1998 OMC 4.3 will not go over 2000 RPM

Papalax

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Jul 4, 2015
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I have a 1988 OMC 4.3 (Model 434APRGDP, also a second sticker with model 985269??). with a 4bbl Rochester Quadrajet. It starts and idles great, but won't go over 2000 RPM. It starts up and idles fine up to about 1800 RPM. Will get to wide open for maybe 5 seconds when cold though, then sputters out, back to 1800.

For this so far, previous owner:
* replaced fuel lines (tank and engine)
* carb cleaned

I ran sea foam thru for about a tank full at the slow speeds and it seemed to get a tiny bit better. I wanted to use it more this weekend so I:
* had carb cleaned (but not rebuilt yet)
* replaced corroded anti siphon valve
* replaced fuel pick-up hose
* replaced fuel/water separator filter
* replaced fuel pump (mechanical)

Still bogged down at 2000. I checked tank vent hose and it had gas in it (I think from overfilling it on my first time i put in new gas). Some have suggested couple be related to an ESA issue (it actually had trouble shifting into forward so I replaced ESA as well). I am at a loss now. Other than checking for a vacuum leak(s) and rebuilding the carb, not sure what to do/look for. Anything obvious (or not) I could be (am) missing. Thanks.
John



 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
I have a 1988 OMC 4.3 (Model 434APRGDP, also a second sticker with model 985269??). with a 4bbl Rochester Quadrajet. It starts and idles great, but won't go over 2000 RPM. It starts up and idles fine up to about 1800 RPM. Will get to wide open for maybe 5 seconds when cold though, then sputters out, back to 1800.

Howdy John!

Welcome aboard!

Well for starters, You might have a look at the following thread. Focus particularly on #14
http://forums.iboats.com/forum/engin...ion-for-diyers


For this so far, previous owner:
* replaced fuel lines (tank and engine)
* carb cleaned
I wouldn't put a huge amount of "stock" in what PO's say. They're usually focused on selling the boat and will likely say anything to close the deal



I ran sea foam thru for about a tank full at the slow speeds and it seemed to get a tiny bit better.
SeaFoam is mineral oil + naptha.......Probably more a placebo than anything else.............


I wanted to use it more this weekend so I:
* had carb cleaned (but not rebuilt yet)
* replaced corroded anti siphon valve
* replaced fuel pick-up hose
* replaced fuel/water separator filter
* replaced fuel pump (mechanical)
What does 'Carb Cleaned" mean exactly? If you just ran snake oil through the fuel, you didn't do anything. So you may have isolated your problem to the carb!


Still bogged down at 2000. I checked tank vent hose and it had gas in it (I think from overfilling it on my first time i put in new gas). Some have suggested couple be related to an ESA issue (it actually had trouble shifting into forward so I replaced ESA as well). I am at a loss now. Other than checking for a vacuum leak(s) and rebuilding the carb, not sure what to do/look for. Anything obvious (or not) I could be (am) missing. Thanks.
John
Probably was NOT the ESA. It might be related IF the ESA is activating when going INTO gear (but that wouldn't be an ESA "problem"........it would be more a linkage and/or switch........AND you would know it when the ESA activated at the higher RPM because of the unique "stumbling" of the ignition. ( I also seem to remember that the ESA doesn't activate above a certain RPM........)

The ESA should never activate going into either gear) It's only supposed to activate coming out of gear (and only in the water....NOT on the trailer running on muffs etc) If it is, your lower shift cable or drive linkage (internally) might be binding and/or requiring MORE force to actuate than it should.


Regards,



Rick
 

Papalax

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Jul 4, 2015
Messages
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Thanks Rick and glad I finally signed up. I appreciate the info and insight...

I knew the PO (actually previous two). He had the RPM issues earlier, but not mechanically inclined to troubleshoot/address anything himself. Got frustrated (and broke...) with mechanic and got tired of dealing with it. It sat for two years and he was going to donate it. It is a 1989 Sunbird Corsair 185 and in pretty good condition, so for a few hundred $$ I took a chance. Legally seats 9, so we do the cocktail, "shore cruise" many nights after dinner. Perfectly suited for that, but my teenager still wants it to go fast for the tubes, etc...

My thinking was all along it was the carb, especially after sitting for a couple of years. I assumed the old gas turned to varnish and was going to run the sea foam first to if it would break it up, just to get it on the lake quicker.

Carb cleaning was just that. Took it off and sprayed cleaner thru all the openings, "just to see".

It also looked like the choke was restricting the larger valves from opening. I disconnected it, but that made no difference. Might not have been letting it warm up enough the first time.

