# Yamaha YS624 surging at high rpms



## YSHSfan

Hello everyone,

I have one of my YS624 that idles beautiful, but at high rpms with or without load surges (gets worse at times).

What are the possibilities for this to be happening.

I've used 2 YS624, 2 YS828 and 2 YS240(Ricky) and all of them were smooth runners at high rpm and with load.

Any ideas on what to look for....? :icon-shrug::icon_scratch::smiley-confused009::blush:


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## cpchriste

I'm working on one with same symptoms. I've finally decided it's too rich, [I live at 8000ft]. I made that evaluation because when I richen the mixture, with my finger partially over the carb opening, it instantly worsens the misfire. I'm going to put in a smaller main jet to confirm that.
You may have a different situation. Have you decided whether it's too rich or lean? You can get a rough idea by slightly using the choke to enrich the mixture. Do that first and then I'll give you a list of possibilities.


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## YSHSfan

cpchriste said:


> I'm working on one with same symptoms. I've finally decided it's too rich, [I live at 8000ft]. I made that evaluation because when I richen the mixture, with my finger partially over the carb opening, it instantly worsens the misfire. I'm going to put in a smaller main jet to confirm that.
> You may have a different situation. Have you decided whether it's too rich or lean? You can get a rough idea by slightly using the choke to enrich the mixture. Do that first and then I'll give you a list of possibilities.


Thanks.
I decided to take the carburetor out and also took the carburetor off another YS624 that I have, both carburetors are in my ultrasonic cleaner as of right now. I'm going to put them through two cleaning cycles and reassemble the needle, float and float bowl (which is all what really needs to be disassembled when cleaning the carbs on the ultrasonic cleaner).
I'm going to drain the fuel, take the fuel tank and fuel valve/filter and clean them up as I found some "grit" in the carburetor.
I'm going to replace the fuel hoses and carb gaskets, reinstall fuel tank, fuel valve, the carburetor, adjust the governor, adjust the carb as needed and see how it runs, if it still surges then I would install the additional carburetor from the other YS624 and see what happens.

So, I think I have a plan.... although I'll be a bit like this while I do some of the repairs.... (but not so bad).
:t09015: :smiley-gen125:


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## cpchriste

You might as well run a wire through the main jet while you're there to be positive it's clean. Almost try to read the jet number: mine was an 80 but there seems to be a 100 installed in some ys624 models as per boats.net. A #67 drill [.031"] drill will confirm you have an 80 jet if you cant read the number.

Consider running some carb cleaner through the pump inlet and outlet and the vacuum side vent port. Not likely a problem but why not be sure it's clean? No compressed air though.

Good luck - stay warm.


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## db9938

And don't forget to use some compressed air, to dry it completely out. The last thing you want, is ice in a small orfice.


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## YSHSfan

db9938 said:


> And don't forget to use some compressed air, to dry it completely out. The last thing you want, is ice in a small orifice.


Thanks db.
Rinsing it thoroughly with warm/hot water and blowing them dry with compressed air is our shop standard procedure after the ultrasonic cleaning cycle.


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## bad69cat

Chances are once you get it cleaned up you will resolve the issue...... you might have to jump up a jet size, but see what you have.


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## cpchriste

cpchriste said:


> I'm working on one with same symptoms. I've finally decided it's too rich, [I live at 8000ft]. I made that evaluation because when I richen the mixture, with my finger partially over the carb opening, it instantly worsens the misfire. I'm going to put in a smaller main jet to confirm that.
> You may have a different situation. Have you decided whether it's too rich or lean? You can get a rough idea by slightly using the choke to enrich the mixture. Do that first and then I'll give you a list of possibilities.


Just to followup - a #75 jet has solved the richness problem.








I bought here: www.amazon.com/gp/product/B003CJKB7S


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## YSHSfan

cpchriste said:


> Just to followup - a #75 jet has solved the richness problem.
> 
> 
> 
> 
> 
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> 
> I bought here: www.amazon.com/gp/product/B003CJKB7S


Thanks for the update.
Hopefully this week I'll be able to put back together my YS624 and see if the surging continues...... (so many projects that I can't focus on one at a time.... :facepalm_zpsdj194qh, but I'm trying..... :blush


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## YSHSfan

Finally was able to put the YS624 back together, started and run it briefly, seems to run fine now. I'll test it tomorrow and report on how it works.


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