mercarb rebuild

[Jcris]

Been trying to figure out how to set the float drop and level on a 2 barrel Mercarb. Got the kit from Mike's carburetor. I also purchased the brass float to replace the existing plastic float. Where exactly is the measurment for the float drop taken?
There's a diagram on the website which shows it to be the lowest point on the bottom of the float. If I set the drop to 1 3/32" (27mm) as indicted by the instruction sheet that came with the rebuild kit the range of travel for the float is minimal, and the needle does not open. Can someone please clear this up for me?
This carb is on a 4.3L Vortec V6
Thanks
I just reinstalled the old (plastic) float and the needle opens consistently . But the measurements don't make sense

 

[alldodge]

There is a float level setting and float drop. The most important is the level setting. Adjustment for drop is done by the tang on the rear of the float. Things start getting off by the info not posted about the metal float. In the pick it shows where to get the measurement from but not the different dimension.

In pick below it shows both but should also have 2 different lengths for drop

Here is out of the Merc carb manual

 

[Jcris]

​ Thanks for the response AllDodge,
The thing that confuses me is the old float (plastic) level is set at about half of where it should be. The old float looks like it was never adjusted. It looks like the plastic float was installed without any adjustment. The tang for drop adjustment and the arm going into the body of the float look perfectly straight.Take a look at the pic and tell me what you think
If I use the lower dot to take the level measurement, as indicated by the Mercarb manual, it measures about 3/8" when it should be 9/16". If this level adjustment were off by that much could that contribute to hard starting? Also, with the float set at 3/8" would that flood the bowl? Maybe this was set up for a solid needle and seat? The instructions show 3/8" as the level for the solid (no spring) set up. Am I making sense?

 

[alldodge]

You may be correct, but just as before the critical setting is the level and not the drop. Now the drop needs to be more if there is a spring loaded needle and seat. The measurement is with the gasket against the top for level. I see a level (float closest to top of carb) of 9/16 with a solid needle to be to low on top dot

If the level was off this could cause hard starting and may even have some issue with idle

If the spring needle is use, the height should be a bit lower because the spring would shut the fuel off sooner. The spring needle also helps with the boat bouncing to help keep it closed and not over fill

 

[Jcris]

Thanks!

 

[Jcris]

The Mercarb rebuild is complete and I noticed along the way a couple things that I thought were odd. First, the float drop and level were both off/wrong. Second, the accelerator pump assembly was longer than the new one in the kit (bottom pic is the new one). It made me wonder if this carb was rebuilt before with perhaps the wrong kit. Maybe whoever rebuilt it made some mistakes along the way? I'm not sure, but it does start much better than it used to. Specifically it starts right up and doesn't stumble and run so rough. I think it was running way to rich at startup which not only made it difficult to start but also affected idle until the motor warmed up and smoothed out. Could that old accelerator pump have been an issue? With the extended length (of the old one) would that change the way fuel was pulled into the motor? I also found the the pump rod and choke not set to spec. I realize these are mostly things that need maintenance from time to time. The carb was very clean inside and appeared essentially new. The bottom line is it's seems much better right away. The true test will come as I begin to use it on the water. Please take a look at the pic and tell me what you think.
One last detail, I did not install the new brass float as I could not verify where to take measurements . On the other hand the plastic float was much easier to set properly. I think my inexperience with carb rebuild is showing there.
Regards to the group

 

[alldodge]

I like the plastic floats.
With the rod being longer then as designed, it would not push the same amount of fuel. The carb linkage only goes up so far, so if its longer, it cannot get a full stroke normally.

Now the next carb will be a snap

 

[Jcris]

you sure got that right

 

[Scott06]

I think you are correct that your carb had been messed with before perhaps incorrectly. Accelerator pump won't affect idle only the moments after you stab the throttle open. On the accelerator pump merc had redesigned the pump for a bigger shot size by increasing the pump stroke. so that I believe is the difference you are seeing. Newer mercarb ( at least newer than my 1990) have a accelerator pump lever with three holes to allow you to adjust the pump shot volume, older one you have to bend the pump rod.

I had had the same issue with the brass float too. I ended up using it just estimating the level off the old float measurement point. Worked fine.

 

[achris]

My first question is why are you changing the plastic float? Is it faulty? If not, why change it... Or do you just prefer the brass float.. If so, again, why? The plastic is more reliable, and being lighter, has less inertia so will maintain the fuel level a little more accurately. The old cork floats, yeah, change them, but the plastic floats, unless it's cracked and filled with fuel, are best left in. They are not a 'service' item and need to be replaced every x hours. If it ain't broke, don't fix it!

Chris........

 

[Jcris]

When I ordered the rebuild kit it was suggested by the parts supplier that the brass float is an upgrade. Specifically that it would not, over time gain fuel and become heavier. Thus making them more reliable. That made sense to me so I got the brass float instead of the plastic one. I didn't realize that setting the correct height was so "unclear". That's what led me to re-install the plastic one. This was the first time since high school that I'd attempted to rebuild a carb so the learning curve was a bit dramatic. Going forward I will keep in mind the adage "if it ain't broke, don't fix it".
I'm new to boats but not young, I'll know better next time. In all aspects of repair.
Regards
Boat sure is running better now. It sure is gratifying to repair something and have it make such a nice improvement.

 

[achris]

... It sure is gratifying to repair something and have it make such a nice improvement.

It is.