Dead Spot in Throttle

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Nov 12, 2009 | 03:23 AM

87HDFXSTC

Thread Starter

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Joined: Sep 2009

Posts: 19

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From: Columbus, OH

Dead Spot in Throttle

I have an '87 Softail Custom with the stock 1340 EVO and an S&S carburetor. I've noticed I have a dead spot in the throttle just off idle, but only when I rapidly twist the throttle. If I roll through the throttle slowly it's fine. It does this no matter how cold or warm the bike is. Any thoughts?

Thanks.

Nov 12, 2009 | 06:07 AM

grbrown

Club Member

Joined: Jun 2007

Posts: 45,429

Likes: 2,898

From: Bedford UK

Quote:

Originally Posted by 87HDFXSTC

Yes certainly, in fact three thoughts!

I fitted an Edelbrock carb to my old Evo which did the same. I paid a Harley mechanic to check it over and he demonstrated that the carb couldn't feed the engine, was starving it, and was not man enough for the job. I needed a bigger carb.

So I fitted a larger carb (SE) and had similar problems! The new carb was too big and was flooding the engine when accelerating quickly! It smoked a lot. So it is possibly one of those extremes, however it could just be poor transition between jets.

I now have an S&S engine in the same bike, with one of their carbs. You can probably download a tuning guide from their website. S&S carbs have pilot and intermediate jets, so your problem may be transition between them. If the carb has been on the bike a long time, check the float chamber is clean. If you find dirt in there, check the jets are all clear, also clean your gas tank and gas tap.

Nov 12, 2009 | 07:03 AM

imrotton2

Road Master

Joined: Apr 2009

Posts: 915

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From: nw alabama

be sure to check for leaks or loose intake gaskets... mite get some good injector cleaner and put in the fuel.. ]

Nov 12, 2009 | 08:26 AM

miacycles

Elite HDF Member

Joined: Sep 2007

Posts: 4,468

Likes: 12

From: Bluffton, South Carolina

Is the accelerator pump adjusted properly, or in fact is is working ??

Nov 12, 2009 | 08:32 AM

shovhd

Cruiser

Joined: Dec 2008

Posts: 234

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From: Courtenay, BC, Canada

You didn't say what model of S&S carb you were running. If it's an old Super B, they had no accelerator pump and will always do that. I think there was an accel pump you could buy for it though. I can't remember, been a long time since I run one. If you have a Super E or G, sounds like you need to adjust your accelerator pump. Someone might have been playing with it and it's way out of wack or your accel pump is f*@ked. Here's a good article on setting your S&S carb back to factory spec. Easier to adjust from there.

http://www.bikernet.com/SandS/PageVi...sp?PageID=1198

Have fun.

Apr 28, 2010 | 04:50 PM

87HDFXSTC

Thread Starter

Novice

Joined: Sep 2009

Posts: 19

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From: Columbus, OH

Well, now that the winter months are over I decided to take a look at the settings on my S&S Super E carburetor and sure enough, they were way off from the factory specs described in the above link. Yesterday, I set everything as the link describes and the bike ran great.

However, coming home from work today I noticed the dead spot coming back. I pulled into my garage and started messing with the settings again and no matter what I do the dead spot right off idle is there. If I twist the throttle quickly, the engine stumbles and backfires.

Any thoughts? I can see fuel squirting into the venturi when I twist the throttle, but again just popping and backfiring.

Let me know, thanks.

Apr 28, 2010 | 07:06 PM

89 FXRS

Cruiser

Joined: Dec 2007

Posts: 213

Likes: 2

Quote:

Originally Posted by miacycles

Is the accelerator pump adjusted properly,

I would guess that is the problem on the nose.

You are getting to much gas when you twist the throttle. Readadjust the acc pump for less gas.

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Apr 30, 2010 | 10:13 AM

the_ogre25

Cruiser

Joined: May 2007

Posts: 204

Likes: 3

the accelerator pump gives the motor a little shot of fuel when transferring from the idle to the main jet. S&S carbs seem to gum up easy from sitting, have you tried pulling the carb and cleaning it with some carb cleaner?