Honda CB450 Boging Down

[Casey Stangle]

My 1970 CB450 was running just great. Then it started to bog down when giving it gas. Bad at a start from a stop sign. Bad when trying to accelerate at any speed. I know it is the right cylinder because the plug is black and gas wet. I took the carb appart and blew it out. Slide seemed to work fine. Good vacuum and did not hang up. Very smooth. If you engage the choke slightly, it gets worse. I swapped the plugs to see if it would go from the right cylinder to the left and it stayed on the right side. Thought a plug could be going bad.

Any ideas?

[Dodsfall]

It's getting too much gas and/or not enough air. It could be the float level is not right, or not sealing. The air filter might be restricting flow on that side or blocked up (mouse nest or stuck leaf?) Check the valves for proper adjustment and do a compression test on that cylinder. Make sure the exhaust pipe on that side is not plugged up with something. Make sure the main jet is installed correctly and not rattling around.

That's all I can think of to check.

[Casey Stangle]

I rebuilt the motor so most of what you mentioned is ok. When I took the carb appart, yesterday, everything seemed fine. I lowered the float level just to try it. No change. I will try turning on the gas and pulling the carb bowl just to see how high the gas level is. That will tell me if it is shutting off.

[Andd93]

I'm having the same problem. It'll start up and idle great and as soon as I get on it and start to ride when I really try to accelerate, it just loses all power and it starts to bog and winds up stalling out while I'm coasting at like 35mph. My buddy said replace the petcock. We rebuilt the carb already and I'd rather try other things before replacing the petcock. The only reason he said that was because as we were draining the gas tank it was hardly even a stream coming out with the petcock set to on...I had a full tank of gas it should have been a solid steady stream right?

[Casey Stangle]

My bike is is not quite that bad. I put a new set of plugs in it and it improved somewhat. The next thing I am going to try is swapping the coils. It could be a weak spark, which was helped out some by the new plugs.

[Casey Stangle]

Since my last posting I swapped coils and rebuilt the carb to no avail. Plot thickens.

[Casey Stangle]

Checked the timing with a light and also checked the advance. Right on. On to the valves.

[LWRider]

Originally Posted by Andd93

I'm having the same problem. It'll start up and idle great and as soon as I get on it and start to ride when I really try to accelerate, it just loses all power and it starts to bog and winds up stalling out while I'm coasting at like 35mph. My buddy said replace the petcock. We rebuilt the carb already and I'd rather try other things before replacing the petcock. The only reason he said that was because as we were draining the gas tank it was hardly even a stream coming out with the petcock set to on...I had a full tank of gas it should have been a solid steady stream right?

Could be the petcock. You should have a steady flow of fuel. But just replacing the petcock may not solve the problem if there is more gunk in the tank. I'd pull the tank and check the inside for rust and other gunk. If not clean then clean it before replacing the petcock. You may be able to just clean the petcock, too.

Cheers,

Mike

[LWRider]

OP. I am assuming your bike also has Keihin CV carbs? If so, make sure when you clean it not only that the jets and nozzles are clean, but also that the air passages to the diaphram chamber are, too. I assume you checked the slide diaphrams? Sometimes it is hard to see pinholes in them.

Another thing just occurred to me. On my 350 the points have very little clearance between them and the points cover. I have had one of the points terminal lug vibrate loose and rotate making contact with the backside of the cover, thereby grounding those points. Took me a while to figure that one out as you can't see it. Check the wires going to each set of points.

Cheers,

Mike

[slumlord]

Originally Posted by Casey Stangle

My bike is is not quite that bad. I put a new set of plugs in it and it improved somewhat. The next thing I am going to try is swapping the coils. It could be a weak spark, which was helped out some by the new plugs.

I saw that you did swap the coils on the theory of a weak spark,and it was not conclusive.
Let's say that the spark is weak [to both sides] from a weak battery. One piston and its compression may be a bit weaker than the other,or just something about it may be not as good as the other side, like timing,or valves or carburetion or any number of things. So when BOTH sparks are weak,the 'best' combination of bad factors will likely show up on that side. So that is how a weak or poorly charging battery can show up on just one side.
As far as electrical problems on one side go-- Every single connection from the points gap,points condition,bullet connectors on the points primary wire, the spark plug wire itself can influence a weak spark to one side,so it is not always the coil.
Lots of stuff to think about on an old bike...

[Casey Stangle]

I re-set the valves. Did not realize that the witness mark on the adjuster has to be pointing outward. You can get the valves set correctly with the adjuster 180 out. Set them to .002" go and .003" no go. Considering that the bike is 42 years old, should the coils be replaced? Was thinking of Dynatech. Any other options on coil brands?

[slumlord]

Z-1 enterprises has a very inexpensive coil. No experience with that brand, but probably what I would do [if my coils failed] is use that coil,the existing points,and then add a Hondaman ignition to the system. Hondaman uses your existing points and coils to brighten up the spark without adding much of a load to your electrical system. On our old weak charging systems,that could be a help.
You could try a Hondaman electronic to your bike as it sits now. Many guys have had good results with it, and the fact that you can remove it in 5 minutes and go back to stock could be pretty helpful to keep you from being stranded if problems arise far from home.
Hondaman hangs out at another website that I cannot mention according to forum rules

[Casey Stangle]

Thanks, slumlord. I found the site and it looks as though they are $77. Do you know if there is any way to replace the wires on the stock coils? Looks as though it is a one piece item.

[gcmoto]

Sounds like a vacuum leak from the diaphragm of the carb. Spray some carb cleaner or starter fluid on the carb while the bike is at idle and running and see if the RPMs go up. If they do then you for sure have a vacuum leak.

[Casey Stangle]

Tried that and the rpm stayed the same. Bought a set of Dyna Coils and have them installed. Am having a problem finding the correct coil wires. Long story. Will let you know if this solves the problem.

[Casey Stangle]

The new coils did not solve the problem. I want to sync the carbs and have a friend with a mamometer. Do you have to modify an old set of intake boots to do this? Don't know where to hook the mamometer up. Also increased the valve lash on the exhaust to .004. Actually seemed to help, but am not sure if I want to leave it that way. Any chance of doing damage?

[WintrSol]

You either have to add vacuum ports to a spare set of boots, or drill the head near the intakes. Some claim that changing out the boots will shift the set point, but that didn't seem to be the case with mine, at least, it wasn't enough to feel. FYI, you have to put a tube into the boot that reaches into the air stream; just making a hole in the side and sealing in a port won't give you much vacuum.