ESA - Sorry, my mis-type. I would shift into reverse leaving the dock, but would not shift out of reverse to forward (when under load in the water). I would turn boat off, shift back to neutral, start it and go into forward just fine. The shift interrupter switch did not look like it was operating "properly" in moving from grove to grove while shifting. I cleaned it and no difference. The overstroke switch is seating on the switch cams oddly. In reverse, it goes over the cam to the back and in forward it barely touches the leading edge. I assume they should rest on top of the cam, in the middle of it, but still looking to confirm that. I found an ESA locally (for same price as on line) and went ahead and swapped out. It shift fine now, but as mentioned a bit longer of a "hiccup" to slow the engine as I would have thought. The idle RPM's were a bit high, so I dialed that down to about 900. The "stumble" was far more noticeable at lower RPM...

With engine off, the shift is pretty effortless both forward and reverse, so it does not feel like the cable itself is binding. Although the shift cable has not been replaced. In talking to my local marina, the replacement shift cable will be red and mine is still black. This is my first OMC and it sounds like the shift issues are the culprits for many of the OMC failures and poor ratings... If the shifting stays easy, I am thinking I will wait to replace the cable at the end of the season or next spring.

Lesson learned on replacing ESA - Original ESA is superseded and new OEM and Sierra part have wire connection in a different location. Original mounts flush against bracket. The new wire location on OEM and Sierra did not match hole in bracket. Thought I would have to cut/fab a new bracket. OEM part came with longer bolts and 1/2-inch spacers. Took me a few minuted to realize, the the spacers are to allow the new wires to route behind the new module to get to the opening in the existing bracket.

Next steps:

* Actually rebuild the carb. Will get a kit and a float this week and report back when rebuilt with an update.
* Will try to find proper interrupter switch setting and see if I can adjust cam to fit, or replace switches then too.

Thanks again.
John
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
My thinking was all along it was the carb, especially after sitting for a couple of years. I assumed the old gas turned to varnish and was going to run the sea foam first to if it would break it up, just to get it on the lake quicker.

Carb cleaning was just that. Took it off and sprayed cleaner thru all the openings, "just to see".


* Actually rebuild the carb. Will get a kit and a float this week and report back when rebuilt with an update.
* Will try to find proper interrupter switch setting and see if I can adjust cam to fit, or replace switches then too.

Thanks again.
John

Ok....more info! Well, you're right about the carb. It's just spraying "stuff" (especially oil mixed with solvent) into it rarely does anything good.

The problem with really old gasoline is that it dries in the float chamber, needle and seat, jets etc and no amount of spraying into the intake gets where it needs to be.

You just need to take it apart and replace the needle/seat and physically clean out the jets, idle circuit etc... The kit gets you there best,

Idle MUST be somewhere around 550-650 RPM. If you're idling any faster, you WILL damage the clutch dogs in any dog-clutch drive (especially a Cobra) AND don't place it in gear slowly. Always put it in gear "smartly" and briskly.

When you go from either forward or reverse to neutral, pause briefly as you apply pressure out of gear to allow the ESA to activate, then pull it out of gear. (it's really not a pause at all)

If you have the original lower shift cable and there's ANY question about shifting, replace it. They were all supposed to be replaced by OMC under warranty.

A properly adjusted Cobra shifts very nice.

Here's some more info you may have seen. http://www.hastings.org/~stuart/cobra/

Also, here's a site where you can view parts numbers etc. http://epc.brp.com/ (email is NOT needed.....just leave it blank)

Here's a manual site but you should get yourself the right OEM manual if you don't have one
http://boatinfo.no/lib/omc/manuals/1...manual.html#/0

Cheers,


Rick
 
Last edited:

Papalax

Recruit
Joined
Jul 4, 2015
Messages
4
Thanks again Rick. I will be ordering a manual as well.

I picked up a good rebuild kit from my local marina. But no-one locally has a float in stock. I can pick on up from quadrajetparts.com for about $8. They have two options, brass and [FONT=Verdana, Arial, sans-serif]nitrophyl. My 2bbl I rebuilt a couple of years had the plastic float. They are the same price and it looks like [/FONT][FONT=Verdana, Arial, sans-serif]nitrophyl is specially designed for gas/oil/etc. applications. I am leaning that way, but wondering if anyone has had issues with them or thoughts on either one. Thanks.[/FONT]

[FONT=Verdana, Arial, sans-serif]John[/FONT]
 

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
I don't see where a compression test was ever done, or flame arrester cleaned, or fuel pressure at carb inlet checked. A lot of basics to check. Try running out of a 5 gallon can of fresh gas if no tools to check pressure. To eliminate ESA, simply unplug it. Was timing ever checked? Tach ever disconnected to eliminate faulty tach as cause.

There's a half dozen other things I'd be looking at before rebuilding the carb. Are we sure the outdrive isn't seizing up? Ever verify the firing order at the distributor? 2 swapped plug wires easier to sort than carb rebuild.
 
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