Bonneville America Forums Forums Technical Forums General Tech Stuttering at 1/4 throttle

I posted earlier about cleaning the in line filter.
After reading some posts I am wondering if something else might be wrong.
I had thruxton needles & changed them to TBS with 1 shim.
The bike seemed to run better for a while.
When I had the thruxton needles in the bike would start with barely any choke.
Now I have to give it full choke.
Also when I am riding in town the bike wil stutter at around 1/4 throttle<2500-3000rpm>.
It is progressively getting worse.
I have changed the vacuum caps,so I guess I can rule that out.
Today before I changed the vacuum caps I was riding about 50mph<3000rpm> & the bike stutterd & also backfired.
Changing needles one time before I didn`t have the diaphrams seated right & the bike ran alright to about 5000rpm & then just lost power.
That is not the case now.
My question is,should I just take the shims out?
My mixture screws are around 3&1/2 turns.
The bike runs strong on wot.
If the fuel filter was dirty I dont think it would,would it?
Would 1 shim on each needle cause me the problem I am having.
If the diaphrams are not seated would that cause the problem at that throttle position?
I guess I am asking where to do I start??
Tbike pipes,unifilter & airbox drilled,130 mains,AI removed.
TBS needles 1 shim.

Just a thought, but check the coil wires where they plug into the coils. They are very loose normally, so they can easily come out enough to cause problems. I had 1 pop out completely when i hit a bump once and since have secured them with tie wraps. It could be that one is loose and at that perticular RPM for whatever reaon, electrical or vibration, it is intermittant. Takes all of a few seconds to put your hand up there and check so you may as well eliminate that as a possibility.

I have been having the exact same problem since drilling my slides this summer. The clutch side cylinder seems to quit firing at partial throttle but if I open the throttle more it instantly comes to life. That side is also running a lot richer than the other. The crazy thing about it is that for 2 or 3 consecutive days the problem disappeared but then returned just as before. Unforetunately when I drilled the slides I also installed new Nology coils and wires and reset the float levels. It does not act like an ignition problem so maybe I have a pinhole in the diaphram or the float level is to high and flooding that cylinder when the throttle is just cracked but the bike idles perfectly and pulls better than it ever did when I make it work. I should quit being so lazy and throw the old coils and wires back on to see if that solves the problem. Better start eliminating probable causes soon or it will have to wait until next summer. If anyone has experienced and or solved this problem please share the knowledge.

Thanks Daz,
I will check that tomorrow.
Doing some Brew now.
High priced Corona extra,thanks to you.

Kit,
I will work on it tomorrow & post back.
Thanks to my buddy Dazco I am into a 12 pack of Corona now.

Daz,
I took a Corona with me out to the Garage.
The wires seem to be tight.
I am now wondering that since I have pulled my plugs so many times that maybe I have a bad connection on that end.
Whatcha think?

One more question.
Can I use a spark plug wire from a Auto Parts store to troubleshoot my problem?

I suppose, as long as it fits the coil. But more importantly, i too am partaking in corona. I just thought you should know that. But seriously, if they are tight at the coils i'm afraid they probably aren't the problem. I doubt jetting is either because it ran fine before with the same jetting. Maybe check the tank breather tube and make sure it's not pinched off at the tank mounts. Probably not since it only happens at that certain RPM, but still a good thing to eliminate that possibility before worrying about more serious problems. Might also want to remove your pilots and blow them out. removing the bowls will also allow you to see if there is any debris in the bottom which would confirm your filter suspicions. Not likely i think, but again this is the process of elimination.

Worse case would be electrical. Dealer told me when he did my that the sympoms for the ignitors going was acting strange at low rpms. Certainly does sound more like carbs though.

Just got back from a 35 mile ride in the rain.
The bike is running ok.
Took the tank off & drained it.
Quite a few gray chips in it.
Probably some of the primer.
Pulled the petcock & it was clean.
I see what Dazco means,I dont see how anything could get through it.
The inline filter was clean,a real pain to get at.
Like a dummy I put it back in,shoulda left it out after seeing the petcock screen.
Drained the bowls,checked the pilots.
Everything was clean.
Rememberd one of Dinquas posts about Sparkplugs could`act up at anytime.
I changed the plugs.
The bike started with out any choke like it usually does when it is over 70 out.
Rode in the rain without one stutter or hiccup.
I had around 5000 miles on the plugs

did you check the gap on the old plugs? They may have worn enough to widen the gao to where the ignition couldn't jump the gap consistantly at that RPM where you had the trouble.

Just went out & checked them.
They are at 38.
When I Sgapped them I think I went around 30.
Had almost 2500 miles on them Sgapped.
The ones I just put in I Sgapped at 30.

There ya go ! Thats gotta be it because i had a similar problem tho not at a perticular RPM, and i found them widened about like that. It's a bit tricky gapping Sgapped plugs so you may have thought it was at 30 but it may have been on the verge of too wide and only took a short while to wear wide enough to cause that. When you gap Sgapped plugs make sure to put the feeler in and move it up and down too find what angle yields the loosest feel and use that angle to set the gap. Otherwise you may gap it at 30 but the actual widest point may be wider than 30, a good bit wider possibly. The angle can vary depending on how short you cut them.

Thanks Daz,
I am going to continue running the Sgapped plugs because they do run better in my bike.
I will re check the gap on the new ones.
I will have a Corona Extra on you.

Nows not the time to mention corona.......i'm done for now and have to wait a week.

1/4 throttle and when starting?
From what I have gathered, this sounds like pilot jets.
Maybe up them? Anyone?

Thanks for the reply,but the bike is running good now after I installed the new plugs.