1988 xr4 150 issues

[adam98]

This is my first merc. Blackmax as I have only had small omc v4's and thought I would run with the big boys but there's a learning curve... Your input is appreciated.
I have a 1988 champion bass 18' with an merc xr4 150. It starts right up, drop in to gear and idles. Any more throttle and it dies unless Im tapping choke constantly getting it to soft surge up to 3-4k rpm with no power and gets boat to 40 but not good at all, almost sounds like knocking so i dont do that to long. Also when it's idling and warm every 4-5sec it coughs like a misfire or air puff sound from power head that can be felt in fuel line pulse. I would think that's a fuel issue as choke has some effect but even if I try to compress bulb and throttle up no change.

Things I checked so far, because is sounds like a fuel problem but may be ignition and could use your insight to keep me motivated. Fresh fuel, new fuel filter, new bulb, new fuel lines, all lines are tight, no restrictions or air bubbles in tank pickup or lines, carbs rebuilt and were very very clean and with in spec. Fuel Pump cleaned and gaskets were intact and clean, bulb stay hard at all times, when idling if I spray carb cleaner into any carb it increases rpm idle, plugs all look same and clean, 125psi all cyl, all connections on block and terminals loosened and tightened while verifying they were clean. I need to check ignition and or stator but not sure where to start. I have a shop manual and will attempt to check ohms and whatnot but its very vague. I just bought a timing light so ill play with that too.
Thanks again guys, Adam

 

[adam98]

Re: 1988 xr4 150 issues

So if I test the stator and to one power pack ohm is correct and to the other power pack its dead... Time to replace the stator?

 

[jigmister]

Re: 1988 xr4 150 issues

if your going to be the mechanic a must have is the DVA adaptor. The OHMS testing method is unreilable. The shops do not even use it anymore.
Go to CDI and use their trouble shooting guide. Along with the DVA you will find the troubled parts in an hour or 2.
If the motor has the idle stabalizer on it that will be the first part to throw in the trash. Be rid of it then begin testing.
The idle stabalizer goes out and causes all kinds of problems. They are no longer available. Once removed the engine gets a new timming spec. CDI guide shows the spec.
ISSUU - CDI Electronics Troublbshooting Guide - 2012 by CDI Electronics
With basic mechanical skills and the above link you will have the merc running like a champ in no time.
Since the compression is good you will get years more service out of it as long as it has good oil all the time and not allowed to over heat.

start on page 83 of the trouble shooting guide.

 

[adam98]

Re: 1988 xr4 150 issues

Thanks for the help!!! I'm checking on that now..I was about to order a stator online, mine looked good but ohms were completely random even with flywheel off. Should I order the stator anyway?

 

[jigmister]

Re: 1988 xr4 150 issues

I would do a DVA test of the stator first. Trigger and switch boxes as well. Also check the rectifeir.
It needs to be all together to test all the parts. At this point you could gamble and put in a new stator then test the parts once you get the DVA adaptor.
your going to want a remote starter as well.

 

[CharlieB]

Re: 1988 xr4 150 issues

Bumping the choke to keep the motor alive sounds like dirty idle circuits.

Have you tested spark? If you have good spark cranking then I would be cleaning the carbs.

As pointed out, DVA testing is the ONLY reliable method of testing the ignition system.

Oh, and always remember that NO RETURN on electrical parts. Stators and switchboxes are not the cheapest parts. You really do not want to spend your money on things you may not need.

 

[adam98]

Re: 1988 xr4 150 issues

Got on the water with no avail....So new Sator didn't cure it but with fresh plugs to read and a timing light I know cyl 1 and 4 for sure are only getting a spark at idle or even intermediate at best.. Also isn't the idle stabilizer timing box same as the warning horn box. So do I just disconnect the three quick connects (then retime)and leave the rest? Dva is on the way but I'm guessing its the power packs. Could be coil or trigger but doubt it.. What a pain. Ill guess just wait for the dva and do it right. I'm sure I can move stuff and wires around to zone in on problem but its to to late after work to be messing around in the dark

 

[adam98]

Re: 1988 xr4 150 issues

I need som help please. Please... New stator so im sure thats good. Finally Got the dva. First CID box read 3-4volts trigger's and 190-200v to coil or output side. Sounds good. So I test the box behind it and about 3v across triggers and 190-200 on first two outputs but 75 on last output... Also If I remove the trigger for cdi bad output and reads it is at 8-10v when running

 

[adam98]

Re: 1988 xr4 150 issues

So is that a bad cdi... Trigger seems low as it should be 4v but each bank is fairly balanced...

