Topic: Serial Number on Engine?

[Huskyoff]

I bought a 78 CB750 and the serial number on the engine is 1078289. From what I've seen online, this seems to be an older engine? Am I looking at this correctly? The carbs are from 77-78.

Thanks!

[ekpent]

Right. I think that the engine is a K1 or 1971.

[Huskyoff]

I figured... Anybody see any issues with the carbs running on that engine? Am I going to run into issues?

[754]

Yup.. you are gonna make all the 77/78 Ks look bad with that combo....

[Huskyoff]

Do you guys think it's worth keeping? I was gonna do a cafe racer but, now, kinda want a earlier model anyway. I've been having a hard time getting it to run properly, do you think it's the mismatched engine/carbs could be a factor?

[Johnie]

I bought a 78 CB750 and the serial number on the engine is 1078289. From what I've seen online, this seems to be an older engine? Am I looking at this correctly? The carbs are from 77-78.

Thanks!

Here is some info from Cycle Chaos about the K1 & K7 serial number for you:

The CB750K1 Four was sold from 1970-71 and was available in one of four colors: Candy Ruby Red, Candy Gold, Valley Green Metallic, or Candy Garnet Brown. The gas tank stripe was gold. The tank, side covers, and upper forks were of the basic color (red, gold, green, or brown). The side covers were smaller and there were no slots on the leading edge. There was a two-throttle cable system (pull open and pull closed). The headlight shell was also the basic color. The exhaust system was a 4-into-4. The engine was a 736cc SOHC 2-valve dry sump inline 4 cylinder linked to a 5-speed transmission and chain drive. The serial number began CB750-1044650.

The CB750K'77 Four K was sold in 1977 and was available in one of two colors: Candy Alpha Red or Excel Black. The gas tank stripe was gold with a white and red pinstripe. The "750 FOUR K" side cover emblem was gold. There was a two-throttle cable system (pull open and pull closed). The exhaust system was a 4-into-4. The engine was a 736cc SOHC 2-valve dry sump inline 4 cylinder linked to a 5-speed transmission and chain drive. The serial number began CB750-2700009.

[Don R]

The carbs don't know what year engine they are on. It's more likely a tuning issue.

[GammaFlat]

Getting the "bang" of the accelerator pumps is not a bad thing.  The only downside I can think of is the pressed in idle jets.  They are still removable but not as easy to deal with as the threaded pre-77 version. 

[Huskyoff]

I found a 1970 CB750... do you guys think this is a good choice as far as parts availability? I've been seeing that most sites list parts for 71-75... Are the carb kits and parts harder to find for the 70?

Also, I think he said the build date was late 69 but the year is 1970. Does this make it more desirable?

Thanks for your help!

[754]

The carbs, CLEANED, will work on any year sohc 750, and will give better response.


If it is late 69 the serial # should be around 14,000 or lower, in
that neighborhood.

 The earlier they are the harder (&more pricey)it is the get the right stock stuff.
 

 Where are you located? If you want to trade a 78 F motor on that 71 engine, I may have what you neeed, but I am in Western Canada.

[Don R]

original parts for the 69, 70 and 71's are a bit more pricey. If you are not doing a resto the good thing is there are so many later parts that can be interchanged. That is also the drawback if you want to restore one, after this many years a lot of later parts could already be on the bike. If you are going to cafe, bobber or etc. many of us here would be interested in early original bits and pieces. See the want ads too.

[Huskyoff]

original parts for the 69, 70 and 71's are a bit more pricey. If you are not doing a resto the good thing is there are so many later parts that can be interchanged. That is also the drawback if you want to restore one, after this many years a lot of later parts could already be on the bike. If you are going to cafe, bobber or etc. many of us here would be interested in early original bits and pieces. See the want ads too.

I'm running out to take a look at the 70 right now. I'll report back what I see....

[754]

How did it look?

 What country/state/province/canton... are you in?

[Huskyoff]

It looked pretty good. Good shape anyway. It was a 1970, manufactured in 10/69. Serial numbers were correct. It had some mods, after market 4 into 1, signal modification.  There was not a factory airbox. There was some sort of after market setup that he had in the barn, (never saw it). He said it fired a few months ago, but the carbs are pretty gummed.

I think it looks like a good start. Do you guys have any reservations on that year? How about the airbox, are they easy to get?

I'm in Washington state, east side.

[754]

The airbox is made by an aftermarket maker.

 For sure that is registered as a 70?, that would be Oct. 69. Some states registered by year it was sold, nit sure all Oct bikes would be 70s but could be wrong.


I have a lower end, number 10,170 ish, which I call a 69, I am thinking was made around the 10th month. I like to call it a 69, tho it was likely registered as a70. It will be a bigbore 970cc, or bigger.

Sounds like you are sorts close to here, I live on HWY97 ..90 miles north of the border

 (husky in your name.. gas-n-oil, or dog?)

[Huskyoff]

I'm down in Spokane.

Yeah, it's registered as a 70. The engine looks as if it's never been cracked. It shows 66k on the odometer. I'm going to see if we can get it to fire to make sure it's not a secret lemon. What do you think is a fair price for this if I can get it to fire?

(Huskyoff was a name I found somewhere along the way... I can't quite remember where it came from)