[have replaced all fuel flow related parts and filters pump, relay etc. bike will start briefly , seconds then dies and successive tries get worse until it sits for awhile. Feels like a fuel starvation problem but got flow through the pump. Anybody have any insights?
Longshot, is the side stand kicked down or kill switch engaged?
"It Starts, runs for seconds, then dies..." ....sounds like a misbehaving fuel pump or something impeding fuel flow....keeping the carbs fuel bowls from refilling.
Is your tank clean?
Try bypassing the fuel pump and fuel filter. Take them out of the equation.
You need 1/4 tank of fuel to get enough head pressure to gravity feed the carbs.
Welcome to the forum
Try and post in the Intro section, tell us what you're doing.
Modify your profile, In your signature line put in the year FJ you have. That info. will appear automatically so you don't have to remind us.
Cheers. Pat
Side stand switch checked , new fuel pump and fuel pump relay. Checked flow at pump outlet good. Going to replace relay unit ( starting circuit cut off relay), if I can get at it without removing cowling. All thoughts and suggestions are appreciated.
I second Pat's advice to hook up the tank to the carbs without fuel pump and see if it stays running.
Will try direct tank to carbs manana, have checked pump is squirting but can't hurt to try. Let you know, thanks for the feedback.
Pete,
Is there rust or dirt inside the gastank? A fuel-line filter would be a good idea generally, and if you already have one, it may be clogged.
Never know where the PO may have put an in-line fuel filter. One guy stuffed a filter right into the gas line, which will catch the crud but it clogs up fast because the filter face is so tiny. Also, there is no way to inspect the "filter" for crud because you can't see the filter at all until you disconnect the fuel line.
If the carbs have crud in the lines, you may be able to blow them clean from the inside or remove the crud with a strong vacuum on the fuel lines.
Amazon and lots of places have clear glass in-line filters with porous bronze filter elements. Easy to inspect and re-new the bronze filter element.
Just shooting in the dark, here.
Pat, not to hijack the thread but as I convert my 86 to fuel pump hopefully this weekend I have the regular yamaha fuel filter under the tank but could I add another smaller filter before the fuel pump or after the fuel pump as an extra level of protection for the carbs?
The oem Yamaha fuel filter goes between the tank petcock and the fuel pump inlet. The filter does a great job catching small rust particles from our old tanks so, no, IMO you don't need anything additional.
If it's that bad, look at electrolysis on the tank and a POR15 or Caswell sealant.
Pete,
If you find a fuel filter on the fuel line, you can tape a strong little magnet to the side of the filter to catch rust and iron particles. You could also stick a magnet inside the gas tank near the fuel outlet. Can't hurt, might help. :yes:
Did the direct connect of the fuel lines even though I have strong flow from the tank, 1/3 full and new fuel filter, as well as strong squirt from new fuel pump. Also blew 100 psl air in carb intakes and fuel line to carbs. It now starts for minute but after revs it fades out. Playing the throttle keeps it going at stalling revs. Can all 4 carbs be gummed up?
I have used lots of gumout carb cleaner and Lucas fuel additive because the gas is old. Would bad gas allow bike to rev at all?
Ethanol laced gas absorbs water. Old ethanol laced gas water fouled crap. New ethanol gas is ok if you don't leave it in Thor fuel bowls.
Don't ask me how I know...
Was bike runnning fine when you parked it or is this a bike you got recently you're trying to get running? If dies early but is ok when more throttle then it might be your pilot circuit. What setting are your fuel mixture screws at?
Quote from: Pete-speed on June 08, 2025, 12:40:49 PMDid the direct connect of the fuel lines even though I have strong flow from the tank, 1/3 full and new fuel filter, as well as strong squirt from new fuel pump. Also blew 100 psl air in carb intakes and fuel line to carbs. It now starts for minute but after revs it fades out. Playing the throttle keeps it going at stalling revs. Can all 4 carbs be gummed up?
Pete,
By all means, get rid of any old gas in the FJ gas tank. If you want to use the old gas, your car can dilute the old gas in the bigger gas tank. I would use top-tier non-ethanol gas for a while, at least. Run a can of SeaFoam (mixed per label instructions) through the gas tank. SeaFoam is magic stuff, but not instant magic. It may take a tank or two of gas with the SeaFoam additive for best results. Is the choke assembly working properly?
After blowing out fuel line the bike can be kept running by playing the throttle and full choke, but only to 1-1.5k rpm and is back firing constantly. Is this typical of timing issue or maybe faulty coils? Idk, any thoughts. Still haven't changed out gas, will do next but back fire issue unlikely due to old gas.
