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high idle speed, low power. mixture problem or else?

600 views 13 replies 8 participants last post by  gsi mike 
#1 ·
I've just bought a 1990 1.2 sting nova.
It runs fine however, it idles about 1200 and i cant get much more than 70mph out of it. I doesnt seem too bad at low speeds but doesnt have hardly n e pull after 4000revs.
Is the problem just too rich a mixture? If so i think i might be able to sort it myself, or is it a timing problem???
 
#2 ·
Probably best to get it tuned. Sounds like the idle could do with being wound down a bit. Check the cap rotor and plugs are ok, if in doubt change them. It might pay to give the carb a clean as well.
 
#4 ·
Sorry that was supposed to be cap and rotor i.e distributer cap and rotor arm. On the carb there should be two screws. One for the idle and another for the fuel mixture. Obviously the fuel mixture screw your really gonna want to use a co machine to get it right. As for the idle screw, you'll see if thats right on the rev counter:D You can go by sound of the engine any way but the rev counter helps. Dont forget to alter any settings once the vehicle is warm. I presume the auto choke is coming off completely, that is if it is auto choke:eek:
 
#6 ·
If it's idling at 1200rpm i would have thought that was idle adjustment required. You may well have an airleak. Check any air and vacume pipes to make sure none have come loose or split.
 
#7 ·
Agree.

Follow the throttle cable up to the carb, you'll see the throttle linkage. At one end (you might want to whip the air filter off) you'll see an end stop screw. This is your idle speed adjuster. Follow the choke cable and check the fast idle end stop screw isn't stuck, holding the revs up. When you push the choke all the way in, it should come clear of the throttle linkage.

The are actually 2 mixture screws on the 1.2's, assuming it has the 1B1 Peirburg carb. There is a big white screw on the front, and a smaller one on the front passenger side of the carb, down a little tube like thing. Play with these as much as you like, but as a safety, remeber how much you turn each one, so you can put it back!

Also check your timing. My girlfriend's 1.2 Nova Antibes had the timing adjusted the wrong way for unleaded fuel. This meant it had uneven acceleration, and would not rev, under load, past about 3500-4000 revs. I had to lower the idle speed to it's lowest once I'd set the timing properly.
 
#8 ·
sorry to look for the obvious guys but fast idle and no top end on a manual choke, first check that the choke is coming off completely. chech the cable / carb link make sure that the operating arm is not staying on when ya push the choke in the cable sometimes slips where its clamped, this would also lead to hot start problems.
 
#14 ·
Quite right Dan problems at idle that dissapear at part and full throttle are usually air leaks as the air flow in creases these become less significant so disappear. Problems at full throttle indicate fuel starvation or aair intake restriction easiest way to find out is to run it at full throttle on the road for 10 mins then stop it and look at the plugs. Sooty plugs overfuelling/air restriction. white plugs weak mixture fuel starvation or use a colortune plug you can see the flame colour
 
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