Topic: 1978 CB750K Carb Intake Boots

[JimsCB750]

I cleaned the carbs last night on my 78 CB750K.   Prior to taking the carbs off, all 4 rubber intake boots failed the leak test with WD40 spray.   The boots are hard from age but not cracked.    Engine does not run right above 4500 rpms and runs exactly the same as before cleaning the carbs so I am focused on the resolving the failed leak test before I do anything else.   

Is it worth soaking the rubber boots in alcohol and wintergreen oil to soften them up?   Or, am I better off buying new ones if I can find them?   I've never soaked carb boots before.   I appreciate the input since this if my first CB750 and dealing with rubber carb boots.    My primary bike is a 2001 MAGNA.   

[BenelliSEI]

Jim..... I’d suggest you buy new ones. At +40 years old, probably the best solution. On my 750K8 the real solution was ultrasonic cleaning (attention to idle circuit) and a really careful carb sync with a four chamber manometer. Good luck..

[JimsCB750]

I soaked the rubber intake boots for two days.    They softened up nicely.   However, after looking them over I do see cracks on some of the boots on the cylinder ends of the boots.    I reinstalled them and gave it a run but they continue to fail the leak test.   Time to buy new ones!

[BenelliSEI]

Good idea!   

[JimsCB750]

I received and installed 4 new carburetor rubber boots, yesterday.   This resolved the rough and hanging idle but it still wouldn't rev up past 4500 rpms without the engine bogging out.   This morning, my son and I removed the pods and reinstalled the original OEM airbox with a new filter which came with the bike when I bought it.   What a difference!!!  The bike revs up like a gem and is running good.   This bike clearly didn't like the pods that were on it when I bought it.  Having read through the forum and seeing that other people ran into issues with pods, I believed that putting the OEM airbox back in was the next best process of elimination with the lousy running engine.     Now that it's running good, I will fine tune it by checking the valve clearances and check the carb sync.    It runs rich with the pods and the original airbox.   No difference with either configuration.   

[BenelliSEI]

Have you checked jet sizes. Sometimes “tuners” up the sizes when going to pods. The worst is if they had a set of jet drills and opened them up. They still read stock, but are not!....