5.7 strange carb issues

[JayEll87]

Greetings from Northern Europe! New guy calling. I’m facing some strange issues with my 23ft Wellcraft with 5.7 Merc Vortec (-00) which I resently bought. I’ve made some basic maintenance to it but the 2bbl mercarb is making me insane..

Originally boat ran quite well despite slight hesitation in smaller revs, on plane she went well. I tried to fix the hesitation and readjusted the float level to specs specified, 9mm(11/32) and drop of 24mm(15/16.) After this engine worked fine on idle but that’s it, hardly 1600rpm and horrible rumble and backfire was created. There was also quite heavy smell of petrol and some fuel was also sprayed from open hull through exhaust. So to my mind it seems that she’s running very rich. She worked much better with original float setting which was somewhat level with the body of the carb, maybe something 13-14mm...She also starts without chokeplate(constantly open) and without pumping gas level prior starting on somewhat cold weather so on that respect mix is also rich..

So, what would be the explanation for this? Timing is checked, plugs and wires are new, fuel filters are new, fuel pressure is 5psi, fuel is changed... so these should all be good.

Appreciate for any help.

 

[Rick Stephens]

Recheck firing order.

 

[JayEll87]

Double checked and firing order is ok. Also I presume boat would not run on plane very well if the firing order would be wrong? Also the issues started after "fixing" the carb.

 

[Rick Stephens]

Probably number one on the list of jobs that need doing more than once is carb rebuilds. Happens a lot.

Hard to know enough details from your post on when things got worse. But if working on the carburetor made it worse, then time to redo it and go through everything in the carb. Run all the ports with a piece of fishing line or wire. Everything spotless. When you did the carburetor the first time, was the fuel clean? Change filters? Water present?

 

[AShipShow]

Did you replace the float or just adjust it? Might want to check that the float is not saturated with fuel.
Did you rebuild the carb and clean it while you were at it or just take it apart to adjust the float? I would take it off and rebuild it and see how it does after that.

EDIT: Rick Stevens beat me to it with his post lol

 

[Rick Stephens]

Did you replace the float or just adjust it? Might want to check that the float is not saturated with fuel.
Did you rebuild the carb and clean it while you were at it or just take it apart to adjust the float? I would take it off and rebuild it and see how it does after that.

EDIT: Rick Stevens beat me to it with his post lol

Mad, you ain't gonna reach me if you misspell my name :^)

 

[AShipShow]

Mad, you ain't gonna reach me if you misspell my name :^)

Why's there gotta be a Rick Stevens AND a Rick Stephens lol

 

[JayEll87]

Hard to know enough details from your post on when things got worse. But if working on the carburetor made it worse, then time to redo it and go through everything in the carb. Run all the ports with a piece of fishing line or wire. Everything spotless. When you did the carburetor the first time, was the fuel clean? Change filters? Water present?

I’ve worked quite a lot with bikes and carburettors are not that unfamiliar so I see that as an advantage I did use compressed air in pretty much all ports I could find, fuel was clean and I replaced water separating fuel filter as well. I emptied the content to a clear container and there was zero water in it.

I took off the float, needle and pretty much all loose items inside and replaced all with new parts found in maintenance kit. Also checked the weight of the float and it was 8 grams with my scale.

Today I changed the float back to the setting which originally worked and went for a cruise, not that bad as with higher setting but definetly worse than originally.. Heavy carb backfire present, on idle she purrs like a kitten also with gear on.. So checked again firing order, vacuum leaks and fuel supply.. From supply pipe (filter->carb) I found a bend which is shown in attached picture. Pipe was so bend that 1,5mm2 wire did not go pass it without force.. This seems quite an obvious reason for fuel issues! Probably working with carb has made this bend worse as pipe is somewhat stiff and carb is difficult to take off without bending the pipe slightly..

 

[Rick Stephens]

I suppose it could be a 'lean sneeze' type of backfire. Lean sneezer more a cough than an actual backfire. Backfire can be caused by a timing issue or the aforementioned and ruled out mis-wire on plugs. Also can be caused by a stuck intake valve.

You can get that stainless line from a Mercruiser parts dealer. That's how I did mine. Seemed a lot smarter with a boat to continue using stainless there. To test your theory, and while you wait on any part delivery, you could cut that crimped part out and just slip a hose over it and use clamps.

Rick

 

[JayEll87]

I suppose it could be a 'lean sneeze' type of backfire. Lean sneezer more a cough than an actual backfire. Backfire can be caused by a timing issue or the aforementioned and ruled out mis-wire on plugs. Also can be caused by a stuck intake valve.

This might be the actual case. I'm not too familiar with the terms as this is my first V8 small block, I've had smaller mercruisers but never the "bigger boy" never had the courage as the gas prices here are currently above 5$/gallon.. earlier this year over 6$

You can get that stainless line from a Mercruiser parts dealer. That's how I did mine. Seemed a lot smarter with a boat to continue using stainless there. To test your theory, and while you wait on any part delivery, you could cut that crimped part out and just slip a hose over it and use clamps.

I'm not sure if this is ready Mercruiser part as previous owner has installed electric fuel pump and pressure regulator to fuel line which push fuel through water separating filter and then to carburettor. Pipes found from internet are connected to mechanical fuel pump and from there to carburettor so I think these don't match. Anyway I work in shipyard and I can make pipe (or maybe a high pressure hose assembly) to this myself so I take that as a first action. Let's hope this is the solution, at least it will for sure limit fuel flow.

