Loosing RPM's 1984 454's

D

dwarren

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This is a carry over thread from SOC. I've replaced the Racor's since then. Still having same exact issue

This is weird, so a little back ground on this boat. New to me 84 37 Silverton. 454's, Carb'd. The previous owner had both tanks pulled and the bottom few inches cut out and re-welded with new bottoms. New fuel systems to both engines including lines, filters (nice new cross over manifold) and one carb rebuilt and one brand new (the engine in question has new carb). I did notice that the boat is hauling ass at 3100 RPM's and WOT was just at maybe 4k (although I didn't push it). I found out that the original owner had swapped the props out for 23.5" (don't know the cup) so that speaks to the lower RPM's (not that I necessarily am going to leave them on as I got the other set in my garage).

So, I've been running this boat pretty consistently and generally, have the feel for it. I had 12 people on a 2Hr ride round trip in some nautical weather this past Saturday and ran like a champ.

Yesterday, on my way back from a short run across the bay (ran great on the way out), the starboard side would not get above 2500 or so....just kept falling out of the hole. I jockeyed the throttle a little and gave it a few pumps. After a short time (felt like an hour but more like a minute) it crawled back up and stayed pretty solid at 3100 RPM's. It seems like the throttle play is off but not sure. at 3100 rpm's the boat usually cruises around 17 Mph. That sounds a little fast for that boat/weight but looking for insight
 
A friend bought some "premium" flex fuel line. This was for a 4-stroke O/B, but the rating would support I/B use. Lost power, couldn't keep it running, had to keep priming the engine with the squeeze bulb. Turned out this "premium" hose had an internal barrier (lining) that came loose and became a blockage. Replaced with "lesser" (but still approved) hose, problem solved. You like to think that a new item takes a variable OFF the table but in this case it put one ON.
 
I replaced the distributors on my boat and two others in the marina due to spark advance rusted. Six engine in all same problem all 454's, 1980's vintage.
 
I thought about that too, however, the distributors are recently removed/refurbished in past couple years when motors were pulled. I may do it regardless but I'm not sure it's my current problem. What kind of replacements did you use?
 
Check the advance with a timing light.
Used Prestolite distributors and 12 volt coils no more resistors.
 
If seriously considering distributor replacement , I'll suggest giving good consideration to the Delco Voyager EST Electronic Distributor kits with all-electronic distributor ( including advance unlike some other "electronic distributors", plus matching coil and cables. The 10 years I had them on my old blue engines they were 100% flawless.

http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-142.html

Read the "About..." :
http://www.michiganmotorz.com/ignitiondistributor-parts-c-32_41.html
 
Refresh my memory on replacement....how difficult? I did do it on a Carver I had years ago but can't remember how involved it got :0)
 
Replacing the distributor is much easier than putting a kit in and it also replaces the bearings.
 
I did the voyager kits a couple years ago, running great since. Not cheap though, it was 700 or so for the parts, and I had a local mechanic do it for around 350, I did not know anything about engine timing.
Really good ignition systems.
 
I'm currently fighting a similar issue with the 454 in my son's boat. (See this thread: http://www.boatered.com/forum/topic.asp?TOPIC_ID=196996 )

Short version: check your ignition timing on that engine as Jim mentioned above. If the automatic advance isn't working, you'll have problems getting the RPM up past mid-throttle range. (On my son's boat, the cutoff is around 3000 RPM, but it could be lower on your boat.) Basically it's around the point where the secondaries begin to open on the 4 bbl carb.

Also, given that your problem is intermittent (just as it is on my son's boat), it's far more likely to be an ignition/electrical problem than a fuel problem. (For the record, we now know his issue is with the ignition timing; it's most likely an electrical failure of the knock control control module which is causing the timing to retard when it shouldn't.)

However, we have spent a *lot* of time (and money) chasing red herrings in the fuel system on my son's boat - to the point where everything apart from the tank itself has now been replaced. And none of that helped. Before you go down the same path, I would take a hard look at the ignition timing first. (I wish we had done so!)

Adam
 
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