RD400 - Back from the Dead

Try bleeding the brake fluid at the banjo bolt at the MC. It is messy, so get lots of protection. If the action is not confidence inspiring, there is air. Possibly you will have to continue bleeding air out of the caliper, but my money is on air at the MC itself. My process is barbaric, but quick, easy and works 100% of the time so far (in hundreds of applications at least). For this bike, fill with brake fluid and after stuffing crazy amounts of paper towels around the caliper crack the bleed screw. Hold your finger over the outlet of the bleed screw and pump the lever. Use your finger like a one way valve on the bleeder. After a few pumps, and there is no need to coordinate the person pumping with the person bleeding - just give it a few full slow pumps and don't worry about sucking air back on the down stroke, your finger will keep that from happening. Close the bleeder and bleed the banjo bolt at the MC. All should be fine if the MC was maintained with fluid. I use basically the same method on everything with hydraulic brakes. Cars take about 15 minutes with all new brakes, MC and dry lines. Messy, but not really much more than with drain lines, collection bottles, pumps etc. And the only thing to clean is the spill and vehicle which is tiny if you are careful. I have NEVER needed a vacuum pump or had to "back fill" any brake system on any kind of vehicle - though I have had some stubborn cooling systems !

Lovely job your doing here - keep it coming!
 
jpmobius said:
Try bleeding the brake fluid at the banjo bolt at the MC. It is messy, so get lots of protection. If the action is not confidence inspiring, there is air. Possibly you will have to continue bleeding air out of the caliper, but my money is on air at the MC itself. My process is barbaric, but quick, easy and works 100% of the time so far (in hundreds of applications at least). For this bike, fill with brake fluid and after stuffing crazy amounts of paper towels around the caliper crack the bleed screw. Hold your finger over the outlet of the bleed screw and pump the lever. Use your finger like a one way valve on the bleeder. After a few pumps, and there is no need to coordinate the person pumping with the person bleeding - just give it a few full slow pumps and don't worry about sucking air back on the down stroke, your finger will keep that from happening. Close the bleeder and bleed the banjo bolt at the MC. All should be fine if the MC was maintained with fluid. I use basically the same method on everything with hydraulic brakes. Cars take about 15 minutes with all new brakes, MC and dry lines. Messy, but not really much more than with drain lines, collection bottles, pumps etc. And the only thing to clean is the spill and vehicle which is tiny if you are careful. I have NEVER needed a vacuum pump or had to "back fill" any brake system on any kind of vehicle - though I have had some stubborn cooling systems !

Lovely job your doing here - keep it coming!

Thanks! I tried your suggestion last night. I did take the caliper off first and ensure both pistons moved when hitting the brakes... then I back-flushed out the bleeder instead of up the line to the MC. I then filled the MC and pumped it a bunch to get as my of the little air bubbles out as possible... THEN I started your method. The "finger over the bleeder" doesn't make much sense. I tried, and tried, but couldn't get any pressure built up it would simply push past the threads in the bleeder or my finger.

I put a hose back on the bleeder and bled as normal... 10 pumps, crack the bleeder, watch for bubbles. Not many if any came out.

I then did the MC bleeding as you suggested. 10-15 full pumps, crack the banjo, get sprayed, close the banjo, repeat.

This did firm up the lever a bit, but I can still pull it back to the bars, all be it slightly stiffer than before. I'm wondering if the MC has more throw than the bars allow... I may try to take the MC off and mount it to the center of an old handlebar I have to try and get more throw out of the lever. It may be what's preventing all the air coming out of the MC. I've heard a lot of people fix this problem by drilling and tapping the lever to install an adjuster bolt in the tab that touches the plunger in the MC...
 
Maybe I have missed the info, but, what brand of color did you use for engine painting? Great work so far!
 
I originally used satin black PJ1 epoxy, but it came out too dull, so I went over it again with DupliColor Engine paint in "Ford Gloss Black".

The wiring is 100%! I was able to fix the dent in my speedo housing with some strategic punch work and a skim coat of bondo. Not terrible, but perfect from about 3 feet away (which is all you need).

Headlight back on, trying to over-night bleed the brakes again. I may have a MC issue at this point, luckily I have a spare.

Just waiting on the adapter for my dial gauge to come in so I can time the thing and set the points!
 

