Leaky Intake manifold??

[GreenFlash]

Hi! I'm brand new to the forum and am hoping to get a little help. I have a 1971 ct70HK0. I'm the original owner and the bike has been sitting for a great many years. Im re-working a lot on the bike, it's all original and actually in good shape. My problem is a leaky intake manifold. When I spray carb cleaner around the gaskets it definitely indicates a leak on both the carb and manifold gaskets. I have replaced the gaskets on both ends of the intake and the heat bushing as well. One of the bolts on the intake manifold was stripped. I re-tapped and installed new bolt. still leaks..... the engine does not idle smoothly or run smoothly at any power range.

I cleaned the carb and replaced the gaskets with a kit ... still runs pretty bad. Seems to be lean. At this point I would appreciate any direction to proceed. New Carb kit with jets .... new manifold, etc... Thanks

 

[69ST]

The intake flanges should have a slight taper...the area surrounding the throat sitting slightly higher than the bolt holes. They don't really warp, the metal is stable and rather brittle. First thing, you need to isolate the vacuum leak(s). It'd be rare to have a situation where a gasket won't seal the head (port) end. At the carb end, it's almost the same thing...and that big O-ring has enough "crush" to seal most any normal tweakage. Last resort would be a thin and I cannot overemphasize "thin" application of silicone RTV; that's a messy, high-risk, way to seal a stubborn leak. Don't even consider doing this until and unless you've exhausted all other options.

As for the carb rebuild kit this one is the most complete. One critical step is cleaning out the emulsion tube orifices, all of them, using a thin wire. Nothing else will suffice, no matter how good you think it looks afterward. Carb spray should be used, to clean...and verify...all of the various passages as being clean & unobstructed. The new pilot jet, included with the kit, should take care of any idle problems.

Keep in mind that it's possible to overlook something with the carb rebuild. Some can be very stubborn and it's tough for a newcomer to figure that out. Second, if the engine is down on compression, or has an ignition problem (too narrow of a point gap, for example, will make an engine run like), it's not going to run right until those issues are corrected. From what you've said, the carb & intake are the logical starting points.

 

[GreenFlash]

Racerx thanks for the reply! I failed to mention the manifold gasket was not an original Honda part. I fabricated one out of FelPro 3046. Maybe this is one of my mistakes. However, the carb gasket was brand new from Partzilla. The carb kit I bought was 16010-102-305 from Partzilla. The big O-ring fit OK but did not have much thickness, in my opinion. Maybe this is one of the issues with the car leaking at the manifold. The gasket insulator is new so that shouldn't be a problem. I'll order a new manifold gasket and carb you recommended.

I'll rebuild the carb again. I was careful the first time but I did not have a complete kit so, this could be all my doing. I assume the kit comes wit the correct jets (#60) for my particular carb?

I used the "battery/bulb" method to do the points/timing the last time. The bulb dims right at TDC per the instructions. I made the assumption this method would set the correct gap in the points? Secondly, if I replace the points and condenser, for my CT70HK0, all they all the same for the models? I have read there may be a difference. I do know I have an Hitachi flywheel if that makes a difference. Once again thanks very much for your help!

 

[69ST]

Verify the point gap, it takes no time or real effort. Also, these ignitions can rival the spark output of CDI. So, if you have a nice, strong, spark...especially if there's an audible "snap" to it, the condenser should be fine.

Main jet sizing varied from #58 up to #65 with the model & year of the carb. Understand that the main jet is but one factor controlling the amount of fuel entering the intake stream. It's only important to understand that your carb needs the same size main jet...and not try to use, say #58 or #64, for example(s). There is one wrench in the monkeyworks...pump gas isn't the same as if was in 1970. Thus, the jet needle height may have to be altered to compensate; in some instances, it is necessary to upsize the main jet. Don't let's go there, just yet. Until we've sorted through the vacuum leak & verified the emulsion tube as being completely unobstructed, that will only add to your confusion.

First thing I'd do is find a twist tie, then strip the coating off if it, to create a makeshift jet file. Then run that through every single wall orifice in the emulsion tube. FYI, the emulsion tube is also the main jet holder. It will have to be unscrewed from the carb body, to access those tiny holes.