WE KNOW IT'S NOT IGNITION .. CHECKING CARBs

[79XS11F]

Brief history
The bike had been running reasonably well but seemed to lack pulling power in the mid throttle range and had a misfire at constant throttle settings and a rough misfire idle. Mostly when warming up.

Last Thursday (July 27) I removed the baffle of my MAC 4 into 1 pipe and packed the outside of the baffle to control noise and possible poor exhaust resonance because the stop plate has been removed from the baffle. I used the bike the balance of that day for a few short trips. there was no change to the above condition it was just less noisy.
I parked the bike that Thursday evening to remove and return the front wheel for a defective tire issue.
Got the tire issue issue sorted and reinstalled on Wednesday (Aug 2) and went for a test drive. The bike was misfiring and had a REAL rough idle but seems OK after a short 5 KM run.
The folowing Thursday morning (one week since being parked)when I went to go to work the bike again had a very rough idle and the bike ran so poorly that I did not take it to work. As we know from the other thread (Timing pickup question) the ignition would appear to be working correctly.
So today is re & re the carbs day to reinstall all the jetting that came with the bike. The jets have been soaking in carb cleaner all night.
While I have the carbs off I will check all rubber seals and blow out all passage ways again.
While I am doing this job I will from time to time take a break and check here for any input that can be offered as to what's going on with this bike.
Rob

[79XS11F]

OK I have the carbs off the bike and removed from the rack.
observations:

The butterfly valve on #2 is a little sticky. It will not close completely on its own. The closing spring feels weak compared to the other 3 carbs.

The fuel supply "T" between #3 & #4 is corroded and sorta just fell out of #3 but was OK at #4.

The chock control rod has a slight bend in it and the retaining guide on #1 is broken off the carb body so the locating ball is missing as well.

Where will I be able to get new "T"s for the fuel inputs to the carbs?

Before I re-jet the carbs .. could these 2 issues alone be the cause of my problems?

Rob

[79XS11F]

Good Grief .. Even with a very good fitting Philip's driver I can not budge the screws that hold the butterfly valve to the shaft of #2 carb. Any trick for that? I don't want to strip the screw heads.
Rob

[underdog57]

dremel or die grind

Makes a world of differance if you grind or carbide burr the swaged end of the screws off...
I'll be putting new screws in and lock tite them in ...

Bob

[79XS11F]

Are you referring to the little bit of the screw that protrudes out the back side of the shaft? Being that I could not get the screw out I put the WD40 to the outer areas and 1 drop on 3in1 oil at the inside of the shaft at both sides. It is moving much better but ever so slightly stiff. At least the butterfly will completely close now. All butterfly's do seal when closed. No detectable air and be blown through by mouth.
I have confirmed that all the jets that came out are factory sizes. They are not clean and ready to put back in the carbs.
Rob

[underdog57]

Yes , the backs of the screws a smooshed so they wont turn out easily ..
I stripped the screw heads on most of mine , after grinding the backs off was able to turn them out anyways...

I was wondering if it was neccesary to remove them or not . I'm putting new seals in at $5.00 each seal ...But the seals seem pretty good anyways ...

Read a lot of people do not have to change out these throttle shaft seals ...

Want to do it right the second time around !!!

Bob

[TopCatGr58]

Hey Rob,

The problems you found with your fuel "T" is probably NOT the reason for the poor running. Clogged T would have meant less fuel, lean conditon, not rich! What you're doing with the OEM jets is the right move. Your carb with the ?weak? spring may be binding on the seal. IIRC, someone stated soaking in mineral oil to rejuvenate the damaged seal from the carb cleaner without having to take it apart!

The fuel "T" is no longer available from Yamaha but MikesXS has a replacement. Rob Reil at motorcyclecarbs.com also offered one, but I can't access his web page?? Don't know if he's gone out of business or what? The MikesXS unit is a simple brass tube with NEOPRENE rubber Orings at the ends to seal the tube within the ports. So...with your old one, since the rubber is disolving, you may want to try removing the damaged rubber, and then go to your local hardware store and get some NEOPRENE Rubber O-rings that will fit on the "T" and inside the carb inlet port. You need Neoprene, not natural rubber!!!

Brass Carb Fuel Line T-Piece
rass Carb Fuel Line T-Piece & rubber seals(2) -
( Fuel supply T pipe that fits between carbs). Replaces plastic coated pot metal
stock fuel T that fits between stock Mikuni BS 34mm. CV carbs used on North
American Market 1980-84 XS650's.
Fits: 80-84 34mm. CV carbs.

Note: Carbs will have to be detached from each other to install and we suggest you
replace the link bar screws that join the 2 carbs together as originals are usually
difficult to remove without

Note: Fuel T 48-0884 is a pressed together assembly
and must be handled/installed with care.


