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150 Fast Strike with full throttle surging

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br1303

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I've got a 1993 Johnson 150 Fast Strike motor on a 93 Ranger 482 bass boat. Motor runs fine up to about 3/4 throttle, but when I try to open her up, it starts surging. Acts like it's short on fuel or sucking air. I've replaced all fuel lines to the engine and replaced the fuel filter and plugs. No Change so far. Has anyone had similar issues? Not sure what I should look for next other that maybe the VRO pump is getting weak???? Thanks
 
Yep, had nearly the same problem on my '96 Intruder 150. I didn't surge, but after 3/4 throttle the engine changed sound (kind of boggy) and wouldn't go past 4500RPM. A simple test is to get clear vinyl tubing and put that between the OMS Pump and the VST. Observe the tubing while running the engine and if you see air bubbles you know there is an air leak somewhere. I went to the extreme on my fuel system, but you can start in a couple places then go from there if needed.

1) Carbs. Have you rebuilt the carbs and ensured there is nothing gummed up? A thorough cleaning and new carb kits may be in order.

2) Fuel Chambers. The plastic fuel chambers (float bowls) on these engines are well known for warping and creating leaks. The only solution is to replace the chambers, you cannot sand them flat because it has a molded ridge for sealing to the gasket. If you replace the chambers, make sure you remove the main jet from the base and transfer it to the new carb. The chambers do not come with any orifice installed.

3) Pressed in BB. There is a pressed in BB on the side of each float chamber. This is needed to seal the fuel galley after drilling/machining in the manufacturing process. The plastic around the BB shrinks over time and allows a leak. An easy solution is to drain the chambers, clean well with carb cleaner, then apply JB Weld over the BB to seal it. I did this on my new chambers to prevent future leaks.

4) OMS Pump. The OMS pumps (VRO) on these engines tend to fail to over oiling when there is an issue on the gas side. Do you notice excessive smoke at all operating ranges? If so, you could have a bad fuel diaphragm in the pump. There are kits to replace just the diaphragm. Personally I replaced the entire pump because I didn't want to trust 26 year old plastic.

5) Fuel selector switch. My 1997 Ranger 461 has duel fuel tanks and a selector switch. The knob was very hard to turn so I replaced the selector thinking there was either gummy junk in the valve or the O-rings were getting stiff.

A final note, when you work on the carbs, be sure to order 12 O-rings for the fuel manifold. Mine were in poor condition and leaked when I tried to re-use them.

KJ
 
Thanks Kevin;
Here's what I found and did...
1. Found the Float Bowls were so warped that you could have slid a butter knife between the bowl and carbs.
(ordered 6 new Float Bowls and Carb rebuild kits)

2. During removal of the carbs, I found several bolts were loose, no doubt causing an air leak between the carbs and the intake manifold.
I also found most if not all main jets were loose in the Float Bowls. Don't know if this was causing an issue or not....

I rebuild all 6 carbs, which included all new gaskets (O-rings) between the carbs and intake manifold. Replaced all 6 Float Bowls and added JB Weld over the BB's on the Float Bowls. Checked all bolts and screws on the motor, just to be sure... Once all work was completed, I did a test run at home and everything looked good, no fuel leaks. Then I took the boat to the lake for a full power test run. Everything seems normal now; I was able to get the motor up to 5,500 rpms with no problems.
 
br1303 said:
Thanks Kevin;
Here's what I found and did...
1. Found the Float Bowls were so warped that you could have slid a butter knife between the bowl and carbs.
(ordered 6 new Float Bowls and Carb rebuild kits)

2. During removal of the carbs, I found several bolts were loose, no doubt causing an air leak between the carbs and the intake manifold.
I also found most if not all main jets were loose in the Float Bowls. Don't know if this was causing an issue or not....

I rebuild all 6 carbs, which included all new gaskets (O-rings) between the carbs and intake manifold. Replaced all 6 Float Bowls and added JB Weld over the BB's on the Float Bowls. Checked all bolts and screws on the motor, just to be sure... Once all work was completed, I did a test run at home and everything looked good, no fuel leaks. Then I took the boat to the lake for a full power test run. Everything seems normal now; I was able to get the motor up to 5,500 rpms with no problems.
Click to expand...
Excellent, I'm glad you got your engine lined out. These repairs/replacements area a decent amount of time and expense, but when completed these old motors will run like new. As I've said many times, much of this is plastic that is over 20 years old and eventually needs replaced.
 
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