VH misting from carb

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Mickypic
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VH misting from carb

Postby Mickypic » Thu Sep 17, 2015 4:17 pm

Finally got my 1949 VH running after 3 years rebuilding it, but I seem to be having a problem with petrol mist coming out of carb and wetting oil tank. I fitted a later one lobe cam, carb is standard with correct jets. Bike starts and seems to run ok apart from misting from carb, is this usual or does it seem I am one tooth out on the timing?
Cheers Michael

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Re: VH misting from carb

Postby john.whiting » Fri Sep 18, 2015 9:30 am

Sounds as though the inlet valve is too advanced in opening,but if you have set the timing correctly,it might mean someone has reground the cam,or the lifter profile.This is another good reason for an aircleaner,as the mist and fuel blown out is highly flammable petrol.Regards John.

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Keith.owen
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Re: VH misting from carb

Postby Keith.owen » Fri Sep 18, 2015 10:43 am

Hi,
I have a 1950 VH with a concentric fitted.

I would very much like to fit a filter but have tried an offset pancake and a tapered filter from Hitchcocks - neither fitted properly.

Doses anyone have any suggestions?

Keith
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alan.moore
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Re: VH misting from carb

Postby alan.moore » Fri Sep 18, 2015 1:03 pm

Certainly sounds like the valve timing is out meaning the compression pressure is blowing air through the inlet valve and then through the carb.

If you have the timing marks aligned correctly I would put a timing disc on it and check where the valves are opening and closing. This thread should give you a lot on info http://forum.arielownersmcc.co.uk/viewtopic.php?t=601
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
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brenton.roy
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Re: VH misting from carb

Postby brenton.roy » Sat Sep 19, 2015 6:47 am

Depends on the cam profile, and cam timing.
If it's a standard cam, you're a tooth out or if it's a regrind, you might need to set the engine timing with a degree wheel. Reground cam timing should be checked in any case.
To alter timing for part of a tooth, you can cut new keyway slots in the cam gear. This isn't difficult.
If it's a HS or aftermarket performance profile, the misting might be normal (late closing of inlet valve to maximise cylinder filling) and will go away at business revs.
Checking engine timing isn't difficult. You then know exactly where things stand. I can post a couple of photo's if needed.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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john.nash
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Re: VH misting from carb

Postby john.nash » Sat Sep 19, 2015 8:29 am

Amal are remaking the flame trap for earlier carbs

viewtopic.php?t=2291

Unfortunately, doesn't fit a concentric and I have the same problem as you, limited space to fit a filter. they do make a short bell mouth, with a fine gauze, which would likely perform the same as a flame trap but not really help filtration that much....
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Re: VH misting from carb

Postby john.whiting » Sat Sep 19, 2015 10:35 am

Heresy to be sure,but in the dim distant past I fitted a later oil tank to my 1950 VG so that an airfilter would fit in.Now I wish I hadnt sold the correct oil tank for $5.A 350 oiltank would likely also provide the space needed.Regards John.

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Re: VH misting from carb

Postby paul.jameson » Sat Sep 19, 2015 9:01 pm

Stop worrying about the misting. I fitted a VH style oil tank to my RH500 earlier this year (it having previously had a 350 size oil tank, petrol tank, engine and gearbox. The oil tank was the last thing to be changed, engine and gearbox being up to the 10,000 mile mark when the oil tank was fitted). I had sprayed the tank with an aerosol and was somewhat annoyed when the black paint turned greyish behind the carb inlet. So it is obviously spitting fuel back at the oil tank. My engine is on a standard A6/664 cam and tuned correctly. Both Rob Jameson and Andrew Grant (amongst others) will confirm that HUG 746 performs well as an RH500 so I can only conclude that the spitting back is a standard fitting.

Ride the thing and stop worrying.
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Re: VH misting from carb

Postby Simon.Gardiner » Sun Sep 20, 2015 12:15 pm

Misting - I agree with Paul (my '53 NH with a single-lobe cam misted the oil tank lots and there was nothing wrong with that engine!)
Air filter - can you fit one of those conical K+N ones?

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Re: VH misting from carb

Postby Mickypic » Sun Sep 20, 2015 8:17 pm

Thanks for replies. I will check timing with time disc. I have looked in book for timing and its says inlet valve opens at 26 degrees before top dead centre and closes at 77 degrees after bottom dead centre but this means that the valve is not closed until piston is nearly half way up on the compression stroke , this would make the mixture come back out of carb. 77 is only 13 degrees from 90 degrees which half way between top and bottom dead centres ?
Cheers Michael


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