1966 Atlas Idle Problem

Beach

Beach

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I just got my 1966 Atlas on the road a couple of weeks ago and it runs great , except for the idle...I have checked the float level and adjusted, checked all openings in carb and made sure the cables are adjusted correctly...It seems to idle too high and I am not sure why....The only thing I haven't checked so far are the springs on magneto advance....I also wonder if worn slides would cause a high idle problem...I am running Amal 389/236 and 689/236 carbs on this bike....Timing is right on......
 
Should be able to adjust the slide and mixture screws right down until it will no longer even idle.
(I know this is stating the bleedin obvious)
No air leaks in the manifolds anywhere ?

Checking that the auto advance un-auto advances could be the 1st step though.
Strobing it with a timing light is the easy way to ensure this - if you have something to point it at.
Even the points in the magneto will suffice, if you mark the housing with a pen etc.
You only need to see that the timing advances and un-advances.
 
Never thought about shining timing light at points.. Will definitely show if advance is working...Will try tomorrow...Kind of at a loss here...No air leaks...
 
Rohan said:
Even the points in the magneto will suffice, if you mark the housing with a pen etc.
You only need to see that the timing advances and un-advances.
Click to expand...


No, the points opening and the spark do not advance in relation to the cam ring, or anything else at that end of the magneto.

You need to mark the engine sprocket or alternator rotor and watch that.
 
Mmm you're right, its only manual advance ones that move there.
And you can manually see they move...

I'll think on it, I strobed it somehow.
 
When I think about it, you wouldn't have to mark the alternator rotor if you only wanted to know if it advances or not, because you'd see the strobe image of the rotor rotate forward.
 
If the AAU were "stuck" in full advance, you most likely will have a hard time starting. Were you in the timing chest recently? Why do you suspect weak springs? Did you install a new timing chain? It is known that too tight a timing chain can cause sluggish AAU return to non-advance position.

Slick
 
It starts ok, but seems to be harder starting than when it first got on the road...I did replace the cam and magneto chains but did not replace the advance springs...I checked float levels yesterday and when I first started bike I could adjust the idle..After blipping the throttle a couple of times the idle raised and I could not adjust down...I will pull the timing cover and check magneto chain adjustment and see if advance returns quickly by hand....

When I checked the advance when putting bike together I noticed the advance wouldn't return while point follower was on high part of cam. but would return when it got off the high part...I thought this may be normal...I also noticed when replacing the chians in there, they both were tight in one position and loose in another...Normal or problem?
 
Beach said:
I just got my 1966 Atlas on the road a couple of weeks ago and it runs great , except for the idle...I have checked the float level and adjusted, checked all openings in carb and made sure the cables are adjusted correctly...It seems to idle too high and I am not sure why....The only thing I haven't checked so far are the springs on magneto advance....I also wonder if worn slides would cause a high idle problem...I am running Amal 389/236 and 689/236 carbs on this bike....Timing is right on......
Click to expand...

re; "It seems to idle too high "
slide sticking :?:

Have you checked the condition of the rubber O ring between the carb and the inlet spacer :?:
after ** years they will perish.
I have found that the best way a home mechanic can get the mixture 100% correct on the pilot jet, is to use a Gunston Coluortune kit,on a warm engine, (There are a few on e-bay) but a word of warning :!: only use it in darkness or you will call it a piece of junk.
 
Beach said:
When I checked the advance when putting bike together I noticed the advance wouldn't return while point follower was on high part of cam. but would return when it got off the high part...I thought this may be normal...I also noticed when replacing the chians in there, they both were tight in one position and loose in another...Normal or problem?
Click to expand...


I have noticed the same effect on mine. The spec on chain tightness is 1/4 inch up/ down play at mid-run of the chain.

It is well to check the timing, but the issue sounds more like an air leak as others have said. One trick to find a leak is to spray WD 40 around suspected joints and look for smoke in the exhaust.

Good luck ... keep us informed.

Slick
 
I did spray wd40 around intake and did not notice change in idle or smoke from exhaust...When I adjust the air jet closed the idle lowers and sometimes will stall...
 
Beach said:
The slides don't stick and the orings are new...
Click to expand...

Then do check that the mag fires at 0 and 180 degrees true. It can be corrected if it is out by more than a couple of degrees.
 
When timing the mag I used degree wheel and piston stop...Then checked that timing was at 28 btdc and that timing was exactly 180 apart..
 
If the auto advance springs are slightly weak, or the unit has slack in the linkage, then a slightly fast idle makes it advance, so making the idle even faster. Making the idle a bit slower, with the throttle screws, can help sometimes. Sounds like that's not working for you.
 

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