New member from the STL. 1981 CB750C

[djpj]

Update:

Master cylinder clean and flushed with new fluid. I'm having a local shop build some new brake lines for me.

Replaced the faulty float valve and all the gaskets and the carburetors don't leak any more. But now I think I have a dead cylinder number 2. I felt the exhaust and they were all super hot except number 2. It was slightly warm but I think that was just from the radiant heat of the other exhaust pipes.

I checked the drain on the float bowl and there's fuel in the bowl. I checked the spark with an inline spark tester and it flashed thoroughly. So I took some extra gas in a pipette and squirted it into the number 2 carb with the airbox removed and the engine smoothed out and the exhaust pipe got hotter. So maybe somehow the fuel isn't getting from the float bowl to the cylinder.

I know the jets are clear and the needle slides easily. The only thing I really changed on the that carburetor was it was missing the accel pump gasket and I replaced the float bowl gasket. Last time I had the carbs together the float needle in the number one carb wasn't letting in any fuel but the number two carb was working fine. Now the number one is working fine and the number two isn't.

Would anything with the accel pump (diaphram, gasket, etc) keep the fuel from flowing out of the float bowl? I don't think I did anything else to that carb from last time. This is frustrating.


PJ

 

[djpj]

I also replaced the passage plugs too because they were all old and hard. I wonder if I need to blow out the passage under the plug with some compressed air.

I don't think it's the float or needle valve because after I found the number two not working I swapped the float and needle valve with number one and I had the same problem.

PJ

 

[dirtdigger]

Float and needle have nothing to do with getting fuel into the cylinder, they are there just to let fuel into the bowl. If you have fuel in the bowl then you have a plugged jet or passage in the carb.

 

[djpj]

Update:

Front brake lines are all put together and new fluid in them. Makes a big difference.

Checked the fuel level in the bowls and it's all good
http://imgur.com/3IcOkia

Then I sync'd them with a home made manometer. Took some brass and put some threads them to mount them to the engine.
http://imgur.com/oHRhSuJ
http://imgur.com/rD1FKk2
http://imgur.com/6d8g2fs

I didn't have the idle set right and it just sucked up the oil at first but once I got it set to about 1200-1300 the vacuum evened out and made things a lot easier. A little hookie but it works.

Carbs are running good but I think the idle mixture is too lean. It will stay idling higher for a few seconds and then come down, it has a short hiccup for a tenth of a second when applying throttle, the idle speed has to be adjusted once the engine is up to speed. So that'll be fixed next. I originally set the mixture screws to 3 turns out. It feels pretty close to what it needs.

http://imgur.com/teCwOwJ

Got the bike inspected and it passed somehow. I blew out a fork seal on the way to the inspection station. I think what happened was the forks didn't have air in them when I got it and so I added about 12 psi to it. When I started driving it the added preload must have just been too much and forced some fluid past the seal.
http://imgur.com/ZQVzkAn

So I get to change the fork seals and I might as well add some progressive springs while I'm at it. I've never done either but I have found some good step-by-step instructions for it. And if I'm doing the front I'll have to find time/money for the rear also.

New to do list:
Adjust idle mixture
Adjust throttle cable
Find a shifter rubber cover
Replace fork seals and springs
Get plates on it.

PJ

 

[Dave]

Then I sync'd them with a home made manometer. Took some brass and put some threads them to mount them to the engine.

That is freaking awesome!

 

[djpj]

Update:

Ordered some Progressive springs and some All Balls fork seals and dust seals. Should be here soon, I ordered them from Amazon.

Couple questions:
1. Does the spacer come with these springs.
2. If not, what size length and diameter will I need?
3. If so, does it need to be cut down?

I plan on putting the springs in with the tighter coils up top and I won't have to adjust the fork oil to compensate.

4. Just regular ATF - Dexron style?
5. What can I replace the air-assisted fork caps with that would allow me to remove the air hose? Any caps that will swap?
6. Am I missing/forgetting anything?

Thanks.

PJ

 

[Flogger]

Nice work... are ya doing anything else this summer or is this the summer?

 

[djpj]

The manual says 8.0 ounces of fork oil. Is this the correct amount when using progressive springs?

I took the forks apart and it was just sludge so I'm beyond due apparently.

