New Owner, Old Boat, New Motor 1981 3.8

I purchased an 81 16.5' OMC
It had a 3.8l V6 i quickly found was cracked.
I took the boat to the motor shop and quickly decided to install a 4.3 in its place. We used most of the parts from the original motor that was able.
I payed a guy to install the motor into my boat. When i picked it up it ran amazing. Purrrred like a little honda. The motor was balanced to so there was no vibration. I took it out on the lake the past weekend and it ran, well good. It jumps out of the water but only pulls 3500RPM's WOT? Seems strange but i dont know boats. When the motor was built they put in a "boat" cam? I think its for more torque but please explain. So we tooled around the small lake for a few hours just fine.... I was doing about 3krpms (no MPH avail) and dropped it to idle. The motor then died and wouldnt start. My and my bro took the top off the carb to let it breath. He has the idea maybe it flooded from the quick deceleration. Nothing... I let it sit another 5 mins... and we got it started by manually manipulating the carb to give it "gas" and we hobbled it to the marina. It didnt like running low RPM's. I just figured i was out of gas. I get the boat home put 5 gal gas into it (20gal tank) and fire it up. Its running and dying alot. My motor is a 4.3 block, 3.8 intake, 2bbl rochester carb, points dist. 3.8 heads, Not sure about what distributor we used. New cap, wires, plugs.... I replaced the coil and it seems to run with out dying now. The big issue im having is a vibration. I have checked the plugs and the tips dont look abused. I almost wanna call it a surg maybe? it will run for like 5 seconds then sounds like it maybe misses a cylinder? I checked the cap its bone dry. I also checked the dist. for loosness(rotation). Nothing. I know nothing about carbs but i replaced the fuel/water filter, and the filter at the base of the carb to.

Someone tell me what the heck to do! I wanna take her out again but i dont want it to rip the motor mounts or something.


I want it to run smooth again and i want it to get better speed and rpm's


Steve

Re: New Owner, Old Boat, New Motor

Make sure all the filters and fitting from the gas pickup tube to the carb are clean rebuild the carb.

Re: New Owner, Old Boat, New Motor

SAomething has definitely happened between the recieving the completed vessel and the first running, and the subsequent running when it performed poorly.

Sounds like you have a mis-firing problem amongst other things.

The fact that it won't idle down sounds like a major Vacuum leak as well.

You need to do a compression check, as well as a fuel pump pressure check.

A "Marine Cam is designed to have the maximum performance at WOT, and this will be achieved only with the correct relationship of the Engine, gearing and Prop.

I would envisage the WOT at being somewhere in the 4,800 RPM bracket, and if it won't get there, it sounds like you also have a timing issue.

Bruce.

Re: New Owner, Old Boat, New Motor

Vacume leak? This is not a vacume motor? There are no vacme hoses.
If Its a timing thing can I just loosn the distributor and turn it while
running ?

Re: New Owner, Old Boat, New Motor

I assume being you just purchased the boat you have never taken it out prior to the bad engine.

It might be time to do some research on the outdrive and prop it is very possible the previous owner has done some changing around with things causing the engine to not reach WOT.

Or it is also possible that it may be water logged. I had one like that drove me crazy thought I had an engine issue turned out the hull had water trapped in it.

Re: New Owner, Old Boat, New Motor

hystat...this is the same guy from Sterndrive.com, how many guys have an 81 Sea Swirl that have swapped out the 3.8 for a 4.3 and used the 3.8 dist, named Steve????

Re: New Owner, Old Boat, New Motor

Boatin_bob, is there an issue here? I just wanna resolve my problems. I use different sites to reach out to more people. Perhaps someone out there has my answer.

I came home today and i did a compression check.
125,105, 110, 135,120,135

I started it after my checks, i know the carb was still trying to give gas into the carb. After starting it up it ran good. I turned it off after clearing it all out and now it wont start. I looked inside the carb and i see a pool of gas. Its sitting now with the top off "evaporating?" What do i do now? Is my compression ok?

