YPVS Loses Position(?)

[2steve]

Not that I'm an expert, but that thing just delightfully rips above around 7k rpm. So much so that the clutch has started slipping - and that clutch slipping didn't impede acceleration either
Surely that can't happen with any type of reed problem.

So much stronger than I recall with the fresh '84 RZ that I used to own. It's at 64.5 mm bore.
Also, as I stated to mnein when he asked for a comparison, there is definitely more area under the HP/Torque curves with an RZ compared to the RD400, (both stock with pipes).

[teazer]

OK.  I thought that is was dying out like a flat battery or fuel, but that sounds more like a pipe effect.  At a steady say 35mph in 5th or 6th, just curing along, if I open the throttle all I get is intake noise as it slows down.  Drop a gear or three to get the revs up and it sings, but at lower revs, no amount ( little or large) of throttle makes much difference, except to intake noise.

I have an older pair of Spec2 pipes on mine and as long as revs are high enough, it is very responsive.

if you could borrow a different set op pipes to do a back to back comparison, that might shed light on things.

[m in sc]

why would the pipes suddenly stop working? its not the pipes. the baffles are intact.

[2steve]

I took it for a spin today. Since teazer mentioned my first post saying I had just changed the needle, it only made sense to change it back. Took the pristine new Toomey needle out of the left carb and put in the chewed-up old one. Turned the coil around, (not flipped, but turned 180 degrees to correct orientation - shouldn't have mattered), and had run a ground from a couple places on the engine to the battery negative and frame with a 4 connection ground wire "harness".

All that to say that the needle change is indicating that the left carb is the issue.
It really does pull through the lower rpm better now but reminds me of why I changed the needle in the first place back in May. Moves more boldly into traffic and is more usable at low throttle.

Will run it again later this week as we are supposed to approach 70 degrees but I feel there might be evidence to convict the left carb in a court of law. Will get it out more on the open road to check what I presume is/was an issue with the new coil.
The new coil wouldn't install the other way because the harness plug wouldn't reach, but since I lengthened the harness with direct wiring, it allowed the orientation that eliminated the ridiculous bends in the spark plug wires.

We'll see. I got my 30-year reward gift card from work, so that will help toward new carbs.
Still can't point to a detail that could be called a smoking gun after all of this. That old left carb that doesn't match with the right likes its old chewed up needle. Meanwhile it's spoiling the show.

Would be a dream come true to have it running great on the road for Spring.
PWK28s, one way or the other.

[1976RD400C]

This is how I fixed my RZ stock carbs. It's kind of astonishing how they transform how it runs. I have them on my 34mm RD400 carbs also. I was skeptical at first but found out, wow. 
https://www.economycycle.com/product/ufo-ultimate-flow-optimizer-for-rds-and-rzs/

[2steve]

I have those on my RD400. Had to fiddle with them because the fit wasn't spot on. They work very well. Pilot size goes WAY down and they make it crisp.

That left RZ carb though, it's not something I want to pour more effort into. Something is wrong with it that just isn't obvious.

Planning to look at the PWK options out there at this time. Can go the DIY route and save a few hundred or Ed Toomey complete kit for $700.

Still appreciate your carb loan offer and UFOs are def good advice.

[automan]

So much for putting it back to stock..........................

[automan]

 

[teazer]

If it runs better with the old bent needle than it did with a nice shiny new needle, which seems to defy logic - Unless there is a matching problem with the corresponding needle jet. Ebay Australia has a Keyster replacement and CSMNL look like they have stock ones.

Might be worth popping them both out and checking the orifice to see if there are signs of gouging or interference on the bad side. If the bent needle has created a larger that spec needle jet orifice, that would create a rich fuel situation causing it to bog down.

[85RZwade]

If it runs better with the old bent needle than it did with a nice shiny new needle, which seems to defy logic - Unless there is a matching problem with the corresponding needle jet. Ebay Australia has a Keyster replacement and CSMNL look like they have stock ones.

Might be worth popping them both out and checking the orifice to see if there are signs of gouging or interference on the bad side. If the bent needle has created a larger that spec needle jet orifice, that would create a rich fuel situation causing it to bog down.

I had this issue a couple of years ago with my RZ. My symptom was a bog at a very specific and very small throttle opening; 6th gear and just under 1/4 throttle was the worst. It was worn needle jets and needles. When the grooves worn into the needles aligned with the top of the needle jets it became rich and started losing RPM. More throttle or less would get me out of the flat spot.

[2steve]

I'm going to drop back and punt the both of them. Wasted too much time this year trying to coax them into working better. Not getting that time back and I became an expert at removing stock carbs. Not really a coveted life skill.

[1976RD400C]

For some reason these bikes are really tricky to get running just right once the original pipes and air box come off. 

[m in sc]

I've never had an issue tuning an rz. tbh, none have been stock, either. those stock us carbs imho are garbage. you can get better performance running Dave f modded 73-75 rd vm28s with a y boot on an rz all day long.

[Kawtriplefreak]

I concur with Mark. The stock carbs are junk.

[2steve]

I concur with Mark. The stock carbs are junk.

And I'm jumping right in on that.

Nobody wants RZ stock pipes. Experience has added stock carbs as well.

On the other hand, the RD400 is running crisp, responsive and quick today at 67 degrees.
Yay DaveF VM28's with fudged in UFOs and ChuckQ "update" porting with FPPs.