81-550T, need 9000 rpm

[Buffalo Bill]

Hey, I still got it, so I have to improve it.
I see in the specs that the engine is rated for 53.7 Hp @ 9400 rpm.
But I don't feel any gains over 7000 rpm, and the engine don't want to rev much over 7000.
My best deduction is that it may be weak valve springs causing valve float.
Any ideas about getting those revs up to 9000?
Thanks!
Bill

 

[cowboyup3371]

I'd like to see what comes from this as I noticed the other day my 550T didn't want to go past 7000 RPM either.

 

[mlinder]

Odd, I hit 11k all the time. Well, not in 4th through 6th, obviously..

Have you made any changes to your fuel-air system?

As in, airbox, filter, carbs, exhaust?

 

[Buffalo Bill]

Some more details?

Some more details?

I'm talking about getting up to 9000 on the road, as it will get up there revving in Neutral.
Let me also say that it's all stock except for a MAC 4>1 exhaust.
I hear some popping and misfire as the revs get up, so I figure it's too lean as well. I've read the carb specs and am considering larger jets and needles.
I'd sure like to get the full HP from the engine.
Bill

 

[tkent02]

Put in the bigger jets, let us know how it works...

 

[mlinder]

I removed the airbox lid. I am running stock pilot jets, slightly enrichened air-screw, and 110 mains. The bike does 110 right now.

Synch your carbs after you rejet. Or synch them regardless.

All of my 11k rpm is while the bike is moving. I don't rev it at idle.

 

[Guest]

what does your plugs look like?

I take my gs550 to 9500 occasionally

 

[Buffalo Bill]

OEM lean for sure?

OEM lean for sure?

I removed the airbox lid. I am running stock pilot jets, slightly enrichened air-screw, and 110 mains. The bike does 110 right now.

I had it up to 98-100 and that's it's best. The glass ignition fuse slid sideways out of it's holder and stalled the engine so I had to coast to the roadside that run, but I've since updated the fuse box.
Thanks for the main jet size.
Bill

 

[mlinder]

It's easier to go 110 in 4th than it is in 6th...

Are you really trying to get to 9k in 6th? That isn't going to happen. I don't have the gear ratios in front of me, but that's something like 155-165mph.

Or maybe I'm making assumptions.

5th and 6th aren't good for much on these bikes outside of getting good gas mileage.

 

[Buffalo Bill]

Are you really trying to get to 9k in 6th? That isn't going to happen. I don't have the gear ratios in front of me, but that's something like 155-165mph.

Or maybe I'm making assumptions.

You're making assumptions?

 

[mlinder]

So... in what gear are you having trouble reaching 9k?

Also, please note that I have 110's with the airbox lid removed. Far too rich with airbox lid on, though a step or two up from stock is a requirement for best performance even with the lid on. These things were jetted so lean to meet EPA standards.

 

[Buffalo Bill]

I'm talking about hard accelleration?

I'm talking about hard accelleration?

So... in what gear are you having trouble reaching 9k?

I'd like to shift on the torque peak at 8200 rpm as I climb through the gears. Right now there's no power gain above 7000 because it progressively misfires as the rpms climb.
I'm going to order 105 main jets today.
As you have your '80 550 CV's currently set up, can it hold an idle at 1100 rpm? Mine will die out if set below 2200 rpm.
Thanks! Bill
P.S. Best 'O luck on that 650 head swap project. Too iffy for me.

 

[cowboyup3371]

So I will back out of this conversation now as I was able to get mine up to 8000 before shifting from second to third. So I wasn't trying hard enough last week. But I do wonder why would you want to do it that way? Is it just to get out of traffic real fast? Only asking because I was sitting at 45 mph by the time I shifted and I don't really need to be doing 100 mph down the road (not that crazy yet).

 

[waterman]

I'd like to shift on the torque peak at 8200 rpm as I climb through the gears. Right now there's no power gain above 7000 because it progressively misfires as the rpms climb.
I'm going to order 105 main jets today.
As you have your '80 550 CV's currently set up, can it hold an idle at 1100 rpm? Mine will die out if set below 2200 rpm.
Thanks! Bill
P.S. Best 'O luck on that 650 head swap project. Too iffy for me.

On my stock 82 550L, I found that shimming the needle really improved the performance. I am also running slightly richer main jet of 97.5 over stock 95. Mine easily overrevs, I tend to wind it out a lot farther since I am used my 650's power. Plus the 6 speed just makes you want to drop two gears and let it howl.

