Carb woes

[Sunsport87]

The scenario: 4160 on an 87 sunsport. Started having poor idle condition. Ran great when into the trottle. Noticed gas droplets fgrom the top bar above the secondaries. Got a rebiud kit. Did thourough teardown and cleaning and used all the pertinent pieces in the kit. Installed and fired it up. Ran rich so tried adjusting the floats but saw the same problem with gas droplets going into the secondaries. Tweaked evert adjustment i could but couldn't stop the flooding. called holley tech and the first thing the guy said it was likely my fule pump putting out to much pressure. Fuel pump is still original but my experience with pumps is when they go bad they get low to no pressure. is an old pump putting out too much pressure a likely problem? What else could I be missing here?

[haugy]

Try tweaking the rear float a bit more. Fuel coming out of the secondaries when idling is too much fuel from somewhere. So start with the fix that doesn't cost anything, adjust the floats. You're using the new needles correct?

How did you set your idle mixture screws (the two screws on the metering block, one on each side)? When dialing a carb in from rebuild turn them from snug to 1.5 turns out. Then fire up the motor and turn them in to dial down the mix.

When you rebuilt the carb, did you blast pressurized air through all the passages after spraying the passages with carb cleaner?

[csuggs]

Sunspoprt87 - having similar issues but not exact (see Holley4160 issues in this section). Anyways, I was also told to check the fuel pump pressure on my 86 Sunsport with original pump. My experience as well as yours is that a pump will likely lose pressure when going bad, but we checked it and it was 5.5psi (the acceptable range is 4-7psi so I was right in the middle).
Is your motor and carb hot when you are having this problem or is when you first fire it up?

[michael hunter]

Make sure the rear butterflies are closed tight at idle.

[DAFF]

Seems weird but try to pinch off the fuel line running to the carb with some vice grips. If the richness continues then 100% a carb related issue. Not the pump or float .....

[rludtke]

I fought the exact problem for several seasons on an intermittent basis, until it worsened to become a constant problem. I was un the verge of replacing the carb when I discovered the problem. I kept finding debri in the float chambers. The debri was lodging in between the needle and seat, then floating away when the engine shut down. This would allow fuel to pass throught the needle valve. The debri was tiny, and there was not a lot of it, but it was the only explenation I could deduce. I discovered that my inlet screen was loose, and could flap open as fuel ran through it.

I cleaned up the bowls, and added an in-line fuel filter at the beggining of last season. I have not had an issue since.

[Sunsport87]

after rebuild I set the mixture screws to 1.5 turns out and floats parallel to top of bowl when inverted. On the water I adjusted both floats down in order to get the valves to close sooner but none of this helped. I tried adjusting the mixture screws in a half turn at a time and it didn't make any difference either. I soaked all the parts in carb cleaner and blew them out well. I didn't soak the main valve body but I did use carb spray and blew out all the passages. I replaced the needles and power valve and all the other parts that came in the kit. My screen look good. Which needle valves would be the primary culprit for a leak? The primary or secondary side? Again, I'm getting gas flooding in from the top on the side with the 2 idle mix screws.

[rludtke]

after rebuild I set the mixture screws to 1.5 turns out and floats parallel to top of bowl when inverted. On the water I adjusted both floats down in order to get the valves to close sooner but none of this helped. I tried adjusting the mixture screws in a half turn at a time and it didn't make any difference either. I soaked all the parts in carb cleaner and blew them out well. I didn't soak the main valve body but I did use carb spray and blew out all the passages. I replaced the needles and power valve and all the other parts that came in the kit. My screen look good. Which needle valves would be the primary culprit for a leak? The primary or secondary side? Again, I'm getting gas flooding in from the top on the side with the 2 idle mix screws.

Hi Sunsport.
When you look down the throttle bores with the arrestor removed, which bores are dripping? The front or the rear? If it is the front, then the primary metering (float) system needs attention, if it is the rear, then the secondary metering (float) system needs attention.

