2+2 - XR2 CVH engine, no idle

[Dave English]

Thought I'd post this for future reference in case anyone else has the same problem. A bit of fault diagnoses is always useful.

Driving to a model aircraft show at the weekend, my 2+2 started cutting out every time the engine came back to idle. A bit difficult to drive like that but I got to show, managed to avoid buying any more toys, and got home again. I did notice it idled when the choke was on until I touched the throttle.

Started playing with it today. First confirmed the fault. No idle unless choke was on and lumpy below 1500 revs.

The anti run-on valve was clicking, so that was okay and, over 1500-2000 revs, everything was fine so timing and ignition should be okay (although a weak spark may give similar problems).

For those that don't know, the anti run-on valve (sometimes called the anti-dieseling valve) shuts off the idle fuel when you turn off the ignition, to stop the engine running-on or dieseling.

To my mind that really just leaves a lack of fuel in the idle line, possibly a blockage. (the Weber carb makes this idle fuel thing a bit complicated, give me a SU carb anyday)

By now the I had the auto choke cover off and could set the choke at any engine temperature, which allowed me to start the engine and get to the carb without it stopping.

So, got the engine started, climbed out, got to the other end of the throttle cable and used that to knock the choke off and keep the engine running. With the other hand I started spraying WD40 into the carb and then let the throttle drop to idle, and idle it did, running nicely on WD40.

Hopefully this has confirmed a fuel blockage at idle, and after using an Air Duster and some Carb Cleaner to no avail, the carb is now sitting on my bench awaiting a service kit so I can strip and clean it.

Of course, it could be something completely different, so if anyone has any other ideas, please let me know.

When it's fixed, I'll let you know what the real problem was!

[chris...@btinternet.com]

I had the same problem once. A new set of fuel hoses fixed it. The old ones had corroded on the outside and were letting air in.

 

Chris G

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[Susan and Martin Scott]

I had similar symptoms (which I thought was fuel starvation), but since fitting a new ignition module to the side of the distributor it's been ok - that doesn't prove/disprove it because it was an intermittent fault on mine.  Seems it's a common problem on Fords and Land Rovers (which have the same module). The Land Rover module (surprisingly lower price than Ford) cost me £20 delivered. All seem to be generic made in China, 'some have heat conducting paste' with the 'kit', some don't.

Martin

----- Original Message -----

From: Dave English

To: Quantum Owners Group

Sent: Tuesday, May 14, 2019 6:44 PM

Subject: [Quantum Owners] 2+2 - XR2 CVH engine, no idle

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[Mike]

My 2+2 would not run at idle. It started fine from cold but when the engine temp reached the point at which the automatic choke dropped the revs to idle, it just cut out. It would start again immediately and by keeping my right foot down I managed to get it to the garage where it was due a service and MOT. They traced the fault to a split in a pipe that was letting air in (or out?). Maybe it was also a fuel pipe, but from the conversation I think it might have been an air pipe that had a split.

So check all pipes!

Cheers

Mike M

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[Dave English]

Hi Mike

Yep, there's air pipes and valves all over the place with these carbs and manifolds. According to my Haynes book, they're part of the 'spark sustain system'.

I'll give them a good look over now the carb is out of the way.

Dave E

[Dave English]

Hi All.

Here's the update for my little tale of woe.

The service kit arrived on Thursday  and the carb was stripped, cleaned and rebuilt on Friday.

I didn't find any eureka bits of muck anywhere but there were some odd bits around which may have added up to a problem.

Today I refitted the carb and, after some turning over to refill the float chamber with fuel, the engine fired up and ran with the choke on and me not touching the throttle.

>>Moment of truth<< After it had warmed up a bit, a blip of the throttle saw it drop to a slightly lumpy idle.

With it suitably warmed up, a bit of tweaking with idle mixture and speed, just using my vacuum gauge and the rev counter, smoothed everything out to a good idle (well, as good as a CVH gets).

Tomorrow, when it's stopped raining, I'll get it outside and get my CO meter on it to set it up properly. - Job done!

So, the questions:-

1.  Did the strip, clean and rebuilt fix it? - Yes.

2.  Did I find a definite fault during the fix? - No, not really.

3.  Was the fault diagnoses correct? - Sort off. Strip/Clean/Rebuild is like turning the computer off then on again, it can fix it, but you don't always know why!

4.  Did I learn anything new? - Yes, the Anti Run-on Valve doesn't shut off the idle fuel, it shuts off the idle air.

If nothing else, I hope the fault diagnoses process may be of some use. It didn't really pinpoint a fault but it eliminated most other things and that's a start.

Just out of curiosity, with the engine at idle, I pulled the vacuum pipe of the carb. It made no real difference, so I won't worry about it in the future.

Dave E

Q2009 - Back on the road.

[Ian Harrison]

An observation Dave. I would expect pulling the vacuum line to the dizzy to make a difference. Blocking the end of the pipe should even things out but opening it effectively gives you an air leak. Have you tested the diaphragm in the dizzy?

Ian

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[Dave English]

Hi Ian

Always appreciate a good observation.

Pulling the vacuum hose can make a small difference, a leaner mix leading to a slight increase in rpm sitting at idle, as you say, effectively the same as a small air leak. It wouldn't be enough to cause the engine to cut out at idle though, which was my main problem.

As for the distributor end, pulling the vacuum pipe off lowers the timing advance by a degree or two at idle, which should slow the engine down a bit.

I set my timing at 10 degrees BTDC, halfway between the 12 degrees when using good old 4-star petrol and the recommended 8 degrees for unleaded (which is 2-star). With this timing, it just so happens that the combined effects of disconnecting the vacuum pipe pretty much cancel each other out when sitting at idle.

Just to add some fun to it, when I was setting up the idle on my CO meter, I found out that my radiator fan switch had failed, leading to a functional test of the overpressure valve in the header tank cap - In other words, the tank boiled over and dumped coolant everywhere!

Dave E

Back on the road as long as I keep moving.

[Jamest142]

Hi Dave

Check the fuse (no 6 if I remember correctly!), mine failed, and the burst the radiator...

Best regards

James T

Q2-002

www.bostin.photography

[Dave English]

Hi James.

I didn't get as far as the fuse. After disconnecting the switch, I used a wire link across the plug to check the fan worked, it did, so the only bit that could be broken was the switch.

It's now been replaced and everything is sorted - until the next time!

Regards

Dave E

[bill]

On my other kitcar I went through a few of the thermostatic switches, a pair welded themselves in so the fan ran continuously, finally I had the thermostatic switch operate a relay which then ran the fan, result, no more switch’s failing, 

Bill

Sent from my iPhone

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[Steve Kodź]

I think that is a design flaw in the early Ford wiring. The fan switches have to switch the entire load of the fan and my H4 burnt through several and also the ignition relays too. These are the green relays in the MK3 Fiesta fuse box.

Bills suggestion of using the fan switch to trigger a relay should help to prolong the life expectancy of all components within that circuit.

Regards,

Steve

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