1981 XJ650 maxim intake boots YICS

I’m kind of with @lostboy - what exactly does surge mean? Drop in rpm like somebody shut off the fuel, or an increase in power/rpm like some invisible monkey was pulling on the throttle? Or something else?

 

Let me explain, got throttle at 7k rpm and up.. rpm does not drop at all, speed goes up giving more gas, this feeling is like fuel on fuel off .... fuel on fuel off...no back fire, something like when you have to turn the petcock to reserve running out of gas ... no loss of spark... thats a surge right, now i am going to give it full throttle, pulling through the surge .. then backing off throttle i see an increase in power around 6k when backed off, the problem is when it gets past half throttle thats when it starts, backing of to half throttle its ok.. so i wind it up again and do the same thing trying to get the sea foam to do its job.... could this be a partial blockage in the mixture screws small passages... gas tank is clean.. petcock filter clean.. brass in line filter clean... fuel flow good .. float bowl levels up to bowl gasket.... all jets clean and passaged blasted with carb cleaner.. no vacuum leaks, spark plugs light tan, clean stock air filter, intake boots to air box tight... no holes in carb rubber diaphragms....

 

I don't think the pilot circuit has that much influence anymore at 1/2 throttle or more - you would be on the main circuit - which mean emulsion tubes. And of course the emulsion tubes have like 12 teeny tiny holes instead of one teeny tiny hole.

So is it almost as if you're running on 4 cyl, then 3, then back to 4?

Could just one of the carbs be starving for fuel? Like a sticky float valve or something? I'd be interested to hear the opinion of somebody who really knows their stuff like @hogfiddles if this sound like a carb issue.

Other thing that comes to mind for me is an intermittent ignition issue.

 

Yeah i made sure them tiny holes were clear in the emulsion tubes twice...no its not dropping a cylinder i dont feel that.... its like i am towing something and the thing i am towing puts the brake on for a split second.... yes starving for fuel, got to be that? but if it was it would not pull through it right......like i said the engine will pull through that spot until the speedo is bouncing off the limit peg, if it was an ignition issue what could that be, i dont feel a dead cylinder or miss fire... coil ohms ok... whats going on with the Main circuit - This kicks in at higher RPMs. thanks for the input.... i guess if the sea foam dont work what next, been trough the carbs three times, going over everything...

 

starving for fuel in the higher rpms makes sense.. like the bowls can not fill fast enough, gas cap vent is ok...has anyone drained the carbs and re filled with sea foam then crank over to start, let soak over night then drain bowls... or should i just go through two tank fulls with the sea foam additive see if that clears out problem

 

What air filter do you have?

 

Stock air filter.... but wait i found something ..i decided to check the fuel flow from the petcock using clear hose into small bottle flow was good..... then i checked the flow through the brass in line filter.... fuel flow slowed down a bit... wow could this be it.... checking the small brass filter the inlet and outlet is not more than an eighth of an inch...fuel line is 1/4 blowing through it its clear but the brass filter does have some restriction, its clean no blockage.... i read somewhere that fitting an in line filter along with the petcock filter has some restrictions,... i remember now, it was on the Honda 550 forum.... road test in the morning fingers crossed

 

The sintered brass filter should let enough fuel flow, a lot of us use them, unless yours is bad. Try removing it and replacing with a straight connector to test. The petcock filter, I don't think will restrict anything as it is a large screen designed to trap larger particles from passing.

 

Well after a run out without brass filter it was a lot better 60 mph 70 mph I could tell the difference winding it to full I felt a bit lag then surge backing off throttle it's ok.. now getting back on freeway up the ramp it felt like a spark problem stumble misfire when giving it full throttle stumble under load.. the spark plugs do look ok, but they have been sitting 21 years..

 

Brass filter with small orifice. NGK BP7ES plugs

 

Looks like the ones I use on the XJ700 and XJ700X with no problems at any speed or RPM's.

