Hesitation at 4500 RPM's

[ceemes]

Got my bike back this weekend, for the second time. Picked it up on Friday and it died after about 42 kilometres, shop picked it up and replaced a fuel filter. Today took it out for a good run and noticed a problem. Up to 4000 RPMs it runs fine, no hesitation or jerkiness, although it does seem to be a lot less responsive ie quick off the line then before, But when I get up to highways speeds which run between 4000 and 5000 RPM's in sixth gear, I start getting hesitation, like its not getting enough fuel. and at around 5000 RPM's, I can actually see a 500 RPM drop on the tach when this happens, which is about once every 10 to 20 seconds. I banged it up past 5500 RPM's and the problem went away and stayed away past 6000 RPM's, problem is, at that those revs in sixth gear, I am pulling in excess of 160KPH or over 100 MPH, something the Queens Cowboys tend to frown on.

When the bike was in the shop, they tore the carbs apart, gave it a sonic bath and replaced some choke components and resynced it. Prior to them doing this, I have no problems at all, the engine purred along at all revs and had plenty of roll on power even in sixth gear at 120 KPH, now when I try to roll on power, its sluggish. I will be taking her back to the shop on Tuesday when they open, but I would like to get a bit of feed back from the experts here before I do.

Thanks in advance,
Ceemes

[HYPERR]

Sometimes the spark plugs get fouled when you run out of gas or the bike dies due to a clogged fuel filter.

[Wrider]

That's very true. Might also want to have them re-sync the carbs. They should have done it at idle, 1500, 2000, and 4000 on that bike IIRC.

[ceemes]

Well, its back at the shop for the third time this week. This time I watched as the tech took it out for a run to see what I have been experiencing. He came back and judging the way the tach was bouncing about, he figured it was an electrical fault, something was knocking out two cylinders for split second every few seconds at between 4000 and 6000 RPM's. They pulled my ECU off and replaced it and still the problem persisted. They then tried a second ECU and still no joy. Anyways, its staying over at the shop and tomorrow they are putting it on the dyno and running an sweep of the electronics and ignition system. They think it maybe a bad coil or two.....hopefully they will finally get it sorted......and to add insult to injury, I took the bus home from the shop....sigh......

[BuzZz]

I'd say coil over CDI box from the sound of it. Possibly a bad plug or two.....
I'd say carburation over both first though..... since that's what was touched right before the problem showed up, that's where I'd start looking first if I was that shop.

[ceemes]

I'd say coil over CDI box from the sound of it. Possibly a bad plug or two.....
I'd say carburation over both first though..... since that's what was touched right before the problem showed up, that's where I'd start looking first if I was that shop.

The carbs and fuel flow checked out fine, although I was lectured about leaving the petcock on primary. Never had a bike with that type of petcock before, three settings, reserve, run and primary and no off.......

Turned out to be the coils, so far anyways. when I called they had replaced the coils and had her up on the dyno doing another diagnostic run and she checked out okay. However, the shop owner asked if he could keep it another night and ride it home just to make sure everything was okay. I said fine and asked how much more I will have to pay.....only C$100......not too shabby. With luck, I will pick her up after work tomorrow and I can finally get back on two wheels properly......bet it bloody rains non stop now.

[NorthernPete]

a hundred bucks so he can ride your bike to his house? Id be all "Ummmm, no, Ill ride it home and let you know if its still pooched"

[ceemes]

a hundred bucks so he can ride your bike to his house? Id be all "Ummmm, no, Ill ride it home and let you know if its still pooched"

Normally so would I, but this time I decided to get it properly test ridden before it was returned to me.......works fine now.