'89 120 surging after 3k with VIDEO

mookieo2

Petty Officer 3rd Class
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Jun 12, 2002
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84
I have been working on this motor for a while and I am not giving up. I had a problem with warped carb bowls and carbs. Sanded the bowls flat and new gaskets. Pumped ball and believe they are sealed. The ball was still stiff a few days later and no signs of fuel weeping out by the gasket. I finally took it for a spin. It started up and idled real smooth and easy. It was pretty quiet. It runs as perfect as I believe an old 2 stroke looper can up until 3k. If I push it past there It starts surging. I can get a whole shot and hit 5k, then it starts surging. I had rebuilt the VRO pump last year because it wouldnt go past 2k. I just replaced the pulse limiter( with blue one). I also replaced the larger fuel lines to pump, limiter, carb distribution T, and fuel tank. The primer ball is also a new style one from a year ago. I am running off of a 6 gallon tank with pre mix.

I apologize for the shaky video but it was really rough out.
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
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No shakes in your vid. In fact, no vid. How are you attaching the video?
 

Bob_VT

Moderator & Unofficial iBoats Historian
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May 19, 2001
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That is the same video??? No help
 

mookieo2

Petty Officer 3rd Class
Joined
Jun 12, 2002
Messages
84
That is the same video??? No help
Didn't realize it posted twice. Compression is 120 on all cylinder, re torqued throttle body bolts and carbs. Didn't get a chance to pull the plugs and see what they look like. Will do today. Think it might be the fuel pump. Before I rebuilt the pump it would only rev to 2k but it would die after not surge. Don't want to just throw a new expensive pump in there to find out its not it. I know its a no no but can I put an electric in it to try for a test run? I would rather waste $50 than $350. If it works I'll spend the money on the real one. The boat mechanics in my area won't touch this motor because its gonna cost more than its worth to troubleshoot and repair. Compression is good and I believe the motor only has 350 hrs on it. It runs smooth probably something simple just can't figure it out.
 
Last edited:

Bosunsmate

Admiral
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Apr 7, 2012
Messages
6,129
Is your prop spun in the hub?
It cant increase rpm that quickly unless its spun or cavitating
 

mookieo2

Petty Officer 3rd Class
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Jun 12, 2002
Messages
84
Is your prop spun in the hub? It cant increase rpm that quickly unless its spun or cavitating
Not sure but if I increase the throttle slowly it does the same.thing. I have another prop laying around. I'll try that one next time. Found a test procedure for VRO pump on max rules.com going to pull the pump and try it.
 

Bosunsmate

Admiral
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Apr 7, 2012
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6,129
sounds like a spun prop to me.
its gripping then slipping then gripping and also a rpm limiter could be kicking in when it slips
 

mookieo2

Petty Officer 3rd Class
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Jun 12, 2002
Messages
84
Took the fuel pump off to test. Found an o ring missing inside by the pulse connection. Put one in that fits good. Haven't had a chance to water test it yet.
 

mookieo2

Petty Officer 3rd Class
Joined
Jun 12, 2002
Messages
84
Finally got to test the boat out. The boat now runs as perfect as that motor can up to 3500 RPM's and between that and 4k it starts to surge a little. Anything over 4k and it goes all over like in the video. There was an improvement with the missing O-ring on the vacuum side but still not perfect. I would assume the fuel pump needs to be replaced.

Does anyone else agree that its definitely the fuel pump?
 

mookieo2

Petty Officer 3rd Class
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Jun 12, 2002
Messages
84
Fixed it. It was the fuel pump. I replaced the VRO with two standard sierrra fuel pumps put together. It only cost me $80
 
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