1989 merc crusier 350

[burned307]

I have a 1989 irvette with a 350 mercruiser inboard. It has the mercruiser thunder bolt iv system. When everything gets hot (not over heating) after running for about 15 mins i lose power and you can hear popping thru the carb. I have rebuilt the carb and replaced the ign coil. and set timing to 8 degrees btdc at idle and best I can tell the advance is working. I was think maybe the ignition module was getting hot and breaking down, but that's just an idea. Also when coming back in after it starts popping it will just shut off. But normally starts rights back up, when i feel like its about to stall i do pull the choke out to see if that helps with no change in the running, so in my mind that eliminates fuel problem. Any help would greatly be appreciated.

 

[Scott Danforth]

What do you mean you pull the choke out?
poping thu the carb is usually a lean condition

 

[Bondo]

after running for about 15 mins i lose power and you can hear popping thru the carb. I have rebuilt the carb and

Ayuh,..... it's runnin' outa gas,.... Move up through the entire fuel system, 'n see Why,....

Run it on a remote tank hooked right to the fuel filter,.... that'll rule out the hull's side of the system,.....

Speakin' of fuel filter, have ya examined it's Contents, for anything but clean fresh gasoline,..??

Is the fuel pump supplin' 4 to 6 psi to the carb,..??

How bad was the carb,..?? maybe ya missed something,....

Runnin' Lean, will set up Detonation, which can consume the motor in minutes,.... holed pistons in no time,....

 

[burned307]

I pulled the Manuel choke out just to see if it changed the running problem, it didn't. because that should have helped if it was running lean correct? The carb was ethanol-ed up, i have changed the fuel filter with a new one and only use non ethanol fuel now, It has a electric fuel pump on it but i have not checked the pressure from it to the engine.

 

[dubs283]

i have not checked the pressure from it to the engine.

this

like bondo said, check entire fuel delivery system,

 

[achris]

I pulled the Manuel choke out ....

What manual choke? There is no manual choke on a marine engine...

 

[Scott Danforth]

What manual choke? There is no manual choke on a marine engine...

exactly......

 

[burned307]

Working on finding a tester for that low of pressure locally, and yes my boat has a manual choke for the carb.

 

[achris]

... and yes my boat has a manual choke for the carb.

Then it's not a marine carb, and needs to be replaced with a proper marine carb YESTERDAY... :boom:

Chris.......

 

[Rick Stephens]

Then it's not a marine carb, and needs to be replaced with a proper marine carb YESTERDAY... :boom:

Chris.......

To reinforce that, automotive carburetors vent out, marine carburetors vent internally. Car engine compartments are open at the bottom, leaking fuel and vapors just blow away. A boat is a bucket, it holds all fumes in the bilge. Any dirt in the needle valve which overflows a boat carburetor makes the bilge a perfect fuel air explosive device - and fiberglass boats burn spectacularly after an explosion. There is no Mercruiser that came with a manual choke. So either someone swapped choke parts around or installed an automotive carburetor. Either way, it is not something I would put my family aboard.

 

[burned307]

I bought this boat from a guy in North Carolina so this is all new stuff to me as far as whats on this boat, so any help would be great. Ok my carb number is 17080565 it is a quadrajet. I can't find any info if it a car or marine carb. I found a tester i have 4.5 psi at the pump and just shy of 4 at the carb, has new line from tank to pump, pump to fuel filter and filter to carb. I have also changed to fuel filter and may have a little water in but not very much.

 

[Bondo]

Ayuh,..... The Quadra-Jet was Oem at the time of yer motor,......

4 psi is pretty much Minimum,..... spec is 4 to 6 psi for carbs,.....

 

[achris]

I bought this boat from a guy in North Carolina so this is all new stuff to me as far as whats on this boat, so any help would be great. Ok my carb number is 17080565 it is a quadrajet.....

Ok, that is a marine carb, but it was never supplies with a manual choke, so someone (not pointing the finger at you) has messed with it... Never a good sign, and makes me wonder what else had been messed with.... Not only that, but that carb is for a 5 litre engine (305), not a 350....

Chris.......

 

[burned307]

The gauge i used was older so i figured it may not be 100% accurate. but at least it was close. Yeah i have found a couple things they have lied to me about, so no doubt its a 305 instead of 350.

 

[achris]

I would start from the basics....Assume nothing. Go though this check list....

So, in this order.

1. Compression tests.
2. Check spark plugs, replace if needed.
3. If points, replace, along with condenser and rotor. Check and adjust, if needed, points cam dwell angle.
4. Inspect distributor cap, rotor and leads, replace if necessary.
5. Check spark quality (needs to be a nice BLUE spark drawn over 1/2").
6. Set timing. Check timing advance is working correctly.
7. Check/change fuel filters and check that the fuel system is not sucking air.
8. Check fuel pump pressure.
9. Check for full opening of the carb. Also ensure choke is opening fully when the engine is warm.

Once those are done, move onto the drive.

1. Pull the drive
2. Inspect the gimbal bearing, bellows and uni joints.
3. Check engine alignment
4. Service the drive water pump impeller.
5. Do a pressure test on the assembled drive
6. Fill the drive with new High Performance Gear Lube
7. Re-install the drive.

Now check engine exhaust manifolds and elbows.

Once that lot is done you now have yourself a 'baseline' to work from...

Do you have an engine serial number by any chance? (here's where to look -> http://forums.iboats.com/forum/engi...d-engine-serial-numbers?p=6661415#post6661415)

Chris............

 

[burned307]

Ok, thanks ill start on that list this week. I just started a new job so it may take a while to get thru it all.

 

[BudL1te]

Just a thought but, Check your fuel for water, Take the line from after the pump and pump some into a clear container like a mason jar, something bigger so splash will not get all over.

Let it sit for a bit and see if you can see any separation, water will sit on the bottom. quick and easy to rule it out.

 

[greno]

You should also have a clear tube running from the fuel pump to the base of the carb. This line tells you if the fuel pump diaphragm has failed. If there is fuel in this line, the diaphragm is bad. But if this line deteriorates it can allow air into the base of the carb creating a lean condition.

 

[burned307]

Redid all of the fuel lines and installed a new fuel pump,and new fuel filter. Drained the old filter with very little water, it ran much better. Only popped thru carb on a hard turn or when hitting a big wake. So i got a bigger fuel pump and made an inline gauge set up. I know have 7 psi at the carb, going to try it again this weekend.

 

[burned307]

Update!!!!! with new fuel pump boat runs great!!!!! no popping or any problems have been out twice just to make sure before i posted, Thanks For all the help