Difference between a late 55hp and a 63hp YPVS engine?

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kjellz
Posts: 69
Joined: Mon Jul 03, 2017 7:01 am
Location: Norway

Difference between a late 55hp and a 63hp YPVS engine?

#1 Post by kjellz » Sun Mar 11, 2018 3:36 pm

Hi
I am trying to figure out my original engine spec, and if the parts I have fits to that.
Finally I wonder what is the difference or what restricts a 55hp compared to a 63hp late ypvs engine?

I found these listing at RD350LC:
Power.jpg
Power.jpg (83.87 KiB) Viewed 3223 times
My 1990 2UA could fit both the 55 and the 63 description, not knowing if Brazil refers to made In or made to Brazilian internal market. Mine was originally made in Brazil and then exported to Italian or Spanish markets.

Secondly I do not know if my engine details can help clarify what spec I have and if it is stock or not:?

Cylinders says 1UA and 1-Y on the other side
Head is 1-Y
Carbs are 2UA-00 and I was told on here that they are "Power jet" carbs.
Exhaust is stock for the model year

Thanks for reading.
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RD350 YPVS 1990
F2 converted to N2 Red/white 1986 - Figaroli pipes

MK
Posts: 814
Joined: Sat Nov 26, 2005 11:44 am
Location: Wolfenbüttel, Germany
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#2 Post by MK » Sun Mar 11, 2018 3:46 pm

If memory serves me right, you had different jetting in your 2UA00 carbs than in the normal 63HP versions (185 mains, 27.5 idle, 60/65 power jet, 5L20 needle, N-8 needle jet)
Check out Xaviers page on what the German 1WW models had and compare the main air jet with your 2UA00. There were versions with 0.7mm and 0.8mm.
You have the 0.7mm so you're NOT done with simply changing all the jetting stuff. You need to modify the air jet which is behind the brass ball on on the carb intake side.

And you really ought to check what I've written in your carb post:
"That looks like the PJ carbs, but your jetting chart shows no PJ jet. That'd mean 180 is way too lean.
Check the tube on the right of your pic. Where it connects to the float bowl, there should be a brass jet inserted (looking from the float bowl). If there is one, 180 seems in the ballpark. If not get what your chart says (250). "
I suspect you have carbs that look like PV, but don't have it active!

Cylinder seems to be the right one, but Xavier states a reduced compression ratio.
I don't know exactly how that was accomplished (could be a thicker base gasket, thicker head gasket or different heads)
So check the thicknesses and if it's the head, either get it machined, get used heads or invest in stuff with exchangeable domes.

Rumors say the ignition curve was different on the Brazilian models, but I never saw any curves, so can neither confirm or deny.
But as I generally advise to get a programmable unit, that'll sort out any issue here.
Bye
Martin

justind97
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#3 Post by justind97 » Mon Mar 12, 2018 8:42 am

Doesn't the Y1 head have slightly less compression than the Y2?

I believe the Y2 was shaved down a little more?

MK
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#4 Post by MK » Mon Mar 12, 2018 8:44 am

Slightly, but not a change from 6:1 to 5:1 as stated above.
If it was mine, I'd measure squish and the volume in TDC on my own.
Bye
Martin

kjellz
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#5 Post by kjellz » Mon Mar 12, 2018 6:22 pm

For the carbs: there is a small jet in the "power jet" circuit so the 65+180 makes sense.
-and will that air jet =0.7 still be a restriction compared to 0.8?

For the heads: do I understand you guys correctly in trying to achieve 6.0:1 for compression ratio as the best attempt to get closer to 63hp with stock setup?
I may need to go about and actually measure the ration and squish as suggested to be sure...

Also, I remember having seen the CCs on here somewhere for the Y-1, Y-2 and Y-3 heads but couldn't find it when i searched: link anyone?

Thanks guys.
Kjell
RD350 N2.jpg
RD350 N2.jpg (55.36 KiB) Viewed 3146 times
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RD350 YPVS 1990
F2 converted to N2 Red/white 1986 - Figaroli pipes

MK
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#6 Post by MK » Tue Mar 13, 2018 3:13 pm

The main air jet corrects the fuel amount at higher rpm.
The smaller 0.7 makes the bike run rich at high rpm with the otherwise stock jetting, so 0.8 will ensure full performance.

I still don't trust that whole setup.
If YAMAHA states there was no PJ in the 2UA00 carbs, then there was none. That means someone already manipulated the carbs (i.e. exchanged them with the PJ ones). In that case he eventually manipulated the carb number 2UA00, too.
This makes it half way likely the air jet already has the correct 0.8 mm.
I'd ride it and check it by plug chops. If that shows overly rich, you know where to seek.

6:1 is the AT LEAST number.
A bit more doesn't hurt if you have high (98+) octane fuel around.
Bye
Martin

kjellz
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Joined: Mon Jul 03, 2017 7:01 am
Location: Norway

Re: Difference between a late 55hp and a 63hp YPVS engine?

#7 Post by kjellz » Tue Mar 13, 2018 4:50 pm

Regarding the 2UA-00 carb:
I agree it is a bit strange if it is a power jet carb and the manual has no mentioning of the power jets....

Also when consulting the Haynes it clearly says main jet + power jets in the specs for the 1UA carb.
Further Haynes is mentioning changing the power jets - makes me wonder how to do that exactly as they are located inside the aluminium hose spigot- heat it? Would be interesting to ID it.

And there is no sign of tampering with the 2UA-00 marking, and I will dig a bit more.
Mikuni 2UA-00 450pix.jpg
Mikuni 2UA-00 450pix.jpg (68.87 KiB) Viewed 3095 times
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RD350 YPVS 1990
F2 converted to N2 Red/white 1986 - Figaroli pipes

hondaror
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#8 Post by hondaror » Wed Mar 14, 2018 3:17 am

The power jets on the 1UA are not removable, and they are different from right to left. TZ race carbs have removable power jets.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

kjellz
Posts: 69
Joined: Mon Jul 03, 2017 7:01 am
Location: Norway

Re: Difference between a late 55hp and a 63hp YPVS engine?

#9 Post by kjellz » Sat Mar 17, 2018 11:00 am

For the 2UA carb I have not been able to find out which Power jets are installed.
However, I found a mod description telling to drill out the installed ones, thread tapping the spout to M4 and install Mikuni N100606 type jets according to needs.

I ordered a set of nozzles covering the needed 60 and 65, and will compare openings to what is installed - if at all possible to tell with this tiny nozzles...
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RD350 YPVS 1990
F2 converted to N2 Red/white 1986 - Figaroli pipes

Bare
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Re: Difference between a late 55hp and a 63hp YPVS engine?

#10 Post by Bare » Sat Mar 31, 2018 11:22 pm

Ooooh.. Quit dicking around and just bin the Crap Mikunis and Fit a pair of genuine PWKS (new preferably)
and experience a whole New world of throttle response , jetting ease/simplicity and above all Reliability.

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