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Discussion Starter #1
I picked up a CB750k5 in October for $300. I knew nothing about how to work on the bike and when looking for info I came across this forum. I have been on here asking lots of questions and have received lots of good feedback.

My goal was to get a bike to use as a daily commuter. I also wanted to try to wrench on something so I thought a winter project would be good. When looking around for decent, cheap bikes I came across the cafe racer concept. I like going fast and I like the grass roots origin of the cafe bikes.

So I thought I'd try my hand at one. I was excited when I first got the bike and made a few poor purchases. The ergo air filters were one of them. The big issue that I have with them is that once you tighten them onto the carb, the rubber loosens up and the filter shakes around.

I did score a used kerker 4-1 and it makes the bike sound better and was a cheap fix for the rusted out original pipes.

Here is the bike i brought home:



It did not run. There were no coils of plug wires. The front brake was frozen. There was no battery and the electrical panel was a field of rust.

So, after getting some advice off of here, I got some dyna coils, wires and electric ignition. Those parts came with good instructions and I was easily able to install all of it.

Once I had coils and did an oil change I pirated my MX battery and tired to start it. All I got was a huge backfire and a couple foot flame shooting out the pipe. While it was cool, I knew it wasn't right.

Again, someone on here set me strait and I found I had the wires routed wrong. I got that sorted and it started, but was rough.

I was psyched to get it started so I cruised it around the block. I found that the stuck front brake broke loose once I put it in gear but didn't engage when i went to use it. The back break was useless so I did the fred flinstone stop.

I pulled the front brake and took it apart and cleaned everyhing but the piston (which I am going to do next). It worked way better.

Next I took off all the lights, crash bars, highway pegs and luggage rack.

Then I tore into the carbs and ended up with four rebuild kits.

The hand controls were useless. They were cracked, buttons missing, hand been rigged to work, and ended up worse after i traded out the stock bars for the clubmans.

FYI, you can still buy the stock right hand control for $50.

I bought an after market left hand switch, rewired it to work, and stuck it on.

I put on new turn signals and have a low profile cat eye break light. The turn signals are cheap, but they were cheap.

I am going to shorten the rear fender just above the odd welds that were on there.



I need to do something about the seat because it is a torn mess. The pan is rusted but a local guy told me he would reupholster it for $50. I might go that way and leave it looking the same. We'll see.



I have some rear sets that I thought would go in the passenger peg holes, but the kerker pipe took that spot. I will try to fab some plates (as shown in my pic) and go from there. I have the clutch linkage so I just need a mounting system.

I also rebuilt the gages because the originals had no glass, faces, lights, and were rusted. The new onces turned out nice. I bought a second pair of ebay and combined the two to work.



Here is a video of how it sounds. When i turn the throttle hard it dies. I need to tune the carbs but I don't know how. There is a guy here in town who has rebuilt a bunch of these 750's and I think i might have him synch them and give the bike a once over for roadworthyness.

http://s234.photobucket.com/albums/ee180/chrisadelman/?action=view&current=P1200128.flv

I plan to have the side covers (not shown) headlight bucket, and tank painted. Probably a gray.

I have a couple months until I can ride. It is 16 degrees here today and there is about 3 feet of snow in my yard.

Please make any suggestions that you like. I was a little apprehensive to post this here seeing as many recent discussions turn into bike bashing. However, I am building this to ride, not sell.
 

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Looks like you picked a tough place to start learning about bikes, but your doing the right thing doing the research, talking to people that have done it before. Keep working thru it bit by bit and you'll get the result you want.
Don't worry about a bit of stray sledging on this site - thats what makes it fun! There is no shame in not knowing everything about your model of bike or cafe style in general. The people getting torn a new arse on here are the ones that know stuff all, claim they know everything and that they are better than anyone else. I reckon you're pretty safe.

Less is More
 

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i like it, it's a good start. one thing, when you cut your fender, get some of that trim chrome thing that people use on their car door edges, that's what i did to cover the sharp edge of my rear fender. as for the seat part, there are quite a bunch of companies that make some fiberglass seats for CBs, or if you want to build your own you can take a tank, cut it, weld it to your seat pan etc. as for your engine cutting out, i would venture into thinking that the carbs might need to be rejetted. those air pods+free exhaust might be what's causing it. but definitely get them synchronized cause that might save you a few headaches.

CB650, FauxCatiFT500
 

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I second that - the folks I tear into come in two categories: one, the ones that attempt (and often succeed) to sell a POS bike for three times its value after doing no more than replacing stock parts with universal aftermarket trash. The other, Carpy. He's a category unto himself. Why? I'll explain in Carpy-speak: his aesthetic blows more dick than a Brighton minger, and checkers are gayer than a village people lookalike contest at the Chain Driver.

