Looking for opinions on pistons and cylinder condition

[ampzip]

An update on my comedy of errors.

Somehow I didn't realize to check if the engine had been bored previously. It had been already once before, so I decided to just hone it and install the new pistons and rings since previous ones were quite wore.

Finally got the parts and installed first cylinder fine. Was fitting piston into the cylinder for the second one and somehow snapped one of the piston rings...

Part numbers were identical on the boxes, both said 25 over. I'm only learning now (manual says nothing about it) that OEM rings need to be gapped?  What is a safe way to do this?

Edit: and maybe dumb question, but could I use one of the old rings in the bottom temporarily?

[1976RD400C]

It looks like the ring in the picture is for the next oversize bore size. How do the pistons fit in the bores without any rings on? You should check that first. Use a .002"-.005" feeler gauge alongside of the pistons to get an idea what's going on.

[ampzip]

Well upon closer inspection, I noticed there is faint numbers on the rings... they are in fact 50 over rings. Unreal. I don't know which seller to go after as both boxes are identical, only the rings were different. Guess I'm just SOL on those.

As far as the piston in the bores, I can barely get .003 to fit.

[m in sc]

its actually comon to file down one size set over to get a perfect gap. so, kind of a blessing. t have trimmed them using a fiber cotton wheel in a dremel, fixtured, and taking small increments off the side. do one side, then the other to make it even. be warned, it does FAST

[ampzip]

Finally got the bike back together, starts really well, and seems to run pretty well, except that it's still very rich, getting lots of smoke, wet oil on plugs.

The guy that did the hone job for me thought it may be that it's over oiling with the pump.

I noticed that part of the oil pump cable is partially broken off (never knew what it was supposed to look like).

In any case, at zero throttle, the raised mark is supposed to line up with the pin, but it's way up from it. It takes about 1/4 throttle for them to line up.

I also measured the gap between the adjustment plate and the pump pulley after rotating the white plate to make the plunger move out. It measured 0.14mm, manual says minimum is 0.15mm and should be 0.20-0.25mm

Wouldn't these cause under oiling if anything?

I was thinking of just trying premix. How can I connect the output oil tubes from the pump so that the pump will still work without being attached to the cylinders? Could I just have a closed loop with all three hoses (one in, two out) connected together and a bit of oil in the line?

[m in sc]

likely not over piling. that gets thrown around a lot by guesswork and is almost never the case. you can run premix, just cap inoffensive the inlet and the outlet lines.  plug the lines to the cyls.

def get a new set of cables. 

[quocle603]

Be sure to upjet when you run premix. A lot of people say 32:1 but with today's oil you can probably get away with 40:1.

[SoCal250]

Based on what I'm seeing in your photos and your explanation of the issue, I'd say your mechanic's advice was 100% wrong. It would be under-oiling not over-oiling! Not sure what logic he was using.

I would leave the pump in place and use it. No need to try some mickey mouse bypassing.

Get a new pump cable. Your DS7 should be the "old style" as used on the DS7 & R5: 278-26321-00-00 CABLE, PUMP
(Not the later cable version 521-26321-00 used with mid-75 model year and up pumps, assuming your pump is original. Refer to Tech Bulletin M8-015C).

Once you've replaced the cable and adjusted it properly then test your pump stroke again. Adding a shim will fix it if it's under the spec. Shims are readily available in several thicknesses and super easy to install. Just take the nut off the pulley, remove the pulley from the shaft, add your shim to the stack under the pulley, and reinstall the pulley.

In addition to the cable damage where the housing fits into the adjuster, it also looks like someone added a new end on it. At least that's what it looks like in your photo. As it rotates that blob (circled in red) will interfere with the roll pin preventing the pulley from rotating as it should.
Also it looks like someone has been messing with the pin (yellow circle). Make sure it's in there tight. But don't push it in too far. I think 4 mm is max, or about 6mm showing (from memory) or the plunger will bind.

[1976RD400C]

It looks like it is under oiling to me too, and you can adjust that with the cable adjuster in your picture but man you have to replace that cable. It looks like someone squeezed a nut on the end of it and it has to swing by that pin at full throttle.

[ampzip]

Thanks for the replies and tips.

Based on what I'm seeing in your photos and your explanation of the issue, I'd say your mechanic's advice was 100% wrong. It would be under-oiling not over-oiling! Not sure what logic he was using.

He hasn't seen the bike in person at all, I just had him hone the cylinders. He was guessing based on the smoking and wet oily plugs.

I just ordered a 278-26321-00-00 cable yesterday from ebay, shipping is taking forever lately and there is a canadapost strike now, so I'm not holding my breath on getting it any time soon. I was just hoping to try premix temporarily.

The fundamental problem at this point is still that it's running rich no matter what. The air screws are out 3 turns and idle screws are almost entirely in to get a good idle.

I really don't have a lot of experience with this. In my mind it's a carb issue, but I have brand now valve seats and and valves, I've cleaned it out, made sure the float arm is at the exact right height (15mm).

I guess next do a leakdown test?

[m in sc]

it has to be a carb issue. make sure the airjets are cleared out. and that the choke isnt hanging open

[Striker1423]

it has to be a carb issue. make sure the airjets are cleared out. and that the choke isnt hanging open

This. I'd honestly take the hardest look at that corroded mess of a carb from your prior pictures. A badly corroded carb can really throw off a lot of the carbs function.

[ampzip]

This is all a learning experience for me, it's really the first bike I've ever worked on at all. That's my excuse for some really dumb mistakes I have made (or didn't know were made by the previous owner).

After cleaning the carbs thoroughly multiple times, it still didn't seem to help.

It's when I took apart the entire throttle cable assembly to replace the autolube cable that I realized that the retainer that goes under the spring and on top of the jet needle wasn't seating properly in both carbs. The needle must have been bouncing around under the crooked clip. I figured out how to properly install that.

Then I realized that it's possible the throttle cables / slides could easily be put in backwards into the two carbs... that's exactly what was happening, the cutaway was backwards, basically starving the carbs of air.

I put them in the correct way and immediately running well... throttle response so good now.

Thanks for all the help troubleshooting this. Managed to fix issues I didn't know I had in the process (like the under oiling). At least I'll finally get to enjoy it a bit this fall!

[m in sc]

sweet! and we have all made the slide mistake at some point.

[quocle603]

sweet! and we have all made the slide mistake at some point.

Such a common occurrence with these things. It helped me diagnose my friends issue with his kz750 years ago. Quick and simple solution, but ran so much better.