750 seca carb mystery

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 ?