idle speed vs idle mixture...

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sundog

Petty Officer 2nd Class
Joined
Aug 14, 2003
Messages
138
Ive got that old 1978 1150 inline 6. while trying to set the idle the other day couldnt seem to get it right...lean or rich, it still is just not quite high enough to idle in slow forward. Manual says after warm up to set the 'idle speed screw' to 650, then in gear, to set the 'idle mixture screw' for best running. 3 questunes-<br />1) where the hell is the 'idle speed screw' (manual dosent say)?<br />2) in setting the 'idle mixture screw', manual only talks about setting the top one...Im assuming I have to set all three the same way?<br />3) unrelated, but I stripped 2 threads replacing 0-rings on my old style trim unit(!@#$!). do I need to buy a new one, or can I get a lower unit?
 
S

sundog

Petty Officer 2nd Class
Joined
Aug 14, 2003
Messages
138
Re: idle speed vs idle mixture...

double !@#!! just looked a mercs parts list and if the trim set bolts dont hold I will be needing a 'valve body and gear assembly', out of stock at $330. cant do that even if it was in stock. think I can re-tap the screws? any other options?<br /><br />thanks.
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,786
Re: idle speed vs idle mixture...

Sundog, I do not really understand the problem you are having with the trim unit. You will need to describe it further.<br />As for the carb idle jet settings. The object is to set them just rich enough to allow the motor to accelerate smoothly. On my 1977 150 inline, the idle speed is controlled by a screw on the black plate, mounted on the distributor. It was a simply a throttle stop. I presume you motor has something similar.<br /><br />To set the carbs: Start with all carbs at 1-1/2 turn out (CCW) from lightly seated. Start motor put in gear and run at lowest speed that it will continue to run. Adjust carbs to get reasonable idle. (not too lean) Now try to accelerate. If it works, your done. If the motor doesn't accelerate, open the top carb idle needle 1/8 turn and try to accelerate. If it works, your done. If not, repeat with mid carb and then bottom carb. If it still will not accelerate sommthly, repeat top-mid-bottom adjustment sequence.<br />It is fairly to set the carbs. If you have trouble, I recommend you check compression, spark and other basic engine systems for proper working condition.
 
S

sundog

Petty Officer 2nd Class
Joined
Aug 14, 2003
Messages
138
Re: idle speed vs idle mixture...

Chris...that answers my first 2 questunes, thanks. I had forgotten about the screw on the distibutor to set the idle RPM (once again, Solec was a wealth **sarcasm*** of information). and now I know what to do with the other 2 carbs. Ill let you know how it goes.<br /><br /> http://www.mercruiserparts.com./Sho...nbr=23&bdesc=HYDRAULIC+PUMP+AND+CONTROL+VALVE <br />as for the trim, after I replaced the o-ring, on the control valve assembly (11), I tightened the 4 set crews which screw the control valve assby into the hydrolic pump assbly. I stripped 2 of the screws (idiotic, I know). the bottom of the hydrolic pump assbly is the valve body and gear assbly shown here as #2...http://www.mercruiserparts.com./Sho...nbr=488&bnbr=22&bdesc=HYDRAULIC+PUMP+ASSEMBLY. I may be able to tap a new screw in if Im carefull, otherwise I guess Im buying a new TT.
 
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