Routing fuel lines on DOHC cb750 and engine number.

H

halftide45

New Member
Hi everyone!

I've purchased a (poorly) cafed cb750. All the pieces are there, though ugly, and it just needs to be cleaned up a little to run (or so I believe). I just finished derusting the inside of the tank. I bought new air, fuel, and oil filters, and new fuel lines. My problem is that I can't seem to figure out how to route the fuel lines. I have done a fair amount of maintenance on outboard engines and lawnmowers but I can't even find the input for the carbs! Embarrassing. If anyone could provide a picture that would be amazing. It's a DOHC, not positive on the year because its different than the frame (listed as a 1979 on the reg.). The engine number is as follows: RC01E-2214074.

Thanks for any responses!
 
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the two right carbs are fed by 1 hose . . the two left ones are fed by 1 hose . . the T fitting connects the two hoses and the hose that goes to the tank.

there is likely supposed to be a small clamp on the rear of the engine to hold the 4 overflow tubes.

102286_01_xl.jpg
 
If you can't hook up a fuel line... maybe you need to get some help.

Who ever let those carbs get that nasty most likely has crusty skiders in his shorts...:eek:
 
barnett468 said:
they came off a baja 1000 bike
Click to expand...

From 1974 and still dirty? whats with the trash in the vent... I've been in racing most of my life and never met anyone that would allow that shit to even sit on the bench like that...

Prepared to Baja:
Pre-Race-0412_Norra-Mexican-1000-sidecar.jpg
 
Hi halftide45,
RC01 was the K bike "touring" model and RC04 was the F bike "sport" model. Your engine is out of a 1981 CB750K. Here is a link to work out what year your frame is from and what year your engine is from.
Go to this site www.cb750c.com and you will get all the info you need about your bike.
Here is a link to the technical docs: http://www.cb750c.com/modules.php?name=Forums&file=viewforum&f=5
If you need to do any work on your carbs the fuel system info from the workshop manual (link above) is great but if you are going to service them this is the definitive guide: http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf
Not knowing where you live this may be of some help. The US models had a vacuum operated fuel valve and accelerator pump on carb 2, that is referred to as the "spawn of satin". The European and Australian models did not have this and therefore carb 2 looks different.
You also mentioned it has been mildly/badly cafe'd. I hope for your sake the airbox is still there. If you are running pods on these carbs it will never run as well again and tuning is torturous. These carbs are fickle and need the air box. The amount of shimming, drilling, jet experimenting, needle replacing and blocking of things is just not worth the loss of performance after you take the airbox off.
I hope this has helped you in some way.
 
Tune-A-Fish said:
From 1974 and still dirty? whats with the trash in the vent... I've been in racing most of my life and never met anyone that would allow that shit to even sit on the bench like that...
Click to expand...

It's "Prize" dirt, and they have since been mounted in a beautifully hand crafted, artisan designed display case and prominently displayed in the workshop.
 
I hope for your sake the airbox is still there. If you are running pods on these carbs it will never run as well again and tuning is torturous. These carbs are fickle and need the air box. The amount of shimming, drilling, jet experimenting, needle replacing and blocking of things is just not worth the loss of performance after you take the airbox off.

You just need to find a good carb man...if the airbox was removed, while not ideal, is not the end of the world...
 
Thank you BrosMSU, those are some awesome links. It's amazing how much info there is online about this bike.

The airbox is long gone I believe. I purchased some new pods for it because thats what I saw on there... again, I'm a total novice.

Unfortunately, after attempting to turn the engine over today, I now believe that it's seized. Also, the oil filter bolt is very mangled. I tried heating it with a torch and liberally applying WD40 all day but it didn't budge, it only rounded the bolt further.

Originally when I was maneuvering the bike around the yard I could only push it in neutral, but eventually the clutch seemed to loosen (does that make sense?) and I was able to push it any gear with the clutch engaged. But still it impossible to move the bike when it's in gear. I guess i'm assuming that in fifth gear it should be possible to push the bike a little or a least rock it, is that correct?

So tomorrow i'll put some penetrating oil in the spark plug holes and see if I can free it up.
 
I just read that 50-50 acetone and automatic transmission fluid is a good place to start as an unseizing brew. thoughts?
 
halftide45 said:
I just read that 50-50 acetone and automatic transmission fluid is a good place to start as an unseizing brew. thought?
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yes, or kroil oil, but both can actually take several days to work depending on the severity of the rust.
 
halftide45 said:
I just read that 50-50 acetone and automatic transmission fluid is a good place to start as an unseizing brew. thought?
Click to expand...
if an engine is seized it is seized for a reason, something is rusted stuck or something is jammed. If your a novice the best thing you can do is to do things properly, don't go experimenting with witches brews. Oil is the best thing for your engine.

