Jump to content

Welcome to TheMalibuCrew!

As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account. It's free and it's easy, so don't hesitate to join the TheMalibuCrew Family today!

Carburetor Questions

Recommended Posts

My buddy's 98 Sportster is a fantastic slalom boat, and he enjoys the top end for bare footing too. It has 800 hours and runs strong. Our only complaint is it has always run rich with gassy smell and smoke especially at idle. Carb has never been rebuilt and idle and float adjustments are correct. Friends have suggested having it re-jetted. Do you think this will help and does it affect top end? It's been "smokey" like this since day one so thinking a rebuild will not affect the condition.  Also more noticeable in colder weather.  Looking forward to the Crew's always excellent advice. Thanks!

Link to comment

I would verify the choke is functioning correctly first.

Jet changes are more of a fine tune, if it's smoking because of a rich condition there is a problem with the carb.

Link to comment

It's been a long time since I had to tune a carb but I do know that if it is rich at idle a jet change isn't going to fix it.  Jets provide fuel at part and wide open throttle.  The engine runs on the idle circuit at idle and that circuit has to be adjusted/restricted and or adjust the floats to lower the fuel level.  


Try try lowering the fuel level in the bowls first if you think it is rich across the board.  If you just want to set the idle mixture

1. get a vacuum gauge hooked up to a vacuum port below the carb preferably in the intake manifold

2. With the engine off.  Gently screw the idle mixture screws in til they bottom out. Then back them out 1 1/2 turns each.  This should allow it to run.  If not bring each on out another 1/2 turn til it will idle.  

3 crank it up and let it warm up.  Then turn One mixture screw in (or out)1/8 turn while watching the vacuum gauge and tach.  If both Tom and vacuum increase do the other the same (you now know you are going the right direction)Do this until you reach the highest vacuum and rpm.  If it picks up rpm to a really high idle while doing this you will need to adjust the idle speed down.  


4. You will know when you have gone too far in either direction mixture wise because the idle speed and vacuum will drop again.  Your goal is the sweet spot with all mixture screws set the same.  


good article here on carb circuits

Edited by rabiddawg
  • Like 1
Link to comment

@Rednucleus:  What brand carburetor is on the boat as that opens the possibility for a slightly different root cause?  There could be a few items causing the issue as noted above.  Do you know if the choke is functioning correctly, you might try running at idle with the spark arrestor (have you cleaned it lately?) off and visually inspect what is happening.  It almost sounds like something is leaking fuel at low engine speeds (has one of the jets fallen off or come unscrewed) that is not as noticeable at higher engine speeds.  For an electric choke, there is an adjustment on the Weber carbs that can make them quite rich at idle although it should go away once warm.

Link to comment

Checked it Wed after several sets and well warmed up.

Choke wide open, spark arrestor looks nice and clean.

Float levels correct.

Idle mix screws both needed closing about 1 turn and seems to have greatly helped the "smokey idle". Did notice when closing the left one too far, engine leaned out and died. Could not get that to happen closing the right side screw, even when closed all the way.

Will be interesting to see how it starts and runs next time out.

Thanks for all your input.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...