[harrywh]

My 81 chey 1/2 ton truck with 350 4 bbl starts and runs great until I floor it or accelerate. Then it seems to bogg . I changed the fuel filter changed the vacume advance diaphrm .I also changed the plugs . the exhaust seems to be flowing fine I don't think theres any restrictions. Any sugestions !!!!!

[78 monte]

Sounds like an excelerator pump problem.Bad diafram or need to change pump cams or try another hole on the cam.

[BstMech]

If it's a Q-JET then check the dashpot on the side of the carb (vacuum chamber attached to the secondary "butterflies"). Make sure it's getting vacuum and that the diaphrahm is good. A quick check is to watch the butterflies while giving the throttle lever a snap to full throttle they should not open very fast. Oh yeah, does it still bog after the engine gains RPM? If so, this is probably not the cause.

[ September 29, 2002: Message edited by: BstMech ]</p>

[harrywh]

Thanks I will try your ideas and see what happens.

[MHenricks]

How many miles on the carb? I agree with you 78Monte, the accelerator pump sound like it's bad or the cam. Usually if I rebuild a carb I'll use a different hole on the pump lever just to make sure the top portion of the pump area is'nt worn that would cause problems

[dirtlmfan]

My '93 gmc with 350/auto does the same thing after I installed a Hypertech Thermomaster Chip and a 1" TBI spacer. My problem is probably the idle control sensor though. Your's sounds like the accelorator pump.