Topic: '78 CB750 Project

[sethmcalister]

Little more work today. Wiring harness is out, airbox and carbs are off and oil is drained. Some more pictures too.

Not sure if I had a leak of some sort, see picture 1.

Pictures 3 and 4, 3 had a screw hole buy nothing was in it and picture 4 has two holes thru the lower triple...does anybody know what the holes are for or night have been for?

No fuel in the float bowls, but as you can see there was some dirt. 

Also, oil looked pretty clean when I drained it. Doubt it was run thru for very long.

Motor says 750E, anything of value with that?

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[sethmcalister]

The welds are not normal. Don't know why they are there.

The cb750f on the airbox is normal. They all say that.

Why do you want to cut the frame? Do you have a need to do it? And by need I mean did you get a seat and figure out that the frame rails are in the way? Or are you just cutting it because you saw it on the Internet and think that is the thing to do. You shouldn't be cutting anything without all the parts in hand and a measured twice. Once it's cut you can't go back, so make sure you have everything figured out.

They had a humongous front fairing on and I know that it was welded on, but dang those are some ugly welds. 

The original seat pan I have has seen better days so it will need to have a little cancer cut off.  Once I cut that off, the end of the frame will stick out.  No cutting until I'm ready anyway!

[sethmcalister]

Regarding your frame: the welds on the down tubes of the cage are not factory, and likely as you suspect from a fairing being mounted. Obviously the rust needs to be dealt with. If you undertake grinding the weld-globs off, do take the next step and re-weld that sleeve. Those sleeves were fine if left unmolested, but there is a good deal of rust as a result of the attachments there, and I'd go the measure of repairing that weld for surety's sake.

Once around the bottom, then up the sleeve on the exhaust side. This will restore all the integrity unless you discover some actual tube rot as you prep for the welds.

The good old seat gusset: if I understood your post correctly, you want to "bob" the seat hoop as far forward as the shock mount? If you do this, replace the cross brace (seat gusset) with some flat stock or square tubing, welded back into the frame at the shock mounts. This serves 2 purposes: lateral rigidity of keeping the frame (under good deal of stress at the shock mounts) in tandem, and will prevent the frame from being "splayed" from seat/rider weight.

There have been many who cut and do not replace this gusset, but it is not prudent. Obviously, check for tire/fender clearance with rider weight and suspension travel to determine where to weld the gusset back.

Apologies for the lengthy post- by the way, nice looking project to start. You live in some damn pretty country up there and were it not for the frickin' winters and black flies, I'd be jealous 

That's great, thank you!  I wouldn't have thought to re-weld the sleeve.  I had planned on using the grab bar to make a seat hoop.  Shouldn't be any need to weld in an additional bracket, right?  Living on the seacoast, I feel that the winters are much milder than where I grew up (about 2 hours north of here).  But yes, the black flies can be nasty.

[sethmcalister]

Many young men now are weak and cannot pull in a clutch lever because they have grown up pushing buttons on a computer and have not done hard work to build up muscles.

Many modern bikes have a hydraulic clutch for this reason.
Often it is not even needed.

But make sure the clutch cable is in good condition and lubricated.

Thanks, lucky.  Those years of division 1 wrestling and jiu jitsu must not have done much for my grip strength...haha!  When pulling the clutch cable out today, the spring tension was pretty heavy - I'm guessing that has a lot to do with it.

Always up for a good laugh so I appreciate the dig!

[sethmcalister]

One other question...on reply #21 (first page), picture # 4, what is that thing?  Is it some sort of vacuum - what does it do?  Is there a way that I can remove it or reduce it's size and move it?

[sethmcalister]

Yeah I've seen the Hondaman book and plan on grabbing one next paycheck. So there was a grab bar that came with the bike. I plan on cutting and welding it up as seat hoop for the back when I cut the end of the frame off.

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[sethmcalister]

Made a little progress. Looking for some help now though fellas. Pulled the carbs apart as best as I could figure out. 1 and 2 are together and separated from 3 and 4. Can't figure out to pull 1 and 2 and 3 and 4 apart though. The manual I downloaded from the site doesn't appear to apply to the PD carbs.