Download every part of the Workshop manual (WSM) and start reading. Word of wisdom for you as a "newbie" refer to the Workshop Manual for EVERYTHING you do. It will save you a lot of time, money & heartache.
Now, If you cant get the oil plug out then chances are, neither could the previous owner/butcher.
Take the top cover off and have a look inside. Make sure both cam chains are intact. if the main one is broken it can fall down and jam between the crank gear and housing. put a bit of oil on the cams while you are there. NOTE & WARNING: do not over torque/tighten the bolts when you are putting the cover back on.

Pull all the plugs out and see what you can inside, hopefully a nice shine and not rusty. Squirt a bit of WD40 or penetrating oil in if you like. You can leave them out while you try to turn it over. Makes it a bit easier and you can see whats going on.

File some edges on the oil bung or cut a slot to fit a blade screw driver or what ever you need to do to get it out. You will need a new one anyway. Look at the oil for any clues, water, metal, black and old etc. Then fill it back up.

Pull the oil filter off and see what has been caught in that. Oil should spill out so have something to catch it.

When trying to turn the engine over (you wont find anything in the WSM about putting in 5th and pushing) you need to take the generator cover off on the right side (no oil in there) and put a socket or ring spanner (not an adjusting wrench or it will end up like your oil drain plug) and try to turn it CLOCKWISE (you would know that though because you read it in WSM). its ok to move it back a bit to try and free the engine.

The above is certainly not the definitive guide to freeing an engine but its better than pouring two substances in an engine that dont belong there.

If it doesn't move and all the clues gathered from the above process tells you the engine has to come out then you have a decision to make.

If your in the US bikes are cheap and the first rule of buying a bike especially your first bike as a newby is "don't buy a bike that is seized"
OR
Print the WSM out and pull that bike apart and put it back together. You will learn so much in bike education than the $2-300 or so you would get for the bike if you sell it as is.
Good luck on your diagnosis doctor.
 
BrosMSU,

I appreciate your taking the time to school me a little. I think some patience on my part will go a long way with this project. I just downloaded the service manual, is there a separate workshop manual that I should look for?

I have tried some pretty aggressive tactics to unstick the oil filter bolt. Is there anything past heating it and using penetrating oil + force that you suggest I try?

I've already drained the oil and it looked relatively clean save a few small particles and a white streak that appeared after it sat for an hour--so no clear diagnostic on my part. Tomorrow i'll clean up the oil filter bolt and have another crack at it and take a look at the cam chains.


Thank you again!
I knew what I was getting into when I bought the bike, so i'm in for the ride.
 
halftide45 said:
I have tried some pretty aggressive tactics to unstick the oil filter bolt. Is there anything past heating it and using penetrating oil + force that you suggest I try?
Click to expand...

transmission fluid is not witches brew . . it is transmission fluid . . neither it, nor the acetone will harm your engine and neither will the kroil oil.

do not heat the bolt unless you are very brave but heat will not heat the threads .


put a 12" or longer ratchet or breaker bar on the socket and simply turn it.
 
Thanks for the reply Barnett468,

I tried to turn the oil filter bolt already and it rounded over. Do you suggest I just file the edges and try again?


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It's very common for the filter bolt to seize, its not the treads so much as the filter housing its self is seized to the bolt/supply tube. Heating the housing and cooling a few times may break the thing loose.

Here's a quote from SOHC that sums it up: :Get a hex nut with a bore large enough to fit over the remains of the old chewed-up hex (presumably the stock 12mm), then weld the new larger hex nut to the old filter bolt, applying the weld inside the new nut bore. The heat of welding may help break the bond between the filter bolt and th housing, but with the new big hex you'll get it the bolt out"

link to forum: http://forums.sohc4.net/index.php?topic=78089.0
 
halftide45 said:
Thanks for the reply Barnett468,

I tried to turn the oil filter bolt already and it rounded over. Do you suggest I just file the edges and try again?


Sent from my iPhone using Tapatalk
Click to expand...

welding a bolt on as tune a fish suggested will work fine but if you do not have a welder you can file the sides gown to the next size which might be american size . . i dont remember right now . . use a 6 point socket only.

you can also simply drill the bolt head off and buy another . . yes its not ideal, or very pretty, but it will work.

one prob is that you can not get any oil to stay on there to penetrate it.
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I don't have access to a welder unfortunately. Why do you suggest not heating the bolt? Just curious.

Cheers


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