1992 90hp crossflow wot power loss.

[Lundski]

I have a project motor ( TJ90TLEND) that I've been working on for the last 4 weeks This motor was a mess and need some TLC. Replaced most of the gaskets and rebuilt the carbs. One thing that i did see that was in question was the float blows housing, they are the plastic type and have a bow to them. I have the new aluminum blows but was unable to install because the intermediate jet needs to be change to 8-32 tread size.

Yesterday was the first time having the motor in the water performing a test run. Motor would not idle but found that the syn of the carbs was off and timing. After some adjustment i was able to get engine to idle. Pushed off from the dock and after a few minutes of running i pushed the throttle wide open had good power. The motor ran great for 3-4 min and then started to loose power. If i pull the throttle back and run it at slow rpm then hit the throttle back to WOT it will take off again and run like a champ then looses power.

I pulled the plugs and they looked golden. Check the Fuel supply to each of the carbs and they looked good no leaks. When i rebuilt the carbs i set the flot drop to 1 1/16-1 1/8" drop. could this be the issue that the high speed jets and the blows are not getting enough fuel to feed at WOT? I'm not sure what it could be at this point but I'm sure someone out there has a idea that they are willing to share. This site if full of technical people that are will to help.

Thanks

 

[ezeke]

Re: 1992 90hp crossflow wot power loss.

The drop on the floats is less significant than the top end which should be level with the carburetor base when the carburetor is held upside down.

Are you sure that you are not overheating when you are at WOT?

Primer bulb collapsed?

The carburetors need to be airtight or you will run lean and ruin your engine.

 

[Lundski]

Re: 1992 90hp crossflow wot power loss.

The temp is fine good water flow. The temp on the heads are 130-139 degrees.
Could the plastic float blows that have a bow to them be causing this issue. I placed a flat edge across the face of the blows and they are warped. I have at least 1/8" bow to them.

 

[Lundski]

Re: 1992 90hp crossflow wot power loss.

If there is a air leak this should be seen in the prime ball not staying hard correct. Also if the VRO pump is disconnected and is leaking air this too maybe causing air in the fuel system? The plugs looked golden brown when I removed them indicating good fuel mixture. Any thoughts?

 

[ezeke]

Re: 1992 90hp crossflow wot power loss.

If you have a leak before the fuel pump, you should be able to see some fuel by keeping a little steady pressure on the primer bulb (If gas can get out, air can and certainly will, get in). After the fuel pump, any gas leak will indicate the same concern. The largest surface where air can leak in would be the between the carburetors and the intake manifold.

Also, if you are using a standard lift pump for fuel, make sure that the gasket between the pump and the engine is airtight and in perfect condition.

The primer bulb should become as though part of the hose once the engine is running. It should not be hard, nor should it collapse at all. If it begins to collapse, either the bulb itself is faulty or you have an obstruction before the bulb as in tank vent, pick-uip, anti-siphon valve or fuel filter.