1993 3.0 smokin after tune up

[Tail_Gunner]

As the header describes after a small tune up (plug's, wires and low speed idle adjustment) the motor now starts just like a champ. However there is a good amount or maybe a fair amount of pure black smoke for perhap's twenty sec's

Prior to the tune one would have to crank the thing so much (maybe a minute or 2) that i was in fear for my starter however there was no smoke or soot.

I have let the motor run twice now @3000rpm for perhaps 5 minutes its fully warmed up to 165-170 and each time @ start agian the next day poof it's like cleaning the chimmeny. Could this be old carbon just be ing blown out or is my idle mixture to rich...........i hope its not the latter it really starts easy........as easy and as quick as my Efi engine. Or do these older motor's just run rich?

 

[bjcsc]

Re: 1993 3.0 smokin after tune up

What do you mean by "low speed idle adjustment"? Do you have a high idle adjustment? If so, you've got problems.

What did you adjust, the mixture or the actual speed setting?

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

Unless thing's have changed a bit there is no high speed idle circut on a old carb (1993) Or i am assuming as much that is i could not find one, The (screw) was located on the exhaust side of the block at the base of the carb, and no there was no setting of the idle speed..........however it does now idle at about 800-1000 which i havnt corrected yet......the boat is still being painted im just messing with the motor now.

 

[bjcsc]

Re: 1993 3.0 smokin after tune up

Good answer. High idle speed adjustments are found on automotive carbs. You need to get the idle down to whatever it should be at (~550 - 650). Sounds like you may have over-richened the idle mixture which, in combination with a high idle speed setting could cause your problem. Is this a 2v Holley?

 

[bruceb58]

Re: 1993 3.0 smokin after tune up

Does your choke start opening up right after the engine starts? Maybe it is adjusted too far to the closed side. Or did you compensate for the choke not adjusted all the way closed by changing your idle mixture.

Also, if you let your engine idle for a long period after it is warm, does it bog down or stall. This would indicate a low speed mixture problem.

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

Good answer. High idle speed adjustments are found on automotive carbs. You need to get the idle down to whatever it should be at (~550 - 650). Sounds like you may have over-richened the idle mixture which, in combination with a high idle speed setting could cause your problem. Is this a 2v Holley?

Stock carb 1993 vintage and yes its a 2bl, i may have (over) enriched the mixture, but it start's with so quickly.......then again it does have a good lump for 10-15 secs i wil check the choke more closely...........i just never seen a car overchoked and start up so fast.

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

Does your choke start opening up right after the engine starts? Maybe it is adjusted too far to the closed side. Or did you compensate for the choke not adjusted all the way closed by changing your idle mixture.

Also, if you let your engine idle for a long period after it is warm, does it bog down or stall. This would indicate a low speed mixture problem.

Actually i did the tune then at a warm idle i adjusted the low speed circut the motor did smooth out rev's went up a tab and it started up quite a bit faster.

The next morning cold it took off in maybe 3-4 secs blew jet black smoke not a huge amount cleared its self in maybe 15/20 secs. ran it @ 3000 for 5 mins or so hoping to clear any build up

Again the next morning same thing............ I hate to mess with chokes........there so damm fickle i guess i will watch how it works.

 

[bjcsc]

Re: 1993 3.0 smokin after tune up

??? Jet black smoke for 15-20 seconds on start up is definitely not working fine...

Black smoke is unburnt fuel. Your rich, no question. Why is the only question...

 

[bruceb58]

Re: 1993 3.0 smokin after tune up

Sounds like it is working fine to me.

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

Well it was a simple solution, I started the engine cold adjust the low speed idle circut COLD, tightened up the throttle linkage and Poof smoke's gone,

Looking back i thought it was good idea to adjust the low speed screw when hot, very bad ideal the choke was set up for cold start's and i adjusted the low @ high heat creating a over rich condition ,,,,,,,,,,,,,,:}...........me bad

 

[Reel Poor]

Re: 1993 3.0 smokin after tune up

The idle speed mixture should be adjusted on an engine that is at normal operating temperature. It sounds like your choke is in need of some fine tuning adjustments when cold (a little leaner).

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

The idle speed mixture should be adjusted on an engine that is at normal operating temperature. It sounds like your choke is in need of some fine tuning adjustments when cold (a little leaner).

I would normally agree with you, however its start's now ln two maybe three turn's no smoke and purr's in 10 secs or less, however it now deisel's when shutting off...................... Id assume my timing is a bit to advanced. Is the shunt used for timing just a wire that short's or close's a circut or is it a specialized tool?

 

[bjcsc]

Re: 1993 3.0 smokin after tune up

Make sure your idle speed isn't too high as that is a common cause of dieseling. The shunt is both of the things you mentioned. They're cheap, assuming your ignition is Delco EST. I'm still pretty cloudy on why they are necessary. When I used the shunt, I could tell it shut down the advance. I followed the procedure and then checked the reference points for advance. My spec is 6* with the shunt at idle (600rpm). Without the shunt I am supposed to see 11* at idle. Other than verifying that the advance is working, I still don't understand why I couldn't just set the timing to 11* and forego the shunt proceure altogether...

 

[Reel Poor]

Re: 1993 3.0 smokin after tune up

Be sure to get the idle speed to 550 to 600 RPM's (boat in the water and in gear). That should cure you dieseling problem. Set the air mixture screws with the engine at normal operating temp, also in the water and in gear. Then set the choke when the engine is cold and has been sitting for a day or so. It sounds like the choke needs to be openeing a little more on start up (less spring tension on choke thermostat).

Link to Your Mercarb Set Up and Adjustments

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

Agreed, however there is no reason a little 2.5 or 3.0 4 cyl chevy engine should diesel at 800 rpm unless there strung that tight............... this is a adventure for me and i appreciate all the reply's

 

[Tail_Gunner]

Re: 1993 3.0 smokin after tune up

:'( I really didnt need this, the carb is making a tick...tick...tick ........er pffft...pffft.pffft solid rythmatic sound and only at low idle (600rpm) I'm sure there's a vavle sticking or is there any other possibilities? If this was a car engine id just take a dollar bill and see if it suck's back into the exhaust but a tail pipe isn't readily avaiblle here.

 

[Don S]

Re: 1993 3.0 smokin after tune up

Weeeeellllllllll, since you can't find a tail pipe to play with, maybe tests like compression tests, leakdown tests, vacuum gage readings will help locate the problem.
You really don't think us poor ole marine mechanics sit and cry in our beer because we don't have tail pipes and dollar bill tests do you?