Engine has trouble idling down
 

Have a mild build 350 in my boat and sometimes (most times) it has a hard time idling down. Sometimes I have to shut it off and restart a few times to get it down to a reasonably safe shift rpm. Engine has LT4 hot cam, 650 demon with electric choke, v6-14 ignition module. Base timing is set around 22 degrees. Could the choke linkage be hanging or maybe to much timing? I've killed 2 drives in the last year and I'd like to get the idle down to about 650. Also, the idle screw adjustment on the throttle linkage is backed all the way off

possible throttle cable problem so unhook the cable and work the throttle by hand blipping it and see if idle returns how it should ?

Also check for resistance in the throttle plate shaft possible bent or stuck or corrosion issues

also adjustment on carb out of spec for your app

also a vacuum leak somewhere at base of carb or intake

Also check timing

make sure your distributor can not rotate - check hold down clamp

87 Magnum - is this right after running WOT ?

Most BG vacum secondary carbs, especially with lighter vac secondary springs, will do this.

The trick; shift to neutral, shut off engine and restart....idle should go back to normal.

You will kill an Alfalfa almost instantly with too high rpm shifting into gear.

BTW: choke has nothing to do with it as I remove the chokes from most all carbs and these will still do it.

22* base timing?

I was thinking at start up - and after engine was warmed up and choke fully opens - does your choke fully open - and he is waiting to put it fwd gear or rev off the trailer ?

so when does the high idle always happen

Backing off the idle speed screw won't lower the idle rpm without adjusting the cable too. Take a look, you'll see why.

Hey guys I got this one...Lol. Sounds funny, but Yes, I'm serious.

The secondary spring doesn't have enough tension to close off the secondaries with air running thru it. Shutting off the engine, stops the airflow. The low tension spring can now close the secondary throttle shaft.

I run into same issues with some throttle bodies with weak throttle shaft springs. And this make carburetor.

^^^^^ exactly and the reason I said to unhook the throttle cable - that will tell you right away if your cable is out of adjustment or bad / needing replacement - the boat is an 1987 is this original throttle cable ? 19897 very possible throttle cable problem

post 7 - I am referring to.

Also when is your high idle ?

29 year old throttle cable or NO - new one was installed ????

And throttle cable correctly adjusted for aftermarket carb whether the cable is old or new - Yes or No ?

I can take you out in a ride in a few boats tomorrow with same carburetor he has that does this too. I can also put in a higher tension vac secary spring that will stop this from happening. Issue, is that it will cut engine power down a decent amt too.

One restart will typically make it go back down to normal idle. Once in a while, 2 restarts.

As far as post #7 - you are correct. Most people don't realize the solid Morse cable combined with a throttle lever doesn't work the same in reagrds to idle speed the same way a gas pedal and carb with a return spring does.

example:

" take your foot off your cars gas pedal and the throttle returns to idle position.

take your hand of the boats throttle lever and it stays where you left it. So, when you put lever in neutral (idle) it leaves carb idle position where the cable dictates.

New cables three years ago. It's a mechanical secondary, not vacuum

SB can I take you out in mercruiser TKS carb app and we will see how high that idle is at start up - talk about high and very load noise - really a poor carb by mercruiser - freakin 110 degrees down here and the carb takes 5 mins to warm up and return idle to normal.

Rut row he says mech secondaries

Rut row is right !

I don't have this one.

Ha !

Your funny sometimes - we can come up some good ones - oh just sometimes we can

Sorry about that. Wasn't even thinking about that when I posted

Actually, it is basically the same I'm talking about. The wound spring on the throttle shaft does not have enough tension to fully seat the secondary throttle shaft. With vac secondries, the vac spring helps (a little) push it back also.

Before trying to add tesnsion, make sure your sec throttle blades are centered (loosen blad screws and open/slam shut throttle a few times to center them) and make sure t blades don't have rough edges that are slightly catching throttle bores.

Sorry, I'm typing in the dark. I do not cell phone text.

edit in; remark is for my bad typing tonight.

I tried to PM you but your folder is full

I will add that Demon Carbs Barry Grant had their share of problems in the marine world - he had even some lawsuits and federal marine recalls for his carbs. So did Holley with Volvo. here is a look at the Volvo service bulletin as we use to have problems with their carbs. read it

http://www.marinemechanic.com/volvo/...2010/23-1-22_A[1].pdf

Hold what I said above for a day. I have another idea (my vac secondary idea works because I've dealt with a few of those) - that I have to check out in person first.

I'll try to remember to do this.

If you boat tomorrow, turn off engine and retsrat. if hung idle, shut off and restart again.

Never, ever shift an Alpha over 800 or so rp. 1k and over it;s a done deal within 1 to 2 to 3 to 4 or so shifts.

Same reason my cell phone voice messages are full.

edit

Cleared some PM's.

Strike two.

One more, you are out, and have to sit back down in the dugout. LOL.

google

volvo penta demon carburetors

we had problems with them also make sure your throttle cable is hooked to the correct spot on the arm. Volvo has a SB about that one to.


I can not post them for some reason.

Demon had a lot problems on the marine end.

Here Bup - this should work;

http://www.marinemechanic.com/volvo/volvo/2010/23-1-20_A[1].pdf

Strike three.........you are out ! LOL.

When links are too long to post on it's own, click on the 'link' tab (in between the emotican tab and e-mail tabl) and enter the url where it asks you to. Watch out, it already puts the http:// part in for you.

Thanks thats one of the many - I am telling you Demon had a lot problems that people were unaware of. Holley to. I wish I could pull up all the federal stuff and post it.

Heck we had hell with a lot of them and had to send a lot back years ago

http://www.marinemechanic.com/volvo/...2010/23-1-22_A[1].pdf

Ok post this to thank you Sometimes I hate the ne

I told you above how to do it. LOL.

Here:

http://www.marinemechanic.com/volvo/volvo/2010/23-1-22_A[1].pdf

hell I am too stupid to figure it out. Jeepers My puter sucks thank whomever I do not have diacom loaded on this one. I told you and asked how are you so good at finding a lot on the net ? remember Still can not believe you found that Training manual online that I sat in on in the Volvo class for that year.