Hard Acceleration Problem

[MusicMan]

I recently received a 98 Valkyrie Tourer from my Uncle. It had sat for 11 months without being started. Needless to say it had some issues when I tried to ride it. I used Seafoam to get it to idle and run at low speed. The problem is with hard acceleration. At closed to about ½ throttle everything is pretty good. When I open the throttle all the way, I have a problem. The engine revs to ~3000 R.P.M. and the whole bike starts to shudder violently. It is like someone is switching the engine off and on at about 5 times a second. It is barely noticeable in first gear and gets progressively worse in each gear. Fourth and fifth gear are very bad. The bike starts instantly, idles good and low speed is fine. I did replace the air filter after I got the bike with no improvement. This is not my first Valkyrie so I am a little familiar with it. In fourth and fifth gear it does not ease into the shuddering, it is just there. It really is like someone is switching the engine off and on rapidly. It’s a pleasure to ride until you really get on it. At 1/3 throttle it easily revs to over 5,000 R.P.M in gear (I did not try it in 5th).   Ideas?

[Ricky-D]

I'd go ahead and install some new spark plugs first off.

Increased cylinder pressures can often cause a spark plug to under perform and not fire at all.

***

[Farther]

Sounds like you might be starved for fuel.  As throttle opening increases vacuum decreases so less vacumm available to keep the petcock open.  Maybe your petcock needs a rebuild.

[Blackduck]

When you changed the air filter did you notice if the baffle or foam pad had been removed from the air box cover?
Sounds much the same as another thread on here.
Again check the colour of the sparkplugs to see if it is a lean or rich condition.
Cheers Steve

[sandy]

This sounds like a manifold vacuum problem. I'd check everything in the induction system. Vac lines, clamps, intake O rings, header nuts too.

[MusicMan]

Changed the plugs and checked compression. Compression is good, 160-170. The old plugs looked good but that does not mean a lot. Changing plugs did help a lot. It still does it but then I have about 8 ozs. of Techron in a full tank (problem was there before I added the Techron). I am thinking that I have a weak ignition problem because new plugs helped but did not solve the problem. 

[wiseguy]

What kind of plugs were in it? what plugs did you put back in? NGK... Champion... Denzo.....?

[MusicMan]

It had NGK-DPR6EA-9, I put in NGK-DPR7EA-9. Evidently, the NGK-DPR6EA-9 plugs are for colder climates.

[Ricky-D]

I don't believe in the "weak" description when discussing electronic ignitions.

They are mainly "off" or "on".

I cannot imagine what part of an electronic ignition would be able to be considered on a course to "weak".

I am not criticizing the comment, but in the Valkyrie ignition there is very little for rider attention if it is working properly, short of spark plugs and ignition timing.

A battery that is not fully charged will adversely affect the ignition to a point where it will shut down.

***

[Fudd]

Sounds like you might be starved for fuel.  As throttle opening increases vacuum decreases so less vacumm available to keep the petcock open.  Maybe your petcock needs a rebuild.

That's my bet, also.

[MusicMan]

The battery is fully charged, alternator checks good and the bike runs good until about 3K RPM and full throttle. I was thinking that the ICM might be malfunctioning at higher RPM. It does take more juice to fire the plug under load at higher RPMs. It is an electronic module and they sometimes do weird things. I was just wondering if it could be the ICM or maybe the Ignition Pulse Generator. Anybody had problems with these?

[YoungPUP]

Thats expensive talk for shooting in the dark. Were there any problems like this before the bike was sitting? Sounds like fuel starvation. What color were the old plugs? Also check the condition of the vac line from the #6 intake to the petcock, they like to split on the ends. A mityvac tool comes in handy for checking the petcock. pull it to about 5lbs and let it sit. see if it bleeds off, if it does rebuild it or replace it

[Mr.BubblesVRCCDS0008]

Could also be the slides in the carbs are sticking. As they rise the needles are lifted and the main jets come into play.They are controlled by vac and springs. If you do remove them and clean them (spray some lub) on them be careful with the rubber  diaphrams as they are not cheap to replace. I too think your problem is fuel related. JMHO

[Chiefy]

  Have had what you're experiencing in a car, the coil was weak.

[MusicMan]

UPDATE!
I should have updated this weeks ago as the problem is solved. I had tried Sea Foam, Techron, and a number of other additives. Each helped a little and did something productive. I still had the shuddering under hard acceleration. I then added about 8 ozs. of Berryman's B-12 to a tank of gas. Within about 200 feet of riding, I noticed a difference. After I ran that tank and one more tank with 8 ozs of B-12 added, the problem was virtually gone. There is just a hint of shuddering under hard acceleration in 5th gear roll-on.  Acceleration is about 98% and part throttle acceleration is very smooth and steady. It looks like the B-12 solved the hi-speed problem. Maybe the diaphrams were sticking causing the hi-speed problem. What I have learned from this is that each product does something a little different. They all helped. Techron did something Sea Foam could not do and B-12 did something neither could do. I am not saying to mix these products, but run different tanks of gas, each with a different additive. Thanks for all of the suggestions. The Valkyrie flat hauls now!