Hey all, This is on my father-in-law's 1995 Mercruiser...it's a 305 or 350. It's pulling fuel past the boosters at idle, leaving the idle mixture screws ineffective and it's obviously running pig rich.... I took the carb apart, and it looked pretty good. I kitted the whole thing; the float was brass and fine. The float level was good. Timing is at 10*, idle is 600-650. After kitting the carb, it still has the same problem. I took it back off and lowered the float 1/8" and the right side booster dried up, but the left side didn't. Fuel pressure is 7.5 pounds. I told my father-in-law that I feel that 7.5 psi is too much fuel pressure for a Quad, and that may be the problem, but I have almost no Quadrajet experience...any other ideas? Anything I'm missing? Thanks! Aaron
The brass float is incorrect for the Marine units and will NOT work correctly at the right float height. Marine carburetors have tiny idle tubes which get plugged up easily, so this quickly puts them on the main system at idle speed. They also use a large diameter fuel inlet seat. If you kitted it with an over the counter kit, it will not have the correct seat in it, which also effects fuel level in the bowl. The accl pumps they come with will also fail in this new fuel, even if they are the blue ones. Also look very closely at the spec sheet and set the float the correct level. Marine q-jets are application specific, and more sensitive to float height due to engine tilt and location, etc..Cliff
That's interesting! My FIL got the kit from Mike's Carburetors or something like that. Do the marine carbs use a nitrophyl float? Are they smaller in volume than the brass? Do you recommend an accelerator pump that will stand up better than the blue one? I did blow out all the passages with carb cleaner and compressed air when I was in there, but that doesn't mean they're completely clean either. Is there a specific way the accelerator pump is supposed to sit on the lower spring in the well? I noticed that the plastic flanges on the bottom of the pump keep getting tangled in the spring, so when I pull it out, the lower spring comes with the accelerator pump. That doesn't seem right. Could the carb have the wrong lower spring? Will any nitrophyl float for a Quad work in this? Sorry for all the questions! Thanks for the help! Aaron
The idle tubes are pressed in to the main body, and are possible what is clogged. You can take a small diameter wire and push to bottom to see if you can clear it. Your accelerator pump shouldn't tangle with the spring either, something odd going on there. I highly recommend Cliffs parts, at cliffshighperformance.com Get the HP pump with garter spring and it will come with the two new springs you need, and the good float, and any other parts that are needed.
Hey Mark you have your jets on the wrong side ! Are those self tapping jets? Or are you running your carb backwards?:eek2:
Aaron, I would call the shop and get one of our Marine kits. They have the right float, high flow Viton needle/seat assembly, and complete Marine accl pump assembly with both springs and new retainer. You will also get a new secondary plastic cam/spring, micro screen Marine filter, gaskets and small parts. Our MB to Airhorn gasket is .015" thicker than stock and will insure a good seal between those parts. The "blue" seals vary considerably in quality, we have our own seal, it will NOT be effected by alcohol, methanol, race gas or any fuel additives.....Cliff PS: I attached a pic of blue seals being replaced (ours is in the upper left corner). The ones that show up on the pumps from the supplier will not hold up in this new fuel.....
are those pump rods longer or shorter than the ones with 3 lines on them .? Is there a sleve kit to get longer stroke on the pump squirt , or is that not necessary, also do you fit the larger 2 barrel pumps by honing them out to fit?
Marine pumps are a LOT shorter than automotive applications. A Marine engine is usually heavily loaded, and quite a bit of throttle applied at cruise so well into the primaries. A short pump still has some pump shot left when going to heavy or full throttle from cruise. Pretty important for those applications. I've never seen the need to incorporate a larger pump into one of these carburetors......Cliff
