Support GPR Camp!!

RS50 AM6 "flat spot" advice

Discuss technical information.
Post Reply
User avatar
Crunchbucket
Posts: 3
Joined: Mon May 20, 2019 9:19 pm
x 2

RS50 AM6 "flat spot" advice

Post by Crunchbucket » Mon May 20, 2019 9:36 pm

Please share any thoughts.

The last 2 rides I did on my RS50 I had to deal with a decently large range of my throttle seemingly not firing. The main cure is to completely open the throttle and the bike starts making power again. Let off even a little and the bike seems to stop firing. Completely peg the throttle and power comes back. Note that this is pretty much at any RPM ranging from 7K to about 11K. It seems to get worse as the bike goes from cold to regular operating temperature. I completely cleaned the carb in between the last 2 rides so that doesn't seem to be it.

My setup is the Athena Powervalve 80CC barrel and head, Dellorto 21mm carb from AFR, stock air box, stock exhaust (with wideband AFR installed), Top performance variable ignition, and VForce Reeds.

It runs a bit rich at higher RPMs, like 11.5 : 1 and I am wondering if I am sort of soaking the plug so that when I let off, it kind of temporarily fouls or something like that. Kinda reminds me of those old WWI airplanes that didn't have a throttle, just an ignition cut.

Going to try to go a little leaner on the main to see if that helps.

Any thoughts?

thanks!
0 x

User avatar
jkv357
Posts: 228
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 441
x 118

Re: RS50 AM6 "flat spot" advice

Post by jkv357 » Tue May 21, 2019 6:03 am

If it runs fine at WOT I wouldn't change the Main Jet.

Something else may be going on inside the carb. Will it run at 1/2 throttle?

How long have you had the variable ignition? Not sure if yours is the same brand that can act erratically, but I know tora tora had some issues with an aftermarket ignition he installed.
0 x

User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

Finding the Trouble

Post by toratora » Tue May 21, 2019 11:39 am

There can be a lot of reasons for this situation, and questions are usually one of the better ways to start dealing with these sorts of issues.

- Did the bike ever run well with the current setup?

Yeah it seems obvious, but sometimes the obvious is where you have to start! If the answer to this question is yes, then it is likely that something in the system as failed, and you can likely fix it by replacing that something.

If the answer is no, then it is going to be a little bit harder to diagnose. Carb settings are possibilities, as are ignition faults. If you have access to another bike (a friend's bike) where you can do some parts swaps this can be an effective trouble shooting technique.

Another option is to try stuff from your stock parts bin. For instance, try swiping out the ignition modules by putting the stock one back on the bike. It might surprise you how much better it will run with the stock ignition. This can occur if the performance ignition isn’t well matched to other components in the system.

As for the carb tuning, like Jay mentioned it is probably not the main jet. There is a section on Carb Tuning here on GPR Camp. It’s probably worth your time to give it a quick glance, and a deeper read for areas that seem appropriate. :paw_prints:
0 x

User avatar
Rj_666
Posts: 58
Joined: Sat Nov 11, 2017 3:13 pm
Location: Tacoma, WA
Replica: 2 x Aprilia RS50
1 X Derbi Senda SM
x 22
x 28

Re: RS50 AM6 "flat spot" advice

Post by Rj_666 » Thu May 23, 2019 9:43 pm

As noted - has it EVER run well ? Is this a condition that has only recently materialized ?

If not.... raise the needle.

Also, let us know what your setup is. The more specific you can be, the better.
0 x

User avatar
Rj_666
Posts: 58
Joined: Sat Nov 11, 2017 3:13 pm
Location: Tacoma, WA
Replica: 2 x Aprilia RS50
1 X Derbi Senda SM
x 22
x 28

Re: RS50 AM6 "flat spot" advice

Post by Rj_666 » Wed May 29, 2019 10:12 pm

All of the above being said.... MANY of us have wondered about the Athena 'Power Valve' kit. Could you give us a bit of background on the bike ?
Is it possible that the power valve actuator (as I recall, this is done using a spring to hold the valve shut, and exhaust pressure to raise it, but I dont recall exactly.

Did you install the Athena kit?
Has it performed as many power valve bikes do?
No offense intended, but are you SURE the powervalve is installed as recommended ? See the link HERE: http://www.athenaparts.com/files/pdfs/P ... 100005.pdf

It almost sounds as if the 'transition' point of the powervalve opening is causing the momentary 'leanness' until the carb can catchup to delivery demand. You may care to inspect the actual powervalve assembly (the 'blade') and ensure it is opening freely, not gummed up with soot.
0 x

Post Reply