other side of the spectrum WOT issue for my 1989 70 hp

[bob johnson]

ok i worte a huge thread on what led up to where i am now, and I figured...no one would read it , it was so long! sooo just the facts...history if asked for it! took the boat out with my son...it ran much better than previously....the tach wasnt working...but i could hear the motor seemed to be over reving....we were doing 25 mph.....70 hp 18 ft aluminum starcraft...we should do over 30!.... took it back in and took off the 13 pitch prop and put the 15 pitch on...and i found that the tach lead was loose where it came out of the control.... we played with the idle a little as well..... then out we went and the lake was a little rough..mostly swells.... so we ran it up and it went up to 5500 and we were doing 32 MPH and it seemed like the speed was increasing but after about 15 seconds the motor died back to 4000 rpm... and slowed to 25..... the last 10% of the throttle did nothingh... actually when we BACKED it off, there was a sweet spot where it picked up about 200 rpms.... and so we played with the throttle and found we could do no better than 26 mph and 4200.... we could never get that 5500 again.... at 4200...the motor sounded fine...... it didnt sound great at 3200-3500....sounded rough... at 2500 it sounded good........so whats going on that allowed me to get to 5500 and 32 mph( seemingly what i want) then it dies out to 4000.....and i have useless throttle motion left!......what avenue should i take to trouble shoot?...i DRED going back to the same mechanic.... should I be looking lectrical cut out...or fuel restriction?.....i took the boat back in and pulled one bowl screw so i could take the high speed jet out and see if it was clean...but it was totally stripped!... the buffoon mechanic ruined the orifice... i ran a wire through it to verify it was open... i never checked the others...motor has GREAT compression... the mechanic went and coated all the electrical connections with the black liquid tape stuff....i have the fuel filter under the cowl and i have a larger in line near the gas tank...which is portable.... we played with the trim.....but with the swells it was useless for a troubleshooting effect.....

 

[racerone]

What is " great compression " why not post the values from a compression test done today ?----Mixing at 50:1 or oil injection ?

 

[jakedaawg]

Bob, you have been wrenching for awhile now... usual stuff here.

comp test
spark test
fuel sample
verify throttle plates open fully
verify max wot timing
verify timer base moves fully
spark test at various throttle positions
of couse you have to fix the carb
make sure it's getting air, fuel, and not filling cowl full of exhaust
Cdi electronics trouble shooting guide to check the various ignition components.

Heck Bob, you're practically a pro now, "you can do this!"

 

[fireman57]

Why not make sure the other high speed jets are clean too? Doesn't take much to clog one.

 

[bob johnson]

What is " great compression " why not post the values from a compression test done today ?----Mixing at 50:1 or oil injection ?

i took them last summer...im thinking 125 across the board...but thats from memory... i didnt take the compression guage on my trip. the boat is 5 hours away... i thought i had paid the mechanic to fix it....while a lot better....it still needs work,,,if someone thought the scenario I explained was fuel..id take all my tools and go visit my son for a weekend again and go through the system...but i am weak on electrical components and their testing..its just another realm as is trying to run the motor at WOT and TEST things.....on lake ontario its sketchy.. and for sure that would have been dangerous last sat..... trying to lean over the motor with test equipment while trying to wind out the motor in the rough water....has spark at idle...seems GOOD too.... since the motor hasnt ran more than an hour since last summer..im going to go ahead and assume the compression is unchanged!.....i ve played with motors but you only know what and where your experience has taken you.....sometimes you need someone more experienced than yourself.....only a fool would just and replace one thing at a time HOPING thats the issue... and $1200 later you havent fixed anything!

 

[racerone]

You mention the motor lost power when using the 15" pitch prop.------So something happened and trouble shooting starts with step # 1 which is a compression test.-----But perhaps you have water in the fuel.----I am not there to look things over.----Even with what many folks think is acceptable compression I have found scored pistons.----Mixing at 50:1 , yes or no ?

