350 carb stolling shifting
 

This is a new 2014 383 stroker with holley 750 (marine) carb. When I shift it seems to overload the power of the engine at idle. It sputters for about 5-10 seconds and eventually will Stoll. Drops the RPM to about 200 from 900.
It's not the shift interrupter switch. It's not a tight cable. It's not timing.
I've changed the power valves to smaller ones 3.0 with no difference.
Thinking about putting Niger idle jets. I've also adjusted the carb with a vacuum gauge with no difference. Any ideas.

How many hours on carb since new or rebuild? Also make sure you have the correct meter block gaskets as well as there in the correct location. I've seen the bowls get screwed in place from holly as well as the demon carbs and the gaskets are not lined up causing air / fuel issues resulting in similar situations. Just a thought any way just in case you didn't ck gasket alignment as well as the proper ones. Seems odd though if the issue just surfaced though.

Also do you have a Vacuum leak somewhere and also maybe ck with a vacuum gauge to see what you have. Make sure your idle air mixture screws are functioning properly. When you say it sputters I asssume its rich and stalling out correct?

Oboy, shift interupter switch means Alfalfa , and the 900rpm drop in gear is beating it !

Whose Niger ? And what's an Idle Jet ?

Are sure its not the shift interrupt switch ? If not then possible misadjusted intermediate shift cable or that shift cable is BAD . If too much resistance is in the workings of the intermediate shift cable when shifting into gear, the engine will stall everytime. 900 rpms is too high for an alpha outdrive and its dog clutch set up. You are wearing the hell out of it.

Q 1 = president. Q 2 = Air Force 1 while (Q 1) kickin it on the golf course.

You say its a 2014 383.. What Manufacture or builder? . What ignition system are you using?

Chris

Niger HUH. LOL. Not sure what I was thinking. I meant BIGGER jets. Allow more fuel??
I have adjusted the carbs with a vacuum gauge with no improvement. Yes I have twins. Same problem both engines. Running Thunderbolt IV ing.

No Alphas here slick. Not with 500 plus HP.

The engines were built by a local builder. From the new block up. Very tight build. The engines have ran this way since the carbs were out of the box a few years ago.

It is definitely a carb issue. I'm going to make a call to Holley tech and see what they have to say.

Its just funny how it can run through all RPM's perfectly, idle at the dock all day long. Put it in gear and it gets dropped to its knee's.

If you actually have 500hp 383's, they will need more initial timing than what the TBolt IV 'normal' modules will give you when your total timing is set correct.

As a close guess, you'll need somewhere between 14-18* initial timing. And that should help things greatly, assuming your carbs aren't way off.

What do you hve for tbolt ignition modules ? 22's or 24's ?

There are no idle jets per say, there are idle feed channel restrictions...but I'm thinking that may be beyond your scope.

Anyway, tuning the carb does nothing without the timing being correct.

I see this problem a lot when auto engine guys build boat engines.

If they idle perfectly out of gear and at all RPM and don't smoke or load up anywhere its likely not the carb - its likely you have a combination of too much cam as well as not enough timing at idle (as SBC mentioned) and a stock Tbolt 4 wont give it to you.

Curious if you know you have 500HP - you should have a dyno sheet which will indicate timing at idle and WOT. The builder should have tuned the carb on the dyno on one engine at min and then copied the settings over - or optimally dynod both to insure you didnt have a vac leak and that they were both consistent.

Was that 500HP dynod on wet or dry exhaust? You would be one of only a few guys with a true 500HP out of 383's in an outdrive boat what kind of exhaust are you running?

My 500HP 406 was on the edge of idling in gear so I know the problem you have.

UD

What I want to know were did the shift interrupters come from and are both motors doing this. More details are needed.

OK. Now we are getting somewhere. I have my initial timing set as high as possible. In the neighborhood of 18. Basically I set the idle to 36 degrees while running engine at 3000 rpm to make sure I got max timing at RPM. When the engine is at temp it starts at the touch of the key. Anymore timing and it drags.
The build was based on a recipe from a Marine engine builder. Custom cut cam, AFR 195 heads, EMI Thunder exhaust, Edelbrock performer RPM air gap intake with the 750 carb topping it off. 509 HP was suppose to be the outcome.

If the thunderbolt ign won't give me the timing required, where do I go from there.

This boat was originally an Alpha boat. Swapped out many years ago to Bravo's.

There is no 'basically' nor 'in the neighborhood' in tuning vocabulary, especially with timing.

Most TBIV advance modules do not stop advancing at 3000rpm. Some go as high as 4200rpm before advance hit's it's peak timing.

Keep reving the motor until it stops advancing and then rev it 200-400rom more to double make sure the advance has stopped increasing.

Does your carb have 2 or 4 corner idling mixture screws ?

"This boat was originally an Alpha boat. Swapped out many years ago to Bravo's." - I guess thats where the interrupters came from...

Can you get the #'s on the stick? - all the timing in the world at idle may not save you.

I ended up running the whole engine advanced a few degrees which got it to work down low with my top end combo.

SBC - 4 corner idle - on a marine 750? Cool - didn't know they had it. Have it on my demon.

"EMI Thunder exhaust," - and 500HP out of a small block 383 are two things Ive never seen co-exist on an actual dyno chart.

I'm guessing if it was even dynod it was done on a dry exhaust.

UD

Damn this is like dragging the info of what happened in a wreck out of the person that caused the wreck...lol.. The no alpha drive info would have been good 10 posts back. If its ANYWHERE close to 500 hp, for a 383 this would have a cam so big it is probably reverting water and putting out the plugs as soon as he puts it in gear.

Chris

All small blocks are 500hp. Did you not know that ?

Only If they have lots of chrome on them and a double-stacked air filter.... Everyone knows that..

OP, throw the interupters in the garbage

I am still wondering if no alphas how did testing the shift interrupter switches come into play and tested good ? post # 1

Mercruiser offers a 383 and has been for years. I think you still can get a carb app 383 - it comes out of their reman / repower division and is a drop in.