MILD THUNDER

iTrader: (3)

Yep.

And the fact you hammer the throttle and eventually it clears up and takes off and runs ok, sounds like a carb/flooding/fouled plug issue. If you cant or don't wanna mess with it yourself, id probably just call these guys up and get a rebuilt carb and exchange yours. Less downtime and bs.

http://www.allcarbs.com/catlist.php

zz28zz

91 was abt the timeframe I was working at the tune-up shop, so we mainly were working on 70's and 80's models. Q-jets didn't change very much so you most likely have the casting plugs I was talking abt.

Sounds like you are running very rich at start-up. The choke as prev mentioned, would be the first place I would start.

When you go to start it after it's been sitting overnight, do you have to crank the starter for a while before it fires, or does it fire up immediately?
If you have to crank for a while, the float bowls are dry and having to re-fill.

FIXX

iTrader: (2)

if that were the case then he would have a long crank time if the boat sat for a period of time..those plugs you guys are refering to the secondary ones are sandwiched between the throttle plate and the main body and the other plug which is open the the primary throttle blades..i have never had one or seen one cause a stumble from sitting for a few hours,,just long cranking time if the boat sits for weeks..

zz28zz

Depends on how fast fuel was leaking into the intake and how long it sat.
If the eng was off for a relatively short period (like an hour or so) and fuel was still puddling in the intake and there was still some fuel left in the bowl, it could fire up immediately but run extremely rich untill the puddled fuel was sucked thru. Opening the throttle would expedite this process; which would match the symptoms he described.

After a few hrs (again, depending on leak rate) the fuel would evaporate and you would just have the long crank time.

Yes, the plugs at the bottom of the main body (in float bowl) are the ones I'm refering to.

In all likelyhood, this isn't the problem, but it is possible. IMO, the most likely cause would be some crap got caught between the needle and seat or the needle/seat assy is worn and can't close completely..

That's why I asked if he experienced long crank times after eng sat overnight. If it fires right up the next day, it's probably the needle/seat. If there's a long crank time the next day, the fuel drained from the float bowl.

ajexpress

Regarding starting, here's my run down:

Per mercruiser manual I start the boat (if memory serves correctly) - 1/2 throttle if cold, 1/4 throttle if warm.

Completely cold start hasn't run that day = Will usually start first try, but I gotta keep the rpm over 1000 to keep her running for a minute or two or she will die. Occassionally she will start stumble then die, but I can keep her running by stayin above 1000 rpm on second try.

Has been run that day = Will kick over on first try....if sitting long time have to keep above 1000 rpm, if not will idle fine.

Run for a while, shut off for under an hour = Sometimes fine, sometimes start right up but stumble at idle and stumble on takeoff as described as the problem in this thread.

If it were a distributor / electrical issue I don't think I would be able to gas my way out of it. You guys are convincing me I need to replace/rebuild the carb.

MILD THUNDER

iTrader: (3)

I agree.

I haven't had many ignition problems that got better with increased Load/Throttle. They normally would get worse with Load/Rpm.

If the plugs wreaked of gas when you pulled them, that also would lead me to a carb issue. Most of the time ignition systems misfire, but still fire the plug. Just at the wrong time.

I'd be looking at the carb being that its 23 years old. Good thing about ignition systems is normally, you can diagnose the problem, by testing individual parts. Rather than throw parts at it. When I worked as a tech at a GM dealer, we couldn't throw parts at things. We had to diagnose driveablity problems step by step. We were able to recommend certain things, but at the end of the day we had to fix the part that caused the problem. If the car had a bad coil pack, crank sensor, pickup coil, or module, we tracked it down and replaced the faulty part. We didn't send the customer home with a entire new ignition system because of one part being bad.

Since its starts ok after sitting for a extended period, then yes, you can pretty much rule out the carb well plugs leaking like Mrfixxall said. It could be a choke malfunction like he said, internal issues in the carb. However, its really not something you can diagnose over the internet. We can sit here and give suggestions, but we aren't actually there seeing whats going on.

Theres a couple ways to handle a situation like this. You can bring it to a shop, and pay someone labor hours to track down your issue. Which can get expensive.

You can try to narrow it down yourself.

You can do preventative maintainence and replace things that may be overdue for replacement. Things like Spark plug wires, cap and rotor, plugs, carberator rebuild, water separator and fuel filter at the carb, sea pump impeller, exhaust riser gaskets, water tstat, and clean all your electrical connections. These are things that after 23 years and 500+ hours, just need to be done.

ajexpress

Plugs, water separator, sea pump impeller, exhaust riser gaskets are all new as of last year (water separator as part of end of year winterization). I'll rebuild the carb or just buy a reman. before the season. I'll also take a look at the maintenance records to see what I can find on the fuel filter, plug wires, cap & rotor, and tstat. The previous owner was anal and documented everything. If it's not listed I'll just replace them so I know where I'm at. Also thinking I should replace the risers and exhaust manifolds since they are original. (fresh water boat). If I'm missing anything from your post let me know.

Thanks to all who've contributed!!!