Sounds to me like you're on the right track. IMHO, you should take the money you'd give to the carb-sync guy and buy a carb balancing tool instead. It'll take you awhile to work it out the first time, but I can't overestimate the value of being able to tune your own motorcycle. You sound like you've got the temperament.

A
 

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Discussion Starter #5
Thanks for the responses. If I didn't have thick skin I probably would have left here a while ago.

Xander,
What adjustment tools are you talking? A carb syncroonizer? Float measurment tool? Both? What else.

I would rather learn to do it myself since I hope this will be the first of many projects. My wife is already asking for her street bike.

Thanks
 

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Definitely get the carbs tuned. Emgo pods have a reputation for restricting air flow (some have even said they're MORE restrictive than stock air filters). Couple that with an open Kerker and you've got an imbalance: too little flow in/too much flow out. Pull them off and start it, see if that changes anything.

In any case, I don't think that is your main problem.

A quality cleaning/rebuild on the carbs could do wonders. Since it is falling flat on its face off-idle, I'd suspect:

1. A clogged fuel passage in the carbs (do these carbs have an accelerator pump? Could be a problem too).

2. Clogged main jet(s).

3. WAY out of balance carbs.

I confess I don't know too much about these carbs, these are just some common problems on bikes that have sat for a long time.

How do the plugs look?

How about the points?

Are you getting a hot spark on all four cylinders?

The above are easy, cheap and necessary things to check out that could give you more clues to where your problems lie.

Sounds like the bike had been pretty neglected/abused before you got it. Nice work so far.

Honda go sideways!

http://groups.google.com/group/co-ohvinmoto
 

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Yep, that's the device. My experience has been that you don't really need a balancer for a 2-cyl, but with four it makes a world of difference. You could also make one - there are designs all over the web for making a carb sync gauge out of household materials.

You don't need a float height measuring tool. You can make that in five minutes with a bit of cardboard.

krapfever's covered the basics. I'll add to that: if you've installed those carb kits you mentioned, I do hope you checked the jet sizes to make sure they were correct (they rarely are). Otherwise, no telling what's in there.

One more thought: if you haven't thoroughly gone over the bike, a sync/tune job will cost you a lot, because that won't be enough to fix it. Here's how that'll go.

"So I tried to tune your carbs, but they kept clogging because your tank's rusted. I sealed it, installed new fuel lines and filters, but they still didn't work because the jets were wrong for your air filters and exhaust. I installed the right jets, and that mostly cleared up the problem, but then I couldn't get it to rev past 5k so I retimed your bike. Still fucked up in the high revs - turns out your advance was stuck. All that wouldn't have taken so long if I hadn't had to replace your rectifier because your battery wouldn't stay charged. Parts weren't that much but it took forever so, ahh, let's see... eight hundred sound reasonable?"

Fix it yerself. We'll help.

Alex
 

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Discussion Starter #9
Krap,
Thanks for the input.

The carbs were rebuilt and are really clean. They have all new jets, gaskets and needles.

I have not checked some of the other things you listed.

To be honest, I don't even know what the points are. I'll look into it in the klymer manual (which is kind of limited)

How do I check for a hot spark and what should my plugs look like.

I never changed the plugs. Does anyone have a suggestion for what plugs to use?

Thanks again.
 

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Discussion Starter #10
I'm convinced, I'll fix it myself.

But where to start?

Here is some info that might help:
No rust in the tank but the reserve straw and fliter in the tank was broken off so i just removed it.

The fuel lines are not new but i did blow them out when i rebuilt the carbs and they are not clogged.

I have stock jets with the exception of a 110 main (105 was stock)

I will change out the air filters at soem point but I'd like to keep the pods I have now, tune it with them on and spend my money on something else (unless the air filters are the issue).

Why would I want baffles? To restrict the outgoing air or to muffle the sound? I like the way it sounds but I'd rather have it tuned right.
 

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Okay, we'll assume the carbs are clean and jetted okay. You may have to re-jet later on depending on what filters and exhaust configuration you end up with. For now, we'll consider you in the ball park with the carbs.

Clymer should cover points check and replacement. Its pretty basic routine maintenance. By the way, just get new points. No sense in wasting time on an old set when they're pretty cheap anyway. I believe the manual will cover "static timing" your points as well. This will only require a test light (a small bulb attached to two wires with alligator clips on the ends -- cheap, like $5 at Napa). Once static timed, again you'll be in the ball park for timing (You'll eventually need to use a proper timing light to set advance timing accurately, but worry about that later). Go slow and for reference take a picture of the old points/advancer plate as it sits in there before you begin messing with it.

