idle musing

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arthur
Posts: 128
Joined: Wed Jun 17, 2020 8:55 pm

idle musing

Post by arthur »

Bear with me while I ponder
As some may know I have a 1975 GT 380 imported from Italy I have spent many hours in the shed tinkering to the point we have been out for a 10 mile trundle
But she still is not running right the left hand cylinder is only warm and seems only to be hitting now and then
I have checked the timing (new points) and as far as I can tell its spot on
All the cylinders have good compression 140 plus on my Gunson screw in tester
and a Good spark .
I am leaning toward the idea that there is no petrol getting in (or rather not enough)

and when she is running on the bench the left hand pipe smokes it just wafts out with no force (could it be the oil injection is chucking neat oil into the cylinder and its getting burnt off but not enough petrol to give explosive combustion.
And the plug is black , oily, but not sooty like a over rich mixture
I did think the pipe may be blocked but I pulled the baffle and its clear all the way through but nasty never the less
I am thinking that the carbs need to come off AGAIN to check the float level and clean the jets (they are new as well)
Good job the weather looks pants for the next few days
Kettletimes3
Posts: 1620
Joined: Thu May 03, 2012 12:58 am
Location: Sunny Wales

Re: idle musing

Post by Kettletimes3 »

Is the fault only there at low throttle,
Does it run on all three when useing over half throttle,if so it’s block pilot jets or passages.
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Alan H
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Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: idle musing

Post by Alan H »

Swap the right and left plugs to see if the issue moves.
I always use non resistor plug caps to improve the spark too - does the left pot have a strong spark?
Try one thing at a time, or you'll never know how you 'repaired' it!!! :lol:
Proof that four strokes are over complicated
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canaletto5
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Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: idle musing

Post by canaletto5 »

Undo the drain screw on the carb bowl to see if there is any fuel in it and how much
arthur
Posts: 128
Joined: Wed Jun 17, 2020 8:55 pm

Re: idle musing

Post by arthur »

Thanks for all your suggestions gents,
I did drain the bowl , although I did not drain the other two so have no comparison (Thing to do today) but getting to the screws in situ is a pain!
Changed the plugs and changed the caps for another set,
It occurs at all throttle openings
So I am leaning towards low fuel in the left hand carb bowl .

Off out just now to get cracking with the spanners here's hoping :D
arthur
Posts: 128
Joined: Wed Jun 17, 2020 8:55 pm

Re: idle musing

Post by arthur »

SIT REP
Got the carbs off and drained them right and center each had a little over 40 ml
left hand 35 ml I don't know if that's enough to have a effect?
Also the left hand float is a bit skewed --- one float higher than the other
So I have leveled them out and set the height to match the right and center .
other than that all looks ok a quick blow out with the air line , out this afternoon to put it all together again we will see how it goes :D
arthur
Posts: 128
Joined: Wed Jun 17, 2020 8:55 pm

Re: idle musing

Post by arthur »

Back again,
All together, primed her up , started third kick!!
running on three :D
needs a good run now to clean out all the crud , check the mixture, and set the tick over .

Mind you something else is sure to go awry before the weekend :lol:
arthur
Posts: 128
Joined: Wed Jun 17, 2020 8:55 pm

Re: idle musing

Post by arthur »

On three sounds good . till the left hand head gasket failed :o
I knew I was tempting the fates '
Mixture spitting out the rear is not good
But when she cooled and I tested compression all three were over 140 whats going on??? was the head expanding just enough to allow the gasket to fail then closing again when cold
I have checked the head bolts torque and all are at 26 lbs ft
It looks like another morning in the workshop to get the top end off .
Is there a diagram any where to show what sequence to tighten the head bolts when its time to put her together again?
OH JOY!
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: idle musing

Post by Alan H »

I think it's marked on the heads.
Proof that four strokes are over complicated
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canaletto5
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Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: idle musing

Post by canaletto5 »

arthur wrote: Tue Mar 30, 2021 8:51 pm On three sounds good . till the left hand head gasket failed :o
I knew I was tempting the fates '
Mixture spitting out the rear is not good
But when she cooled and I tested compression all three were over 140 whats going on??? was the head expanding just enough to allow the gasket to fail then closing again when cold
I have checked the head bolts torque and all are at 26 lbs ft
It looks like another morning in the workshop to get the top end off .
Is there a diagram any where to show what sequence to tighten the head bolts when its time to put her together again?
OH JOY!
Do you mean spitting out of the gap between the head and the barrel? Also, I know it sounds daft but 140 psi seems high. I think these are generally around the 110 - 115 mark. Kev
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