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Makotosun

RT3 carburetor reassembly

  • RT3Mike
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Replied by RT3Mike on topic RT3 carburetor reassembly

Hello everybody - well I have her all put back together and I think she looks pretty nice overall.  It was quite the journey getting it all done as this is my first Yamaha so I felt like was flying blind at times figuring out where everything goes.  I still have some cleaning to do but this project is more of a renovation than a restoration. I was able to get it started fairly quickly, however am still having some carburetor issues.  The RPM's like to hang up high until I pull in the clutch and let it out again, then it seems to adjust itself fairly quickly. Kinda scary though if you are trying to stop. I have everything adjusted to what seems correct.  Any suggestions?  Also, my brake light seems to stay on bright as if the brake is being engaged. Any thoughts on that?  Check out the pics and please let me know if you have any ideas on the carb and light situation.  Comments on the bike welcome - good and not so good. I'm no pro here. 
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22 May 2021 16:01 #21

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Replied by Lizeec on topic RT3 carburetor reassembly

I’ll chime in on the brake light issue, verify the front & rear brake switches are working properly, verify wiring is correct, verify grounding is not the issue, lastly verify you have the correct bulb by wattage and voltage, also verify it is inserted into the socket correctly, it is easy to force it incorrectly by not having the little locating pins on the bulb not in the correct orientation in the socket.
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22 May 2021 16:12 #22

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Replied by Mothersbaugh on topic RT3 carburetor reassembly

On the idle problem, have you lubed the inner throttle cable, checked to see that the carb mounting bolts are not so tight they warp the carb body and pinch the slide, checked the throttle cable routing to see that the routing is not causing a binding somewhere, and checked the throttle cable splitter to see that it is operating smoothly?
22 May 2021 16:17 #23

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Replied by Pete-RT1 on topic RT3 carburetor reassembly

If it's not the throttle hanging up then it could be an air leak.
I would do a pressure test.
Bike looks great 

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Yamaha CT1-B
Yamaha CT1-C
Yamaha AT1-C
Yamaha CT3
1978 Yamaha DT175MX
2020 Honda CB500X
Last edit: 22 May 2021 16:24 by Pete-RT1.
22 May 2021 16:23 #24

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Replied by msavitt on topic RT3 carburetor reassembly

I don't know if you have an air leak or not, but after melting down my DT360 late last year and buying a piston that cost more than my first three cars, I am replacing crank seals on any old geezer 2 stroke I decide to restore or even just to just get running, assuming such a machine exists.  Even leak a leak at slightly warped carb intake flange on my DT1E has it running like a 10,000 rpm diesel with key off, talk about freaking out!

On the throttle wires, I begun following the process in my Clymers which as me establishing a bit (0.5 to 1.0mm) slack at the throttle grip, then same at the carb top, then dialing in the oil pump so dot lines up.  This along with nicely lubed up cables insures that there is enough slack all around so that the slide comes down against the stop screw vs being hung up ever-so-slightly by the cable.   

I have very little experience with these bikes but am slowly accumulating a long list of things not to do!

Good luck with your ride.
Martin
22 May 2021 17:52 #25

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Replied by msavitt on topic RT3 carburetor reassembly

wow what a beauty!
22 May 2021 17:53 #26

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  • RT3Mike
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Replied by RT3Mike on topic RT3 carburetor reassembly

So I found a ground wire in the headlight bucket that had come loose. I still need to fire it back up to test that. The headlight worked fine before I tore it apart so I'm hoping that's what it is.  I don't have the skills to check the rest of the wiring as suggested. I'll just have to play with the wiring to see if there is a broke wire or something like that, I guess.
As far as the throttle, it snaps back while running and not running so kinda strange. Msavitt, I am not sure how to find an air leak.  That one is over my head for sure.  I may need to take it in to someone for the carb issue. It starts and idles just fine and pulls like a train when I give it throttle with no miss.  I replaced the two into one cable connector as it was broken when I bought it and was hoping that was the issue..... not so much. I'll check back in when I have  chance to start it again to see if the electrics are working better with the headlight ground connected. Thanks everybody for all of the input. 
22 May 2021 18:10 #27

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Replied by Pedalcrazy on topic RT3 carburetor reassembly

I have an RT3 and did a complete rebuild last year so I have some experience with your model. When I finished mine I tightened the 2 carb mounting nuts to the cylinder pretty tight. Heck the studs are pretty beefy! Well I experienced the throttle hanging up a bit before returning to idle. One of the experts here suggested to loosen those nuts slightly because that could be distorting the bore in the carb for the slide. I was skeptical but did it. Yeah never hung up again. Be sure you have new gaskets and the correct o-ring when bolting the carb and intake to the cylinder.

On the brake light...The switch for the rear is adjustable by turning the plastic nut up or down where it mounts. You may need to adjust that and the brake adjustment wingnut on the rear brake rod. The front switch really isn't adjustable (unless you have the skills to carefully remove and disassemble it...probably not your issue).  Make sure it is connected  and moves freely (it is controlled by a little nub on the bottom of the front brake lever.

That'll get you started!
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
1968 DT1 (3)
22 May 2021 18:44 #28

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Replied by RT3Mike on topic RT3 carburetor reassembly

Pedalcrazy  thank you for the detailed information.  I followed your instructions on the rear brake and nothing changed.  Ends up I have a short in the front brake light switch - If I move it around a little bit the tail ight goes out and then once I pull the hand lever or push the foot brake lever, the brake light comes on. 

As far as the carburetor I have taken your suggestion and loosened the nuts.  I cannot find the the O-ring as it is out of production.  I recall inspecting the O-ring and it looked fine. I don't recall seeing a gasket and as I look at the carburetor, I don't see the edges of one either. Could this be my issue?  I looked on Partzilla and I don't see a gasket between the carb housing and the cylinder head mount unless the gasket you are talking about is the valve seat gasket? See photo below.

Really appreciate the great knowledge. 
23 May 2021 14:11 #29

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Replied by Pedalcrazy on topic RT3 carburetor reassembly

My exploded view shows gaskets on both sides of the reed block. From there working towards rear of bike should be gasket 275-13556 (plenty on EBay now), then intake manifold (black plastic insulator really), o-ring 93210-37140 (four sellers on EBay now) on end of carb, then carb. All gaskets and surfaces need to good and clean. If nuts holding carb on were super tight then possibly warped carb mounting flange. Wouldn’t be the first one LOL. Can be remedied by sanding on a flat surface. Short story is all sealing surfaces must function to keep excess air out when throttle slide is returned to idle.

edit...I should add when searching for parts on EBay put “Yamaha” first then the part number you want.
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
1968 DT1 (3)
Last edit: 24 May 2021 10:56 by Pedalcrazy. Reason: Adding
24 May 2021 10:54 #30

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