Having just purchased my '86 340 DA a week ago, my surveyor pointed out that the Starboard engine was not idling down as far as it should (950rpm). Figured a simple back off of the idle screw, but nope! That engine will start and warm up fine, then will not drop to 700. If I shut it off and restart will idle at 700 until I move the throttle, then will not drop below 900 even though back on the stop. My carb guy suspects the timing advance is hanging up...any other ideas before I rip the carbs off for rebuild?
Quirky 454 idle issue
- Thread starter Cbach
- Start date
CliffA
Well-Known Member
- Dec 29, 2009
- 4,712
- Boat Info
- 2001 Sea Ray 340DA
Name: 'Happy Place'
4.5kW West. Generator
Purchased Nov. 2014
Fresh Water Use
- Engines
- Twin Merc. 6.2L (MPI)
640 hp (Total)
Raw Water Cooled
V-Drive Transmissions
what type of choke system does the carb have?.....if it has the type that incorporates a 'fast idle cam' it may be possible that the settings of this cam are not exactly right and the choke is not pulling off all the way once the engine is warm.....
it probably would not hurt to place a few drops of PB Blaster cutting oil on the timing weights in the distributor....if the weights are hanging up some the PB Blaster may clean out what ever is causing them to stick.....
you could also run a can of Sea Foam carb/injector cleaner through the carb while the engine is running to see if it can clear out any blockages in the carb....let the engine warm up and run at around 1,000 - 1,200 rpm and SLOWLY pour the Sea Foam directly into the top of the carb just a little at a time...the engine will likley stumble a few seconds and then clear out and run smooth again...you may even see some smoke come out the exhaust...keep doing this until the whole bottle of Sea Foam is gone...you will likley want to either clean or replace the spark plugs after this since the Sea Foam will loosen any carbon that has built up on top of the pistons...this carbon can/will build up on the plug firing tips and can cause some misfiring until the plugs are cleaned or replaced...
good luck...
cliff
Last edited:
hottoddie
Well-Known Member
- Jan 11, 2012
- 2,230
- Boat Info
- 1986 Sea Ray 390 EC
Garmin 4212 Chartplotter
Garmin 24 HD Radar
Garmin 546s Plotter
- Engines
- 454 Crusaders
Are the engines Mercruiser or Crusader? They use completely different ignition systems.
They're Merc's and the engine in question is a new Jasper long block with the original QuadJet and mechanical choke. I'm sure the carbs need rebuilt, but even so a carb issue doesn't really seem to coincide with what it's doing. The gas is old but was stabilized, and weather permitting I'll get a couple cans of Seafoam in both tanks and some fresh fuel and filters in them this weekend, along with inspecting and lubing the weights in the distributor and fogging the carbs with Seafoam. What's the desired idle speed on these engines? I assume 650-700.
Thanks for the inputs!
Thanks for the inputs!
Last edited:
dlvwill
Member
Check for worn throttle shafts/bore in the base plate of the QJet. They can bypass enough air to case the high idle problem. May explain why it shows up after a restart after moving the throttle.
CliffA
Well-Known Member
- Dec 29, 2009
- 4,712
- Boat Info
- 2001 Sea Ray 340DA
Name: 'Happy Place'
4.5kW West. Generator
Purchased Nov. 2014
Fresh Water Use
- Engines
- Twin Merc. 6.2L (MPI)
640 hp (Total)
Raw Water Cooled
V-Drive Transmissions
that is the correct idle rpm range for my 5.7L (350 cid) according to my Merc service manual, so i would 'assume' the same range would be used for your 454.....don't know for sure though..
cliff
hottoddie
Well-Known Member
- Jan 11, 2012
- 2,230
- Boat Info
- 1986 Sea Ray 390 EC
Garmin 4212 Chartplotter
Garmin 24 HD Radar
Garmin 546s Plotter
- Engines
- 454 Crusaders
While the throttle plate on a Qjet can cause a problem it's not very common in the marine application only because the throttle on a boat is not moved much and the engine hours vs. automotive is low so therefore less wear. I would disconnect the throttle cable and operate the throttle by hand and see if it changes. Could be a sticking or worn throttle cable.
To the OP the distributors on the Mercruiser do not have springs and counterweights, The advance is all electronic. The Crusaders have mechanical advance with springs and counterweights like mine. Check the 4 bolts (studs) that hold the carb to the manifold as the base gasket will compress over time and may cause a vacuum leak.
CliffA
Well-Known Member
- Dec 29, 2009
- 4,712
- Boat Info
- 2001 Sea Ray 340DA
Name: 'Happy Place'
4.5kW West. Generator
Purchased Nov. 2014
Fresh Water Use
- Engines
- Twin Merc. 6.2L (MPI)
640 hp (Total)
Raw Water Cooled
V-Drive Transmissions
i thought about a vacuum leak also being the cause of the high idle but i believe that would be constant while the engine is running....the OP stated the idle rpm's drop back to normal if he shuts down the engine and restarts so i am thinking that rules out a vacuum leak.....i agree that a sticking throttle cable or carb linkage may be the problem....
cliff
cliff
Sticky or misadjusted linkage was my first guess, but I verified it was coming fully back against the idle screw. If a quick inspection, new filters, fresh fuel and some Seafoam ingestion doesn't prove out anything in the morning I'm going to swap the carbs to isolate them.
