Topic: a few problem to fix while tank is at paint… help please!

[USCG_C130]

hey everyone well i have been searching on here but was hoping for  some expertise ( especially dealing with carbs since i know very very little) well i am trying to get the bike running smooth while the tank and seat is at the paint shop, but here is what i am having trouble with

so i cant get my 73 cb750 to run very well. when i bought the bike it did not run so i completely disassembled it, i rebuilt the top end with new  rings and had the cylinders honed and measured and was told they were good here is a picture of the  measurement i was given(see below) i also did all new gaskets and valve seals cleaned everything up and re assembled. i also had my carbs rebuilt by a member who cleaned and reassembled and  bench synched, i  haven't done anything to them my self. i have the bike put back together but 3 of the bowls were overflowing so i  slightly adjusted the tab. now i am knowing i should have measured the floats. but in some other things i am having these problems of concern.

right now i have a jimmy rigged fuel supply, it has temp V stacks and pretty much straight headers on it waiting to be able to ride it to a exhaust shop for the muffler. as far as i know the carbs were cleaned and put back together. all new plug and wires and coils, pretty much everything on the bike is new.

#1 cylinder  the plug is black and wet, see picture below also today after adjusting the float again not only did it still drip from the drain line it suddenly just dumped all the fuel being fed to it all over the floor, it was strange and has never done it before.

#2 cylinder seems to be fine although i didnt get this plug out (the mosquitoes were getting BAD)

#3 pulled plug and it also was BLACK and wet and did smell like fuel

#4 cylinder had a very black plug and did NOT smell like fuel, but was dry and  the header for this cylinder is getting a fair bit hotter than the others (from reading i am guessing this one is running lean)

and i also seem to have some smoke coming from my exhaust and from what i see it looks like it may be oil and it coming from #4 the smoke it white/maybe blue and is there when i start it up but i havent ridden it long enough to see if it goes away.

also i have a direct reading gauge and as im starting the bike it take a few second for oil pressure to build, is this normal? when i first had the bike running i dont remember this taking nearly as long.? but when it does build is is running at about 60-65 PSI  with 20W 50 oil


so with all these issues is there any advice? i did get my timing finally set today  which made me happy since its my first time ever setting timing. but i though after getting my paints and timing all set it would run better but it does not seem to be. i think this may be easier with a better and bigger fuel supply, but does anyone have any direction for me? should i pull the carbs and sort through those one my own and would a compression test be telling me anything?

again please for give my ignorance or lack of knowledge i am getting to a damn frustrating point on this project


thanks
Chuck

[nevernoluck]

Set your float levels right per specs, you can probably get it to run to get exhaust but I'd haul it there and have it done as all carb adjusting is going to be affected by exhaust, is your rigged fuel supply vented? Last thing you will end up doing is a vacuum sync

[Bootlegger56]

If I were unsure about the carbs I would pull and inspect/clean the jets, emulsion tubes and bodies, set the float height per specs (you can make a simple gauge from a credit card) and bench synch them yourself.  (Not questioning the rebuild of the member.  I would just do it for my own education and peace of mind)  Its not a big deal.  If you can do a re-ring and top end overhaul you can rebuild carbs.
 
If it pukes out one or more of the overflows initially don't assume its a problem.  Sometimes it takes a little bit for the float needles to orient themselves and seat properly.  Try a light tap with a plastic handle of a screwdriver on the offending bowl.

I wouldn't read too much into the plugs initially until you confirm the carb condition especially since you adjusted the float level tabs without measuring the float height.  Search and read the suggestions on using clear plastic tubing to confirm fuel level in the bowls.  I like that method and now use it to adjust my float heights.

Overall...I would do a 3K tuneup from beginning to end and verify everything again.  It gets easier and quicker every time you do it.

You mentioned new plugs, wires and coils.  How about the resistor plug caps?  One of mine was initially bad and made the bike run rough.

Don't get frustrated with the bike.  Working out problems on a 40 year old machine is part of the fun in owning one of these relics.  If it gets too bad...just walk away and come back later.  Read through the forums and ask questions.  There is plenty of willing help on this site.  Even the experts get stumped by problems.  The trick is not to give up.  After pulling my K5 out of a wood shed I worked on it for six weeks every day before I even tried to start it and then fought most of the problems you are describing for several months. 

 

[USCG_C130]

hey guys sorry this took me awhile to get back on to but again stuck with a 24 Hr shift at work and was beat when i got home, so tomorrow i am going to pull the carbs and  take them apart to verify where all my jets and needles and clips are and then i will attempt a bench synch my self and also reset my float level since i  screwed them up. wish me luck with all this since i have NO experience with carbs but i am sure i will be fine. heres a great deal of info on carbs i found and plan on reading and following.


http://www.hondachopper.com/garage/carb_info/carb_info.html

http://www.salocal.com/sohc/tech/carb/carb.htm

@ bootlegger56  i did see that credit card gauge trick on here and may do that if my calipers with the depth gauge doesn't end up working. also do you or anyone else know where to get the part or what will work that screws into the bowl to make the clear tube float gauge?

