750 seca carb mystery

I rebuilt the carbs on my 750seca project. complete disassembly soaked metal parts in lacquer thinner
everything spotless. replaced throttle shaft seals, float needles and seats, new mixture screw "O" rings,
float bowl gaskets, cleaned main jet 120, pilot jet 40, cleaned air jets main 225 pilot 80, slides drop smoothly
when lifted.
OK carbs back in/ test bike. start up with choke 1/2 engaged, when warm can't disengage choke and have to
keep playing with the choke between over revving and engine dying. Cannot rev the engine. when throttle is
revved the engine dies.
Pulled carbs and replaced more parts. New accelerator needles/emulsion tubes/main jets-122, new pilot jets-43, new mixture screws/springs/washer/"O" rings, polished slides, diaphragms all OK, new springs on choke
plungers, pilot tubes in float bowls clear, set float drops with gauge, reinstalled carbs, rubber manifolds tight.
OK, test bike . The symptoms are the same bike will only idle when the choke is balanced between over revving
and dying, also both times #1 pipes stay cool. Test spark/ strong all 4, compression 121 straight across. Engine
still dies when throttle is revved.
Any ideas ? Bad 1-4 coil ? bad TCI ? pick up coil ? I even swapped mufflers thinking one could be restricted,
but no change with new set. Any test suggestions ? Oh yeah and the mix screws turned out 2+1/2 turns both times. HELP

 

When it dies does it stink of fuel? If not it sounds weak (it would need to be very weak to do this ).
Did this start suddenly without you doing anything or after a rebuild?

 

Did you bench synch carbs? And have you done a running synch, I use a 4 vacuum gauge manifold . Sounds like your idle is low try turning it up and then take choke off . Are your mixture screws set at 2.5 turns out? That is the best starting point. A cold cylinder can be as simple as a bad plug or cylinder not getting fuel . Try this with fuel bowls filled with fuel open drain screw , and see if fuel drains out if very little drains you have a float problem....did you set float height when you did carbs? These are some items to check.

 

"Set float drops with gauge" what does that mean?
And how carefully did you bench synch them?
What does "#1 pipes stay cool"mean? Is that one, the same one or one diffErent one?
Sounds like you need to take more care over the whole process?

 

It sounds as though the pilot fuel circuit is (probably internally) clogged............a bike that will only run with the choke engaged is a typical symptom of this problem (the pilot (idle) circuit being clogged requires an alternate source of fuel, and that alternate source is the separate supply from the starter (choke) system.

 

The bike was a wreck when purchased. I swapped the engine, wheels, driveline, and wiring to a straight frame. Front end on blocks, the PO started engine
and it idled and revved with throttle. I've redone 3 xj650 carbs and a kz1100 with success. Did this one thoroughly. Bench synched with a c-card strip and
set float drop to specs with old c-card. Running synch and wet set come after bike will idle. Never had to hold idle with choke so much, over rev or stumble
and revving throttle kills engine. Bike has orange spark and good compression. Cheap parts kit from ebay, maybe defective ? first rebuild w/original parts
and new float needle etc. second rebuild w/all kit parts. Test both times w/same symptoms. In anyone's opinion could this be a tci problem ? Also, when
nursing the idle with choke carbs pop intermittantly.

 

Soaked the carb bodies in solvent several days (w/rubber off) I know the pilot tubes in float bowls were clear. pilot clog could be up inside carb bodies maybe one or two crabs, but
all 4 ? will test coils, wiring, pick up coils. have 3 other hs-32 carbs, was thinking of starting over w/diff. carb. cleaning and swapping parts and jets. could a bad TCI box cause this ?

 

Yes, it could I believe.
One thing you need to do is wet set the floats - bike doesn't need to be idling. The dry synch you've done will be fine.
You can squirt leaner through the idle galleries to check them, the main jet/emulsion tubes are simple.
Let us all know how it goes.

 

Couldn't do running synch w/bad idle. I drained gas out of float bowls before second rebuild some drained more gas than others. I polished the float needle seats w/q-tip, polishing compound and
drill. All were clean ditto rubber tips. If I rebuild a spare hs-32 carb set with new xj750 seca parts and get the same results that would point to timing, right ?

Following a tip from a youtube video I tested the ignition in each cylinder by removing the airbox cover and filter and squirted starter fluid into each intake manifold.
if the cylinder tested surges the problem is in the carb and not the ignition. If the idle has to be controlled with the choke the problem is in the pilot circuits. I removed the
tank and fastened a funnel and plastic tube to the carb fuel intake and poured in seafoam enough to fill the float bowls full and circulated the seafoam through the carb bodies
using starter fluid to idle the engine. All the pilot jet passages should be full of seafoam now. I will drain the seafoam out of each float bowl in a couple of days, reinstall the tank and fuel line,
and run gas through the carbs to see if the seafoam cleaned out pilot circuits. If that doesn't work I'm going to rebuild one of my spare hs32 carbs with xj750 jets and newparts.