CliffA
Well-Known Member
- Dec 29, 2009
- 4,712
- Boat Info
- 2001 Sea Ray 340DA
Name: 'Happy Place'
4.5kW West. Generator
Purchased Nov. 2014
Fresh Water Use
- Engines
- Twin Merc. 6.2L (MPI)
640 hp (Total)
Raw Water Cooled
V-Drive Transmissions
just for giggles before you swap carbs you may want to consider the suggestion from 'hottoddie' (love that user name) and disconnect the throttle cable from the linkage and rev the the engine by hand a few times to see if the idle rpm's drop back to normal...i have seen even the slightest amount of adjustment error in the cable cause the idle rpm's to be high even though the carb arm appeared to be completely snubbed against the stop...then if that doesn't work your idea about switching carbs around is a good one to see if the problem follows that carb....
cliff
But, if he turns it off and turns it back on it is fine....that seems to me it would not be the cable...
CliffA
Well-Known Member
- Dec 29, 2009
- 4,712
- Boat Info
- 2001 Sea Ray 340DA
Name: 'Happy Place'
4.5kW West. Generator
Purchased Nov. 2014
Fresh Water Use
- Engines
- Twin Merc. 6.2L (MPI)
640 hp (Total)
Raw Water Cooled
V-Drive Transmissions
hottoddie
Well-Known Member
- Jan 11, 2012
- 2,230
- Boat Info
- 1986 Sea Ray 390 EC
Garmin 4212 Chartplotter
Garmin 24 HD Radar
Garmin 546s Plotter
- Engines
- 454 Crusaders
Thanks Cliff
Like all good captains I named the boat after my wife (our last name is Todd). At 62 she still gets looked at all the time (and no surgeries to help). Also a Hottodie is a drink made with tea, honey and your choice of booze. I make sure the ingredients are on board at all times.
Ray
And that is why mine is named Always Starboard.
Hopefully this weekend will prove the end to my idle issues, as during investigation I found all the filters full of crap/rust, the timing on that engine off, both carburetors in questionable condition (full of crap, accelerator pumps not working, secondaries not fully closing), and on that same engine the connector inside the ignition coil was not there!
It's all going back together with new parts and rebuilt carbs Saturday, going to feed her a few hundred in fresh fuel and Seafoam, then out on the lake to see what happens. While I do love working on it, it's time for a little R&R while sipping a glass of Glenfiddich 21
It's all going back together with new parts and rebuilt carbs Saturday, going to feed her a few hundred in fresh fuel and Seafoam, then out on the lake to see what happens. While I do love working on it, it's time for a little R&R while sipping a glass of Glenfiddich 21
CliffA
Well-Known Member
- Dec 29, 2009
- 4,712
- Boat Info
- 2001 Sea Ray 340DA
Name: 'Happy Place'
4.5kW West. Generator
Purchased Nov. 2014
Fresh Water Use
- Engines
- Twin Merc. 6.2L (MPI)
640 hp (Total)
Raw Water Cooled
V-Drive Transmissions
Hopefully this weekend will prove the end to my idle issues, as during investigation I found all the filters full of crap/rust, the timing on that engine off, both carburetors in questionable condition (full of crap, accelerator pumps not working, secondaries not fully closing), and on that same engine the connector inside the ignition coil was not there!
It's all going back together with new parts and rebuilt carbs Saturday, going to feed her a few hundred in fresh fuel and Seafoam, then out on the lake to see what happens. While I do love working on it, it's time for a little R&R while sipping a glass of Glenfiddich 21
good luck...from your description of what you found i am surprised the engine ran at all.....you are doing the right stuff...i am betting the engine will run well for you after the work....i know all to well what you mean about working on a project to the point you need a break....i used to own a 1994 Jaguar XJ6 that required me to spend more time working on it than driving it....eventually had enough and sold it......but it was sweet to drive when it was running good....
cliff
Now it's just pissing me off! Everything back and still the same issue. Verified it's a timing issue though, as it's fine when cold but as soon as there's a little heat in the engine it stays advanced and will not drop back into base timing, which is what's causing the high idle. Weird that it clears after shut down and comes back with RPM increase. Into the distributor tomorrow for a checkout, clean and dielectric all connections/ground, then I guess a new module on order if it doesn't clear up!
hottoddie
Well-Known Member
- Jan 11, 2012
- 2,230
- Boat Info
- 1986 Sea Ray 390 EC
Garmin 4212 Chartplotter
Garmin 24 HD Radar
Garmin 546s Plotter
- Engines
- 454 Crusaders
If these are Crusader 454 with Prestolite distributors then it is likely the advance mechanism in the bottom of the distributor. Either the springs are broken, stretched or the counterweights are sticking. You will not find the springs as they were discontinued many years ago. I know where to get suitable replacements. Most people replace the whole distributor with Delco HEI units, but make sure they are marine rated.
No sprung or weighted advance mechanism in these Mercs. Swapped the modules..no change, swapped distributors..no change, so ignition is out. Got frustrated at the whole thing and decided I needed, after a month of owning and never leaving the slip, to at least get out on the water. Carbs are fat, which the builder said they would be at factory spec, but then after putting around for awhile and running her up on plane, then coming back down, that engine wanted to stay at 1800 RPM!!! After playing with it a bit the idle came back down...and GET THIS, for the next half hour it ran perfectly, both in sync at 600 in gear, seemingly no more issue and I couldn't get it to recreate!
So I'm convinced I simply have a separated fuel issue, and the PO's statement that the fuel was only a few months old and had been treated may not have been the whole truth. How this explains the issue I'm not certain, but heck...it's about all I have left!
So I'm convinced I simply have a separated fuel issue, and the PO's statement that the fuel was only a few months old and had been treated may not have been the whole truth. How this explains the issue I'm not certain, but heck...it's about all I have left!
