JGB

What causes fuel pressure to rise to the point of needing a regulator? Motor is 1985 merc 260 Carb. I am just trying to get a handle on this. I have been having some carb issues and I am down to where if the carb is not the problem too high fuel pressure is. Thanks

mopower

If you have the stock Merc mechanical fuel pump , it's unlikely the pressure would increase. I'm running Carter mechanicals (140 gph)on my 540s and they are internally regulated for 7 psi. I also have 4 pressure gauges , 2 electrical on the dash and 2 mech. right at the carbs for a second opinion and they never change.
If you're still battling the idle problem , it's more than likely the float level or the needle and seat. It seems the common problem here is the fact that this problem appeard with the rebuilt carb...right?

JGB

ok so now the guys at the carb shop are pulling it apart again and rechecking everything. My problem before the carb rebuild was that the secondaries in the carb where sticky and weren't opening all the way and who knows what else was sticky also in the carb. It had a rough idle after running a 30 min run and lost a bunch of top end speed.So I had it rebuilt, ran it, ran very smooth for 10 minutes on the hose and then it puked with what seemed like a flooding condition. I saw some fuel exit the exhaust also. I then shut off the fuel valve and the carb burned the fuel that was in it fine. turned the fuel valve back on and it flooded and stalled immediately. Thanks Mo

Jim

RickR

Check the tangs on the floats. Especially if the floats are nylon.

I bought a problem HP 500 carb that flooded the owner's engine soooooooo much the he got rid of it.
Turned out to be weak tangs on the float that control the inlet/float valve.
You could set the fuel level but after a few minutes the tangs would bend out of shape again from the fuel pressure (6psi) and fuel would come out the J tubes..
The newer black floats (Nyglene?) have much stronger tangs.

RickR

BTW: HP500 carb is a 4150 Holley, but I have seen the same problem with a Carter 2 bbl

JGB

Thanks I'll mention that to the carb guys. I appreciate it.

Jim

JGB

RickR, Just spoke with the guy rebuilding the carb and he says that's what he rebuilt the carb with. The new newer style black floats. It'll be ready by 4:00 today so hopefully I just got a bad set in the first rebuild. I'll let you all know how it goes. I'll install and run tonight with crossed fingers.

Jim

David

The Rochester QuadraJet is also known for the float becoming "logged" (saturated) and not having the correct bouyancy specs.

JGB

ahh haa. So it could be this is a POS to begin with ? Is there a solution? or just replace the carb with a Holley or edelbrock? Thx

David

Actually, the quads aren't really that bad a carb. If he used the newest style float, you should be OK there. I didn't know if you were still using original parts.