Just the other day did the valves and the cam tensioner followed by timing and its still rough but i really think my carbs just need a little love so i will attend to that on my  3 day weekend. and yes the resistor boots are all new too i hope one isnt bad, but once i get the carbs sorted i will keep that in mind if i still cant fix it.
thanks for the encouragement i need it sometimes and it really helps to just walk away for the night too.

okay one last question for all you carb GURUs according to the hondachopper chart my 73 750 equipped with kei hin 657A carbs should be stock with 110 mains 40 slow  jets and 4 JN(<-- not sure what JN is yet) and 1 for the screw, is this correct? and since i have a stock motor running a 4-2-1 (with a quiet core cone so good back pressure) and a chrome bread box filter with 3 sides blocked off like the link below, what would any one recommend for jets and tuning, i have read the FAQ but i am still new at the carbs and not sure where to go any advice will be very welcomed

http://www.lowridersbysummers.com/twt/13/index.html

[K3Owner]

You know, the old school for car repair in the simpler days of carbs was to always look to electrical first. That should still apply to the Hondas. Your plugs, at least two, appear fouled. Why not buy new and verify that the sparks fly on all? You'd have that out of the way. After that, pull the carbs.

To test the plugs, ground one to the frame and open the points cover. Toss a piece of paper between the points gap so it's open and jumper from the yellow or blue wire on the points - alternately ground it to the points plate with the ignition on and the kill switch in Run. When you lift it, the plug should spark. Do this for all your plugs and then install them - if the points are then set correctly, are in good condition and it's statically timed (as you hinted), you're done with electrical.

After that, move to the hell that is carburetors  .

[USCG_C130]

ahhh yes the carbs are turning into hell while i had them apart i started to  take apart the linkage and plate in order to sand blast some parts and paint them  since my stuff ins looking a little rough. well to say the least it was a pain in the A$$ to get apart because of, well see the pictures below.

i am at a loss of where to even get the bushing that goes in the holes on the plate that you can see in the picture. one of them is fine the other just crumbled when i got it out but it does explain why sometime my throttle would stick a little and not spring closed quickly. does any one know where to get this part? its goes to the plate in the picture and is from a 73 CB750 with Kei Hin 657A carbs?

and thanks K3owner i do know all my plugs are firing from the hot headers and they are brand new dont even have 1 mile on them all that black is just from trying to get the bike to run right but after i get to that point i may go ahead and get a new set but well see when i have it running

[USCG_C130]

ahhhh great looks like the only way to fix that is to make a new bushing or buy a whole new plate. so ill be keeping my eyes peeled on ebay and seeing if i can find any tubing at work that may work, what a bummer!!!


hey if anyone has an extra stay plate for sale  let me know. LOL

[K3Owner]

You need some positive reinforcement! These machines are old enough that you are going to have days like this. Treat it as a positive - you found a problem! The machine and your confidence will be better for it.

Someone on the list should have what you're after...

[USCG_C130]

You need some positive reinforcement! These machines are old enough that you are going to have days like this. Treat it as a positive - you found a problem! The machine and your confidence will be better for it.

Someone on the list should have what you're after...

You can say that again!  And alway try to remember that these are old machines and need a little more love and work than new bike but I'm just so close to having it done that I'm getting antsy to finally have it on the road. But I did find a member In the parts area who has what I need so hopefully this week ill have my new stay plate and new jets and my tank and seat back wnd be ready to rock. I'm just not a pacient person with stuff like this lol but I'm working on it thanks for the encouragement!

[lucky]

Quote:
" to ride it to a exhaust shop for the muffler. as far as i know the carbs were cleaned and put back together.


You do not take a motorcycle to an exhaust shop for a muffler.
No such thing exists.

As far as the carbs go assume nothing and do not believe in rumors.
Remember the Military teaches you to not listen to rumors. LOL
Remove the carbs. Remove the float bowls and see if they need cleaning.
It is not a car carb though. No need to completely disassemble the carbs really.


JN means JET needle. OR slide needle that goes into the main jet.

The number 4 refers to the clip on the needle being in the fourth groove down from the top of the needle.

All you need to do is make sure the float bowl is clean and make sure to remove the brass jets and make sure you can see daylight through them. Especially the idle jet.
Be very careful with the floats so that you do not bend them. They are delicate.

IF you have not replaced the float needles for years then I would replace the float needles and seats. Measure the float height like the WORKSHOP MANUAL tells you.

[USCG_C130]

thanks lucky and you are right we are taught not to listen to rumors as those rumors tend to change daily. and right now i do have the carbs disassembled and checked the float needles they all seem to be good and no worn grooves in them and they all look to seal.the float are off and i will reset the float hight. and i will defiantly take your advice and pull the idle jets and peek through them and run one of my carb cleaning tools through it too.

and sorry for the confusion on the muffler area i have the stock headers and sand blasted them and painted with some exhaust paint and i ordered a new collector and 18" quiet core cone from cone engineering and i have no gas or experience with welding stainless so i am going to have a shop with some experience weld up those parts for me i know there are clamps and such but if i can get a good deal ill just get them welded.

and JN now makes sense thanks for the advice