Waiting on the springs to come in the mail next.

Flogger: Getting this thing road worthy is my main goal. Then putting new lights on it. Maybe this fall/winter/eventually doing a new paint job.

PJ

 

[Flogger]

JB weld works great for repairing side panels on the inside... keep those in good repair, they are expensive to replace...

Was asked in a PM how to do this...

1. Clean with a good cleaner to remove any oils.
2. Rough up surfaces with 400 grit sandpaper.
3. Fix area with Original JB Weld.
4. It cures faster with a little heat(heat lamp). Don't over heat though.

If the repair is only on the inside, just apply on the backside. Works great to fix tabs or nobs broken off on the inside. If the break is all the way through, use JB Weld on backside and refinish the outside after the JB Weld has cured. Use any filler, puddy, or refinishing on the outside that you would to repair and then paint...

 

[amc49]

Use same amount of oil with other springs............

Hope you made up FOUR of those depression tubes for carb syncing, one at a time does not work for several reasons. You DON'T want them set at a higher rpm where vacuum 'evens out', that's how you mis-sync. Sync is always much closer the closer you are to zero throttle and the levels bouncing all around, that bouncing can tell you much.

If you haven't blown any air under the rubber plug then most likely you have missed the idle jet too, it resides under that plug. Your model either screw-in or pressed-in jet there, if it has screwdriver slot it's removeable. That extremely small hole in it often why one cylinder does not run and fits on these DOHCs keeping them open. Use the smallest string on a guitar, the 'E' string as a cleaning tool, the .013" diameter wire is perfect for cleaning that jet out.

The entire DOHC idle system gives rookie tuners utter fits because it's more complicated than most, it's hooked to the primary main system and they work in a seesaw back-and-forth action that can complicate things. If the idle is lean because that idle jet plugged then the seesaw action makes the primary (which swings into action immediately as idle drops off) then go super rich to drive you batty with conflicting perceived running. How the bike won't idle from plugged jet and lean yet it wets out the plugs like too rich or flooding.

Drives 'em crazy I tell you.

 

[djpj]

amc49,

I had two carbs hooked up at the same time to the home-made manometer. Not one at a time.
I couldn't get anything balanced until about 1200 rpm then check it again at 1000 and they were still level. I'm fairly certain they are set.

I did get the passages cleaned out after I took the carbs apart the second time. I put some cleaner in there, pushed about 40 psi, and ran a wire around in it. That definitely helped when I couldn't get the number two cylinder going.

Thanks for the help with that. I didn't know how that idle system worked.

PJ

 

[djpj]

Update:

Forks are done!

I purchased from Amazon
All Balls dust cap + fork seal kit. Part number: 56-115
Progressive Springs. Part number: 11-1106

I followed the directions posted
http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=244
http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=23136
http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=12937
as well as a youtube video:
https://www.youtube.com/watch?v=reQ6qLQgvx0
I didn't follow the video on a few parts. Namely the use of motor oil in the forks and I believe they cut off the old fork seal while it was still on the upper fork (horrible idea).

I basically kept the upper fork in the mount until the fork was in two pieces then took it all out of the triple trees. I also ran some metal polish on the fork upper where the fork seal would glide then cleaned off the polish with some alcohol.
http://imgur.com/tRkFRwf
http://imgur.com/T8aVGEW
http://imgur.com/2FG4wIb

Then I cleaned all the parts inside and out. I used a little brake cleaner and high pressure washer. That got all the sludge out of the little spots.
http://imgur.com/ImwBfns

After I got the parts clean, I put the two halves back together as per the directions. I used the old fork seal to help drive in the new one. Then I put them back into the triple. Easy if you put them back together in the right order and remember to put the drain plug in (lost a cup of oil in that mistake).

Time to compare the new vs old springs.
New on top and old on bottom.
http://imgur.com/lX4dOte

For a spacer I used 1/2" pvc. I bought the 3/4" as the springs are 1" but I guess pvc is measured ID and I measured the springs OD. The 1/2" pvc worked well.
http://imgur.com/v0netrU

Measuring time!
Old springs - 22.75"
New springs - 19"
So spacers were cut to 3.75" and sanded the edges and cleaned them of any loose debris.
http://imgur.com/d5tsl0F

I put in fresh 8 oz of fork oil, then placed in the progressive springs with the tighter coils up top near the cap.
Tip for putting on the fork cap. Try screwing them on without the spacer in to determine where the threads lock in, remember this position. Next remove the cap and put the spacer back in. Now push the cap back on with the handle of a hammer, smallest one you got. You should now have enough room to put the 17mm wrench on the fork cap and twist that sucker until the threads are fully seated. Now you can take off that hammer and twist the cap fully on.

