1982 Yamaha XJ750 Seca Idle and Carb Issues

My roomate bought an XJ750 Seca for $500 a couple of weeks ago and after a carburetor rebuild there are a couple of issues.

#1 Cylinder 3 has a rip in the carburetor diaphragm. I have read a lot of the repair information on the forum and the Permatex and Plasti-Dip solution might be the answer. If anyone has a spare, please PM me with the price (I would rather just replace it but we are working on a tight budget)

#2 Starting Issues. Sometimes I can go out and hit the start button and she's ready to go... Other times it refuses to start until a few good shots of ether. I figured that the diaphragm would have some effect but it is only one carb out of four...

#3 Idle. The bike has a very low idle (~500rpm) and it doesn't matter how far you turn that idle screw in. Sometimes if you turn the screw until it becomes tight to turn the bike, every now and then, will jump to a 4000rpm idle. It almost seems like a jet is still clogged but everything has been cleaned.

The bike revs fine with no hesitation and seems to perform well out on the road. The whole in carb three's diaphragm is about 1/16" wide so I don't know how much effect it has on the bike. All the plugs have been replaced and as Robert said in an earlier post, I douched the living dog snot out of each carb. Any help is greatly appreciated. Thanks!

-Austin

2006 Suzuki Boulevard M50
1983 Honda CM400T
2006 Suzuki GZX250 (Wife's)
1982 Yamaha XJ750 Seca (Roomate's)

 

You are right, it sounds like a clogged jet. If the idle and starter jets are in fact clear then I would suspect that the mixture screws may be turned in too much. This would explain the low idle and the bike running well at above idle speeds. You could turn the pilot mixture screws in and back out to 3 turns. Do a search on the carb diaphraghm and see what comes up. I have never fixed one but some here have. Care must be taken that a fuel resistant RTV is used or it will break down and clog the carbs right away.

 

Repair the rip with "Liquid Electrical Tape"

Smooth-out the diaphragm on a Martini Glass and tape it down so the rip slides together and the rubber is in the correct form and not "Pulled"

Using a few drops of the Liquid Electrical Tape ... Use an ARTIST Brush ... and cover the area to be repaired.
Clean the brush.
Let the repair dry. (10-minutes)
Second coat.
Clean the brush
Dry.
Third coat.
Brush.
Dry.
Flip-over repaired surface.

Do other side as stated above.

Carbs:

Clean Fuel Bowl Lower Jets which allow Starter Jet Well to fill.
Probe Brass Extension Starter Jet Supply Tubes which extend into Fuel Supply Well.

Remove Pilot Jet and Pilot Mixture Screw, (spring, washer & o-ring).
Blow stream of Carb Cleaner through PILOT FUEL JET port and let the Pilot Jet Air Passages Flush-out.

Remove MAIN FUEL JET and washer.
Press-out Emulsion Tube through TOP of Carb.
Clean and inspect the 18 - 20 Metering Ports.
Blow-out the MAIN AIR JET Passage while the Emulsion Tube is extracted.

 

Hello , after cleaning my carbys out today I realized that two of the needles under my diaphram were not springing like the other two . I pulled them apart and I can't seem to free them . Is there some way to fix them or are they meant to be like that ? If not does anyone know where to get new ones

 

Hi wormburner, welcome. Forum etiquette dictates that it's more polite to start your own thread regarding your troubles, so as not to "hijack" and possibly stop the original poster's issue being solved.

That said, this is also a 6 year old thread so I doubt you'll cause a problem, however starting your own thread is much preferred.

 

Thanks , sorry .

 

The PO might have substituted Non-spring loaded Diaphragm Assys.