No power below 3k

Hey everyone just bought an 82 XJ650J and am having a bit of a problem with it. When I ride, there is absolutely no power below 3000 rpm. Once the tach hits 3k, it takes off like a rocket. The bike also wants to die at idle once it has had a chance to warm up. Any ideas?

I just joined the site and am loving all of the information available

Thanks

 

Welcome to you Brando!
I'll ask if you know how long the bike sat before you got it.
If it sat for a few months, you should consider pulling and cleaning the carbs. My gut feeling is that you have some crud in the pilot jet.
The next investment you need to make is in a maintenance manual for your bike. Check with Chacal (our resident XJ parts man) for the correct books for your bike. The book will help you troubleshoot and fix anything on your machine. It will pay for itself very quickly.
Hope you enjoy yourself here, let's see some pictures!

 

my bet would be pilot jets too....

 

Thanks for the insight. I have already gone through the carbs, but didn't touch the pilot jets since mine were still sealed under the brass plugs. The bike had sat for about 10 years when a friend of mine bought it. Two years and a couple of carb cleanings later, I bought it from him never having solved this issue.

As an interesting aside, I took out the pilot screw on a two of the carbs, and I couldn't find a washer or an o-ring under the screw. The carbs are the stock HC32s and it was my understanding that those should be under the screw

 

Pilot Jets and Pilot Air Passages.

You absolutely NEED Pilot Mixture Screw supplied Fuel to supplement the Lean condition thaht occurs as the Bike is coming Off-Idle before the Main Jet Fuel Supply kicks-in.

My guess is that you have clogged Pilot Jet ... clogged Pilot Air Passages and no Pilot Mixture is available to support Ignition.

From your description of what is going-on ... I'd say you should Clean your Carbs and do a whole Carb Tuning procedure to make for a trouble-free Fuel Delivery situation.

We just had a GIRL pull the rack and clean them ... your turn!

 

what does this add to responce??
that sounds degrading to me,that kind of crap in most of your posts is why I dont viset this site much anymore

 

It means there is no Silver Bullet or Snake Oil Remedy.
It's going to require you removing the Carbs from the Bike and thoroughly Cleaning them.
Wrench and screwdriver time.
Determination and goal achieving.

You need a Carb Cleaning and a tune up.
That the only woman I know of that has ever done this job herself just got done and has her bike running nice was just my attempt at levity.

You didn't get it.
That's OK.
Sometimes I don't get it either.

I try not to put crap in my posts.
I've helped enough folks to date that I ought to be allowed to say just exactly what I think needs to be said and you weigh that with what others throw-in to the mix.

I try to make doing this fun.
But, sometimes theres no fun in it.
But, I try just the same.

The price is right.
Don't cost nothing.

 

Geico, so easy a caveman can do it
come to think of it mine doesn't have much power below 3k either the fun starts at 6k, these aren't torquers their screamers

 

Yes. But you need the response below 3,000 to fully enjoy the cruising aspect of these Bikes.

Without a steady Idle and the ability to get the Bike up-to-speed getting away from a light or joining traffic on a ramp ... it's more than a bit unsettling to not have the low-end present.

That comes from having the Pilot Mixtures dialed-in right. There's no way around it unless you fancy revving-it-up and keeping the engine in the lower power band with blipping the throttles ... which is a waste of Fuel and a little embarrassing to have to do so.

 

These bikes ( 750 and 900 ) will pull smoothly thru the grass at 600 RPM ' s with no problem, if everything is working right.

No bucking, or stalling. And no real power, but a steady pull at below idle speeds.

 

I can get my bikes to "Pull" with heavy manifold vacuum from low rpm's in all gears.

There are many times, in traffic, when I've slowed down to a near crawl and need the power and have put it on in second gear.

If the bike isn't responding to Throttle-on in the lower part of the range ... either the Pilot Mixtures are incorrect ... likely too Rich ... or the Diaphragm Pistons aren't rising fast enough to bring-up Main Jet Fuel.

Both situations are easily corrected.

First, clean and POLISH the Diaphragm Piston Bores to insure that the Diaphragms are going to rise with Manifold Vacuum and the rapid flow of Intake Air.

Second, do a series of Plug Reads and make sure that the Pilot Mixtures are set to not offer an overly Rich Mixture when the Bike is Throttling-up from a situation when the Throttles were closed.

The Pilot Mixture setting is delicate.
The window between too Lean and too Rich is narrow.
Well within an eight of a turn ... just a few degrees.

You have to "Play" with the Mixtures over time to find the spot where there will be sufficient additional Richness supplied to answer for the rush of Lean air entering the Head ahead of the Main Jet Flow.

The duration is short.
But, there is the briefest time when the Throttles are wristed open and the Main Jet Flow follows.

You need to tune the Pilot Mistures to defeat that Moment with a supplemental flow of fuel to MAKE the Engine respond to the Throttle opening.
Right there you are Tuning for PERFORMANCE.

Too much Pilot Mixture Fuel and the Ignition bogs down.
Too Lean and the Ignition of gases waits for the Main Jet Supply.

Within that window is a tunable degree of Performance.
A supplemental supply -- Lean -- causing a Powerful Ignition and rapid acelleration.
A supplemental supply -- Rich -- causing a slower Ignition of gases making for a smooth and steady application of power.

That point ... between Speed and Smoothness requires nothing more than the a "Nudge" of the Pilot Mixture Screw to change the Ratio and ammend the performance of the bike.

Getting ALL four Carbs to be within that narrow window is the fine art of tuning.
Most of the feedback is felt and heard.
You get the idea from repeated Throttle openings.

Feeling how the Bike responds to the selected Pilot Mix coming off-idle.
The other feedback is Plug Reads.
You adjust individual Cylinder's Pilot Mixture by studying the Plugs and making (my-nute) adjustments to the Screw.