Reassemble and it is done.
http://imgur.com/iz9HKf4

Thanks for everyones help with this. It was way easier than I anticipated.

PJ

 

[amc49]

Higher rpm to even out misses absolutely all the individual cylinder differences you can get with lower rpm, slight valve leaking shows best at the lowest rpm you can get. One doing that will skie higher and why you compare all 4 to each other at once. It greatly clarifies your engine condition. You put restrictors (make 'em if you have to) in the lines to get the rpm down lower and still readable, the restrictors dampen out the extreme movement (which may easily be showing you a sticking or leaking valve if you don't ignore!) to make them easier to read. Any fluid that worked with those big fittings was way too thick (you said OIL!!! NO), if really set right and proper fluid used then setting with no restrictors almost always sucks up whatever fluid you're using to run it through the carbs. Why mercury (for weight but NOT restricting) or water (both harmless if they go through engine, you hope anyway) is generally used.

You not only measure at a constant rpm, you measure the levels at slight throttle accel movements too, that tells you how well the carbs truly track with each other and pull away from idle, measuring at a certain rpm steady misses 100% of that. You can have a dead even idle (or so you think) and the motor go spastic for a second as soon as you pull throttle away from it. Simply getting them all even really means they are only synched at that one exact point, it shows nothing of what happens say 3-4 degrees of turn later. You can do your simple sync with 4 drill bits of the same size and no work needed running at all. The smaller the drill bits the better. You can even sync that close with no bits at all, simply use the first transfer port that appears as soon as the throttle just breaks open, get all carbs exactly the same and done. You can do that with carbs out on the bench. I presync like that all the time and rookies commonly think the carbs are fully synced but do them right and then they see the difference, it's in how the bike pulls away at very low throttle amounts, a four done right will sound like a smooth turbine, not done and it will idle fine but an expert can tell as soon as the throttle gets worked it's still not right and in varying degrees. You get a slight burble when it should be dead smooth without that. Idle and pulling away from idle are two absolutely different things and a good sync fixes both. I found all this out the hard way knocking heads with Kawasaki dealers back in the mid '70s, they were absolutely clueless and I was forced to learn how to do it on my own, needless to say they screwed my bike up worse and worse the more they worked on it. The same with all the OEMS that state all you have to do is 'get them even', that grossly understates what you are doing there because the statement is issued in relation to brand new engines that should be much closer in static and dynamic states, you don't have that luxury with old used stuff. Often with older engines you will be splitting effects to try to average conditions out there. Doing that, I can convince somebody that an engine that does not run good for spit runs excellently to the average guy, he cannot tell it.

 

[djpj]

So I'M BACK. I've been gone for military duty and busy at work but I did get some stuff done.

I attended my first Vintage Bike Night at Schlafly Bottleworks. Some people really loved that front fairing.
http://imgur.com/yqc9q4y

On the trip home I noticed two things:
1. Part of the front fairing flew off on the highway and landed in the bushes. So that thing's got to go.
2. A creep to a high idle when it's really hot. Went home and tested for a vacuum leak to discover carb insulators 2&3 were cracked but didn't show until it was really hot. So I ordered new aftermarket ones.

The front fairing pretty much fell apart as I took screws out.
http://imgur.com/JwRNXex

I then replaced the insulators on the carbs and no more leak. While the carbs were off the bike I discovered an issue with the accel pump circuit. The fuel would drip out of the accel injectors and not spray, and carb 4 wasn't getting any at all. So I replaced the diaphragm, spring, boot and all. Then I stuck a needle in the accel injector of carb 4 and got some air flowing through it. All good now.

amc49 convinced me I was being lazy with the carb sync so I bought some real gauges. I connected all four gauges together and then connected that to cylinder 2 to adjust them to be equal. Then I connected them to the individual cylinders and set my idle at 1000 and sync'd them. The idle could still probably come up a hair. The idle also still has a slight rumble to it but it's more smooth and accelerates quick and smooth now. The accel pump really made a difference.
http://imgur.com/MPOJDAp

While I was there I replaced my old horn for a new Wolo type. I'm considering running a dual (hi/lo) setup in the future.
http://imgur.com/VqRTfLo

Next, it's onto the front lights.

