Lack of power

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Petebarn
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Lack of power

Postby Petebarn » Tue Sep 11, 2018 11:30 pm

Took the350 nh out for a run OK for 10/15 miles stopped for 10 minutes it wouldn't start run it down hill and bump started it to get it home it starts OK now but don't like hills I've checked timing and tappets ect I've got to say for an alloy head it runs very quiet any suggestion s greatly appreciated. Pete

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Eero.Korhonen
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Re: Lack of power

Postby Eero.Korhonen » Wed Sep 12, 2018 8:38 am

Hi Pete,
Have you measured compression pressure? What kind of piston do you have?
Br, Eero
Ariel VH 1954, IZH 350 1962, H-D Sportster Hugger 1992, AOMCC Member 133

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chris.shearwood
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Re: Lack of power

Postby chris.shearwood » Wed Sep 12, 2018 12:24 pm

Petebarn wrote: OK for 10/15 miles stopped for 10 minutes it wouldn't start


Difficulty with hot motor starting suggests a magneto condenser problem. Next time it won't start when hot check to see if you have a good spark. Bring along another spark plug with the gap opened up to an eighth of an inch or so for testing purposes.
1946 4G, 1950 NG and 1951 VH

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Eero.Korhonen
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Re: Lack of power

Postby Eero.Korhonen » Wed Sep 12, 2018 12:40 pm

Chris, do you mean 3,175 mm?
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Ariel VH 1954, IZH 350 1962, H-D Sportster Hugger 1992, AOMCC Member 133

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chris.shearwood
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Re: Lack of power

Postby chris.shearwood » Wed Sep 12, 2018 6:12 pm

Eero.Korhonen wrote:Chris, do you mean 3,175 mm?


Hi Eero,
Yes, 3.175 mm is what I mean. When the motor and sparkplug are hot it is handy to have a spare (cool) plug in one's pocket to make testing the spark a simple matter of pulling off the high tension cable from the hot plug, attaching the cable to the cool plug, placing the cool plug on the motor somewhere to ground the body of it and then kicking the kickstarter to observe the spark. Out in atmospheric pressure a good magneto should be able send a spark across an eighth of an inch gap.
Regards, Chris
1946 4G, 1950 NG and 1951 VH

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Eero.Korhonen
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Re: Lack of power

Postby Eero.Korhonen » Thu Sep 13, 2018 8:07 am

Thanks for that, Chris.
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Ariel VH 1954, IZH 350 1962, H-D Sportster Hugger 1992, AOMCC Member 133

Petebarn
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Re: Lack of power

Postby Petebarn » Thu Sep 13, 2018 3:41 pm

Spark OK ,good compression when cold but less so hot,I've checked tappets, no smoke or knocks ????

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Re: Lack of power

Postby Simonjones » Sun Sep 16, 2018 8:24 pm

I’m not in any way an expert but I had similar power issues with my ally head NH when it got hot. I have a feeling mine was at least partially caused on the fueling side of things. It seams better after fitting an insulating spacer between carb and head.
1950’s NH350 bitsa 1949 Triumph Speedtwin

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Re: Lack of power

Postby nevhunter » Sun Sep 16, 2018 11:06 pm

With some "stainless" exhaust valves you need much more tappet clearance than originally recommended. I've had to use .012" to retain clearance when on load on some SV motors. SV cylinder also distort more than OHV ones due the location of the exhaust port near the side of the cylinder. Having an extra comp ring can help there. Nev.

Petebarn
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Re: Lack of power

Postby Petebarn » Tue Sep 18, 2018 7:29 pm

Thanks all I've lifted needle one notch and it seems better I'm away at the moment will give it a good run when I get back lots of hills down here to try it on.


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