Amal Premier - Casting Porosity?

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Gadge

Gadge

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Been wrestling with an idle issue on my 850 for some time - I've been through most of the great advice on here. It's a pretty standard 850 set-up - pea shooters, thin ham can. I fitted a new set of Premiers just as Covid hit. It runs very well off idle but I've been struggling with the right pot. Exhaust pulses are weaker and more variable than the left pot. Popping and back firing. It has good compression, right about 155psi, left 150psi. Recent Tri-Spark, strobed to 31 deg (I think from memory), new coils. Both plugs pretty sooty after idling. Valve clearances checked. No sign of air leaks with spraying the usual places. Carb are well balanced (using Don's gantry). Float heights set so fuel level is about 5mm below top of float bowl (measured with the AN pipe gizmo).

I've swapped the float bowls (complete) from side to side and also the removable pilot jets. All the idle passages +pilot jets seem clear (carb cleaner and compressed air +visual checks).

I've just stripped down the carbs (again) with a view to fitting the old body on the right with the jets, float bowl, float, slide etc. from the Premiers - to try and see if it made any difference. Going over all the idle passages again I spotted what I thought were specks of dirt near the spray tube and close to the pilot hole exit into the venturi. On closer inspection that are actually (at least) pits in the casting. I can feel them with a pick but can't get a thin piece of wire into them. Hard to tell if they are just surface defects or more. See the pics attached.

I'll get an email off to Burlen but wondered if anyone had seen similar? Could it be casting porosity?

Very open to other suggestions for other things to try, it is getting rather frustrating and I'm missing getting some riding in!

Thanks,
Gary

Premier Left.jpg
Premier Right.jpg
 
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Yep you have some holes, but unless they meet up with the pilot circuit then they are not doing anything to the idle.

Have you tuned the carb idle mixture and speed on a fully warm engine or are you using the default 1.5 turns out.
 
kommando said:
Yep you have some holes, but unless they meet up with the pilot circuit then they are not doing anything to the idle.

Have you tuned the carb idle mixture and speed on a fully warm engine or are you using the default 1.5 turns out.
Click to expand...
Understood and agreed. I'm at the racking brain end of this! More questioning if there is porosity visible then is there something I can't see.

Yes, have been round the pilot setting tweaking many times. Left side can get nice even exhaust pulses fairly close to the 1.5. Right side I'm struggling to get even pulses and consistent idle regardless of pilot screw setting.

As I said, open to suggestions. I feel like I've tried all the obvious stuff. I'll be delighted if I've missed something easy!
 
Is the spray tube facing the wrong way on the right side carb?
 
You say ‘struggling with the idle’… can you be more specific in describing the symptoms?

Are you still running the #17 pilot jets (2 identification rings)? Many struggle with these and fit #19 pilot jets (3 identification rings).
 
Had a similar problem with the premiers on my 71 750,switched to 19 pilot jets, what a difference, couldn't be happier, ticks over like a good un.
 
Pilot jets are 19s, 3 rings.

I'm struggling to get a decent idle. Anything below 1100 revs is hit and miss and sometimes dies. As I said, left side seems to dial in well with the pilot screw. Right side uneven exhaust pulses, weaker than left. Seems to hunt and pops from exhaust. Pilot screw doesn't seem to make much difference.

I know it sounds like an air leak but I've been over all the places it could be and can't find any sign of one. Carb nuts aren't over-tightened (just enough to flatten lock washers). Smear of hylomar on the tufnol insulators.

Original question about the porosity I know is straw clutching.
 
Ok, I’m clutching at straws too matey…

The stay up floats in Premiers often have burrs that foul the fuel needle and can cause issues there.

Also, some on here have reported being at the end of their tether with Premiers and they tried the old plastic floats and voila, sorted. If you’ve got some old carbs kicking around it might be worth a try.

I fact, if you’ve got some old carbs kicking around maybe try the old one on the offending side?

Finally (shudda been firstly) you have tried new spark plugs right ??
 
On about third set of new plugs since I started trying to sort this. I do listen ;)
 
marshg246 said:
Let's go a little old school. While running pull the plug wire on the bad cylinder and note how it runs and at what RPM. Put the wire back on and pull the other one. How does it run and at what speed. I know you said the carbs are synced, but at idle or wide open? If the bad side doesn't run the same as the good side, most likely either the mixture or slide height is wrong (throttle stop when no gantry). Try adjusting the air screw to get it to run the same.

I'm 99.99% sure your problem is not porosity.

I have no experience with Don's gantry. On a Triumph Trident, the gantry causes out of sync at idle when synced at wide open if there is any looseness in the gantry
Click to expand...

Gadge said:
Thanks Greg, I wasn't sure if the old school approach was OK when using EI setups like the Tri-Spark?
Click to expand...
 
Is pulling ht lead off a running engine good practise if EI is installed? I beleive some verbage around this in Trisparks guide book.

You say you've balanced the carb. I assume by the standard sticks and cable sync methods? Have you tried a flow balance with a manometer like CarbTune or Twinmax or vacuum gauges? My new premiers were not dialing in via other methods. Hooed up a newly bought carb tune and found vacuum levels left/right quite a lot different. Took more than 1.5-2 turns of left side cable slackening to get them equal just off idle.
This was right after doing the sticks and fingers on the slides "balancing".
 
marshg246 said:
To do it correctly per Tri-Spark you would shut the engine off, pull the wire, leave the plug in place, plug in a spare spark plug and lay it on the head. Then start it. That's is certainly the safest way and as a dealer I suppose I shouldn't say another way. The way I wrote is how I do it though.
Click to expand...
I thought the issue was only when the spark has nowhere to go? So, with a wasted spark ign, so long as one plugs is sparking nicely, all should be well. I think…
 
Great info guys. A few things for me to try.

I'll report back on progress/findings.
 
Gadge said:
Great info guys. A few things for me to try.

I'll report back on progress/findings.
Click to expand...
I see you have swapped over bits and pieces but have you actually swapped over the carbs complete? I had brand new Premiers on my Trident and went through all the things you have done. Then I swapped carbs and the idle issue followed. Turned out to be a faulty carb. replaced by supplier and new one cured issue. A latter report from Burlen said they tested carb and it was faulty but they could not actually determine why?
 
I had exactly the same issues with Premiers.
Had them apart and cleaned 3 times.
After sometime discovered a tiny exhaust leak at the rose on the right cylinder.
Moving on from that due to an oil leak I lifted the head.
Found carbon deposits on RH exhaust valve face.
Also a large lump of carbon building up on the RH piston.
4 hrs of cleaning head, valves and regained. Cleaned pistons.
First start up there is a noticeable difference as to how well it runs at low revs.
Have to re calibrate primary jet and tickover but will run it tomorrow if it’s not raining!
 
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