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Author Topic: R28/R27 Carburetor  (Read 407 times)

Vbiker

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R28/R27 Carburetor
« on: May 15, 2023, 07:53:38 pm »
Hi everyone, just wondering if anyone has an R28 with the lift throttle. I have one and it’s giving me a fit. If you can get it too idle it will speed up on its own, slow down quit sometimes. Has a mind of its own. Weird.

MadeForThat

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Re: R28/R27 Carburetor
« Reply #1 on: May 15, 2023, 10:29:22 pm »
Don't have this engine or the carb, but when little engines doesn't seem to hold the fuel settings you set and nothing is moving, then likely you are getting bubbles in your fuel line. I have started installing little check valves to keep the fuel from backflowing, as especially on hit miss models, they sometimes can't afford a few cycles to prime the fuel again when it drops. Might be worth putting a flex tube fuel line to monitor for bubbles or backflow, until you can rule them out.

gbritnell

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Re: R28/R27 Carburetor
« Reply #2 on: March 19, 2024, 06:13:42 am »
Here's the problem. With the cylinder separation angle at 45 degrees the intake manifold is very short. As rhe engine heats up the manifold transmits heat into the carb and that causes a vapor lock condition. I'm guessing your engine starts good and runs good for a short time but then starts to falter. Here's a quick check. Watch the fuel line and see if the gas seems to be pushing back when this occurs then put your finger on the carb. I'll bet its hot! Put a small piece of ice against the carb and it should smooth right out. I built a 90 degree V-twin and had the same problem.  The cure was to make insulator spacers between the manifold an head. I think ththese engines just have O ring seals so I don’t know what to tell you. 
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