RZ running on one cylinder below 6K RPM

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expat
Posts: 451
Joined: Thu Sep 16, 2010 12:26 am
Location: Massachusetts

RZ running on one cylinder below 6K RPM

#1 Post by expat » Fri Nov 16, 2018 7:08 pm

My sons RZ recently ran out of 2 stroke oil and he had a mild seizure. (The bike!) It scored both pistons and cylinders but didn't lock up.
I have a spare motor so we swapped cylinders and threw in a new top end kit.
The bike fires up but only on the left cylinder.. If you rev it, the right cylinder kicks in around 6k RPM.
I checked the reeds and right carb, all look ok, The plug is sparking and swapping the HT leads did not reverse the problem onto the other cylinder..
Any thoughts?

I suspect maybe RH crankshaft oil seal but would a seize cause it to leak?
I haven't done a leak down test which I know would be a good base line test yet (need to buy a test kit) but wanted to poll the audience for any additional ideas...
85 RZ350
88 YSR50
82 RD350LC (Current project)
06 Triumph Daytona 675 (track toy)
97 Honda RS125 (race bike #1)
99 Aprilia RS250 (race bike #2)
89 RGV250 VJ21
85 RG500
85 RZ350 Hybrid
86 GSXR750

brrrappp
Posts: 603
Joined: Tue Sep 18, 2018 10:21 pm
Location: USA

Re: RZ running on one cylinder below 6K RPM

#2 Post by brrrappp » Fri Nov 16, 2018 9:57 pm

expat wrote:My sons RZ recently ran out of 2 stroke oil and he had a mild seizure. (The bike!) It scored both pistons and cylinders but didn't lock up.
I have a spare motor so we swapped cylinders and threw in a new top end kit.
The bike fires up but only on the left cylinder.. If you rev it, the right cylinder kicks in around 6k RPM.
I checked the reeds and right carb, all look ok, The plug is sparking and swapping the HT leads did not reverse the problem onto the other cylinder..
Any thoughts?

I suspect maybe RH crankshaft oil seal but would a seize cause it to leak?
I haven't done a leak down test which I know would be a good base line test yet (need to buy a test kit) but wanted to poll the audience for any additional ideas...

FIRST-- Check to see if the vacuum hose that connects between the RIGHT CARB and the Fuel petcock diaphragm side is firmly connected at both ends and does't have an air leak. It you are using a "test tank" then you need to pinch that vacuum hose or plug it.
That is your problem- I'm 85% sure of it.
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Vac hose to fuel petcock
Vac hose to fuel petcock
Vachose.jpg (103.11 KiB) Viewed 558 times

expat
Posts: 451
Joined: Thu Sep 16, 2010 12:26 am
Location: Massachusetts

Re: RZ running on one cylinder below 6K RPM

#3 Post by expat » Sun Nov 18, 2018 8:06 pm

Thanks for the response.. the vacuum hose was OK but when I re-checked everything, I noticed the link pipe had fallen off.. problem solved!
It must have dropped off when I reinstalled the carbs after putting the new pistons in and I didn't notice. It was your diagram above that prompted me to have a closer look..
Thanks for taking the time to respond so thoroughly. Bike is running like a champ again now!
85 RZ350
88 YSR50
82 RD350LC (Current project)
06 Triumph Daytona 675 (track toy)
97 Honda RS125 (race bike #1)
99 Aprilia RS250 (race bike #2)
89 RGV250 VJ21
85 RG500
85 RZ350 Hybrid
86 GSXR750

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