slight stumble in '65 40 selectric

[dafox99]

Guys,<br /><br />I love my big twin. Idles great, starts great, top end is perfect. While it's not a big problem, it's more of a nuisance ... right in the mid range (I don't have a tach .. maybe 2500 - 3000), it has a slight stumble/miss. Runs perfect just below, and just above. I've tried to richen the low-speed jet at little, but I don't think it's helping. Is this a characteristic of the motor, or do I have something a little off? Carb is recently rebuilt, new coils, new plugs. I haven't de-carbed in a loonggg time (could that do it?)<br /><br />Thanks.

 

[Paul Moir]

Re: slight stumble in '65 40 selectric

Just off the top of my head, but have you got the carb synced properly?<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=033290#000006 <br /><br />The only other thing that occurs to me is in the mid-range the ignition system is working it's hardest & it's not the most powerful in the world to begin with. Try buffing out the points and getting it all set up deadly. See if that doesn't help.

 

[dafox99]

Re: slight stumble in '65 40 selectric

Very colorful engine! That yours? Hmmm. I may have mine set up a tad different. As I read your instructions, the throttle should start to move when the cam mark is at the manifold pointer. I didn't really check that. I set my cam roller so that it touched at the cam mark and ignored the manifold pointer (heck .. didn't even know I had a manifold pointer). I'll buff the points as well. Any suggestions on point gap? I think I had it set to .020 .. that sound right?<br /><br />thanks!

 

[Paul Moir]

Re: slight stumble in '65 40 selectric

That could be your problem then. I made up that post because the description in the Seloc manual is so poor at describing the procedure. <br /><br />0.020" gets a Big Twin to where it needs to be. If you have a timing light and some time to spend, you can set it exactly. But it's not going to make much difference on these.<br /><br />Click my "Man-Next-To-House" icon to see the whole engine. That's a 28hp which is a economy engine. It doesn't have the super-quite mid-section like yours, but a lot of the parts are the same or similair.

 

[dafox99]

Re: slight stumble in '65 40 selectric

Well there you have it, then. That should be an easy adjustment. I'll give it a shot. I do have a timing light, but I think I'll just take some 400 grit to the points and re-set to .020.<br /><br />VERY cool motor!

 

[Paul Moir]

Re: slight stumble in '65 40 selectric

Thanks. <br /><br />If you don't mind, have a look at the RD-23 post a few down. I'm wracking my brain trying to think of what would cause a clunk when reverse is engaged on one of those, but I don't have one here to really look at. I'm thinking he's got the reverse lock screwed up or perhaps it's something simpler...

 

[dafox99]

Re: slight stumble in '65 40 selectric

Jeez .. we are all typing at once on that one. By the time I told him where the lock was and to check a couple things, you and another guy already had two posts! You guys are fast!<br /><br />I think we need to better define "jump" on that one. Deciding it's normal is asking for trouble, IMHO.

 

[dafox99]

Re: slight stumble in '65 40 selectric

Hey Paul. finally did the re-link'n'sync. Tah dah! Runs perfectly throughout powerband. I didn't touch the points as I was wanting to know which fix fixed it. I hate it when I do three things to something and then don't know which one did the trick for next time. One question .. I think I've been setting up these old motors wrong for years. I've always adjusted the roller so that it touched the mag plate at the mark. Did all these motors setup the same?