86 70hp johnson vro ,intermediate throttle bog-stall

wahoo 16 · May 30, 2008

just want to start by saying this is a great forum, and i have gleaned many helpful hints. my problem is stalling at 1700-2000 rpms. if gradually accelerated, motor sputters, shakes and stalls. if throttled up in one hard push, motor jumps to full rpm no problem, can run all day like this. power head completely overhauled, sleaved, pistons, rings , bearings gaskets, etc.
all new hoses clamps, no air leaks in fuel supply lines. carbs cleaned and checked. linc and sync as described in omc service manuel. idles great, shifts and runs low speed no problem, just loss of mid range throttle. any help would be great. do not know which way to go, ignition? fuel?. upon visual inspection of carbs, i do see #1 carb spitting fuel, with occasional sneeze.
compression even at 130. if i key the primer at the stall point, motor catches and runs great. any suggestions, THANKS

kenmyfam · May 30, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

Welcome to iboats.
Sneeze usually means running lean. My "guess only" at this point is a fuel / carb issue. There are plenty of folk with more experience that will be along shortly with better advice. Most likely a blocked or damaged mid range jet / needle.

wahoo 16 · May 30, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

yes, that is what i am thinking, just hate to tear into them again without being sure. one other thing the machine shop installed boyesen reeds on intake manifold.

kenmyfam · May 30, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

Wait for some more opinions from the other guys. They will be along shortly and I am off to work !!!!

wahoo 16 · May 31, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

worked late friday, took all 3 carbs off , cleaned them out again, #1 sneeze gone. idle air bleed orifices #28. linced and synced 4 degree atdc as per manuel. test drove, still weak at 1600 1800 rpm, sputters and stalls if not primeresd or throttled up. could the orifices be to small? could the boyesen reeds require change in pickup timing? thanks for any help.
dan

Reggie08 · May 31, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

I'm by no means an expert, but when you rebuilt the powerhead, did you bore the cylinders over or are they still the standard size? Reason I ask, if you did, I'm wondering if maybe you don't have a high speed jet issue i.e., the jets are too small causing a possible lean issue.

I recently rebuilt an 85 'Rude 90hp and the cylinders were bored .030 over with the exception of one which is .040. A local mechanic told me typically when that happens, the carbs need to have larger jets to accomodate the bigger cylinders. I'm not saying that's what is causing your problems, but maybe something to consider. I don't think they're too terribly expensive either.

wahoo 16 · May 31, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

i am not really sure, block was machined and sleeved, then assembled as short block by local outboard machine shop. it runs great at upper end of throttle, so i was not thinking high speed orifices would be a problem. thanks i will check into that.

Reggie08 · May 31, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

For what it's worth, we just came back from the lake and my motor didn't run well at all. Not sure if it was the high speed jets from a 115hp motor I installed or if I had a spark issue (I'm thinking spark issue). So if you change em out and go to the lake, take the original jets with you so you can change them back if the motor doesn't run well. Least you can eliminate the jets either way.

wahoo 16 · Jun 2, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

reset pickup timing to 1 btdc at larger cam mark, aligning larger cam mark w/ center of throttle cam follower. seems to work much better. only very small shutter at 1700 1850 rpm. gonna run it over to shop this evening, they will check it out tuesday mornig. check link and sync, if that checks out swap carb orifices, they say 86 3 cyl carbs very quirky to set exactly right with fixed jets. will spend 1-2 hours before deciding if further tinkering will be needed. they stated that ater 6-8 hrs there have been three over the years that they just couldn't smooth out mid range throttle. at 110 dollars an hr that is an expensive proposition. they should know a lot more after 1-2 hr, and decide then how to proceed. will post results in day or 2. thanks

wahoo 16 · Jun 3, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

shop called, said all fixed, linked/synced, disassembled carbs ,reset floats. purrs like a kitten! 2.5 hr labor. we go for a ride , slow area 1400 rpm , real smooth, throttle down hard, she leaps out of the water screaming at 5200rpm, throttle back to 1400 ,slowly ease throttle up to 1700-1850, she just dies. three omc certified techs scratching their heads. reiable local omc/yamaha certfied shop. many repairs over the years for friends and aquaintences. left it there for another night, see what they come up with.
motor on a 16 ft split console wahoo. anyone have any clues. thanks

wahoo 16 · Jun 4, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

anyone? how about small hole in one of vro diaphrams? worn ball joints from throttle lever to timer base? dead spot in timer base? malfuntioning powerpack or coil? just pondering, rainy today, don't know if i will here from them today. anyone with similar problem that has posted resolution?

wahoo 16 · Jun 4, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

engine model #E70TLCDC 1986 70 hp vro

wahoo 16 · Jun 4, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

time to go to work, don't know when i will be home today with this lousy weather.

wahoo 16 · Jun 4, 2008

Re: 86 70hp johnson vro

Re: 86 70hp johnson vro

if i understand correctly, there is no intermediate throttle adjustment on the 86 carbs. they are going to drill the orifice hole in the carberator throat. i was down there for an hour or so talking to them. the only other option is to locate a set of 89 carbs which HAVE intermediate adjustment, 150 each/unavailable anymore. used? good luck. told them to go ahead and drill. they will call tomorrow and let me know

wahoo 16 · Jun 5, 2008

Re: 86 70hp johnson vro ,intermediate throttle bog-stall

they believe that for some reason (like change in cylinder volume due to sleeving during rebuild) the fixed intermediate fuel circuit is no longer providing adequate fuel volume at the problem area in rpm range (1700-1850). drilled holes inside throats of carbs to provide more fuel for intermediate circuit. they have eliminated most of problem, afraid to drill any larger for fear of messing up idle fuel cicuit. found 89 carbs on bombadier website 365 dollars x 3, to much money! i guess we will learn to work around problem area in throttle and live with it. anyone have a set of late production 1989 carbs for a 70 hp they want to part with? anyone with fixed intermediate jets ever experience anything similar after machining and rebuild? thanks to all

wahoo 16 · Jun 6, 2008

Re: 86 70hp johnson vro ,intermediate throttle bog-stall

picked boat up, ran it for several hours , can hardly feel the stutter in midrange rpm. idles great, maybe a little rough 1300-1500, but very smooth thru-out rest of throttle range. max rpm 5450-5500, 45 mph. i watched them drill the holes, this is a sure cure for this problem.

wahoo 16 · Jun 8, 2008

Re: 86 70hp johnson vro ,intermediate throttle bog-stall

ran 8 gallons thru motor, cruising all weekend, not one stall. paid for 3.5 hrs labor. kinda steep but nothing like a working boat, turn key and go w/ confidence that nothing is wrong. (until the next thing that goes wrong!)

86 70hp johnson vro ,intermediate throttle bog-stall

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