 

from past experience I found that using a gauge to set the float drop put the level within a few mm of the desired level. OK for now
to run tests and apply seafoam. Through trial an error I can pull a set of carbs, work on them and get them reinstalled in a few hours.
I built a rack to hold the carbs while I wet set the levels. I'll see if the sea foam works and if not I'll rebuild another set of carbs.

 

You might want to boil the carbs for a while and see if the will clear the pilot circuit. I use plain water, but some folks use lemon juice. If it is varnish the hot water will desolve it. After boiling it 10-15 minutes blow it out with carb cleaner and then air.

 

I use tfr, it has caustic and detergents, ali, brass and copper come up great after a boiling in the ultrasonic cleaner. Doesn't loosen stubborn float chamber jets though...

 

Carbon tetrachloride used to be the goto tool of choice, particularly for 2 strokes de coking, believe it's been banned now though!!

 

How about vinegar ? Will boiling the carbs in that, clean out the pilot tubes ?

 

It probably would, but it might darken the aluminum body of the carb. Hot water is all you need for varnish. I think the critical part is flushing out the passages with carb cleaner before the carb cools enough for any varnish to have a chance to perhaps harden again.

 

I've heard of using jewelery cleaner, not sure what it consists of but supposed to work well

 

It’s just liquid soap used in ultrasonic cleaner with warm water. I doubt that water in an ultrasonic cleaner gets very hot, at least the small one I have doesn’t. With an ultrasonic cleaner the trick is being sure the water gets into all the small passages.

 

I filled the float bowls with seafoam, waited a day and vibrated the carbs with a palm sander. The idle performance improved
and now I could rev the throttle without killing the engine, but it was still balky so I drained the gas out of the bowls again
and once again filled with seafoam. This time I'll wait a couple of days before testing and I'll vibrate several times. And like
the big guy says "we'll wait and see"

 

My cleaner boils!

 

Got the engine to idle smoothly with no choke after warm up. I can rev the throttle without killing the engine but the rpms drop back down slowly
and the #1+#3 headers are still cold, telling me that the pilot systems in those carbs are not supplying fuel to those #1+#3 cylinders. Maybe boiling
is the answer but maybe I can clear those pilot circuits with carb cleaner and compressed air.

 

What is the most common place for the pilot system to clog ? In the carb section views it looks like the pilot air jet, the mixture screw ,the pilot tube in
the float bowl and the pilot fuel jet are all connected. I repeatedly shot berryman's cleaner into those holes with the jets and mixture screws removed and followed up with 100 psi into the same holes hoping that the compressed air would blow the clogs out. after several treatments, I'll reinstall the carbs
and see if there is any improvement. If the clogs persist, I'll strip all the rubber seals etc., separate the carb bodies and boil them.

 

what is tfr ?

 

Getting the pilot circuit clean usually does require stripping the carbs down and giving them a good soak is Berrymans or simmilar.
You're fighting against 90º turns in a very small passage.
inside your carbs.pdf

What youre doing will sometimes work, but as you're finding it can sometimes be a waste of time.

 

While you have them off, do both.

 

Tfr - traffic film remover, if you have a heated ultrasonic cleaner it works well. However, I've also had to resort to rodding the float chamber "jet". On the subject of the float chamber passage, I don't believe it's connected to the primary fuel system - just the startup enrichment- or am I wrong?

 

The fixed enrichment jet (in the bottom of the float bowl) is on its own circuit. The removable pilot is on a seperate circuit.
The fixed enrichment jet almost always needs to have a bit of music wire run through it to get it to clear.


joejr2, the brass tube, and the tube in the float bowl are both part of the enrichment circuit.
Sometimes you need to blow air, or carb cleaner, backwards from the outlet holes in the carb body (near the top of the throttle plate). The one that the throttle plate almost covers is the pilot, the other is the enrichment (you'll want the enrichment plungers out when you do that one, or at least have them open).

 

Thanks K-moe on Monday I'll split the carbs off the racks, take off the throttle plates and seals and boil the carb bodies in water

 

Maybe test the pilot circuit this way first.

1. Drill an old pilot jet so that the straw from the carb cleaner fits snuggly in the hole.
2. Leave the pilot air jet in, but plug it with a wooden q-tip that is covered with a bit of heat shrink tubing.
3. Install the pilot screw without o-ring, set it to 2.5 turns from soft seat.
4. Blast the carb cleaner through the modified pilot jet and it should look something like this:

 

Today I stripped the carbs again down to the bare bodies and boiled them in water with a little simple green.
I've got them almost reassembled. Tomorrow I'll finish and get them back on the bike. I'm hoping that it
will idle better and accelerate smoothly.

