1990 Evinrude 150 XP not revving up when accelerating

Hi I am looking for some help with my old Nitro 185 TF that I just purchased cheap. First of all the Evinrude XP 150 (TE150SLESB) does not want to idle at all. I probably need to clean the carbs, but if I rev it in neutral it fires right up and I can get it in gear..that’s when it gets weird. When I try to accelerate I put it WOT and the engine does not rev up at all until I have someone go to the front of the boat and I play with the trim. Then the engine RPMs start to go up slowly and it helps if there is waves on the water and then once it eventually planes out it runs absolutely perfect when I am on plane. It has a 14.25 21 pitch prop on it. It just has me so confused as to why it runs so well once it gets on plane but out of the hole it doesn’t want to rev up more than 2000 RPM until I trim it up even when I’m not on plane yet. My old bass boats I always trimmed all the way down and then trimmed up as I got on plane. Thx for the help

i'll bet your exhaust relief ports are underwater when you try and take off causing too much back pressure. Try taking off with the motor trimmed level.

Funny you say that. I have to trim the engine up in order for it to rev at all to get it on plane

Any updates on this I have a 175 xp that does the same thing

If the prop has vent holes, put plugs in them

No vent holes on my prop

Need to have the link and sync checked/insure all linkage is working smoothly and not sticking. Insure plastic roller is on carb shaft that touches throttle advance cam. Compression test first. Do all these things per your OMC(not Seloc or Clymer) service and repair manual or have a reputable tech do it. (Cant do link and sync in the driveway.) If it has been sitting for a long time, rebuilding the carbs with OMC kits would be in order as replacing all hoses(ethanol resistant OMC or equivalent), filters especially under the hood using the proper OMC nylon hose clamps, not zip ties.

Do a compression test first.:thumb up2:

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Originally Posted by omcforever

(Cant do link and sync in the driveway.)

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Must have back pressure on motor I assume?

For years, on the muffs was the only way I did the sync and link.

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Originally Posted by 316jughead

For years, on the muffs was the only way I did the sync and link.

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After I spent $$$$$$ on test wheels,, everything goes to the ramp..LOL

Is there a certain compression tester i need, also what is the process when doing the test. Engine warm, plugs out anything else

An auto parts store will rent you one. Do both cold and warm. Doesn't matter if all the plugs are out or not.

Ok just did it warm probably not good sign range between 80 and 88 with all plugs out. Do the carbs have to be open

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Originally Posted by 316jughead

For years, on the muffs was the only way I did the sync and link.

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jughead Is right. Sync and link is synchronizing the moment of the throttle plate/s start opening to a specific point in Idle ignition timing. This does not require exhaust back pressure. In some cases the engine does not need to be running. It is making sure that all throttle plates begin to open simultaneously and the throttle pickup roller starts this action aligned to a molded-in specific timing mark on the armature or timer base. All Movement synchronized to start not to early and not too late.
sorry to be nit picky but this is the most basic adjustment commonly messed with and screwed up on this engine.

Yeah if it’s not compression it’s most likely what it is because the guy I bought it from said the carbs were “rebuilt “ but who knows what buddy did it and if it was done correctly