New member, '52 VH500

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Leslie.Ore
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Re: New member, '52 VH500

Postby Leslie.Ore » Mon Mar 09, 2020 1:38 pm

Have a look at your timing again.

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Re: New member, '52 VH500

Postby PeteL » Mon Mar 09, 2020 2:07 pm

Thanks Len.
I presume you mean Ignition timing.
I set it on 1/2" BTDC as accurately as I could, and had the lever at about 1/3 maybe 1/2 advanced.
Do you think the flash back would be caused by too much advance ?

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dave.owen
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Re: New member, '52 VH500

Postby dave.owen » Mon Mar 09, 2020 2:10 pm

With full advance on the lever , set to 5/8 points just opening.

Or if easier points opening at tdc with lever fully retarded.

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john.whiting
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Re: New member, '52 VH500

Postby john.whiting » Mon Mar 09, 2020 2:17 pm

Funny you should mention this..... a good many years ago I bought a 500 Red Hunter with very low miles that had a fire that melted the carby and the magneto......the owners had sold off the forks ,too.....think I paid $10 or maybe $20 for it.....Bought a set of forks with front wheel off George Buckley for $5 ,I think....... the 20" wheel was a big downer in those days,no tires.

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Re: New member, '52 VH500

Postby PeteL » Mon Mar 09, 2020 2:51 pm

Well as I had the spark lever somewhere mid way, I'm going to reassemble the carb and see if I've stopped the leakage and then try kicking it over, with extinguisher handy, on full retard and then on full advance.
One or the other should result in no flames and one might even result in engine running.
I settled on 1/2" before TDC as the most often given setting in various handbooks & manuals for my year and model of ariel.

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Re: New member, '52 VH500

Postby PeteL » Mon Mar 09, 2020 3:25 pm

Well the carb continues to drip copiously after the float has been tickled and drips steadily for several muinutes even if the fuel is turned off, which does not seem normal to me.
Or maybey my memory of how they behave is at fault !
So I have not carried out my experiments with timing adjustments while there is fuel slopping about so freely.

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alan.moore
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Re: New member, '52 VH500

Postby alan.moore » Mon Mar 09, 2020 7:16 pm

I have found that the pre monobloc is quite sensitive to being over flooded by tickling. There is a small U shaped hole on the left side of the body just above the large plated bottom nut. If you tickle it too much fuel will flow out of this hole for some time until the level drops in the float bowl (the idea is that it prevents fuel running into the inlet port).

As you have found out, trying to start a bike with a carb even slightly wet on the outside with fuel is not recommended as a small backfire is likely to ignite the fuel vapour.

Does the carb drip fuel if you just turn the fuel on and then leave it a while with no tickling?

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1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
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Re: New member, '52 VH500

Postby PeteL » Mon Mar 09, 2020 9:14 pm

Thanks, that's encouraging.
It dosn't seem to drip when fuel is left on and not tickled, which did make me wonder.
If it is due to over tickling, it seems to take a long time for the surplus to stop running.
As I have a small remote fuel container I can suspend beside the bike, I will take the tank off tomorrow and connect to this remote supply. This will make it easier, both to see what's happening to the fuel level, and to try starting without so much risk, if fire does occur again.

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Re: New member, '52 VH500

Postby john.whiting » Mon Mar 09, 2020 10:50 pm

The army bike instructors used to purposely set fire to the carbies of the WM20s,and pretend they hadnt seen it .....then at the last moment ,they would kick the bike ,and rev the motor ,sucking all the flame in.......The claim was that with the carby on fire ,the bike would always start.......As a kid ,I always remember being viciously kicked back by Ariels ,starting them in bare feet.

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alan.moore
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Re: New member, '52 VH500

Postby alan.moore » Mon Mar 09, 2020 11:22 pm

Pete
If it does not leak without tickling it suggests the fuel level is about right. I have read that if pre-monobloc over tickled it does take a while for the flow to stop.

FYI: The correct fuel level is when it is at a point between the centre and the bottom of the pilot screw head. I have made up an adapter that screws into the threaded drain hole which is located on the arm of the float chamber (it normally has a slightly domed blanking screw in it). With a piece of clear tube on the adapter you can hold it against the carb and see where the fuel level is. You can adjust the level to some extent by rotating the float chamber around, after slightly loosening the bottom union bolt. You will see the effect of this on the level of fuel in the adapters pipe. (Don't forget to tighten the bolt again!).

If the level is still slightly too high options are putting an additional fibre washer between the top of the float chamber arm and the large carb body nut or (and this is what I had to do on my 276 carb) file / junior hacksaw saw another groove in the float needle just below the original one.

If the ignition timing is correct check you have clearance on the inlet valve adjuster. If the valve is held open by a tight adjuster then, if you get it to fire, you will get a flashback through the carb.

Another thing is try starting just using choke (no tickle) or just a quick tickle i.e don't hold it down until fuel flows out of the tickler.

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t


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