Topic: Problem revving out in 5th

[Retro Rocket]

Hi guys, i have a friend who has a very nice K2, it has stock pipes {341's} and carbs, it now runs a dyna ignition with 3 ohm coils. The problem is that the bike will not go over 75-80 MPH in top gear, it pulls like a normal bike in the lower gears, but just hits a wall in top gear. Russ isn't a noob at all and is at his wits end trying to figure out the problem. I asked about the gearing and he had an 18 on the front with a 45 {i think} on the rear so i asked him to swap over to a 17 on the front to see if it made any difference but to no avail. It has a stock airbox with brand new filter, new reg rectifier, carbs have been gone over, floats set at 24mm then 26 mm, no change to performance. He has basically covered everything that you could possibly think of so anyone have any suggestions.?

Here's a pic of the bike in question, oh and it has 130 compression across all 4 pots.

[Rgconner]

But it revs to the red line in other gears?

Interesting. That would have been my first guess, the timing not advancing enough or something like that.

Just my two cents, but I am thinking maybe change the needle clip position?

I presume a plug chop looks ok?

[MCRider]

Confirm Sprockets as a 18/45 is taller than any OEM stock. Dropping the front to a 17 just makes it equivalent to OEM 18/48. But this can't be the root problem.

The bike in stock trim should have no problem pulling redline in 5th, so before applying bandaids I'd return it to pure stock, check the compression, timing, then cry, pull hair out etc.

Oh, I see you've done compression. 130 is a little low IMO. 160-170 would be better, but still 130 shouldn't be bad enough to limit top end. Just not crisp. I wouldn't expect your symptoms till 110 or lower.

From what I've read if all else is stock as a board, I have to suspect the Dyna. When they go bad they can be very fickle, no logic to the failure symptoms. Get a points plate and try it then.

[Rgconner]

That is why I wondered if it revs out in lower gears.

If it is the Dyna, it "should" be the same issue in any gear.

That is the theory that I have, and which is mine, and what it is too... =)

[754]

 It may not be an issue in other gears, hardest pulling is in top gear.. I would swap back ignition ..easy to do..

[MCRider]

That is why I wondered if it revs out in lower gears.

If it is the Dyna, it "should" be the same issue in any gear.

That is the theory that I have, and which is mine, and what it is too... =)

Agreed, that's why I added "no logic to symptoms" which is typical with electronic failures, in my experience. Point: my recent work with a Prestolite ignition. Worked when i parked it. Now it times up one moment. Go away and try again, won't time up. And my wife's VCR failure. WTF! No logic to symptoms.

[Jerry Rxman Griffin aka MuthaF'er]

The clutch isn't slipping with that load is it?

[seanbarney41]

fuel supply? slightly slow flowing petcock or fuel lines?

[Doctor_D]

The clutch isn't slipping with that load is it?

Then it would redline, but not accelerate.

[Jerry Rxman Griffin aka MuthaF'er]

The clutch isn't slipping with that load is it?

Then it would redline, but not accelerate.

Yeah, I didn't see anything pertaining to rpm, only speed and with the load of 5th that could cause slippage.

[Retro Rocket]

Thanks for the replies guys. It did the same thing with the stock ignition, it will not rev out in 5th {its in the title } The guy is a mechanic and has been through everything more than once, i thought maybe the low compression combined with tall gearing may be partly responsible but there must be something else. won't rev over 7500-8000 in top....  Russel has joined the forum so he should be able to help out with more info....

[TwoTired]

Has he tried reading clean plugs after a plug chop during the rev problem?
Timing advance checked?

um, is the speedometer sticking?  <---longshot

[Doctor_D]

The clutch isn't slipping with that load is it?

Then it would redline, but not accelerate.

Yeah, I didn't see anything pertaining to rpm, only speed and with the load of 5th that could cause slippage.

I think the title of the thread covers rpm's.   "Problem revving out in 5th"

 

[Doctor_D]

In all seriousness, how's the leakdown?  Compression is only half of the equation.

Cam gear could be off a tooth.  That would be a pretty extreme case, but if the cam was that far advanced he'd have no power at higher rpm's.  Speaking of the cam, if a lobe went bad he might be down on enough power to not be able to wind it out in top-gear.  Are all the exhaust pipes reading the same temp with an infrared thermometer?

[Retro Rocket]

In all seriousness, how's the leakdown?  Compression is only half of the equation.

Cam gear could be off a tooth.  That would be a pretty extreme case, but if the cam was that far advanced he'd have no power at higher rpm's.  Speaking of the cam, if a lobe went bad he might be down on enough power to not be able to wind it out in top-gear.  Are all the exhaust pipes reading the same temp with an infrared thermometer?

Leak down hasn't been done as far as i know, bike runs well in lower gears so i doubt the cam is out a tooth, not sure about exhaust temps. One thing i do know is that the bike has been like this since he bought it, he has been right through the carbs multiple times, checked out the breather in the tank, checked fuel flow and replaced most of the electrical components with new, still has the same problem. I suppose the top end may need closer inspection..
Thanks for the input Dave...

[Retro Rocket]

Has he tried reading clean plugs after a plug chop during the rev problem?
Timing advance checked?

um, is the speedometer sticking?  <---longshot

I suggested the "long shot" speedo thing and he even had that rebuilt, i'll ask about the plugs..

Advance checked with both stock points and Dyna...

[dave500]

tried new plugs?plug cap resistance?bunged up exhausts?

[754]

 I think you can sopt cam being off a tooth with a degree wheel...

[Retro Rocket]

tried new plugs?plug cap resistance?bunged up exhausts?

You've seen the bike Dave, its very clean, most parts replaced with new, revs its tits off in the lower gears, just won't pull in top gear, a leak down may provide some answers....

[dave500]

yeah i think 130 is low i wouldnt be happy with that,has he got a leak down tester?

[Retro Rocket]

yeah i think 130 is low i wouldnt be happy with that,has he got a leak down tester?

I don't think so Dave. Russel has joined the forum but isn't very good with computers, hopefully he will chime in with some more info....

[scondon]

You've seen the bike Dave, its very clean, most parts replaced with new.........

Clearly that must be the problem. If it goes any faster people won't be able to admire/gawk at it. Rub some dirt on it

When Russell gets on maybe he can tell us what needle position and main jets he has. Also, if he has a spare float bowl he might wish to try the clear line method of checking his actual fuel level in the bowls. Lower gears are very forgiving, but 5th gear can certainly be difficult if one of the levels is off, especially with the final gearing he's using.

[scottly]

Also, if he has a spare float bowl he might wish to try the clear line method of checking his actual fuel level in the bowls.

1+

[Retro Rocket]

he's pretty switched on and has measured and tried a couple of different heights for the floats, i will suggest the clear line method and see how that goes. Wouldn't that effect revs in all gears though.? Or would the extra fuel needed for the load in 5th allow this to happen.?

[dave500]

three teeth smaller on the rear can cause a bit more load,what is the stock gearing meant to be?