 

I took the boiling advice. I pulled the carbs off the bike again (xj750rh) , completely disassembled them, even throttle plates and shafts and took them off the racks. I put all four of them
in a pot of water with a little simple green and boiled them for 1/2 hour then blasted all the openings with berrymans B-12 followed by compressed air, repeated that a few times and
reassembled the carbs back on their racks. I wet set the carbs to specs and put them back on the bike. This time the bike started up w/enrichment and warmed up ok allowing me
to goose the throttle. Every few throttle pulls the rpms climed to 3k rpms and dropped back very slowly to 1k. Pipes #s 1,2,4 got hot and now number 3 stayed only warm. The # 3 cylinder has
120 lbs compression and that plug gets spark. All I can think of is that there must be the mother of all clogs in the # 3 pilot fuel circuit. I traded the # 2-3 coil with a good one to see if that was it
but there was no change. I'll probably get a used #3 carb off ebay, boil the hell out of it and soak it in laquer thinner. Then trade all the parts from existing #3 to see if that will fire up # 3 cylinder.

 

You need to perform a running synch before you make any rash decisions. A colortune procedure would also be useful.

 

Make certain the spring, o-ring and washer is correct on the mix screw.

Gary H.

 

I bought a color tune set a whie back but never used it what is the proper procedure ? A link would be helpful .

 

I put new washers and "o" rings on all 4 mixture needles.

The original fuel jets were 120 and 40 the new ones in the kit were 122 and 43 would the larger jets make a difference ? should I go back to the old jets

 

A completely stock bike is much easier to get right. Modifications to the air filter and exhaust make it much harder to tune. So get it as close as you can to stock. Also, have you verified that there is no air leak around the intake or intake manifold gasket? I had a torn intake gasket that was causing problems. As Chacal said, if you haven’t done a running sync you need to do it before doing anything drastic.

 

He was taking about the order those parts go onto the mixture screw. First the spring, then the washer, then the o-ring. Some people have been known to put the washer on first, or last, causing the o-ring to not seal.

 

I'm a bit suprised you don't try harder to verify the pilot circuits are all working before putting the carbs back together, then onto the bike? Surely rigging up an aerosol carb cleaner and firing it into the fuel passages of each one, and then comparing each one is easier? You could use water if you wanted to? Check the flow from each progression hole, with the mix screw all the way in?
If the passage is blocked, it will be more boiling to clear it - I wouldn't recommend drilling out the plugs.

 

I learn something new everyday. Ok, so the header for #3 cylinder is only getting luke warm compared to the other three. If I synched the other carbs to #3 would that bring #3 cylinder
online so that it's header would get sizzling hot as well ? I tested last week and #3 was getting spark I'll test again in the morning. All the mixture screws were opened 2 1/2 turns.

 

Maybe. If not, try bumping the choke on just a wee bit and see if that brings #3 to sizzling life. If so, then that points to a clogged pilot fuel circuit, or some other issue with the pilot fuel circuit on that carb.

 

I installed new aftermaket carb holder manifolds and gaskets and the airbox/carb manifolds were in really good shape. No air leaks that I could find. Once again, would synching the other
three carbs to #3 cause #3 to start firing and make the header hot like the other ones ?

 

I ordered an hsc-32 ( #3) carb body from ebay. It will be here in a couple of days. I'll soak it in solvent and boil it etc. then transfer all the parts from existing #3 onto it. Hopefully the replacement
won't have a clogged up pilot circuit as well. By the way is there a link to instructions on how to use a colortune ?

 

Yeah I put on the spring, then the washer, then the tiny "o" ring last. I even put the smoothest side of the washer next to the "o"ring. I turned the carbs upside down and fitted the mixture screws
into their holes with a tweezer from underneath so the washers and "o" rings wouldn't drop off in the holes and get installed crooked.

 

Over the last month I soaked that #3 carb body in Lacquer thinner for several days and boiled it for an hour on two occasions. I think it may be haunted or have bad karma. After all that cleaning
I assumed it was unclogged. Anyway I'm getting really expert at taking the carbs on and off that bike quickly.

 

Thank you sir that was a godsend.

 

Hey where did you get your throttle shaft seals can I get the store number or part number

 

See the reply in the thread that you started.

 

The spark tester shows spark being delivered to plug #3. I just had a brainstorm ! I connected the #3 plug cap
to the #3 plug with the plug tester and and saw a spark when the engine was turned over. Would it be possible that
the #3 plug is getting an acceptable jolt but the electrodes down in the chamber are not sparking ? I'm going to swap that plug
and check.

 

I thought I answered that already, but don't see it here. Are you working on this in two threads, or am I mixing people up who have the same problem?

The answer is yes, your plug could be faulty.

 

Yes I asked that question on another thead before mine because I thought that guy might have a similar problem. Anyway that hunch paid off.
I swapped the #3 plug out for a new plug and that cylinder lit up right away, the pipe getting as hot as the other three. So, the lesson is, " The plug tester
can show a spark but the plug might still be bad "