Re: Honda CB750 Rebuild - Bikes Running Decent But I Have Some Real Concerns

Posted by Re-run on
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Honda-CB750-Rebuild-Bikes-Running-Decent-But-I-Have-Some-Real-Concerns-tp4050853p4050881.html

Really strange on the float needle seat. As long as the float stops flow though, it should be ok.

What do you have the idle mix screws turned out to? Since the carbs have been synced, the idle mix tuning could be done. best results are from an external tach instead of the bike tach. The bike tach is not nearly accurate enough.

Have you checked your compression and performed a leakdown test? Just to make sure everything is generating compression and holding it decent?

I would also bump the valve clearances up .001  Intake set to .003 and exhaust to .004. the stock clearances are not really enough once the engine gets hot. Increasing them will reduce valve wear and allow things to flow a bit better though noise might be slightly higher.

The cooler inner temps would generally indicate that those cylinders are running cooler either from being richer or not completely firing. The outside cylinders are exposed to more cooling. Tuning the idle mix might even those out some.

The quick and dirty way to tune idle mix is to start and get the motor to normal operating temp. hook up a tach and set idle to about 1200 rpm. Turn the fuel screw till the bike hits its highest rpm, then turn it out slightly so that rpm drops about 50. Start with carb 1 and just repeat for each carb through #4. After you set each carb, back the idle down to 1200. While doing this, a fan should be pointed at the engine to provide cooling air flow.

Ultimately, if everything checks out, the engine should be fine.