750 seca carb mystery

He already fixed that issue.

 

Forgive me, lost the thread over time. Std jets then, chacals shaft seals, and then it should be good?

 

I think so.

 

Okay I was sceptical of the colortune plug, I'm old school after all and have to admit it is the coolest tool ...my bike starts without the choke now ,plugs look great , bike was running lean before and hot . I always thought I had carbs dialed in good , well now I do

 

Last week I pulled the carbs again ( I'm getting really fast at this 45 minutes) and switched the jets back to stock. I found that 2 of the throttle plates
were installed backwards and the "o" rings I substituted for regular throttle shaft seals were too fat and were preventing the springs from closing
the throttle plates properly. Sometimes, I could get the bike to idle smoothly and at other times it would surge up to 5000 rpms. I flipped those throttle
plates around and substituted better "0" rings as throttle shaft seals. Monday I'll reinstall those carbs and hope performance improves.

 

I found that the color tune showed blue from about 1 turn out until the screw became loose at over 3 1/2 turns out.
I did notice that the blue flashing was smoother at a certain point between 2 1/2 to 3 turns out and the white pops stopped.
Otherwise the blue color was easy to see but the cylinder could be still be rough.

 

Where can a guy get #11 "o" rings. Autozone, Pepboys and O'reilly's only sell assortment boxes and none of the rings can be doubled up without
jamming the throttle shafts. I went to the Napa store and they acted like I was crazy. If there is another source like maybe a plumbing supply
store I could try that also. Do you know in mm what are the i.d., the o.d. and diameter of #11 rings are ? Or, do they have another size designation ?
I found a ring that fits both tight against the wall of the seal recess and around the shaft but there is about a 1/32" space to the plastic washer. also,
I was looking for silicone grease and they all offered me was dielectric grease. Is this the same stuff ?

 

#11 is by the U.S. sizing standard. Most automotive applications use metric sizing now (and almost all auto store employess don't know about anything that isn't listed in the compter inventory. Sad times that we live in).
This chart has the info you need.
https://www.marcorubber.com/o-ring-size-chart-as568.htm

You can buy #11 orings online all day long. My local ACE hardware store stocks them.

Dielectric grease is a type silicone grease, and is suitable for your purpose.

 

you'll get a few spares to share with friends and neighbors
https://www.mcmaster.com/#o-rings/=1dimfv5

 

I have gone over these xj750 seca carbs several times in minute detail. I've given more attention to this set than the 4
other sets I did for 650 maxims, and the maxim carbs run great. I'm obviously doing something wrong here that I haven't considered.
Two Questions. When I swapped pods for an airbox, I used a box from an xj650 seca. It had a different style cover and air inlet than
an xj750 RJ cover. Could this be a problem of too much or not enough air ? Also, I cleaned and saved the air jets existing ( #225+#80),
are those the correct size ? The new fuel jets are ; main-#120 and pilot-#40.

 

Yes.

No.

 

It could be that there is something wrong with the carb bodies. Have you carefully inspected them for cracks or defects?

When the air jets were reinstalled were they put in the correct locations, and not what the manuals show?

 

Thanks Rooster. I tried the test and it worked well. I was able to blow out the pilot circuits of all 4 carbs. I've been busy since your post
and it took me a month to try it out myself but I will use it from now on. One more Question though, Is there a similar test for the enrichment
circuit ? It would be great to be able to back flush somehow, by blocking off holes, to make sure the tube that sticks down into the float bowl
is clear.

 

This will help you see where the circuit runs.
Inside your Carbs

 

I used a similar method as with the pilot circuit using some small gas line (think weedeater) and attached it to the straw on the carb cleaner and to the brass tube. You can then block the small hole in the brass tube near the base of the carburetor and blast away (watch those eyes). Carb cleaner should exit in the choke plunger hole and under the diaphragm where the air inlet hole for the choke is located.

 

It took

OK. So, I examined a junk Hitachi carb and I see an air hole in the air chamber just over the pilot air jet. It connects directly to the enrichment plunger hole.
That connecting tube is about an inch long. A half inch along that connecting air passage the enrichment fuel jet tube intersects it from below. If the plunger
is down, and I squirt carb cleaner into that air inlet above the air pilot jet, wouldn't the carb cleaner then squirt out of the brass enrichment jet ?

 

Yes it should, but it will most likely just dribble out of there as it might be difficult to build pressure through the air intake hole.

 

To clean the enrichment jet you really need to take the float bowl off. Anything that gets blown out if it will just end up getting back in there eventually unless the bowl is removed and cleaned out.

 

here's how to modify a red or black tube to clean out those enrichment jets
https://drive.google.com/open?id=1JXXdJ4gZg8_KOzr5N2mEOTNkEltPoqms

 

Hooray ! I finally got the carbs set right and the engine runs smoothly. I pulled the carbs I had been working with and ordered another set from ebay
I cleaned up this new set and used the original parts instead of the Chinese parts off eBay. I did replace the float needles and seats though. I followed the youtube
video instructions for blowing out the pilot circuits, posted by Rooster 53 with great success. and back flushed the enrichment circuits similarly. Polished the vacuum cylinders,
cleaned and blasted all the jets w/ compressed air, bench synched, wet set and installed them. The bike started right up but high revved, I opened the mix scews to 2.75 turns.
Now it runs the way it should, idleing at 1.5k rpms and when goosed, it Quickly returned to that 1.5k idle. Thank you all for the great tips ; K-Moe, Rooster 53, Chacal, Jetfixer,
Pollock, Tabaka 45, and Minimutly. Next I'll do a running synch.