Topic: New guy engine questions

[XN]

Just picked up a 78 CB750K and dang is the top end loud. I understand and expect some noise, but I'm almost afraid something is wrong. I adjusted the cam chain adjuster while running per the service manual, but I don't think it helped much. Is doing it static with the engine off a better way to do it? I also plan to adjust valve lash this weekend and hope that takes care of most of it. Any thing else I should check or look at?

Second question: I'm having carb issues. The bike doesn't want to run very well at idle when cold, I don't get much of a rise in RPM with the choke on and to keep it running I have to adjust the idle speed while cold, but when it gets hot it then idles at 2500. My plan was to adjust the pilot screws and then adjust the idle speed does that sound like the correct way to go about it? I also plan on checking the points before that...

Thanks

[WHALEMAN]

What manual advised adjusting while running? Check FAQ for correct method.

[XN]

What manual advised adjusting while running? Check FAQ for correct method.

The Honda shop Manual...

Here's a snap shot of it.

[MrZxp]

Is doing it static with the engine off a better way to do it?

Definitely. The shop manual has got it wrong in this instance. Here is the proper method...



It wouldn't hurt to remove the tensioner bolt arrangement completely as well and give it a thorough cleaning, as "gunk" can build up over time preventing it from "springing" as it should.

I also plan to adjust valve lash this weekend and hope that takes care of most of it. Any thing else I should check or look at?

That will help. Also a carb synchronisation will be an immense help, preferably with Morgan carbtune or similar, but at the very least a bench synch will be beneficial. Search for bench synch here on the forum.

Second question: I'm having carb issues. The bike doesn't want to run very well at idle when cold, I don't get much of a rise in RPM with the choke on and to keep it running I have to adjust the idle speed while cold, but when it gets hot it then idles at 2500. My plan was to adjust the pilot screws and then adjust the idle speed does that sound like the correct way to go about it? I also plan on checking the points before that...

The 77/78 models are cold blooded creatures. This is a consequence of emissions regulations of the time. However, full choke should raise RPM's sufficiently to allow the engine to warm up. Removal and and thorough cleaning of the carbs will more than likely clear up your problems. Once again the search function on this site will help you, also the FAQ section.

Cheers, Phil

[mystic_1]

The 77/78 should have a fast-idle cam on the choke linkage, have you checked to see if it's engaging properly?

Regarding your noise, definitely do a valve adjustment after you've got the cam chain sorted.  If you don't think the tensioner is doing it's job it's easy to pop it off and clean it up, three bolts holding it on and only a small gasket to replace.  Sometimes the setscrew chews up the adjuster rod and locks the assembly up.

If the bike sat for any length of time without running, a full carb cleaning may be in order.

cheers
mystic_1

[eldar]

Well lets see. The cam chain can be adjusted both ways. Pick one, it does not matter. One down fall on the static method is that it may make the chain a little too tight. the other method requires the carbs to be synced as if the engine is not idling smoothly, it will bounce around and the chain may not get tight enough.

The tensioner WILL probably be gummed up. Remove the 3 bolts. pull the unit off. CAREFULLY loosen the bolt that holds the rod as that spring is pretty strong. Clean the crud out and it will be good for another 10 years. the gasket will not need to be replaced unless you somehow tear it. I have pulled mine off 3 times and never replaced it once. It does not leak. See the unit does not get an oil bath, it just catches a little now and then and the oil generally drains back to the engine. So unless it rips, you most likely will not have to replace it.

For the choke. Set you idle when the engine is hot. From there, unless you have some reason to, you do not need to set the fast idle. It does nothing except allow you to take your hands off the throttle when cold. I suppose, if you start your bike and then get gloves and stuff on, then it helps. Me, i get ready before even starting the engine.

Regardless, take an afternoon to pullthe carbs off and clean them.
It is easy if you take your time and do a good job. And above all, CLEAN THE IDLE JETS. Lots of people miss them.

you need help with that, let me know. I am pretty good with these carbs.

[mrbreeze]

After doing everything these guys are suggesting plus the things you are already doing....the most important thing you will do to make your bike run alot better and eliminate the top end noise is synch the carbs.Don't worry about bench synch. That is just to get it in the ballpark to run. As mentioned,the Morgan Carbtune is the bomb but there are other manometers you can use (vac gauges,mercury tubes ,etc.) If you plan on keeping the bike and/or working on other multi-carb bikes...the Carbtune is what you want.

[XN]

Thanks all!

What makes the Carbtune better than other manometers?

[mrbreeze]

The way it is built and operates. It consists of metal rods enclosed in tubes. Vac gauges can get out of whack from each other and Mercury is messy and hazardous.There are instructions out there to make your own manometer (if you want to go on the cheap). If you just want a trouble free set-up that should last forever and make the task of carb synch a breeze...fork out the extra bucks and buy a Morgan Carbtune. Note.....I don't work for them......Hell....they are on the other side of the planet from me. I'm just a satisfied customer!!!

[XN]

Hot dang! Got the valves done, pulled apart the cam adjuster and adjusted per the above instructions, new plugs, did the bench synch, set the fast idle (ran out of adjustment but its at 1200 and thats enough.

She's running a lot better and 90% of the top end noise is gone!

Thanks guys!