[benco]

So I recently got a 1974 CB450. I have tried a 2 sets of coils, both used. Spark seems decent. I have adjusted the timing according to Bills method and also check a with a timing light. The time looks great, the advance is going a little to far. But the problem I seem to have is idling and popping. I have gone through the carbs twice and the jets look clean. The bike will idle if I leave the choke closed just fine with no back fire. If I open the choke it will rev up and then die usaully if I let it down below 2000 RPM. Also it backfires at low RPM.

Also I drove around a little and it seems to loose power at about 45mph then will either come back or if I let off gas it might reset and come back a little.

Also I have adjusted the valves according to shop manual.

I have made new gaskets for the carb intake boots, so I think I eliminated any leaks there.

Help any suggestion.

I am gonna try and pick up a new set of coils and wires tomorrow. Will these make a difference if they are a higher Ohm rating on the coils?

Thanks

Ben

 

[Bird76Mojo]

If you're gonna switch coils then I'd go by Bills replacing method, using stuff from MikesXS.

Get that timing spot on first. Then take all of the jets out, and verify that they're ultra clean, as well as the throttle slides. Search for "straw test" on here, after you verify that the carbs are spotless.

Have you done a compression test yet? If not then borrow or buy a tester and do one. Report your results back here.

GB :mrgreen:

 

[Bird76Mojo]

Also, while running, you can spray WD40 around the carb boots to check for air leaks. If you've got one, you'll know it.

GB :mrgreen:

 

[benco]

Man this is great, I didnt expect to get this much help so fast. lol

I ran down to the shop to do a quick compression test with my brothers cheapo hold it in the plug hole tester. I could see the guage on both cylinders bounce up to about 145lbs. Might get a little more with a screw in tester.

Also noted the plugs are both black, maybe from running with it choked?

It passes the straw test.

 

[Bird76Mojo]

Yeah the plugs are probably black from choking it like you said.

It only takes a couple minutes for your crankcase to partially fill with fuel/oil mixture, and one time running it may be enough to do some major damage. :?

I hope those comp numbers come up a little bit with a screw in type tester. I'd check it and see, cuz right now you're at or below the minimum compression numbers....

You might also give some thought to buying the "annotated 450 manual" on CD that Bill offers.. It's LOADED with info on these great old bikes, and it's a bargain!

GB :mrgreen:

 

[KERRY]

It sounds like the carbs need cleaning, like your low-speed jets aren't delivering any fuel. that seems commonly to be the case with these carbs when they aren't run for an extended period - fuel varnish plugs up little air passages you can't get at. Get an immersion tank (paint can) carb cleaner at your auto parts shop. Used to cost about $16, probably more now. They last a very long time, though. Tear your carbs down (one at a time - any questions about re-assembly, check the one that isn't apart) and soak them. Don't soak the top - the solvent will dissolve the plastic, and it generally doesn't need cleaning, anyway. As far as going beyond the advance limit, that will produce a loss of power at higher revs. Apparently, the fly-weights of the advance mechanism initially had little bands of some sort around the part that hits the stops, and they deteriorate and come off. That lets the weights go out a little too far, giving you too many degrees at full advance. I've corrected this by tapping the stops inward a little, using a dial caliper to get them both the same distance from the axis. I thought it would take a number of tries 'til I got it right, but my advance timing fell within the marks on the first try.

 

[benco]

So I got this thing running good at higher RPM. Still dieing at idle though. I noticed that the exhaust gas on the left side is quite a bit hotter than the right. I swapped coils and still the same thing, right side gas colder. I triple checked the timing and its good.

Also the right side plug is wet with fuel. I can increase the throttle on the right and it revs up.

I tried closing the idle adjustment screw and the same thing. Still to rich.

Any Suggestions?

 

[dlslick]

Sounds like plugged idle jets and carbs out of synch to me.
I struggled with my CB450 for quite a while getting the jets clean. I thought for sure that I had them clean but when I put the carbs back together I still had the symptom so I cleaned them again and it finally started idling. The synchronizing of the carbs will fix the unequal exhaust pressure.
Don

 

[66Sprint]

You DO realize that the pilot jet and slow jet are both "stacked" in the same hole?....

 

[benco]

Alright, I finally got this enrichment figured out. I shined a light in the carb while running at idle and could see fuel coming out of the main jet. So i swapped needles with the good side. Problem now on the other side. I cleaned the needle with some scotch bright and it helped but still not perfect.

Anybody got a needle or 2?

I will get the number off it shortly.

For what ever reason this cylinder doesn't seem to mind the running rich as much and i can idle at 1000 rpm \


Thanks for all the help guys