I also started this thread in the Technical Q&A section in the general forum but it might be in a better place here. Could somebody help me out on the following issue. I have owned a '78 US spec. 308GTS for 2 years now and am currently facing the problem that it is not running smoothly at cruising speed. It is very hesitant and it feels as if not all cylinders are adding to the power. However as soon as I touch the acceleratorpedal it is pulling like hell up until over 7500 RPM. Also at idle it is running smoothly. - The car is US spec. but with airpumps and retarded breakerpoints removed. So I am running on 1 set of breakerpoints per distributor. Timing is set at 7 BTDC - Oil / Oilfilter / petrolfilter / airfilter / sparkplugs / timingbelts + bearings where replaced last year less than 1000 miles ago(by myself). Car was running fine after that. - Ditributor caps / rotor / sparkplug cables / extensions look OK - I checked timing which was OK - I checked the sparkplugs visually and with timing light with running engine, both were OK - I checked the airflow through the carburetors and synchronized them with the help of a WEBER synchrometer - With the help of a CO meter I adjusted the mixture screws on the carburetors All the above did not help. Is there anybody out there that has some tips and tricks to solve the problem. If not I will bring it to a specialist but I rather have a try myself before. Regards, Ronald Koers, The Netherlands
What are the jet settings? What is the altitude of your location - Netherlands, so assume no altitude. What is the relative humidity of the air in your area - moist/dry etc. To note: Factory settings: Venturi 32mm Aux venturi 4.50mm Main jet 125mm Air connector jet 220mm Emulsion tube F24 Idle jet .50mm Pump jet .45mm Needle valve 1.75mm Float measurement 50mm Pump exhaust valve 100mm Hope this helps Dwight
I did check and clean all idle jets and mainjets but have not written down the type. So I'll hve to come back on that.
Is there a specific rpm where this issue is most common? It this is incomplete combustion at steady throttle/cruising than it could be an issue of the engine either being too lean or too rich. It could be a combination of incorrect ignition timing at specific rpm and carburetor jetting. Also, are both distributors advancing exactly together? I get a similar issue when cruising at steady speed, but it is almost not able to be noticed and it is only when cruising in 4th or 5th gear below 3k rpm. When the main jets are in their band of operation this issue is non-existent.
Current carb.settings - Main jet 125 on tube is also engrave F36 and on screwside it says 200 - Idle jet .55 But actually I did not change anything on the jets. In the past the car has been running fine with these settings
Ok so you got: Main Jet=125 E-tube=F36 Air corrector jet=200 Idle=55 I'm not sure about this but your E-tube might be a little too big.
Balancing was done this summer by myself however with my limited experience it is still possible that this was not good enough. I used birdman's carb synch tutorial. On the E-tube : it might be a little big but it was in the carbs already and the car has been running fine with it for a lot of time
Ronald did you have this problem before you did the carb tune up proceedure? Also did you remove the carbs to clean them or rebuild them. I don't believe you have a problems with the jets or any other components if you did not change them. So it is in the tune up where something has changed. Maybe a vacuum leak around the throttles or a gasket. I would suspect that you may have to tweak the idle mixture screws. You could be a little lean causing a slight miss in the mid 2000 rpm range. Just a suggestion. Also someone mentioned in another post that they had the same problem and would adjust the throttle cable to 2500rpm and tweak the idle mixture until the miss went away. Also you might want to use a hotter plug. I use NGK 5's in my 77 and it runs well for all normal driving. Good luck.
Steve, The problem started this spring. Together withh the fact that my hydrocarbon emissions were rather high according to to the shop that performed the emissions check I started to do a tune-up. Have to say that this is the first car that I am working on the carburetors. I ordered a flowmeter through Superformance UK and borrowed a CO meter from a colleague. As for the synchronization, this is taking some time but it really is no rocket science. Adjusting the idle mixture is less easy for me. The way that I proceed is looking at the CO meter and adjusting the CO to a level between 0 and 1 % in order to make sure that it is not running too lean. Am I making some wrong assumptions in the above ?? Please advise. Tomorrow I will perform another synchronization an idlemixture adjustment. Thanks for the tip on adjusting the idle mixture at 2500. I will try that also. I will keep you informed !!!
Dear All, It took me sometime but I finally solved the problem. First I checked and adjusted the ignition timing to 7 BTDC. Then a synchronization and mixture adjustment (by CO meter). No result ! Because I am reluctant to bring the car to a 'specialist' I decided to take of the carbs and clean them. I took them all apart and cleaned the parts. I found a lot of carbon particles. After checking on this forum it seems that they were coming from the cannister of the emission system. Because this is not in use anymore I decided to block the hose from the small electric airpump to the airfilter housing. Carbs were rebuilt and float height was checked and adjusted. Carbs were re-installed and synchronized. Mixture was set by listening to the engine. Then a testdrive : result >> No more hick-ups, just a smooth drive !! Through 'marktplaats.nl' a sort of dutch e-bay I acquired a colortune adjustment sparkplug. This weekend I set all the mixtures by using the colortune. Result is a perfectly idling, accelerating and cruising 308. Thanks for all your help !!!