Not sure how to update profile but details are I have a 1991 FJ1200, have been riding it for 26 years. Had hydraulic clutch go and after replacing that 2 years ago had dead battery. Sat for about 2 years due to other life demands, and I also have a 1987 XLH with a 89 cubic inch engine so I still had a ride, had this 25 years, now at 70 rather ride than wrench but bike not cooperating
Not sure about mixture settings but was running fine before I let it sit during clutch repair over 2 years ago
Pete,
Backfiring would not surprise me with old gas, because a lot of unburned gas is going out into the exhaust system. I would doubt that you have timing or equipment problems, with a bike that ran well when it got parked. It is far more likely that the carbs need a fuel additive, and old gas is a likely suspect, too.
If you have not used fuel additives before, at the gas station, put the carb cleaner into the gas tank -before- filling the gas tank. Then the gas pump will put a hard stream of gas into the gas tank that insures a good mixing. Same goes for using that old gas in the car - put the old gas into the car gas tank just before you fill the tank at the pump.
Drained the tank and filled with new high test, reinstalled new fuel pump and blew out fuel lines. Now bike starts and can rev up to 3.5k momentarily but then fades out after few seconds and can be kept running with throttle play but again backfiring and can't get revs up above 1.5k although will idle sometimes. Poured old gas with all the additives in my 14 year old Tacoma, didn't read idea to put in new additives in tank first, get sucked in first in time. Still baffled why she won't rev up higher and why it dies out, and backfires a lot. Maybe new coils and plug wires? Any more ideas I'd appreciate the help
What condition is the battery in?
And what voltage is the charging system putting out?
brand new battery and kept on trickle charger for all the starting attempts. seems to be putting out charge when reved to 3k+ as headlight gets bright but as it bogs down light dims out also
anybody ever had to replace the digital ignition unit (TDI)?
Check the fuel level in the carb float bowls. You could be flooding out (high level) or starving (low level)
Pete,
High-octane gas burns with LESS power than low-octane gas. Non-ethanol top-tier regular gas would be a good choice for this time.
Give the SeaFoam a day or three to work its' magic. I'd expect things to improve somewhat each day.
You can tell if each cylinder is firing by (carefully) taking the temperature of each pipe by hand when started cold, or with a temperature app on a modern cellphone when hot. A remote infrared thermometer (~$ USD 35.00) works best, there. Try to borrow one, and see if you like it.
If revving keeps it alive for a second, my first guess would be gummed up pilot jets.
Thank you Red, simple but smart. Checked pipe temps, by hand, left two cool, thought i hadn't warmed it up enough, right two pipes scorching. so it looks like left coil is not working, finally a solid lead. Glad i didn't fully fill tank. pulling that and will test coil assembly. Spark plugs are all new but question, been running NGK DPR7ea-9 plugs, R is resistance version for rfi suppression and only available version, but manual say DP8ea-9, does 7 vs 8 matter and if so which is best. have to travel so will update results when I return.
Your firing order is 1-2-4-3 meaning cylinders 1 & 4 share a coil and cylinders 2 & 3 share a coil.
If your left 2 cylinders are cold (#1 and #2) it's not your coils.
My money is on gummed up idling and pilot circuits in your carbs.
Cheers
Pat
Pete,
If you can find non-resistance plugs, you can still have max spark Voltage and radio noise suppression (better than resistance plugs or resistance wires). Inductance spark plug wires are a continuous wire, spiral-wrapped, no carbon or resistors, feeding into the spark plugs. Why that works is a long story, but it does. That is what the hot-rodders use.
Actually, since few music lovers listen to AM radio lately, you may not have any problems using solid-core spark plug wires, although those MAY interfere with your other radio gadgets. A good auto parts store should have all of these options.
Inductance spark plug wires are the best, IMHO. They suppress radio noise, there are no resistors to worry about, and the wire does not go bad when you bend it once.
Some spark plug caps have resistors inside. You will not need (or want) those types of spark plug caps, with inductance spark plug wires. Resistor wire and resistor caps work to suppress radio noise by reducing the spark plug voltage (bad plan).
Switch the plug wires.
Pull the #4 plug wire and put it on #1, put #1 on #4
Pull #2 wire and put it on #3, put #3 on #2
Do the left 2 cylinders still stay cold? If so, your wires are fine.
If the problem was in the plug wires, your left 2 cylinders (#1/2) would now wake up and get hot, and your #3 and #4 would now be cold.
