Silver Century plus not revving up

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rstumpy
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Silver Century plus not revving up

Post by rstumpy » Mon Sep 11, 2017 3:00 am

Greetings all...just returned to seagulls...previously had a flock but my (now) former mrs. forced their removal.

I'm away from home (and special tools) on a job, but recently rescued a 13' wherry and a '72 Silver Century plus (WSPC 1561C2) from a journey to the landfill. Salmon are running here so had both in functional shape in a couple evenings so I could fish the river.
I did all the usual seagull life-giving procedures...she came back ok and starts and remains running...just one glitch...
Warm or cold, the gull four-strokes and will not tach-up. Runs indefinitely, exhaust level normal, temp and waterflow fine...no backfires but am getting residue on the storm hood of the carb as four-stroking will do. Did a proper job cleaning carb and fuel system. Did points, new plug, fresh non-ethanol 91 octane fuel at 10:1 mix, etc.
The carb is an Amal 46NL. Don't have my jet tool with me but carefully checked with an indexed drill bit (smooth end) and I believe it's still jetted 10:1. Needle and float appear fine and clip is in the notch.
Yesterday enroute to my salmon spot I fussed with the fuel tap and tank vent until I figured fuel flow was reduced to a minimum...she smoothed out and ran up to a decent rpm for my 20 minute run...not perfect but not stroking. The day before it had smoothed out for a few seconds before stopping after I shut off the fuel tap to coast in to my fishing spot, so I figured too much fuel might be it. My '46 Taylorcraft aeroplane (like an Auster) jumps a few rpm just before stopping by shutting off the fuel, but it's a four-stroke continental engine. ;-)
There are no other problematic symptoms. Compression is 65 lbs. Spark is fine. No improper leaks or seeps anywhere. On the off chance that I'm mistaken about the carb being jetted for 10:1 I considered trying 25:1 fuel, but I have always run 10:1 in 'gulls and prefer that...plus, seems to me that 10:1 mix in a 25:1 carb would lean things and prevent the problem I'm having, not cause it. Again, the needle is fine and the (plastic) float looks fine and bubbles not a whit when immersed in a water bucket.
Apologies for the long post but the devil's in the details. Figured it's something simple and my seagull memory is failing me.
Thanks!

rstumpy
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Re: Silver Century plus not revving up

Post by rstumpy » Mon Sep 11, 2017 4:58 am

Oops...left a couple of other details out...

Engine height is correct...I made a collar to lift it a couple inches so it was right with my gear and I in the boat in operating position.

Carb doesn't leak with tap on and the tickler functions properly, hence I had assumed the float and needle are working correctly.

As stated previously, I went through the fuel system, cleaned both filters, the carb,fuel line, boiled the tap cork, etc.

headdownarseup
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Re: Silver Century plus not revving up

Post by headdownarseup » Mon Sep 11, 2017 8:57 pm

Has your carb got a choke flap? Are you leaving the choke on for too long?
Fuelly/oily residue inside the cowling is pretty normal for a 46n carb, all my 102's do this (so do my 40's) and run like a champ.

Is the throttle slide adjusted correctly, is it sitting within its little "guide" inside the carb body.
20thou gap for both plug and points, although you could try and reduce the points gap a little to maybe 12-20 thou and see if it runs any better like this. 65psi on the compression is pretty good for one of these, so i don't see it being a problem with lack of compression.
The higher the engine revs the less it will 4 stroke within reason. I feel there may be some experimenting left to do in order to find where the engine is happiest.

Chances are that you still have the original 10:1 jet being that your engine is a 72 motor, but you never can tell if anyone has been inside your engine before you ,so worth double checking this.


Good luck with the salmon :P


Jon

rstumpy
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Re: Silver Century plus not revving up

Post by rstumpy » Mon Sep 11, 2017 10:21 pm

Thanks for the reply Jon.

Carb slide is in good shape, installed correctly and is happily moving through it's full range.

I was thinking along similar lines earlier...have had the points at several settings between 14 and 20 thou, no discernible differences, back at 20 thou now.

Actually is starting easiest with a slight tickle and partial choke, then no choke immediately and she goes.

Hence my quandary....she just chugs (4-strokes) from idle to full throttle, which is producing perhaps 1700-1800 rpm chugging. Will do that with some variation indefinitely. The slide is fully up at full throttle as well.
But when I close the fuel tap to the point where it's barely open, and leave the tank vent barely open for good measure, after a few seconds she'll smooth out and run up to proper rpm.