I didn't have a small enough guitar string but everything seems to be clean. All the jets squirted carb cleaner thru no problem. I don't know how to test the accelerator pump though to see if that will squirt cleaner thru it...any words of wisdom flybox?

The carb bodies are pretty dirty so I'm going to grab so.e of the cleaner dip and let them sit for a day to clean em up all purty.  I think the gaskets would have been reuasable bit since they had gasket sealer I'll replace them to be safe.  Do you guys use the gasket sealer or do you recommend just the gasket?

I want to get this right the first time so any advice will be greatly appreciated. Thanks in advance guys.

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[sethmcalister]

While cleaning my carbs last night, a couple of the washers came out of where the pilot jet/needle goes.  What's the order for the o-ring and washer?  I would think that the o-ring goes first, then the washer, then the pilot jet/needle.  Can somebody confirm? 

In this thread, http://forums.sohc4.net/index.php?topic=48858.0, post # 22 Tugboat says that the bung can be pressed out.  Is he referring to the brass piece above and to the right of the screw hole?  I can't see how I would ever be able to get a pair of pliers onto that bung as it's seated below the hole.  Perhaps I'm looking at the wrong bung?

Also, in this thread, http://forums.sohc4.net/index.php?topic=136153.0, post # 5, flybox mentions the accel pump nozzles.  He says to spray carb cleaner through and watch it come out the nozzles, but I'm not sure how to spray through (unless he's meaning the tube should be removed from the carbs)?  Also, I don't appear to have the brass inserts.  It looks like one of the hoses has one or two (I haven't tried to stuff a screwdriver through the hoses as I didn't want to ruin the brass inserts if they were in there), but the others don't appear to have any of the inserts. 

Flybox goes on to say that if missing, I can get some brass hobby tube in 3/16" OD, cut at various lengths.  I'm not sure what hobby tube is?  How should they be cut to length?

[mcswny]

You can also get  rear hoop from the forum as well

http://forums.sohc4.net/index.php?topic=120877.0

[flybox1]

if you remove the tubes between the carbs(clear in the above photo) you can spray carb  cleaner into the barbs that the tubes attach to, and clear out the nozzles.  wear safety glasses, carb cleaner stings the eyes

I used 3/16" brass hobby tube.   harisuluv says OEM is 4mm OD/2mm ID
The stuff is easily found online for a few bucks.  Saw or dremel cut and ends cleaned up.
you'll need the following lengths 2 pieces  @ 350" and 4 pieces @ 450"
2 of the .450" pieces go between carbs 2&3
One each of .350" and .450" go between the outer carbs.

[sethmcalister]

Thanks, Fly - will you see my previous post from last night and throw some words of wisdom at me?

[sethmcalister]

Carbs are cleaned and almost back together.  The manual I pulled form the forum, however, isn't for my PD carbs.  What are the stock settings?  If I haven't changed anything on the main jet, floats, do I still need to sync and measure the float height?  If so, how do I go about accomplishing that?

[flybox1]

yes, you should verify float height.  14.5mm which happens to be equal to the top of the pilot jets.
you should complete a bench sync, and then plan on doing a vacuum sync when all else has been completed and the bike has been warmed up...

[sethmcalister]

I've made quite a bit of progress, apologies for no updates. Carbs are cleaned and the bike has started and gone for one small (slow and brakeless) jaunt around my neighborhood.  Carb #2 is leaking so I need to pull the float bowl off and check that the gasket seated properly. Front and rear blinkers are on, headlight bucket is in, buy I didn't realize until I ordered a headlight that it didn't have the retainer so I'm trying to track one down that fits. 

The bucket is off a 78 750F.  I'll need to wire in the plug for that and the rear brake/tail and blinkers. There are a coupla things I'll be looking to you all for as far as, what is this, where does it go haha.  Seat has been re-foamed and waiting on a temporary cover.

While my tank is with the body guy, I three on a tank my cousin found for me st a flea market for $12. I believe it came from a 550, but it doesn't fit the frame rails. I really like the look of it over the 78 tank though so I may try to widen the tunnel and run that. Plenty more to do, but I'm getting closer.

