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Re: Engine Troubles

To: Thomas James Pokrefke <>
Subject: Re: Engine Troubles
From: Bill Schooler <>
Date: Sat, 07 Dec 1996 15:34:48 -0800
Thomas James Pokrefke wrote:
> I have been having trouble with my engine lately.  In the low to mid rpm
> ranges, when I am acclerating, the engine is not 'right'.  The engine
> runs rough, and then after about 3600 rpm, clears up and storms right up
> to redline.  I think that the carbs are either flooding ath the low rpms,
> or the timing is not right.  I checked the timing last night, and it was
> dead-on.
> Does anyone have an alternative method of checking the mixture settings
> on the HS-4's?  My 'lift the pin a 1/16" and listen to the increase in
> engine speed method" seems to have failed me.  All suggestions
> appreciated, except putting on a Weber.
> Thanks in advance,
> Thomas James Pokrefke, III (I run fine at all rpms)
> 1970 MGB (runs rough in the low- and mid-ranges)
> (runs rough in the upper-range {ie-500+msg})

We have similar cars - mine's a '69 - and I would suggest the following 
1.  I really don't mean to insult your intelligence, but have you checked 
and/or topped up the carb dampers?  Assuming that the oil level is okay, 
2.  Make sure the pistons are not binding as they go up and down.  Fuel 
deposits can sometimes hamper smooth movement. If all seems well, then 
3.  Check proper functioning of the distributor centrifugal advance, 
making sure nothing is binding or sticking.  (My thought is that perhaps 
the centrifugal advance mechanism might be sticking and not giving you 
full advance until the revs get to a point where it "breaks free".  
Probably not very likely, but worth a check.)

Glad to hear you're not giving up on our "proper" carbs!  You might 
remember that setting the mixture at idle with the "lift the piston" 
method is supposed to get things right for the entire range - but that 
assumes everything else is functioning properly!  Whenever I've had 
trouble adjusting the SUs, I have been able to trace the problem back to 
some other system in the engine.  One really wierd trouble was carb 
related, in a way.  I was having great difficulty getting things to "run 
right", until I discovered that when I replaced a pair of pancake air 
filters with the original types that I had installed the backing plates 
upside down.  Upon inspection, I found that the air holes on the backing 
plates were not matched with those in the carb body, preventing proper 
functioning.  Until that time, I had never known there was an "up" or 
"down" to those things.  Turned 'em over and it tuned and ran like a 

Check it out and let us know how it goes.


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