Need a carb

RDDave · January 22, 2026, 07:59:10 PM

Quote from: 1976RD400C on January 22, 2026, 10:46:39 AMDid you check that the choke plunger is sealing ok?

I have tried to block it, but seems difficult and I am not sure that I actually had it completely blocked. Any suggestions on how to make sure it is blocked? I just stuffed some thin plastic under the plunger. I think it was blocked, but not for sure. And wouldn't the right get the same extra fuel as the left if it were leaking? I have ran it extensively both with and without the cross over. No difference.

RDDave · January 22, 2026, 07:59:55 PM

Quote from: JKV45 on January 22, 2026, 12:28:27 PMAs I suggested in another carb-related thread, if you can't end up finding a new carb, or one to swap for a test, contact Gordon at https://customcarbservice.com/

If he goes through the carb(s) you can be sure it is functioning properly.

I will keep that in mind. Thank you!

RDDave · January 22, 2026, 08:02:05 PM

Quote from: quocle603 on January 22, 2026, 03:21:45 PMIf you want help, feel free to DM your phone number and maybe we can problem solve?

Super! Thank you. I have a thing or two to try including trying the hotter plug on that side. But we are getting some real winter weather tomorrow, so it may be a bit before I can test.

I just may take you up on that.

m in sc · January 22, 2026, 08:48:11 PM

fwiw if the oil line is that stiff... prob a good idea to replace it.

RDDave · January 23, 2026, 08:31:30 AM

Good idea. That way I could try the right hand carbs that I have. Got a best source for that line?

JKV45 · January 23, 2026, 09:38:23 AM

Probably not an issue here, but there is an increasing number of counterfeit spark plugs on the market, and they are getting really difficult to spot.

Buying plugs, and many other items, from eBay and Amazon can be rolling the dice these days.

Legitimate dealers and established parts stores tend to be a safer option.

quocle603 · January 23, 2026, 09:46:01 AM

Quote from: RDDave on January 23, 2026, 08:31:30 AMGood idea. That way I could try the right hand carbs that I have. Got a best source for that line?

You can get them from john at economycycles

https://www.economycycle.com/product/yamah-oil-pump-line-pump-to-carbs-90445-05m07-00/

RDDave · January 23, 2026, 06:33:18 PM

Quote from: JKV45 on January 23, 2026, 09:38:23 AMProbably not an issue here, but there is an increasing number of counterfeit spark plugs on the market, and they are getting really difficult to spot.

Buying plugs, and many other items, from eBay and Amazon can be rolling the dice these days.

Legitimate dealers and established parts stores tend to be a safer option.

Agreed! I have started using the NGK Iridiums. I get them from O'reilly's. Usually only about $3 more than the regular copper. The advantage for me being that the seem slower to foul and I can clean and re-use them several times as I experiment. The regular coppers are usually done the first fouling. And the Iridiums come with a 1 year warranty. They are no brainers for me in this scenario.

RDDave · January 23, 2026, 06:35:20 PM

Quote from: quocle603 on January 23, 2026, 09:46:01 AM
Quote from: RDDave on January 23, 2026, 08:31:30 AMGood idea. That way I could try the right hand carbs that I have. Got a best source for that line?

You can get them from john at economycycles

https://www.economycycle.com/product/yamah-oil-pump-line-pump-to-carbs-90445-05m07-00/

That seems like the way to go. Now, I just have to get enough for an order.

Thank You!

teazer · January 23, 2026, 06:45:39 PM

Quote from: RDDave on January 22, 2026, 07:59:10 PM
Quote from: 1976RD400C on January 22, 2026, 10:46:39 AMDid you check that the choke plunger is sealing ok?
I have tried to block it, but seems difficult and I am not sure that I actually had it completely blocked. Any suggestions on how to make sure it is blocked? I just stuffed some thin plastic under the plunger. I think it was blocked, but not for sure. And wouldn't the right get the same extra fuel as the left if it were leaking? I have ran it extensively both with and without the cross over. No difference.

There are probably others ways to do it, but I use a MityVac or copy with hose and a tapered tip which is inserted into the outlet on the motor side of the carb. Apply vacuum and see if it holds it. It's a bit of a PIA to keep the tapered tip in place and not leak, but patience pays off.

RDDave · January 23, 2026, 06:58:26 PM

quocle603 · January 24, 2026, 08:39:52 AM

Quote from: RDDave on January 23, 2026, 06:33:18 PM
Quote from: JKV45 on January 23, 2026, 09:38:23 AMProbably not an issue here, but there is an increasing number of counterfeit spark plugs on the market, and they are getting really difficult to spot.

Buying plugs, and many other items, from eBay and Amazon can be rolling the dice these days.

Legitimate dealers and established parts stores tend to be a safer option.

Agreed! I have started using the NGK Iridiums. I get them from O'reilly's. Usually only about $3 more than the regular copper. The advantage for me being that the seem slower to foul and I can clean and re-use them several times as I experiment. The regular coppers are usually done the first fouling. And the Iridiums come with a 1 year warranty. They are no brainers for me in this scenario.

I went that route then just decided its better to just get the factory plugs and get my rd running fine. Been in your shoes before, figured it out and was happy. Then it will happen again, its part of the course.

RDDave · January 24, 2026, 08:39:05 PM

I don't know if it's par for the course. My '73 DT250 doesn't get anything other than gas and oil and the the occasional basic/simple routine maintenance year after year. Now, I don't put a ton of miles on it, but it just starts and runs like these bikes have always ran for me; dependably. This RD is atypical. But I will get to the bottom of it and then it will be just all the other Yamahas I have had; a real joy.

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Need a carb