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Old 24 November 2014, 09:49   #1
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Country: UK - Wales
Town: Bangor, North Wales
Make: Tornado
Length: 5m +
Engine: Evinrude 70hp OB
Join Date: Nov 2001
Posts: 93
Next problem, old Evinrude 70HP surging and no power

Having got the idle RPM to a sensible level, I took the boat out on Saturday. Everything worked well, except when I tried to open the throttle. WOT would stall the engine, judicious increase of throttle would cause the engine to start to surge. It did go nicely just off idle. It really feels like fuel starvation to me. I got my son to try and pump the primer while opening the throttle. It had no effect at all. After leaving the boat over lunch, it briefly went really well, and then was back to fuel starvation.

I think that it is not the fuel pump as pumping the priming bulb had no effect. Also unlikely to be air leaks. I conclude therefore that it must be the float valves on the carbs? I would be more than happy to debate this reasoning as carb rebuild kits are going to cost me a bit. What do you think?

PS. Do I actually need carb rebuild kits at 20+/carb?

All the best

David
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Old 24 November 2014, 10:56   #2
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Country: UK - Scotland
Boat name: Wildheart
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+1. I've had a Suz, a Yam & my current Merc all do the same thing.



To test - forget priming - I assume you are on electric "remote control" choke? - (If not you need a fast fingered volunteer by the engine!)

When it starts to go funny - just blip the choke - and I mean literlaly tap the button / twitch the switch - if it then takes off like a scalded cat as you relese the switch your idle mix is just slightly too lean. Ipve never had to move the adjusrer more than 1/8 of a turn from the "manual's going in point "

I can't rmember if I read you had changed prop - my Merc did that after I went from a 13" to 14" pitch - the extra load was enough to tip it over the edge, and like you it was fine when stone cold.
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Old 24 November 2014, 15:03   #3
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Make: Ribcraft 4.8m
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RIBase
Had similar issue that drove me nuts. I stripped carbs a number of times and they were clean as a whistle. Double-check butterfly choke valve opens properly. I got the timing reset which sorted the problem.

Rule out all other factors such as renew primer bulb on fuel line, clean or renew inline fuel filters and use new spark plugs.
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Old 24 November 2014, 18:51   #4
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Country: UK - England
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Make: Honwave
Length: 3m +
Engine: 20hp 2stroke Mariner
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Quote:
Originally Posted by spartacus View Post
Had similar issue that drove me nuts. I stripped carbs a number of times and they were clean as a whistle. Double-check butterfly choke valve opens properly. I got the timing reset which sorted the problem.

Rule out all other factors such as renew primer bulb on fuel line, clean or renew inline fuel filters and use new spark plugs.
Hi all

A quick suggestion would be HT leads or coil,make sure your lead is inserted properly.
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Old 25 November 2014, 04:41   #5
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Country: UK - Wales
Town: Bangor, North Wales
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Length: 5m +
Engine: Evinrude 70hp OB
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Posts: 93
I have seen a HT problem that left an engine that ran fine at all but WOT, where it would miss like mad/die. I don't think that could be what we are seeing here because it will surge when on the edge of the problem. I don't think that could happen with a HT issue. The manual warns that the fuel pumps are a known weakness, so might do that at the same time...
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