Re: New Owner, Old Boat, New Motor

found a number on my distributor.

http://www.marineusedparts.com/servlet/the-308/OMC-3.8L-PRESTOLITE-MARINE/Detail

Re: New Owner, Old Boat, New Motor

the 105, 110 next to each other could be blow bye but is ok.

I still think it's classic idle circuit blockage. Fits it to the T the symptoms.

Re: New Owner, Old Boat, New Motor

ok, it seems i have the wrong distributor in my boat. Nothing is going to run right with it in there. Im just bid on one on ebay. When i get it i will get back with yall.

I might also get my carb rebuilt.


BTW, boat has been out of the water for a year and a half... so i dont think its logged.

Re: New Owner, Old Boat, New Motor

Prinler said:

I came home today and i did a compression check.
125,105, 110, 135,120,135

I started it after my checks, i know the carb was still trying to give gas into the carb. After starting it up it ran good. I turned it off after clearing it all out and now it wont start. I looked inside the carb and i see a pool of gas. Its sitting now with the top off "evaporating?" What do i do now? Is my compression ok?

Click to expand...

"Pooling Gas" is indicative of a badly seating Needle Valve in the fuel bowl, and if that is the case, you will have trouble starting a flooded engine.

Starting a flooded engine in a boat is the same as starting a flooded engine in a car. But, the results of backfiring can be more disastrous in a boat than a car. When the fuel evaporates, then it should start as normal, but it takes a long time to evaporate on its' own.

The Compression readings are on the low side for a good performance, and with the 2 lower ones, being just below the average, it still should have some performance, but the figures aren't that good.

You need to perform the "Wet" Compression Check, whereby you squirt a bit of engine oil into the cylinders, and after a couple of revolutions of the starter, to seat the oil around the compression rings, then take a new set of Compression Pressure readings.

If the readings increase remarkedly, then the Rings are shot, but if the pressures stay much the same, then you have a Valve Seating problem.

No engine will achieve optimum performance if it isn't working correctly.

Bruce.

Re: New Owner, Old Boat, New Motor

i think after running it a while and he does a compression test the numbers might get better.

I think the major area of concern for NOW is the carb. We get a fuel pump psi reading ? I forget already and i am to tired to go back and re-read the the whole post.

Re: New Owner, Old Boat, New Motor

Not fuel yet. Its a mechanical one. Again original 81 equip. I can only barrow 1 tool at a time from Uncle Bryan yesterday was a Compression tool. By reading the past post tho i think i still need it tho. for the WET test. I Pray to god the rings are good. The heads are 3.8 1981 heads, i had them done 2 times... once by a mexican shop that didnt speak english. They didnt even grind the surface. they charged me $100 and put some rings on the thingies...(i forget the name). I then took it to the engine builder and he said "who the hell?" "this looks like a Tiujana head job" i told him they didnt speak any english and he said he would not warranty the motor is he used them... i then paid $180 for him to REDO it to his anal specs. So i figured i was good. I do have a set of 4.3 heads i can take to a shop tho. Have them clean them up and i can always plop them on top later if we find that the compression is in fact a head issue not a ring issue(cross your fingers for me). Rings, piston, rods are all 100% new. Original, nothing fancy... Original spec items just to be clear. Im not expecting high compression. Just consistant, decent compression...

I will be out of town sat-sat next week so dont close this, i will be back working on the boat then.



Also one last thing. I looked at this website... they responded when i inquired about it... here is his email.
Hi Mr Pritchard;
Thank You for your interest in a carburetor for your 81 Sea Swirl. We do have that carburetor in stock. It is my stock number Y40-2. The cost would be $258.00 + shipping exchange or we can rebuild yours for the same price.
Our Lifetime Warranty guarantees this will be the last carburetor you will have to purchase for this engine.
Our valued customers can use our "Ask Art" technical support line. We can also fax or e-mail vacuum and electrical diagrams.
Please call me toll free at 1-800-250-8746, between 7:00am & 5:00pm, Mon thru Fri, EST or e-mail us with any questions.
Thanks
Butch Fernandes
Guaranteed Carburetors
1-800-250-8746

Lifetime? for $258? Can this be legit?

