running problem

[mickman77]

hey everybody. what a great site. have a question. took the 400 sbc out of my '77 k20 and set a 454 in it's place. the 400 had a 3 line fuel pump and the BB has a 2 line. couple of guys told me to just cap the return line and don't worry about it. well, problem is, it will idle and drive down the road just fine but, when you slow down to make a turn or traffic, it wants to stall like it's vapor locking. feather the pedal and it stays running. otherwise, it stalls. no vacuum leaks that i can find, timed right, new plugs and all that. for the life of me i can't figure this out. would a vapor can hooked to the return line solve the problem?? please advise if you have an idea and thanks ahead of time for any responses.

[vtwinsport]

Have you an aluminum intake and carb setup?

[vtwinsport]

The fuel system needs to vent so plugging the line that would go to the vapor cannister will pressurize the system and cause extra fuel to be pushed into the float bowls. Probably causing the flooding. Check your plugs, they could be might black about now. Also, do you see black smoke upon warm starts and when you floor it?

[pilotj]

I've had my return lines blocked off and havnt had any problems at all. (my 79 model has return lines for automatics but manual trans trucks didn't have them). Do you have a fuel preasure regulator on it? Is it a high preasure pump? I doubt it's a vapor lock issue. It sounds like a float level issue or fuel is pushing past the neddle/seat. It's the fuel retun line to the tank you plugged, not to the vapor cannister, right?

[mickman77]

think i got it. 454 has a performer cam and intake so i completed the package and put a new performer carb on. presto, no more idle problem. thanks again for your inputs.