XJ700 Bogs at High RPM (under load)

My bike (86 700 airhead) is acting strange . In neutral, or with the clutch pulled in, (aka not under load), my bike will freely rev to my heart's content; however, once you go into gear (accelerating) and try WOT, the engine starts bogging at 7.5k rpm in 1st and around 6.5k every gear after that. The bike barely hits the end of the torque curve in first, doesn't reach it in any other gear and gets nowhere near the top of the powerband (or redline, 10k, for that matter).

I noticed three things, primarily:

1) If I flick on the choke, it will freely rev all the way up to redline and will continue to drive normally at lower RPM as long as I remember to turn the choke back off.

2) If I cut back on the throttle, say only 1/2 or 3/4 of WOT, then the bike will rev all the way to redline, albeit VERY slowly, hardly how you would want to gain speed very fast.

3) The higher I have the bike set to idle via the throttle plate adjustment knob that controls all four carbs - the knob located between cylinder 2 and 3's carburetors - the the easier it will rev as well as the higher it will rev. When I had my bike idling at 1500 (purposefully, for testing's sake, BTW), it would rev to 9k without hesitation, but still wouldn't quite reach the 10k redline, but that is a VERY high idle just to get full performance. Since the high idle test, I have retarded my idle back to around 1000 RPM (any lower and it will stall).

[Aside from number 3:] This leads me to fuel starvation at WOT. I believe that is safe thing to ASSume? Where should I check first? I believe the inline fuel filter is good (running w/ petcock on PRI and not ON resulted in no difference). I cleaned the carbs when I first got the bike (and did so 3 times before reinstalling, because they were horribly dirty), so dirty carburetors are out of the option. I suppose the jetting could be off? If it's the jetting, I could care less to fix the problem until I fiddle with the exhaust and get a K&N filter.

I do want to mention that I believe my valves need adjusting, because there is a rattle that sounds like it is coming from the top end. [If it is the valve train] I am ASSuming that my valve lash is on the loose side (aka not opening the valves enough aka possible fuel starvation). I plan on fixing this around January/February ish when I get my fork seals, speedo drive unit and front tire replaced.

I also want to mention that my bike is currently NOT running an air filter (just haven't gotten around to replacing it).

I thirdly want to mention, that my clutch is starting to slip, but only under sudden heavy throttle (like cruising at 3k then suddenly floor it). I do not see how this would effect bogging at high RPM though, because the bike would rev higher but not move accelerate any harder if it were clutch slippage.

Recent work consists of tune up (only replacing one boot, because that one broke), oil change and new rear tire about 2000 miles ago (almost a year), and I replaced my carb to engine manifold boots just about a month ago (the one's I had were horrendous like "I'm surprised the bike even ran" bad). It wouldn't surprise me if my carbs are a little out of sync because of this, but obviously as the bike doesn't hang at high RPM and does not have any other issues, they are not significantly out of sync to worry about. There are no cracks in the either the air intake or manifold boots as of now. Brand new vacuum line to the fuel petcock, new vacuum caps on the manifold boot nipples.

 

I had an issue with a Honda alot like this. In one of the four carbs the float was about 2mm lower than the rest.
The bike would bog down almost like a cylinder was missing.

 

so you have all these things that you need to do and expect a fix all answer?
Do a compresion test
adjust the valves
put an air filter in it
did you go to the church of clean? or just spray some cans at your carbs?
IN THE CHURCH OF CLEAN
wet set the fuel level
adjust the mixture screws use a color tune if you have one
sync the carbs.

you may have to clean the carbs again
do the slides pass the clunk test?
check the diaphrams for leaks

 

Put a air filter in it.

 

You did a good job explaining the symptoms and I agree if it wasn't for #3 I would say fuel starvation. Check very close for some kind of mechanical hang up in the linkage, #3 is weird.
You say it will die if you set idle below 1000. That may be carbs out of sink and one is going fully closed and you loose that cylinder and die.
Before pulling the carbs wave an unlit propane torch around the boots and throttle shafts to look for a vacuum leak.
I'm reading between the lines now: You have 4 posts, did you just get this bike and this is a problem that came with the bike or has the bike run good and this is new?
Please give a little more history on you and the bike and we may have a better insight to what the problem is.
Good luck.

 

if you want to red line your bike you should do all the required maintance steps that probaly have not been done by po .
so you put 2000 miles on the bike with no air filter?

 

All of the engines I've ever seen run without air filters are scheduled to be torn down at the end of the racing season.
Also, running without a filter causes the fuel mix to go leaner.

 

I agree with k-moe. Why in the world would you want to run without an air filter?!! It's going to run very lean and unless the main jet has been replaced there's no way it will provide enough fuel to compensate for the amount of air it's getting especially at WOT.

I have an 85 xj700 and it came with an UNI foam filter and completely stock jets. When I installed the stock paper filter it immediately started running very rich and almost fouled the plugs before I realized what was going on. Installing a stock air filter and re-tuning the carbs--especially the pilot screws-- will go a long ways toward solving your problem.

Hope you haven't already ingested enough dirt to damage the engine because I don't think rings for the 700 are available anymore.

 

The linkages are all clean and free of obstructions, operating properly. I did a final ride to school and then up to my mom's house to winterize my bike (sadly, it's that time of year), and I noticed that it actually does idle a tick below 1k, probably somewhere between 800 and 950. As far as heavy throttle bogging, the bike came that way, but like I said, I bought the bike with "I'm surprised this bike even starts" bad carb boots, so I disregarded it until I finally found a set for my XJ700 for a reasonable price (which the bike is continuing the trend even with the replaced boots).

