Idle troubles

[TAC_Double]

ok,

I have been working on this for a couple of weeks, I can't get the motor to idle very well. I have rebuilt the carb, new coils, points and plugs. Done the decarb.

When I first rebuilt the carb, I had the low speed needle back 1.5 turns. Fires right up. But when I back the throtle down, she stalls. The idle stop is no help. Went to the lake, she idles great, but no top end. barely could get the boat to move. I adjusted the plstic knob on the end of the throttle cable, and got the topend, but lost the idle.

What am I doing wrong? I have a manual, still not having any luck. makes for a long day when she stalls all the time.

1975 40hp 40555C

 

[F_R]

Re: Idle troubles

Will it idle with the control cable disconnected?

 

[TAC_Double]

Re: Idle troubles

no.. tried that. I just don't understand it

 

[Silvertip]

Re: Idle troubles

Idle speed and idle mixture are inter-related. Both of those adjustments must be made with the engine in the water -- not on muffs as there is no backpressure when running on muffs. Disconnect the throttle cable. Setting the idle mixture at 1.5 is only a starting point. You adjust idle speed so the engine will just stay running -- it doesn't matter at this point what the actual rpm is. Then adjust the mixture for best idle. Set the idle speed down and repeat the mixture adjustment. When the idle speed is set to spec, fine tune the mixture for best idle and then back it out about 1/8 turn. If you fiddled with the throttle cable, put the control box in neutral and while holding the throttle linkage against its stop, bring the end of the cable up to its attachment point. If the cable and linkage do not line up exactly (don't push or pull anything) adjust the trunion (threaded barrel on the throttle cable) until they do line up. Reattach the cable. Move the throttle lever full open. Check the throttle butterflies in the carb throat. Each should be perfectly horizontal in the bore. If not, you need to do a link&sync and you need a manual for that. Check your library.

 

[mudd_mickey]

Re: Idle troubles

Do you have Link n Sync instructions in the manual?

I'd try a link n sync then adjust the carbs. Here's a good post by Joe Reeves that should help but pretty much states what Silvertip said.
http://forums.iboats.com/showthread.php?t=167352

Are you just replacing stuff like crazy in hopes that fixes it or are you running tests on these components first? We assume you have compression and feel it's a solid motor otherwise.

Good luck.

 

[TAC_Double]

Re: Idle troubles

I do have the instructions. But they are a little hard to follow and the photo's suck. I'll give it a shot and see what happens...

I did a compression check and all is well. Both cylinders are sitting at 125psi. And the parts I replaced were needed. The coils were shot and the points were in need as well. This engine sat outside for about 5 years.

The motor runs great now, other than the idle issues. Once I get that worked out... I will be a happy boater.