Xj750 Maxim Not starting

Anybody can help me with some clues about my bike not starting.
All seem OK. Spark, gas, carbs rebuilt, good battery....
The engine turns than sometimes cicks in and revs for 3 seconds than dies...
I suspect the mixture jets - not properly adjusted.
any suggestions?
THanks

 

When you cleaned the carbs did you make sure the little tubes in the bowls were open and clean. You should be able to squirt carb cleaner thru the small orifice in the bowl itself and it come out of the hole in the bowl flange Thats the supply for the enricher circuit. The mixture jets should be set at about 3 turns out from lightly bottomed but they should not effect the starting. Are your plugs wet after start attempts? If you remove all 4 plugs and lay them on the head and crank it do you get nice fat sparks?

 

Hello, thanks for your reply.
Yes. I have done all this. carbs are clean. All enriching circuits are clean and open. I have sparks. I have set the mixture jets to 2 and 1/2 out.
I have started the bike before taking the carbs off this time. The reason i took apart the carbs again - to replace the throttle shaft seals, suspecting an air leak that made the engine run erratically. I have also bench sincronized the butterfly valves so they open and close together...but while doing that i forgot how much the opening should be for them.
Now, while trying to start it....i only could have it run for 4 or 5 seconds, than would not start again. I guess i have not enough airflow in the carburators due to a too closed butterfluy valve. THe spark plugs are wet and if i clean and heat them - the engine would start, run smoothlly for 3 seconds and than die.
The enriching circuit seems to not affect at all the starting, which tells me again i might not have the butterfly valves open enough for a good air intake. I definettely have fuel but not enough oxygen to give me a good burn.
Am i right so far?
My question is, how much open should the butterfly valves be.
So far I started to try form fully closed and maybe 3 turns off the ideling main screw, but as i cannot see inside the carbs i cannot tell how open they are...but tonight i would try to give it much opening and see what hapens.
Keep you posted...
Thanks

 

Have you seen this on how to bench sync your carbs?
IT WORKS and should get you started.

http://www.xjbikes.com/Forums/viewtopic/t=4434.html

ab

 

Are you still on the original fuse box? The crimped connections aren't reliable and can cause those kind of symptoms.

 

I have already bypassed the fuses on the fusebox. I realized that some time ago..> Thanks for the hint....Appreciate it.
Also I will check the link for bench tunning the carbs. Thanks as well.

Still - any hint on how much the throttle valve should be opened....???Does it make it harder to start if too much throtle is given? as this is a CV carburetor...
Thanks again guys...

 

throttle blades should be open the thickness of a 3x5 index card after bench synch.

 

OK. Thanks.....Let me go home and try.

 

Do a simple test.

Spray some Starter Fluid in the Airbox.

Try to start the Bike.
IF it runs briefly ... the Problem is FUEL Delivery.

IF it don't even cough ... it's likely IGNITION Related.

IF the Bike ran before you Cleaned the Carbs.
Bench Sync for Throttles CLOSED ... 3X5 Card Feeler.
Preset Mixture Screws to: 3-1/8 Out.
Rich.
Get it running.
Move them back toward 3 if they're too Rich and Bogg-Out.

((Thats about where we were finding BLUE Colortuning the other day.)

 

Thanks.
I will try that either.
First i have to set the butterfly valves to the mentioned opening, than finetune the mixture screws.
If i get it started and have it idle satisfactory, I a going to resinchronize the carbs and colortune.
Hopefully it will start.
Just got home after a bicycle ride from work, and am im a bit tired, and on top of all it rains and is cold.
I have to leave it for tomorrow.
Keep you posted
Thanks again.
Titus62- the new rider on the block...hahahha

 

With a flashlight and positioning your eye, you can see the idle screw end where it touches it’s plate (with carbs on bike). Back off the idle screw to where you can see the end is no longer touching it’s plate. Then turn in idle screw till you see it touch the plate and begin to move the plate. Then turn screw one full turn, maybe two. That should be plenty to open the butterflies enough to start bike. (two turns could be too far and the bike will race at start – turn off bike and re-adjust)
Also if it’s butterfly position that is the issue, you can hold open the butterflies with the throttle at startup.

