Slight hesitation off idle 5.7

[Simanski]

So I have had more then one issue, but I feel like I'm getting close to 100% with my engine. Ill start off with my dumb mistake I made which was I didn't close the dog house before winter and my cover leaked filling my engine with water. It filled the carb and bent the throttle plates wide open! I had a heck of a time finding replacement plates, ended up buying a junk carb from a marine salvage. Put those plates on my original carb but the boat was smoking a bastard and running rough. So I cleaned out the "junk" carb and put the plates back on that and put that carb on the engine. No more smoke but it still ran rough. I discovered a cracked sparkplug, I just replaced the one plug cause I put all new plugs in last year. But I did check all the others and they were good. Running better but still crappy. Went to check my timing and it was very close, so I decided to dial it in and WACK I got sapped off the cap! So I got a new cap rotor and the sensor in the distributor. BTW this is a TB V system. It runs way better now.....BUT I still have a slight hesitation right off of idle. Sometimes a backfire happens. I hate throwing parts at it till its solved but that seems to be the only way to get this engine to 100%.

So just to recap
New wires about 2 years ago
New plugs 1 year ago (one plug last week)
New Cap, rotor and sensor last week
New fuel filter
Timing checked good
Old ass carb I feel like is suspect might be next to go
I tried adjusting the idle mixture screws but cant seem to make the hesitation go away. (I did this in base timing mode) I can make it worse but not go away.
My other issue and I'm not sure if this is related or not but I cant get over 3600ish rpms at wot. I know this could be prop pitch and stuff but I wanted to get rid of that pesky hesitation before go into changing props. especially cause its a brovo 3 with twin props. $$$

Also if I ease into the throttle it seems ok but if I hit it hard it stutters. accelerator pump seems to be giving a good shot of gas as well right from the start.

before I replace the carb I'm wondering if there is something I should look at closer and does this defiantly sound like a carb issue. (now that I replaced half the ignition system.)

 

[Fun Times]

Being you have a backfire type event and not going over 3600 RPM and knowing water entered the inside engine, you may unfortunately have a tuliped valve or similar issue inside the engine... That and/or water in the fuel.

More testing is needed to know for sure.
Hoping for an easy fix, good luck.

 

[achris]

.... Went to check my timing and it was very close, so I decided to dial it in and WACK I got sapped off the cap! So I got a new cap rotor and the sensor in the distributor. BTW this is a TB V system.

You put it in 'base mode' to set the timing?

 

[stang32]

if you got hit when adjusting the timing, there is bleed throough on the wires, if the voltage can jump from the boot to your hand, it can jump from the boot to another or ground. replace the wires.

 

[Rick Stephens]

Like to hear in detail what all was done to rebuild the carburetor. Step by step - how clean were all the little passageways? Did you do a full disassembly and rebuild? Did you use a OEM carb kit or a cheapie chinesium one? How do the check balls look? Is there deposits built up in the bottom of the bowl?

 

[Simanski]

Being you have a backfire type event and not going over 3600 RPM and knowing water entered the inside engine, you may unfortunately have a tuliped valve or similar issue inside the engine... That and/or water in the fuel.

More testing is needed to know for sure.
Hoping for an easy fix, good luck.

Would a compression test rule this out? I did a test after I de watered the engine, they all seemed good so I didn't write anything down. But I can do another compression check and give details in a day or 2 when I get the guage from our shop and it's not raining lol

 

[Simanski]

You put it in 'base mode' to set the timing?

Correct I jumped out the wire next to the carb to ground to put in base mode.

 

[Simanski]

if you got hit when adjusting the timing, there is bleed throough on the wires, if the voltage can jump from the boot to your hand, it can jump from the boot to another or ground. replace the wires.

I had a cracked distributor cap that caused my shock. Which greatly improved the engine but did not get rid of the hesitation and lack of wot rpms. I can grab a few wires to see if I get a shock from them but I ran it at night and didn't see any jumping from the wires. These wires were new about 2 years ago but they aren't genuine merc wires. I got them on Amazon that had some bad reviews and side good. Not opposed to new wires as a trial step but I think I'm going to look deeper into the carb first.

 

[Simanski]

Like to hear in detail what all was done to rebuild the carburetor. Step by step - how clean were all the little passageways? Did you do a full disassembly and rebuild? Did you use a OEM carb kit or a cheapie chinesium one? How do the check balls look? Is there deposits built up in the bottom of the bowl?

