Topic: "Beater" .. 77 CB750F2 .. The engine is now apart

[hashvm]

Hey all 

so after finishing (almost) my CB550 project I couldn't just resist getting a new toy to get my wrenches working again 

Yesterday I picked this guy for $650. Its a 1977 CB750F, the one with the black engine. here are a couple of pictures









I know it has a lot of work to be done to it, but the idea is to get it running and (hopefully) ride it sometime this summer.

I did a quick compression test on it as well (cold one since it doesn't run currently) and the numbers came out to be: 110,100,108,98 ( I know this sounds really low)

a little about this bike:
It hasn't ran in a long time (seller says around 10 years)
the head gaskets are worn out (could this be the reason for the low compression?)

The plan for today is to get it hooked to a battery, put some fuel in it, and try to fire it up

- Hashem

[calj737]

Be careful with that headlight rats nest loose and unconnected when you fire it up. There will be live wires very near loose grounds, and shorts are very possible. Best to quickly tape off all the ends unnecessary to fire the bike.

I wouldn't worry a bit about the compression numbers. Easily attributed to a bike that's sat, cold motor, possible obstructed carbs/air intakes. Drizzle some penetrating oil through the plug holes into the cylinders while you work on the rats nest.

[SOHC4 Cafe Racer Fan]

Pretty good deal.

Clean out your gas tank, petcock and fuel lines first if that's going to be your fuel source for this fire up.

[hashvm]

Be careful with that headlight rats nest loose and unconnected when you fire it up. There will be live wires very near loose grounds, and shorts are very possible. Best to quickly tape off all the ends unnecessary to fire the bike.

I wouldn't worry a bit about the compression numbers. Easily attributed to a bike that's sat, cold motor, possible obstructed carbs/air intakes. Drizzle some penetrating oil through the plug holes into the cylinders while you work on the rats nest.

Thanks for the advice cal, I'll differently tape off every connector

I was really questioning the numbers on the compression gauge but again I don't have much experience with the 750s 

[hashvm]

Pretty good deal.

Clean out your gas tank, petcock and fuel lines first if that's going to be your fuel source for this fire up.

Thanks, any advice for cleaning the tank of surface rust?

[hashvm]

So I wanted to fire the thing but ... one of the throttle cables is actually cut so I'll need to get a new one first.

Went on to look to the next thing ...



opened a couple of body bodies and they actually seem clean! I guess maybe the PO cleaned it but didn't get the chance to fire it?

took this guy apart as well



Ugh, this is gonna get cleaned, and I'm also getting some new rubber boots for it

That's it for today .. oh by the way, do you guys know what part of the wiring harness is this?



-Hashem

[Bankerdanny]

That filter looks like it was never replace from new.

I and a lot of members here used The Works toilet bowl cleaner to clean the inside of the tank. It's very cheap and available at most hardware stores and Home Depots.

A search of the site should turn up several threads on the process. Make sure to carefully tape off around the filler opening and the petcock as it was damage your paint (I speak from experience).

[hashvm]

That filter looks like it was never replace from new.

I and a lot of members here used The Works toilet bowl cleaner to clean the inside of the tank. It's very cheap and available at most hardware stores and Home Depots.

A search of the site should turn up several threads on the process. Make sure to carefully tape off around the filler opening and the petcock as it was damage your paint (I speak from experience).

Thanks Danny,
I'm planning on using the works method as mentioned .. I'll post pictures of the after 

[70CB750]

Following, good luck 

[02z06dave]

That wiring harness part looks like it's for a windjammer. Probably why it doesn't have a headlight on it.

[hashvm]

That wiring harness part looks like it's for a windjammer. Probably why it doesn't have a headlight on it.

Good call .. I haven't thought of that

[hashvm]

So yesterday I was bored waiting for my throttle cables to arrive, I decided to check if the the harness and electric starter are working ..

hooked up the battery .. and ....





Tried to start it (just to see if the starter works) and at the first button touch ..

That got me like .. 

However as you can hear there is this whisling sound ..

sounds like a non-lubricated moving part to me .. a chain maybe?

I just got the cables in today but I wanted to hear your opinion on this sound first before trying a real fire up ..

-Hashem

[seanbarney41]

Last time I heard that sound I ignored it.  Got the bike started, tuned, rode it for about a mile...and in that small amount of running destroyed the camshaft, cam journals, and all of the rockers...it was nearly the exact same bike too, a cb750f3.  Try lubing the cam through the inspection caps before turning it over again and see if the noise stops.  Even if the noise does stop, make sure you have oil being supplied to the cam and rockers before running the engine.  Oil pressure alone proves nothing.

I eventually replaced the cam, towers, and rockers and the bike has been fine for 12,000 miles or so.
Project thread here...
http://forums.sohc4.net/index.php/topic,133916.msg1502254.html#msg1502254

[hashvm]

Last time I heard that sound I ignored it.  Got the bike started, tuned, rode it for about a mile...and in that small amount of running destroyed the camshaft, cam journals, and all of the rockers...it was nearly the exact same bike too, a cb750f3.  Try lubing the cam through the inspection caps before turning it over again and see if the noise stops.  Even if the noise does stop, make sure you have oil being supplied to the cam and rockers before running the engine.  Oil pressure alone proves nothing.

