Evinrude xp100 WOT wont go passed 4000 rpm. Pulling my hair out! *Update*

[FMJshooter]

Hi new to posting here but been reading using the search for a long time. Anyways here's a summation of a long story. I recently acquired an evinrude 100xp with a rebuilt power head. It's been giving me some issues and I have it narrowed down to two things, power pack or wrong carbs for this engine. Motor came with a brand new CDI pack but a bad stator may have killed it.

the problem is the engine hits a wall at 4000 rpm. Prop is a 17p on a 17 foot javelin bass boat, comes out of the hole like a bat out of heck then just hit's a wall at 4000 and I'm getting about 35 mph (got 50 mph out of the 115 previously on it). When I bump the primer solenoid the rpms drop quick so it's not a lean condition either. . Ran it on a test fuel tank just in case with same results, DVA tested the entire ignition rebuilt the carbs etc.

DVA test showed a shot stator and low voltage from the power pack. One of the charge coils was swollen and cracked so I figured that was it but NOPE!. Changed the stator and the power pack is still reading low voltage on the orange leads to coils (thinking bad stator killed power pack?) I went ahead and ordered a new power pack that should be here by Wednesday.

However out of boredom I pulled one of the main jets out of the top carb to see if it was running super rich or something and it's a 56c which according to the parts lookup belongs in carbs for a 90 hp so if anything it should be lean but when I bump the primer rpm drops so that doesn't seem to be an issue. Both carbs on this motor are stamped for 1 3/16" venturi's so I'm thinking these did came off a 90. My real question is should this 100 have 1 5/16" carbs? Would that little difference in venturi size rob me of 1500 + rpm? I'm thinking not but it's been eating me for a bit now.

Any thoughts on the matter may help me sleep until the power pack gets here!

 

[emdsapmgr]

I am not sure what size the throats are on the 100S models. The 115's were all pretty much the 1 5/16" throats. I'd be surprised if the 100S models were the 1 5/16" carbs, but it's possible. These engines made their debut in 1988 and continued at least thru 1991. That first year, the main jets were .057's and then changed to .060 mains in 89 and continued at that size thru the 1991 units. So, your jets would indicate the carbs you currently have could have been from an 88/90 model. You can swap for a set of 1 5/16" carbs and you should pickup some hp. I'd agree with you, that the swap, while beneficial, is probably not the reason the engine won't go over 4000 rpm's. Could be 200-300 rpm's difference, however. (Why not try the 115 carbs from your old engine?) So, a couple of things to check: 1. That engine originally came with a VRO fuel pump. Is it still there, or was it changed to a pre-mix pump? Not all premix pumps are equal, but many look the same. You could try constantly squeezing the hose bulb. See if it makes a difference at WOT throttle. 2. When the new power pack is installed, do a test: after the engine is well warmed up and is running under load in the lake, remove the cowling and put an inductive timing light on each plugwire. Check the flashes in the gun for spark. All 4 should be strong, and rhythmic. You should see misfires or weak firing with this method. 3. Pushing in on the choke when running is a valid test for lean condition-yes, it sound like it's not lean..4. The engine swap should not have made a difference to the tach, but I'll ask anyway, is it still set to the #6 pole positon? 5. I've seen engine swaps that have resulted in throttle cable misadjustsments. Pull the cover off the airbox and put the throttle all the way down: do the carb butterflys open completely (till they are exactly flat?) They may not be opening fully, or could be overrotating and partially re-closing. Many engine swaps required cable adjustments on the engine end. 6. Make sure the spark control lever is connected to the timer base (the link arm with the ball and socket) and that it is advancing the timer base fully when at WOT.

 

[FMJshooter]

Thanks for the reply! The tach is set for 6 pole but I think I may need to test it for accuracy anyway though my gps mph does seem about right for 4000 rpm. link n sync has been checked a few times throttles are opening flat. The timing advance is working but I've only been able to check the total advance while cranking and not under load, may have to bring that to a shop and have that checked. The vro is gone but the pump seems to be the correct one from my research on this site. I have tried to force fuel in with the bulb with no change. If the power pack doesn't fix the issue I will surely try the timing light test that's a good idea!

The 115 I blew wasn't an OMC unfortunately so the parts are no good to me.

 

[FMJshooter]

Well raised the motor and replaced the pack still the same. I checked the dash tach with an inductive meter and was getting around 4600-4700 rpm so the tach is off. I checked it on all four plug wires and they seemed to read the same rpm which seems to tell me that there is spark. Almost wondering if there's some odd ignition issue that's causing the tach to read off. I did change the rectifier with the stator but could weak/bad flywheel magnets cause a weird pulse reading? I also dva tested the new stator output to the power pack at idle speed and I got 200v on one wire and 160v on the other which is in spec but should these be closer?

Going to pull carbs tomorrow and really check them over with a fine tooth comb because at this point I'm thinking the motors either running fat or has some weird ignition issue. Maybe I ought to do the running dva test at the problem rpm on the lake? Maybe a timing light test will tell me something the tachometer wouldn't?

I had a mechanic look it over quick and he says the thing should be running around 45-47 mph with a 21 pitch prop I'm running a 17 and getting 36. This thing is driving me nuts.