It sounds like it’s possibly getting too much fuel for some reason -
(‘THe spark plugs are wet’ ; ‘The enriching circuit seems to not affect at all the starting’ )
Check the adjustment of the choke cable to carbs, you may somehow have the choke plungers pulled up beyond control of the choke cable.

 

Here is something interesting, that has been bothering me for long time now.
I have all settings as mentioned. Mixture screw 2-1/2 to 3 turns out, throttle valve opened as per your advice, enough gas, plenty of power from the battery.
Engine turns over but not even a sign of starting. If i take the spark plugs out, they are wet, but not too much, and if i point a torch flame toward the spark plug opening, a littel whoos accompanied by a small exlossion comes out form the cylinder- denoting there is gas ...
If i check the sparks, I have sparks on all 4 plugs. I have the gap set to 0.7-0.8 as per specifications. if i hook up a voltmeter parallel with the primary of the ignition coils i have the needle moving up and down. BUT NOT EVEN A SIGN OF STARTING...
With or without choke , engine turns over but sounds like with no sparks at all. Even if i put some starter spray into the airfilter box- nothing...But funny thing i have sparks. Maybe not strong enough?
Tonight after cranking it over and over for maybe 15 minutes in total, i only got a 2 second start, but i could not keep it running and died. Since than, nothing.
What i also noticed, if i heat up the spark plugs and clean them, i have a better chance of getting it running for couple of seconds. but it would die anyhow.

 

Your quote:
‘What i also noticed, if i heat up the spark plugs and clean them, i have a better chance of getting it running for couple of seconds. but it would die anyhow’

Why do you clean the plugs before testing again? What is the general condition of the plugs you are using?

It sounds like you are trying the correct things. It does sound puzzling.
Just curious, as a reference, when was the last time the bike did run?
Did you verify the choke plungers are not somehow permanently pulled up?

I agree it sounds like it’s getting plenty of gas to plugs.
(This may seem counter intuitive, but ..)
Something that has always worked for me to get an internal combustion engine started at least for a few seconds (assuming it does have spark) is to squirt a teaspoon of gas into the spark plug hole, twist spark plug in finger tight, connect spark plug cable and give the engine a spin. Try that with all 4 cylinders together.

Maybe your fuel supply is contaminated? The pugs are wet, but what is the wet?

 

Return to START.
Do Not Pass GO.
Do Not collect $200.00

Put the Petcock in PRIME.
Hook-up a hose to the No.-4 Carb Float Level Port.
Open the Drain Screw and COLLECT some Fuel in a container.
Then, raise the Hose alongside the Carb and Check Float Height.
This exercise will FILL 1, 2, & 3 while you do this.

Now, we got gas.
So, now we try and run this baby again.
Maybe she goes.
Maybe she don't.
I'm thinking you got a shot at does.
BUT, ...

If it don't.
You take another shot.
TCI-Box.
Filled-up Fuel Bowls and a TEST TCI.
Varoom, ... or NO Varoom.

Varoom. Confetti.

No Varoom. Compression Test.

 

Another trick you could try. Since it appears it may be getting too much gas and quickly flooding as starting or just after starting. Cut-off the fuel supply. Disconnect the fuel line and try starting the bike. It will eventually go thru the gas in carbs and hopefully at some point of running out of gas, run for just more than a few seconds. Depending on the results it may point to the issue being too much gas getting dumped into the intake by the carbs.