DISCLAIMER: I've never changed the points on a CB750, but the same basic principles should apply. If anybody knows better, feel free to flame me.

Checking for good spark involves pulling a plug and re-plugging it into each plug wire one at a time, laying it on the motor and bumping the starter. Look for a nice, blue spark arcing from the plug. It's also good practice to unscrew the plug caps from each wire (yeah, they just screw into the wires) and snipping 1/4" to 1/2" from the end of the wire then firmly screwing the caps back on.

Plugs to use: NGK's. I don't know the specific plug for the CB750.

Plugs should look like mocha (a.k.a. light brown). You'll be checking the plugs first at idle (this will tell you the status of your idle circuit, choke circuit and timing-at-idle) and again later after you've got the idle set and you've taken it to 5000 rpm or so. This check will tell you how things look off-idle and advanced. (I like to take the bike for a short ride for this second plug test as you get an indication of what's happening "under load" as well).



Honda go sideways!

http://groups.google.com/group/co-ohvinmoto
 

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quote:
I'm convinced, I'll fix it myself.
There's a good lad.

quote:
But where to start?

Here is some info that might help:
No rust in the tank but the reserve straw and fliter in the tank was broken off so i just removed it.


The fuel lines are not new but i did blow them out when i rebuilt the carbs and they are not clogged.
You got an inline fuel filter on there? Add it to your shopping list. $4.00

quote:
I have stock jets with the exception of a 110 main (105 was stock)
Cool.

quote:
I will change out the air filters at soem point but I'd like to keep the pods I have now, tune it with them on and spend my money on something else (unless the air filters are the issue).
Yeah, K&N's are expensive. But those Emgo's really are crap in my opinion.

quote:
Why would I want baffles? To restrict the outgoing air or to muffle the sound? I like the way it sounds but I'd rather have it tuned right.
You can tune an open pipe, no problem. But, do your neighbors like you? How about cops?

I'm all for a mean sounding bike, but wait till you leaving for work at 7:30am and the early morning stillness is shattered by a roaring Kerker.





Honda go sideways!

http://groups.google.com/group/co-ohvinmoto
 

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quote:
I put in an electric ignition, do i still have points?
You're kidding right? After all that....jeez.

No, man. No points. The only thing you'll have to do to adjust timing is rotate the igniter plate to adjust for advance.

I'd still check the spark and snip the wires just to be thorough.

Honda go sideways!

http://groups.google.com/group/co-ohvinmoto
 

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Discussion Starter #15
Krap,
Sorry, but I did write in my first post that I put in dyna coils and ignition.

After one of your responses i went on google to find out what a point is. That's when i thought i might have ditched them.

Thanks
 

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If you installed new coils, I'm going to presume that means you have new coil wires (replaceable ones even!) so you need not trim them.

Here's what I'd check if I were you:
- Are all four cylinders firing? While idling, pull each plug wire one at a time and then reattach (so that there's never less than 3 cylinders running). Each time you remove one of the wires, it ought to slow the idle down or kill it entirely. If it does nothing, that cylinder's inactive. Figure out why.
- Look at your plugs. There are charts all over the place online, as well as in every decent car or motorcycle manual, showing the visual differences between plugs running rich, lean, detonating, etc. Figure out where each cylinder's at with said chart.
- For kicks, change all the plugs and see if the problem goes away. If it does, you probably still have an issue to address, but that's almost a surefire implication of the carbs (or a weak spark, though it for the most part eliminates a mistimed spark).

There's more but we'll get to that.

Put an inline filter on your fuel lines or all this work will be in vain.

Alex
 

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I use those little filters on everything. They work great, are cheap and you can actually see when you have a ton of shit in there instead of guessing. Jeff at Z1 Enterprises is great. Hell, the whole staff is.

Shitcan the Emgos and buy some K&N's or UNI's. You'll thank yourself.

Gas Right, Clutch Left
 

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Discussion Starter #20
So, I took the air filters off to see if it ran any better but it did not. It would not run unless i kept on the throttle.

I put them back on and it ran fine through 5000 rmp.

Then I pulled one plug wire at a time. I started with the one closest to the choke (riders left). Nothing happened. It didn't make any difference. I know there is a good spark because it shocked me. Then i held the wire close to the block and the spark was blue and seemed strong. I pulled the plug to see if it was fouled. It was very clean, looked like it had never been used. I put the wire back on the plug and started the bike. It ran the same. I then held the plug close to the block and saw a good spark.

I then pulled the second wire (2nd from left side) and the engine died. Then the 4th and the engine died, then the third and nothing happened. I did not pull that plug yet.

If the plug works, the spark is good and the carbs are rebuilt, what could it be? How can I tell if fuel is getting in there?

Thanks
Mut
 
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