No power under 2500rpm

I just bought my newest headache, joined this group and now I reach to your collective knowledge like reaching for tylenol on a Monday morning.

So, here's the deal. I just rebuilt and sold a 1977 XS750 triple. Loved the bike, but too heavy up high for my verticle challenge. I subsequently bought a 1982 XJ650RJ Seca. Love the shape, similar look but lighter and no points and condensers.

No info from previous owner, but it is a low milage bike with a 1 owner history. It came with a new never installed tank, a new never installed timing chain and a spare bank of used carbs. Receipts show that tank and chain were bought in 06. Sounds like a rebuild put on hold then abandoned, but who knows. Bike is stock, including pipes and air box.

This is what I am facing right now. Bike runs well and pulls strong. Runs great cold, but when it warms up, different story. There is no power below 2500rpm or so. Literally have to nurse it away from lights. After that, plenty of pull. I suspect from experience that it is an idle circuit thing, but the "only when hot" is a bit perplexing if that is the case. From what I have read in here it could be anything from an air leak to a cheeseburger stuck in the air box.

It is my daily rider, so I am trying to avoid a complete tear down until the snow flies. Then you will see me on here a lot, no doubt.

Any thoughts or suggestions on a trouble shooting sequence?

Thanks in advance

 

If i'm running lean pilot circuits I get this type of take off. Of course, these engines don't make a lot of torque/power till 3k anyways so.

 

Check your valve clearances straight away. "Starts right up cold, won't start warm" is often a symptom of some tight clearances.

Or carburetion; but you can't adjust the carbs if the valves aren't in spec.

The timing chain was likely purchased out of ignorance, those are usually a high-mileage item.

 

Thanks guys, unless that is sexist, then, thanks folks.

I will start there this weekend. Want to do this in order so I am not chasing my tail.

 

^I love that response.

You, my friend, are already a welcome addition with that attitude.

 

Thanks guys. Would like to say that I checked the valve clearances, but.....

Got all the stuff out, put on a pair of coveralls to do all the work. Good start, right? Well, then comes the curveball. Turns out there is something about a guy in coveralls as far as a certain redhead is concerned. One thing led to another and in the end, there was no time left to turn wrenches.

I have been just riding back and forth to the office and the other day had to go a bit further afield. After a good run on the highway, her attitude is much better (the bike not the redhead). Not bogging on the low end after warming up anymore. Still reluctant to idle though. Not sure if this adds any insight.

There is an oil leak in the head somewhere, so I am going to wait for the gasket set to arrive before doing the valve clearances. Does anyone know a source for shim sets in the great white north?

 

Oh Ya. Forgot to mention. Starts fine hot or cold. Not sure if that changes the valve thing. Not that it matters a whole bunch, Since they will get checked when I start chasing the oil leak.

 

I suspect that your carbs were gummy and that you have cleaned out some of the gum by driving it. My bike started terrible and had no power on throttle. Adjusting the valve clearances and cleaning and synching the carbs turned it into a rocket.

Unless you have a fuel filter in place there is gonna be lots of little rust specs all over the carbs. My carbs had rust particles in every nook and cranny. You have to disassemble to get these particles out.

Do yourself a favor and perform the routine items: valve clearances, clean carbs, synch carbs. Its inexpensive to do and not incredibly difficult as long as you take your time and follow the FAQ instructions. Install a $1 lawn mower fuel filter. No more rust in your carbs.

 

Took the sidecutters to the fuel line as soon as I popped the gas cap and saw inside. I don't know where you get your lawnmower filters, but mine was almost 3 times that price. Holy crap!!! Oddly, not much crap has collected yet. All the flakes have probably already made their way down through into the far reaches of It'llnevercomeout land.

The bike came with a spare set of carbs, which rocks. Ordered a rebuild kit last night. The intention is to clean and setup a set. Once they are done on the bench, I can pop them on for final adjust with minimal downtime. Then I can clean and prep the second set so they are ready to go next round. Probably excessive, but, if ya got em, may as well use em.

On a side note, as I look over my shoulder to see if my Bonneville is listening, this freakin thing is the most fun I have had on a bike in a long time. I cannot believe the power. It is also incredibly nimble in the city. I am loving it. Totally unexpected suprise.

 

And the prize goes to........... The piece of crud crowd.

Couple of bits of crud floating around in the carbs. Minor cleaning took care of it. When the other set is fully cleaned and synched they will go on, but for now, all sorted.

Thanks all.

 

You still need to check the valve clearances. If neglected, they're long overdue; and you don't want to damage the motor.

I hope you checked the rear brake before you started riding it: http://xjbikes.com/Forums/viewtopic/t=15874.html

 

YIKES!!!!!!!!!!!!!!! Looks like I know what I am doing this weekend.

I should average my two bikes and all will be good. I have a '76 Bonnie that will only stop at times if you book an appointment far enough in advance.