 

[JayEll87]

I'm back again. Long story again, sorry for that.. Fuel side is fixed and all SHOULD be ok now but it's not. So now fuel pipe to carb is new, water separating filter new (again), carb rebuilt fully and all possible passages blown with compressed air, fuel pressure adjusted to 6psi but no.. She won't work fully.

Went for a 4hr cruise with my wife and first half an hour or more we just went on slowly. I tried few times to accelerate but she won't go, after oil temp was 70degrees Celcius I tried to give her some gas one more time = sneezing, coughing but after revs reached 2500rpm she calmed down and went on plane.. After this no issues during this trip. 26-30 knots with 3400rpm nicely with no drama for 3hrs straight. Went off plane and tried again, same thing = sneezing coughing between 1500rpm-2500rpm..

Some local guys said that timing must be the reason, I checked this. I only have one timing line in damper and then another one in block. I presume with timing lamp which has possibility to advance the light in the lamp itself these lines should be aligned when timing on idle is 8degrees? It was not, I had to advance lamp 36 degrees to have lines aligned, so base on this timing was off for over 20 degrees? Before I do any adjustments I'd like to have confirmation from here what I did wrong.. I presume she would not run if timing would be off this much?

 

[Rick Stephens]

engine serial number?

 

[JayEll87]

Om365765

 

[achris]

Ok. You need to put the ignition system into 'base mode' to set the timing, and yes, you need an advanced timing light, set to a 10 degree advance. The alternative to an advanced timing light is to mark the damper with a line at 10 degrees BTC. I would do that with some simple math. You can measure the diameter of the balancer (in mm). Multiple that by 0.087266. That gives you the distance (in mm) from the single line on the balancer that you need to draw a new line, and that's your 10degrees BTDC mark. (for 150mm balancer, it's 13mm, for a 200mm balancer, it'll be 17.5mm). Then set the ignition in base mode, point a normal timing light at the marks and adjust the distributor accordingly. Once you've done that, you're Finnish. :facepalm:

Any timing indication you have with the system NOT in base mode, is meaningless (to us). That's just by the nature of the program coded into the module... But from what you're saying about the timing, it doesn't sound right. You need to set it in base mode and adjust accordingly.

Chris.......

 

[JayEll87]

Right, I'm aware of the "base mode" however so far I've not found the PUR/WHT lead anywhere. Motor for this boat is not original (as can be seen from the serial ) and previous owner has made some "adjustments" to the ignition part. So it has electric distributor, original Mercruiser ignition coil and MSD CDI. Where should the thunderbolt module be as I have not found this anywhere which makes me wonder the adjustment even more.

I will pull the plugs next when I'm going to the boat, just to see if they are all the same or is there possibly some mechanical issues as well.. Oil looks oil and othervise there are no issues but I'm starting to be afraid of some larger mechanical issue which might be causing this.

 

[achris]

... and MSD CDI. Where should the thunderbolt module be as I have not found this anywhere which makes me wonder the adjustment even more.....

Sounds like the previous owner(s) removed the Merc distributor and put a non-genuine one in. In which case, you may need to find the model and as much information on that unit and do some google searching.

Chris....

 

[JayEll87]

One more thing I noticed today is that timing does not change despite revs do.. So I have 36 degrees on idle as well as on 2000, 3000 etc revs and I presume that's about right when cruising on higher revs only. So could this be the reason? Timing adjustment is not working.

 

[JayEll87]

Here again Not a surprise that timing was not adjusting properly, there was slight rust present.



Spent a fortune on MSD marine distributor and swapped it in. Problem is.... STILL there! Timing is checked and base is now 10 degrees, and max. is 33 degrees. Timing curve is like below.



So cold engine/warm engine, idle is perfect and starts up immediately.

Cold engine acceleration:
Link to onedrive for a video
https://1drv.ms/v/s!AuS-dF3NSopHg9NNph-EGzjDObC-uA

And once she warms up:
https://1drv.ms/v/s!AuS-dF3NSopHg9Rg5k8hr_afzgcQYA

Works like this until cools down, so if we're anchored for a 30+ minutes, she's sneezing again.

I still haven't pulled the plugs to see the color or if there's water in the cylinders, also could vacuum leak have something to do with this? Or still fuel related..? :S

 

[JayEll87]

Hi again, no reply to my previous mail and I haven't really had time to check the issue any further.. However, yesterday I pulled the plugs and there was no water coming out of any of them. Attached somekind of a photo of them, can more professional eyes spot something I didn't? Or are these ok?

Again, below the link to video of the acceleration. After this sneezing(I presume?) phase is over, boat runs like no care in the world.. I'm running out of options so any help again would be appreciated.

https://1drv.ms/v/s!AuS-dF3NSopHg9NNKuQL3GPhmjCHlw

 

[AShipShow]

Maybe I missed something in earlier posts, but why in the world do you have a distributor with springs and weights on a 2000 vortec 5.7 motor?

EDIT:
Looked back a couple posts and it looks like you have quite the cobbled together ignition setup...
It looks like the previous owner was using a mechanical advance ignition setup... which means the thunderbolt module probably doesn't exist in your engine compartment as it was probably mounted to the old distributor...

I'm guessing they ran into a situation similar to the one I just had... My thunderbolt module failed and its a small fortune to replace... However, instead of switching to the Delco electronic ignition, it looks like they went backwards in time...

Also, that might explain why your new MSD distributor didn't fix anything, because if you wired it in to the existing harness, theres no module there to control the advance.

My recommendation at this point would be to follow what I did, and replace your ignition system with a Delco EST system. It was very easy to install and worked perfectly...