 

[bob johnson]

You mention the motor lost power when using the 15" pitch prop.------So something happened and trouble shooting starts with step # 1 which is a compression test.-----But perhaps you have water in the fuel.----I am not there to look things over.----Even with what many folks think is acceptable compression I have found scored pistons.----Mixing at 50:1 , yes or no ?

yes mixed oil 50:1.....fresh fuel..... it had power with the 15 pitch. we ran well about 3000 rpms . then got out far enough to run it wide open, she ran straight up to 5500 rpm smoothly increasing speed the whole way all the way 32 mph..... then is just squatting back to about 4000...with no response in the throttles last movement...throttled back and found a sweet spot that it liked......which suggest an electrical issue.......soo i cant check compression for a while...my son doesnt have the equipment or even a truck to tow the boat with right now.... i know a motors health starts with compression and I verified it when i bought the motor...

 

[racerone]

Good luck with the project.

 

[bob johnson]

looking for that tip to direct me based on the info( little as it is) wether Im looking fuel or electrical.....sometimes people go through the same scenario and can tell you a direction.....if its electrical ill just drive it to a mechanic again..if it sounds like a fuel delivery, id tackle that..i have a set of 1987 70 hp carbs that i had a guy rebuild , sitting at home...( dont know if ill get into a link and sync issue with foreign to the motor.... carbs)..

 

[fireman57]

Again, did you make sure the other high speed jets were clean. If you have one that clogs with a piece of crud it will do what you are describing. When you hitt your 5500 rpms the junk might have dislodged and you got fuel to that cyliner then it picked it up again. You want fuel to all cylinders if for lubrication if nothing else.

 

[fireman57]

If you can run it at night with the cover off you may see a plug wire arcing or electrical somewhere arcing when it gets a load on it at higher rpms.

 

[bob johnson]

the motor is not near me now..it is 5 hours away...so im collecting "possible checks" for the next time i go back.... and for sure i have planned to removed the bowl screws and try to remove the other high speed jets if i can, if not...then run a wire through them to make sure they are clear...i have spare carbs that are rebuilt alreadfy by a mechanic near me.... from a similar year motor...but i worry about the linkage not being in sync with the timing.... since they were on another motor...... that way i can skip over that stripped drive high speed jet...... i actually have to now worry if i removed any more brass trying to remove that one HS jet... and if i did shave a little...where is it now?......i think on a 3 cylinder if i was arching out..id never even get close to 4200 rpms..... i had that happen once on another motor... the spark plug wire was shot... and it was arching to the motor..... motor ran awful!....

 

[flyingscott]

Are you running the vro pump? Or are you running an old style pre mix pump.

 

[bob johnson]

Are you running the vro pump? Or are you running an old style pre mix pump.

the motor has a VRO fuel pump on it... but the oil line is plugged and i premix the fuel

bob

 

[fireman57]

Oil line needs to be disconnected and the nipple where it draws it open.

 

[racerone]

What oil line should be " open " and why would you want it open ?

 

[fireman57]

The oil line from the VRO where attaches where the fuel line goes into the engine hookup. It needs to be open for correct fuel flow to the engine. Good friends with my local dealer and when I disconnected my VRO and went to premix he said that oil line had to be left off and not to block the nipple. He even showed a service bulletin on it when I asked why too.

 

[bob johnson]

Oil line needs to be disconnected and the nipple where it draws it open.

not sure if Im reading that right... the oil hose coming out of the fuel pump that I currently have plugged....needs to be open?...if thats not what you ment...what are you calling the nipple?

 

[fireman57]

Yes the end of the VRO oil line should not be plugged into the engine. What the line connects to.

 

[bob johnson]

Yes the end of the VRO oil line should not be plugged into the engine. What the line connects to.

im not following that advice...it certainly seems like it would suck air.....and that seems to be one of the things you definately dont want your fuel supply to do......hmmmm....... i have four motors that have that line plugged... and three run good..........