Topic: Senior project for high school - 78 CB750K

[madmtnmotors]

Yup, you're dead right, as usual Wilbur. Thanks for pointing that out.

Not always! You're pretty sharp cal, so I had to double and triple check my logic. Electrical can be maddening!

[Restoration Fan]

So hook up that spare coil and start that puppy! 

I'm going to definitely do that tomorrow.  Logan is going to bed now to get ready for his AP Calculus final tomorrow.  When he gets home tomorrow, he and I will swap the coils and try to fire it up.

I do have another question though regarding carbs.  The 2 connections shown on the carbs from above are on carb #2.  The one with the rubber lines between them is where we've been connecting the fuel line.  But what connects to that other connection?

[seanbarney41]

no  wonder the carbs overflow! top nipple is bowl vent, bottom is fuel inlet...PD carb guys please double check and confirm this post.

[sethmcalister]

That is correct, I've made that mistake myself already!

Sent from my A0001 using Tapatalk

[danyo]

^^^ correct Sean. Black rubber connections are vents. Aluminum with orings - fuel line. I hope after that online ignition surgery patient (Stella) tomorrow will start new life !!! Good luck guys.

[Restoration Fan]

no  wonder the carbs overflow! top nipple is bowl vent, bottom is fuel inlet...PD carb guys please double check and confirm this post.

Should there be any kind of rubber hose on the bowl vent or just left open like that?

[seanbarney41]

no  wonder the carbs overflow! top nipple is bowl vent, bottom is fuel inlet...PD carb guys please double check and confirm this post.

Should there be any kind of rubber hose on it or just left open like that?

generally yes, I have never had any success with the PD carbs and don't know as much.  Earlier carbs have about 18" of hose attached to the vent nipple, looped over the airbox, left open to atmosphere at the other end.  Bike should run and idle ok without vent tubes, but some have reported problems at speed with no hose or even incorrect length hose, caused by air drafts.  Hondaman claims performance gain by drilling airbox and inserting vent tubes, although other experts disagreed strongly and I have heard of no one confirming benefits.

[Restoration Fan]

Thank you, sean!  I'll ask Bill Benton the next time I see him (hopefully tomorrow or day after) if he knows what the usual size line was on there.  It won't be something to keep me from trying to get the bike started but I'd like to have it set up properly when it's ready to ride. 

[seanbarney41]

I think anything in the ballpark as far as length and diameter should be fine.  I have been fortunate to always have what was on there oem, so have never needed to experiment.  If you have trouble finding exact dimensions, I have a couple racks of PD's I could dig out and check.

[Bill/BentON Racing]

Wow, y'all been busy. I told you all this is in the manual! Haha.Lol I'll be home tonight if needed, Bill

[martin_uk]

Thank you, sean!  I'll ask Bill Benton the next time I see him (hopefully tomorrow or day after) if he knows what the usual size line was on there.  It won't be something to keep me from trying to get the bike started but I'd like to have it set up properly when it's ready to ride.

Fuel feed is to tube connected to metal joiners with O rings.

Vent connects to other connector and runs over top of air cleaner, not sure of original, but run mine down to same point as overflows.


I used 3.7mm on the overflow pipes which feed down through a special guide plate 2015_0215engine0008 by nitram2010, on Flickr at rear of crank case and through wire guide at centre stand clamp.

2015_0418eng0010 by nitram2010, on Flickr

[Maurice]

Thank you, sean!  I'll ask Bill Benton the next time I see him (hopefully tomorrow or day after) if he knows what the usual size line was on there.  It won't be something to keep me from trying to get the bike started but I'd like to have it set up properly when it's ready to ride.

Fuel feed is to tube connected to metal joiners with O rings.

Vent connects to other connector and runs over top of air cleaner, not sure of original, but run mine down to same point as overflows.


I used 3.7mm on the overflow pipes which feed down through a special guide plate 2015_0215engine0008 by nitram2010, on Flickr at rear of crank case and through wire guide at centre stand clamp.

2015_0418eng0010 by nitram2010, on Flickr

Hold on, isn't that vent supposed to go to the oil tank??

[evanphi]

Thank you, sean!  I'll ask Bill Benton the next time I see him (hopefully tomorrow or day after) if he knows what the usual size line was on there.  It won't be something to keep me from trying to get the bike started but I'd like to have it set up properly when it's ready to ride.

Fuel feed is to tube connected to metal joiners with O rings.

Vent connects to other connector and runs over top of air cleaner, not sure of original, but run mine down to same point as overflows.


