mcman56 Posted October 1 Report Share Posted October 1 I have a 2016 300 4T standard model. It has started to produce a little pop in the exhaust when closing the throttle from small to moderate openings. The pop is not loud but sort of echos in the exhaust. It starts, idles and runs well but has become cold blooded so needs to run for several minutes before it will take any throttle when cold started. I checked valve clearances and cleaned the carb with no affect. This is with California pump gas. Has anyone experienced this? I'm not sure if I should go up on the pilot size or raise the needle. Carb access is not great on this bike. Quote Link to comment Share on other sites More sharing options...
lemur Posted October 1 Report Share Posted October 1 CV carburetor running lean, just like CV carbs were designed to do. You might try raising the needle if the problem happens at greater throttle opening. What does the spark plug look like? & does it smoke at the exhaust &/or is the engine full of carbon ? Quote Link to comment Share on other sites More sharing options...
mcman56 Posted October 2 Author Report Share Posted October 2 Plug color is a bit uneven but doesn't look too bad. It doesn't smoke. I am running much leaner than stock jetting. When I got it in 2018, it had the factory jetting of 27.5 pilot and 120 main but ran poorly. The advice was to go richer but when I went that way it was worse so I went the other way. It kept running better the leaner it got so I ended up with 17.5 and 115 which is much leaner than all recommendations. The engine is getting up near 300 run hours so I wonder if it has slightly less vacuum and is less tolerant of lean jetting. Quote Link to comment Share on other sites More sharing options...
lineaway Posted October 2 Report Share Posted October 2 With lean jetting the valves could be slowly fading with the heat. Try a compression test. Also the intake boot is prone to cracking. Quote Link to comment Share on other sites More sharing options...
mcman56 Posted October 13 Author Report Share Posted October 13 In addition to the diaphragm for the slide, the carb has a diaphragm with spring on the side. On a CV carb diagram for a different bike, I see something similar identified as a coasting enricher. I think I have also seen something called an anti backfire valve on other carb diagrams. Could that be the culprit? Is the purpose of such valves to prevent a pop? The bike runs well so I'm reluctant to change jetting. MK-BSR33-79-Detail-Sheet-copy.pdf Quote Link to comment Share on other sites More sharing options...
lemur Posted October 13 Report Share Posted October 13 3 hours ago, mcman56 said: ... coasting enricher. ... For all intent purpose that would be a tiny mechanical fuel pump that activates when the throttle returns to idle position. No such thing is shown on the diagram you attached. & If the bike runs well you really should not be messing with the jetting, but 🤔 if changing the jetting is simply moving the e-clip on the main jet needle I think I would try that. Quote Link to comment Share on other sites More sharing options...
konrad Posted October 13 Report Share Posted October 13 3 hours ago, mcman56 said: I see something similar identified as a coasting enricher. .... Could that be the culprit? Is the purpose of such valves to prevent a pop? Yes. Yamaha used that on some conventional carbs. Could be a torn diaphragm or gummed up. Suggest you disassemble and inspect/clean. 1 Quote Link to comment Share on other sites More sharing options...
lemur Posted October 13 Report Share Posted October 13 Guessing konrad refers to part 11 and associated bits 👍 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.