Background: My '83 gsl w sidedraft runs rough, decel's rough although has good power. No vacumm advance in place, dizzy vacuum lines open to the atmosphere. Power drops off between 5000 and 6000 on a good day. Timing marks are gone, but the dizzy hold down bolt was right in the middle of the slot it goes through. I rotated the dizzy clockwise (advanced?), and test drove. Less rough and now revs to about 6800 before power drops off. The scary part is that when the power drops off at 6800 it drops off very quickly, as it used to do at 5500. Is this loss of power normal? I would have expected a flat spot not a very abrupt drop off. I am getting good spark at all 4 plugs, haven't yet adjusted the trailing advance.

 

Could be getting to rich when your up in that part of the powerband? Have you tried leaning it a tiny bit?

What exhaust?

 

I don't know how to lean it other than during idle. Don't know much about the carb, although it is a Weber 45 dcoe clone. It is a side-draft, and the intake manifold is short, just sticks straight out of the motor sideways, instead of curving up and over the top of the motor. I don't have a heat shield between the carb and exhaust manifold, I wonder if that is a concern. Rats nest is disconnected.

Exhaust looks like any pre-cats or whatever have been removed, so there is a straight pipe going to the main cat which is in stock location, and either a stock muffler in stock location, or maybe a racing beat muffler. By the way, at full throttle it sounds amazing, like a combination of racing motorcycle and formula one race car .

 

So it's probably not an exhaust issue with flowrate. Not familier with that carb but there should be a lean adjust on it. Probably want to get a manual on the carb.

 

you need to get smaller idle jets..the idle jets control idle and also when not in progression..they have a really big influence on how the car runs...the mixture screws don't really do anything if the idle jets are to big...

 

My idle mixture screws are quite effective, I can kill the motor by turning them too much, or get it to idle smoothly. Should I still go smaller? I don't understand how the idle jets would affect the performance at 6800 rpm, though. I trust your judgement, and "credentials" in other words the car in your signature tells me you know what you're talking about. How will the idle jets affect the high rpm perf?

Dave

 

nvm..just read more of your posts...your idle jets have a great deal with how your car runs..whenever the gas isnt pushed all the way down while in progression..but if your having problems near the top...then it could be your main jets, one thing to make sure..weather you are running rich or lean..you should invest in an aem uego or some wideband gauge...install this in the header of your choice..you need it right about wear the firewall is...also..don't have to but might wanna invest in a heat shield..when the intake is really hot it doesnt atomize the fuel as well...especially with your lake city intake...

 

Given that changing the timing affected your problem, I would recommend you keep your focus there first. Your carb may need additional tuning, but you really need to have the ignition timed correctly before that can happen either.
It's a shame your timing marks are gone, because if you just time it by ear at idle, you will likely be too far retarded: you will run smoothly and have plenty of power up high, but toohigh in the rpm band to be really usable. If you are experiencing a power drop off and rough running/pinging high up in the rpms, this most likely means that you are too far advanced. If you go too far retarded you will probably experience little low-end power, and poppy little backfires on deceleration. If you advance too far, the low end will be good, but you will experience drop-off/pinging at the top, and possibly higher engine temps. If you advance way too far, it will buck and shudder at idle.
Best of luck.