The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
It is currently Fri Mar 29, 2024 10:49 am

All times are UTC




Post new topic  Reply to topic  [ 5 posts ] 
Author Message
 Post subject: Sprint Idle
PostPosted: Wed Nov 06, 2019 9:43 pm 
Offline
TDC Member

Joined: Tue Oct 15, 2019 9:00 pm
Posts: 282
Just fitted alloy carb mounts and tweaked the carbs and sorted the choke cable properly to get a decent fast idle and easy starting from cold. All is good BUT (there is always a but!) I have got the idle set at around 800 rpm (fast idle 1500 rpm) but at 800 rpm the engine is not as smooth as I would like. It is OK at 1500rpm. Happy with the carb balance and mixture (CO around 3.5% and not much reaction when lifting the pistons). The engine will "happily" idle down to 500 rpm But anything less than 1000 rpm and it gets a bit "lumpy" not excessive but not smooth. Timing is spot on and both mechanical and vacuum advance are working OK. Carbs are recent recons from Robsport.

Not having had experience of the Sprint engine before the question is does the engine naturally idle a bit lumpy or is there something amiss somewhere? Other than the lumpy idle it seems to run great, instant pick up, revs freely and pulls like a train - loads better than before.

Any comments gratefully received.

Roger

_________________
1975 Sprint Man O/D in Honeysuckle Yellow
1971 Stag Auto White

Too many cars, too little time!


Top
   
 Post subject: Re: Sprint Idle
PostPosted: Thu Nov 07, 2019 11:02 pm 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Mon Dec 03, 2012 6:04 pm
Posts: 1549
I had a similar problem, in my case it turned out to be duff cheap rotor arm ( I use the large cap and the 1300/1500 rotor arm), ignition timing slightly out and vacuum leak (cracked breather).

Now you say the mixture is fine and you obviously have a gas analyser and the timing is fine. Have you checked for a misfire caused by one of the plugs not firing properly at low revs?

Another suggestion, is I don't know how accurate the rev counter in a Dolly is. It could be out a bit, though others will be able to clarify that.


Top
   
 Post subject: Re: Sprint Idle
PostPosted: Fri Nov 08, 2019 10:51 pm 
Offline
TDC Shropshire Area Organiser

Joined: Sun Aug 21, 2011 5:12 pm
Posts: 7014
Location: Highley, Shropshire
In my general experience, the idle on a Sprint is never silky smooth, you wouldn't be standing a threepenny bit upright on the cambox, even if it WAS flat! I think it's something to do with the limits the single cam imposes on this engine!

If the idle is constant and unwavering, i'd call that good enough!

Steve

PS I've just fitted a set of alloy mounts to a Sprint myself - and had to strip and rebuild the linkage cos I couldn't then get the hot idle below 1800RPM! All is well now though, it's crisp throughout the range and idles happily at 800rpm in neutral and 600rpm in drive (It's an auto so a good idle is pretty vital) This one too is a tad lumpy but it's no big deal and it doesn't cut or hunt.

_________________
'73 2 door Toledo with Vauxhall Carlton 2.0 8v engine (The Carledo)
'78 Sprint Auto with Vauxhall Omega 2.2 16v engine (The Dolomega)
'72 Triumph 1500FWD in Slate Grey, Now with RWD and Carledo powertrain!

Maverick Triumph, Servicing, Repairs, Electrical, Recomissioning, MOT prep, Trackerjack brake fitting service.
Apprentice served Triumph Specialist for 50 years. PM for more info or quotes.


Top
   
 Post subject: Re: Sprint Idle
PostPosted: Sat Nov 09, 2019 2:31 pm 
Offline
TDC Member

Joined: Tue Oct 15, 2019 9:00 pm
Posts: 282
Thanks, I have checked (actually replaced) the breather pipes and also checked timing and mechanical/vacuum advance - so they are all OK. There is no misfire, the exhaust note is pretty stable as is the idle it is just "lumpy" i.e. the engine moves about quite a bit (yes the mounts are a bit soft - on the todo list - and I don't think the front stabiliser bar thingy helps as it tends to make the engine skew rather than rock which accentuates the problem)

Steve, I think that answers the question - "idle on a Sprint is never silky smooth" - and is kind of what I assumed. My son has a 106 Rallye with the 8 valve 1.3 engine and the idle on that is similar - i.e not smooth, so as you say could be related to the more aggressive cam timing.

Roger

_________________
1975 Sprint Man O/D in Honeysuckle Yellow
1971 Stag Auto White

Too many cars, too little time!


Top
   
 Post subject: Re: Sprint Idle
PostPosted: Sun Nov 10, 2019 9:59 am 
Offline
Future Club member hopefully!
Future Club member hopefully!

Joined: Mon Dec 03, 2012 6:04 pm
Posts: 1549
Quote:
Thanks, I have checked (actually replaced) the breather pipes and also checked timing and mechanical/vacuum advance - so they are all OK. There is no misfire, the exhaust note is pretty stable as is the idle it is just "lumpy" i.e. the engine moves about quite a bit (yes the mounts are a bit soft - on the todo list - and I don't think the front stabiliser bar thingy helps as it tends to make the engine skew rather than rock which accentuates the problem)

Steve, I think that answers the question - "idle on a Sprint is never silky smooth" - and is kind of what I assumed. My son has a 106 Rallye with the 8 valve 1.3 engine and the idle on that is similar - i.e not smooth, so as you say could be related to the more aggressive cam timing.

Roger
I don't think it should moving around excessively, once I had mine setup properly it wasn't doing that. Saying that i have replaced all but one of the engine mounts, including using the alternative gearbox mount recommended here, plus a new steady bar. So that could be the reason for the difference.


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 5 posts ] 

All times are UTC


Who is online

Users browsing this forum: Bing, Trendiction and 27 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Limited