88spl help!!

[boredindaboro]

I have an 1994 88spl. The issue is I'm about 1200 rpm off of proper wot. When I move the control to max throttle it coughs. I believe it is running rich but I can't just change the jets because the carbs have been swapped, and I believe the venturis are different sizes. How would I compensate for this? I'm almost positive it's a rich issue and I believe leaning it out slightly will get me the extra power/rpms it is supposed to have. I don't remember what size the original carbs venturi was but I remember commenting the replacements were larger. I know there was a difference in the main jet size but I'm not sure where or what size I need to correct this issue. I'm open to other suggestions but I've already repropped and it made no difference in rpm. The symptoms are hard hot restart, low rpm at wot, rich blue smoke, dark dark plugs. Thanks everyone for your help.

 

[interalian]

Have you just picked up this motor or is it a new problem on a motor you've had for time? You can find the venturi sizes cast into the face of each carb - probably 1-3/16 on that. I wouldn't recommend tinkering with jet sizes, but they should be #56C (accessible behind the side drain plug). Coughing sounds like you're running lean, not rich too. Have you tried pumping the primer ball when running WOT?

I'd do a spark test at WOT. Put a timing light on each plug sucessively and watch for dark spots in the light when running WOT. You need a helper and calm seas.

But check compression first. Should be within 5-10% of each other.

 

[ondarvr]

According to a very knowledgeable person that used to frequent this site and did a great deal modifying on these motors, when switching carbs the jetting normally isn't far off. I had one of those motors, but never modified it, so I can't say from personal experience.

What I can say is check the compression before doing anything else.

 

[emdsapmgr]

I'd do some research on your carbs. What size is the venturi? Stamped on the front of the carb. Could be 1", 1 3/16", or 1 5/16" Then spend some time on the factory master parts lists: epc.brp.com. What size main jets came in your original carbs? Do the current jets match up with the originals? Ondarvr is right, when rejetting, start with the original jets sizes, then slowly move up a size or two. Keep in mind, you don't want to run it hard on jets that are too small. (you will lean out the mixture and could wind up with a blown powerhead.) Jetting is not easy. It takes a lot of time to switch jets between carbs, charting top rpm and operating characeristics for each jet set. Not to mention that brass jets are very expensive and you may need to go thru 3-4 sets during testing.