I should add that the above is under a load. In neutral it will tach-up but not smoothly to about 3500 rpm with the fuel tap full open.

Seems the issue must be fuel related, and I was thinking it has to be needle and float...but both are in good shape and the needle/float shut the flow off with the tap fully open (meaning the carb isn't dripping fuel). The needle only has one slot, and the float clip is in it solidly. No provision for any adjustments there. Considering this it seems odd that she will suddenly run up proper when I fiddle with the tap and find the "sweet spot" in relation to restricted fuel flow.

I'm at a loss (not unusual).

Thanks,
Bob

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Charles uk
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Re: Silver Century plus not revving up

Post by Charles uk » Mon Sep 11, 2017 11:06 pm

Lower the float on the needle to the bottom notch & try again, If that doesn't cure it, strip & clean the needle valve well & try again.
Make it idiot proof and someone will make a better idiot.

headdownarseup
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Re: Silver Century plus not revving up

Post by headdownarseup » Mon Sep 11, 2017 11:16 pm

2 notches Charles?

Never heard that before. You sure??


Pointy end of the needle valve pointing uppermost (into the float bowl cover)
Unless there's something i don't know about, there's just 1 notch on there which is what sets the float level.


Jon

rstumpy
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Re: Silver Century plus not revving up

Post by rstumpy » Tue Sep 12, 2017 1:10 am

Thanks fellas,

Only one notch on the needle.

Pointy end is up.

I have given thought to carefully filing a second notch 1/4" below the first...or perhaps attaching a small amount of fuel-safe foam underneath the float. That being said, the carb is clean and in good shape, so is the float and needle, and I sure can't see why it shouldn't work as designed without Rube Goldberg mods, so not going there yet.

Will give the needle valve well another going over though. Was cleaned thoroughly already but my infallibility is questionable at best.

Thanks
Bob

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Hugz
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Re: Silver Century plus not revving up

Post by Hugz » Tue Sep 12, 2017 1:47 am

I had an amal that to the naked eye was spotless. Cleaned it again with rattle can carb clean and l was amazed at the improvement.

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Charles uk
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Re: Silver Century plus not revving up

Post by Charles uk » Tue Sep 12, 2017 6:39 am

2 notch needle S22/014.
Make it idiot proof and someone will make a better idiot.

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seagull101
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Re: Silver Century plus not revving up

Post by seagull101 » Tue Sep 12, 2017 4:33 pm

I have never seen a 2 notch needle!

headdownarseup
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Re: Silver Century plus not revving up

Post by headdownarseup » Tue Sep 12, 2017 5:23 pm

Nor me!

Got any pics Chas.?
More specifically, which years were these needles fitted into gulls? Is it a late model fitment... or is it intended for foreign climates with hotter/colder temperatures?

rstumpy
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Re: Silver Century plus not revving up

Post by rstumpy » Tue Sep 12, 2017 8:19 pm

I wasn't aware of a two-slot needle for the Amal 46 either.
Perhaps it's intended to compensate for different fuels? Different fuels have different specific gravity. I set the float in a stromberg carb on 1940's vintage aerocraft differently dependent upon intended use of 100ll avgas or non-ethanol mogas (autofuel).

I'd sure like a pic. Would like to know the measured needle length and position of each notch even more. If they're close to each other my guess may be correct...in which case I'd be tempted to file a second notch in my needle at the appropriate location.

Keith.P
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Re: Silver Century plus not revving up

Post by Keith.P » Tue Sep 12, 2017 8:40 pm

I just walked into the shed and opened one Amal carburettor float cap and I found.

tambikeboy
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Re: Silver Century plus not revving up

Post by tambikeboy » Tue Sep 12, 2017 8:54 pm

:lol:
Roll me up and smoke me when I die
Regret is just a memory written on my brow

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Charles uk
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Re: Silver Century plus not revving up

Post by Charles uk » Tue Sep 12, 2017 9:00 pm

Rstumpy, I won't be where the carb bits are for a few days, why not try trial & error, take a ring binder hole punch & punch some holes in an old inner tube, push the dot of rubber onto the float needle, push the float down a bit & slide the dot into the notch, try 2,3,4 dots with the top one always in the notch, then file the notch where you get the best running, without the mixture getting too weak.

How high do you run above sea level, are you in the Rockies?
Make it idiot proof and someone will make a better idiot.

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