Topic: Can't find engine vin? CB750

[seanbarney41]

Frank, what exhaust did you order?  Most new exhausts nowadays use neither the early or late system.  So if you got the K4 spigots, they would be removed and discarded, but you may not need to obtain the late model split collar set up.

[ChopSticks]

Thanks flybox just to confirm its in the black part of the engine right? Hard to see on my phone

What does the 410 stamp represent?

754 won't be able to confirm the exhaust for a few days

Other than the exhaust and carb boots anything else that I should be aware of prior to looking for parts?

Just curious is the reason why the carb boots are different between the K and F due to the actual carbs? Or has the port distance/location changed from the F head also?

If I were able to find F carb boots would the K carbs fit? Or would I need to ultimately modify them no matter what?

[754]

Clutch may be differet, valves and keepersvif itsan F, and pustons for 77/78 are different. F cam is hotter.
 The difference in intake rubbers is shape,length and the mounting.

[seanbarney41]

this thread is getting kind of useless without pictures...wish I had more

Yes the F3 boots are different because the carbs are different

Port distance/location did not chang between early K and F3, overall diameter of the individual ports is slightly bigger

Early K carbs will NOT fit F3 carb boots nor will F3 carbs fit early K boots.

[ChopSticks]

Alright alright, I completely agree I'll go take pictures now, it's a little troop from where I am currently staying, just so I don't miss anything what exactly should I take a picture of? it's not stored in an electric available garage so I'll try my best with lighting

so far I need to take a picture of the 410 top view engine head and exhaust set up, anything else?

Also should I stop using the manual that I downloaded from the site? the general information / technical date only goes up to K4

[seanbarney41]

the picture you posted is good enough.  I can see that you do indeed have K1-K6 carbs mounted on what really really looks like an F2/3 engine.  So, when you get your new boots, just compare them to what is on there so you will kno what needs to be done to make them fit.  I can also see that the exhaust that is on the bike now uses the F2/3 style split collars.  Unlikely that any new exhaust you buy will use these, but that is not a problem.  Just use what the exhaust supplier supplies.

I was wanting to show YOU pictures of all the different parts we have been talking about.

The next question...did the po that installed the F3 in the K4 frame get the chain line right?

[ChopSticks]

Ouch gotcha yeah pictures would be amazing, I'm def more of a visual learner

Not sure if the old boots will tell me how to make them fit, one was really badly ripped, actually now kind of makes sense why it was

http://forums.sohc4.net/index.php/topic,154841.msg1772239.html#msg1772239

I would only really need a new exhaust if there are currently leaks right? Is there any sure way to check? Similar to spraying starter fluid on the intake side?

How can I check if the chain line right?

[seanbarney41]

straight edge against both sprockets should sit nice and flat...

if there are problems here, there are relatively easy fixes for this too

[ChopSticks]

Just so I'm clear, like this?



The red line would be something solid and straight like a ruler? if the rear sprocket/wheel is from a K would it be completely obvious with this test? or could my alignment just be off from the rear axle set up?

would the fix be changing the sprocket or simply spacers?

[seanbarney41]

your drawing is exactly correct, it should be pretty obvious, but do make sure your axle adjusters are the same side to side...you would probably even be able to just eyeball any mis-alignment by sighting along the chain

...so what happened is in 1977 honda put a double row countershaft bearing in, which moved the front sprocket outboard 10mm

To correct the problem of having a 77/78 engine in a 74 frame you will need the rear sprocket carrier from a 77/78 cb750 f or k and I can't remember what you end up doing for wheel spacers.  It is posted somewhere on this site.

or buy a 10mm offset rear sprocket from Cyclex

[ChopSticks]

Alright, I'll put that on my list next time I get to the bike. This might be a long shot but if the rear sprocket is off 10mm could I just use washers as a spacer between the sprocket and hub? (I'd also get longer bolts to make up for the spacers)

[ChopSticks]

Any idea what this hole is on the intake side between 2 & 3 valve tappet covers? The blue stuff is just painters tape on the carbs holes

[flybox1]

head vapor vent.
route a new tube on it, or add a small filter so no debris gets in.

[ChopSticks]

Okay, nothing was original connected or at least I don't remember taking anything off, any idea the diameter of the opening? 5.6mm? Should I just tuck the tube down similar to the carb vent/overflow tubes? Or should it be connected to something else?

[flybox1]

Okay, nothing was original connected or at least I don't remember taking anything off, any idea the diameter of the opening? 5.6mm? Should I just tuck the tube down similar to the carb vent/overflow tubes? Or should it be connected to something else?

I dont know the routing on earlier K bikes.
For the later F and K's, there is a collector/separator under the battery box the hose attaches to, and then is routed to the ground.
google image search "CB750 breather filter" and you'll see plenty ideas
Moisture will condense once the vapor cools, so if you fashion something yourself, you'll want a place for the vapor to collect, which you can empty on service intervals.  The remaining gasses can and should be plumbed back into the airbox.

[seanbarney41]

Alright, I'll put that on my list next time I get to the bike. This might be a long shot but if the rear sprocket is off 10mm could I just use washers as a spacer between the sprocket and hub? (I'd also get longer bolts to make up for the spacers)

theoretically, that could work...in reality I don't think the nuts would thread on all the way and that could be a safety issue...and I don't know how those bolts come out of the sprocket carrier

[ChopSticks]

I dont know the routing on earlier K bikes.
For the later F and K's, there is a collector/separator under the battery box the hose attaches to, and then is routed to the ground.
google image search "CB750 breather filter" and you'll see plenty ideas
Moisture will condense once the vapor cools, so if you fashion something yourself, you'll want a place for the vapor to collect, which you can empty on service intervals.  The remaining gasses can and should be plumbed back into the airbox.

Any pic of the collector/separator? From the parts list I see the tube I'm the head cyclinder cover but can't find what it leads to, and I googled the breather filter which just looks like a baby air filter. What exactly is the purposes of this? Will it work even tho there's no collector/separator?

[flybox1]

The collector/separator was a device used to meet EPA pollution standards. 
It wasnt used on every one of these bikes. It wasnt used on your K4.
Just run your tube down to the ground.

It looks like this, though. 
3 tubes:
IN @top (vapor) from the head
OUT @side (gasses) back to the airbox
OUT(red)@bottom (moisture) down to the ground