My friend has a 86 Z28 which had a stock carburated 305. He yanked it and installed a GMPP 350 h.o. crate motor and bolted all the 305 components onto the short block. Most of the time the car bogs at higher RPMs. Seems like it isn't getting enough fuel or the timing isn't being set properly. Has anyone encountered the same problem? Is it the carb? Distributor? Fuel pump? ECM? Any help would be appreciated.

 

Welcome aboard.

Start with fuel filter (if not already replaced). Then fuel pump. Could also be a clogged pick-up sock in the fuel tank.

Some of these cars also go an electric pump in the tank. If it is shot, the mechanical will have a hard time keeping up.

 

sounds like a lack of fuel to me too. unfortunately, im not that good with carbs, but when i put my 350 HO in, i had a similar problem.

just check everything, including the pump, etc.

-brian

 

Do you think it is a fuel delivery problem, or do you think my friend needs a bigger carb? It's the stock 305 carb.

 

Yeah, I'd start with a new fuel filter, which is inside the fuel inlet nut on the front of the carb, where the fuel line goes into it.

 

i know NOTHING about carbs, so I don't know...but, I would check on the carb board to see what they may have to offer. I know that a few guys over there know a LOT about that stuff.

-B

 

stock 305 carb = LG4

change the exhaust

my car had the same engine.....and from looking at the exhaust manifolds, that has *got* to be one of the most restrictive designs GM ever dreamed up....and all done for emissions purposes (I think)

anyway, if the exhaust is too restrictive, I could possibly see it bogging slightly at high RPM, particularly if the catalytic converter is getting clogged....though I'm by no means an expert, so don't quote me on that

plus going from completely stock LG4 to a "high output" 350 means the exhaust is choking the engine even more

 

Yea, its probably a combination of lack of fuel (like said above) and a very restrictive exhaust system.

 

You have to tune the carb for the bigger engine. Also a bigger exhaust for the increased flow

 

I had a similar problem with my 86 T/A after a 305-350 HO swap. The solution was to add an electric fuel pump back by the fuel tank to act as a booster for the mechanical pump. The mechanical pump will regulate the final pressure to the carb. The car use to fall flat @ 4500 rpm in second gear, now it pulls strong to 6000.