YZF750R runability problem - Yamaha Forum : Your Yamaha Motor Products Community & Resource
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post #1 of 1 (permalink) Old 09-12-2019, 07:59 AM Thread Starter
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Join Date: Sep 2019
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YZF750R runability problem

Hello everyone. I am working on a friend's 97 750. The problem is that it really hesitates in low rpm. Just falls on it's face as soon as the clutch grabs. Runs quite well without a load.

Originally it didn't run. Fuel was stale. I cleaned the carbs although they did not look like they needed it. Took them apart, soaked them, put them back together and synced. Seemed to be lean at idle, I put 40 size pilot jets. It's better, but not good. Seems too rich. No matter what adjustments I make, it just isn't right. For fuel mixture screw adjustment, I ended up with (turns out, from cyl 1 to 4) - 4, 4.5, 1.5, 4. Plugs show rich condition.

I decided to check the valve clearances.

From cyl 1 to cyl 4, left to right, exhaust clearances are

.229 .229 | .203 .229 | .229 .203 | .229 .203

Intake valves are

.152 .076 .052 | .152 .051 .102 | .102 .102 .102 | .127 .127 .127

Do you think those clearances are enough to cause the problem?

A stretched timing chain can compound this problem? How does one test a timing chain wear?

The bike runs very well once the engine is up past 4k RPM.
GinoMachino is offline  


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