Alright, lemme know

Steve

Re: New Owner, Old Boat, New Motor

listen i got a 2 barrel rochester on my 86' used the original carb off my 2.5 mine runs great, rebuilt the carb 5 years ago but i'm like a nut with the fuel water sep i keep a eagle eye.

Re: New Owner, Old Boat, New Motor

Ok, well i got my pertronix in the mail while away. Im attempting to install it now. I will let yall know what happens.

Re: New Owner, Old Boat, New Motor

Ok i got it installed. Its running but still has a small vibration. Off to get a timing gun.

Re: New Owner, Old Boat, New Motor

Ok wet compression test.
125, 120, 135, 135,120,135

looks better but what does it mean? If wet is higher that means its the rings and not the head?

Re: New Owner, Old Boat, New Motor

I came home today and i did a compression check.
125,105, 110, 135,120,135
Ok wet compression test.
125, 120, 135, 135,120,135

looks better but what does it mean? If wet is higher that means its the rings and not the head?

Click to expand...

Yep. Piston Rings in 2 & 3 are not sealing as good as the rest.

Bruce.

Re: New Owner, Old Boat, New Motor

Ok, i rechecked the gap on my plugs. They are were all different but all around.06
The motor valve cover calls for .035... so i re gapped it. I also cleaned them with WD40 and a wire brush.

It still runs unbalanced. Now with the electronic distributor(pertronix) plugs are set right, new coil. thats all for the electrical right? I didnt time it but the distributor does not rotate.


Now im working on fuel. I replaced the old rotted fuel hose. I removed the stainless line with rubber. I also added a 3rd clear fuel filter so i can see it flow. Looks ok. Its flowing... I cant measure the pressure but i did crank it over with the line not connected to the carb. It flows good. I dunno how much pressure tho.
Still runs crummy.

I dont see how but could this be my recently rebuilt carb causing my motor to shake?

Could this be my valves? someone in RL told me i need to have them serviced? Can someone explain this?

Thanks everyone!

I know i dont have enough time to consider my motor "broken in" but i dont want the engine to shake and damage the boat.... i read it should be broken in while running correctly! So HELP!

Re: New Owner, Old Boat, New Motor

Firstly, the Plug Gap on the Rocker Covers is going to be for the opriginal Ignition that came with the engine. You will have to consult the Petronix paperwork to see what they recommend for their system.

Unbalanced firing indicates a problem with each cylinder firing, whether it be low compression on one or two, which is what the Compression Check indicated. Could mean that the Plug Leads are breaking down. Are they Carbon or wire leads?

Are the Plug leads on the correct plugs?

What is the Distributer set at, as far as Advance goes. It mightn't have moved, but it could still be out of timing, especially if you replaced a set of Points that had had the timing set for.

Pitting in a different Ignition source is definitely going to require the Distributor to be re-set.

You said that the Distributor doesn't rotate. Are you saying that it is stuck in the block? or the Advance Mechanism isn't working? Are the Mechanical Advance weights moving under the Rotor Button?

As far as the re-built carby goes, is there a vacuum leak anywhere?

Bruce.

Re: New Owner, Old Boat, New Motor

I love all the questions you asked me. That gives me alot to think about and do.

Yes i have low compression due to a half ass break in due to it dying on me and me being scared and pulling it off asap.

The plugs and wires are right out the box. so i have not looked but im assuming they are fine.

As for them being plugged into the right ones? en less pertronixs runs a different order? i dunno. I only take 1 wire off at a time. then replace it before moving to next plug. it was working remember.

I have not timed it yet. Im going to try to barrow one tomorrow. What i mean by it wont rotate is that i gripped it and twisted to see if it would move at all. not even the slightest wiggle. its bolted down tight. Thats all i ment.

Vacume leak? I have a 17080050 2bbl. It has a heat choke. (dunno what that means really) I dont know how to check for leaks. Im clueless on checking but willing to learn.

I really do love troubleshooting things like this. Im glad you guys tolerate me.

