XJ700 Bogs at High RPM (under load)

I already did, it made the bike run like complete s**t!

I haven't looked at the plugs after replacing them. Is ~1.5k miles enough to get a decent reading on how well the engine is running?

 

I FIXED IT!!! ... well sort of.

I put the airbox cover back on WITHOUT the filter installed, and took a ride hoping it would restrict the air intake enough. Sure enough: redlined like no tomorrow, both cold and once warmed up! Didn't need the choke this time. Rode to the station to fill up some gas, and threw some fuel system cleaner in the tank just in case I happened to miss a few spots when cleaning the carbs. Man, I was so ecstatic that I was redlining it the whole way home! ... well not literally, I did down shift, but I redlined when accelerating then shifted and cruised at 4k.

I think it's pretty clear at this point that my bike has been rejetted or the jets had been drilled out at some point in time. There is no doubt that even if I threw a brand new air filter on it that it would still run like s**t.

 

MY BIKE + OEM AIR FILTER = RUNS LIKE S**T! ... damn do I have record it and upload a video to prove it?! I haven't tried a K&N / UNI yet.

 

It might be worth the try to put an air filter allowing more free flowing than the OEM. I'd also follow Dragsta's suggestion about reading the plugs colour after killing the engine at high revs, to know exactly how lean it could run around redline.

 

Which points to you needing to rejet, and/or try a K&N, and maybe calm down a little. Avice, don't seek it unless you plan on listening. What the collective is doing is trying our damndest to keep you from holing a piston; which would mean that all the money and effort you've spent ends up being wasted.

 

I planned on listening from the beginning, but when people tell you test ride with the filter and I already said it four or five times that my bike runs like absolute crap with the air filter installed, then it is quite easy to become agitated, it's almost as if we are going in circles about this.

Should I go for a K&N or an UNI?

 

If it were me I'd save the money and find out what jets are in the carbs first. Then I'd weigh the cost of used (or new if you want to splurge) jets vs. the K&N. I'd also consider whether a stab in the dark with a different filter is better than going with what is known to work (stock jets). Even if it runs well with a less restrictive filter you may still be too lean at high RPM. Engines looooove being too lean. They will make really good power when lean, until all of a sudden, they don't.

 

Stock jets are 36.5 pilot and 107 main for the airhead models, correct? Any way to tell if they had been drilled out aside from the obvious marring from drill bits?

I'll take a look at them tomorrow or Tuesday, depending on weather.

 

+1.

+1.

Gary H.

 

you can tell the hole size by inserting a a drill bit to check size., i think a 40 j
K-moe posted how to tell which size bit to use i think a 40 jet is a .40mm drill bit
this is how he stated it
The jets are sized by the minimum ID in hundredths of a millimeter, so a 40 pilot will accept the shank of a 0.40 mm drill.

 

A new one.

 

I came late to this one. I just read the whole thing, and there's one thing that may have gotten overlooked... @quentin you, mentioned a fuel filter on there, right? Is it the brass kind, or the paper one? If it's not the brass kind, this could be choking off the fuel flow..

 

It's brass.

 

So I went for a highway cruise today, bike felt very responsive. Rode about 6k RPM the last couple minutes of the ride, and cut the engine there and cruised to a stop to look the plugs.

Spark plugs are from left to right of engine, facing the front wheel (cylinder "one" is at left "foot" and "four" is at right "foot").



The threads kept appearing darker than they actually were, despite using flash. I also want to note that these are the plugs that I have also ran for the last 1500-2000 ish miles, if need be I could always buy a new set of plugs and do another ride + high-speed cut off (which would be ideal to get the best results for air/fuel mixture, correct?)

NOTE: Sorry if the photo is huge in appearance, PhotoBucket is being slow with its edit renderings.

 

They all look too dark, but it could be the picture that is not good enough.

 

Retake with the plugs laying on a tablecloth or towel, and without the flash.

 

Should I reuse the old ones or go ahead and splurge on some new ones, for the sake of the "argument"?

 

You can keep using the ones you have for this purpose. So long as you have the correct heat range plug, they will self-clean every time they get used. The color is just what's left from the last few combustion cycles (I'm talking about ground strap color here, not ceramic color).

 

Sorry that I haven't replied yet. Not much chance of ride in the snow

 

Ya. You got hammered all of a sudden. My brother lives in the Wilamette Valley, and he had a 2 1/2 hour commute last Friday trying to avoid all the mudslides and washouts. I'm glad your side got all the snow. It's much more enjoyable.

 

Well I talked to my mechanic about the "runs like crap with air filter in" issue and he thinks it may just be the fuel mixture screw is set a little too rich (which the holes have been drilled out, so it is plausible). What I am gonna do is I am gonna take the front wheel off (tire needs replaced), replace my speedometer drive unit (new cable, speedometer turns when turning the cable, but doesn't register when riding), and I am gonna buy a new OEM air filter to see if the one I have is just too dirty for the bike to function properly. If the filter does not work out, I'll just bring the bike in for a carb tune and sync (which will only cost me about $65-100 until the end of January) and hope that fixes it.

 

Not sure about the 700 compared to an XJ 650.
But on the 650, it is the odometer that runs off the front wheel; the speedometer cable hooks up to the front of the engine where the oil is leaking from . . . .
This is on my list for 2016 :
http://www.xjbikes.com/forums/threa...il-seal-replacement-w-pics.19538/#post-164299

 

?????????
All the speedometers I've ever seen or worked on were either wheel driven or transmission driven (all are wheel driven on an XJ). I think you mean that the tachometer is driven from the engine (at the exhaust cam).

 

Yeah, I was gonna say he's thinking of the tach. I was referring to my speedo which is driven by a sealed unit at the front wheel. When pushing to bike, there is a sound of rattling/scraping coming from the from the front wheel hub, I'm hoping the tangs are just bent and I might be able to fix it, otherwise Im hoping my local moto-junkyard has a replacement.

 

Yep, color me stoopid for 2016.

 

Welcome to the club! I've been a member since '78.

 

Quentin, I have a very similar issue with mine.. Did you ever get this resolved?

 

This thread is over two years old, and Quintin has not been seen here since.
Please start a new thread for your bike so we can be of service.