1985 Evinrude XP150 surging above 35mph

[Bigcountry7704]

I have a 1985 Evinrude XP150 E150STLCOS on a 1989 stratos 179v bass boat, it has a 6” jack plate with the center of shaft sitting 4-1/2” below pad and a 23P 4blade shooter prop. The ensigns starts up super quick, and runs fine up until about 1/2 throttle getting on plane and about 35mph once on plane. At that point it starts to surge, it’s like it drops rpm the gets a surge of power and you can feel the boat wanting to take of and fly when the power comes in then it drops back down. The more throttle you give it, the harder it surges. Compression is 109-110 on all cylinders, has new coils, new power packs, new engine wiring harness, had my bait mechanic check my regulator/rectifier and he said it was good but on the borderline of going bad. VRO has been deleted and has two non vro pumps mounted to the block as a replacement. Someone please help me figure this out, it’s about to drive me crazy!!!!

[omcforever]

Next time it does the surging,,,push the primer/choke and see if it picks up......let us know. Could be a fuel delivery issue. If so, maybe junk in the carb, clogged filters/water separator, ect. Or may need the carbs gone thru. If it doesnt change then most likely electrical/ignition related.

[NoZero]

Carb been cleaned? Mid-range jets??

My blind-bottom guess would be a fuel passage in the carbs.

Someone will be along that knows much, much more than I.

[omcforever]

Someone will be along that knows much, much more than I.

[omcforever]

Also, you need a new boat tech,,,not a mechanic.

[omcforever]

When did the surge start? After deleting VRO or before? Did it start all of a sudden or gradually?

[omcforever]

When converting to 2 pulse pumps, you must unplug #6 cylinder bank on the block front half and install barbed fitting for pulse to that pump (#4 has a barbed fitting already). Pitch the pulse limiter/arrestor. Run a pulse line to each pump off of #4 and #6 bank. Fuel line from tank goes to inlet on bottom pump. Outlet on bottom pump goes to inlet on top pump. Outlet on top pump goes to fuel rail. No metal worm clamps but OMC #0320107 zip ties.

[omcforever]

I have seen "mechanics" try and "T" off only one front half pulse fitting limiter/arrestor to run both pumps. Pulse has to be staggered between different crankcase pressures to work properly.

[Bigcountry7704]

Thanks for the input, I have tried pushing the key in when it does it and it makes it bog down, also tried squeezing the primer bulb when it does it and that doesn’t change anything. I also verified that the fuel pumps are routed correct and the barbs on #4 and #6 aren’t clogged. The surge was there when I bought the boat but motor has great compression and I got it for a steal so I went with it. I’m starting to wonder if it isn’t a stator or timer base issue ��

[omcforever]

Thanks for the input, I have tried pushing the key in when it does it and it makes it bog down, also tried squeezing the primer bulb when it does it and that doesn’t change anything. I also verified that the fuel pumps are routed correct and the barbs on #4 and #6 aren’t clogged. The surge was there when I bought the boat but motor has great compression and I got it for a steal so I went with it. I’m starting to wonder if it isn’t a stator or timer base issue ��

Had the boat been sitting for a long time? Do you know the maint history of the boat? Invest in a real OMC service ad repair manual and familiarize yourself with it. If it has been sitting for a long time, I would go thru the carbs, with OMC kits(could have a float/needle and seat issue issue), replace all filters and replace all old fuel lines. Replace plugs QL77JC4 at .030. Have link and sync done to verify proper timing/linkage movement. Then verify/test ignition system per your OMC manual.

[omcforever]

What are the compression numbers? When I work on an outboard, I verify compression, proper fuel flow, good ignition system.

[Bigcountry7704]

Compression is as follows left bank=110,110,111 right bank=110,109,110. And I was thinking I should rebuild the carbs anyway just because. I took them apart to clean them and the looked super clean but I know that can mean absolutely nothing if they’re anything like a automotive carb.

[316jughead]

Welcome to the forum. Like omcforever said get the real OMC service manual, no aftermarket. Only use marine fuel hose and BRP primer bulb. You might want to look at the timer base linkage, is the arm with the rubber stopper on it moving all the way to the stop, you can verify this with the motor not running. In the throat of each carb you will see a small brass tube. This tube must be touching the side of the throat, they are glued in place, but if someone soaked the carbs in carb cleaner the tubes sometimes move away from the throat. omcforever is our cross flow motor, like yours, expert, he's a good one.

[omcforever]

In the throat of each carb you will see a small brass tube. This tube must be touching the side of the throat, they are glued in place, but if someone soaked the carbs in carb cleaner the tubes sometimes move away from the throat.

Yes sir Jerry,, I have seen quite a few like this and have some in my junk metal bin. Never ever soak a carb in carb cleaner,,,the OMC repair manual explains how to properly service them. Also inspect throttle shafts for wear and slop in the carb body. Can cause issues as well. Some of these carbs are old like us,,,

[omcforever]

omcforever is our cross flow motor, like yours, expert, he's a good one.

By no means do I consider myself an expert on crossflows. I have just destroyed, blown, modified, tore up so many in the past 25 years that I know what NOT to do,,,,

[bighare]

By no means do I consider myself an expert on crossflows. I have just destroyed, blown, modified, tore up so many in the past 25 years that I know what NOT to do,,,,

betcha is more liKe over 35 years since they stopped making them in 1990/91 ;)

[omcforever]

betcha is more liKe over 35 years since they stopped making them in 1990/91 ;)

actually 1997,,,last year for the crossflow V4.

[omcforever]

I collect old crossflows,,,its an illness. LOL

[bighare]

actually 1997,,,last year for the crossflow V4.

ok that one I’ll give ya

[ChampioNman]

ok that one I’ll give ya

No rookies here on the old stuff. G2's that's a different story.