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Weber 40mm on 1100
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Author:  jakothechicken [ Tue Jun 09, 2015 9:02 pm ]
Post subject:  Weber 40mm on 1100

Hi all,
just discovered this forum today. Looks like an excellent resource. nice work.

I'm hoping someone can offer some assistance with an issue I'm having.
I have a 40mm weber on an 1100 A series, in my clubby. It's been working beautifully for years. Recently it's started to get very stubborn about starting when warm / hot.
Cold starts are fine, and very easy, but if I've been on a nice long run, and turned of the engine for 5 minutes, it takes ages to start again.
Not really sure where to start with this one.
Any ideas would be very much appreciated.
Thanks in advance.

:D

Author:  ba_dm_tsh [ Wed Jun 10, 2015 1:49 am ]
Post subject:  Re: Weber 40mm on 1100

Have you changed your fuel filter recently? It may be clogged up.

The next place I would look would be the float and float valve. If there is an issue now and it's not filling to the correct level it's either low: allowing the heat from the exhaust to boil off the fuel or high: flooding the engine which then won't start until the excess fuel in the cylinders has evaporated.

Next check would be for an air leak. Check everywhere past the front flange of the carby right to the manifold face of the head. You can use just about anything for this that gives a directed spray (like brake cleaner/contact cleaner/etc cans with the fine nozzles) - just spray it around any potential leak areas sparingly while the engine is idling and listen for a change in the engine note.

You may also find it is an ignition issue. Resistance in wires and contacts etc increases with temperature. So if your coil, points, HT leads, primary wiring (12v), and/or plugs are on the way out they may be prone to fail at a higher temperature. Best to check over the entire ignition system to make sure it's tip-top.

If all of that checks out then you may have an issue with your valves/valve seats causing compression issues but if it was the cause then I would expect it to run poorly most/all of the time.

Let us know how you get on :)

Author:  goodie [ Wed Jun 10, 2015 8:02 am ]
Post subject:  Re: Weber 40mm on 1100

My first thought was ignition / timing , seeing as it's only doing it when hot :idea: .

Author:  cranky [ Wed Jun 10, 2015 9:12 am ]
Post subject:  Re: Weber 40mm on 1100

Another possibility is a vapour lock in the fuel line. If the engine is hot and switched off, the heat in the engine bay can increase dramatically, potentially boiling the fuel in the lines if they are exposed. Depending on your setup/pump/float levels, and the condition of your inlet valve on the carburettor (they can stick) you may have a shortage of fuel, and it can take some time for the pump to clear the line.

Some time ago I bought a Carter rotary vane type pump, and while it sounded racy (read unbearably noisy for everyone else) it would only work when the car was cold, or travelling at full chat on the highway. After fiddling around with it for a week or two, I junked it and got a facet rally type pump, which solved the problem almost immediately. I don't think the Carter was suited to the small and constant variations required at relatively low pressures and volume. I also got a decent air/fuel meter and fuel pressure gauge and a filter King regulator. With these in place, I was able to monitor the fuel flow and pressure, and adjust it much more carefully.

I have read wildly conflicting opinions on what fuel pressure best suits weber carburettors. My experience is that it needs a substantial pump, but fairly low pressure, so that a decent volume of low-pressure fuel can be added quickly (those accelerator pumps can chew through it). I found my engine worked best with about 3 1/2 pounds of pressure, and the problems I had before completely went away.

Having said that, the other suggestions above are just as worthwhile....

Author:  jakothechicken [ Wed Jun 10, 2015 11:22 am ]
Post subject:  Re: Weber 40mm on 1100

thanks Cranky,
Just tried it again with same results.
Your first suggestions is how it feels when turning it over. Feels like there's no fuel in the line, which could suggest evaporation.
If this is the case, would some sort of heat shielded hoses help?

Just checked my fuel pump. It's a Facet electric fuel pump (STC505), which is supposed to have 5-6 PSI. inline filter is nice and clean.
How do I check fuel pressure? Do I need to put a gauge inline?

Working my way through the list of other suggestions. Next up, will check for leaks.

thanks again.

Author:  cranky [ Wed Jun 10, 2015 12:15 pm ]
Post subject:  Re: Weber 40mm on 1100

Hi again, this is what comes of being at home during the day :D there is plenty of housework to do, but somehow I don't get around to it as quickly as I should....

The pump you have should be fine. I suggest you actually check the flow,

BUT BEFORE YOU UNDO ANYTHING IN THE FUEL LINE....Disconnect the battery!

If you want check the operation of the pump, run a circuit from the battery to the pump and back again with five amp electrical wire. It's worth building yourself a little circuit with proper connections and a hold down switch.. that is you have to keep pressure on the switch to maintain the circuit. Then in the event that you catch on fire, you are likely to at least stop the pump!

It's a good idea whenever you are checking fuel issues to have an appropriate fire extinguisher on hand. The one time a friend and I didn't have one, we were taught a little lesson, but that's another story... It's worth investing in a handful of proper hose clamps that can be attached and removed quickly..

Disconnect the pump output hose, fitting two metres of clear plastic tubing to a large plastic bottle, say 2 L at least....make it all secure, and keep the bottle well away from the car, and with the circuit/switch see how long it takes for the pump to fill it. A good healthy flow should be about a litre in 30 seconds or under.

