RD400 first run after rebuild, very low power

[Striker1423]

250 main jet is still a huge jet. Not revving out under load is a typical sign of being rich. I just went through the same thing on my bike. Dave F modded 350. I'm headed back down to around a 190 or 200 main.

[ElFuegoBlanco]

250 main jet is still a huge jet. Not revving out under load is a typical sign of being rich. I just went through the same thing on my bike. Dave F modded 350. I'm headed back down to around a 190 or 200 main.

I might just do that. At least down to 220. I definitely have a stuck float though. I managed to leave the petcock open and woke to a pool of fuel on the ground.

Once I get the brake situation sorted, I'll fit a new float and see where I stand. If it's still rich, I'll go down to 220. Thing is, I'm not even sure if it's getting to the mains. After the first few minutes of running, it won't even rev in neutral

Rob

[m in sc]

thats probably the float creeping fuel in. def get that sorted 1st.

[ElFuegoBlanco]

Rear brake is back in action. I managed to fit an ebay MC with only a little bit of frustration.

Waiting for float needles and a replacement throttle cable from economy (the carb end of my cable are kinked a little and the price of the cable dropped). Once they're in, I'll be back at it.

Some down time to work on the xs750

[m in sc]

did you buy that XS750 that was wrecked at the gap recently? just curious.

[ElFuegoBlanco]

Nah, I've had this one since 2008 or so. It somehow keeps running so I keep riding it.

Unfortunately the Yamaha Triples forum that had a huge amount of knowledge went away unexpectedly and a lot of information on these old bikes was lost. It makes me happy this forum and the UK forum are still active.

[ElFuegoBlanco]

While I'm waiting for a new throttle cable and float valves to ship from Economy, I'm verifying the timing.

What does everyone recommend for the timing on this bike?

It's a 76 rd400 with aftermarket exhaust, rd350 y boot k&n filter, one size up pistons. I'm not sure what other info would be relevant.

Thanks! Rob

[m in sc]

2-2.1mm btdc.

[ElFuegoBlanco]

Awesome, thanks. I'll go ahead and set it today. Hoping the parts ship soon so I can get back to it.

[Clem710]

Back to the reversed slides experience, I like to forget to hook up the choke crossover:)

Maybe make sure your floats are actually floating while you are in there as well.  The float shutoff valves that are all metal never seem to cause issues for me but maybe I'm just lucky.

If your floats arent floating, the local small engine sling blade swears by SealAll.  I've used it a few times and dont remember having to go back and fix anything.  Its like a thick, old school model glue with a good bit of solvents in it, I keep it in a jar after the tube is opened.  Make sure the floats are dry inside first. 

[ElFuegoBlanco]

I've had the float needles fail on my xs before. It explains why I have a bag full of 5 or 6 float needles that don't fit the rd, unfortunately.

Both floats do float. They both look to be in good shape, too.

As for the crossover, I'm sure it was connected, but I have been having choke issues. The choke won't stay actuated. When I release the lever, the choke disengages. I don't think it's related, just an observation.

The new float needles/seats and throttle cable should be in on Friday. Unfortunately, with the throttle cable price dropping by $100, it pretty much immediately went on back order. So I switched the Economy order to an aftermarket cable.

[Clem710]

Well since mine is on the floor in pieces, this is mine open and closed, 77 400, pretty sure stock. It will definately stay on riding it slowly, warming it up, I dont remember if it vibrates closed if you forget to close it, feels like it might but I think I can ride it with it on.  The little cam like arm is pretty stiff and, without looking it up, I'd guess is what makes it "spring" closed or open.

[m in sc]

yes thats stock. make sure OP that the spring is above the lever perch like in pic, not below it, ive seen that mistake a lot.

[ElFuegoBlanco]

Well since mine is on the floor in pieces, this is mine open and closed, 77 400, pretty sure stock. It will definately stay on riding it slowly, warming it up, I dont remember if it vibrates closed if you forget to close it, feels like it might but I think I can ride it with it on.  The little cam like arm is pretty stiff and, without looking it up, I'd guess is what makes it "spring" closed or open.

Thank you! The pictures were exactly what I needed to figure out what was going on with the choke lever. The spring arm was in the right place (thanks M) but had nowhere near the same angle as yours relative to the lever. the lever would almost get caught by the cam, but failed to catch more than half the time  You're right, it's quite stiff, so I don't know what happened to it. Maybe left in the actuated position for 35 years? I removed it and bent it just slightly upward to match the angle in your pictures and it seems to be much more functional now.

Parts are scheduled for early delivery today, so I should be back to turning wrenches very soon.

Rob

[ElFuegoBlanco]

Looks like I'm back to square 0 or -1.

Fitted the new throttle cable, calibrated the oil pump gap, set timing to 2mm btdc.

It started on the second kick but I'm sure I blew a head gasket on the rh cylinder. Smoke is coming out between the head and cylinder. Oil is dripping down both exhaust headers

 

Edited to add: I still have compression on both cylinders. They're identical at 110psi

Edit 2: whoops, that was at closed throttle. At WOT, they're 120psi.