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1979 R65- Little or no vacuum on RT Carb

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Timmonsg
Posts: 4
Joined: Sun Sep 26, 2021 2:10 pm
Location: Tupelo, MS

1979 R65- Little or no vacuum on RT Carb

Post by Timmonsg »

Please forgive me if I lack specificity but I will endeavour to be as accurate and concise on my dilemma thus far. My newly restored/freshened up R65 gives no noticeable response to Rpm's while adjusting the airscrew on my flat top (CV) (No OEM diaphagm spring) Bing carb situated on the rightside of the engine. Leftside carb is very responsive to airscrew adjustment. Rightside compression checks to be a maximum of 135 Psi. (Leakdown test has not been performed on that cylinder). Leftside carb checks to have a maximum of 132 Psi compression. Breakin (only rings were replaced) mileage thus far is approx. 450 miles thus far with an exceptionally smooth operation at cruise speeds and in between. Idle lacks the smoothness one normally achieves with a properly tuned carb setup. My carb kit lacked the jets and needles. The needle jet has some elongation due to needle action and I will get the appropriate kit soon to replace all jets and needles to hopefully cleanup the idle. Engine has been correctly static- timed and confirmed dynamically to include the proper advance attempted at higher RPMS. Both intake and exhaust valves are properly adjusted i.e. .004 and .006 respectfully. Say all that to say this; when the manometer is hooked up to the vacuum ports next to the airscrew adjusters I get two inches rise in mercury on the leftside but no indications on the right. Switched my vacuum gauge lines and that side of manometer reads correctly so as to eliminate a problem with my manometer lines. The rightside vacuum port is free and clear of all debris and for the life of me I can not come up with a plausible reason why sufficient vacuum is not present on the rightside port. If you stick your finger at the open port you can only feel a faint pulsating vacuum. Remove the screw totally and that side of the engine exhibits no rough idle whatsoever. I can certainly go back and reverify that the "circuitry" of the carb is clear and unobstructed but it will be the third time. Place your hand on the filter side of the carb while it is running and you can starve/choke that cylinder to where it shut down. Plenty of vacuum force is felt at the palm of your hand when doing so. Ok, I will stop now so please dive in if you choose and I promise I will appreciate any and all suggestions.
Greg in Tupelo
'67 R60/2, '79 R65

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schrader7032
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Re: 1979 R65- Little or no vacuum on RT Carb

Post by schrader7032 »

Welcome! Is it possible the diaphragm is torn?

It won't make any difference with your problem, but I'd suggest increasing the exhaust valve clearance to 0.008" or 0.20 mm. That's a little better for the life of the valve/seat.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Timmonsg
Posts: 4
Joined: Sun Sep 26, 2021 2:10 pm
Location: Tupelo, MS

Re: 1979 R65- Little or no vacuum on RT Carb

Post by Timmonsg »

Thank you for that Kurt. Failed to mention that the diaphragms are not new. Since this model for two years did not require springs in the top caps I thought it best have new ones installed and they appeared to have no tears. Your right on the exhaust valve clearance. What can I say; other than I'm a gambler by nature. Thanks again and I will take your advice on the .008.
Greg in Tupelo
'67 R60/2, '79 R65

Timmonsg
Posts: 4
Joined: Sun Sep 26, 2021 2:10 pm
Location: Tupelo, MS

Re: 1979 R65- Little or no vacuum on RT Carb

Post by Timmonsg »

Oops Kurt. Diaphragms are new! Fat finger syndrome caused me to imply that they are not new and that's incorrect. By the way; I've been getting all my parts thru Max BMW.
Greg in Tupelo
'67 R60/2, '79 R65

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schrader7032
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Re: 1979 R65- Little or no vacuum on RT Carb

Post by schrader7032 »

Just make sure the diaphragms fall into the groove/tab meant for them. If you have a massive leak somewhere, try spraying w/ some carb cleaner all around. If the RPM changes, track down why.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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schrader7032
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Re: 1979 R65- Little or no vacuum on RT Carb

Post by schrader7032 »

Just to add, valve clearances are set for each cylinder with piston at top dead center on the compression stroke. Once one side is set, the engine must be rotated 360° to set the other side.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Timmonsg
Posts: 4
Joined: Sun Sep 26, 2021 2:10 pm
Location: Tupelo, MS

Re: 1979 R65- Little or no vacuum on RT Carb

Post by Timmonsg »

Yes Sir, I will reconfirm the diaphagm "cleats" are seated properly along with resetting the valves. Thanks again.
Greg in Tupelo
'67 R60/2, '79 R65

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