I eventually replaced the cam, towers, and rockers and the bike has been fine for 12,000 miles or so.
Project thread here...
http://forums.sohc4.net/index.php/topic,133916.msg1502254.html#msg1502254

Oh man you have no idea how grateful I am that I didn't get a chance to try it last night 

One other thing tho, how do you connect the two push-pull throttle cables? I looked into it last night but it didn't make since compared to the ones on my CB550

[seanbarney41]

...cables kinda loop around to the back of the bellcrank, iirc, when you twist the throttle the throttle shaft turns the opposite direction of the 550?  ...hard to remember, I used early carbs on my F3

[hashvm]

So last week I tried to start the 750 but with no luck

It starts with a try to clean the tank using the works method to get to this result ..



However, 10 minutes later .. the tank got orange-ish although I was very careful and used acetone to get all the water out 

I got the tank on the bike .. connected the carbs .. and tried to fire it (without the air filter)

the good news: The whistle sound I heard in the video in my previous reply was due to mask tape I put on the intake .. some the cam is safe! 

the bad news: I tried to fire the bike after connecting the fuel lines to the carbs .. but it didn't work 

It seemed that whenever I pull the throttle, the carbs do not deliver fuel to the intake .. I looked through the carbs and the little jets infront of the choke plate (I think that's part of the accelerator pump?) don't spit fuel like they should .. sound like a cleaning problem?

well, I checked .. I opened the carbs one by one .. starting with carb body one to see this ..



look at the floats pin holders!! one turned out to be broken! 

checked the jet on that one .. and



Hmmmm ..

I checked the other ones but they were all clean and good ..

I really don't know what was the cause of not delivering fuel ??

I'm totally lost at this point .. could it be a timing issue?

- Hashem

[hashvm]

Can someone explain to me how these those engines suck fuel off the carbs?

I spent hours trying to think about the cause of this but got nothing.

Could it be that I wasn't connecting the air filter or any pods on the other side?

In the meantime I think I will look for new intake boots and probably some pods to try to get this figured out.

One other thing I remembered is that when I filled the carbs with fuel, carb #2 (the one connected to the fuel line coming from the tank) was dripping from the venting pin bellow, which made me think that it was overfloating without providing gas to the other carb bodies. But when I check the other ones they all had gas 

[seanbarney41]

Your gonna have to totally rebuild those carbs.  They are filthy.

[flybox1]

Your gonna have to totally rebuild those carbs.  They are filthy.

Amen to that!
Just look inside that main jet tower.     Isht is growing in there!
You'll need to pull the slides, polish the needles, remove the needle jet, and clean the inside of the tower.
All the corrosion on the emulsion tube you are holding is on the inside of its holder. 
Pilot jets will need to be removed and treated the same, along with A/F screws.  Carb cleaner spray thru everything.

[hashvm]

Your gonna have to totally rebuild those carbs.  They are filthy.

Your gonna have to totally rebuild those carbs.  They are filthy.

Amen to that!
Just look inside that main jet tower.     Isht is growing in there!
You'll need to pull the slides, polish the needles, remove the needle jet, and clean the inside of the tower.
All the corrosion on the emulsion tube you are holding is on the inside of its holder. 
Pilot jets will need to be removed and treated the same, along with A/F screws.  Carb cleaner spray thru everything.

Thanks guys for the help .. I started pulling the carbs apart last night but got stuck pretty quicly

I was able to get these two guys no problem



But what about these two? do they come off as well? Because I looked in the manual and it shows an older carbs anatomy + I know that on some of the later models some parts were fixed there (i think the needle is on the 1978 models)

The ones I mean is the needle valve seat and the other brass jet



Also, have any of you guys use the keyster kits for these before? Or is there any better kits?

Thanks again and sorry for the many questions

- Hashem

[seanbarney41]

Needle jet can be pressed out with a piece of wood once theslide is removed.  All aftermarket kits are garbage.  Clean your brass or oem keihin only...rubber and gaskets from honda

[martin99]

That tube (pilot) is pressed in. Hold the carb body firm and give the tube a firm pull with grips, a little twist as you do so and it will come out. You can use something to protect the outside of the tube from the grips, but a small amount of damage here doesn't affect the bike. I've applied a little localised heat before which can help if they're really stubborn. Don't be tempted to skip this step, cleaning those tubes was the one thing that made a night and day difference to the tickover on my F2.

Personally I've never replaced the needle valve seats on these carbs. The needles are (should) be viton-tipped. If there is no visible wear on the seats you will probably be fine with new needles. As has been said, beware non-genuine stuff.

[hashvm]

It's been a while since I posted here
I had to travel to Colorado to attend Pikes Peak International Hill Climb for the first time and man that was a nice experience!

Back to the CB750 ..

First things first .. 2 of the cylinders weren't getting a spark ..

I checked the coils and caps and they were all okay ..

So I went and got a new points plate after discovering that the points for cylinders 2&3 has a carbon layer on top! 



Hooked it up, checked it and it was all good

next was cleaning the slow jets .. it was a ***** to get out



took a look at the tank but the cleaning trial didn't go so well 



So .. I made a temporary one 



I also got some pods just until I get everything sorted out



Then it was the moment of truth



I tried and tried that night but without a result .. it started for about 5 seconds only 

woke up the next morning and I was feeling good .. checked everything again and it I found that I can raise the choke lever a little more with my finger

then .. boom It fires!

It's so lean though still and I'm suspecting a vacuum leak

It only run on full choke and full throttle .. and dies right after I let go

But for being in rest for more than 10 years without running .. I'm kinda satisfied

- Hashem

[Gene]

Get your makeshift tank above the engine - you may find you have better luck.

[hashvm]

Get your makeshift tank above the engine - you may find you have better luck.

Overflow cause the carbs to start leaking