Part #48-0884 $15.00 USD EA.
*********************************
Replacement Rubber T Seals
Replacement Rubber T Seals for Brass fuel Line


Part #48-0885 $1.00 USD /Pr.
**************************
http://www.motorcyclecarbs.com/ But I tried to go to his page, wouldn't display?
**************************

T.C.

[79XS11F]

I seem to have the butterfly on #2 working petty good. I think the issue is over spray from when the engine was spray painted in the frame. There's over spray on lots of parts So i have cleaned up as much over spray as I can off the outside of the bodies and things seem to be working smoother now.
Question. The air vent "T"s are in VERY good condition but are a little shorter across the top of the "T" Being that the air vent "y"s are above the fuel level could I switch them off with the fuel supply "T"s so I can get this puppy back together this weekend?
Is gas fitters Teflon tape OK in contact with gas? I was thinking that is I can switch off the "T"s I could wrap the 1 damaged "T" with a few wraps of Teflon tape and use it until the end of the season or until I drop the other engine in it the bike.
Rob

[TopCatGr58]

As long as the upper "T"s will fit securely in the lower fittings so that there isn't a fuel leak, then you should be good to go. As for the teflon tape, don't know how it reacts or not to fuel, vapors or the liquid state?? You might test the tape by putting a small amount in a little cup of gas and see what happens!? Otherwise you could use regular O-rings on the upper T since it usually isn't exposed to liquid gas!
T.C.

[79XS11F]

Originally posted by TopCatGr58
As long as the upper "T"s will fit securely in the lower fittings so that there isn't a fuel leak, then you should be good to go. As for the teflon tape, don't know how it reacts or not to fuel, vapors or the liquid state?? You might test the tape by putting a small amount in a little cup of gas and see what happens!? Otherwise you could use regular O-rings on the upper T since it usually isn't exposed to liquid gas!
T.C.

This is what I was hoping because both upper and lower "T"s are the same DIA and the uppers are indeed in very good shape. I guess I will pop some Teflon tape into some gas and see what happens. I do know that Teflon is one of the most chemical resistent products know to man but with my luck .. gas isn't one of those chemicals it's resistent to lol lol
Rob

[skids]

Some models (all?) of carbs will have hemispherical screens at the fuel valve inlets. These things can plug up with rubber bits from orings, petcock gaskets, and hoses. Then, you will have fuel starvation problemos. It is something to check. Make sure that the petcock operates properly as well. You know, clear line on the outlet and suck on the vacuum hose while it is connected.

Regarding the enrichener mechanism, make sure that all of the choke plungers open and close properly. There still should be a detent ball on the other end, I think and really, that is a convenience so that you don't have to stand there and hold the lever... no big deal.

I have used mineral spirits to shrink the throttle shaft o-rings after a dunk treatment. It works, but of course it was a mistake to dunk them with the throttle shafts in place. I am exclusively a carb spray guy now. Yomamma supposedly has a dip solution that is oring-safe... Never tried it.

Teflon tape? I have been told it is a quick way to mess up brake fluid. I am not sure about gas. Get a shot glass and observe an experiment.

Originally posted by 79XS11F


This is what I was hoping because both upper and lower "T"s are the same DIA and the uppers are indeed in very good shape. I guess I will pop some Teflon tape into some gas and see what happens. I do know that Teflon is one of the most chemical resistent products know to man but with my luck .. gas isn't one of those chemicals it's resistent to lol lol
Rob

[79XS11F]

OK I just got in from Canadian Tire and they has O-ring kits for fuel injection systems at 12.99 and there are 4 in the pack that will work for me on the fuel supply "T"s :-)
I have all the jets changed back to what was in the bike when I got it. So now I need to rack them, install them and sync them. I will keep my fingers crossed and up date you later today
Rob

[underdog57]

Safe dunking cleaner

The mechanic at Yamaha here said the yamaha cleaner is safe on o-rings ....
I wanted to see the o-rings , they are 27 years old . From what I see they look like very good neoprene .,.Might not bother on another carb job ...

Bob

[79XS11F]

Re: Safe dunking cleaner

Originally posted by underdog57
The mechanic at Yamaha here said the yamaha cleaner is safe on o-rings ....
I wanted to see the o-rings , they are 27 years old . From what I see they look like very good neoprene .,.Might not bother on another carb job ...

Bob

If your referring to at the fuel supply and vent "T"s ... my bike has no O-rings there. The steel "T"s at their carb entry points are covered with what looks like rubber about 1/16 of an inch think and there are 2 ridges formed into that rubber coating that act as O-rings.
Rob

[79XS11F]

NO LUCK .. running worst then ever now. Couldn't even sync the carbs. That's it for today for me. I will "putter" with it tomorrow.
Rob