Does it only drip during idle? If it does not drip when the engine is off, or when the throttle is advanced off of idle, then it is possible that the idle air bleeds are not set correctly, or there is a clogged air passage internal to the primary metering block. The two srews on the side of the forward metering block (the part the float chamber bolts up to) are for adjusting the idle air bleeds. This adjusts the amount of air that is bleed into the idle fuel circuits. Carburators require airflow to meter fuel. At low airflow speeds, they can not meter fuel very well, so the idle fuel metering is accomplished by a special circuit within the carb. This cidle circuit is turned on an off depending on the throttle position, and is not used except when idle is required. Because the the surface tension of the fuel requires a higher airflow, fuel would just dribble out the discharger at low airspeeds if it wasn't pre-mixed with some air. These air bleed adjustments allow more or less air to pre-mix with the idle circuit fuel. The idle air bleed adjustments are only found on the forward Primary system. You can remove the forward float bowl, then remove the metering block from the throttle body. Soak the metering block in carb cleaner, remove the idle air bleed adjustment srews (needle valves) and blow out every passageway with compressed air. Replace the needle screws, and pre-set to 1 1/2 turns out from full closed. Reassamble.

If fuel born debri is causing the problem, then it would potentially affect both the primary and secondary systems, as the fuel supply is common between the two. Consider replacing, or adding (if you don't have one) a 5 micron in-line fuel filter.

[Sunsport87]

Fuel drips in the front bores. I can't really get the motor to keep running at idle. With the trans engage knob pulled out i have to keep the throttle almost full forward just to keep it running. So it does continue to drip even with the thottle out of idle. When I rebuilt the carb I had the metereing blocks disassembled and soarked the in carb cleaner. Then blew out the passageways with compressed air before re-assembling. I set the metering screws at 1.5 turns out. The carb is doing the exact same thing now that caused me to do the rebuild in the first place only worse. I may just need to disassembly and try cleaning everything again. At idle where is the fuel flow being metered? Is it through the primary mixture screws or through the needle valve? seem like with the float adjusted low to shut off the valve early it should reduce the fuel flow but when I did this it didn't make any difference. Maybe something is causing the needle to not seat fully. Thanks for the explanation/tips Rick.

[rludtke]

Fuel drips in the front bores. I can't really get the motor to keep running at idle. With the trans engage knob pulled out i have to keep the throttle almost full forward just to keep it running. So it does continue to drip even with the thottle out of idle. When I rebuilt the carb I had the metereing blocks disassembled and soarked the in carb cleaner. Then blew out the passageways with compressed air before re-assembling. I set the metering screws at 1.5 turns out. The carb is doing the exact same thing now that caused me to do the rebuild in the first place only worse. I may just need to disassembly and try cleaning everything again. At idle where is the fuel flow being metered? Is it through the primary mixture screws or through the needle valve? seem like with the float adjusted low to shut off the valve early it should reduce the fuel flow but when I did this it didn't make any difference. Maybe something is causing the needle to not seat fully. Thanks for the explanation/tips Rick.

Because it drips when the engine is off, it is not the idle air bleed ciruit, as that will only function when air is running through the carb (engine running).

I suspect that if you closely examine your primary needle valve, you will find a scratch on the needle, or a tiny foreign object in the seat, or possibly resting near the seat.

To help either confirm or deny that the float adjustment is incorrect, you could make a large adjustment to lower the float setting. Remember, bending down the tab on the float increases the float level setting, and visa-versa. Decreasing the float level means that the float and the fuel level does not raise as high to close the needle valve. Make sure yoou are moving the parts the correct way, it is easy to get the mechanism confused, and move things the wrong way. Don't ask me how I know. :)

If, by making a large decreasing adjustment to the float level, the dripping stops, then your float level was probably too high. Slowly increase the float level until the dripping starts again, and then adjust it back until it stops. Drive the boat to see if it stumbles on acceleration.

If you make a large adjustment to lower the float setting, and the dripping continues, then the level adjustment was probably not the root cause. This leaves only a foreign object, or a damaged valve as the reasons. You could replace the needle and seat, as they are cheap. Considering that you just overhauled it, your valve assembly is probably new.

So, look closely for dirt, hose slivers, etc, getting into the inlet portion of the float chamber as they can lodge into the needle valve. It only takes one tiny object to cause dripping.

These old boat hoses can give off rubber, especially now that we have methanol mixed in the fuel. Those tiny bits of rubber end up in our carbs. Add an in-line filter, and clean out the junk in the carb, and I bet the problem will go away.

Good Luck Sunsport87!