Another test you can do is to disconnect the input line to the pump (should be after the filter from the tank) and check the flow just under gravity. Again, before you do this, disconnect the battery terminal so there is no chance of any spark.

To continue checking the lines, move forward and check any hose connections, any twists or kinks in the line and in particular, any loops which leave a section of the line higher than any other part before it reaches the carburettor. Ideally the fuel line should reach its highest point at the carburettor inlet – that way any bubbles are likely to get flushed out of the line when the pump turns on. Do all of these checks with extreme care. There will be fuel vapour involved, so if you can do it outside, a well ventilated shed, perhaps with a fan blowing across the car (but not closer than 3 m away).

I once rebuilt a Jaguar E type motor with Triple 2 inch SU's. It would start, it would run at low speed, it would rev with no load, but it was a complete dog under acceleration. Three weeks of investigation, which returned no improvement, ended when I finally got to the carburettor float bowls and discovered that during the couple of days I had the the carburettors on the bench, pesky wasps had filled up the inlet tubes and the CV tubes with mud, wasp eggs and paralysed spiders. Some fuel was getting through, but not enough. I guess I could have marketed the system as a way of reducing petrol consumption and promoting the environment, but it didn't work out well for the car, the spiders or the baby wasps...

Regarding shielding, if you have a weber and extractors, you're going to get a lot of heat at the back of the engine bay. Traditionally, the fuel feed comes up fairly close to the exhaust and then across the firewall. In my case, I've taken it from metal pipe at the back right hand side, even further to the right, next to the radiator and up side of the engine bay through one of the holes in the reinforcing gusset, up to the back of the firewall at the top (where the windscreen wiper cable sits) across the engine bay and down where the brake master's usually are to a fuel filter regulator, with a plumbed in electronic pressure gauge as the final component before it reaches the carburettor. if you put a pressure gauge anywhere else in the line, and may not reflect the actual pressure reaching the carb, and your regulator should be just before it, so the fuel pressure throughout the rest of the system is high enough to maintain flow and reduce vapour blocks. I know this setup contradicts what I said earlier about make carburettor the highest point, but if you shield the line (I use the corrugated metal heat/sound shielding from super cheap, it's pricey but very easy to work with) this arrangement works well.

You can also obtain heat shield for the carburettor itself, bolts on the underside, but I haven't tried that. You can also wrap the exhaust headers, and their various pros and cons to that. I know that in some racing setups, the fuel line goes through a bucket of ice or chilled water, but this doesn't really work for a road car (although you could incorporate a champagne bucket.

I know these issues can be irritating, particularly if you have to get someone somewhere at a certain time... but if you have a bit of time, it can be quite interesting to chase down these little gremlins. Often the solution is very simple. An old mechanic I used to work with said that whenever there was a problem with an engine, it was either "fuel or spark" and that's still true in most cases, although I would add "operator error" as being just as prevalent a cause in my case, coupled with a complete inability to leave anything that's running well, well enough alone.... :D

Author:  jakothechicken [ Wed Jun 10, 2015 1:11 pm ]
Post subject:  Re: Weber 40mm on 1100

Thanks for this. Looks like I'll be taking the day off work tomorrow and getting dirty.

Will let you know how I go.

:D

Author:  DOZ [ Tue Jun 30, 2015 8:19 pm ]
Post subject:  Re: Weber 40mm on 1100

So long as there is fuel in the carby the engine will start - Try a spray of start ya b#$%^rd - this will tell you a fuel issue straight away.

Points ignition? Change the condenser and coil.

Author:  1310/71 [ Wed Jul 01, 2015 1:42 pm ]
Post subject:  Re: Weber 40mm on 1100

With the car running, carefully spray a small amount of start ya bastard around the mounting gasket between the carb and manifold and listen for changes in rpm. It might be your leak is there, and time for a new gasket.

Author:  drmini in aust [ Wed Jul 01, 2015 6:56 pm ]
Post subject:  Re: Weber 40mm on 1100

1310/71 wrote:
With the car running, carefully spray a small amount of start ya bastard around the mounting gasket between the carb and manifold and listen for changes in rpm. It might be your leak is there, and time for a new gasket.

People mostly use the Lynx or similar O-ring kits on DCOE Webers fitted to Minis, instead of gaskets. Supposedly to avoid vibration from the motor getting to the carby. What does this do anyway, on a road car? Flood? Froth the fuel? or what?
Problem 1, people overtighten the nuts so they don't flex as intended anyway.
Problem 2, the O-rings go hard with age, then leak fuel out and can suck air in.
For 25 years (since I flung the O-ring kit away and ran with a stock gasket) my 45 DHLA Dellorto carby (functionally the same as a Weber) has given no trouble. And at one stage this included track days using 8000+ rpm. No problem.
Soooo, what's wrong with using a gasket on a Weber instead? A stock Fiat 124 sedan (single 38DCOE) just ran with a gasket.

edited, for clarity.

Author:  1310/71 [ Wed Jul 01, 2015 10:25 pm ]
Post subject:  Re: Weber 40mm on 1100

I was actually using a generic term "gasket" to mean the mounting kit Doc.

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