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Old 15 January 2016, 15:30   #1
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Mariner 40hp with Yamaha 703 control box

Hi

I have Mariner 40hp on a rib which I bought last year and it is connected to a Yamaha 703 control box which worked fine last year. Towards end of the season I had top off the engine whilst on water and noticed that when the the controls were full throttle the engine wasn't and the butterfly part was not fully open. So we tried it goin along and manually operated the engine and there was a lot more revs in the engine. So we adjusted the throttle cable and the boat would go faster but the idle was to high. Is there any other way to adjust this or is it because the Yamaha controls don't really work with the mariner and don't have enough throw when you push it to full throttle? Any ideas?
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Old 16 January 2016, 01:37   #2
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Welcome to the forum.

The Yamaha/Mariner 2-strokes, are great engines. Leave the remote for the time being.

With the air-box off and the throttle control cable disconnected, check that the butterfly choke valve on the top carb fully opens and closes in sync across both carbs. There is manual adjustment you can make with the carb linkage rod. The butterfly valve can sieze, so check it moves freely.

I'd also drain the carbs and collect the fuel to check there's no contamination. There's a hex screw on each carb (fuel bowl) to see its nice and clear. There's a fuel filter on the engine next to the fly-wheel so check this too. Also check the fuel hose to the engine snaps on properly, and that the 'o' ring in the connector isn't dislodged.

Pull the spark plugs and check the condition. If in doubt replace them. If the engine is running right, they'll be dry, with a light brown powder dusting. Oiled plugs or a lot of carbon build up could be another issue.

Connect the remote back up withe air box off. At full throttle the carb valves should be fully open, again in sync. If they're not, then there is some adjustment you can make on the cable.

If it's reving high, then the fuel-air mix pilot screws may be out of adjustment. Normally with these engines, they should be 1 1/4 to 1 1/2 turns out from lightly seated.
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Old 17 January 2016, 02:40   #3
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Thanks for the reply.

The butterfly is working and isn't seized but it doesn't fully open when the remote control box at full throttle, maybe it opens 3/4's I assume this should be fully open? but when I adjust throttle cables for it to be more open the idle is too high. Is this because of the control box being a different make? I don' think it would be to do with the fuel air mix as the engine runs well and the fuel filter is clear.
I will drain the carbs and check spark plugs in a few weeks when I get a chance. Just trying to work if the control box is correct or I should look for a mariner on ebay during the winter.

Many thanks
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Old 17 January 2016, 11:07   #4
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Check that the control box is matched to engine ie,they both are either push to full throttle or pull to full throttle,I had the same problem with a Quicksilver 2000 which is more or less the same as the 703. If they are not the same you can convert them.Let me know and I'll post the instructions on how to do it.
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Old 17 January 2016, 14:40   #5
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So is the case that if it was the other way round I would get restricted revs in forward and reverse wouldn't be affected? how would I work this out? I'm not sure if it would be this as the rib go's quite well does 25mph. could this still be that is reverse pull throttle?
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Old 17 January 2016, 19:31   #6
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Disconnect throttle,check which way the throttle requires to be moved to get full throttle,remember the throttle also works the opposite way for the fast idle/ warm up facility hence the boat will still run with the remotes working in reverse to engine.
Now push throttle handle to full throttle position and observe which way the cable moves,then you will have your answer.
As a matter of interest did you have to adjust throttle cable to get it to fit?

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So is the case that if it was the other way round I would get restricted revs in forward and reverse wouldn't be affected? how would I work this out? I'm not sure if it would be this as the rib go's quite well does 25mph. could this still be that is reverse pull throttle?
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Old 18 January 2016, 15:10   #7
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Ok great thanks. I will have a look next time I get a chance. I didn't have to adjust it to fit as the boat came with this set up.
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