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Great Idle But Cuts Out When Slightly Throttled!


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#1 89Miniac

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Posted 04 August 2018 - 11:46 PM

Hello everyone, after 5 months of doing a full suspension rebuild, brake and clutch rebuild, carb rebuild and new fuel lines, she was finally ready to drive. So I thought. I start her up and she idles perfectly, giving me hope. The second I blip the throttle even slightly, she was to cut out. I pull the choke and the revs go up, even pressing on the throttle then she still wants to cut off. Does any one have any ideas or might possibly know what's wrong? Any help is greatly appreciated!

#2 Moke Spider

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Posted 05 August 2018 - 12:54 AM

Sounds like it could be very lean or still cold.

 

Let it warm up to near running temp and then go from there.



#3 Retroman

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Posted 05 August 2018 - 12:58 AM

Check the oil in the carb dashpot too

 

And and its a big AND is it fresh fuel...?



#4 89Miniac

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Posted 05 August 2018 - 05:40 AM

How would I be able to change the richness without changing the idle, because adjusting the jet just pushes down the choke which raises the idle. And even once it was warm it didnt act any different. As for the oil in the dashpot, the oil is fresh and at the correct level. The problem could be that when I pull the piston up it doesnt fall slowly, it shoots back down.

#5 Bat

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Posted 05 August 2018 - 06:20 AM

Hi,

Back off the adjusting screw on the linkage a little, not the one on the carb body. I think there should be a gap there anyway.

Then as you adjust the jet the cam can move without upsetting the idle.

Readjust the screw as required so you still have at least a 1/8" gap when you've finished. 

If your cold idle is way too high with the choke full out you can back it off some more.

 

If you've got the correct oil in the dashpot then the piston should fall at that speed unless the dashpot or piston is worn out.

I think the test is to remove the dashpot assy, then plug up 2 small vent holes in the piston and without the spring in there the piston should hold in the dashpot and not fall out.

Hold it above the bench and be ready to catch it just in case!

Cheers  :proud:



#6 andyapanel

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Posted 05 August 2018 - 11:47 AM

It could just be a sticking Carb piston.



#7 Retroman

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Posted 05 August 2018 - 01:18 PM

Before you start adjusting the mixture you need to know if its wrong

 

Set it to a fast idle and use the dashpot lifting pin method...if it dies its lean

 

When the mixture is correct revs should rise slightly then settle back

 

If its rich then revs go up

 

And from before;

 

And and its a big AND is it fresh fuel...?



#8 89Miniac

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Posted 05 August 2018 - 04:55 PM

How high should the piston be lifted? The fuel is fresh and the carb does move freely so that's good haha. I dont have the piston lifting pin but I'm able to move the piston up about an eight of an inch and the idle goes up by what sounds like a hundred or 2 rpms. Should it be going higher or is that how it's supposed to be? Even after adjusted it still cant reg past idle without acting like its starved of fuel, that's just what it seems like

#9 cooperd70

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Posted 05 August 2018 - 05:47 PM

faulty plug perhaps. had that on my car before...idle fantastic go to put your foot down to pull away and no power and almost cuts out.

#10 89Miniac

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Posted 05 August 2018 - 06:51 PM

When you say it almost cuts out, does it actually shut off or does it stay running but barely keeps an idle with the pedal pressed?

#11 Moke Spider

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Posted 05 August 2018 - 07:50 PM

Checked the fuel delivery rate and pressure?

 

Checked the float bowl fuel level?



#12 89Miniac

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Posted 05 August 2018 - 08:00 PM

How do i check the delivery rate and pressure? And what should the level be in the float bowl?

#13 Moke Spider

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Posted 05 August 2018 - 10:01 PM

The pump should be able to deliver 1 ltr a min, easy way to check that is grab a 1 ltr bottle and let it pump for 30 seconds, it should end up about 1/2 full, but really, even 1/4 full will be OK.

 

The pressure, you need a gauge for and ideally you'd like to see around 2.5 to 4 PSI pressure at the Carb.

 

What type of Carb do you have? (HS or HIF)



#14 89Miniac

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Posted 05 August 2018 - 10:20 PM

I have an hs4 carb. Everything on the carb moves how it should and I know my fuel pump works I just doent know the specifics or pressure and output. Before i started working on the car the fuel system wasnt too bad, just at higher speeds it would bog down. I'm just so confused because the idle sounds great and smooth but any little throttle cuts it down

#15 Retroman

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Posted 05 August 2018 - 11:37 PM

Its sounding more like it's an electrical issue...

 

Make sure all connections coil / dizzy are clean and tight the wires to each connector are good and not green

 

I have had similar issues with dizzy caps tracking in the wet

 

to be honest it could be anything but I would start there






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