Square 4 MKI - more troubles

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Gui.dorey
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Square 4 MKI - more troubles

Postby Gui.dorey » Sat May 09, 2020 6:19 pm

My Sq 4 keeps giving me trouble. I'm beginning to believe she has something against me.

After blowing the Otto head gaskets, I am using copper ones as I couldn't find new Ottos.
After reassembling the head and torquing everything properly, she started easily, did the first heat cycle in the garage and retorqued again. Most nuts had lost some torque - maybe a flat had to be turned. Then I went off for the first ride. She ran perfectly for about 20 miles, engine running very smoothly, but then after a run where maybe I pushed her too hard, I felt a loss of power followed by a change in tone, and the gasket had blown again. After getting back and cooling down, there was indeed a noticeable torque loss on most nuts.

So the head came off again and I started anew. Triple checked everything and one thing I noticed was that the holes on the gaskets for the head bolts were catching on some of the bolts maybe preventing the gasket from laying completely flat. I opened up the holes a bit and checked gaskets would fit completely flat, everything spotlessly clean, gaskets anealed, and everything reassembled, retorqued, valve gaps set, etc.

The first start was again easy, and I let her idle for about 10 min before shutting off. The next day torque was rechecked, and this time only one or two nuts needed a slight tightening and a slight adjustment on the valve gaps. Already a good sign. Second heat cycle and this time only one nut had to be tightened a tiny bit. Valve gaps rechecked, but no adjustment was necessary So today I wanted to go for the first ride, just around the block and taking it very easy, and this is when the new troubles started.

She was much harder to start, but she did, however she didn't seem to want to idle when I pushed the bi starter in. As I put her into gear and tried to drive off, she didn't want to go and wanted to stall. I managed to take off eventually, but the engine did not pick up and died after a bit. Restarting was then uncharacteristicaly harder and I barely managed to go up and down the road. She had no power, the engine wouldn't pick up, ran erratically and wanted to stall. Playing with the bi starter in and out, did not really make it better or worse. Parked in neutral in front of the garage she would idle, but not as steadily as before, and strated dying if the bi starter was pushed all the way in. I rechecked the pilot screw, but it was where it always had been at about two turns out. I could keep the engine running, but only with a bit of throttle or the bi-started a bit out.

So it seems to me like the symptoms of:
1. Not enough petrol
2. timing off or not advancing
3. valve timing

Fuel flow from the tank seems fine - checked. I will check the carburetter again as it was on and off several times to get to those two impossible nuts under the manifold. Maybe some debris got in there. And also a look at the petrol tap. Before you ask the petrol tank is half full. :D

The timing seems strange as I didn't touch the distributor or anything that could affect the timing. Unless the advance mechanism stopped working for some reason, but this seems unlikely. I do get a good fat spark on all 4 plugs.

As far as valve timing, the only thing I can think of would be the tappets. If during assembly I did something wrong and one is not sitting properly on its guide cup. But if it was so, would she even start and idle?

Anyway, maybe you have some other ideas and suggestions. Hopefully I'm just missing something stupid.

Cheers
Gui

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simon.holyfield
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Re: Square 4 MKI - more troubles

Postby simon.holyfield » Sat May 09, 2020 7:05 pm

Can you tell us about the fuel line size, fittings and route to the carburettor? I had a problem like this on first start up....
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

Gui.dorey
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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Sat May 09, 2020 8:20 pm

Simes, not sure of the size, but it‘s a rubber line without a filter making a nice U from the tap to the carburettor. Shouldn‘t be that though, as I‘ve had the same line for a while and never had any problems with it. It must be something that happened on this last repair. My last ride was on Tuesday and she was running beautifully.

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paul.jameson
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Re: Square 4 MKI - more troubles

Postby paul.jameson » Sat May 09, 2020 8:47 pm

What sort of rubber?

When I was at university, a few years ago now, a friend had a car which went well enough until he put his foot down, at which point it cut out but would restart easily enough. He was a chemistry student and had fitted the rubber pipe from a bunsen burner to the car. This frayed internally and stopped the flow of fuel when demand was high.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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simon.holyfield
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Re: Square 4 MKI - more troubles

Postby simon.holyfield » Sat May 09, 2020 8:51 pm

Gui.dorey wrote:Simes, not sure of the size, but it‘s a rubber line without a filter making a nice U from the tap to the carburettor. Shouldn‘t be that though, as I‘ve had the same line for a while and never had any problems with it. It must be something that happened on this last repair. My last ride was on Tuesday and she was running beautifully.


OK. I have had trouble with air locks when following the wrong route. Have you had the Solex apart? Sounds like a jet blockage to me.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

Gui.dorey
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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Sat May 09, 2020 9:01 pm

Could be. I had the Solex apart and completely cleaned during the rebuild. But I am leaning towards something like that. Or something in the tank got loose and is blocking the petrol tap. But since I had the carb out and back in quite a few times, some debris might have creeped in there. The fuel line is of course a proper fuel line btw. I did check the flow out of the fuel line, and it seemed fine. Anyway, I'll start looking at the carburetter and fuel supply tomorrow to see if I find anything.

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simon.holyfield
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Re: Square 4 MKI - more troubles

Postby simon.holyfield » Sat May 09, 2020 9:23 pm

Did you put a strainer in the banjo? I went through a period of picking up stuff in the idle jet. A bit disconcerting in slow corners...
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

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Re: Square 4 MKI - more troubles

Postby camstevens » Sun May 10, 2020 2:29 pm

Hi Gui
I would also say a blockage......I had that problem too, and it really doesn't take much muck...at all! I fitted a small in-line filter and that nailed it. No more cleaning jets/carbs in strangers' driveways ;)

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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Sun May 10, 2020 6:23 pm

So I took the Solex apart and cleaned everything again, although I didn't find really anything to cause a blockage. There is a gauze strainer on the banjo by the way.

After reassembly, I rechecked the flow out of the tap/fuel hose and appeared fine, so off to a start. She started easier than yesterday and took off, but was still struggling and it kept misfiring one or the other cylinder. So if not the carburetter, it had to be the petrol supply from the tank. This was confirmed as I backed up into the garage. My garage is under the house and acessed by a ramp, and I always back up the bikes into it to be able to ride straight up the ramp. As soon as I was on the incline the rpms picked up dramatically, I suppose as the petrol rushed to the back of the tank rainsing the level around the tap. I had maybe 1/4 in the the tank.

So the tank was emptied and the tap came out, and indeed the strainer was covered by muck on the bottom bit. Everything blown clean, checked by blowing that everything was free and back in. This time I installed a clear petrol line to see the petrol flow. It flows, but Still not quite happy with it. Might just buy a new tap to see if there is a difference.

I'll report the next time I can take her for a ride if there is an improvement. Didn't have time to try again today.

Cheers
Gui

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Re: Square 4 MKI - more troubles

Postby Gui.dorey » Sun May 10, 2020 7:26 pm

Meant to ask before but forgot.
What type of petrol tap is everyone using on their Square four?
Mine is a BAP tap. Could this tap be causing trouble by not having enough flow maybe? Any experiences?


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