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Old 27 February 2015, 12:53   #31
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For comparison, here are the two carbs (one is a spare). I have cleaned them and blown the through but haven't tested either:

First one is the Yamaha one:



The float rests nice and parallel to the body of the carb.



The second, Mariner, one doesn't:



The Mariner one (that has been going for about twenty years) seems to be missing a brass 'standpipe'.



One of the plug caps was unscrewed and only just making contact...
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Old 27 February 2015, 22:52   #32
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Both of those carbs show signs of contaminated fuel.

I can't remember the float height for one of these.

I don't think either height is correct. One is too high and one too low.

Try setting the better carb in between the two for now. That's why your needle jets not working.

Use the float chamber with the brass needle.

At least we know the plug was tracking.

Lastly, a fuel pump can affect starting once primed. If you have a burst diaphragm and you pump fuel into the bottom cylinder, it will flood. So check your fuel pump and renew the small gasket behind it.

To check a fuel pump, remove the bolts and squeeze the fuel bulb (a good one). If fuel shoots out of the Middle hole, the diaphragms shot. If not, remove the pipes and check the valves inside. Blow into the pump in the direction of flow and the suck. You shouldn't be able to suck. Then suck the opposite end of the pump and then blow. You shouldn't be able to blow. If the pumps gone, it's not worth stripping it. Just buy a new one. Remember to grease the bolts and apply a light film of grease to the gasket. This allows you to reuse it. Do not overtighten the bolts.

So, if you have a dodgy carb. A potential worn fuel pump (tbc) and a tracking plug, there's a good chance you've found the problems. Make sure you clean the tank and put an inline filter in the fuel line before it hits the engine.
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Old 27 February 2015, 22:58   #33
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If it will unscrew, remove the brass main jet. But be very careful to use the correct screwdriver. On slip and it's broken. Pop out the other brass tube, they have small holes in them and are famous for getting blocked.

Jets do wear with fuel going through them. If one has a smaller hole in it, use that one and check the plug colour after a run. It should be dry and tan. Dry and white is too lean, black and oily is too rich. It is the main jet that will dictate that, assuming your mixture screw is at 1&3/4 turns out from lightly seated.
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Old 27 February 2015, 23:41   #34
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Sorry, that should read - it is the main jet and float height that dictate that.

Measure your float heights with a ruler in the closed position and set it in between the two as a guide. I don't recall them being level, but certainly not sitting way down either.
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Old 28 February 2015, 00:03   #35
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Lastly, clean the outside of the carb with alloy wheel cleaner. It will come up well
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Old 28 February 2015, 06:13   #36
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Quote:
Originally Posted by RIB-Teccie View Post
Lastly, clean the outside of the carb with alloy wheel cleaner. It will come up well
So it does!

A bit of Googling showed the float level to be 18 0.5 mm which turns out to be 'level'. The actual float valve had a bit of stiction in it. Even though it would have fuel pressure behind it, this probably wouldnt help.
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Old 28 February 2015, 13:22   #37
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Quote:
Originally Posted by RIB-Teccie View Post
If you have a burst diaphragm and you pump fuel into the bottom cylinder, it will flood. So check your fuel pump and renew the small gasket behind it.
Quote:
Originally Posted by HughN View Post
Any thoughts about why it is reluctant to start but runs happily after that?
Have you seen a motor with a severely leaking fuel pump that idles well, and doesn't foul the lower plug? If it were mine I would be replacing the fuel pump anyway per it's age and cost is cheap, I paid $12 US, but most likely it is not the problem. Pulling the plugs would more quickly determine if there is a fouling problem.

Hugh, carb kits are cheap at around $15 US dollars. Plus it will come with a new float seat. It should be smooth up and down. It is the up part that is mostly important to stop the fuel flow.

Any question about ignition leads means they should be replaced. Tracking can not be cleaned.
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Old 01 March 2015, 10:39   #38
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Generally with a holed diapragm they are sticky to start and idle fine. I've seen this many times, which is my second check after spark. If they are severely torn then it has an effect but strangely once the revs are up as fuel is sucked into the bottom pot. The other issue is the valves not sealing properly. That can cause rough idling.
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Old 06 March 2015, 07:42   #39
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I agree with Davie. If it runs and starts great while warm. You have a Choke and possible chocked-timing advance. Problem. If so it should not be overly hard to adjust, you might want to look up the choke setting specs for that motor and year. After years of use and failure to properly lube the choke levers and exterior moving parts, they wear, eventually putting the choke specs out or in the extreme-inoperable. Many motors (my Merc too) had the same cold start problem the year I bought-it. During the winter I took a serious look at the Choke operation to find the Choke to throttle cam was warn to the point it did not open the throttle at cold starting. Sanding and epoxy fixed the problem completely..not to mention removing ,cleaning lubricating all external parts. Starts cold the first pull now.
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Old 06 March 2015, 11:56   #40
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Today was the first time I have been able to take another look at it. With a new primer bulb, cleaned carb, repaired spark plug lead and a slosh of new fuel it did actually start quite easily!

It then slowed to a halt - the bulb had gone soft so I probably have an air leak in the fuel system somewhere . The strange ticking noise must have been the ignition lead as the noise is no longer there.

Thank you all for your help - we got there in the end.

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