Topic: Won't stop smoking

[Kaman]

I am at the end of my sanity with my cb guys.   this is the first bike I ever bought and admittedly mistakes were made first by buying this bike and secondly while working on this bike myself. With little to go on but some YouTube videos and a handful of tools I had no choice but to do it myself because after the puchase of my 1976 cb750f I was told it would cost 2,600.00 to fix. Long story short and 3 years later I have a total of 23 miles ridden on this bike. Here is my question. What would cause the bike to smoke little to none when the choke is on then as soon as I turn the choke off it begins to pour smoke out of the exhaust. I can't tell if the smoke is blue at all it appears to be white however this bike has no radiator and with how dry Arizona weather is always especially now during the summer I doubt it's condensation. Please any advice is much appreciated thanks all. I'm so tired of working on this bike I just want to enjoy riding it for a change

[DaveBarbier]

How are you operating the choke? It would not be the first time someone shuts the choke off thinking they're engaging it and vice versa.

Have you performed compression or leak down tests?


Did the shop that quoted you $2,600 give you a diagnosis?

[madmtnmotors]

What part of AZ? We have some very knowledgeable members out that way. What "work" have you done so far?

We like pictures too!

[CycleRanger]

Howdy! Welcome!
You should have come here sooner. 
Let us know what the shop said would cost so much to fix and what you've done so far.
You can download a shop manual here:
http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual

Don't worry, they're in english.

[Bodi]

What work did you do?
The choke doesn't do much, moves the vacuum out in the carb at low throttle to suck in more fuel... just richens the mixture a lot.
Probably oil smoke? Upside down rings or loose valveguides usually the cause.

[Kaman]

Hi guys thank u so much for a speedy and kind response. The shop that gave the quote was Steve's cycle and the only thing they said was it had no compression in cylindars 1 and 2 and the battery didn't recharge. Now I found out that it was a blown head gasket and it was blown between pistons one and two. Now after fixing that I had carb problems and electrical issues from day one this was all compounded by my lack of knowlage on the topic. Also I had an exhaust valve snap off inside the cylinder . It went through the piston and seriously dented the heads. I have since bought new heads pistons valves springs and gaskets. The pistons came with new rings. Also I should mention that the heads I used to replace the bad ones were used. I don't know why the carb choke would matter in the smoking I just know that the second I flip the lever down or choke off it starts smoking. Could the valves guides be the cause of the leak     

[Kaman]

I just read a part of your message that I didn't see about the valve guides . So that's what I was thinking. I'm positive I put he rings in the proper order thanks I'll see what I can do with this info

[calj737]

The comment about the choke is perhaps you're operating it backwards. Can you take a clear picture of the carbs, choke side so we can verify you're moving the lever in the correct direction?

[Kaman]

As soon a possible I will take the pic. I have the the air filters off and I can litteraly see the choke come up and down . Lever down choke is off lever up choke is on

[PeWe]

When my bike blew hole in a piston many years ago it smoked a lot, white smoke.
You have to be your own mechanic except machine jobs. Just pull the engine and lift the head and you'll see. Compression test with a cheap compression gauge.

[Don R]

  How many miles on the new rings, did you hone the cylinder between ring jobs, does is smoke so bad you can't just ride it and rack up a few miles to see if it calms down?

[HondaMan]

Hi guys thank u so much for a speedy and kind response. The shop that gave the quote was Steve's cycle and the only thing they said was it had no compression in cylindars 1 and 2 and the battery didn't recharge. Now I found out that it was a blown head gasket and it was blown between pistons one and two. Now after fixing that I had carb problems and electrical issues from day one this was all compounded by my lack of knowlage on the topic. Also I had an exhaust valve snap off inside the cylinder . It went through the piston and seriously dented the heads. I have since bought new heads pistons valves springs and gaskets. The pistons came with new rings. Also I should mention that the heads I used to replace the bad ones were used. I don't know why the carb choke would matter in the smoking I just know that the second I flip the lever down or choke off it starts smoking. Could the valves guides be the cause of the leak     

Yes. Almost all of the CB750 heads I see today have worn (or fully worn-out) valve guides, particularly if they were for sale separately from their engine.

Here's another item: taking a set of cylinders and dropping in a different set of pistons will always (ALWAYS) cause oil to leak past the rings. They must be mated together, from the get-go, by boring them to match the (oversized) pistons, and new parts installed. Engine's internals are not quite like replacement parts on other parts of the machine (like car brakes, sparkplugs, or the like). In truth, I have never seen a set of pistons from an engine get put into another engine without full machine work, and seen them work. Usually they will not even generate much, if any compression. :/