 

OK. A little bit of history on my story. This bike i am working on i got form a neighbour. It sat on his driveway for 20 years not even moved. When i got it was fully seized, rusted and gummed up. I did rebuild it completelly. After finishing everything, including carbs, painting and soo on, I started it and was able to run it. It ran satisfactory , but not ballanced and sometimes high on idle. This happened some time ago. I have decided to change the TCI. bought a used one form eBay- did not change much. Than i took off and recleaned the carbs- several times...every time running even better than before...But what i noticed over time, was that i always had problems starting. One time i decided to try it every morning before taking the car and driving to work. Some morning it started some other day - dead meat. This "game" is being going on and kept bothering me...and made me go soo deep into it.
What bothers me now, while doing this tests with you, guys online, is that i am not getting even one cyclinder to fire...If it fires for couple of seconds, runs fine on all 4's and exhaust pipes are equal in temperature.
May i have too much gas into the cylinders?
By the way- i did the compression test- I will give you the readings, not equal on all fours but satisfactory.
To me looks either an electrical problem of some kind or some carb problem...Float bowl level too high and flooding the cylinders with too much gas???
Thant do you thing?

 

Sorry for my typing errors.
My last sentence should read: WHAT DO YOU THINK???
I was i a hurry to type and did not spell check.

 

The "Test" is Starting Fluid.

Shoot Starting Fluid in the Air Box Intake.
Try to Start.
Pops, coughs, tries to go = Fuel Delivery
Nothing happens = Ignition related.

IF you ran this Bike before and it is as you say,... I would strongly suspect the Black Box.
Seems like it wants to run the Bike ... but, as soon as the Bike Starts (3 or 4 secs) it fails and the Bike goes dead.

 

A few of your quotes:
‘the engine would start, run smoothlly for 3 seconds and than die.’

‘i only got a 2 second start, but i could not keep it running and died.’

‘I have decided to change the TCI. bought a used one form eBay- did not change much.’

And this quote:
‘One time i decided to try it every morning before taking the car and driving to work. Some morning it started’

How long did it run on the mornings it started?

From the above, it seems to indicate you have ignition spark ok and thus the issue is the air/gas mix.

Possibly contaminated fuel.
Try a fresh new supply of fuel by using another temp tank or draining the current tank. Drain carb bowls between the disconnect of old and connect of new gas supply.
Do you have a gas shut-off on the setup? Maybe a clogged fuel filter?

I did not find any mention of your air filter. What is it’s condition?

 

A variation of the Starting Fluid Test would help settle things.

See if it will START on Starting Fluid.
IF is does ... TRY to KEEP it running by giving it spurts of Starting Fluid.

IF, ... it starts ... AND ... will STAY running on spurts of Starting Fluid, then your NO START Issue is FUEL DELIVERY Related.

IF, ... it starts ... AND ... WON'T keep running on the Starting Fluid, ...
You have some problem that is more IGNITION / Electrical Related.

If you HAVE Spark.
If you TRIED Starting Fluid.
And, the Bike will NOT RUN ...

YOU NEED INFORMATION.

The results of an Across-the Board Compression Test with Throttles Held WIDE OPEN conducted with a FULLY CHARGED Battery and the TCI Unit Unplugged.

You must begin a "Return to Square One" Diagnosis and Troubleshooting Step-by-step verification and check-off.

 

Are you getting spark on all plugs, and are you getting good clean gas into the carbs? I had a similar problem - the petcock was plugged with chunks of rust from the tank

 

OK. I just returned from the garage, after spending some time with my bike.
Before doing anything else, i just pushed the start button to see what happens. Just turning over but not starting, not even a caugh- as expected.
What i did next- i unscrewd all spark plugs, grounded them and exposed to see the spark. Seemed to have spark, but what i noticed was NOT SAME INTENSITY AND VIGOR ON ALL PLUGS. Before putting them back into the cylinders, i have replaced number 4 with a spare i had around (which i calibrated to 0.8mm gap), just because seemed to have the weakest spark. Once in their place i cranked it again and IT STARTED - but as per the sound i could swear only on one cylinder. Indeed, after runnig about 15 seconds, i tried to give it some chock , IT DIED. Touching the exhaust pipes i noticed just the number 4 hot and number 2 little warm...the others cold.
Interesting- tomorrow i am going to get some new plugs.

 

new plugs and gapped properly may help.

