Topic: Losing patience with a CB450 K6 - fuel in exhaust

[the-chauffeur]

I've been rebuilding a K6 450 twin over the past 6 months or so and after a whole lot of work and a bunch of new bits, it's pretty much all back together. During the process, I've overhauled the top end, replaced the pistons, cam chain, reground the valves, stuck in new points and rebuilt the carbs. But for the life of me I can't get the damn thing to run - even badly.

So what am I up against?

The good:

- It's got pretty decent compression, although not quite the levels listed in the various manuals (although I have a feeling that's something to do with the pistons/rings not having bedded in yet)
- it's got sparks; no trouble there
- it's got a new wiring loom, so everything there works
- the cams are timed with the engine, so it turns over fine
- the cam chain tension has been set
- the insides of the carb caps have been carefully honed (just to clean them up a bit) and are fitted the right way round/onto the matched carb bodies
- fuel is getting through into the engine
- no apparent leaks from any of the new gaskets

The not-so-good:

- it absolutely refuses to run . . . on either side
- fuel is making its way into at least one of the two exhausts (so much so that I found it dripping out after cranking the engine a few times)
- every so often, the bike backfires big time (oddly enough this only seems to happen on the same side as the leaking exhaust)
- airboxes are off (for ease of access to carbs)

I'm guessing I'm up against a couple of, erm, problems - one is the valve clearances; the other is the ignition timing.

I know that the clearances on these bikes are supposed to be a bit of a bastard to get right (they're incredibly narrow gaps), but is it conceivable that I've managed to get them so badly wrong that fuel is going straight through? I was real careful when I was regrinding them to make sure they closed perfectly, so I can't really understand what else it could be.

And I have to confess that ignition timing (at least, getting it to the point where the bike runs) is my achillies heel. Once I've got to the point where the bike runs, great - I've got plenty of diagnostic gear to accurately dial in the ignition. But it's the getting to that point that I think is making my life hell right now.

Any advice to save me from myself - or just jacking the whole lot in - would be very greatly appreciated.

Thanks in advance.

Neil

[CBGBs]

If you have a good condenser, I would suggest that you perform static timing on the engine. You can use a simple trouble shoooting light or a volt meter will work fine.  Place your leads on the point and ground to test for voltage as you turn the crank. On the firing cycle you will find that energy flows as you turn the crank up to the firing mark, and then it should stop immediatly at the firing mark. Turn the points plate to adjust the leftside point and then you will do the same for the right side and adjust the points gap to alter timing. Double check that both points are gapped within spec. This just might solve your problem. I had a bike that strangly fired right up and ran well, until 2 weeks later the timing was out and it didn't run anymore. I had spark and fuel. It was very frustrating.

[w1sa]

+1 on the timing.
You say you're getting fuel, but too much fuel could be a problem at this stage as well.
Did you check float heights and sync the carbs? Mixture and idle screw settings appropriate for initial startup?

Also, you mention valve work. If you have ground/lapped the valves and seats be careful not to set your valve clearances too fine as they will likely reduce the clearance upon start-up/initial running. Too fine a setting and you may find as the engine runs and heats, the valves may fail to close properly, (in short time). I'd add a thou or two to the valve clearances (as widely recommended) and re-check clearances after each run cycle to determine what's happening..............some of this activity can be repetitive and grinding  .......just continue eliminating the obstacles one by one.......good luck 

[tbpmusic]

Probably the timing - you should go to this site and read the 450 section discussions, a wealth of info on your bike.......

http://www.hondatwins.net/forum/index.php