Steve

Re: New Owner, Old Boat, New Motor

G'day Steve,

It is a bit hard trying to diagnose things when one is so far away, but here goes.

Okay, the lowish compression on a couple of cylinders will give it a "bit" of a "Miss" but not in regards to actual really bad running. Just not firing really on all cylinders, and as it is a 6 cylinder engine, any cylinder down is going to make it run a but rougher than say an 8.

I don't think the low compression on just two would be because of poor running in. If it was poor running in, then I would be looking at all cylinder pressures being low.

Whenever I tale Plugs out of boxes, I always check the gaps to make sure that what is meant to be the gap, is the gap. Never assume anything. One never knows just how carefully people handle packages.

Ok, so you did them one at a time, which is good, so go to the front of the class, but you still haven't said what material the Leads are made out of, but as you say, they are new, then they should be okay, no matter what they are. Carbon Leads do break down, and are really only for cars, as they help to control the Static that interferes with radio reception.

Definitely time the distributor to the specifications on the Petronix Box, and if nothing is mentioned there, to the Engine Specs.

Okay, I understand what you mean about the clamp being tight. I had an engine where the Distributor was siezed tightly into the opening that I had to destroy it to get it out.

A Heat Choke on a Carby means that the Automatic Choke operation is controlled by the heat that comes up through a metal tube that is inserted into the Exhaust Manifold

As far as a Vacuum Leak, that can be checked by listening for "Hissing" sounds around the base of the carby, and other methods that I won't go into in case you aren't confident in applying a stream of LP Gas around the engine bay and observing any changes in engine revs.

One method I have used is to het a 3 foot length of garden hose, and with one end stuck in your ear, move the other end around the various areas of the engine where a leak could occur. Heads to Manifold, Carby to Manifold, etc. The Hose method is another way of listening for engine rattles and knocks, but I prefer to use an Automotive Stethoscope for these diagnoses.

Have fun,

Bruce.

Re: New Owner, Old Boat, New Motor

"As far as a Vacuum Leak, that can be checked by listening for "Hissing" sounds around the base of the carby, and other methods that I won't go into in case you aren't confident in applying a stream of LP Gas around the engine bay and observing any changes in engine revs."

Yes i use some kind of canned gas and spray it around and look for changes in motor rpm. I did this with my passenger car. I will try it tomorrow.

Do you think once i break the motor in fully i will get a smoother running motor? Can it smooth out?

I do notice that when i turn off the motor i hear a like squeek as it comes to a stop? oh god i hope its not the bearings! Or a cylinder!

Re: New Owner, Old Boat, New Motor

If the rough running is now, I can't see it being gone after running in.

Got to be something wrong somewhere, and usually electrics will cause rough running, like out of tune, shorting out, etc, etc.

Now, the Squeek? That is a new one on me as it could be anything from a fan belt too tight....... but, I gotta ask, is it a deep squeek, or a high-pitched squeek, or a mid-range squeek?

Inquiring minds need to know these things.

Bruce.

Re: New Owner, Old Boat, New Motor

i think it might be the rebuilt alternator. i know the guy put it into a parts washer and then painted it. Can i just spray lube into it to check?

Re: New Owner, Old Boat, New Motor

well shoot, the guy put a buncha paint on the timing marker plate.
Can someone tell me what 10deg BTDC is? Thats what the valve cover shows it wants form the old 3.8 better yet... can you show me where the line should line up at?

Re: New Owner, Old Boat, New Motor

ok well this is where i think it goes and i have it set here. Still running like ass. I tried to advance and retard it a little and same issue.

ues.

Re: New Owner, Old Boat, New Motor

Well, that is a sure way to recondition the outside of the Alternator. Will do NOTHING for the internals, but wreck them.

Now, 10 Degrees BTC means 10 Degrees of Advance, that is the ignition will fire at 10 crankshaft degrees BEFORE the piston reaches Top Dead Centre.

You will have to scrape the paint off the marker, and the plate that is attached to the Timing Cover, so you can actually read the numbers stamped in there.

Bruce.