Linkert Carb blows gas out of the overflow relief hole.

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Pete T
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Linkert Carb blows gas out of the overflow relief hole.

#1

Post by Pete T » Tue May 06, 2014 8:39 am

When I prime-kick my '56 with full choke, it spurts a noticeable amount of gas out of the overflow hole (just above the float bowl, on the throttle body facing the rear cylinder).

Gas also is forced out past the low-speed needle if I block the overflow hole with my finger while kicking with full choke. Once the engine is running, there is no further gas leak. The only reason it concerns me is that the bike is not the best of starters, and I am wondering if the gas is being blown out of the hole instead of being sucked into the engine while priming.

Apart from this, the engine runs great. I did try blocking the overflow hole with a grommet, it started well but ran very rough on the road, I think with fuel starvation.

4,000 miles ago I rebuilt the engine with a new piston, new Vtwin barrels, new STD heads (awesome!).

I have only just started to notice this as I have recently fitted a smaller tank, and can see it happening. It has probably been doing this for thousands of miles.



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Re: Linkert Carb blows gas out of the overflow relief hole.

#2

Post by john HD » Tue May 06, 2014 10:22 am

Pete,

It sounds like you need to pull your float bowl off and see what the float is set at. Also what condition it is in.

john

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Re: Linkert Carb blows gas out of the overflow relief hole.

#3

Post by 58flh » Tue May 06, 2014 12:10 pm

PETE--I am not an expert on linkerts!-(I get by with help on this K-BASE!)-Anyway I did see a hole that was .250 on a linkert that was somebodies attempt at --I DONT KNOW!-PERFORMANCE??)--Anyway I did manage to fix this leaker by threading in a small mainjet!-(like an airbleed).The JET was small enuff to not leak & allowed sumping while Prime-KICKING!.---Guys here are real GOOD with issues as yours & PICS. are really good to post!---Respectfully---RICHIE

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Re: Linkert Carb blows gas out of the overflow relief hole.

#4

Post by 1962FLH » Tue May 06, 2014 1:42 pm

Pete what cam are you running?

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Re: Linkert Carb blows gas out of the overflow relief hole.

#5

Post by Cotten » Tue May 06, 2014 2:43 pm

Pete!

The overflow hole cannot be blocked because it also vents the headspace above the fuel.

John and 1962FLH may both be right.
If the float isn't floating, and the fuel level is too high, then overlap from a rad cam could cause reversion that ordinarily would be relieved at the mouth of the carb, but is blocked by the choke, thus pressurizing the bowl.

Beware of heavy floats, whether brass, gas-logged corks, or certain new nitrophyll productions from an Indian distributor.

Let us know what you find inside,

...Cotten

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Re: Linkert Carb blows gas out of the overflow relief hole.

#6

Post by 1962FLH » Tue May 06, 2014 2:56 pm

If you run a performance Cam with lots of overlap; the intake and exhaust valves are open at the same time for long enough duration to push air into the carb bowl through the main nozzle with the choke closed. Block the vent hole and it will find another place to relive the pressure. However As John stated check your float adjustment; when set correctly this should not be noticeable.

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Re: Linkert Carb blows gas out of the overflow relief hole.

#7

Post by Pete T » Tue May 06, 2014 9:26 pm

Thanks for all the replies.
Checked the float today, it was a fraction high but good condition foam. I set it right but the blowback continues. I also wondered about cam, but it's a standardish Andrews as far as I can remember, and anyway the blowback only happens on full choke. 3/4 choke, no blowback. Like I say, it's not a serious problem, just seems to stop the cylinders fully priming, making starting procedures unreliable.
I also really gassed it at medium revs, 4th gear today, and there is no visible venting.

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Re: Linkert Carb blows gas out of the overflow relief hole.

#8

Post by Larry » Wed May 07, 2014 1:44 am

ALL of my Linkerts blow fuel out the vent when kicked over on full choke.

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Re: Linkert Carb blows gas out of the overflow relief hole.

#9

Post by Pete T » Wed May 07, 2014 7:52 am

OK so now we know. It's supposed to do that!
Thanks Larry

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Re: Linkert Carb blows gas out of the overflow relief hole.

#10

Post by Cotten » Wed May 07, 2014 12:04 pm

I beg to differ, Larry and Pete!

How far do your machines lean to the left on the jiffy stand?

....Cotten

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Re: Linkert Carb blows gas out of the overflow relief hole.

#11

Post by Pete T » Wed May 07, 2014 12:25 pm

Mine is standard lean on the stand. I thought Larry had solved it!

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Re: Linkert Carb blows gas out of the overflow relief hole.

#12

Post by Larry » Wed May 07, 2014 12:38 pm

The carburetors flood when kicked over repeatedly on full choke. Isn't that the described situation?

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Re: Linkert Carb blows gas out of the overflow relief hole.

#13

Post by Pete T » Wed May 07, 2014 12:54 pm

I prime with one kick on full choke. A small amount of gas spurts out of the overflow hole on compression stroke. Doesn't happen on 3/4 choke.

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Re: Linkert Carb blows gas out of the overflow relief hole.

#14

Post by Cotten » Wed May 07, 2014 1:23 pm

Larry!

If you have to kick more than twice with the choke on.. its a starting issue!

Still, this is not a common complaint.
Flooding in itself is nearly always cured with a proper float and adjustment.
(Flooding while sitting is a petcock problem.)

Excessive kicking with the choke closed should still draw only into the bore of the carburetor.
To exit the overflow from the bowl, the fuel level must be far higher than proper, or forced out.

....Cotten

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Re: Linkert Carb blows gas out of the overflow relief hole.

#15

Post by Cotten » Wed May 07, 2014 3:13 pm

A photo for clarity, Folks!

Note the white arrow shows a shallow hole drilled vertically into the 'roof' of the bowlchamber, and the black arrow shows the gallery drilled horizontally from the outside to intersect with the vertical hole.
74OVRFLW.jpg
The fuel should be 5/8" of an inch from the 'roof' , when the machine is level.
If the machine is tilted to the left, the fuel gets much closer.

If the petcock leaks, it will be higher for a cold start.
If the float is not of proper buoyancy, the level will always be higher, leading to a rich condition.

....Cotten
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