SQ4 Mk2 starting issues

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berniejones
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SQ4 Mk2 starting issues

Postby berniejones » Thu Mar 12, 2020 8:50 am

My bike has covered around 200 miles since full rebuild.
It's often taken upwards of 15-20 kicks to start from cold and i've assumed that's down to the long inlet tract from the SU.

However, after being stood over winter it won't start and I have to give up due to exhaustion!

Spark seems good - although new battery on order - so I'm guessing fuel related.

I suppose the carb could be a bit gummy after being stood for a few months and maybe I should pull the jet block and clean.

Does anyone else have similar issues or other ideas please?

Thanks,
Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
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simon.holyfield
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Re: SQ4 Mk2 starting issues

Postby simon.holyfield » Thu Mar 12, 2020 9:10 am

I have a Solex on mine as you know Bernie.

I'd be looking at the choke mechanism and the float height if my experience with SU H and HS carbs on various BMC cars is anything to go by.
cheers

Simes

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harry.thompson
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Re: SQ4 Mk2 starting issues

Postby harry.thompson » Thu Mar 12, 2020 11:35 am

I have always been very happy with the SU carb and I set mine up strictly following the destruction sheet with standard jets and needles. Mine will always start with a couple of kicks cold and mostly one kick when warm. As Simon says, the float height is something to check first. Are the plugs wet or dry to indicate fuel flow after so many kicks? If the float height is good and flowing properly then check other blockages and gumming up issues, its an easy carb to clean. Jet centring probably won't cause a starting problem but will affect running once you are off the choke so look out for that. Make sure its not a timing issue though...I get the idea that this is something that was never quite right in the first place and has been getting worse.

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Re: SQ4 Mk2 starting issues

Postby roger.fellows » Fri Mar 13, 2020 6:36 am

Try leaning the bike to the left after turning the fuel on. They like to have plenty of fuel in the tank, not just enough to get to the carb.

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berniejones
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Re: SQ4 Mk2 starting issues

Postby berniejones » Fri Mar 13, 2020 7:34 am

Thanks all - will check all advised and post results.

Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631

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Re: SQ4 Mk2 starting issues

Postby alan.moore » Fri Mar 13, 2020 6:42 pm

Bernie
I had a similar issue with my VH refusing to start after being layed up for a few months. I drained the carb and set up an auxiliary fuel tank with new fuel and it started up straight away. Looks like the fuel in the tank had 'gone off'. Worth trying it with some new fuel before you delve any deeper.

Cheers
Alan
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berniejones
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Re: SQ4 Mk2 starting issues

Postby berniejones » Sat Apr 11, 2020 10:48 am

Some progress I think.... I had previously set the float height as 'per book' but decided to raise it a bit. I set it so that it wasn't quite overflowing from the top of the float chamber then set the mixture nut at 1.5 turns out.

I also advanced the engine a few degrees and it started after a few kicks. It will idle but not particularly smoothly so I think I need to adjust both the timing and the mixture.

Does anyone have any tips for adjusting that nut with the engine running? I can't get my mitts in there so am thinking of maybe making up a custom spanner to do the job.

Finally, the coil I've fitted is a generic Lucas 6V - should I be looking at a specific coil type instead?

Many thanks,
Bernie
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631

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Re: SQ4 Mk2 starting issues

Postby Paul_Linden » Sat Apr 11, 2020 11:48 am

My Mark 2 used to have a starting problem, about one in every twenty cold starts it just wouldn’t start. Starting warm was fine. In the end the ‘fix’ that worked is as follows: if it doesn’t start when cold within 5 kicks then I put the choke lever all the way down, open the throttle all the way and it starts. I then put the choke back on until it is warmed up.
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Re: SQ4 Mk2 starting issues

Postby Dean Mitchell » Sun Apr 12, 2020 1:54 pm

Could it be a starting technique problem. I was shown by a good friend how to start my one, like he does with his one. On with the fuel , full choke, su carb, leave ignition off, two or three kicks, then half choke, ignition on , a little throttle and it would start fine.
Dean.

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Re: SQ4 Mk2 starting issues

Postby berniejones » Sun Apr 12, 2020 2:46 pm

Many thanks all. I'll experiment with the tehniques - it is now starting so I think the main problem was either fuel level or retarded timing.
'56 SQ4
'52 BSA M21
'56 BSA M21 combination
'61 Dommie 99
'64 B40 SS90
'65 A50CC project
AOMCC# 4631


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