I finally spent the money and bought some 4 screw Z Therapy refurbs which I have installed / tuned them (including valve and adjustment). The car runs great until it runs for a bit at operating temperature and then it bogs down (feels like a vapor lock to me - I've had the problem with a flat top hitachi equiped 260z in the past). If I shut it down and let it cool off, it'll run good again until it warms up again. The funny thing is that I did not have this problem before I installed the new carbs. I've insulated my fuel rail and that did not seem to help. Heat shield is in place between the header and the carbs. Any ideas?

 

If you're running a mechanical pump it might be a little weak. Try pulling a little bit of choke when it slows down. If it runs better then it's the pump. If that's all good then try backing the thumb screws at the bass of the carbs out 1/4 turn at a time. If it runs worse go the other way. Did you balance the throttle linkage? Make sure your choke cable isn't pulling partial choke when it's off.

 

Yep, I did balance the throttle linkage, but will check it again. I installed an electric pump by the gas tank and I can see that my fuel filter is completely full, so the problem resides between the filter and the carbs. I was thinking that it could be the mechanical pump, so checking it will be a good place to start. I'll go through your other checks also. Appreciate the info!!

 

I'm sure you got a low pressure pump like 5 psi max but if the mech one is bad it could slow down the fuel. Try disconnecting the hose to see if you are getting good flow into a bottle. I had a problem with those see thru filters not allowing enough past. Maybe contact tech support at Z therapy.

 

yeah, the back pump is a low pressure one. Now that you mention it though, it was sounding like it was struggling when I was running the car not too long ago. The sounds went away and I did not think much about it until now. I assumed that if I was getting fuel to my front filter, then all was good (at least with the fuel delivery up to the front pump). I'll try your choke test and see how the car reacts. If it helps, I will revamp the entire fuel delivery system (probably need to do it anyway). It's just funny that the car begins to run bad after it warms up. It runs really sweet before it bogs down though, so I'm excited to clear this problem up.

 

After checking everything out last night, I definately have fuel delivery problems. Gas sputtering into the front filter and barely anything getting to the carbs once the car has warmed up. Question, do I even need to run a back electrical pump? Will the front mechanical pump pull enough to sufficiently supply my carbs?

 

The 260 was made to run hotter because of smog requirements. That's the reason for the dual pumps. The rear pump has a pre filter and a filter screen inside the pump intake port. You will have to pinch the inlet and outlet off to change these out. Consider draining the tank and replacing all the hoses. Do this outside the garage. It's suprising how far a 1/2 cup of gas will cover especially when your laying under the car and you don't see it coming.

 

Problem solved. Rear pump removed and the car runs great. Good call TheRamz!