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)

 

the air filter is a component of the air box system and carbs its resistance to air flow regulates the air flow which regulates the jets and also will affect mixture, choke also depends on air flow. when you cleaned out the carbs did you varify that enrichment circuits were clear
i think you have to revisit the cleaning of the carbs but you can wait till you get an air filter to see if that is your problem
a little light reading for you
TECH TOPIC: The Real Costs of Maintenance
IN THE CHURCH OF CLEAN
THE SECRET LIFE OF CARBURETORS
Something New, Something Naked
TALKIN' TECH: Various thoughts on various issues

http://www.zrxoa.org/webpages/techinfo/carb/carbtuning.html

The Information Overload Hour

you may want to consider not running the bike untill you get an air filter your bike your choice

all air filters are the disposable kind some just last longer than others

 

as long as you trust him with your life,
this site will show you how to do all that work your self saving $$$ and getting the satisfaction of knowing how to do it and that you did it. tire mount and balance i can see letting him do thats $20 , speedo drive unit oil and filter, air filter seals about $75 in parts and you should have done that your self
speedo drive unit covered in diy forums

http://www.xjbikes.com/forums/threads/how-to-change-your-fork-seals.8355/

http://www.xjbikes.com/forums/threads/seized-speedometer-drive-unit.33009/

so your at the spending a lot later stage because you did not replace the air filter just threw it on the ground and kept riding

depends on where you buy it and who does the work
diy forum has clutch replacment thread
CLUTCHES 101-Part 1: the 400/550/600s with pics
www.xj4ever.com sells clutck kits start a conversation with member chacal he will not steer you wrong and it will be the parts you need.

your valves are more likely tight that loose the valve clearance and shim replacment is covered in the diy forum
AIRHEAD VALVE ADJUSTMENT with Pics

a sense of humor helps too

 

When it is cold it needs more fuel to run, hence the choke. In your case, without the filter you are getting so much air that even the choke can compensate. I think you are back to the lack of an air filter being your main problem.

 

The way I understand it, the only reason a lack of air filter could cause your enrichment circuit not to work properly would be that it would allow the carbs to suck too much air too easily compared to the volume of gasoline, and cold air is not good to warm up an engine.

Edit: sorry, I said the same thing as Tabaka45...

 

Set it up and dial it in correctly and whatever throttle you'll need to accelerate in any situation will be there.

Gary H.

 

If you call $35 spending "a lot more" LMAO And I have a sense of humour, all my friends will tell you that, I just don't put up with insulting comments like "might as well throw sand down the carbs and put the bike out of her misery."

The air quality of where I am is more then clean enough to run without a filter for around 1500 miles, especially taken into consideration that I only rode it [this year] about 10% annually what most riders in my area do. The only time the air is not clean enough for that is when you get some d-bag with a diesel rolling coal thinking he is oh so cool...or when we have a windstorm, which isn't even an annual occurrence (we only get them every 2-3 years). If riding without an air filter for a short period of time (and minimal distance) was going to do significant damage, my engine would already be toast. And seeing as how I haven't lost a single mL of engine oil, I think it's fair to say that I have not scored my cylinders at all from sand, dirt, or other particles entering the engine from the lack of an air filter; and it's not like I'm riding on the freakin' forest service roads, kicking up dust everywhere I go, either!

As an added fact, the reason the air filter was never put back into the airbox was that when I got my bike, it needed new carb boots and I thought it wouldn't take forever to fix so I didn't even attach the airbox boots back to the carbs thinking they'd be right back off within a week or so, but I had forgotten about the airboots/filter after a small while. It took forever to find carb boots for my 700 for reasonable price. Now I have the air cleaner boots on (as well as new manifold boots), but haven't gotten around to wiping off/cleaning the air filter yet (if possible). EVEN IF I HAD MY FILTER INSTALLED, the cracks were so damn big on the manifold boots, it would've have the same effect as riding without an air filter anyways!

 

Quentin, your defensive nature belies your sense of humor.
These guys know ALOT, they could write an XJ Wikipedia page.
Heed the advice given, come to terms with knowing that you may not know everything and you will be rewarded with the best running Yamaha in town.

 

You obviously think you have everything under control, so good luck.

 

I cleaned the air filter up real nice to get rid of all the grass, dirt, sand, etc. Threw it on the bike and it actually made it worse. The bike bogged at 5k rpm and would barely idle letalone move under its own power. I could only ride 5mph in 1st gear, "flooring" it....Something tells me that this bike was rejetted/tuned for a K&N or pod filter set up and the second previous owner was too cheap to sell the bike with those so he sold it with the regular airbox/filter, and that may be the reason why the dude I bought it off decided to sell it, because he could never get it to run right with the factory air filter? Unless of course, the carbs just need synced again which would be an obvious because apparently everything little thing you do on this bike requires a carb sync. I might see if someone in my area has a K&N I could borrow for a test run on my bike before I tear the carburetors apart for a potential rejet / bench sync.

Anyone know of a intake manifold / single carburetor mod that was available (or done) on these bikes? I know there was once a kit you could get for the Honda V-4 motors that you could put a single VW carb on and it ran all cylinders straight from it.

 

when you say it is worse with a clean filter,do ypu mean it is worse than with the same filter but dirty, or worse then without filter ?