I used 3.7mm on the overflow pipes which feed down through a special guide plate 2015_0215engine0008 by nitram2010, on Flickr at rear of crank case and through wire guide at centre stand clamp.

2015_0418eng0010 by nitram2010, on Flickr

Hold on, isn't that vent supposed to go to the oil tank??

The crankcase vent, yes, goes to the oil tank. The carb vent just goes to atmosphere.

[Maurice]

Ok I read again and misread, tanks evanphi.

[martin_uk]

Double checked and overflow tube I used was 3.2 inside and 7mm outside.

Used the same for vent but had to warm to fit carb connection, so may be best to try to get some original size.

Listed as 3.5 here (item 44) also note vent pipe clip (6) that fits to one of the air cleaner fixings screws.

http://www.cmsnl.com/honda-cb750k-750-four-k-1978-usa_model7244/partslist/F++15.html#results

[martin_uk]

2015_04233final0024 by nitram2010, on Flickr

2015_04233final0023 by nitram2010, on Flickr

The guide clip on stand clamp bolt was fitted to upper section on bike originally, but seemed better with my exhaust position on lower position.  I marked carb vent with white tape just so I could identify.

2015_04233final0017 by nitram2010, on Flickr

[Restoration Fan]

Martin,
Those photos are phenomenal.  Thank you, my friend!

[martin_uk]

Martin,
Those photos are phenomenal.  Thank you, my friend!

No problem, happy to help.

The overflow hoses originally had thin wire clips at carb end and a rubber holder to group together before they go through the pressed steel guide at rear of crank case, by engine/ transmission breather spigot.

[edwardmorris]

Info for the general audience, if you're looking for OE hoses in specific sizes, here are some part numbers from my compulsive searching.

Honda OE Hoses

Fuel tube - 1 Metre long
Part number          - ID    - Color
95001-3500160M - 3.5mm - Black
95001-3500150M - 3.5mm - Black, braided exterior
95001-4500160M - 4.5mm - Black
95001-4500150M - 4.5mm - Black, braided exterior
95001-5500160M - 5.5mm - Black
95001-5500150M - 5.5mm - Black, braided exterior
95001-7500160M - 7.5mm - Black
95001-7500150M - 7.5mm - Black, braided exterior

Vacuum tube - 1 Metre long
Part number          - ID    - Color
95005-3500120M - 3.5mm - Grey
95005-4500120M - 4.5mm - Grey
95005-5000130M - 5.0mm - Black
95005-5500120M - 5.5mm - Grey
95005-7000150M - 7.0mm - Black
95005-7500120M - 7.5mm - Grey
95005-8000120M - 8.0mm - Grey

[danyo]

^^^ how good to have guys like you Rafi. Thanks!!!

[edwardmorris]

Happy to help 

[Restoration Fan]

I was hoping to come on here with a video of her starting but we're not quite there.  We got the issues with the coil sorted.

As it turns out, it had nothing to do with the coil itself; our problem was that the black/white wire was shorting out because it was pinched underneath the bolt that passes through the little 2-piece clamp that connects the coils to the frame.  I went to take the coil off this morning because I was going to replace it with the old coil...just to make double sure before I contacted VintageCB750.com about replacing that coil.  Once I did that, I noticed the shorted wire and had to remove the old connector and rewire that blade connection and get rid of the pinched piece.

So now we're getting spark on all 4 cylinders and she's coughing and occasionally we'll see some black smoke coming out of the exhaust but she just simply isn't getting enough gas through the carbs to combust.  So we pulled the carbs and airbox off the bike and I've made an appointment with Bill Benton's House O' Honda Fun for tomorrow evening to get the carbs all skippy.  Once we do that, we will give it another go at starting her up.

[calj737]

Glad you sorted your carbs out. By the way, you did return the BLUE/GREEN wires to their proper locations, right? If not, your timing could be so far off that Stella won't fire. (I mean, as long as we are overlooking things standing in the way, what's another simple fix, right?)

And I still think you and Logan are 1:1,000,000 despite not being the lottery winners to receive a dead Pamco 

[Bill/BentON Racing]

Dem built in extra kill switches will do it every time! See y'all tonight,  Bill

[madmtnmotors]

you did return the BLUE/GREEN wires to their proper locations, right?

+1

And I still think you and Logan are 1:1,000,000 despite not being the lottery winners to receive a dead Pamco 

I thought we determined there was no problem with the Pamco ignition?