'70 25 hp 'rude - how well should it idle?

[BF]

Hi there,<br /><br />Just curious... my 25 hp runs great at WOT (where I use it mostly), but I always use a 6hp kicker to troll, partly 'cause it's quieter, but also because the 25 doesn't idle too great. It had all new ignition parts the beginning of last season, and I also did a carb kit, thermostat, impeller and plugs. It runs great from fast idle up.<br /><br />Slow idle is a bit rough, and it invariably stalls every few minutes. Restarts easy enough. I've optimized the idle mixture... (gets worse in both directions). <br /><br />Any ideas? Or do these older point ignition ones just not like idling that great? (I doubt that... my 6 hp has points, and doesn't stall in hours of trolling).<br /><br />thanks in advance

 

[CATransplant]

Re: '70 25 hp 'rude - how well should it idle?

Well, it's not the point and magneto system. My old 1958 35hp Big Twin idles like a dream. It will just go blub-blub-blub all day long if you like. About 500 rpm, maybe. It trolls at under 2 mph.<br /><br />So, it's not the ignition system on your boat, which is almost identical to mine. A rough idle is usually a low-speed circuit problem in the carb, bad plugs, or some other such thing.<br /><br />I'd start by working with the low speed needle setting. If that doesn't do it, then I'd give the carb a good disassembled cleanout, including a good soak in carb cleaner and a blowing out of all passages in the carb, removing any welch plugs to get access to the internal passages.<br /><br />Also, check compression. It will idle better if both cylinders are even. Check for any air leaks anywhere in the fuel system, as well.<br /><br />Your 25 should idle just fine.

 

[BF]

Re: '70 25 hp 'rude - how well should it idle?

thanks for the speedy response...<br /><br />as mentioned, I did the carb kit thing last season. It's idled this exact same way since then. (and I didn't have it before that) and yes, I'm pretty sure I did a good job. Yes, I pryed out all the little plugs (welch plugs I guess?) and the lead shot so I could actually see that the low speed orifices and all passages were clean. Also, I used the kit that replaced the float and needle valve too.<br /><br />I didn't mention, but the engine has great compression. 125+ on both (it had seen very little use).<br /><br />I'll look into the air leak idea. Maybe I'll try new plugs too.... at least it's encouraging that it should be able to do better. Certainly I'll look into it.

 

[BF]

Re: '70 25 hp 'rude - how well should it idle?

so an update.... I had a few minutes to look at it last weekend. I swapped out the NGK B7S's that were in it with J6C's and the idle improved quite a lot (still not great).... but; then I noticed that the upper plug wire was pulled almost completely out of the plug boot. Hmmmm... I pushed it back in, but I think the end of the wire inside the boot is shredded up a bit. Anyway, the jury is still out whether the plugs were an issue at all, or whether it was just I had jiggled a plug wire that was going bad. Next time I'm out, I'll trim 1/2" off the plug wire and put a new end on it. When I'm sure the wire's good, I'll try both champion and NGK's and see if there's a difference. For NGK's I think it should've had B8S's in it anyway. That's a hotter plug and listed in the service manual as the alternative to J6C's.<br /><br />Also... the link and synch wasn't spot on... butterfly opening too early. That also helped to some degree.<br /><br />anyway... hopefully I'll get it sorted out next time.