And for everyone else commenting about the lack of airfilter: yes, I have ran the bike without an air filter for around 2k miles (probably more like 1500), but I have seen worse (motorcycles running without airboxes aka bare open carburetors, not even pod filters), so I am not the only one (HELL! The mechanic I consulted with didn't even judge me for not running an air filter, he just sits there making comments about how he's/ seen/heard worse).

I found the old air filter I pulled out of this bike. I obviously have the little plastic "tab" that screws onto the top of the airbox that holds the filter in place (as well as lets air into the box), but my filter is something else. It doesn't look very disposable (this might just be coming from a car mindset), as it has a plastic frame all around the filter element; however, the filter element looks like it's just a traditional paper element, but smells of an oil based substance? Here is a pic:


Would that just be a regular $15-$20 filter or would that be a K&N filter? (I have never seen a K&N in person, so forgive my newbile-ness)

 

EDIT: my bike is an 85 year model, not an 86; if this may change anything.

 

quentin,
Stick around and you'll come to see that this is not a "flame the ignorant newbie" kinda site. We are here to help and learn from each other. Many bikes, including mine, have been brought back to a very reliable condition and I am constantly learning new things. We don't sugarcoat the advice or information. It's all legit and will be given to you straight. Personally, I prefer it that way. Welcome aboard.

Gary H.

 

yup thats your air filter 36$ from a dealer, stock are paper. some people do oil them K&N filters usaly get oiled.
it coild be oil from breather tube from crank. If all that stuff was on the filter when you pulled it out you will want to clean out your air box

http://www.yamahapartsnation.com/oemparts/a/yam/500426a9f8700209bc788696/air-cleaner
you can use this link to look up parts on your bike and cross referance to other bikes
www,yamahapartsnation.com

 

k&n filter 57$ 20$

https://www.chromeworld.com/1985-yamaha-xj700-maxim-parts/fuel-and-air-filters/air-filter-nu-2283

 

That is the stock filter. I had the Uni shown above but never got the bike to run properly since it does allow a greater flow of air and thus requires pilot screw adjustment and probably a larger main jet if you are going to run at WOT. I've never had my bike over about 7,500 rpm so I can't comment on the WOT issue with the Uni filter. It does need to be oiled and I have a full quart of the stuff that you can have if you are anywhere near Brunswick, GA. I finally ordered the stock filter, from Chacal I think, returning the bike to stock configuration and then setting the pilot screws was easy, especially using a colortune plug. The paper filter was not cheap, somewhere between the K&N and the UNI, but it was worth it to me to get the bike running correctly. The service manual says the stock filter should be good for about 15,000 miles. While the pilot screws can be adjusted to compensate for a filter that allows more or less air than the stock filter there's no adjustment for the main jet other than changing it and that gets to be trial and error. The pilot system is the main source of fuel at idle and up to 1/4 throttle and then the slide needle and main jet become the main source of fuel so adjusting the pilot screws only marginally helps at higher throttle setting. Keep it simple, keep it stock, and avoid a lot of headaches.

 

If you run the bike with no air filter and the jets in carbs are still stock, that in itself could be a good reason why it bogs at high revs. It could be interesting you do a plug chop at high revs to see your spark plugs color.

 

stock air filter eliminates the is its, once you get the bike running how you want it you can start experementing with different filters.
stock filter will last a long time just clean it use canned air if you do not have access to compressor

 

think of it this way see all that sh#$ on your air filter? with out it that wonderful stuff is now in your carbs and cylinders. you may as well just throw a hand full of sand into the carbs and put the bike out of its misery.

I garenty your mechanic has seen worse and not advising you to put one in imeditely is how he makes his living.

so you can spend a little now or a lot later.

if you want to save money do it on other things ,
"oil filters? we don't need no stinking oil filters"


for the younger crowd


but my self i change/clean my lawn mower and snow blower air filters too.

 

How about you learn the whole story before deciding to respond like a prick. The air filter didn't come out of the bike looking like that. All the dirt and grass and s^&t is from me not storing it in a clean, dry place.

I take it the stock air filters are the "disposable" kind then?

 

This mechanic is trustworthy, otherwise his shop wouldn't have been operating for the last 3 generations in his family ... this is completely setting aside the fact the he is the #1 recommended mechanic in my city (ask any biker and they will point you straight to him); so good in fact, people come from out of town to get their bikes serviced specifically by him. And even if he is trying to pinch a little more money from my pockets, I'd rather spend $350 at his shop and get my forks reoiled/sealed, front tire mounted and balanced, speedometer drive unit replaced, oil changed, and a new air filter than go to some other shop in town and pay $280 for the fork seals alone.

As far as the spend a little now or a lot later, that's why the bike is getting FULL service before returning to the roads late winter / next spring. Everything that I know is wrong with the bike is getting replaced or fixed.

Speaking of replacing parts, how much is a clutch pack? Mine is on its way out (random 3/4 WOT or more throttle while cruising will cause the engine to blip before pulling). I have adjusted the clutch twice, but you can only do it so much until you need to replace it.

BTW I don't ride like a dick, I usually shift around 5-6k (usually going no more then 1/3 WOT) and cruise around 3.5-4k - engine feels happy, I get about 40mpg, I'm happy. I'm only worried about not hitting redline because sometimes you need to aggressively accelerate in order to get out of danger and I'd rather not be SOL.

 

Quick question, would a lack of air filter cause my choke to not work at idle in cold conditions? My bike won't hold idle when cold with the choke on, and it wont idle (very well, anyways, usually stalls within 5 seconds) without it either (and doesn't change with any variation/manipulation of the choke), so right now I have to manual hold the revs to 1.5k until it gets to temp (usually why I ride right away rather than let it warm up)