Fuel On The Roof

What model and year is car @Ducked?

I support this. Let’s see what happens (please document).

[quote=“shiadoa, post:4, topic:182822, full:true”] technically you do some awesome things …
Sarcasm now. At least I HOPE it is.

If you REALLY think gravity feeding a carburettor (assuming it works, might not. AND I might blow myself up) is “technically awsome” maybe you’re not Taiwan’s answer to Maclaren after all.

It does work… I always used gravity feed for both carburettors on all my Ducatis.

Actually, that’s not true. I had one with a fuel pump once.

OK, all my GOOD Ducatis.

Its a 1986 Daihatsu Skywing. Mechanical fuel pump with three pipes. (in, feed to carb, and I assume return). I suppose it might be possible to disable it by taking the piston/plunger thing out but I don’t really want to take it apart. Can’t just take it off because that causes an oil leak.

Whats this @Ducked jive?

No you are fine … it’s me I don’t trust with petrol :blush:let me ponder a sec

Did it slowly progress into this condition, or did it suddenly start doing this? If it is carburated, check the intake manifold carb attachment points and emissions and other vacuum lines for an air leak. Also check for wear in the butterfly shaft pivots. If everything is tight, you might need to see if any of the jets or emulsion tubes are clogged. If it is overfueling, check that the float is not punctured.

Don’t doubt it can work by design, and I have heard of it working as an improvised response to an emergency (one of them being the Japanese invasion of Malaya, though admittedly it didn’t fix that.)

Unclear at the moment whether this particular improvisation is going to work, though I have hopes. I’ll try starting the siphon with a syringe tomorrow. If I can’t get that to work I’ll give up.

I’m not sucking on any petrol siphon tubes. Done that before and didn’t like it.

I don’t really understand half of what you say. All activity on my roof runs primarily on ethanol and I’ve been quite happy with that. Also, I do agree you should probably stock up on Guinness.

Thanks. Think it was sudden onset but its been doing it for a while now.

Other possibilities considered are vacuum leak (Probably favorite but can’t find one blowing butane over the pipework) ignition fault (probably need an oscilloscope) Carb blockage (stripped and cleaned a couple of years ago so reluctant to do it again) and exhaust blockage (Rear section backflushed with a hose. Spacer and port made and negligable back pressure measured, BUT not monitored while driving and showing fault. Might need to revisit that.)

I’ll try the question again, as I’m here

Is it ok to block off delivery by the fuel pump, or is this likely to damage it?

If you just disconnect it and block the output, it may damage the diaphragm inside the pump. Unless it has a direct over pressure line that dumps back into the fuel tank (which it may).
On engines that I modified in the past, if I removed the fuel pump, I fitted a blanking plate and gasket, for example when installing an electric fuel pump.

My apologies for missing your question.

Missing questions is normal. Answering them much less so, so thanks

Seems to have worked fine. There seems to be an excess return line, though I havn’t disconnected it to confirm what its doing.

Got the siphon started with a 30 ml hypodermic. I initially relied on the tube self-sealing round the needle hole, but it seeped fuel after a while

I’m using a cut-up renal dialysis set. These have injection and sample ports (?) in them, so I cut up another. to get a sample port in the right place to start the siphon with the 30 ml syringe…

I put a line clamp that came with the set on the pump outlet tube to give control of its output, so I could use it to top-up the fuel can, which I put in front of the windscreen rather than on the roof, to see what was going on.

Started it on butane since the float chamber was probably dry. (Actually I always start it on butane since the choke doesn’t work, and its just better) Safer to run it without the air cleaner since it wont get so hot and I can see better, but that is another variable, plus I don’t actually LIKE running it without an air filter.

About 20 mins run up and down a quiet road, air filter off, max speed 80kph. No misbehaviour.

Put the airfilter back on for maybe 10 mins of similar (interrupted when I left the line clip on the fuel supply closed, which stopped the engine. Restarted OK from when clip opened).

Then it started to rain, no good because water will get in the petrol and the can is tied to the windscreen wiper, so I stopped under a bridge. Perhaps a bit of heat-soak while stopped for about 10 mins.

Short burst of Kangaroo on driving away. I’d have liked to drive for longer to see if I could get it to do it again, but a hefty incoming thunderstorm stopped me.

So not conclusive but looks like it isn’t the fuel pump.

I get that a lot.

Seems to be something to do with that ancient Jewish philosophical question that is unaccountably used as a greeting here.

(How should I know “Why Golem”? Am I a rabbi?)


That good or bad?

I like your methodology to problem solve, and I always prefer to fix things rather than replace them. My family calls me the patron saint of lost causes.
But, 80kph with a can of gas tied to your windshield wiper? That’s a bit risky. I must be getting old.
If you need to regularly start that with choke or butane, I’m guessing you have a vacuum leak somewhere. What is the compression like? Have you done a leakdown test?

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There was an element of risk, sure, but I had my Guiness cans at the ready.

I gave the petrol can a good shake (actually lashed to the wiper spindles rather than the wipers, which I removed) and it seemed pretty secure. I’ve done some sailing, and I was in the TA Royal Engineers (sounds better than Boy Scouts, though that would also do) so I have some faith in knots and lashings.

Compression is OK, though the tester (bought in Japan) was supplied with the wrong port adapter and I can’t get the right one unless I go to Japan and steal it, so for now I’m relying on the conical push-in thingy which isn’t very accurate.

Don’t think a leak-down test is a DIY proposition, AFAIK.

To find a leak the next step might be to make a smoke machine, not impossible but a hassle.

An alternative would be to run butane into the sealed off air intake and then look for leaks with a naked flame, but that does seem a bit too risky’since there might be quite a lot of gas in a sealed-off space.

Over the last couple of months, when I didn’t have time to fiddle with it, I’ve painted the carb and intake manifold a couple of times with sunflower oil, in the hope it would seal off any leaks. Seems it hasn’t, but there might have been some improvement. Don’t think I’ve ever heard of any commercial gloops for sealing off vacuum leaks.

OOPS! ANOTHER patent opportunity gone. There goes my luxury yacht AGAIN!

I’ll give it another coat and then I’ll take it in for inspection, since I’m already rather late.

At least you were prepared!

Reverse engineering that idea, if I could get some dry ice, and put it in the sealed-off intake tract, could I look for a leak based on the naked flame going out?.

Seems safer

Hmm…dunno if I can get dry ice though. Perhaps scooter exhaust. With a 2-stroke it might work as a smoke machine too.

Have to avoid over pressure which could actually cause leaks though