Topic: Web Cam #41 in a hi-comp 849cc, advantages?

[HondaMan]

Hi Mark, would this mean that "normal" guides will be loose now in the OD? If my guides are stuffed do I need the cycleX ones again.

If you used the CycleX guides last time, use them again. I have a "test head" here where I play with these things (the #4 chamber is utterly destroyed, so I don't feel bad about using it for unspeakable experimentation...) to see how they work out.

I found that installing an APE guide in a stock Honda hole, then removing it, lets me reinstall the stock cast iron guide a little too easily, which means it would transfer less heat to the head (not a real good thing, at least for exhaust guides). But, following that experiment, I can then install another APE guide and it is still tight.

When I do the same steps with the CycleX guides, the APE guide is a very light press fit after, and the OEM guide can be pushed in by hand. But, even after I removed the CycleX guide, it still took considerable pressure to reinstall it the second time, and it was still hard to remove the 2nd time, meaning it still had good contact with the head.

CycleX also sells "oversized" guides. I once got a set of these by [their] accidental shipping, still have 7 of them. They are intentionally oversized for heads that have suffered many guide changes, I imagine. AKAIK, they are the only folks who [wisely] offer these guides, unless they just happen to fit the SOHC4 engines from some other bike out there? In any event, they make a good repair for oversized holes. It is always possible, if needed, to use these, but it might be smart to turn them down a bit first. I did just this with a set of those when I ordered them for my own head after the machine shop twice changed first Stellite and then bronze APE guides, over-reaming all of them (I'm STILL mad about this!): I turned off about .0008" on average to fit them into the head. It only takes a couple of minutes with emery paper on a lathe to spin them down.

[Nic]

Thanks mark, yeah I remember the debacle you had with the machine shop. I'm sort of feeling that way now that I have to spend a whole heap more on something I "thought" I did right the first time.

[banzaibob]

I guess that this thread took such an interesting turn that it spawned a spin-off. http://forums.sohc4.net/index.php?topic=135107.0

Anyway, I went for a longer more comprehensive ride today and there is good news and bad news.  The bad news is that the spark knock is still there.  The good news is that it manifests itself with a VERY narrow throttle setting, I would say something like: 2500-3500rpm at 17 to 20% throttle.  Basically if you don't want it to knock simply throttle up or down a little more or less.  Another piece of good news is that at highway speeds the F2 cam makes it pull a lot stronger.   

Ambient temps were around 55º.  I imagine that that rattly knock is not going to get any better in higher temps.  However I can't help believe that this isn't a carb issue at this point.  I have to believe that at .047mm aperture, the pilot jets are rich enough.  Especially considering that around town running with very little throttle (25-30mph) there are no issues.  Is there only one throttle slide offer for stock CB750 carbs? I have already shaved about .007" off of the backs of the slides per Ken CycleX suggestion.  There appears to be a very narrow sweet (sour) spot. 

[HondaMan]

I guess that this thread took such an interesting turn that it spawned a spin-off. http://forums.sohc4.net/index.php?topic=135107.0

Anyway, I went for a longer more comprehensive ride today and there is good news and bad news.  The bad news is that the spark knock is still there.  The good news is that it manifests itself with a VERY narrow throttle setting, I would say something like: 2500-3500rpm at 17 to 20% throttle.  Basically if you don't want it to knock simply throttle up or down a little more or less.  Another piece of good news is that at highway speeds the F2 cam makes it pull a lot stronger.   

Ambient temps were around 55º.  I imagine that that rattly knock is not going to get any better in higher temps.  However I can't help believe that this isn't a carb issue at this point.  I have to believe that at .047mm aperture, the pilot jets are rich enough.  Especially considering that around town running with very little throttle (25-30mph) there are no issues.  Is there only one throttle slide offer for stock CB750 carbs? I have already shaved about .007" off of the backs of the slides per Ken CycleX suggestion.  There appears to be a very narrow sweet (sour) spot. 

If you've now changed the slide cutaway...what is your air screw setting? And, while I don't remember at the moment (and am at work, can't go back and read all the posts just now...), are you running pod air filters, or stock airbox?

[banzaibob]

The only changes to the slides were to file of about .007" off of the backs of each slide.  Other than that they are stock.  I am running a stock airbox with the main opening widened a bit.  I am using a Sportster element screen which is bent to shape and fits perfect.  Around that I have stretched some green UNI oiled foam. 

The air screws were all set differently while the engine was warmed up.  It is usually the last thing I do before the final fine tune carb sync.  While its running at the lowest possible idle, I turn each screw in all the way and gradually turn it out until the rpms come up and it runs smoothly.  After a few throttle blips I recheck the sync.  I hold the rpms at about 4000-5000rpm.  If it runs rough (in this case it did) I will adjust the idle stop so that the engine "idles" at 4000rpm.  I then further fine tune the air screws so where it smooths out and runs evenly.  Lowering the idle back down to 1100rpm, I then double check the sync a final time and then I button everything up and go for a spin.  I would guess that the air screws are all set at between 1 1/4 turns out to 2 turns out depending on the cylinder.