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Offline Exceedbikes

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Exhaust smoke
« on: March 30, 2017, 11:42:25 AM »
I've just bought a 1976 cb750f1 which is really clean. However, it's been standing for months. I charged the battery, put fuel in and it started almost straight away. There is excessive smoke coming from the exhaust. I only ran the bike for a couple of minutes then switched it off so it did not get up to a decent running temperature.  Can anyone advise what the likely cause is.

Many thanks
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Offline flybox1

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Re: Exhaust smoke
« Reply #1 on: March 30, 2017, 02:48:58 PM »
Blue smoke, not dissipating, is burning oil - Run it for a while, might be a stubborn ring or valve seal needing some encouragement.
Keep an eye on it...
Disappearing white smoke is condensation, probably from hibernation.  Keep riding it, and always get it to op temps.
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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Offline ekpent

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Re: Exhaust smoke
« Reply #2 on: March 30, 2017, 03:05:21 PM »
 Fly gave a good description. Just have to get out and ride it under a load for awhile to see whats up. So blue is oil,white is water and if a friend behind says he sees black smoke that's too much fuel.
« Last Edit: March 30, 2017, 03:06:59 PM by ekpent »
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Offline PeWe

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Re: Exhaust smoke
« Reply #3 on: March 31, 2017, 08:57:19 AM »
My bike got very dense smoke when cyl 2 piston got a hole, wrong kind of port tuning :) . I remember it as white greyish in my mirrors. I continued to drive 10km to a friend. This was many years ago.
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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Bodi

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Re: Exhaust smoke
« Reply #4 on: March 31, 2017, 02:51:16 PM »
For storage I shoot a fair bit of 2 stroke oil in each cylinder then kick it over a few times. That makes quite a bit of smoke on first start. Could be something like that?
Definitely warm it up. The smoke will either clear up, or if not whatever the problem is won't cause major damage.
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Offline Don R

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Re: Exhaust smoke
« Reply #5 on: March 31, 2017, 03:29:44 PM »
 Usually, in PO speak months = years. 2 years were at least 5 etc. I agree, ride it and watch for issues. I like to increase the distance from home as I get more familiar with it.
 
 I've seen guys freak out and take their engine apart before giving it a chance to clear up. Checking things is a good idea and as always, the 3,000 mile tune-up.
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Offline Airborne 82nd

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Re: Exhaust smoke
« Reply #6 on: March 31, 2017, 03:33:17 PM »
When I bought my bike it smoked quite a bit from all four cylinders. It had sit for 5 years. It took about 100 to 200 miles for all the rings to settle back down. This was after I pulled the plugs and put some oil in the holes. But it did clean its self out. After I did the 3K and went through the carbs. Give it a little time. This is normal after a older engine that has sat for a while.
All American Every Day All the Way. Airborne
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