DUI Timing adjustment help..... and MSD parts interchangeable?
 

I have a DUI on my 489 stroker making 537hp/594tq but am having a hesitation / bogging issue when getting on the throttle from idle while trying to come up on plane.... I am running a Speed Demon 850 carb that was on the motor when being dyno'd but has kind of had the bog all along...
I sent off a spare Holley 750cfm to Nickerson Performance to build up to my exact specs of the motor, cam, heads, etc.... BUT I want to make sure everything is on point with the ignition as well.

That said I am running a DUI distributor with initial timing of 12deg and total of 36... AFAIK, the distributor is all stock inside besides replacement cap/rotor...
One of the guys at Nickerson said to run the medium silver spring on one side, and the heavy gray spring on the opposite, and install the black heavy bushing. BUT these are MSD parts he is referring to... When I check into DUI it seems as if they dont sell the parts to adjust the timing curve but you need to send it back in to them.... Normally thatd be OK but I dont want to send it in with the beginning of the season coming.

Are the MSD HEI parts interchangeable with the DUI HEI so I can try out the combo they are recommending??

That said, does my symptoms point to a fuel or timing issue??

Thanks in advance....
Chris

Sounds more like a fuel issue to me.

That's what I was thinking... The boat will idle fine and once it is cruising, there is no lack of power or hesitation at all.
Just was thinking maybe timing advance issue but sounds more like accelerator pump or powerjet, no?

It sounds like a lean spot in your carb tune. It's fine at idle under no load but stutters when tasked? I'm no expert on the matter but that's been my experience tuning motorcycles.

You have to send your distributer back to DUI for a change. I've only called them once about a different issue but a real person picked up the phone and was technically competent. I'd wait until you try the new carb first though.

Do yourself a favor and buy a decent carb. Speed Demon=junk. Nickerson modified carb = bigger piece of junk. Buy a new Holley or a Quick Fuel and go boating. After you recover from the sore rectum you recieved from dealing with Nickerson get a decent ignition.

Sounds like the accelerator pump is bad, not properly adjusted or too small.

will run better with more base timing, but your issue is in the carb, also the 850 @ that power is iffy, 750-800 much better choice

Thanks for all the replies.... I'll ignore the timing for now as I know it's set properly and advance comes in good... I'll see what Nickerson carb acts like, and in mean time am going to try fine tuning the Speed Demon. If neither work out I'll be buying something new like Black Baja suggested....
Thanks again guys

I sent my DUI's to them for a tune and had them back working flawlessly within a week.

What would you suggest for initial/base timing? What's usually best for total timing too thats still safe?

I have no idea what ideal timing would be but my DUI is giving me 18* at idle and 36* max on my 502.

34 to 36 total for an engine like yours. Big cams allow more initial timing for a quick,cleaner start.You want the motor to have as much initial timing as possible without kicking back or dragging down the starter and at the same time still have plenty of initial timing to get quick,easy starts.This will also help with a nasty,rich idle and will give you a better response to carb adjustments. The amount of advance in an MSD is adjustable by changing the bushing you mentioned earlier. The black MSD bushing gives 18* of advance. When set at 36 total you would have 18 initial. Not sure what DUI does to control the amount of advance in their distributors. Question, does your engine idle strong and clean or weak and rich?

I guess from what im reading you have no choice but to send the distributor back to DUI... It seems as if the engine idles OK, but if anything Id say a little rich. Never stalls in or out of gear....


Thats about the timing that one of the guys was telling me... Did you have DUI set the distributor to 18* advance when you bought it or were you able to adjust yourself?? Mine has 24* advance built in...

Thanks, Chris

I've had a 850 Sea Demon and 650 Sea Demon. Both where great.

I had a friend of a friend of a friend's dad who owns a carb/ignition shop and I gave it to him to check out. I had no idea what he did until I just checked my timing last night. I don't know how it came from the factory but it seems to work well with my motor.

On a side note - when starting her up after the winter the tach doesn't work. It's entirely possible that I hooked the power wire to the tach lead at one point but can't be sure and it's possible the 20 year old guage gave up the ghost. I tried checking the tach lead while running with a test light but it just glowed steadily. I checked the interwebs on how to check the distributor signal but to no avail. Any tips? Sorry for the thread jack.

DUI has no user adjustments, but they have always helped everyone I've seen writing about it. They individually curve each diz for your needs.

To check the tach check the tach terminals for running voltage at the power stud, ground at the GND stud. And if you don't trust the gray wire run a temporary jumper from the coil negative to the signal stud on the tach. If it doesn't work Mercruiser says dump it. They don't give a test.
Tachometers can fail, my 88 took a dump in 2010, made my engine stumble too. POS, only lasted 22 years in a wet outdoor environment!