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VM34 vs. 920R starting problem

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VM34 vs. 920R starting problem

PostAuthor: sdrexnefex11 » Tue May 14, 2019 8:55 pm

Hello all - My XV920R with Mikuni VM34's is extremely hard starting to the point of draining a fully charged battery. It typically eventually starts but only after ~5+ minutes of multiple start attempts and severe battery drain. When i can get it running it runs great--idle to WOT. It typically fires right back up if i turn it off and leave for a few mins up to about an hour. However, if i let it sit for over an hour it's back to extremely hard starting. Same holds if i let it sit on a trickle charger overnight or for days.

Here's some info to help diagnose:

Jetting attempts:
1- 145Main, 25Pilot, 1.5 air, 2.5 idle, clip 2 from top - barely starts, only after ~5mins of attempts. Runs good after starting.
2- 145, 20, 1.5 air, 2.5 idle clip 2 from top - barely starts, only after ~2 mins of attempts. Runs v good after starting.
3 - 145, 17.5, 1.5 air, 2.5 idle clip 2 from top - barely starts, only after ~5 mins of attempts. Ran poorly, repeated low backfire at idle, died, couldn't keep running.
4- 195, 22.5, 1.5 air, 2.5 idle clip 2 from top - would not start

Electrical:
-Battery - Anti Gravity 1201, 12 cell, 360 CCA
-Ricks Lithium RR
-Battery holds at 13.7 - 13.5 on full charge
-New starter
-Plugs: BP7ES, .7mm

Exhaust:
-Custom w/slip on 2.5 cone eng
-slight baffle (i have neighbors)
-still very loud

Air Filter:
-K&N

Misc potential clues:
-Carb floats are good 22mm
-All vacuum lines deleted
-Frame powder coated
-Ground to bat>engine; 6 AWG marine
-Second ground to bat>frame; 6 AWG marine
-Spark coming through both plug wires on start
-Plugs look fine after riding

I've combed the interwebs for clues on how to get this starting well and have tried many different tweak to no avail. Appreciate any guidance or suggestions.

Thanks in advance.
Last edited by sdrexnefex11 on Wed May 15, 2019 9:02 am, edited 2 times in total.
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Re: VM34 vs. 920R starting problem

PostAuthor: bstig60 » Tue May 14, 2019 9:34 pm

Increase the pilot jet size. That is what is used to start and idle. What plugs are you using?
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"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: VM34 vs. 920R starting problem

PostAuthor: sdrexnefex11 » Tue May 14, 2019 9:46 pm

The plugs are BP7ES with a .7 mm gap.
I’ve tried up to 25 on the pilot with same conditions. Any specific size recommendations?
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Re: VM34 vs. 920R starting problem

PostAuthor: bstig60 » Wed May 15, 2019 8:20 am

The stock pilot on the 34mm is #35; air 2.0 .... Plugs, get rid of the NGK's and go with an Autolite AP63 Platinum. Gap them at 0.028 thousands. These are one step hotter and seem to fire easier.
Sounds like you are not getting enough fuel. I assume you have checked to make sure you have good spark.....
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province, and Country.
It is easier to help you if we know where you are.


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Re: VM34 vs. 920R starting problem

PostAuthor: nanno » Wed May 15, 2019 10:29 am

Have you tried:

a) spraying some brake cleaner into the inlet
b) taping up the inlet(s) let's say 20% of the surface?

If so, what where the outcomes.

Personally, I'd recommend getting VM38s, they are proven to work and there's a good jetting-baseline floating around in this forum. How do I know it's good? I originally did it and various people have reported that it works fine for them as well.

Cheers,
Greg
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: VM34 vs. 920R starting problem

PostAuthor: sdrexnefex11 » Wed May 15, 2019 12:14 pm

Thanks guys - 35's, Autolites on order.
VM38's are out unless these VM34's fully take a S on me.
Actually tried throttling the air flow with a HDPE intake cover w/progressively more holes drilled--didn't seem to work. Will try simpler method again(aka tape)--good call.
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Re: VM34 vs. 920R starting problem

PostAuthor: Den. » Wed May 15, 2019 7:25 pm

Video on jetting Mikuni VM carbs
https://www.youtube.com/watch?v=67Nb3DI-B3s

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Re: VM34 vs. 920R starting problem

PostAuthor: Manitobarider » Sat Jun 22, 2019 7:45 pm

I run VM34s as well and they are great.
I used to have trouble starting but my spark was weak so I changed to a single fire coil and AP63s and it starts super easy. I didn't go for the Accel coil but another brand that some of the harley guys use.

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