 

Worse then without a filter.

 

Hum...too much air without a filter , and not enough air with a stock filter...that's what you think? and a K+N filter would be fine because it would be the right compromise?

 

Might be, that's sort of what I am thinking.

Bike runs normally until you hit about 7k without filter; hesitates to idle as well as under load with filter before it completely bogs out at 5k and then just stalls. Petcock is working fine, even tried running it on PRI and didn't change a thing (vacuum line to diaphram is new). I didn't even buy the bike "running normally" because it had the massively cracked manifold boots when I bought (more appropriately they had chunks missing from the rubber).

 

See my reply in your other thread: http://www.xjbikes.com/forums/threa...and-should-i-colortune-before-or-after.76718/

You need to open the carbs back up. Something is still not right in there.

 

As in tear the carbs apart to check jetting, etc?

EDIT: do you suppose my bogging could be the intake valves closing way too fast at high RPM? I know for sure that I need to adjust the valves, the lash is loose enough it is causing an audible rattle).

 

these bikes sound like a sewing machine when the valves are adjusted right.. you should check your valves because if they are out of spec you will not be able to sync or tune it correctly.
did you clean the asperator tubes under the main jets ,the little holes in the sides?
could be the vent in the gas cap is stuck.
why not just replace the air filter to eliminate it as a problem

 

It's rare for XJ valves to be too loose; clearances tighten as they wear. Tappy valves are happy valves.

All of what XJ550H said, plus fuel levels being low can cause that issue. IIRC you had a shop clean the carbs. Did you ever open them up to check the work?

 

First things I think of are:

1. Valve clearances
2. Tci breakdown at higher rpms

 

What is tci?

 

I didn't have a shop clean the carbs, I cleaned them.

 

I understand that I will not be able to tune or sync correctly if my valves are out of spec, hence why I plan to check my valves and then sync/tune.

Didn't recognize any holes.... It'll be at least mid January before I even think about trying to ride in this weather, I'll probably "rip" the carburetors back off, give them ANOTHER thorough cleaning, making sure to clean every nook and cranny I seem to find.

I'm not worried about the gas cap vent being stuck. If anything, it's venting too much! The whole damn gasket needs replaced (gas will slosh out if filled too high).

I am a little hesitant to buy a filter before I find out for sure whether my bike has been rejetted for an aftermarket air intake. That way, if it has, I can just buy the appropriate air filter and only be out the door $30-50 instead of $80-120.


Is there a way to identify the jets? Like do they have any markings to depict how big it is, or do you have to measure the internal jet diameter?

 

Stock jets are stamped with their size. Stock needles are ink stamped (though the ink is usually worn off).
What the stamped size won't tell you is if a PO drilled the jets out to a larger size. 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.

 

little holes like shown above part shown is just an example and may not be your part

 

I've been Googling quite a bit here and there about "motorcycle bogs at high RPM" and I am finding SEVERAL people claiming that the kickstand switch could cause this? I know mine is not the best...it shuts the bike off when you put it down (with bike running, obviously), the bike will not start with kickstand down at all (even in neutral with the clutch pulled in, the only thing that happens in this case is my oil light comes on), and just recently the switch has been sticking in the "deployed" position (you have to bend over and pull the tab out to start the bike. (but that might just be the colder weather?) *fingers crossed*

I think I'm going to head over to my mom's house tomorrow, go for a ride with the relay that connects to the kickstand switch disconnected (causes the switch to behave as if the kickstand was up) and maybe, just maybe, that will be the problem. Another thing I am going to try is putting the air box "cover" back on (the piece that you unscrew to gain access to the air filter...if you're running one)...I didn't have that "cover" installed when riding without the filter. This should, theoretically, "richen" the air/fuel mixture at least a little bit (by reducing the amount of air that can physically enter the air box at any given time), meaning I should be able to get to a higher RPM before it bogs. I'll probably measure the fuel level in the float bowl while I'm there to get that argument square...on fuel level, I seem to find conflicting sources: some people say the fuel level on the 700 airhead should be 1mm +/- below the carb body, others say it should be 3mm +/-, which is it truly?

It neither of these works, I'll probably tear the carburetors off again to do an inspection/cleaning.

 

Can't speak for anything but Hitachi carbs from a 81 XJ650 Maxim.
3mm +/-1mm.

As long as the filter itself is in the proper position I am not sure if having the cover on (prefered) or off will make a big difference. However since the bike was designed to be run with it on, I certain would recommend putting it back on.

My understanding (and it appears yours also) is that too much air creates a lean condition. I was led to believe that running lean creates high RPM's not bogging . . . .

 

The kickstand switch is just a switch. It interrupts power to the TCI via the safety relay. It cannot cause anything other than a stalled engine if it s faulty. It cannot cause a bog of any kind.

 

from info overload
Hitachi HSC33 series (XJ700 models):

-Fuel level measured via the clear-tube gauge: 1.0mm +/- 1mm (.039" +/- .039")

photo just to show where you measure and how to tell if bike is level

 

put the cover and the filter back on

 

I guess I missed the first part of the forum, and read back only to the top of the page ( my bad). .....yeah, it could still be a carb issue, too

 

how's the plugs look?