 

[adam98]

Re: 1988 xr4 150 issues

Oh and all cyl have good psi and get spark but I'm thinking spark is intermediate. Timing light looks consistent then will flutter randomly

 

[adam98]

Re: 1988 xr4 150 issues

I'm going to order 2 cdi box's.. I put a good trigger on the coil with low spark and it was strong, and switched a trigger wiire on low cdi output but it was still low so. Cdi it must be. It it really nessicary to order 2 cdi's

 

[CharlieB]

Re: 1988 xr4 150 issues

If the boxes are already CDI then it is O.K. to replace just the one bad box. Any other brand you should replace both.

Edit; when testing trigger output you really should disconnect the throttle cable so you can swing the linkage from idle to WOT and back while cranking and testing. You want to see if trigger output fails at any point in the wire movement indicating a broken wire losing contact when moved/pulled, then spark fails.

 

[adam98]

Re: 1988 xr4 150 issues

Not sure if both are cdi.. so ill order 2. also Good idea...I was thinking those tigger wires look like trouble. Will do, but cdi says 4v and I'm 3v on 3 banks and 2.5v on the other 3 banks.. Not sure if that's to low.

 

[pepescot]

Re: 1988 xr4 150 issues

I had similar issues with my Force 50. Then 2 weeks ago when temps were in 90's I saw the priming bulb was pi**ing gas all over the inside of the boat. Turns out it had a pinhole leak that sucked air when it was running. Replaced the prime bulb and all is well.

 

[adam98]

Re: 1988 xr4 150 issues

I wish...replaced bulb, lines , filter, and pump has good fuel pressure and I put a clear line on to look for air bubbles..

 

[adam98]

Re: 1988 xr4 150 issues

Ok still need help. New stator, switch box's, fuel lines and filter and bulb, plugs, fuel connectors, and clean carbs, good fuel pressure, did time and sync, hauls butt now. But idle isn't strong at low idle. At 1k rpm its really smooth but when I reduce idle timing to get idle down to 800 its gets weak and not steady almost has a miss... And I think the timer plate is still not 100%.., tested fine but still intermediate acceleration issue and the fix is play with timing advance wires. And I don't care for the major power band. weak idle kinda weak off idle but at 2k rpm straight to bat out of hell!!!

 

[adam98]

Re: 1988 xr4 150 issues

So why do the starboard side carbs visually flow fuel at idle and passengers side carbs dry at idle.. I assume the drivers side get more fuel pressure but is that right... Also at idle I'm -5 on timing to get it below 1k rpm and yes carbs are in synic and closed 100%??? Even at 0 degree at idle it runs at 1500 or +. And sometime needs choke to get on plane but all carbs and floats in spec and clean. I'm stumped

 

[CharlieB]

Re: 1988 xr4 150 issues

First off, if the idle stabilizer is still installed, remove it and drop it into the trash. Reset WOT timing to 21 BTDC, 23 if you run a better grade of fuel.

Float height is critical to idle stability as is total cleanliness of the small idle passages. A good spray chemical like wally world super tech carb cleaner immediately followed by a minimum of 100 psi clean air to make double sure all fuel and air passages are clear.

Idle speed is adjusted with idle timing, the carb butterflies have a drilled air bleed which is the ONLY air allowed at idle, the butterflies MUST BE fully closed. Final adjustment must be done ON the water and IN Forward gear. Adjusting on the hose you will have to leave the idle about 950 as once in the water the exhaust back-pressure increases and lowers idle speed.

 

[adam98]

Re: 1988 xr4 150 issues

Did all that, I'm sure its lean off idle and sometimes at idle. Bulb firm and does now change when I squeeze it durning a off idle bog or hard to start. Floats were free and in spec. And when I start motor with filter disconnected fuel shoots out steady with good pressure.
And totally diff sudden problem.
I I just noticed my oil res. cap must not hold psi cuz if I squeeze bulb hard enough fuel will slowly go up in to oil tank. Not good. And when running and I remove res. cap, tank is not over filling... A few weeks ago it did.

 

[CharlieB]

Re: 1988 xr4 150 issues

Most probably bad check valves in the oil system.

Do you have a service manual? A FACTORY manual is best as it covers everything in great detail. Aftermarket manuals leave a lot out.

Idle fuel passages are SMALL, and can be difficult to get totally clean. If squeezing the primer bulb hard as overcoming the float needle/seat and slightly flooding any carbs that were slightly lean due to either dirty passages or low floats, then the carbs still need attention.

Make SURE that all floats are almost exactly the same. Most all Mercs run best when the top of the float is parallel with the carb body when the carb is held upside down.

Using the lil red tube on the carb cleaner spray thru every passage while watching the discharge , you want to make sure all passages flow as well as possible and approx the same as the other carb(s). If even one carb ihas a reduced flow the holeshot is affected, once the motor reaches 2300- 2500 it's off the idle circuits and well into the main and runs fine.

Sometimes I find crud so tough it requires a breadbag wire tie stripped of its paper and used to poke thru the jet/passage to dislodge the sorta crystalized gunk.