Attachments

  • 20992708_10100400964795767_6671779171838072429_n.jpg
    20992708_10100400964795767_6671779171838072429_n.jpg
    158.9 KB · Views: 275
  • 20992600_10100400962630107_7460359267006727263_n.jpg
    20992600_10100400962630107_7460359267006727263_n.jpg
    70.7 KB · Views: 266
  • 20953923_10100400962605157_6780461299590942948_n.jpg
    20953923_10100400962605157_6780461299590942948_n.jpg
    94.2 KB · Views: 257
  • 21032352_10100400962525317_8886765843485057887_n.jpg
    21032352_10100400962525317_8886765843485057887_n.jpg
    85.1 KB · Views: 262
  • 20992991_10100400962570227_561913962420014379_n.jpg
    20992991_10100400962570227_561913962420014379_n.jpg
    103.8 KB · Views: 261
  • 21034406_10100400962460447_9088101764437705806_n.jpg
    21034406_10100400962460447_9088101764437705806_n.jpg
    81.8 KB · Views: 261
Last night I was able to pull the baffles, check for carbon (hardly anything in there), set the points gap to .014", set the timing to .070" (1.8mm) BTDC, put the new petcock on the tank (had to wait to source some fiber washers, found them at the hardware store for .20c!), and threw some fresh gas in it....

It started 3rd kick! Needs some adjustments, but it runs!
 

Attachments

  • 21078539_10100401491580087_5398881864668890481_n.jpg
    21078539_10100401491580087_5398881864668890481_n.jpg
    89.7 KB · Views: 269
  • 21032511_10100401491530187_81395311429385339_n.jpg
    21032511_10100401491530187_81395311429385339_n.jpg
    98.7 KB · Views: 259
  • 20993950_10100401491615017_6982161799659506021_n.jpg
    20993950_10100401491615017_6982161799659506021_n.jpg
    90.5 KB · Views: 260
  • 20992777_10100401491560127_5519563633042686955_n.jpg
    20992777_10100401491560127_5519563633042686955_n.jpg
    93.8 KB · Views: 249
  • 21077353_10100401491510227_151610251835534564_n.jpg
    21077353_10100401491510227_151610251835534564_n.jpg
    84.7 KB · Views: 272
Very nice work, you should be proud of the results!

Now for some riding and tuning! :D
 
Absolutely inspiring, it's nice to see these old bikes being brought back to their former glory. Makes me want to do a full rest on my GT250.
 
Thanks for the responses!

Currently battling 3 gremlins.

1- Rebuilding the Tach.. all the dashpot oil turned to molasses and it was non responsive. Its torn down waiting fluid. (You can see in the picture the clear lid removed form the pot.)

2- the LH carb keeps overflowing. I checked float height and its spot on, I think its hitting the inside of the bowl. (I just had them off to chase a bad idle issue... check those emulsion tubes!)

3- Slight top end rattle on the RH cylinder. I think the rings are binding causing the piston to rock on the rings... tore it down and there was minor scoring. Going to double check the bore later this week. Hopefully another quick fix.
 

Attachments

  • 21105480_10100402311347267_4207254357451910863_n.jpg
    21105480_10100402311347267_4207254357451910863_n.jpg
    46.1 KB · Views: 563
  • 21077756_10100402311307347_3473510610334310599_n.jpg
    21077756_10100402311307347_3473510610334310599_n.jpg
    99.6 KB · Views: 565
  • 21034259_10100402311262437_7742772767423859547_n.jpg
    21034259_10100402311262437_7742772767423859547_n.jpg
    84.2 KB · Views: 568
  • 21034332_10100402311287387_4445249262950807001_n.jpg
    21034332_10100402311287387_4445249262950807001_n.jpg
    88.7 KB · Views: 266
A common reason for the bowls overflowing is the float mechanism hanging up. Make sure the floats slide smoothly on their pins obviously, but closely examine the brass arm. If there are ANY wear marks on either the arms where the float pins push on them or on the tab that pushes on the needle, smooth them out perfectly flat with a fine file or sandpaper block and then polish them smooth with at least #600 sandpaper. Both areas tend to wear only where the fuel level is maintained, and the tiniest hump or notch will keep adequate pressure from the needle. Also a good idea to polish the needle and seat with a Q-tip and rubbing compound as well as the bore for the needle. Always use OEM needle and seat assemblies as aftermarket parts are often slightly different in assembled length which screws up the geometry for proper fuel level, though unless you see actual wear or damage to the ones you have you won't need to replace them to correct the problem. Often it is perceived that replacing the assembly cures the overflow issue, when actually the tiny physical difference in the parts moves the set point slightly enough to no longer hang the mechanism at previous wear point.
 
