Fuel starvation after rebuild?!

[Zep25]

Just rebuild my ‘89 v6 crossflow 150. 150stlcem. Started her up for the first time yesterday. Didn’t blow up so I was pretty excited Used new alcohol free 25:1 oil mixture off of external plastic 5 gal jug. Primed with bulb until firm, no leaks noted, started right up. Idled a bit high (I think) and slowly idled down and stalled over a few minutes. Did not see any fuel leaks anywhere. Primer bulb was soft as usual. Reprimed until hard and held prime, started right back up.... 45 secs later, idled down and stalled again. Can squeeze the primer bulb to keep motor running. Clearly a gas starvation issue right?

Air leak somewhere?
idle screw adjustment?
recheck timing?
New fuel pump? Oil side already disconnected for premix. Pump was rebuilt with new diaphragm/kit during rebuild.
seems like the primer bulb is ok?

thanks for any help.

 

[racerone]

A primer bulb does NOT stay hard once motor has started.--------What sealer was used on crankcase joint ??----Recheck fuel pump work..

 

[Zep25]

Yes, primer bulb seems to be working properly.
Gel Seal II per OMC manual for crank seal.
I’ll pull the pump and take another look at the diaphragm.
Anything else that may cause this problem?
Thanks.

 

[racerone]

Test run with a different gas tank and hose.

 

[Fed]

It's quite normal to have to push the key in (bump) if a cold motor starts to die, just until it warms up & settles down.

 

[JerEazy]

Is 25:1 a bit lean? Maybe switch to a 50:1 to stay running? Not sure if 25:1 was required for “break-in” i’ll leave that to those smarter than I.

Also, do you still have the slow speed jets at “base” setting? May need adjusting.

 

[racerone]

???----25:1 contains more oil than 50:1 I hope.

 

[Zep25]

Yes. Using double oil per break-in instructions.
I did let the motor warmup for about 10 mins (as I squeezed the primer every ~1 min to keep it running) so I don’t think it was just cold.
Pulled all the jets and cleaned them well when I rebuilt the carbs. I’m not sure how to “adjust” the low speed jets as the orifice is a set size on those.
I did increase the high speed jets 2 sizes, but that would not effect the idle issue.
Thanks to everyone for the help.

 

[JerEazy]

???----25:1 contains more oil than 50:1 I hope.

Yeah - more oil means less gas - less gas runs lean. My old Yamaha 2-stroke runs like garbage (if at all) if I over mix the oil - so it was just a thought.

 

[JerEazy]

I’m not sure how to “adjust” the low speed jets as the orifice is a set size on those.

Thanks to everyone for the help.

Just checked your carb parts diagram again - and you’re right - there’s no adjustment on them. My mistake on an assumption.

 

[racerone]

edit

 

[Zep25]

Think I’ll just try the regular 50:1 mix and see what happens. Running lean makes me nervous.
Will also run my primer bulb/line straight to the fuel pump intake and see if my line under the cowling has a small air leak.

 

[racerone]

A V-6 running too " lean " at idle will stop running.----It does not damage any parts.-----Running lean at full throttle is a different story.----You have opened up the jets so full throttle lean will not be a problem.-----What was done during the rebuild ?----Bored out with new O/S pistons or something else ?----Do you have spark that jumps a gap of 3//8" or more on each lead , yes or no?---Perhaps look at synchronizing throttle and ignition timing.-----If throttle plates open too early the motor will STALL every time !-

 

[Zep25]

Tried regular 50:1 gas mix and same issue... starts up fine, then over about 30-45 secs it slowly loses rpms and stalls out. Can keep it running by pumping primer ball. Tried bumping with key choke and it reved up quite high. A little concerning-ly high since I’m still limiting rpms for breaking-in purposes.
Was still running on original vro (oil side blocked), so I may replace with a new non-vro anyway for piece of mind.
Rebuild included bore and hone .003 over on all 6 cylinders. New pistons, rings, gaskets, upper and lower crank bearings. Rebuilt carbs.
Will check spark tomorrow. 3/8 or 7/16 jump?
Carbs seem to open all at once. Need to check if butterflies go exactly parallel with wot, but don’t think that’s part of my issue as of now.
Also broke the spring on my hotfoot. Gotta replace that too. The joy of boat ownership.
Thank you as always!

 

[racerone]

The fuel pump is not working.-----Should be easy to figger out why.----Issue with + and - pulses from crankcase.---Bad pump or issues with fuel line and pick up tube inside fuel tank.

 

[Zep25]

Swapped out for new non-oiling fuel pump and replaced fuel lines from intake under cowl to pump with 3/8id hose. Fired right up and idled without pumping the primer.
Still feel it’s idling a bit fast, but have to get my tach working to verify.
Question- I don’t think my throttle linkage is operating correctly. Should the timing ring advance to full as soon as I increase the throttle from idle?
thanks