View Full Version : Gas smell at idle

09-08-2010, 09:42 AM
I have a 1992 Maristar with a 351 Indmar and a 4160 (i think) 80319 Holley 4 bl.

I am getting a strong gas smell at idle - people in back are getting loopy. It seems as though it is idleing pretty slow ~200. Could low idle be the problem, or is it just running to rich? Otherwise it runs great. What is the target idle RPM for this engine?

I put in new plugs but that didnt help. If it is the idle adjustment, could you give me some pointers on how to correct?

09-08-2010, 11:13 AM
Is this a new problem or was it like this when you bought it? Your idle speed is too low if your tach is right. There is an idle speed adjustment screw on the passenger side of the carb where the throttle cable ties into the throttle body. There are a few mixture screws on your carburetor also. Your carburetor may need more then just idle speed adjustment. Do a search on how to tune a holley. There are better people who know how to tune a holley. I just do trial and error.

09-08-2010, 11:31 AM
I am the second owner and it has always been like this. I believe the idle is low because it is lopes and when in gear, the boat seems to shake a little. I really dont know how to describe it. When I tap the throttle and the tach reads around 600 it is much smoother. Do you know what the idle should be?

I have the .pdf on tuning the carburateor and it says that there is a primary adjustment (the one you describe) a secondary screw. It says that "the adjusments should be made to both the primary and secondary screws in equal amounts". What does that mean?

09-08-2010, 11:49 AM
Just means that on both sides of the carb, there are mixture screws. if you change one, change the other the same amount. Good rule of thumb is turb them all the way in (right) then slowly turn them left until it runs a little rough. then turn back to the right a full turn. Should end up being about 3 full turns from all the way in.
Hope that helps

09-08-2010, 12:44 PM
If you are really idling that slow you would smell some raw fuel. Your idle speed should be in the neighborhood of 600 - 800 RPM at idle in gear. Need to set it in the water. On the trailer won't work.

09-08-2010, 02:06 PM
It specifically says - secondary throttle stop screw. I also found the part around mixture screws.


09-08-2010, 02:08 PM
Thanks thatsmrmastercraft. That is what I was looking for. So just put it in gear and turn the idle screw on the side? Can you comment on the secondary screw?

09-08-2010, 02:59 PM
Idle speed adjustment is done by turning the idle stop screw (to use Holley's terms). The secondary throttle stop screw's function is to keep the secondary throttle plate from becoming closed to the point where it would be jammed closed.

09-08-2010, 03:21 PM
One a side note, make sure to run your blower good and long. Don't want to blow you boat sky high before you get it running right.

09-08-2010, 04:27 PM
Will do. Always run the blower. I will let you know how it works. May be a couple of days.

09-08-2010, 05:46 PM
Would the engine run at all at 200 rpm's, and wouldn't it die wen you put it in gear at such a low rpm? I would check the tach as well. Engine timing check would be a good idea while you're at it too.

09-08-2010, 05:54 PM
Runs well. It just runs very slow. you know blub blub blub blub. etc. It runs much better a little faster though. It may not be 200. That may just be the bottom.

09-08-2010, 06:39 PM
Ill bet the tach is off quite a bit. On my 92 prostar, there is an adjustment on the back of the tack that was hidden by the bracket that holds it in. I tweaked it till it matched what my perfect pass said. It was about 400 RPM off down low, and almost 800 off at WOT.

Too high an idle speed is not good for your transmission as you put it in and out of gear. I would try and find a way to verify the RPM, and adjust the idle screw to shoot for 750 in neutral and 600 in gear.

09-08-2010, 07:37 PM
Set your idle at 600-800 in neutral with the idle stop screw. If you mess with engines enough you will get a feel for the idle rpm. I hate it when people idle down anything too much. These engines need to turn some rpm at idle to be right and idling down an engine to make it lope is foolish. Then see where it drops down to in gear. Don't mess with the secondary stop screw. One problem at a time.

09-09-2010, 09:18 AM
Without a perfect pass, can I calibrate with a timing light?

09-09-2010, 10:36 AM
The goal of adjusting the idle-mixture screws is to achieve the highest possible idle vacuum at a set idle speed. I would suggest 800 rpms.

(Set both screws at the same to begin with) With the engine off turn one screw all the way in while counting the turns. Now turn it back to where it was and check the other side to make sure they are the same.

Start and get the engine to operating temp. The choke must be completely off.

Attach your vacuum gauge and start by turning one screw 1/4 to 1/2 turn in. If the vacuum goes up then do the same to the other side. If the vacuum goes down then turn one screw out 1/4 to 1/2 turn out. Keep doing this until you get a the highest vacuum reading.

As suggested run your blower to remove gas fumes.

09-11-2010, 07:27 PM
Thanks for the help guys. I took the boat out, cleaned the carburetor and the idle jumped back up and it tach'd in at 650 at idle and ~700 in neutral. Timing was spot on as well. I am glad I cleaned it first. Runs great.