I had a TCI that would only fire two plugs. Replaced and it was back to 100%

 

Interesting - the TCI i have right now on the bike is one i bought form ebay - it does not mean is good, but, if i put a voltmeter on the primary of each ignition coil, i can see the needle going up and down - meaning it fires both coils. I also have brand new coils, which were working fine, before. The only thing i did not consider to replace, although farelly new- were the spark plugs. I bought them 2 years ago and made less then 100 km on them. Do you reccomend any good plugs? these one i bought from the auto shop in town, showing them the originals i had when i bought the bike.

 

I think from your last testing I have a theory.

You could visibly see spark on all 4 plugs. That means both coils are working.
Yet after running on what sounded like firing on fewer than all 4 cylinders, you found only # 2 & 4 exhaust warm/hot.
The proper coils wires connection should be:
Left side coil wires plug to cylinders 1 & 4.
Right side coil wires plug to cylinders 2 & 3.

If you have connected right side coil to # 1 & 2 and left side coil to # 3 & 4, only #’s 2 & 4 would be properly connected and thus fire with proper timing to combust.
???

 

NGK BP7ES. You could use whatever plug brand you like but that's what I've got.

You want a BP7ES not a BPR7ES the R is for resistor and your plug caps take care of that.

You do have the ocrrect plug caps right?

 

OK. THanks for the plug type.
I have the original cap plugs - and last time whne i checked htem the resistance was ok - as per specifications. I have to recheck it , though. Is it really neccessar this resistance in the caps?

Thanks a lot.

 

And also the TCI- is it regulating the intensity of the spark? I know it regulates the timing as per the engine conditions.
And again_ was it just a coincidence that the number 4 fired after replacing the plug? was it just because the replacement plug was dry? Why am i wondering is - I bought all 5 plugs same time, form the same batch, i had all of them running , and now all of a sudden 3 of them fail at the same time? Hard to believe? Could there be the plug caps? can i just bypass them?
Thanks

 

This is my understanding....

The TCI controls when the coils fire. So long at it's passing 12V to them you they should be good.

The resistor caps are needed to slow the spark. without them you'll get too quick a spark and it may not light the fuel.

New, clean and properly gapped plugs will at least remove them from the trouble shooting.

When I was having my issues I had old plugs. Figured out it was the TCI but still replced the plugs. They were a year old and plugs are cheap. Pulled out the manual for the gap spacing and it's small very small. .024" I believe. The plugs came out of the box at around .035" So I had to adjust. Smaller gap = thicker spark.

Then with everything working again I pulled off one plug wire and the plug, put it's new plug on the valve cover and cranked to see the spark. Nice big blue spark. Tried the old plug on the same wire, thinner and weaker spark.

 

Titus62, the TCI is nothing more than the ignition switching control. The intensity of the spark is determined by the coils, wires and plugs. It is possible to foul some or all of your plugs if the conditions are right (i.e. continued flooding of the engine without ignition). Always have spares on hand. I carry 4 spares in my kit. I would think checking your cap integrity would be a great idea.
Iwingameover, you have just about everything correct.
The resistance in the ignition is primarily to get higher voltage for the spark and act as a "noise suppression" system. The greater the resistance, the more voltage that is needed to jump the gap.
In general, the XJ is supposed to have a BP7ES plug set between .028-.032" gap.

 

Thanks Robert.
Would i be ok without the resistors in the plug caps?

 

Yes and No. The resistor that is located in the cap is needed to complete the circuit path through the cap. You have to have something in there to complete the circuit.
If you change out to resistor type plugs, yes, pull the resistors out and put in a suitable substitute conductor.
Remember, you need to balance the components to make sure that the overall resistance remains more or less the same or you run the risk of burning out the coils. Common sense says leave well enough alone and replace the defective components with like replacement items but you be the judge of what you have on hand and can afford. Caps run about $6-8USD apiece.

 

Ok. Got it. THanks.