 

[djpj]

I had to completely disconnect the front wiring to get the fairing off.
http://imgur.com/a/bRVRx

The original harness was all chewed up with splicing tools. Worthless crap destroys the old wiring so I had to replace portions of the wiring.
http://imgur.com/BNQfMvG

Pulled the wiring up an through the brake bracket and labeled all the wires.
http://imgur.com/UGx2ivj
http://imgur.com/iNQ5Sz9

Removed unused wires and cleaned up the area making sure not to leave any exposed wires or un-soldered joints. I also added a new headlight plug and extended the headlight wire to make it easier to stuff into the bucket.
http://imgur.com/f14kKXR
http://imgur.com/4ZLvUwH

Now it is time for the aftermarket fork mounts and turn signals. I thoroughly sealed the turn signals with some silicone. Slight overkill.
http://imgur.com/M9JFXzp

Then I mounted the turn signals to the headlight mount and clamped them to the forks.
http://imgur.com/hdlY73u
http://imgur.com/PMa4VPX
http://imgur.com/rxwbhJr

I used part of an old military rubber boot for a washer between the headlight and the mount. This should keep it from wiggling and won't be too unisightly.
http://imgur.com/tDdSB4K

All ready to go (or so I thought).
http://imgur.com/JtiHaO3

New headlight from Amazon. Looks great.
http://imgur.com/KxPEwsZ

Connected and tested.
http://imgur.com/yP2GRyI

Then I went to mount the headlight and found the mounts were too far apart. So I flipped the mount and got them closer together. Crisis averted. I'm going to buy some acorn nuts later to cover the threads of the bolts. I then opened up the headlight bucket, wound the wires in, and put it all back together. Beautiful.
http://imgur.com/KDFplnK
http://imgur.com/c0L76fV (Here you can see the mounts flipped and threads sticking out. I also did get more of the wiring hidden in the bucket after this photo)

 

[djpj]

Next I needed to replace some of the dash lighting. While I was replacing two bulbs I figured I might as well go ahead and replace them all with LEDs. The gauge lighting is good but the idiot lights were INTENSE.
http://imgur.com/Bxb5EIH

I figured this would be a problem riding at night so I decided to diffuse them with some paper. I took the cover off and taped paper up behind the colored lens. This did the trick.
http://imgur.com/9jrVYMf

 

[djpj]

Now is the time to go ahead and mount the tank and finish up the front and middle of the bike. I had left the tank on a drip pan in case the petcock leaked a little and I guess it had tipped over at some point. This cause fuel to slowly leak out the cap and down the side of the tank. What I was not prepared for was the fuel to slowly get under the base coat and peel it away..... Damnit!!!
http://imgur.com/b9u6CoL
http://imgur.com/GNCTn9D

Luckly I was planning on painting the bike. I wasn't planning on painting it so SOON....

 

[djpj]

Next I replaced the flasher relay with an electronic one so fix the LED flash rate. Cylinder style from NAPA, ziptied in. Perfect fit and function.
http://imgur.com/9ogzLOg
http://imgur.com/vCBYtiw

Then I started working on the tail light. Silicone EVERYWHERE!
http://imgur.com/Bc7Gr0o
http://imgur.com/1DchYLh

I then plugged it in to realize it has something like 8 yellow LEDs for integrated turn signals (which I do not want) and only 2 red running light LEDs and 4 red brake light LEDs. So I'm going to take it apart and replace the yellows with reds and increase my running lights for safety. Hopefully I don't screw this up too bad. I ordered my dashboard LEDs and these new red LEDs through superbrightleds.com. They have an impressive selection, especially since they had those old type for the dashboard.

I also grabbed a few strips of bright red LEDs to mount later for an additional brake light. Safety first.
http://imgur.com/YTNCi4x

I think this will turn out like I hope. The tail light is currently small but these additional LEDs will make a big difference.

PJ