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I recently bought my first motorcycle, a CB750 Custom. I have loved these bikes ever since I first saw one. I would consider my self fairly mechanically inclined, but totally new to the motorcycle world. The man I bought the bike from got it on a trade and never got it running (don't think he tried very hard though). I cleaned the carbs and hooked the bike up to a car battery, just until I buy the proper one for it. The plugs look almost new (should i change them anyways?). It really tries to start and gets SO close (including the occasional backfire!), but won't quite fire up. I disconnected the tank before trying to start due to gunk being in there. I have a bottle filled with brand new gas siphoning into the newly cleaned carbs. All of the plugs create a nice fat spark on the head, the plugs coming from the left coil are on 1 and 4, the right is 2 and 3. I'm using starting fluid to give it the little extra something and it gets SOOO close, but just won't quite "take over on its own." The pilot screws are only backed off 1.5 turns per the owners Manual instructions, but I see y'all saying to back it off 3 turns. Would this be a big factor in the bike not Turning over? I also need to change the oil as it is barely reading on the stick. Any thoughts, comments, or "you're doing it all wrong" is welcome! I'm excited to join the club and look forward to leading from y'all! I tried to attach a photo of her but since I'm using my phone, it may not have worked.
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Administrator
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It sounds like the wires to the coils are reversed. I think it is blue to the left coil (1, 4) and yello to the right coil (2, 3). However they could be switched at the spark units. Hard telling on these old bikes what has been done in the past. Most of the bike work I do, is undoing what some wanna-be mechanic has hacked up.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Thanks for the quick response Tools! I've been lurking around here and you seem to be a wealth of knowledge. I compared to the manual and to your comment (which both agree) and they are wired correctly. And I totally agree about undoing work previous "mechanics" have done. Everytime I hit my blinker on my 4x4 project, the radio turns off and the speedo pulses to the rhythm of the blinker due to DIY aftermarket stereo wiring haha.
Any thoughts on weather or not the pilot screw adjusting would have any effect? Also, I have yet to bench sync the carbs. I kinda just wanted to get her started then fine tune everything. I didn't think this would affect its ability to start, just its ability to run well.
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Administrator
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Welcome in Bigwig.
I'm not trying to nitpick your terminology so forgive me if I sound critical. But you mentioned your fuel bottle was "siphoning" fuel to your carbs. It won't really work like that since they won't draw the fuel in. It has to be gravity fed to them. Most likely,you already know this,just putting it out there just in case.
I'd start with Tools' advice and go from there. Good luck!
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Administrator
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If you are sure that ALL the wiring is correct, next is the timing. You can static check it if you do not have a timing light. Then if that is correct, run a compression check.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Administrator
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sounds like fuel, or the lack thereof, to me.
are the plugs wet when you pull them?
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Ya, I'm with moto. I would bet that since you had "gunk in the fuel tank" that you have gunk clogging your carbs.
There may be other issues as well, but I see a carb cleaning somewhere in your future.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote: Strawberries for supper. Yes, I am a lucky man.
My cb750 video site
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Administrator
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He said it would not run on starting fluid. If it was a fuel issue it would run on starting fluid. The popping, and backfireing indicate a timing/ignition problem.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."
1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Administrator
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He says it almost starts with the sfluid, maybe just not hitting it enough
with the can of fire. For it to run, he's got to stand ther spraying while it;s running.
Strong, fat spark, if it shows compression, and no gas on the plugs after tryingto start,
pull those carbs, boil them or whatever, pull the jets like Tools shows, set the air screws at 2, heck 2 1/2
from seat, do it till you have a wet plug after cranking that thing for 10, 20 seconds.
If they're wet, yes, look elsewhere.
Took me 4 tries, yes, carbs pulled and cleaned them 4 times, before they worked.
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Wow, thanks for all the responses! The bottle is gravity fed, thanks for checking though! I will check the timing as soon as I do some research on how to do that on the bike. I feel like it's a fuel problem as most of you do as well. I will go through the carbs again and let them soak a little longer than last time and just be more thorough with my cleaning. I probably won't get to her till Wednesday, but I will be sure to keep y'all updated. I'll also back off the pilot screw a bit and see it that helps. The plugs did not smell of fuel like it would on a engine that is getting a lot of fuel which leads me to believe that the fuel is not getting there like it should.
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Administrator
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are you removing the jets and blowing out the real small openings that dump
into the airflow? You need at least 100psi. They are like, real small passages.
A thin guitar string pulled what looked like snot out of mine, air and starting fluid
helped.
The little holes that are right around the edge of the choke butterflies when it's closed,
in the throttle body itself, you gotta get the crap out somehow, open that pinhole passage up.
All 3 of them.
The spark plugs will tell the tale, wet, fuel is flowing, dry, still clogged.
A clean tank with 2 gallons or so pushing gas down into the carbs might help also......
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My e string on my guitar became my best friend during my carb cleaning. I was able to get the 3 small pinholes under the butterfly, two of then seemed shallow though so I might not have made it all the way through with the e string. I sprayed some carb cleaner down the holes that hold the primary and secondary jets, but ill try to see if i can grab some of that snot stuff out of them. I honestly only let them soak in pinesol for less than an hour because I was so excited to put them on and give her a try....rookie mistake. The gaskets weren't in great shape so i odered some and I'm waiting on those to get in before I clean the carbs again.
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