85 xj700 maximx

has anyone got any idea why my bike runs only on number 2,3 and 4 cylinders that is until i disconect the vacume pipe from the inlet boot then number 1 srarts to work [ when the engine is running] has anybody experienced this or have any sugestions as to whats causing it so that i can sort the problem out. many thanks

 

I am assuming the vacuum tube is connected to the number 1 inlet. If so, you could be running too rich on that cylinder, extinguishing the spark. Removing the vacuum tube could be allowing enough extra air in for detonation.

Check the idle mixture screws. Set the number 1 screw out to 2.5 turns out as a starting point and see what happens.

 

thanks i,ll check it out.

 

Are you checking at low speeds? If so, then I would go with mestnii's thought. Also, pull the plug for #1 and see if it is more white than tan. If so, you are running a little lean in the cylinder. Go ahead and pull all of the plugs to compare.

 

the bike has no road tax yet so i cant ride it on the road, i noticed that number 1 exhaust doesnt get hot and there is a gurgle noise in the exhaust pipe and it sounds a little bit chuggy with a very slight backfire until the vac pipe is taken off all done while bike is stationary. thanks for the info i,ll take a look and let you know how i ge on, thanks

 

To be clear, is the vacuum hose that goes to the petcock attached to #1 or is that attached to #3 like normal and you are removing the cap from the #1 vacuum connection?

 

The vac pipe is conected to#1 inlet and petcock. when i remove vac pipe from #1 inlet the exhaust pipe gets hot . Until i do that the exh pipe stays cold . ive just aquired a colour tune so i,m going to give that a go and see if that solves the problem. should the vac pipe be on #3 ? when i got the bike it was on #1 so thats where its stayed since, i just assumed that it was right.

 

my two x's come off of number three.

 

you have fuel coming from the vac line into the cyl I would bet. pull the line off cap the barb and plug the line from the petcock. set pet to PRI and test things out. don't leave it there because if you have a leaky float valve fuel will leak out of the airbox or into the engine and mix with the oil. Not a good thing.

 

Really? Mine comes off of #2. #3 has the radiator pipes around it. Does it go between the two back toward the carbs or around one of the radiator tubes?

 

thanks i,ll give it a try!

 

If you have California model carbs on that bike, there is a separate brass nipple on the #2 carb only that is for the emission control system (not on the intake mnaifold, but up by the idle mixture screw boss ).

 

Yes, I do have a set of CA carbs, but when I got mine the petcock line was going to #2 intake manifold. Can someone take a picture of how theirs is routed to #3? Looks like mine got switched at some point.

Sorry to hijack the thread.

 

It doesn't really matter, as far as I can understand, which intake the petcock vacuum line is attached to, as long as the other three are blocked off tightly.

On X-models, the intake port caps are of a special design on the #1 and #4 carbs, since those caps accept the mounting ears from the "5 VALVE" carb side covers..........so the water-head owners must use either intake #2 or #3.

 

Chacal, that's very interesting, I didn't know that, but it is good to know, thaks

 

As does mine.

 

I suspect that they use number 3 for the vacuum as that is the one to which all the others are tuned. That way if you are adjusting any of the other carbs, your adjustments don't screw up fuel flow. So while not a requirement to be on #3, it is probably the best recommendation.

 

I agree. The "strongest" (i use the term loosely) carb is 3. Its like your main determiner carb. Mine is attached to #2, but she's closely related to 3 and 1. #2 controls 1 and 3 controls 2, so i figure I'd leave my intake vac line at the medium

 

I've had the regular and x models. I've seen the regular maxim's come off number two, same with the older model maxims. I've had four maxim x's and all came off number three.

 

Interesting,

From the frame of reference of "sitting on the bike" and assuming I'm correct the carbs are numbered left to right, 1-4, then my vacuum tube comes off number two.

Runs great so I'm loathe to mess with it right now.

 

this may just be a coincidence but after 3 months of trying to sort out the problem on my 85 maximx of it not firing on all 4 cylinders, with lots of info off you guys and lots of time trying out your suggestions, today i decided to try putting the vac pipe on #3 inlet instead of #1 which it was on when i got the bike. low and behold the bike started up first time as usual but it now ran on 4 cylinders instead of three. so could it make a difference as to which inlet the vac pipe goes on? very interesting. not set the carbs up on the colourtune yet as i,m waiting for the adaptor to arrive via post. i,m so looking forward to riding the bike and getting some enjoyment out of it, i hope this has solved the problem once and for all.

 

Yeah!!!!!!

 

I just checked the two factory Yamaha manuals I have. The xj700n comes off of number 2 for sure, very good picture. The xj700x is a bit fuzzy, but from what I can determine, it comes off of number two as well. I'm going to have to give this a go as my redone x is a bit cranky. I know for sure it doesn't come off one or four though. I always thought it came off of three because this is the carb you sync to. Man, learn something new every day.

 

Well it must of been a coincidence, yesterday i started my bike to do the colour tune and it was back to its normal self not firing on #1 and a slight back fire, but i went ahead and did the colour tune to try and work out whats happening. #1 and#2 there was no colour in the colourtune plug i could only see a spark no matter how much i adjusted the mixure screw, if i reved it up quickly there was a yellow ring which according to the instructions there should be .#3 and #4 seemed to be as they should and ran with a blue ring. today i took the carbs off the bike once again and stripped them down totally cleaned them cleaned all the holes out. putting them back together tomorrow, hope it does the trick .

 

cleaned everthing and put back together bike ran better but still not quite right on #1 the exhaust only gets warm when on tickover, hotter if you rev it but not as hot as the other three . does anyone have any suggestions as to what this could be. thanks

 

Nige, didn't think of this before. I had an xj700 airhead that was giving me fits. No. 1 wouldn't fire right, only on 3 cylinders. Anyway, I got so mad, I pulled the carbs apart but didn't think to check the idle mixture screws before. I pulled them apart only to find that there were parts missing and some of the o rings were put in incorrectly. I still wasn't getting a good fire though, so I took the no 1 mixture screw out, and shot a good amount of carb cleaner in the hole while it was on the bike....worked like a charm and I referred someone else to this on the forum and they used compressed air...they said the bike ran fine after that. Let us know!

 

Thanks for the suggestion. ive had all the mixture scews out whilst carbs were off the bike, carb cleaner and compressed air went through the holes. i reset the screws at 2.25 turns out. i will try it anyway and let you know. the mixture screws, am i correct in saying that firstly the spring then the washer then the o ring ?thanks

 

if you are stacking them on the screw nige you are correct. If you are putting them in the hole, oring, washer, spring then screw.

 

thanks, i got that bit right.

 

If the valve clearances were out on#1 cylinder would this make the engine do what its doing ?cant think of anything else, hope its not that though as not sure i can get the shims in england. anybody know?

 

I am pretty sure Chacal can ship there.

 

thanks mike.

 

Check your compression. You have spark correct? What about the cdi? Good connection there? one of the first things I do on a bike I get is go through and clean all of the connections and after they are clean, hit them with dilectric grease. Have you taken her out for a good ride? I've seen a few bikes do what yours is doing and I just took them for a ride with high octane gas and some seafoam and give her a good running and that will sometimes clear them up as well...gotta be something there.

 

hi, yes i have a good spark, all the wiring and conections were checked and sprayed when i put the loom back on the bike after it was powder coated. i,ve not tried a compression test so guess i,ll do that next . i need to pay for road tax before i take bike on the road but that idea sounds favorite. i dont know what seafoam is though, do we have an alternative over here? thanks