The oem FJ silicone plug wires with stainless steel cores are extremely durable.
forgot the firing order, was reminded when I saw the connections, outer cylinders-left coil, inner-right. respect Pats advice but not sure how to clean the idling and pilot circuits in the carbs. Do I have to remove them to do that or is there an easier way to flush them out? will try swapping plug wires.
Quote from: Pete-speed on June 13, 2025, 02:21:08 PMforgot the firing order, was reminded when I saw the connections, outer cylinders-left coil, inner-right. respect Pats advice but not sure how to clean the idling and pilot circuits in the carbs. Do I have to remove them to do that or is there an easier way to flush them out? will try swapping plug wires.
Pull them, disassemble them, ultrasound them, reassemble, set floats, reinstall and balance them.
after swapping plug wires got same result, left two cylinders cold, right two hot. should get a battery for my DMM thermocouple detector, save my fingers. anyway, does this take me back to clogged carburetor pilot circuits? and if so what would you recommend. as an aside, question about plug type was difference between the 8 and 7 version but appreciate info about RFI.
If only way is full disassembly and ultrasonic cleaning that will relegate that to a job for the fall. no chance High pressure air into the fuel line blow thru the clog or other degumming fluid? Not lazy just don't have the time and I do have another ride.
Gotta take them apart. Lots of small passages.
In the old days before ultrasound cleaning we would do a multi day soak in a bucket of Berryman's carb cleaner.
https://www.autozone.com/fuel-and-engine-cleaners-additives/carburetor-and-throttle-body-cleaner/p/berryman-chem-dip-carburetor-and-parts-cleaner-96oz/139313_0_0
Then blow them out with air.
Sometimes it worked, sometimes we had to do it over.
I've been told that the new low VOC formulation of the Berryman solution is not as effective as it was in the '80/90's.
Ultrasound is the way to go.
I'm running my bike now with a little seafoam in the gasoline and I do think it's helping to clear the pilot circuit in the carbs. Def get that old gas out of there put some fresh gas and maybe try some seafoam in the gas. Some people fill the carbs with just seafoam and let it sit overnight and then drain it and do a mix of 75% gas 25% seafoam and run it for a few mins and let it sit again
Don't soak your carbs in straight Seafoam, it will damage the aluminum.
https://seafoamworks.com/questions-and-answers/can-sea-foam-be-used-for-soaking-carburetors-solved/
It looks like Seafoam says you can soak carbs in Seafoam
Ok, thanks, I recall other FJ'ers warning about soaking in certain cleaners damaging the aluminum surface.
If Seafoam does not specifically state that's it safe for aluminum soaking in full strength, (like the Berryman's carb dip) I would be leery.
Perhaps Robert @ RPM can chime in....he's seen his share of fucked up carbs...
Quote from: Pat Conlon on June 14, 2025, 02:53:59 PMOk, thanks, I recall other FJ'ers warning about soaking in certain cleaners damaging the aluminum surface.
If Seafoam does not specifically state that's it safe for aluminum soaking in full strength, (like the Berryman's carb dip) I would be leery.
Perhaps Robert @ RPM can chime in....he's seen his share of fucked up carbs...
We use the ultrasonic with chemcrest cleaning solution. After hot tanking them to get the dirt and crud off. I don't use seafoam at all so I have no clue.
Pat,
Some have tried using Simple Green to clean the bike aluminum. Bad Plan. That stuff does damage aluminum, at the molecular level. This damage is called Hydrogen Embrittlement. It makes aluminum prone to cracking. That may not be obvious with just a quick swipe with the cleaner, but it happens. Definitely you do not want to soak anything aluminum in a bath of Simple Green. There is a separate product, a version of Simple Green made especially for use on aluminum, which should be all that anybody needs to hear. The makers of Simple Green are fully aware of this issue.
Thanks Red, now I remember you mentioning that, also IIRC there was something about a fella soaking his carbs in lacquer thinner....
let me try and find the post.
pulled out the air box, plan to drain the float bowls, let sit for a while. any comments as to whether this is a good or bad idea. additionally, if when I disassemble the carbs, are replacement float bowl gaskets available anywhere?
Check out post 9 in my thread.
https://fjowners.com/index.php?topic=19343.msg197040#msg197040
Read the whole carb rebuild story, guess I can fabricate gaskets if needed but heard mention of rebuild kits. Are there carb rebuild kits for a 1991 FJ 1200?
http://www.rpmracingca.com/
Quote from: Pat Conlon on June 16, 2025, 01:42:01 PMhttp://www.rpmracingca.com/
And more specifically:
https://www.rpmracingca.com/proddetail.asp?prod=3XW-14984-00&cat=39