Back drag carburetors

[VIPEagel3]

I have a 1985 90 hp inline (6) Mercury. This motor has been setting for several years before I received it. The reason for setting was loss of power. I recently (the past month) was able to fix that problem with a new switch box. Now, on to getting the motor to run smooth. I do have a manual for this motor, that is how I determined that it has back drag carbs on it. Question is, how difficult is it to rebuild these carbs? How do I determine which kits to buy for these carbs. The reason for wanting to rebuild them is, not running smooth, sounds of flooding out at times, excessive gas seepage from carbs - linkages- hoses. Thanks in advance for any info...

 

[jimmbo]

The Tillotson carbs used on these engines are very simple. They do have a float design that, at least on my 84 115, had a tendency to jam in the fuel bowl. They also have an odd ball way of setting the floats. A good manual is handy to have for that.

Back Drag refers to a modification Mercury did to their carbs in the mid 1970s to improve fuel economy. Instead of just venting the fuel bowl to atmospheric pressure, they put in a metered/restricted vent, then between the vent and the fuel bowl ran a vacuum line to a fitting downstream of the throttle valve. So under high rpm high manifold vacuum part throttle conditions, the fuel bowl would see less than atmospheric pressure and the result was a lower fuel flow thru the carb. Only problem was it worked well enough to cause a too lean condition with today garbage gasolines. Mercury now recommends the vacuum hose be pulled off the fuel bowl, a ball bearing jammed in it and the hose reattached to the fuel bowl.

http://www.iboats.com/mall/partfinde...n_id=194206218

 

[VIPEagel3]

Thanks Jimmbo for the response... Just guessing that the link you left at the end is the carb kit I need for the carbs I have?

 

[Jackasp]

I also have a 1985 90 HP Mercury that was used infrequently for a few years and I am having trouble getting full throttle. I went through the fuel system cleaning and replacing everything up to the fuel filter with minor improvement. What is a "switch box"? Thanks for any help.

 

[jbcurt00]

Jackasp, discussing your motor and problems in VIPs topic, is considered a hijack. Start a topic about your '85 Merc and ask there...

 

[VIPEagel3]

I also have a 1985 90 HP Mercury that was used infrequently for a few years and I am having trouble getting full throttle. I went through the fuel system cleaning and replacing everything up to the fuel filter with minor improvement. What is a "switch box"? Thanks for any help.

It is what supplies the power to your coils.. Then the coil supply power to your spark plugs... There is wires that come from the switch box to the coils. If I knew how to post a pic of it, I would.