Hi,
Occasional poster but mainly a lurker as I’m not a side valve owner I do like the good nature and helpful attitude of the forum, and I’d like a little help now please.
Rebuilt my Mk1 Concentric with new parts (needle, needle jet and hard anodised slide) whilst the bike was getting tricky to start it would start, now if I’m lucky it will catch but mostly won’t, when it does catch it won’t respond to the throttle, 8 stroking and generally gasping either for fuel or air (not decided which yet) and then dies.
Any thoughts on what’s going on?
always go back to the last thing you did; sounds to me as if you have done something silly in the carb.
Have you another carb however bad that you can use? that will eliminate carb probs as it is likely not the carb thats at fault.
In my experience novices tend to blame timing or carb for any problem.
when you give it a good flood and a few kicks then remove the plug is it wet?
You do have a big fat blue spark? Suppressed plug cap? chuck it.
Good compression?
Hardest thing in the world is to diagnose at a distance.
fuel
spark
compression
its fault lies in one of those.
suck squeeze bang blow in that order
What bike would help.
I have had bikes (e.g. T110, but also a ZZR1100) where the body of the carb/carbs had worn or warped, so fitting new internals didn't help.
The ZZR really annoyed me (I had two at the time and it was the newer bike I had probs with), as I kind of expect stuff to wear on older machines.
Regards
Pat
email (option): sacombsashtrees@hotmail.com
As Ken said - if it was ok, go back to the beginning.
Is it flooding or does it need a longer tickle than before to get it started ?
You say it 8 strokes - could be flooding, in which case look for a trapped float - after a rebuild i give the carb a good shake before fitting - it should rattle if the float is free.
I presume the overhaul kit came from Burley Amal or someone genuine, theres a lot of s**t being sold in Ebay land....?
email (option): ginantonik@tiscali.co.uk
Favourite problem on Mk1 'Eccentrics' is a blocked pilot jet. Due to problems on two strokes back in the sixties, Amal deleted the removable jet and went over to a sized bush pressed into an almost hidden cavity with little hope of being able to clean it by normal means.
There are a number of websites dealing with this.
http://www.jonsnell.co.uk/images/tuning_and_using_amal_mk1_concentric_carburetters_.pdf
The pilot bushes seem especially sensitive to ethanol-based corrosion.
With twin carbs, it's usually fairly obvious what is happening but I can imagine that on a single, the symptoms can be obscure.
RIK's answer is the main problem with the mk1,
The 'problem' with the two strokes was simply not enough variety of low speed jets.
I should have asked if you had similar problems before 'overhaul'.
The 'best' mk1's use the two-stroke body (i think the Wassel uses this) - allows cleaning of removable pilot and can change sizes.
Beware - the two-stroke needle, needle-jet and needle jet holder are different than the 4 stroke ones.
They are also different from the monobloc and mk2 - i've seen an Ebay site offering these parts for ALL amals ??????
Only the main-jet is common.
Thanks for all the help.
Well got the bike running seems the old carb was FUBAR.
So new body sorted it, more or less. Got a new problem now, the bike is detonating (pinking) under load in the region of the needle jet. I'm guessing the mixture could be weak and I may require a bigger jet, currently running a 106 jet and have the needle set to its highest point.
Hi Phil
Do you mean flames are coming out of the mouth of the carb?
If so, double check the timing.
On second thought, check the timing anyway.
If it is pinking, the noise (a "tinkling" sound) should be around the region of the cylinder head.
Regards
Pat
email (option): sacombsashtrees@hotmail.com
Just read the whole thread. What bike is it?
email (option): sacombsashtrees@hotmail.com
Hi Pat / Gents,
Not spitting out of the carb, but under load the engine knocks (its only started doing it since I've messed about with the carb).
The engine seems to be running a good deal hotter, as I can really feel the heat on my RH leg, where I didn't notice it too much before the carb rebuild.
If I retard the ignition then it starts to backfire out of the exhaust.
From what I've read this points to a weak mixture.
The bike is (well is now) a BSA DBD34GS with Catalina head (small valve) running a Mk1 932 Concentric with 270 main jet, 105 needle jet (highest setting), 2 stripe needle and hard annodised 3.5 slide. With this set up before I rebuilt the carb it was running fine. I'm assuing that it had all worn and been adjusted to a point where it was happy.
I've rebuilt the carb with new body, new jets, new needle and new slide and whilst I've now got it starting (it was a pig to start hence the carb rebuild) it seems to be running hot and until warmed up seems hesitant on the throttle from about 1/8 to a 1/4 open.
I'm thinking of going up a needle jet size to 106 to see if this helps or dropping the slide down to 3.0.
Thoughts please?
Sounds weak - go up to 106 and while you are at it buy a 107 as well.
At approx £4 each, they are a cheaper option than a slide ....
Make sure they are for a 4 stroke Concentric mk1 !!!
What body have you gone for?
With what you replaced i'm surprised you did'nt buy a new carb ?
If a 4 stroke body, then you are stuck with playing with the air-screw trying to sort tick-over/slide transition - what effect does screwing in/out air screw have ?
Where in the world are you?
Iv got a Commando with a single Amal mk1 concentric conversion. The manifold is held onto the head by just two bolts. The other day I went a long ride. At the start it was running perfectly, by the end it was running like it had a weak mixture. But it always restarted if I stopped, just ran a bit badly. I assumed the pilot had become blocked. When I looked at it I found both bolts holding the manifold to head were gone. The carb manifold was just hanging against the head by the cables and pipes. So the mixture must have been massively weak.
The point I trying to make is that I think engines can run with the carb miles out of spec, and I think your problems may lay elsewhere in the engine.
Peter, I think that's more the magic of Commandos ! They just keep running when other bikes would stop. If you look around the average NOC meet you wonder how half of them got there...but they usually get home again as well !
Hi Nigp,
thinking along these lines, i'll give it a go, would rather it was too rich than too weak.
Cheers
Bloody hell, I've never thought of Commando's as being reliable !?