A On going Problem

[Phunahm]

Hello I have a 86 mercury 150 xr2 SN 0A933978 Ive had an issue with the Idle/hole shot for years....Idle surging between 700-1100 rpm and bogging on hole shot....Here a list what Ive done to try and fix..... IGNITION*** Stator,rectifier,regulator,CDI switch boxes,plugs,wires,Idle stabilizer was removed and timing set to 23* Checked spark on all Cylinders sync and linked numerous times.. Marked flywheel for all cylinders for TDC to check for fluctuation, BTW i wasn't throwing parts I did have a bad stator charging side,, Fuel System*** Rebuilt carbs,replaced all fuel line from tank to engine including a filter,rebuilt fuel pump. Misc** compression is 120 on all,I replaced all bleed lines and valves and verified they were in correct orientation. Hole shot issue**** I dropped to a lower pitch still bogs was a little better but still there...upper rpm performance is great.**** I decarboned using sea-foam and gallon mixture with second can,,,,,,,,Now I pretty confident the ignition is working properly ,so I was looking into the fuel system again yesterday it was idling with muffs on and surging as usual so a pump bulb make sure it was hard it was,, but I felt something when the engine missed while idly the bulb went soft for a moment then back to hard did this every time it missed...... Does this sound like a reed issue? Thanks for any input

 

[Faztbullet]

Some motors will lean spit on hose due to no backpressure. Make sure all butterflys are closed and leave about a 1/8 gap between roller and cam and retest.

 

[Dukedog]

coupla ?'s....

any jettin' changes?
carbs... cleaned with all new gaskets? how were floats set?
how was idle timing set? on tha hose? in gear in tha water?
idle rpms? how did ya get there?
max rpm?
link and sync by manual (oem or aftermarket) or other?

 

[Phunahm]

All procedures were done by OEM manual.... All rollers do have that clearance I repeated that step many times, Timing was all done first by indexing and step by step from the manual, yes boat was on the hose however does the same in the water. No no changes to the jets and the carb rebuild was by complete OEM kits floats were set per manual 1/16 below flange. max RPM is 5700 @62 the upper rpm runs smooth as silk...

 

[Dukedog]

yes boat was on the hose however does the same in the water.

this is not right.... idle rpms should drop slightly when motor has a load (in gear/in tha water)... are you setting idle rpms and or speed with "timing only"?

 

[Dukedog]

sometimes ya gotta "stray" a tad from tha book.... set tha floats by holdin' tha bowl "upside down".. tha float will be slightly higher than tha bowl castin'... adjust tha float to where it is slightly higher (when upside down) but level all tha way around with tha bowl castin'..... as for idle timin' pay no attention to numbers "by tha book"... change timin' and/or idle rpm/speed to whatever you and tha motor like while in gear in tha water.... timin' is tha only adjustment for any thing idle.......

ya might look at tha reeds if ya can... yours has vertical reeds and i can't remember how well you can see 'em lookin' through tha reed plate.... look for any gaps that may be 15/20 thousands or more....

 

[Phunahm]

Im setting timing by cranking per manual. at a running idle on hose the idle timing is 11* and cranking with timing arm at WOT its 23*

 

[Dukedog]

11* before or after tdc? below is tha absolute best way ta come up with idle speed and timing......

"as for idle timin' pay no attention to numbers "by tha book"... set timin' and/or idle rpm/speed to whatever you and tha motor like while in gear in tha water.... timin' is tha only adjustment for any thing idle......."

thats after its made sure all three butterflies are completely closed and tha slight gap at tha roller and cam....

 

[tommarvin]

I would test the coil, power pack, trigger. You said you replaced the CDI switch boxes, and stator please test them also if you can.

A DVA ignition tester on E-Bay costs I think about 100 bucks, you may what to get one, ignition parts are expensive.

Testing before Guessing.

 

[Phunahm]

I have a DVA, And initially check a ways back I don't remember the numbers but if they failed Im sure I would have looked into that BTW thank you guys for trying to help the Packs are new I literally just put in last week. the coils tested god both with a My fluke and a plug spark tester I was getting well over 5/8 inch plus spark bright blue BTW I replaced the trigger also didn't mention that above .....

 

[DavidMoore]

Odd
I have a gut feeling that you have a sticky check valve in the primer bulb and it only shows itself at a low flow rate, could you try another one?

 

[Phunahm]

primer bulb is a new one, I think Im going to try what Dukedog said with the timing I was reading the manual again last night plus a lot of google searches I think advancing the timing at idle from 11 to 6 or 8* might do the trick however ice is on the lake now so I cant really do anything till then........

 

[Dukedog]

tha numbers are good for base line and/or startin' on tha hose after some parts get changed....sometimes they're good and sometimes not.... forget 'bout 'em when ya get it in tha water.. jus make sure its warm and trimmed level.... don't adjust anything but tha timin' screw... thats tha reason tha carbs have an "idle circuit" that gets no adjustment other than a jet change (for other reasons)..... ice sucks!... gl with it.

 

[Phunahm]

Thank you all. Ill give the result when ice melts god i hate winter.. ..

 

[sutor623]

Have you tried to connect to a remote fuel supply to rule out an air leak in your fuel tank?

Have you tried the cylinder drop test at idle? Pull the spark plug wires one by one and see if all CYLINDERs act the same when you pull the wire. (Disclaimer* Wear gloves and dont shock yourself!!)

On another note, I was chasing my tail with an issue similar to this and ended up having scored piston skirts and cylinder wall on one cylinder. BUT, compression numbers were perfect. Even passed a leak down test. Go figure........... I would think that you either have air entering from the boat side fuel tank or there is a minor mechanical issue in the block affecting crankcase compression at idle. Do you have access to a bore scope by any chance?

 

[Phunahm]

Ive had heads off and the cylinders were perfect below ring line..... and yes I ran engine from a can idled the same..... thanks

 

[sam am I]

Bleed Restrictor's...........Merc Service Bulletin 92-15

"1992 and Previous 135 thru 225"

"bogging on acceleration on the models listed"

This service/mod narrow's the bleed restictor's holes/porting up so less of an excess of fuel that has accumulated (very evident/visible when running clear tubes) in the bleeder tubes/ports during idle times is dumping in all at once......i.e., An excess of fuel is reservoir'ing and then sucking/dumping in on sudden acceleration/hole shot (causes coughs/bogging). That's my theory anyway and I'm sticking to it..........

Also tweak idle screws just on the edge of too lean(go 1/8 to 1/4 turn towards rich from lean roll).

Worked for me, runs much "snappier", much quicker to respond......BTW, I replaced the right angle fittings at the block, and didn't used the inserts in the tubes (Not sure they even sell those anymore anyway)

 

[Dukedog]

just a little info.....

those went nla pretty quick... had very little (if any) effect on tha v6.... made it worse in most cases 'cause it wasn't tha problem ta start with.... ALL horse power v6's from '76 ta '90 use wh series carburetors which do not have an "adjustment/tweakin' screw" of any type...... only controlled with jetting size, both idle and mains which make timing, ign. parts, carb health so important...... idle tweaking screws came out on tha wmv's in '91 along with tha "fat block" (slang term for tha next generation v6 small block)...... .

 

[tommarvin]

I'm guessing a air leak in a carb gasket(s)
You said all ignition parts tested ok. You said the lake was ice, you have all the time in the world till the ice melts..
Why not yank the carbs one more time, and take a very close look for an air leak, can't hurt?

 

[quicktach]

Check that the barb fitting has tape on it's threads where it screws into the fuel tank and that the fitting is tight.