 

Thanks huntchuks I will continue with the sea foam and replace plugs at weekend, but I can feel the problem when the engine is only under a load, hard acceleration through gears on incline could be ignition ..? So far done 65 miles seafoam

 

Today i will have gone through a tank of gas re topping off this morning with two gall (and seafoam) container.... its not the spark plugs... but i did see a difference when i removed the brass in line filter.. 1/4 hose coming off petcock then into 7/64th hole to filter?... Noah has a thread going above mine...1985 XJ 700 breaking up under load.. ..could i have a bad TCI box... going back to yesterday pulling from the lights up the ramp accelerating it felt like a bop bop bop no spark but pulling through it as speed increased... will test another forty miles today..

 

After run out today i am starting to think the needle and emulsion tube are they the right ones in there or miss matched....from last owners 21 years back, i will now go from surge to stumble feeling at wot....or could be both, them parts are the only two things that regulate fuel flow...

 

I haven't exactly caught up with the thread, but I've found it to be advantageous to use a spray-on gasket dressing on the intake gaskets prior to assembly.

@glennyboy Don't take that to mean you need to redo that work. Just food for though later on.

 

I was also thinking about the diaphragm springs if i stretch them a bit... could the pistons be lifting up to soon, too much volume of air...what have i got to loose at this point

 

I wouldn't mess with the springs, they are really there to ensure the slides drop when needed. I'm sure they have some effect but it'd be minimal compared to the jets/slide hole. The hole in the slide and the air jets "meter" the rate that the air moves back and forth due to the difference in pressure between the top of the carb and body. The needle moves up too to allow more fuel.

Definitely sounds fuel related, electrical drop outs have a very definitive feel. If the carbs are rebuilt correctly with the correct stock parts and fuel levels set correctly it should run well. I know that doesn't help much but I'm out of suggestions at this point.

 

I decided to replace the spark plugs even though they looked ok, only non resistor i could get were champion N6YC ... Pulling up the onramp no stumble going through the gears, thats a plus ... not as much surge at 70 mph... its still there but waiting for the tank to get low after seafoam... i did pull the caps checked the needle jet they dont have any code numbers on any.... could they be the wrong ones?... i may have to replace the jets and emulsion tubes if things dont improve.... thanks for the help guys

 

Was the needle jet brass stock, i know my emulsion tube is brass and the jets should be stamped Y10... If no number on jet could it be wrong size mine are alloy with no letters

 

Yesterday it would not start neutral switch on gearbox, drained the oil to try and remove it...oil drain plug had black sludge on it, just done 300 miles, could this be clutch friction material, the new oil was a bit darker..... sorted the switch out in another post... This engine was not started for 21 years, the engine oil smelt bad... anyway i eventually got it running, i think the clutch plates are about done.... could this be my surge problem at higher rpm, clutch takes up drive at the end of clutch lever travel but no slipping going through the gears 36k bet that clutch has never been replaced... i have to take a look

 

clutch friction plates hard as rock will replace

 

Well guys i found the problem something i failed to check from the start .. one of the coils failed the secondary test wires ok, two of the dam caps have them carbon inserts unscrewing it spring/ washer ..other coil does not have that type ... bet thats my ignition breaking down at higher rpms,. fitting new caps..waiting for new clutch..

 

That'd do it.

 

Coil 1 and 4 had the removable carbon insert had no ohms ..cleaned them up, removed the carbon and made steel instead .... now no resistance on them ..coil 2 and 3 can not remove resistor different caps... they check out at 6k ohms so i will leave it at that until road test.... spark plugs non resistor... hope this fixes the dam surge.... if not i will have to start a new thread lol this one is getting long

 

My XJ700S has resisters in two caps and none in the other two (one coil with/one coil without). This is the way they came from the factory, from all that I have read.

 

Don't start a new thread. History is important when diagnosing a problem.

 

That varied with model.

