carb help?

[maineiac5586]

ok, my 76 500 is killing me. i pulled the carb because i had a bog when accelerating. adjusting the idle mixture screws made no difference to performance. after pulling carbs i found restriction in passage for idle mixture screw. cleared restriction and checked rest of carb, all checked out ok. reassembled carbs and installed on engine. fired it up tonight on the muffs and started with idle mixture scres out 1 and 1/2 turns from lightly seated as per manual. starts fine every time, bog is horrible to the point it stalls engine when acclerating. played with idle mixture screws and can get a change in the way engine is running when adjusting but bog doesn't change. just for a test i backed the idle mixture screws almost all the way out and was able to remove most of the bog but this doesn't seem right. any idea??????? i should note engine reved cleanly on the muffs before removing restriction from idle mixture passageway.

 

[Chris1956]

Re: carb help?

Those carbs are pretty simple, and do not have any midrange jets or needles. I therefore do not think you can address the mid range problem directly. I would doublecheck the float heights and especially the float's condition. The old foam ones tend to disintagrate.

The sidebowl carbs (you have these?) tended to need to have a rich idle mixture, in order to accelerate smoothly. After you get the carbs clean, set the idle needles to 1-1/2 turns out and warm and run the motor at idle until you achieve the smoothest fastest idle. Now try to accelerate. The motor will likely bog. If so open the top idle mix screw 1/8 turn and try again. If ti boggs, open the lower carb mix screw 1/8 turn and repeat until you have a smooth acceleration and reasonable idle. Hopefully the midrange issue will be better.

 

[maineiac5586]

Re: carb help?

thanks, what i did tonight was run it again and while it was bogging i squeezed fuel prime bulb efectively shooting gas into carb, bog went away, was able to duplicate this several times (bog without squeezing/ok while squeezing bulb). pulled carbs off found top carb float was set at different level than bottom carb. the top carb's float was angled away from carb body when carbs were held upside down. The bottom carb's float was level when carb was held upside down. do you think this could be it?? DO i need to measure float adjustment or is eyeballing them good enough? should they be level with carb body when held upside down? also, any way to check my fuel pump diaphram? I have the type built into side of carb. thank you

 

["G"]

Re: carb help?

Maine... Once you set the floats correctly, (eyeballing really isn't good enough) be sure you have the carbs syncronized to each other. Next be sure you syncornize the carbs to the primary and secondary timing. Very simple process if you have the Chiltions manual to provide values. Once you've done all that you shouldn't need to screw around with the idle jets. As for the fuel pump diaphrams; replace them while the carbs are off off the motor. If you squeeze the bulb and resolve the running that is prime suspect. They are super cheap and available through Sierra at your auto parts store. Remember to look for ethanol issues like floats, gaskets and diaphrams that are swollen, broke down etc.