Newbie here with a slight miss below 4000 rpm HELP...

I jst got a 98 vfr800 and when I first test rode I didn't really notice but when I was on my way home with it I noticed an v-twin vibe like on my victory Jackpot. I suspect the V4 would be much smoother.
The miss seems to go away about 4000 rpm.
I pulled the tank off and noticed the vacuum diaphram hose was missing is this some sort of mod?
I also found the 2 rear plugs loose to my liking.
Any help on where to go would be appreciated.

Thanks....

 

With no known history or miles I would recommend a full service, the whole enchilada, and go from there. It will eliminate many things and give you a good base line for all other service needs in the future.

 

+1 service

I'd change the plugs, oil, oil filter, coolant and see if it makes any diff.

Could fuel be an issue? Has it been sitting around? If so it might be worth getting rid of the stale fuel..

 

Would you recommend fuel inj cleaner?

 

I can't recommend injector cleaning products it as I haven't used them, and don't know if there are downsides to injector cleaner.

Hopefully one of the experienced guys here can chime in about that.

 

First thing to try is almost always inspecting or replacing with new plugs if it's running rough or not running on all 4 clinders. Can you check for FI codes ?? Low fuel pressure ??

Changing coolant or oil is not likely to improve running in this case.

 

Almost anything other than a fuel related issue would be worse at higher RPM than this sounds. I'm not an expert either; but the thing about carbs (the '98 is carbureted, yes?) if they've sat for an extended time is that where you will notice the problem first is at lower RPM and smaller throttle openings (idle and pilot passages are smaller...).

Is this miss something that happens at a steady speed only, or does she miss at WFO as well?

So far with the evidence provided, I'd swap the plugs and pour in a few ounces of a good carb cleaner (PJ1 or equivalent), then go for a ride and see if the problem doesn't correct itself.

 

The 98 is fuel injected.
I don't know how to check codes and I will check the fuel pressure in the next couple days.
I plan on tune up air filter the works.
Do you guys run a K&N or factory?
I rode it about 50 mile last night and it seem to run better, I think it may have some gas left in it from last year.
Thanks for the info so far.

 

I stand corrected. Geez, they were ahead of the game, eh?

 

My 99 did not like to run smoothly at lower rpms on the gas we have now with the ethanol in it until i did the PAIR blockoff. I can also recommend startron or the stabil ethanol treatment. These bikes were never meant to run on fuel with ethanol in it.