 

[emdsapmgr]

You've done some nice testing. Sounds like the fuel system is ok, based on your fuel primer test. You may want to try another tach. The cranking output on the ignition side of the stator should be at least 150 volts, so it checks out ok. Low stator voltage can cause an intermittent miss at high rpm's. Sometimes it's difficult to pinpoint. Best to do your high voltage output tests after the engine has completely warmed up. Weak ignition components tend to work fine when they are cold, the crap out once the engine warms to normal operating temps. What compression does each cyl have? Have you pulled the airbox cover off to be sure the throttle plates are perfectly level at WOT? They actually can be inadvertently adjusted to overrotate and begin to close again....

 

[FMJshooter]

Yep throttle blades are perfect even called in a favor to a marine mechanic to look over my link n sync and he says all is okay. I pulled the fuel pump just out of curiosity and it did have a small tear in one of the gaskets. Doubt that's my problem as squeezing the bulb didn't effect anything but I ordered a rebuild kit anyways. Once that's in I guess I'll do the running output test at the problem rpm on the water maybe it will point to a bad flywheel or something. I'm almost tempted to pull the flywheel now while waiting and seeing if any of the magnets feel week with a screw driver or if something on the timer base, new stator looks off.

 

[racerone]

The 100XP is really a 115 HP marketed as a " super 100 HP motor "---------Does it have the bubble at the back of the motor ?-------I would remove one bypass cover to see how big the transfer ports are as the 90 HP block has smaller intake ports.

 

[FMJshooter]

Thank you for mentioning that exact thing has been on the back of my mind but I try to trust people.The plug on the top of the block was painted over and real hard to read. I just scraped off the paint and filled it in with white chalk and guess what J90MLCDC ! So looks like I have a damn 90 horse and this "mechanic" has been blowing smoke up my butt letting me pull my hair out for the last month?

I really don't mind if it's a 90 as long as it gets me to my fishin holes I'm happy but being lied to is not something I take lightly!

 

[FMJshooter]

Well regardless of the whole 90 vs 115 deal I decided to go through a few things again anyways. I pulled the timer base, carbs and fuel pump, the timer base had a real small crack maybe 1/4" in between a couple of the pickups so out of curiosity I epoxied it. Went through the carbs again and everything looked okay but I cleaned/ blew out all the passages again for good measure. Also rebuilt the fuel pump because it looked pretty tired. Well I took it on the lake and BINGO! She ran right up to around 5500! I stopped fished for a while then fired up to run again and she didn't want to start, once she did DANG IT! problem is back again.

So now I got to figure out which of the three repairs I did where the one that temporarily fixed it :facepalm: I guess I'll pull the timer base again and see if my ghetto epoxy job came off if so I'll assume that the base is bad. If not I don't know what the heck is going on with either the carbs or the fuel pump. Hoping to god it just wasn't some weird coincidence and I can actually narrow it down for good. This thing is really beating me over the head.

Anyone have a timer base crack like that and cause problems?

 

[emdsapmgr]

As a guess, I'd think that you've solved the fuel issue. Good news that it will run 5500. Right on target. The engine would not run that rpm with a faulty fuel pump. An it's not the typ of device that works one minute and and not the next. I'd be thinking that a cylinder is losing spark. Weak ignition components tend to fail-once the engine warms up to normal operating temps. That may be what's happening. So, when it craps out again on the lake, quickly check each plugwire for spark. You may be only running on 3 cyls.

 

[FMJshooter]

Yep I took it out last night and it was acting up again so I hooked up the inductive tach to each plug wire again and #3 would read intermittently at the problem rpm. Only part that isn't new is the timer base so I ordered used one that supposedly came off a good running engine. I know I could be replacing one defective part with another but this thing has smoked my budget, going to cross my fingers and hope this will do it. Seems I may have somehow fixed it temporarily when I took off the timer base the other day

 

[emdsapmgr]

The timer base is probably a good place to start. See what happens if you swap it out. If you find the spark dropout is random, that could be a weak stator. Not enough voltage to fire each spark plug on every rpm.

 

[FMJshooter]

Yep that's what I was thinking too but changing the stator to the new cdi unit changed nothing. I really should run a dva output test at the problem RPM but boy is tough to reach those coil leads while the boat is in the water! Easiest way may be to beach it then pull the back of the boat towards shore some and and do a little wading. Touching wires in waste high water just feels plum wrong though!

Thanks again for the reply will keep this updated as I (hopefully) figure this out.

 

[FMJshooter]

Well dang belated update but I think I may have figured it out. Pulled the carbs and noticed someone had stuffed a couple red gaskets up into the well that the emulsion tubes run through. I guess someone figured since these gaskets come in the carb kits that's where they go. They where pushed way up in there where I couldn't see them the first time I had the carbs apart but a couple slid down the tubes this time and where covering the vent holes next to the tubes. So I'm thinkin when they're under vaccum they where sliding down the tubes and plugging the vents.

I can't get the gaskets out, I can barely fit the smallest allen key I have in the gap they're stuffed in. I pushed them up in there tight for now, If this solves the issue I'm going to have to go back in and figure out how to get the darn things out. Gaps too small to get a pick or anything in there, might have to find some real small diameter screws or something and try and dig them out. :facepalm:

 

[fmjnax]

Try some piano wire. Snip it to a point and bend a very tiny hook. You can find piano wire in all sorts of diameters at a hobby store (and probably a music shop, among others).