On an unresponsive or erratic tach or speedometer you can soak a cotton ball in kerosene and place it in one of the back light holes. Place the gauge upright for a few days and it will oil it up without disassembly.

Sent from my SAMSUNG-SM-G930A using DO THE TON mobile app
 
clem said:
On an unresponsive or erratic tach or speedometer you can soak a cotton ball in kerosene and place it in one of the back light holes. Place the gauge upright for a few days and it will oil it up without disassembly.

Sent from my SAMSUNG-SM-G930A using DO THE TON mobile app

Wow, that's good tip!
 
jpmobius said:
A common reason for the bowls overflowing is the float mechanism hanging up. Make sure the floats slide smoothly on their pins obviously, but closely examine the brass arm. If there are ANY wear marks on either the arms where the float pins push on them or on the tab that pushes on the needle, smooth them out perfectly flat with a fine file or sandpaper block and then polish them smooth with at least #600 sandpaper. Both areas tend to wear only where the fuel level is maintained, and the tiniest hump or notch will keep adequate pressure from the needle. Also a good idea to polish the needle and seat with a Q-tip and rubbing compound as well as the bore for the needle. Always use OEM needle and seat assemblies as aftermarket parts are often slightly different in assembled length which screws up the geometry for proper fuel level, though unless you see actual wear or damage to the ones you have you won't need to replace them to correct the problem. Often it is perceived that replacing the assembly cures the overflow issue, when actually the tiny physical difference in the parts moves the set point slightly enough to no longer hang the mechanism at previous wear point.

The second time I had it apart, I thought it was hanging up on the non OEM gasket I had installed. I could place the bowl on, shake the carb up and down, and couldn't hear the float jumping.

The needle and seat are stock, with 0 wear on them. They seal at the slightest touch of the float when the carb is on it's side.

I think the problem is that the floats themselves are hitting the sides of the bowl. The float hinge pin is smooth as silk, and the little spring plunger is working in the needle correctly.
 
clem said:
On an unresponsive or erratic tach or speedometer you can soak a cotton ball in kerosene and place it in one of the back light holes. Place the gauge upright for a few days and it will oil it up without disassembly.

Sent from my SAMSUNG-SM-G930A using DO THE TON mobile app

Really?! This stuff was STUCK on. I needed to hit it with brake-cleaner to remove it, and the dash-pot was completely empty. It basically puked itself into and around the friction (centripetal) drive. It was dead from 0-3000 RPM, then jumped from 3000 to redline (on a drill) and then hung up around 4000 when letting it drop to 0. The bike was stored at a 45 degree angle for 10 years up against a tree, outside, with a tarp over it with the bars turned. Basically the worst way to possibly store a tach... lol.

I just filled it up with silicone 50000cts oil (RC Car Differential Oil, basically) and it works perfectly! I just stuck it back together last night and re-installed. It's super responsive, drops back to 0 smoothly, and holds steady at all RPM. I was testing it with a cordless drill, as currently I don't want to run the bike until I get the top end sorted.
 
I missed something here. Were the carbs rebuilt and if so why is there so much corrosion on the needle jet?

How do the floats touch the bowl and stick? There's not a huge amount of clearance in there but they can't touch unless they are quite badly bent.
 
teazer said:
How do the floats touch the bowl and stick? There's not a huge amount of clearance in there but they can't touch unless they are quite badly bent.

Right. It should be super easy to eliminate this as problem - just put the floats on their pins and set the gasket on the bowl and see if they can touch. I've never seen this as a problem, but it is totally possible especially if the gasket is old, used, and dried out. I just looked at one that has been parked on my desk for forever and the gasket has shrunk a bit and curved inward toward one of the floats. It isn't hanging the float, but I can see it doing so potentially. Easy to trim a bit off the inside and eliminate it as a problem though.
 
Quick little update.

Carbs are back to 100%. I was getting a back knock on the right cylinder, took it all apart and it turns out I was out of round. I was hoping the honing would've fixed it, but it seemed to have made things worse.

I took the cylinders off and mailed them out to a machinist friend. He's got them squared up, bored out, and honed, just waiting on getting them back.

The floats WERE touching the sides of the bowls... a quick tweak and re-check before re-assembly and they're 100% now. No leaks.
 
Back
Top Bottom