Have 1979 F800 dump truck that won't start unless I pour gasoline in the carbruator. While running at idle and atempt to give more gas the engine will bouge down. Will speed up if slowly increase the gas pedel. Connected a vacuum gage to carb ports and have no vacuum. Engine starts instantly when primed w/gas. What would I need to check for from this point. The intake manifold had hole in the left side by the center of the carb.area. Someone had plugged this and it was leaking so I pluged it again using Mag steel putty. Pulling the manuall choke closed has no effect on starting. Only start by priming the carb. Appreciate any help you can offer. Thanks Keith

 

What carb ports are you trying to get vaccum from? Any of the ports on the body, and above the base of the carb are ported, and some of those are timed. In those ports there shouldn't be vaccum at idle. You need to hook the gauge directly to the manifold. There should be a port either on the base of the carb (5/8" port) or on the manifold itself.

 

I checked port to the vac advance at high rpm , also the port to the two vac.storage cans at both high and low rpm. Will check out the larger port in morning and get back to you. Thanks Keith

 

Found and repaired vac leak under spacer plate under carb. Replaced gasket, cleaned area good and remounted carb and tried for vac. Have 15 in vacuum on line to dist. advance. Still have to prime carb. to get it to start, then it only runs until the primed fuel runs outThis happened for 4 different primings, then I can keep it running, but it still bogs down if I try to rev it up too fast or too quick. Does it sound as though I may need some carb. repairs? Thanks again Keith

 

It sounds more like the fuel pump has taken a dump...... You might try rebuilding that carb, but I think a 750cfm replacement would be a better option. The factory holley was governed at a pretty low speed, the motor you have probably won't want to turn many more tha 4500 rpms so get a tach too..

 

What source for a replacement carb. would you reckomend? Will change out the fuel pump after I test it if needed. Thanks again, Keith

 

Fuel pump tested out good. Went to Orielys to price a carb. Will be in tomorrow. Sounds like I am down to either a rebuild or replacement carb for the next thing to try. Since they don't have a rebuilt carb and I don' want to rebuild it (don't know what I am doing in this area) I will buy a new one and hope I am right. Thanks PFOGLE for your help and listening while I am trying to walk myself thru this. Keith

 

Sounds like the accelerator pump in the carburetor isn't squirting. It may be seized or leaking. Your new carb should solve the problem. Good luck.

Lou

 

Installed new carb. Problem taken care of . Thanks to all who supplied their input. PS this carb makes the rest of the engine look bad since it is so shinny. well, I'll cover it up with a new air filter element and the old air cleaner so it wont look so bad. Thanks again PFOGLE and MANGLASS. Yes the accelerator pump seemed to be dripping. Keith