Cb 450 Power loss @ 70-80MPH

J

jeffrontheimmortal

New Member
Recently my '72 CB450 keeps bogging down on me constantly at about 70-80mph and slows down to about 45mph max! I can accelerate up to 70 or 80 and it will stay there for about 5-10 secs then it will just begin to slow down and only go 45.

I'm still not sure if whether its stopping or slowing down that "resets" the engine and allows me to go up to 70-80mph again but every time it "resets" it will do the same thing, 70-80mph then bog down to 45mph.

I have recently replaced the coils with new Dynatek coils which solved my one cylinder firing issue. Do you think the coils have anything to do with this?

Or could it be a timing issue?

Live Free. Ride Hard.
 
More than likely a fuel delivery issue, I have dealt with this before.

I would start simple, and pull the tank and check the petcock for flow, then get to the floats in the carbs if the petcock has good flow.

By your description, I am 90% sure you have a float issue, remember to check any valves that are actuated by the float, and not just height adjustments.
 
I rebuilt the petcock so I know its getting good flow and the lines have recently been replaced but the routing was giving me some trouble. I couldn't figure out how to mount them with the filters on and keep the filters from melting slightly due to engine heat.

Is it necessary to run filters or does it make much of a difference?

Also, Assuming the lines are good, how would i check the float level and know where it should be?
 
jeffrontheimmortal said:
I rebuilt the petcock so I know its getting good flow and the lines have recently been replaced but the routing was giving me some trouble. I couldn't figure out how to mount them with the filters on and keep the filters from melting slightly due to engine heat.

Is it necessary to run filters or does it make much of a difference?
Click to expand...

What sort of filters are you running? Sometimes the paper element filters will restrict flow enough to give you problems.

Also check that the tank is venting properly. If it's not, it will stop flowing after a while.
 
I was using filters with a bronze element. I got some new fuel line but am waiting on some other parts before i go to work on this project.

What is venting?
 
In order for gas to flow out of the tank, air has to be able to come in to take its place. This is usually accomplished through some sort of valve (or just a hole) built into the gas tank cap.
 
you may want to check that. I know the three 450 tanks I've got here all need the vent cleared out. Try this, take the rubber gasket off the cap and run your bike. If that clears it up...there you go! Cheap test
 
I'm having trouble routing the fuel line with filters as well. That's stupid how it's laid out.

Not to threadjack, but since we're talking about syncing carbs, how do you set the air mixture screw? Are you supposed to adjust it to the point where it makes the bike idle at a high rpm? Then turn the idle speed down using the idle screws?
 
I'll give that test a try. I had a problem at one point with the engine running weak if the tank is less than half full so now i just keep it pretty full to avoid this problem. What was your suggestion to fix this problem?
 
After driving this afternoon and having it stall out on me repeatedly I think it is a fuel delivery issue b/c one of the filters has pinched off and is not getting gas to one cylinder. I was running vacuum line but went and got some actual fuel line.

Does the type of line use effect fuel transportation?

I'm thinking now that it isn't so much a speed issue that triggers the "bogging down" its the amount of time before the fuel remaining in the carbs are used. I couldn't even get it up passed 45 today it would start making a misfiring or backfiring sound and just turn into a noise machine with little power going to the wheels.
 
Know it's been said, but +1 on the floats. Had the same issue (at a lower speed though) and it was my floats.
 
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