Engine goes lean while accelerating under half throttle

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Rubarotary
Posts: 30
Joined: Thu Jul 14, 2016 11:20 pm

Engine goes lean while accelerating under half throttle

Post by Rubarotary » Tue Aug 16, 2016 7:07 pm

Hi everyone,

Last week i went For a Drive For the First Time in a couple of years And everthing was ok accept that the engine goes lean ( 15,6 ) while accelerating under half throttle.

It's a freshly rebuild engine everthing original except Air pump removed .
Afr on idle is 12,6 And full throttle it's 12,2

Any Help would be appreciated.

Ruben

TOOL
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Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Engine goes lean while accelerating under half throttle

Post by TOOL » Tue Aug 16, 2016 7:26 pm

Idle is controlled via idle circuit.
Half throttle is primaries.
Full throttle is primaries and secondaries.

I suggest you check the primary jets aren't blocked.
There's access screws at the bottom of the bowls. No need to disassemble but probably a bugger in situ.
Back in sunny France

Rubarotary
Posts: 30
Joined: Thu Jul 14, 2016 11:20 pm

Re: Engine goes lean while accelerating under half throttle

Post by Rubarotary » Tue Aug 16, 2016 8:03 pm

Ok thanks For the explenation i'm gonna try it tommorow .
I don't know much about carbs only basics so many thanks :-D

Rubarotary
Posts: 30
Joined: Thu Jul 14, 2016 11:20 pm

Re: Engine goes lean while accelerating under half throttle

Post by Rubarotary » Thu Aug 18, 2016 9:57 pm

So i checked the primary Jets And they were ok there was a little dirt in the bowls though, but i dissasembled the carb to see if the next Jets in line weren't blocked but these were Fine as well.
Since i had the carb open i cleaned up everthing And there was one Jet blocked it's the one on the left side at the bottom of the Picture it's a size 150


Image

But since i did this the front rotor almost gets No Gasoline And the rear one gets Plenty.
In the weekend i'm gonna try to measure Flow on each Port but in the meanwhile if somebody has any ideas there very welcome

Thanks ruben

TOOL
Posts: 2509
Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Engine goes lean while accelerating under half throttle

Post by TOOL » Fri Aug 19, 2016 5:47 am

It almost soundsike you've dislodged a blockage and shifted it somewhere else.

Check the needles and seats.
Back in sunny France

Rubarotary
Posts: 30
Joined: Thu Jul 14, 2016 11:20 pm

Re: Engine goes lean while accelerating under half throttle

Post by Rubarotary » Fri Aug 19, 2016 6:23 am

I'm guessing you Mean the needles And seats in the float Chambers ? Is it helpfull to lap the needles Back in to place ?

TOOL
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Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Engine goes lean while accelerating under half throttle

Post by TOOL » Fri Aug 19, 2016 7:40 am

Yes, that's the ones.

The washers underneath the seats set the height so keep them together.

Also check the coarse filter at the inlet to the carb.
Back in sunny France

Rubarotary
Posts: 30
Joined: Thu Jul 14, 2016 11:20 pm

Re: Engine goes lean while accelerating under half throttle

Post by Rubarotary » Fri Aug 19, 2016 9:21 am

Ok Will try this All this Evening, thanks a lot For the support :-D

Rubarotary
Posts: 30
Joined: Thu Jul 14, 2016 11:20 pm

Re: Engine goes lean while accelerating under half throttle

Post by Rubarotary » Sat Aug 20, 2016 5:07 pm

Coarse filter is Clean, needles And seats are ok as well i'm gonna try to measure Flow in each barrel but i measure the clearance between the primary throttles And this was the Same so i don't think this is gonna be a problem .

Just one question at idle the primary Jets shouldn't give any fuel Right ? Because fuel should be coming from the idle jet

TOOL
Posts: 2509
Joined: Thu Sep 01, 2011 10:30 am
Location: Var, France (ex NZ, ex UK)

Re: Engine goes lean while accelerating under half throttle

Post by TOOL » Sat Aug 20, 2016 7:51 pm

Correct.

Activate the throttle and the accelerator pump will squirt a jet of fuel into each primary to help the transition from idle to primary circuit.

Check for air leaks too.
Back in sunny France

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