 

Well after sorting the plug caps out and replacing the clutch i was back out again, the surge was still there at 6k and up, i ran it with the surge for nine miles pulled over shut off engine... pulled the plugs ... white tips ..lean... set back off and after six miles or so the surge got worse oh shit as speed dropped ..ahh time to turn reserve on, came back to life again, but still had surge 6k so i thought thats my problem lean condition... so that surge feeling is like running out of gas but not as bad because the engine will pull through it. Pulled the choke on a bit made it rough too rich..The champion plugs seem a bit hotter so i put the NGK back in still the surge ..fixed one thing plug caps...fuel flow is good from the tank on and reserve, so whats my problem, the needle jets dont have any numbers on them ... why lean, could it be wrong size needle jets from past owners.. all the other jets are stock in the correct order, fuel height spot on, no vacuum leaks gone through a can of carb cleaner, even used propane..slides ok, stock air filter, strange why it runs perfect under 6k...before pulling carbs again i will put a 15 thou washer under each needle jet bring it up a bit make richer ... so its getting more air than gas ? if that dont work then new needle jets/emulsion tubes...

 

The two holes are facing the front close to butterfly is that correct.

I see now washer under jet will not work

 

Is this the correct size for the Y10 jet.

 

I can put a small metric rubber washer under jet bring it up 1/32nd

 

I’m too lazy to read read the whole thread. I can’t recall if you did this but I’d pull the carbs and set the fuel level 1mm higher and test again.

 

It seems a little fishy to me that the needles have no markings. Maybe you’re right @glennyboy - maybe they are some incorrect needles causing a problem. That’s the sort of thing that would cause a previous owner to say “jeez, I just rebuilt the carbs and it runs like trash, I guess I’ll just get rid of it”.

 

Fuel levels up to the gaskets trying this first.


My choice is to try this first with rubber washer .. or bring float level up, i did notice that most autos with stromberg carbs have the gas up to the top of emulsion tubes mine has the level lower ? but its up to the bowl gasket.. or get the rebuild kit with jets/emulsion tubes etc

 

That didn't work carbs off for full dismantle

 

The jet was higher by 2mm using washer, i was able to get a better mixture adjustment ...had good mid range but after 5k it had the surge, carbs off, rack apart found nothing wrong, boiled in soapy water, soaking overnight in strong stuff the wife uses in the washing machine lol...church of clean..getting rebuild kit, i dont understand whats going on, the new jet and emulsion tube etc coming ...if that dont fix it its got to be ignition?

 

A quick thought.
Are the air jets in the correct positions? (opposite of what the service manual shows is correct)
Did I ask that already?

 

Yes air jets in right order ..carbs back on the rack all clean, waiting for parts

 

Dam it I think I found the problem the floats were in upside down ... The past owners not the one I got the bike from put em in like that I never gave it a thought putting them back in same way.

 

Well that’s interesting

 

Yes its is ...even upside down the float height was ok, just less travel for the float, fitted right way it travels more, would this have anything to do with amount of fuel in the bowls?... I watched that Ausi guy doing a carb rebuild u tube..me thinking ...What did i miss.... and there it was

 

Do you have a good new fuel line that's properly routed/oriented? I had a problem once where the fuel line kinked when I fastened the tank which caused fuel starvation.

 

It absolutely will effect how much fuel is in the bowls. It's also a fairly common PO issue with Hitachi carbs.

 

Guy's I am loosing my mind I need a vacation I had the float's in the right way will not fit upside down

 

You sure? The one in the photo looked upside down

 

Upside down in the picture.

 

Yes upside down in pic me thinking it would work lol until i installed the float needle ..no way ..they will not work that way... all back together with new jets emulsion tubes etc ..wet float height 2mm below bowl gasket, engine running ..mixture done.... not run out yet..had to throw the towel in, dam humidity plus 90f never get humidity here in C/A.... I have a gut feeling i will still have the surge, only thing left is the TDI

 

Test ride this morning 5k 6k 7k no surge .... but if i snap it to full throttle i get the surge or could be stumble and it pulls through it maybe i am expecting to much.... maybe a slow TCI..i will leave it at that as i dont think i will be needing FT... came home pulled spark plugs, look ok, burning clean not lean/not rich ..adjusted mixture screws 1/4 turn out more, steady idle 1,100 rpm.... got side stand sorted out nice to have that working...

 

If it was the TCI I doubt that you would have any improvement.
A TCI failure won't clear itself up. It'll either not spark at idle, or lose reliable spark as the RPMs rise.
If you get to where you do suspect a faulty TCI there are a several of us that will be happy to test it on one of our bikes.