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post #1 of (permalink) Old 08-14-2003, 09:38 PM
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Yamaha 175\'s - need some tech help

Hi there,
I'm glad to have found this site and have a tech question if anyone can help.

I have two Yamaha 175's (1978,1979) that are having a related problem. Both are DT models. They both have not been used for about a year and neither one will stay running without the choke. In addition to that, one stalls out when giving it more than a little throttle. I can run while giving it very limited throttle but any more than that it quits. Any suggestions?
I'm a novice at bike mechanics at this point.

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post #2 of (permalink) Old 08-15-2003, 08:55 AM
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Re: Yamaha 175\'s - need some tech help

maybe carbs need to be cleaned.
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post #3 of (permalink) Old 08-18-2003, 08:49 PM
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Re: Yamaha 175\'s - need some tech help

I have a 1980 MX 175 with the same problem. I even bought another carb off another bike, and it still does the same thing. I see that someone else has the same problem, there must be someone out there who has ran into the same problem?
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post #4 of (permalink) Old 08-20-2003, 06:13 AM
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Re: Yamaha 175\'s - need some tech help

You'll need a repair manual--you can still get them, I just got one for my '73 CT175.

Your description sounds like one doesn't idle, but will run if you keep giving it gas, right? If so, you need to adjust the 2 screws that relate to the idle. There is a standard procedure for that. It is in the repair manual--or I'll quote it if you want.

For both of them:
Of course, you replaced the spark plugs already....

Look for obstructions in the exhaust--mine was originally blocked with about a cup of water in the bend by the cylinder.

Definitely clean out the carb, get rid of all the old gasoline, put a new gas line filter in, get a new air filter, and check the points if you have them.

Check the reeds--they should lay flat against the reed block. If they don't, try turning them over; if they still aren't right, get replacements. Boyessen makes some.

And then if that doesn't work, you can pull the cylinder and check for carbon build-up in the ports, and on the head.

Those are the first things I'd try.
post #5 of (permalink) Old 08-20-2003, 12:41 PM
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Re: Yamaha 175\'s - need some tech help

The carb has already been cleaned and it was pretty yucked up but still the problem on the one cleaned still persists.
The air filter was cleaned months ago also and was not ridden betwen then and now but it is clean. Shut off valve also checked to ensure flowage. Have not got to the other though yet.
I can run the bike with the choke out for quite awhile but as soon as I turn the choke off, it dies and the two adjustments should be set with it off I believe.
We've fiddled with them any way but no change.
We'll go onto the the others steps you mentioned.

I'll give update. If you have any other thoughts let me know.

Thanks - Elizabeth

post #6 of (permalink) Old 08-20-2003, 11:00 PM
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Re: Yamaha 175\'s - need some tech help

Just a note:
I re-cleaned the carb's by letting the parts soak in a really good carb cleaning solution, as recommended in the manual, for about 1 1/2 hours and that seemd to take care of the choke problem on both bikes. I took the one with the stall problem out for a very short ride around the block and the acceleration seemed okay but will have to check it on a longer run tomorrow.
May as well check the other things too while I'm at it.

Thanks for all the help!!

In 6 months I've become (unvoluntarily) a dirt bike and MGB mechanic.

post #7 of (permalink) Old 08-28-2003, 08:21 AM
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Re: Yamaha 175\'s - need some tech help

You only have one idle screw on these bikes. The other is an air screw. Turn the air screw in all the way, then, out for 1 3/4 turns. The air screw is on the opposite side as the idle. The air screw is the one farthest to the rear of the carb. Run NGK B8ES plugs.
post #8 of (permalink) Old 06-10-2007, 05:55 PM
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Lightbulb Maybe this will help....

One more thing if it is not running correctly, you have changed the plug, cleaned the carb, and checked the pipe, then maybe you need to look into changing your jets in your carb to a bigger or smaller jet just depending on which one makes it run better, If you remove the carb and look on the bottom then there is 4 philips head screws remove that plate and get the number of your jet. Get one 2 sizes larger and one 2 sizes smaller replace them and go with the best size for you and your bike. O and you mite wanna clean the pilot jet....
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