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Sq 4 MK II (Solex) Reluctant to cold start

Posted: Thu Mar 07, 2019 1:50 am
by pauldridge
I now have about 250 miles on the complete engine rebuild on my '53 Sq 4. I have already gone through 3 oil/filter changes/head re-torque/valve adjustment procedures to be on the overkill side. The bike is performing like a champ.. minimal oil leakage, smooth and consistent power throughout the range.

My only problem is with cold start. Most of the time, it just refuses to start via kickstart when cold. It seems a full kick is only good for a single revolution of the crank, more or less, and that may be part of the issue. I have had to resort to a push start down a short incline on our driveway, which always gets results. Once the beast starts from cold, even if running for less than a minute, then it is quite happy to respond to a single kick for subsequent starts. today I push-started the bike and then rode it 20 miles out to my shop to complete the turn signal installation. I had to start it a couple of times due to stops enroute.. every time, a single, leisurely kick did the trick.

However, after the bike sat in 50F degree temperature most of the day, it refused, once again, to revive itself via kick start, and I had to leave the bike and drive my pickup truck home. .

This is getting frustrating. The bike performs beautifully once started and warmed up, and the 3-position Solex "bi-starter" seems to be doing its job (start with knob full out, reduce to half position after 30-45 seconds), then full off in a few minutes.

But, from cold, that one-revolution kick just doesn't get it.

I've completely disassembled and cleaned the Solex carburetor, including the "bi-starter" (simple at best, with minimal gaskets), and have used new gaskets every time I've removed the carb-to-head manifold and carb-to-manifold. As near as I can tell, I do have the 'bi-starter" knob adjusted so that full out does give full control deflection at the device.

it just runs so beautifully throughout the range from idle to 70-75 mph after a 2-3 minute warmup, but so frustrating from a cold start.

I hope someone can give me a clue as to how to avoid asking for a push start at my next biker gathering!

As an additional input, yes, I just replaced all my HT ignition leads, have new spark plugs and points, and have very carefully checked timing for TDC at static. Also, because when hot, the carburetor drips a bit of fuel if left on the side stand, I have taken to always storing her on the center stand, and running the fuel bowl dry at idle upon shutdown.

Again, the bike performs almost perfectly once started and warmed up.. no missing, no hesitation, pulls right off from a dead stop like a freight train!

full bike-2.jpg

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Thu Mar 07, 2019 10:31 am
by john.whiting
The bi starter obviously isnt working for whatever reason........I suggest the fuel supply may be blocked...or maybe the air supply...(.that should cover it.)

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Thu Mar 07, 2019 6:55 pm
by chris.shearwood
pauldridge wrote: Also, because when hot, the carburetor drips a bit of fuel if left on the side stand, I have taken to always storing her on the center stand, and running the fuel bowl dry at idle upon shutdown.


Hello Paul,
What happens if you leave the float bowl full? There should be no leakage if the bike is on the rear stand. Also, what grade oil are you using? At fifty degrees Fahrenheit straight 50 would get thick enough to make it difficult to spin the motor fast enough to start.
Regards, Chris

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Thu Mar 07, 2019 8:32 pm
by paul.jameson
I can only think that the problem is in the bi-starter area. I would attack with a jet from the air compressor to see if that helps. You haven't got the square gasket between the carb sections blocking one of the passages due to being 90 degrees wrongly aligned by any chance? An outside possibility is incorrect jet sizes as one of them is different for the 1953 Mk II in comparison with previous bikes.

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Thu Mar 07, 2019 10:37 pm
by pauldridge
Hi Paul,
Thanks for that suggestion. My notes re: jets that I observed when disassembling the carb: . 120 170 26

I WILL take a look at that gasket next time I have the carb off. However, I am inclined to agree with Chris's note regarding thick oil. I am still running 40 wt non-detergent, and, yes, the engine is VERY stiff when cold. Sometimes it is all I can do to get it to turn over the first few revolutions but then it frees up. Today I had to get my shopmate give me a push from cold. it took two clutch engagements to get it going.. then, after about 45 seconds or so, I let off the throttle for a second and the engine died. I was able to restart it then with the easiest of a single kick. Ran it a bit longer on the full extended position, then idle for a couple of minutes on the mid position, and she was good to go.. the exact same scenario played out on my previous cold start a week ago.

It may be that the combination of a brand new, fairly tight engine, combined with thick oil in winter time is all that is needed to prevent the engine from spinning over long enough to start?

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Fri Mar 08, 2019 12:41 pm
by chris.shearwood
Paul,
That 40 weight oil should be O.K. for 50°F temperature. To eliminate the oil as a cause of your problem why not change what you have in there for some synthetic 15W-50? What lubricants are you using in the primary case and gearbox?
Regards, Chris

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Fri Mar 08, 2019 1:03 pm
by pauldridge
I am sticking with the non detergent oil during break in period, and I do have an oil filter. Spring is on the way so I will endure until I get about 1000 miles on the engine

Phil

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Fri Mar 08, 2019 8:12 pm
by simon.holyfield
Phil, I ran sae 40 for a bit here in the UK. In December, at about 2-3 degrees C I had to bump every cold start; I use Penrite Shelsley Medium these days which is 25w-70 I think - my bike kicks over much more easily in the winter.

By the way, my big ends are quite 'loose'; I'd probably be using 20w-50 if they were closer to standard spec.

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Fri Mar 08, 2019 8:20 pm
by pauldridge
Thanks Simon,
I'm going to go with your premise, and assume all will be well once the engine is broken in and spring arrives (next week for sure!)

Phil

Re: Sq 4 MK II (Solex) Reluctant to cold start

Posted: Mon Mar 11, 2019 6:42 pm
by MARK.WALSH
Paul
when you get the bike running what happens if you apply the bi-starter when warm?
If the answer is no change, then the bi-starter must not be functioning as the bike should instantly stall
Regards
Mark