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[sethmcalister]

Little bit closer.  VIN verification completed last week.  Headlight retaining and mounting ring came in.  I need to wire up the plug and put my headlight in.  Will be rebuilding my front caliper tonight I hope.  Need to wire the front and rear blinkers and bleed my brakes.

Then it's the front fork seals, attaching my seat since the PO cut the mounts off and I should be good.  Here's where it's at right now.  The tank that's on there is from a 550 I believe so it doesn't fit.  I'd like to make the tunnel wider so it will fit since I'm still waiting on my tank from the body guy, progress picture for that too.

[sethmcalister]

More Pictures

[lucky]

Look on the right end of your carb bank, on the seam, right above the bowl....there should be a stamp.    PDXXXXX
that'll be the carb model #
PD42B and PD41A's are common for the 77/78 CB's

1977=PD41A
1978=PD42B

The 1977 carbs have adjustable slide needles.
The 1978's do not.

I would not take the carb rack all apart. Just remove the float bowls and clean.
Remove the idle jet and clean till you can see daylight through it.
Put in 4 new float needles. NEW.
Set the float height according to the Clymers' manual or other workshop manual.
Put the float bowls back on.

[sethmcalister]

Hey Lucky,

I've already pulled the carbs out, apart, apart again and put them back together and back on the bike.  It has run, just not for very long yet since the stand-in tank doesn't fit the frame. 

[sethmcalister]

Are there any tricks to getting the cylinder out of the brake caliper when it's completely stuck?

Also, with led blinkers, how do I wire or hook in the electronic three pouring relay? I can wire, but I don't always understand it.

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[sethmcalister]

You were right, grease gun worked like a charm!  Will be putting a new cylinder in tonight - didn't come with a new seal though, should that be a problem?  Old seal isn't hardened at all.

[sethmcalister]

Okay, I was just going to use some silicone sealing grease for the backs of the pads and some brake fluid for the cylinder, but I'll take your advice.

[sethmcalister]

Caliper has been rebuilt and front brake is bled. Front forks were rebuilt today. Working is mostly fixed... there are still two small problems.

The blinkers only flash before full click on the switch. Once I hit full switch they just stay on. Second problem is the front so switch. Before the button is depressed the brake light is on, once the button is depressed the brake light shuts off and only the taillight is engaged. The mount for the front stop switch is broken so I'll need to pick up a double banjo with the pressure switch. Hopefully that will solve that issue.

Tank is done but is going to be sealed Wednesday night.

I don't have a good method for mounting my seat aside from wire tires since the PO cut the hinges and lock off.

Motor mounts need to be tightened and mirror reinstalled.

Think that's it.

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[sethmcalister]

I had to order a pressure front brake switch from vintage cb750 which took care of my front brake.

The blinkers haven't been fixed but they blink so I'll leave them as is for now.

Headlight high beam doesn't work now which I believe is because of trying to stuff the wires into the headlight bucket.

Motor mounts are in and tight.

Hit the tank with the first coat of matte clear.  Gotta hit it with another couple coats and throw the mirror in. Forgot the petcock on the 550 tank I gave my body guy.

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[sethmcalister]

Well I thought I was ready to go tonight.....and another roadblock.  The gasket in the petcock was jink so I wasn't getting fuel to the carbs.  Then I realized I put the fuel line on the breather nipple instead of the fuel nipple.

I finally got it to run...but fuel flows out of the #4 carb overflow tube and the exhaust on #3 and #4 aren't getting hot. I'm pretty sure I have a small exhaust leak on #4 but am not sure if that is adding to the problem.  I ran out of daylight so Saturday I will check spark on all four. Make sure they're getting fuel and if so I'm not sure what to check after that. If they're not all getting fuel I'll have to pull the carbs again and reclean and more than likely replace all the jets and internals.

Thought I was so close and now I'm just super discouraged.

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[Ravie]

If you are going to ditch that cafe seat I would love to take it off your hands. Let me know.