Topic: CB750A Hondamatic Carb Question

[tomswift]

I am bringing a '76 CB750A back to life - not run in 20 yrs, 5500 miles on the speedo, all original - and I have read that the carbs needed tweaking from the stock condition to make it run like it should.... does anyone have experience making these carbs run at their best?

I know that the fuel pump is important and when disassembled for cleaning I noticed the diaphram was sealed at the tiny in/out orifices. I have carefully opened them up and have the fuel pump working better. I read on another post that raising the float level a bit would help as well as moving the main jet up to a 105 from a 102.

Any additional tweaks or suggestions would be appreciated

[bucky katt]

wow, i learned something new today. i had no idea that the 750a had a fuel pump

[tomswift]

sorry - not fuel pump, accelerator pump

it is in fact a fuel pump, but since it pumps only about 1cc of fuel directly into the carb throat it is referred to by it's specific mission

[fishhead]

A good carb cleaning will go a long way. If the accel pump diaphram is also 20 yrs old it probably should be replaced also as they get hard with age.

   I've never tried it, but the later K/F model carbs are a little bigger than the A carbs. The A model specific parts (vacuume diaphram, etc) could be transfered over to the larger PD carbs be a "possible" upgrade over the smaller A carbs.
 Like I said, I havent tried putting the larger carbs on the A (I dont own an A model), but it could be done rather easily.

[tomswift]

carbs have been thoroughly cleaned, and bike is running okay. One of the early magazine articles on the CB750A mentioned that the bike tended to run rough at highway speeds and that Honda had issued some directive/service bulletin to correct the problem.

I have already discovered that when cold the engine seems dragged down by the transmission/cold oil - letting it warm up a bit really makes a difference. I do wonder if anyone has a suggestion for removing the last 2 qts of oil that hang up in the torque converter during an oil change...it would be nice to put the entire 6.5 qts of clean oil in the bike at oil change time!!

[Spanner 1]

 The oil capacity on the A is 4.2 quarts good quality 10/30....never heard of 2 quarts not draining !
The carbs are 24 mm as against 28mm on the K and F models... no conversion possible, no benifit anyway as the A compression is lower and the cam milder ( I think ).
Caution with those little square things in the acc. pump fuel way, they are 1-way valves to stop the fuel just returning into the acc. pump sump when the diaphram is released.....
Cant think of any carb improvement over stock....bike should rev. freely and do at least 90 mph @ about 8,000 rpm.... hope you haven't damaged the acc. pump valves, good luck with your A.