Can you do a plug chop at various throttle settings to get an idea how lean you are? I would check 1/3 and 1/2 throttle along with wide open just to get an idea.

I am a little surprised that it doesn't idle under 2000 rpm, I wouldn't think a pipe would make any difference at idle:-k. Maybe someone can enlighten me why this is so.

 

[mlinder]

I'd like to shift on the torque peak at 8200 rpm as I climb through the gears. Right now there's no power gain above 7000 because it progressively misfires as the rpms climb.
I'm going to order 105 main jets today.
As you have your '80 550 CV's currently set up, can it hold an idle at 1100 rpm? Mine will die out if set below 2200 rpm.
Thanks! Bill
P.S. Best 'O luck on that 650 head swap project. Too iffy for me.

Nice to get a bit more info there.

The fact that it won't idle properly (mine idles below 1k if I set it there) means more is going on.

Possible issues: (probably more than one of these)

Not firing on all 4 (at least not all the time)

• Bad coils
• Bad plug wires and/or boots
• Ignition timing off (do you have electronic ignition? My 80 does, my 78 does not, I dunno about yours)
• If not electronic ignition, points are toast
• Carb Boot leaks

Other possible issues

• Carbs very out of synch
• Bad Carb diaphragms
• Low cylinder compression
• Bad valve clearances
• Bad battery/ground
• Bad advance unit (mechanical or CDI, depends on your ignition)
• Very clogged jets

When you get your 105's in, please re-clean everything in those carbs. Check everything on them. Just popping in 105's is not going to help you without making sure any of these other issues are not at fault.

Lets hear more about your ignition, yeah? Tested coil resistance? Plug wire and plug boot resistances? Checked advance with timing light? How much voltage at battery terminals at 5 grand?

 

[mlinder]

I am a little surprised that it doesn't idle under 2000 rpm, I wouldn't think a pipe would make any difference at idle:-k. Maybe someone can enlighten me why this is so.

It's not the pipe. Something else is going on.

 

[mlinder]

So I will back out of this conversation now as I was able to get mine up to 8000 before shifting from second to third. So I wasn't trying hard enough last week. But I do wonder why would you want to do it that way? Is it just to get out of traffic real fast? Only asking because I was sitting at 45 mph by the time I shifted and I don't really need to be doing 100 mph down the road (not that crazy yet).

The little inline 4's, especially jetted as they are from factory, do not really start making power til 6.5 grand. For spirited riding, I like to keep the engine speed between 7 and 10k rpm.

 

[tkent02]

Short shifting a 550 at 8,200 will put you into the next gear well below the torque peak, it probably won't pull fifth or sixth any higher, especially in headwind or up a grade, and of course depending on sprocket ratios. Shifting at 10,000 or so, it is already in the torque peak when it gets to the next gear, should be able to pull it on up.
If you want to shift at 8,200 and keep accelerating, get a bigger engine.
Or make yours a 650.

 

[Buffalo Bill]

Some work history?

Some work history?

Mlinder, Here's your list with my response:

* Bad coils---------------------------------------replaced, no change
* Bad plug wires and/or boots------------------maybe, but they look good
* Ignition timing off.--------------------------- N/A 1981 has electronic
* If not electronic ignition, points are toast----N/A
* Carb Boot leaks------------------------------------I cant find any leaks

Other possible issues

* Carbs very out of synch---------------They're synched
* Bad Carb diaphragms-----------------they look good
* Low cylinder compression------------just replaced the rings
* Bad valve clearances------------------in spec
* Bad battery/ground----------------------battery is OK, and grounded
* Bad advance unit------------------------maybe, never tested
* Very clogged jets------------------------clean, microscope inspected

Haven't put a timing light on it yet, I'll try that. :-k
Charging voltage 14-15 volts

Too much to check in a day, plus I spend most of my time working for money.
Thanks!
Bill
P.S. Have installed new intake O rings as well.

 

[mlinder]

Dun worry, I'm at work now, getting paid to talk to you.

Please stick a timing light on there. Check advance.
Also check plug wires and boots resistance.

What plugs are you using, out of curiosity?

(Ignition timing can still be off with elec ign. Not often, but it does happen.)

All 4 headers getting hot, right?

15v sounds a tad high...

Best of luck! If I can think of anything else, I'll post, but checking plug wires and boots (and while you're at it, you can check coil resistances too..) and checking timing and proper advance, I think you may find the culprit.