85' 90 hp V4 Johnson power loss at WOT

[bobaschmidt]

I have a 90hp Johnson that for the past three weeks has lost power. What has been done, you ask? 1 decarbon the engin, it would go WOT but jerk, like a surging motion. 2 changed the plugs (one plug was clean on the outside and dirty electrode), it helped the idle a bit but could not maintain WOT now down to 3/4 to prevent bogging down. 3 changed the plug wires and inspected the top two jets (I could not get to the lower jets without carb disasembly) very clean. now down to 1/2 and hard to get on plane. 4 half can of decarb spray, thought the first can may have loosen something into a ring, no help now down to 1/4 and very upset. I have my boat on the dealer schedual but two plus weeks out. I hope you can help? Thank you, Bob

 

[DJ]

Re: 85' 90 hp V4 Johnson power loss at WOT

Bob,<br /><br />Don't go any further without checking the compression. If one cylinder is low, you'll know you're going to have to go deep.<br /><br />If the compression is all OK. Then I'll bet you have a clogged carb. jet. It just happenned to my 83 Rude 90.<br /><br />The carb's. are easy to remove and rebuild.

 

[OBJ]

Re: 85' 90 hp V4 Johnson power loss at WOT

Hey Bob...welcome to the iboats forum....<br /><br />Your mech's shop sounds like mine....2-3 weeks hang time....that time of year.<br /><br />Here's some things to look at...<br /><br />Check the ground leads coming from the power packs. Ya' got one on each side. Make sure the grounds are tight.<br /><br />Do a compression test. All cylinders should be well over 100psi and about 5psi with on another.<br /><br />Check your spark. A good spark should jump a 7/16 gap and be hot and white.<br /><br />Check fuel connections for lose hoses. A hose can be lose and suck air yet not leak gas. Weird I know. Make sure the fuel tank is vented.<br />Also check for any kinked hoses.<br /><br />While the engine is running, take a little soap solution and paint it on the VRO seams. These are where the differnt parts of the pump body meet. Any bubbles and the pump isn't doing it's job.<br /><br />Look at the starboard side of the carbs where the linkages are. Have someone goto WOT while you watch the links. Motor not runing of course. Are both carb links moving in unision? <br /><br />Get a Service Manual for the engine. They are still available at the dealer. Read the troublshooting section after the fuel section.<br /><br />Your problem is progresive and sounds to me like either a bad cylinder (which is not good), your losing fire on at least one cylinder intermitently or some foreign junk floating around the carb bowl.<br /><br />Keep us posted on what you find. Thanks!

 

[bobaschmidt]

Re: 85' 90 hp V4 Johnson power loss at WOT

Thank you for the replys, I checked the fuel system up to the carbs - OK, the carbs are in sync both top an bottom. I will do a compression test tomorrow to see whats up. I may also take off the carbs and clean the jets and passage ways if the compression is good I will post the findings. Thanks again, Bob

 

[bobaschmidt]

Re: 85' 90 hp V4 Johnson power loss at WOT

Compression is 130 pt, 125 pb, 125 st, 130 sb. looks good to me? I will open up the carbs to look for problems. <br /><br />Any other Ideas? I could use the help guys, Thanks, Bob

 

[bobaschmidt]

Re: 85' 90 hp V4 Johnson power loss at WOT

Cleaned the carb, no problems found, going out for a run to see if that may have helped?<br />Thanks, Bob

 

[bobaschmidt]

Re: 85' 90 hp V4 Johnson power loss at WOT

Started out great, slowly started to surg again and then only 3/4 on plane. Makes me think it is a fuel problem. I tryed the primmer but no change. <br /><br />Question: can the fuel pump surge fuel to the carbs? What is the best way to test the fuel pump? it is a VRO but disabled running 50:1 in the tank.<br /><br />Thanks for your help, Bob

 

[Solittle]

Re: 85' 90 hp V4 Johnson power loss at WOT

What exactly did you do to clean the carb?

 

[bobaschmidt]

Re: 85' 90 hp V4 Johnson power loss at WOT

just clean all the parts and blow out the passage ways.

 

[bobaschmidt]

Re: 85' 90 hp V4 Johnson power loss at WOT

Found the problem. It was a crack in the VRO oil line. As mine is disabled I never looked at the oil line. It was sucking in air and leaning out the fuel. The fix was to remove the oil line and plug the VRO at the pump. Boat is running at 5800 rpm WOT @ 41.5 mph GPS, the best it's ever run. Thank you for all your help Bob