New to forum and carb questions

Hmm that could be the problem. When I set float height I measured 3mm from the center of the float to the carb bowl surface on the carb. They are supposed to be 17mm? I have a float level gauge that's what I used. Seems like I did that wrong, they were already at the 3mm setting when I took of the bowls. Yes I made sure air jets were correct located. Pipes equally hot. I also synced and colortuned after reshim. I also had to "repair" the carb boots as they were pretty bad. I used shoe goo, and liquid tape. I sprayed around the boots and no increase in idle. I still wonder if this could also be the culprit. I am also concerned about the float level now !

 

You set the floats to the fuel height spec.
Here's the full procedure: Setting the fuel levels

 

Wow thanks k-moe I failed to do this one right! Thanks for this

 

So far they are out of spec! Gap was probably 20+ mm. Oh the joys I have had to fix from the PO.

 

Floats set to correct levels. Carbs reinstalled... problem still there. Hanging idle slow to return and hit a wall at 5500 rpm. If I stay in 2nd I can sometimes push it past 5500 to 8k or so but 3rd to 5th the bike stops dead at 5500 rpm. Any suggestions? Thanks everyone, this bike has been a chore to get right.

 

Have you got decent compression? If yes have you tried raising the needles to see if it helps? You could be getting too little (or far too much) fuel from the mains.

 

Long shot but are the needles ok? I discovered yesterday after a frustrating couple of weeks not being able to get past 60mph and 6k revs that cylinder 2 wasnt performing as well as the others.

I'd checked shim clearances, colortuned and vac synced as usual but the culprit was the needle. All floats set to 17.5mm as per instructions and wet set was in spec. The needle spring (the circled part in the pic) was too weak so wasnt giving the support to the float flange and was allowing too much fuel in.

Have you checked the spark plug colour to see if it's running rich / lean?

 

I will check that. When I had the carbs off the float needles looked ok visually so I put the orginal ones back in. They were the only thing I didnt replace during the rebuild because of that. I have 4 new ones ill swap in to see if that makes any change. Thanks, this may be it. Could this possibly be a TCI box issue?

 

Best way to troubleshoot a TCI is to try another one - do you still have the black label one you purchased earlier? A timing light can also be used to check for advance, although being precise is a bit difficult without some pretty decent equipment. And, just a stretch on an issue is the hodgepodge of parts you have. I don't know all the details, but I do know the reluctors are different on the 650 Seca engine. What I don't know is what might happen if a 650 Seca reluctor was combined with a red label TCI. I do know the converse of that, and that dwell time is considerably different when using a 750 Seca reluctor with a green label TCI as compared to the red label TCI. And to check - the 750 Seca (red label TCI) is 20.5mm, the 650 Seca is 17.75mm measured at the very end closest to the pick-up coils.

While you have the carbs off check the slides by lifting them and noting how they return. Improperly installed slides or holes in the diaphragm is going to cause a major loss in power and limit the revs if the slide is not lifting. With the caps off the slides should lift and clunk to the bottom of their stops. With the caps on they should be slower to return, which indicates and airtight seal is present. I found this video of a guy demonstrating a defective installation where the diaphragm was not properly installed in the groove. You can also run the bike with the air box boots off and verify the slides lift when the motor is revved.

 

Thanks for the info rooster. Yes I still have the black box (4h7) TCI. I will swap that back in but I seem to remember it still ran the same way, 5500 wide open. I did have an issue last week where the float was sticking closed on #1. I figured it out because the pipe was not hot on that cylinder. Ill check carbs again.

 

TCI swap to black box 4h7 did not change problem. I pulled the carbs and put new float needles in. They are different than the black rubber tipped that were installed. They go further in. Will report back when reinstalled.

 

Be sure to set the fuel levels again. Not all float needles are of the same height.

 

New float jet needles installed. Carbs reinstalled and black box tci swapped... problem still there, sputter and no go after 5500 rpm. Also now I have no adjustment via the idle knob its idleing at 2,000 rpm wont move when turned counter clockwise. Still have the slow to return hanging idle as well. Figuring it needs re colortuned but still not go after 5500. Voltage regulator seems pretty hot, could this be the issue? Either that or carb boots to head?

 

The voltage regulator is supposed to get hot. As it regulates voltage it dumps the excess to ground and turns it into heat (essentially).
When you had the carbs apart did you polish the slide bores? Did you check the slide fit to be sure they can't hang up?

 

Yes polished the bores and the slides move freely and passed the clunk test. I actually checked them 3 or 4 times just to make sure and they are good. This whole problem is like hitting a governor that's why I am now thinking it may be electrical. Does advance increase at 5500? I also have a cx500 and when the high speed coil fails on those you cant past 5000 rpm that's what this all reminds me of.

 

So did you do this? Or did you check that the slides don't quite clunk as demonstrated in the video?

 

Rooster, yes I checked the slides and they move well. Clunk test follows the video exactly. I am going to go through the wiring to see if there is a problem there. On the regulator plug output the red wire must have gotten hot at one time because the connector was melted there. I also plan on checking the reluctor out and wiring leading to the TCI.

 

Wires look fine. I did manage to get the idle straightened out, some things changed when I corrected the float. Still having the same issue as mentioned before. Frustrated.

 

I'm a bit late to the party but does the xj750 model carbs being talked about here have pilot screws on each carb?
Not the pilot air jet or any of the other jets but a pilot screw?
The one that adjusts fuel/air mix at idle.
Just a thought.

 

Yes they are there. I have them about 2 3/4 out via color tune. I plan on rechecking the vacuum diaphragms with a magnifying glass after reading similar stories on this awesome forum. Ive gone over just about everything, valves, sync, colortune, fuel delivery, ignition. Nothing has changed this problem and I must be missing something.