the mixture screw - if I twist it anti-clockwise the stuttering gets worse with the lift pin, and eventually with enough half turns the engine starts to stutter without the lift pin being touched. But it's not riching up if I go clockwise.

I think this is something that is best left to somebody who knows what they're doing. It's not like an SU carburettor is rocket science, but I'm just not familiar enough with this side of things, and I think I'd be better off watching and learning from somebody rather than diving in. God alone knows what the result might be.
 
i wouldnt worry about the timing light. I simply take the dizzy to the point it runs fastest then retard it just a smdgen so it sounds smooth.... If it then pinks then retard until it doesnt...

I dont know how hif carbs behave so i cant really help with that...

Rich.
 
Here us what i do, and it seems to work for me. To set my carbs I do lots of measuring! Please check the books for how many turns in/out everything should be for the base settings, I can't remember them!

I balanced the carbs by removing the dash pot, spring and piston. Mine were rebuilt not too long ago (mileage wise) by me so I know that the gaps on the butterflies when fully closed is correct, which is a key starting point.

Then disconnect the linkages between carbs and wind the stops for both out fully until they are in their full resting position. Now wind each stop screw in carefully so that this is now just touching when closed.

Then add the book figure for base number of turns to each stop screw- I can't remember what it was...

Now you have two carbs that are balanced at idle, but not connected.

Now adjust the connecting rod until it looks like its the right length to not push/ pull anything. Connect it and see if the slave throttle position is moved at all. If it does open the slave throttle, then adjust and try again.

Keep doing this until at rest both are closed. Then operate the master carb and watch the butterflies on both. You will probably find that there is a delay before the slave opens, due to slack in the ball joints on the linkage. Very carefully shorten the linkage by a tiny amount and operate the throttle again. Repeat until both open identically.

Now you have carbs that are balanced through their operating range.

Next is the fuelling. I wound each mixture screw fully in to lower the jet, then raised them by the book figure, which is something like "adjust so flush with the bridge and then turn two and a half turns in ". Use a set of vernier calipers to check each jet is same distance down from the bridge

Now reassemble and start the car. When its at normal operating temp adjust mixture evenly on each carb to obtain highest rpm, and use the lift pin method to check where you are. Once done you can remove the tops of the carbs and check jets with verniers again if you like.

Then setup the choke - I haven't done this properly yet!
 
My advice would be to hang fire untill you have sorted the pump, either repair of the mechanical or fitment of the electric. There actually is a company here in NZ that makes a range of electric pumps in all styles and pressures, push or pull based in the north island, they mostly export to the classic market, in there range is a vane pump ie no nasty thunk and pulse noises in your vehicle.

Graeme
 
That's a very good set of instructions, Quagmire. It should be stickied somewhere. I presume all this is done with engine warm and filters/elbows off. Next thing, where you say "adjust mixture evenly on each carb to obtain highest rpm", I assume that the idle speed will then need to be compensated for. How do I achieve correctness here, with two screws to fiddle with?

Graeme, you haven't given your default answer* to this problem! Anyway, the old pump might be leaking but it's still delivering fuel and I'm now suspicious of the LHS carburettor in particular. John did a great deal to get the car running way better, but he's not a carburettor man (Hondas, laptops and OBD2 plugs are his thing), so I won't hold him to account. I've had at least two bad experiences taking the car to supposed professional experts for carburettor tuning and had it completely f***** up (the last f***-up by a classic car specialist was what John did his best to fix) so I'd like to sort it without throwing good money after bad.

*Graeme's default advice to anybody experiencing carburettor trouble: "Fit a Weber."
Warren's default advice to anybody experiencing gearbox trouble: "Fit a ZF."
 
There is a possibility i guess that it's sucking in air as well as spitting out fuel so Graeme could well be right on the wait and see thing... (only just occured to me...)

Rich
 
Thanks Andy, and I've found some other stuff too on the web. I'm going to have a crack at it because it's practically impossible to find anybody to do it for me at this time of year, and I want the car in reasonable enough shape to tackle either of the two trips we might undertake straight after NY. One is shorter but involves mountain passes, the other a long drive up through the North Island. Lots of mixed driving. Transmission and tyres are all ready, but the carbs and fuel pump are determined to make trouble. What kind of idiot attempts to own and maintain a 40 year old car?

By the way, this video - https://www.youtube.com/watch?v=ASeMfXfjNpw - was not in that list on the P5 forum, but covers the HIF carburettor quite nicely.
 
OK, here's what I found. I followed Quagmire's instructions, complemented by other stuff on the Net. Pulling out the pistons, I found that the port carburettor (the one that was still lean when the mixture screw was wound all the way in) had about 5mm of crosshatch pattern poking out where I've marked with the red arrow. I tapped it in until it was the same height as the starboard carburettor, and now it is much better, but the problem is still there to some extent. I assume that the more the needle is tapped up into the guide, the richer your starting mixture is going to be. What is the correct position for the needles in the guide?
 

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Late afternoon UPDATE:

I tapped the needles up until their tops were flush in the tops of the collars, which seems to be the way they are in every photograph I can Google. I then put everything back together, started the car and twiddled the mixture screws until I got things sort of right. It's rather difficult when you don't have all the gear and you don't really know what you're doing. I couldn't quite get the lift pin test to behave as I thought they should, which is a lift in revs and then a settle back to the original idle. Right now if I lift either pin I get a very slight rise in revs, and then a slow settling back to something a bit below the previous idle. Release the pin and there's a small, brief blip in the revs and the engine returns to idle. However, going either side of that I get the definite too lean or too rich symptoms.