So I have I just blasted some carb cleaner through all the ports and cleaned the inside of the carb and slapped it on. (This was the junk carb I bought for the throttle plates) it was sitting on a shelf in a trailer box at a marine salvage. My original carb I accidentally bent the metering rod when I put it back together that's what was cause the engine to run rich. But I don't think my original one ever ran right. I rebuilt the original one when I bought the boat 5 years ago and it always seemed to have this hesitation. I figured I would try this different carb cause what the heck I had it. I'm going to take it apart again and go a little deeper this time and check the check balls you spoke off. They could be gummed up. I'd like to think I'm handy with carbs but who know I could be missing something. If I find something obvious then I may throw a rebuild kit at it. Cheaper then getting a new one.

 

[Rick Stephens]

Do it the right way. Be thorough, follow the Marcruiser manual - it actually is really good. Get a kit and go through everything. The tiniest little thing can cause hesitations or burnt valves. Pay attention to every passageway. Run a piece of heavy fishing line through them. Make sure the float adjustment is spot on, not just close.

 

[stang32]

I had a cracked distributor cap that caused my shock. Which greatly improved the engine but did not get rid of the hesitation and lack of wot rpms. I can grab a few wires to see if I get a shock from them but I ran it at night and didn't see any jumping from the wires. These wires were new about 2 years ago but they aren't genuine merc wires. I got them on Amazon that had some bad reviews and side good. Not opposed to new wires as a trial step but I think I'm going to look deeper into the carb first.

at the very least you should be using sierra wires,

 

[Simanski]

Update:
Before going on the water I replaced my wires. I spayed the old ones with water and did see a spot or 2 of arcing. I bought oem wires this time. They even felt better going on. Solid click on. I also took the carb off again and went through it throughly. The floats were way out of adjustment. I was very excited cause I'm knocking out issues left and right. Running on land though still hesitation and back fire. I put in base time mode and adjusted the air mix screws. Got it to run pretty smooth from low idea to full bore. But not 100%. I put it on the water.... worse then it was last time out! :-( I also tried adjusting air mix screws to 1 1/4 turns like the manual said but still ran crappy. But one weird thing if from an idle I hit straight to wot opening the secondarys it would almost power through it without back fire but if I ease up to wot at 2k rpm it backfired like a mofo. I am almost ready to throw in the towel and buy a replacement carb. There isn't much left on the ignition side. 2 tests I have not done yet is compression and fuel pressure. But I don't think that would cause this kind of problem. If anyone thinks I definitely should i will. I'm still at 3600 rpms for wot but I'm starting to feel that's just what it does giving the pitch of the prop I have.

 

[Rick Stephens]

Backfire = lean. Quick way to burn a hole in a piston. Go through the carburetor.

 

[dubs283]

2 tests I have not done yet is compression and fuel pressure. But I don't think that would cause this kind of problem. If anyone thinks I definitely should i will.

I thInk you should, it's what I would do. More interested in the fuel pressure than the compression at this point

 

[Simanski]

Figured I give another update... so after spending all day Sunday swapping distributor and going through my old carb and putting that back on then putting my original distributor back in cause nothing was changing the problem. (Also accidently cooking my water pump cause I forgot to put the dang water on once) I decided just for the hell of it to do a compression test. What the heck the motor was already worm from my testing other things. Well cylinder 3 had 6psi :-( . Idk if my compression check before I missed that one cause it was just a quick check or it was a new development. But after removing my exhaust manifold and shinning a light in the spark plug hole I can see the exhaust valve is not closing all the way. I started the process of removing the head.

 

[Rick Stephens]

A valve problem would be the golden answer to your issues. Easy and simple compared to all the other possibilities. Congrats!

 

[Simanski]

Boy what a difference when your running on 8 cylinders instead of 7. I climb into a plane super quick and I had 4200ish wot rpm. About 48mph. I probably could of got more but I was in a small pond so I ran out of runway. My only slight issue I have now is between 1k and 2k it still has a tiny hesitation, but not all the time just sometimes and it's very minor now. Im convinced it's the carb. My question is the manual says to put in base timing mode and to adjust the mixture screws 1 1/4 turns. That's is. No fine tuning? Could that adjustment be the cause of my hesitation. I say hesitation but it is super minor. Like I can feel it's there but it's not like it causes any major issues. Then again I was by myself on the boat. That could change when I put a few of my hefty friends on the boat.

 

[Rick Stephens]

A slight hesitation in the transition between idle and main jets is something plugged in a transition port.

The recommended 1 1/4 turn is a starting point. You then tune to best mix and reset idle speed. This will have only very minor effect on performance over 1000 RPMs.