TOPIC: Mercury Woes...

Heres one for ya...

Last Summer, i rebuilt the carbs and did a link and sync on my 1970 1350. After much trial and error, i got it running pretty good but i was still getting an occasional leak from the top carb.

Today, i pulled it out of mothballs getting it ready for the summer and low and behold, all three carbs are leaking. It is dumping fuel out of the front of the carbs. It still runs and if you give it a quick blip of the throttle, it goes away entirely and stops leaking.

So what gives...i was thinking stuck floats but i replaced the floats, needles and gaskets and adjusted them to factory specs but they still dribble fuel upon the first firing. Seems like once the motor is started and a small amount of throttle is applied it goes away completely and is fine for the rest of the day. It doesnt seem to be causing any performance problems, once the motor is warmed up but its an annoyance none the less...

Any ideas?

Jeff, If it makes you feel better my inline 6 merc drips fuel after I shut it down and trim up the motor. Maby its normal, I dont know.
So It wasnt doing this before, last year??? Mike

Triming your motor up and leaking would make sense...that fuel in the bowl has to go somewhere when you tilt your motor.

It only very slightly did it out of the top carb after i went through all those troubles last year. It wasnt enough to warranty ripping everything back apart to fix it. But now that its doing it on all 3, its time to address the problem.

Its just odd that once you give it a short, quick rev, it goes away. Is there something that the floats are snagging on or something??

Jeff, this is normal. When you squeeze the primer bulb you generate up to 12 to 14 PSI of fuel pressure which is more than the needle and seat can hold back. The extra fuel flows into the carb throat. When you take it off idle it draws that extra fuel into the engine. Don,t mess with it, its ready to run

Doesn't sound normal to me! My carbs don't leak, even when pumping the bulb. I did have an issue with the needle valves binding in the seat. I got rid of the rubber tipped valves and fiber seats. I went with the complete brass needle and seat. I also had a bent float pin on one carb, not allowing full travel. Just some thoughts.

marathon6 wrote:

Doesn't sound normal to me! My carbs don't leak, even when pumping the bulb. I did have an issue with the needle valves binding in the seat. I got rid of the rubber tipped valves and fiber seats. I went with the complete brass needle and seat. I also had a bent float pin on one carb, not allowing full travel. Just some thoughts.

I didnt think it was "normal" either...a carb should only take in as much fuel as the bowl will hold...not overflow spilling it all over the inside of your motor which that alone is a major fire hazard!

Do you have any references for this conversion or part numbers?? Im thinking its an issue with the needles and seats more so than the actual floats.

I too have had issues and never use the rubber tipped needles now only the brass & stainless needles

I have various Mercs & (to me) it isn't uncommon for them to leak a bit when priming. Personally I don't see it as an issue - providing they don't leak when running & have never worried about it & never had a problem as a result. I tend not to prime them so 'hard'. Agreed new needles & seats along with free moving floats should stop it & that would be the best option, but I am a lazy bugger so if it only does it when primed hard I don't worry.

My '84 115 was leaking on priming from the top carb when used for the first time this season last weekend, on the first start up, but sorted itself out on later starts on the weekend. And the carbs were just rebuilt!! (no new needles though - they arrived from the US to late.

Geoff UK

You have to check the position of the "flaps" that go over the needles in two positions so you check the closed and open drop level. The little spring thingy on the float needs to be correct height too.
Your seat may have been damaged if using the wrong screw driver to tighten or you may have left out or doubled up on the washer that seals the seat to the carb, check that. It's not unusual to bulb prime so hard fuel squirts out into carb throat but this should not be the case running. Trimmed you should not see fuel dribble if floats are set up correctly. Tilted up all the way you might get a dribble. I suspect there is something wrong with the adjustment of the flaps or the float spring, or the seal washer set up under the brass seat. I have had no issues with rubber tip or otherwise on the needles for what ever it's worth.
Last thought is that the butterflies are not synced the same and the top one is slightly open drawing more fuel into the throat than the motor can draw in from there due to poor atomization because of slow speed of air flow at idle. The carb butterfly connectors between carbs have adjustments so they are all "closed" and go all the way to WOT together.
My two cents.
Randy

i used one of these when i did the carbs in my 50hp and it helped set them more accurately.