I noticed that if I then adjusted the idle it slightly stuffed up the mixture, and so I went around in a few circles until everything seemed OK. I have set the speed at about 700 in N, and there's a drop back to about 550 or so when I put the car in D. I kicked off the idle adjustment by backing both throttle stop screws off until they just barely touched the stop, and then wound them back in three half turns (stated somewhere as the rule-of-thumb). Subsequent adjustments were equal turns on both screws. I ditched the lock nuts, by the way, and substituted old alternator brush springs, which work quite well! By the time I'd faffed around to the point of diminishing returns, I could make out a teensy bit of smoke coming out of the tail pipe if I really squinted hard, but interestingly the exhaust note sounded better. Somebody commented the other day that they thought it sounded a little lean, but I just made a non-commital grunt and promptly ignored him; however there is less pffff and more rumble now.

Things will certainly not be perfect because, as I said, I barely know what I'm doing, but my motorway test run (well driven now after all the ZF testing) found the car pulling cleanly and, I'm quite sure, with more power than before. It just seemed smoother and cleaner somehow. No big clouds of smoke out the back, so I can't have stuffed things up too bad and over-enriched it. And a kind of hissing noise under acceleration, a sound I thought might be a vacuum leak but couldn't trace, has gone. The car is quieter when I have my foot down.

I have previously stated that I thought the car was running well, but this is compared to what it was like prior to the last fiddle with the carburettors, when it ran like a sack of the proverbial. Clouds of black smoke, poor idle, hesitation. I might have to retract the adjective "well" and substitute "better" in its place, because tonight it really seemed like things were better again. It felt a bit more like a V8 should do. More sprightly.

So, could one carburettor running particularly lean ruin my fuel consumption? Sounds a bit counter-intuitive at first. Is the leaking pump just part of the equation?
 
WarrenL wrote,...
So, could one carburettor running particularly lean ruin my fuel consumption?
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I think that would depend on the type of terrain and the style in which you were driving Warren. On flat terrain and driving nice and steady, I would expect a reduction in fuel consumption. On the other hand, lots of climbing and a heavy foot so as to extract better performance would deliver an increase in fuel consumption.

The SU's can be set to deliver better fuel consumption by running leaner, (not to the point of causing engine damage), or delivering more power by running richer, with an increase in fuel consumption.

Do you know which needles are fitted Warren? Are they the original BBG?

By the sound of it, your engine is running much better, so when your new pump is up and running and the old pump bypassed, the real tests can begin.

Ron.
 
Oh no, not pinking. A kind of hiss under moderate acceleration or harder. Hard to describe. Others didn't notice it, but knowing the car well I could hear it amid the general engine noise. It has disappeared, so I'm picking it was something to do with the lean carburettor.

On a bit of a fang (that's a word I haven't heard for a while!) through the countryside last night it gave a hiccup once or twice when accelerating moderately through 70 mph in top gear (about 2500 rpm) but I subsequently wasn't able to get it to repeat the feat so I can only assume a bit of crap was passing through the system.

Anyway, it seems better. Perhaps in the New Year it will be time to get a professional to look at it, but I''m getting a bit tired of paying professionals to not do the job properly, so maybe I'd be better off buying a Unisyn and learning how to do it myself.
 
At least you'll always have it and if it isn't right first time you can go back and tweak it...
 
rockdemon said:
At least you'll always have it and if it isn't right first time you can go back and tweak it...
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That sort of behaviour got me in to a lot of trouble as a youth... :LOL:

John
 
Oh! I forgot to mention that the starboard carburettor, the one apparently behaving, had had the little bias tab ground off the needle guide. Seems OK without it, but I think I'll try and track down a new guide.
 
WarrenL wrote,...
had had the little bias tab ground off the needle guide. Seems OK without it, but I think I'll try and track down a new guide.
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Replacing the guide with one that has not been ruined is an excellent idea Warren. The reason that the HIF6 uses swinging needles, so it is my understanding, is that they provide smoother acceleration when compared to the HS6 which runs fixed needles. The little tab places a bias on the needle, so it does not require centring within the jet, in contrast to the fixed needles which must be centred.

Ron.
 
My new Huco pump arrived today, less than a week out from the UK. Not bad going, but I guess that the actual Christmas post rush is over by this time. It's now installed just behind the left headlamp bowls, and wired back to the a/c pickup (reference number 70 on my wiring diagram (86.00.01 Sheet 2 in the workshop manual). Ignition on and you can hear the pump priming, but it's not at all intrusive. And then it started, no leaks. I'll call it job done, but the proof of the pudding will be when the fuel consumption improves. I didn't have a chance to go for a drive, but I did notice after testing the pump that the block has dried off behind the mechanical pump (which is still there for now, just disconnected.

I had to cut the fuel line behind the olive on the old pump to plumb in the new one. Having a full tank of gas on board I figured that I'd just saw through the line quickly and jam the new hose on before too much petrol was lost. I had the front jacked up as high as I could get it, I had a basin sitting in a large shallow tray, I had all the tools at hand... and I still managed to screw things up and spill a good litre of petrol on the garage floor, maybe more. The hacksaw blade broke half way through, I accidentally kicked the tray out of the way... it was all a bit of a disaster despite my careful planning.
 
spill a good litre of petrol
Click to expand...
probably not as much as you think. When i worked in a petrol station as a youth, you soon learnt that petrol spreads much thinner than water!
 
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