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Unable to get reliable tickover

Chris Launders

Well Known and Active Forum Website User
VOC Member
Help.
Had a twin for a year now and I am still unable to get it to tick over properly.
BTH mag,two front heads,1-3/8 ports,mk3 cams, 32mm mk1 concentrics,20 pilot 106 needle jets, needle in
middle 3-1/2slide.
All the usual things done, carbs stripped and cleaned several times,new stay up floats,float level set accurately,tappets done and timing double checked.Runs great but it either ticks over at 1500rpm when its hot or cuts out,losing patience but don't know what to try next other than get some different carbs which is expensive.
No trouble with my comet which also has a mk1 or my norvin which has mikuni's.
 

mr.hutch

Well Known and Active Forum Website User
VOC Member
Hi chrislaun,
I have just looked at my notes from when I last reset the carbs on the outfit. This was some years ago and have had no reason to alter them. The carbs are the same as yours, I also have mk3 cams, but a manual advance and retard lucas mag, although this is probably unimportant.
The settings however are somewhat different, as follows, Pilot 25, Needle jet 106, Main jet 320, needle in the bottom notch.
I bought both carbs new from Hitchcocks, back in 95 and at that time they supplied a very useful leaflet on tuning Amal carbs and general information, which may still be available.
Hope this may be of use as I know how frustrating poor tickover is.

All the best mr.hutch :D





Help.
Had a twin for a year now and I am still unable to get it to tick over properly.
BTH mag,two front heads,1-3/8 ports,mk3 cams, 32mm mk1 concentrics,20 pilot 106 needle jets, needle in
middle 3-1/2slide.
All the usual things done, carbs stripped and cleaned several times,new stay up floats,float level set accurately,tappets done and timing double checked.Runs great but it either ticks over at 1500rpm when its hot or cuts out,losing patience but don't know what to try next other than get some different carbs which is expensive.
No trouble with my comet which also has a mk1 or my norvin which has mikuni's.
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Chris, Can't say too much because mine are not good but I think 20 is too small for pilot, I agree with Hutch, 25. Are you sure there are no leaks on the manifold or the carb' face is not flat ? Good Luck Bill.
 

Len Matthews

Well Known and Active Forum Website User
VOC Member
Are you using Amal's stub to flange adaptors? These have been known to be the source of induction air leaks and caused the problem you describe.
 
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Chris Launders

Well Known and Active Forum Website User
VOC Member
Hi Len. It is fitted with two homemade double flange manifolds,will try 25 pilots tomorrow if i have them,at present i am one full turn out with the 20s.I don't think i have any air leaks but will try the old wd40 trick.
 

Howard

Well Known and Active Forum Website User
VOC Member
Hi Chrislaun,

I don't know if this is relevant. I just had a problem with a friends Comet that was having pilot jet problems on a new Mk1 Concentric. After lots of frustration I finally realised it had 2 pilot jets (or at least 2 restrictions) there was a pilot jet behind the pilot air screw and a pilot jet in the float bowl. I took the one out of the float bowl and it cured it instantly.

The symptoms were poor lumpy low speed and the air screw could be screwed right in without much variation.

H

ps Now I've written that, I'm pretty sure my Mk1s have two pilot jets, so it may just be the sizes that were wrong. Anyway - it's a fairly quick thing to try, just take the float bowl off and unscrew the jet from there, if it changes things for better or worse it's a reasonable pointer to the problem.
 
Last edited:

Howard

Well Known and Active Forum Website User
VOC Member
Hi chrislaun,
I have just looked at my notes from when I last reset the carbs on the outfit. This was some years ago and have had no reason to alter them. The carbs are the same as yours, I also have mk3 cams, but a manual advance and retard lucas mag, although this is probably unimportant.
The settings however are somewhat different, as follows, Pilot 25, Needle jet 106, Main jet 320, needle in the bottom notch.
I bought both carbs new from Hitchcocks, back in 95 and at that time they supplied a very useful leaflet on tuning Amal carbs and general information, which may still be available.
Hope this may be of use as I know how frustrating poor tickover is.

All the best mr.hutch :D

320 main??? The next size up is removing the jet altogether!!! :)

Vins never cease to amaze me, my engine sounds simillar spec to yours and Crislaun's (plus 9:1 and Pazon) It goes like the clappers on 260 mains and a very open "silencer" at the moment.

Agree about the small pilot mine's running 30, 3 1/2 slide, needle in middle notch.

H
 

Chris Launders

Well Known and Active Forum Website User
VOC Member
Fitted 25 pilot jets,no air leaks,better but still to take out for a run.front 3/4,out rear 1 turn.took air screws out,restricters
inside, seem to remember someone saying these are too small for twins and need drilling out to 40 thou.before that will try with no pilot jets.
 

Chris Launders

Well Known and Active Forum Website User
VOC Member
Tried with no pilot jets,better still but still erratic with both air screws at 3/4 turn out.Then came across Jim Mosher's post
on thevincent.com a really enlightening article. All my mk1's(2 on the bike and 4 others) all had 25 thou restrictor, so away to a model shop for some drills.The 1mm (40thou) were too short but the 1.2mm were long enough so used one of these to drill through the restrictor.Then fitted 30 pilot jets,set the air screws at 1-1/4 turns out and kicked away.UNBELIEVEABLE
ticked over without altering anything at all,picks up better and shuts off cleanly dropping instantly to a steady even beat.
All I need to do now is go for a long run to see what its like when really warmed up.
 

Howard

Well Known and Active Forum Website User
VOC Member
Tried with no pilot jets,better still but still erratic with both air screws at 3/4 turn out.Then came across Jim Mosher's post
on thevincent.com a really enlightening article. All my mk1's(2 on the bike and 4 others) all had 25 thou restrictor, so away to a model shop for some drills.The 1mm (40thou) were too short but the 1.2mm were long enough so used one of these to drill through the restrictor.Then fitted 30 pilot jets,set the air screws at 1-1/4 turns out and kicked away.UNBELIEVEABLE
ticked over without altering anything at all,picks up better and shuts off cleanly dropping instantly to a steady even beat.
All I need to do now is go for a long run to see what its like when really warmed up.

Crislaun,

That was my next suggestion. Now try the float setting and the cut down needle jet tube (I forget the name) they're all worth doing.

Interesting you like size 30 pilot jets, I found that suggestion somewhere else on the many Amal tuning sites, and I find there's so much torque available at virtually no revs.

H
 
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