 

Well I'm really loving this site! With all of the running issues I have been having I find something that could potentially be a culprit. I ran the bike on old plugs... needed to reclean the carbs. So I did! BUT I also put in new plugs that I bought from a local atv/bike/sled distributor of parts and accessories. Well they sold me BPR7ES plugs... me knowing I had BP7ES, seeings that he even asked me before looking in his jim dandy little NGK book. So now I know why I have weaker spark.. I almost blamed it on the coils! I guess its time for new plugs! Thanks guys!

 

The TCI can effect the intensity of the spark. If the TCI supply voltage is low you can get weak spark on all four when the plugs are out of the head and laying on the engine hooked up to the wires. When you put the plugs in and they are under compression they will not spark or spark very intermittently. Check the ignition fuse holder clips and replace them if they are corroded. Also make sure the grounds to the TCI are clean. Make sure every connection between the pickups to the plugs is clean Just had this very same scenario on a XJ1100 last week.

 

I think this is great.
I thank you guys.
We really seem to get to the bottom of this...hahahah
I am picking up the new plugs today at noon, as they did not have them in stock and had to order them.
I am wondering, and i will check this once i get to my bike, as Danstone mentioned, what kind of plugs i had before. R's or no R's.
I will aslo check and eventually rewire the TCi conenctions. Just to be certain and exclude faulty ones.
Will keep you posted.

 

I will respectfully disagree. The TCI is nothing more than a transistor switch. It cannot regulate the amplitude of the spark. Low battery voltage, corroded ignition lines, bad caps, or bad plugs are the players in a weak spark issue. I completely agree with the rest of your advice however. Sound investment in piece of mind.

 

The coils input are just two wires, one ground the other input voltage. The input voltage (positive side) is hard wired to system 12volts (reference schematic). The TCI controls the ground side of the coils primary.

The TCI provides the timing to the coils. The coils generate high voltage on the secondary when the 12volts at the primary is interrupted (open circuit) by the TCI.
The coils need the 12 volts input to produce the high volts output. Lower voltage present at the primary side of coil will result in lower high voltage generated on the secondary side of coil. The coils operate as a fly back transformer. The secondary produces a multiple of the input voltage that was present before the input was interrupted.

So will lower voltage at the TCI produce a weaker spark? Not directly, but the TCI should be seeing the same system 12volts, and lower system volts will produce a weaker spark.

 

Hey guys , It is 12 midnight at my place. I have returned earlier with my new NGK BP7ES new plugs. Did not have time to try them, but just out of curiosity i have done a search under my old plugs. They were Champion RN7YC, which correspond to NGK BPRRRRRRRRRRR7ES, damm RRRRRR.
Cannot wait to put them on tomorrow.
Will let you know
Good night
Titu62

 

URRRRRRAAAAAAAAAAAAAAAAA....
FINALLYYYYYYYYYYYYYYYYYYYYY
I replaced the plugs with the good ones and it started at the first turn.
Unbelievable.....Hahahahahahha..>What a goof the clerc at the auto shop who sold me the first set of Plugs. I have also measured them with the ohmeter and have big resistance...the new ones - 0 - nothing...
That was the reason i had faint sparks and erraric running.
Now runs on all 4's, exhaust pipes are same temperature,
Now i have to colortune, as it seems to be running rich. Than ballance. or the other way around?
HAHAHAHAHHAHA
I even cannot stop laughing and i already had a couple of beers....to celebrate....So I will leave the rest for tomorrow....
PARTY TIME, now....
THANKS SOOOOOOO MUCH.....
WE figured something out together.
Titus62


GOOD STUFF

I wil lkeep you posted.

 

OK guys. My bike is like new now....Starts at a quarter turn. Idles good.
I have colortuned just to have a good start before ballancing....What i noticed , on the 3rd cylinder, i had to close the mixture screw completelly and still did not achieve the proper color of the spark...seems that the butterfly valve is too open and the bypass littlel holes are compensating- am I correct? Probably when synchronized i will do again the colortuning....
THANKS AGAIN guys.....
GOOD TEAM WORK....
Thanks to everybody....
Good to have you around
TITUS