How do I adjust the idle speed of a 97 Challenger

[Scott Campbell]

Greetings. After having some work done on my carbs one of my engines idles quite high. Not sure how high as the tachometer for this engine is broken. How do I slow it down?

TY

 

[Guest_User]

Greetings. After having some work done on my carbs one of my engines idles quite high. Not sure how high as the tachometer for this engine is broken. How do I slow it down?

TY

single or dual engines?
you should get an inductive tach and not try and guess... in water should be 1500, and out of water, as in when flushing would be 3K+-.

you also need to verify if the throttle cable or steering assist isn`t hanging up the throttle.
Now, in quite a few cases the MAG carb seems to stick at the throttle shaft. a simple test would be to start the boat in the water, as it is idling high as you describe, reach you hand under the airbox and see if the throttle linkage can be moved to slow down the idle. If it can, then you either have the throttle shaft sticking or the cable...
It is a crazy procedure to check and make sure everything from oil injection pump cable travel, throttle cable tension free at WOT, and the steering assist all at the same time... including a reference/index mark on the linkage attaching the 2 carbs together to check for carb sync. assuming you have the 787 engines.

this worked for me by the book for base idle adjustments, and it was very very close to 1500 in water idle.

turn the idle speed screw (T) out until the throttle plates are closed or there is a gap between the end of screw and carb tang/lever. Now turn in the idle speed screw (T) until it just comes in contact and touches the carb tang/lever. Turn the screw in 2 full turns!... this should get you in the ball park...

There are a few aftermarket tachs that run off the spark plug wire... Tiny Tach commercial, made by Designs technology, and TTO, hardline and a few others you can find on Amazon... here is the link for the TT commercial unit...

http://www.tinytach.com/

hope this helps somewhat...

 

[Scott Campbell]

Thanks. I have the twin 787s. I'm pretty sure it is a screw adjustment as the guy how worked on it said he turned one back 1/4 turn as the screw was all the way in and he did not think the engine would run if the screw was all the way in. I'm not sure which screw he adjusted though and reading some of the other posts hopefully it was not one of the lean/rich screws or I will risk damaging the engine. So which screw is the "idle speed screw" that you mention above? Thanks also for the tinytach suggestion. I wouldn't mind getting my tach working (one works the other doesn't) - any tips on diagnosing the parts that needs to be replaced to get it working would be appreciated. My fuel guage also doesn't work but the oil low light that is part of the fuel gauge does.

 

[Guest_User]

Thanks. I have the twin 787s. I'm pretty sure it is a screw adjustment as the guy how worked on it said he turned one back 1/4 turn as the screw was all the way in and he did not think the engine would run if the screw was all the way in. I'm not sure which screw he adjusted though and reading some of the other posts hopefully it was not one of the lean/rich screws or I will risk damaging the engine. So which screw is the "idle speed screw" that you mention above? Thanks also for the tinytach suggestion. I wouldn't mind getting my tach working (one works the other doesn't) - any tips on diagnosing the parts that needs to be replaced to get it working would be appreciated. My fuel guage also doesn't work but the oil low light that is part of the fuel gauge does.

that would make me a little nervous right there of the guy who worked on the carb did not know the difference between the idle screw, Low speed adjuster and high speed adjuster without any further explanation. The only adjuster that comes to mind with you saying it was closed so "he opened it up a 1/4 turn" would be the HS adjustment. They are closed slightly and provided enough fuel for a stock engine. Turning it out 1/4 turn will just make it a bit rich. but that did not correct your idle adjustment issue...

My suggestion would be to obtain a shop service manual download or purchase one so you can get familiar with the different screw/adjustments and what they do, or serious damage could def result.

I believe if you follow the throttle cable to the throttle wheel where it is attached to the carb, under that you`ll see a screw that looks like a "T" on the MAG carb.
where you can plainly see that it is the idle speed adjuster. this is what I was referring to, 2 turns in from just making contact.
The low speed adjuster also looks like a T, but it is threaded into the carb body and the opposite end is not visible.
The High speed adjuster is also in the carb body and should have a black plastic limiting cap on it to prevent more than 1/4+ turn out.

at this point you should check that the carbs are in sync, correctly adjusted, and the cables adjusted for full pull without putting undo stress on the carb linkage...

 

[Scott Campbell]

that would make me a little nervous right there of the guy who worked on the carb did not know the difference between the idle screw, Low speed adjuster and high speed adjuster without any further explanation. The only adjuster that comes to mind with you saying it was closed so "he opened it up a 1/4 turn" would be the HS adjustment. They are closed slightly and provided enough fuel for a stock engine. Turning it out 1/4 turn will just make it a bit rich. but that did not correct your idle adjustment issue...

My suggestion would be to obtain a shop service manual download or purchase one so you can get familiar with the different screw/adjustments and what they do, or serious damage could def result.

I believe if you follow the throttle cable to the throttle wheel where it is attached to the carb, under that you`ll see a screw that looks like a "T" on the MAG carb.
where you can plainly see that it is the idle speed adjuster. this is what I was referring to, 2 turns in from just making contact.
The low speed adjuster also looks like a T, but it is threaded into the carb body and the opposite end is not visible.
The High speed adjuster is also in the carb body and should have a black plastic limiting cap on it to prevent more than 1/4+ turn out.

at this point you should check that the carbs are in sync, correctly adjusted, and the cables adjusted for full pull without putting undo stress on the carb linkage...

Thanks for the great info. The work he was supposed to do was just to clean the carbs as a preventative maintenance task but ended up turning one of the screws as I mentioned. It did not idle fast before he cleaned the carbs. Would turning the high speed adjuster screw or the low speed adjuster screw change the idle speed of the engine? If not than I would guess that the screw he adjusted was the idle screw.

 

[robomatic12]

Changing the low speed adjuster can change idle speed. You will want to verify it is close to OEM specs. The 787's should be 1.5 turns out.