Starting Trouble

[Ericcb750]

Hey Guys,
     I finally finished putting together my winter project, 1978 Honda cb750 K . I can't describe how attached to this bike i've gotten from restoring the entire thing. I can't see myself getting rid of this thing. Anyway, I put all new fluids in this past weekend and tried firing her up but i'm having some problems. If I give it a few twists of the throttle so the Accel Pump sprays some gas in, it will start for a few seconds and then die. The battery is in good shape and fully charged and I Have static timed it very well. I did clean the carbs pretty well but that was a few months ago. I put all new jets and everything in .  I'm just wondering if anyone has had similar issues?

     They are the stock keyhole top carbs and I currently have the stock air-box and stock 4-4 pipes. I put in the 35 and 110 jets. Any help/tips would be a big help on this because although the bike looks amazing, I want to take this thing out for a rip. Thank you all for your help. Take care .

[TOOLS1]

Definitely sounds like it is starving for fuel. Check the pilot jets, and passages for blockages.
TOOLS

[Re-run]

So, all new jets, even the press in jets? Did you bench sync the carbs so the slides are open the same amount? Did you set the fuel screws to 1.75 turns out? How clean were all the passages?
Did you set your float level to 14.5mm, +- .5? Have you verified that fuel is filling the bowls? You can do this by getting clear fuel tubing and hooking it to the drain nipples and bending the lines up without kinking them. Open the drain screw and see where the level is. All 4 should be about even, just a bit below the top of the float bowl.

Are you using the choke? When cold, these bikes require choke to start. Make sure the flaps are closing all the way when you pull the choke knob.

Have you verified that your timing is set right? It starts but it maybe it is too far off to run.

[Ericcb750]

Hey Guys , thanks for the help. I pulled the carbs to clean them again last night. I figured it couldn't hurt even though they look pretty good. I also removed the plugs and I definitely got some anti-seize on the plug ends when installing them. But I checked and I have pretty good big blue sparks.  I had the screws at 1.5 turns out and I did use the choke. I'm thinking it's maybe the idle circuits. This is my first rebuild at this level so I'm learning as I'm going. I've never had a bike with Points before but I have set the static timing based on the manual and on Honda Chopper as well.  

  I think the anti-seize that was on the plugs was not helping the situation but they were wet with fuel, Probably from the accel pump which is working great. I verified that all the bowls are getting gas because I opened the drain screws and the same amount came out of each. I'm going to clean those carbs out again and I'll keep you guys posted.  Going to be a bit of tinkering, I wish there were some guys around here used to working on older bikes like this that I could learn from. Anyway, hopefully I'll have this stuff all buttoned up and I'll try starting again by this weekend.

Thanks for any help, I appreciate it.

[Ericcb750]

So I figured out the issue. After double checking the carbs, spark, points/condensers, etc. I had one more thing that I thought may be the problem. I had a 50/50 chance and with my Luck I lost. When I installed the camshaft after the rebuild, I lined it up perfectly with the timing marks but unfortunately the darn 4th cylinder was on the compression stroke instead of the 1st cyl. It is my first rebuild so lesson learned , but damn really? Now I have to pull the whole engine again and fix it. I dont' think there really is anyway to pull the valve cover while the motor is in the frame huh? If anyone knows how , any tips would be a huge help.

I'll be diving into this over the weekend so I'll keep you all posted to how things are going. Take it easy.

[TOOLS1]

" When I installed the camshaft after the rebuild, I lined it up perfectly with the timing marks but unfortunately the darn 4th cylinder was on the compression stroke instead of the 1st cyl."

That does not make any difference. The engine can be timed to either #1, or #4. Besides if the cam was out of time it would not run, and you would need all new valves.
TOOLS

[Ericcb750]

Hi Tools,   Oh really? Is there a way for me to fix this then? Sorry this is my first one so I'm kind of new to this.

[TOOLS1]

Turn the crankshaft 180* and then #1 will be the cylinder at TDC.

Now, when you say it starts then dies, does it actually "run" for a few seconds, or dose it "pop, and backfire?"
TOOLS

[Ericcb750]

Hi Tools, Thanks for your help. It actually does run for a few sec's. No backfire or popping. But it just won't stay running. The bike ran great when I first bought it back in August but there was a head gasket leak which I the main reason I rebuilt it. I'm confused because i've made sure to clean everything really good, I have a inline paper fuel filter , fresh gas, new NGK Plugs and boots, battery is good.  I'm just not familiar with these enough to know what's wrong. I'm getting a nice fat blue spark from all 4 plugs so maybe my timing is not quite right?   How does the advance / retarding of the timing plate work? Is that only for setting the strobe timing >?

[Ericcb750]

Or if when the cam is lined up correctly and the "T" - 1-4 cyl's  are in line, can I adjust the valves for 1 & 4 cyl's opposite of where they are now? This way the 1 cly's valves will be closed and the 4 cyl's will be open ?

[TOOLS1]

This has NOTHING to do with your valve/cam timing. You are not getting FUEL. Check your carbs! Also did you re-build the engine because you had oil leaking between the fins between the head, and cylinder, or because the compression was low?
TOOLS

[Ericcb750]

I re-built the top end because of the oil leak between the head and cylinders. I'll check the carbs and clean them again.

[TOOLS1]

That is a common area for these engines to leak.  A lot of people think it is the head gasket, but its not. What it is is the 6 rubber gaskets (nickles) under the cam towers that cover the head bolts. They dry out, and allow oil to seep out between the fins.
TOOLS

[Ericcb750]

Alright that makes sense. When I put the head back on I put new pucks underneath the cam towers and gave a tiny bit of Silicone gasket sealer on the bottom side of the pucks (open to air) but I made sure there was none of the sealer on the top of the pucks. I appreciate your help on this and i'll keep you posted as to whats going on. I did not know that about the Cam so thanks for letting me know. I read on the SOHC 4 fourm about the Advancer being 180 out but I didn't remove that from the engine. I'll try the carbs first and go from there.

[TOOLS1]

It would not even matter if the advancer is 180* out. It would still run. You should quit wasting your time over at that other forum.
TOOLS

[shinyribs]

TOOLS1 wrote

That is a common area for these engines to leak.  A lot of people think it is the head gasket, but its not. What it is is the 6 rubber gaskets (nickles) under the cam towers that cover the head bolts. They dry out, and allow oil to seep out between the fins.
TOOLS

So true. I thought I had a leaking head gasket too,until Tools told me about this. Mine was leaking to the point where it was actually slinging oil on me as I rode. I couldn't wear any good pants or keep the bike clean whatsoever. I went to the hardware store and bought a piece of fiberglass rope. The stuff they sell to gasket wood stove doors with. I just pushed it in between the fins it let it absorb the oil as it came out. I changed it once at about 5,000 miles and it really didn't even need it. Another 7,000-ish miles later it's replacement was still in place and looking good. Cheap,quick and easy fix. You can't even tell it's there. Just keep on riding.