86 mercarb float level questions

[paultjohnson]

Ok, so I didnt have time tio get a rebuild kit, but wanted to take top of carb off to retrieve a piece of debris that possibly had fallen into carb [prev post] I also had fuel trickling down venturi cluster after shutting down engine. This started after using vac cleaner to attempt removal of debris thru bowl vent.
Did a quickie clean, pulled out needle, seat, float, venturi cluster, power valve assembley, float bowl jets. Reassembled, weighed float, supposed to be less then 9 grams, mine was almost 9.3 g, checked float level still a perfect 9/16 [ spring type needle ] Checked float drop, it was 1.25 in which, ironically, is what the Merc Man #6, I believe,[Boatinfo] incorrectly said in should be. After I got it back together, I discover the drop should be 1 3/32. So now the drop is almost 5 mm more then it should be. Had to leave it, went boatin, ran well, except for some surging, which I think I totally eliminated with idle mix adjustment.
My questions, what would the result I should have noticed with the incorrect float drop and overweight float. What would it cause to happen? I have a full rebuild kit coming, and I will do it right the next time, Im just trying to understand my carb... Anyone Thx

 

[paultjohnson]

Re: 86 mercarb float level questions

Can somebody plzx tell me the effect of a slightly heavy float and too much float drop ??? Thx ^^^

 

[makonnen]

Re: 86 mercarb float level questions

The short answer is that the carb will run leaner if the float is sunk or is adjusted too low.

The reason is because a greater "float drop" = a lower float bowl level = a lower fuel level in the port that feeds the main venturis. That means it requires more airflow through the venturis to draw fuel if the fuel level is a bit lower.

I should add that this is not the correct way to adjust for a rich carb. The proper way is to change the jets and needles.

If the float level is way too low, it could cause a lean backfire at part throttle. A lean backfire will pop back up the carburetor.

 

[paultjohnson]

Re: 86 mercarb float level questions

The short answer is that the carb will run leaner if the float is sunk or is adjusted too low.

The reason is because a greater "float drop" = a lower float bowl level = a lower fuel level in the port that feeds the main venturis. That means it requires more airflow through the venturis to draw fuel if the fuel level is a bit lower.

I should add that this is not the correct way to adjust for a rich carb. The proper way is to change the jets and needles.

If the float level is way too low, it could cause a lean backfire at part throttle. A lean backfire will pop back up the carburetor.

Ok... if its running a little lean cuzx' of a slightly heavy float, and a bit to much drop, what is that going to do to the performance of my engine ? It seamed to be running well, but wasnt really able to give her a WOT run due to heavy waves, boat traffic,wind. What changes might I expect when I get my new float in and the drop set to the correct 1 3/32 as opposed to the 1 1/4 I have it at now ? Inquiring minds want to know Thzx

 

[Don S]

Re: 86 mercarb float level questions

Float drop does nothing for running. and will not cause it to run lean. All it does is keeps the float from touching the bottom of the fuel bowl so it doesn't stick there.
A heavy float will sink, which would tend to allow too much fuel into the fuel bowl by not shutting off the fuel with the needle valve, and if it sinks enough the carb will flood into the throttle bores.

Instead of beating around the bush, what problem are you having? It may not even be float level related.

 

[paultjohnson]

Re: 86 mercarb float level questions

Hey Don I am not really having a problem anymore. The prob started with that little bit of debris that had gone down that overflow [prev post] Hooked up a little straw hose on a vacuum, vacuumed thru that orifice I had pictured earlier. Then started it on muffs. After shutting it down, I had gas trickling out of venturi area into bore. I dont know if the vacuuming triggered that problem by upsetting crud or whatever in the float area. I didn't have time to get a rebuild kit so just took the top of carb off, did what I could [plzx read 1st post] I put it back together with the original parts cuz it was Sat nite and I wanted to go boatn' Sun. Mem wkend. The fuel trickle was gone, started ran well on muffs. Went to river Sun, ran well except for the surging at low to mid speeds, which I was able to adjust away with fuel mix adjustment. Couldn't go WOT due to conditions. Thats why I am wondering if I should even bother tearing back into at this time as it actually is running really well. Read here there is only a 50/50 % sucess rate on home carb rebuilds. Maybe I should leave well enough alone being that its boatn time. Will it do any harm to leave it as is for now. and/ or what might I gain by putting a new float in now, and resetting the drop from 1 1/4 to 1 3/32. Current float weighed in at 9.3 Grams-shouldnt be over 9. The interior of the carb was amazingling clean . IMHO my storage procedure of using non-ozy prem and stabil has worked extremely well.. This is the first time the carb has ever been opened up. [since 86] Its my nature to over-analize, but I like to be thorough. Ya know how there is always that one idiot in the neighborhood that washes of his push mower when hes done cutting the lawn ? Well thats me ... Sorry for the long winded posts... Thzx

 

[makonnen]

Re: 86 mercarb float level questions

Ok... if its running a little lean cuzx' of a slightly heavy float, and a bit to much drop, what is that going to do to the performance of my engine ? It seamed to be running well, but wasnt really able to give her a WOT run due to heavy waves, boat traffic,wind. What changes might I expect when I get my new float in and the drop set to the correct 1 3/32 as opposed to the 1 1/4 I have it at now ? Inquiring minds want to know Thzx

I doubt float level has anything to do with a problem like that. Incorrect float level will only make slight changes in air-fuel mixture. On the extreme side, a sunk float (ie: if you have a saturated foam float or one of those old brass ones thats damaged) will cause the fuel pour out of the venturis.

It sounds to me like you should be looking at the power valve circuit which works off manifold vacuum to work against spring pressure to CLOSE the power circuit. A loss of vacuum in the intake manifold indicates WOT / high throttle / high load ... this allows the power valve spring to lift the valve delivering a larger amount of fuel.

So what happens when you crank open the throttle? Does it backfire? If so thru the carb?