Reduced Power

I have a 1981 Australian XJ650, same as US "RJ". I have refurbished the bike, including KY-0511 Keyster Carb Kit. It starts beautifully but has little power until about 3000rpm when it takes off like a "cut cat". I've have a MC mechanic check it out, the pilot screws are even at about 2.5 turns out, but we can't get power lower down. Could increasing the main jet size help with getting more fuel into the cylinders at low revs? Also the spark plugs show the engine is running lean (whitish colour). Any help appreciated. Thanks, Stephen.

 

A bit more info please Stephen - standard / aftermarket exhaust?, airbox / pods?, etc.

Have you checked for air leaks at the manifolds / butterfly seals? Sounds like it might be sucking some extra air in at low RPM.

BTW - changing the main jets should have no effect on low RPM (they affect WOT).

 

Hi Hillsy,
The bike is standard, it does have a Motad 4-1 exhaust system, otherwise I've kept everything original. I replaced the V-seals at the ends of the shafts, although these didn't appear to be a really good fit and spacer washers, E-clips. New Carb Kits, KY-0511 which has Main nozzle; #110 main #40 slow jet, but on XJ4ever his main #110 and #50 slow jet, hence my querying the Jet size. We can't find any sign of leak at manifold, in fact the MC mechanic thought this would be the problem.

 

The lower size pilot (slow) jet could be the problem. It will affect (to some degree) the mixture straight off idle.

But if the plugs are lean, you could probably go a size or 2 up on the mains as well (seeing as you have an aftermarket exhaust).

 

Thanks Hillsy, I'll get some jets from XJ4ever and play around a little. Cheers, Stephen.

 

Thats what she's soundin like to me too. Pilot jet mix up. Classic.
How are you figuring she's lean? At Idle? or are you doing a plug chop? If so, at what RPM?
Another good test for leaks is the propane torch test. Its easy and quick.
-Chris

 

Hi SLKid,
The MC mechanic has had this bike for a while checking the carbs, manifolds, etc, and he was the one who removed the spark plugs and they looked more white than brown. And it was him who suggested playing around with the jets. He would take it for short rides around his industrial estate after making changes, and was aware it was running lean. Regards,
Stephen.

 

Understood. But to be honest with the lessons I have learned here I'd check it for yourself. When you drive these bikes around and then shut them off after you dismount instead of waiting a few min to idle you could get "inconclusive" spark results. EX: Plugs that are mostly white and have brown near the bottom or brown flecks.
If it is still mostly white after lettin her idle for a while I'd adjust her air/fuel ratio via colortune.
After thats complete try a plug chop.
Drive around for 10 miles or so and then on a long stretch of road hold your throttle at a regular cruising RPM, (What you normally coast around on. Mine's about 4-4500 RPM) Hit the kill switch and keep the throttle open and coast to a stop.
Let her sit for a bit and then check the plugs. Still white?? Larger Main Jets. Brownish? Then you're in the clear
-Chris
VERY Beautiful bike BTW
I'm jealous!
super jealous

 

Thanks SLKid, both for the advice and for the compliment. With this bike, my objective was to learn to spray paint, so all the painting, engine, frame, panels was done by me (I had the decals made for me, original design but in white). Cost a lot in paint, and it took me 3 goes to get the frame right, each time taking back to bare metal, but preserverance paid off.
I will do exactly as you suggest, and where do I get a "colortune" plug from? I did install a KY-511 Carb kit, which included a new needle (for each carbie), and I'm wondering whether this isn't quite the same as the original. If so, could that explain it running lean at low revs, and going like a 'cut cat' at 3k rpm? Maybe, with the 'colortune', I could play with the needle heights, or even simply put the old ones back.
Again, thanks for your help, regards, Stephen.
PS. I've already bought another bike to restore, a 1985 Yamaha SRX600. I love the sound of a "single". Same treatment as the XJ650, take it down to nut and bolt component level, re-zinc plate all nuts and bolts and replace all bearings, seals, gaskets etc as I'm rebuilding it. Strip, repaint, etc.

 

Check out our resident dudeman supplier Chacal. Awesome guy. Got a colortune from him for 50 bucks. You screw it in where the spark plugs go andit shows up a color when you tune the bike on.
If it is Orange, it means you are running rich on that cylinder from that carb at Idle. (Or up to 3k RPMS, about when the Pilot jets stop working) You'll take a small screwdriver and turn the Idle Mixture Screws screws out or in untill you acheive a Dark Blue flame in the colortune with no white. White is Lean. Blue is a "perfect" Idle mixture
Here's a rundown on stock carbs jets in your 650
Main Jet Size: 110
Pilot jet size: 40
Piston Needle: 20

I got my bike and its carbs were rebuilt with a 650 carb set. So I know the 650s carbs intimatly
-Chris
I learned how to spraypaint and ride and wrench and fabricate on this bike too in the past year Good times

 

Thanks SLKid, I'll get one ordered from him right now. Thanks, Stephen.

 

Hey Stephen.............actually, your bike uses the following combo of jets in stock configuration:

Main fuel jets: #110
Pilot fuel jets: # 40

Main air jets: # 50
Pilot air jets: # 195

Main jet needle: Y-11


The needle that comes in the Keyster kit is un-marked, and therefore it's hard to say what "size" it actually is; I would assume that it's the Y-10 size as used in most 650 models (except yours!) since that is the most common size. However, I have no way of knowing what the dimensions of the Y-11 needle is, since I've never had an original to compare with.

However, the main jet needle is really active only after you come off-idle, and into that "cut cat" area of the power band..........

 

Hi Chacal, I've sent you an email as I'm 'busting' to buy a Colortune Plug from you. Can you send my a quote number to my email address please. Thanks, Stephen.
I had not forgotten, and as soon as I have the bike running properly, I am going to be sending you my original needles to see what the difference is between Y-10 & Y-11. Cheers.

 

Hey Stephen..........I already sent you a reply for the Colortune plug about an hour ago......are we back to having e-mail problems again?

 

Hi Chacal,
I definitely haven't got it, can you please send me the cost & quote number to me as a PM. Thanks, Stephen.

 

Done!

 

Lol leave it to chacal. He is, of course, right again