Topic: 550F odd running issue

[Stev-o]

My bike has developed an issue, it will not run over 5K RPM after approx 20 min of riding time.

It starts normally when cold, idles normal after warm, starts immediately when engine is warm and will run up to redline when first start riding but after 20 min, will "dog" over 5K. Rides fine under 5K.

Bike is stock including airbox and 4 into 1 exhaust, except for Dyna installed last year when restored, and plugs appear normal.
Bike had full tuneup approx 300 miles ago including plugs, caps, petcock, air filter and carbs cleaned. And cleaned again since. I had not ridden it before then.
 
At this point I'm thinking it's ignition, coils going out when hot? I have a buddy helping me w/this and he is stumped too.

Have you encountered this issue? What do you suggest, please help! Need to get this thing running great for the Rally next month.

Thanks.

[Deltarider]

I'm thinking it's ignition, coils going out when hot?

Could be, but unlikely both die. If you suspect one have coil tested by specialist. How far dyna'd are you, just coils or the whole thing?
But first:
1 Sure about what the plugs tell you? Do they all appear normal?
2 Does your tank vent?
2 Suspect the last things you did, like your petcock. Make a mental list of what you've (mal)handled lately.
3 Fuel lines in good order and not kinked?
4 You don't have any extra inline fuel filters, do you?

[mlinder]

Also, check for a dropped mainjet. Might have one inthe bottom of one (or more) of your float bowls.

[Deltarider]

I had a jet dropped in the bowl once, but that was the slow jet. When leafspring is well in position, it's hard for a main jet to fall down.

[shizzomynizzo]

Had similar issue with my 550. Turned out to be a cracked spark plug cap. Ride it until it starts doing it. Then bring it in a closed garage and rev it up and look for sparks in the dark.


If you want to avoid breathing in all that CO, just swap out new caps...it's only 20 bucks  

[Stev-o]

I'm thinking it's ignition, coils going out when hot?

Could be, but unlikely both die. If you suspect one have coil tested by specialist. How far dyna'd are you, just coils or the whole thing?
But first:
1 Sure about what the plugs tell you? Do they all appear normal?
2 Does your tank vent?
2 Suspect the last things you did, like your petcock. Make a mental list of what you've (mal)handled lately.
3 Fuel lines in good order and not kinked?
4 You don't have any extra inline fuel filters, do you?

1. All plugs normal.
2. Have tried running tank cap loose
3. Fuel lines good, no kinks and no inline filters.
4. NGK plug caps are new.