Help with 1999 Mercruiser 5.0 305 Thunderbolt V Ignition!! Backfire through carb

[alldodge]

The rebuild kit will provide the adjustments and how to do the internal ones. Outer ones we can help with.

Give us your motor serial number and we can find the correct rebuild kit.
I'll add this, I'm just one guy which believes your running lean, others have posted that its an electrical issue. I'm just one guy and one opinion, just saying what I would do, others can differ

 

[precool26]

I will have to get my serial when I get back home tomorrow. As far as that goes, I heard on here I believe that 99% of home rebuilds dont go right.. I would seriously consider a reman or prof rebuild for myself. I just want to know how to adjust the outers so that I have the engine running right as far as correct adjustments on carb and my timing...

 

[precool26]

Could you tell me how I need to adjust the carb and the choke....

 

[funk6294]

I will jump in here for just a sec and agree with AllDodge that I think your running lean. When you disconnected the choke and it was running better and the idle speed went up all point to a lean condition. First things first confirm you have good fuel pressure. Check the inline filter for water (unscrew the filter and dump the contents into a clear container and then let it sit. If there's water it will show up on the bottom), and replace the filter if you haven't done so in a while. If that all checks out move on to the carb.

 

[precool26]

Ok. I will do these things and get back to you. The only thing I worry about is what if I cant even get it to stay running to check the fuel pressure?

 

[funk6294]

You will know pretty quick.

 

[alldodge]

Could you tell me how I need to adjust the carb and the choke....

The only thing I worry about is what if I cant even get it to stay running to check the fuel pressure?

Initial setting for the choke on a cold motor is the choke plate should be closed with a 1/8 gap at the top. The choke adjustment is done by loosening screws on the dash pot and rotating. The choke should open and close with turning the dash pot when cold. Don't try to adjust the choke plate after motor has been started.

The rod on the linkage side of the carb can be bent for adjusting the choke, BUT it would be very rare if this would be needed. Only way the rod would be out of adjustment is if someone else tried to adjust before or was damaged. If choke does not move freely, check the choke rod first and its linkage.

There is a idle speed adjustment screw on the same side as the choke rod. The idle speed Mixture screws are at the base of the carb. If motor won't idle, turn screws all the way in to where they just stop going in, do not tighten further, this will damage tip. Then turn out 2 1/2 turns

 

[precool26]

Ok, so I went to adjust my card and have some question. When I adjust my electric choke to give that 1/8" gap, where does my idle adjust screw need to be? should it be completely free of touching that wheel? How does that need to be set?

 

[precool26]

what should the process be? loosening that idle adjust screw, then move elctric choke until I have my 1/8" gap, then set my adjust screw? I have messed with that adjust screw so much, I dont remember what position it was in.... sorry. I believe my manual said to screw it in just until it touches the wheel, then turn an additional 2 turns... it this correct? and if so, does that need to happen first, then adjust my electric choke?

 

[ihc1470]

I think I am going to steer you off in a different direction. More than once I have found a cam with a flat exhaust lobe will do just exactly what you are describing. You maybe able to see that on a vacuum gauge if you can find a port to connect to. If not pull the valve covers and see what your valve lift is like. I could be quite wrong with this thought but it sounds like you have pretty well covered the fuel and ignition systems. Be sure to tell us what you find. Dennis

 

[alldodge]

Ok, so I went to adjust my card and have some question. When I adjust my electric choke to give that 1/8" gap, where does my idle adjust screw need to be? should it be completely free of touching that wheel? How does that need to be set?

The idle screw has nothing to do with the choke, its only used to adjust idle speed of the motor. It can be touching, or not touching, but if it's not touching it will be idling to low if it will idle at all. Basically it should not be touched unless the idle speed needs to be changed.

what should the process be? loosening that idle adjust screw, then move elctric choke until I have my 1/8" gap, then set my adjust screw? I have messed with that adjust screw so much, I dont remember what position it was in.... sorry. I believe my manual said to screw it in just until it touches the wheel, then turn an additional 2 turns... it this correct? and if so, does that need to happen first, then adjust my electric choke?

Two additional turns in is the correct starting place.

 

[jimmbo]

Make sure to keep the spark plug wires separated from each other, especially #s 5 and 7. Take the carb apart and check that the power valve is operational, and that its actuator is not sticking

 

[precool26]

Ok, these are great suggestions for tomorrow!. I do have news. I took it to a friend of mines shop, where he has a guy who knows about boat engines and is a carb guy. We got to looking around at it and found out that when I turn it on and advance the throttle it wasnt even priming the carb, so he told me to replace the pump. I went to advance auto and got a mr gasket electric pump, for carbed engines and threw it on real quick. still nothing. It will idle, but if I get on it, it will advance for a second or two then die out, only restarting after I prime a couple more times. This on the water btw. It cranked fine at my house on the hose, so I thought maybe that was it! after launching it, thats what happened...... GRRRRRR

 

[alldodge]

The Mr Gasket fuel pump is not ignition protected and not USCG approved for a boat. You need to remove/replace with an approved pump, otherwise you, your friends and anyone around may be hurt or killed when you blow up.

If the carb has no fuel going in when the throttle moves forward you need an accelerator pump. Also sounds like you need a good carb overhaul or replacement.

 

[thumpar]

You need the accelerator pump not fuel pump. You might as well get the whole carb rebuild kit. They are cheap. For the idle screw you adjust it for the idle RPM. You want to be at 650-700 RPM.