Mercruiser 230 inboard wont go over 3k rpm

[chrismurr1]

Hi all, need your expertise again. My starboard engine wont exceed 3k rpm. here are the details.

1984 Merc 230 (305). new quadrajet carb (if you read my idle post a few months back...yes i got it tuned out and its happy from what i can tell). new mallory marine MBI distributor, bosch platinum 4 plugs and wires. timing 8 degrees BTDC @ 750 RPM. max advance on the dist is 24 Degrees (same as the TB IV ignition on the port side).

fires up cold without issue, just hit the key and your gold. after getting out to the no wake zone i can take her quite easily to 2500 rpm and it can run all day like that. when i try to take it to 3000 it will go there and i can run like that for like maybe 30 minutes before i start to loose rpm. when i try to take it up to 3500 rpm (that will put me on plane without the trim tabs). it will burst to 3200 and drop back to 3000 then no matter how much throttle i give it (all the way to WOT) it just stays at 3000 and after a few moments will start to loose rpms.

now a few months back, i had this engine up to 4k rpm and cruising and that same day i lost my distributors pickup and fuel pump (that was with the original TB IV ignition at the time). it hasn't run that well since. I have since replaced the fuel pump and obviously the ignition system (last week the ignition amp went out and took the coil with it, it was far less expensive to put the mallory system in than replace the amp and i like the all inclusive design of the mallory, had it on my last boat and never a hiccup).

the only thought i had but have not tested yet is..... possible that the Platinum 4 plugs arent sufficient enough?

you help would be greatly appreciated. i have put about 400 into replacing parts and i still cant get her where she needs to be and the king mack fishing is almost gone......

chris

 

[dubs283]

Re: Mercruiser 230 inboard wont go over 3k rpm

i don't know about the plugs (spec is AC MR-43T) but i do know i would not trust anything mallory makes

 

[Bondo]

Re: Mercruiser 230 inboard wont go over 3k rpm

Hi all, need your expertise again. My starboard engine wont exceed 3k rpm. here are the details.

1984 Merc 230 (305). new quadrajet carb (if you read my idle post a few months back...yes i got it tuned out and its happy from what i can tell). new mallory marine MBI distributor, bosch platinum 4 plugs and wires. timing 8 degrees BTDC @ 750 RPM. max advance on the dist is 24 Degrees (same as the TB IV ignition on the port side).

fires up cold without issue, just hit the key and your gold. after getting out to the no wake zone i can take her quite easily to 2500 rpm and it can run all day like that. when i try to take it to 3000 it will go there and i can run like that for like maybe 30 minutes before i start to loose rpm. when i try to take it up to 3500 rpm (that will put me on plane without the trim tabs). it will burst to 3200 and drop back to 3000 then no matter how much throttle i give it (all the way to WOT) it just stays at 3000 and after a few moments will start to loose rpms.

now a few months back, i had this engine up to 4k rpm and cruising and that same day i lost my distributors pickup and fuel pump (that was with the original TB IV ignition at the time). it hasn't run that well since. I have since replaced the fuel pump and obviously the ignition system (last week the ignition amp went out and took the coil with it, it was far less expensive to put the mallory system in than replace the amp and i like the all inclusive design of the mallory, had it on my last boat and never a hiccup).

the only thought i had but have not tested yet is..... possible that the Platinum 4 plugs arent sufficient enough?

you help would be greatly appreciated. i have put about 400 into replacing parts and i still cant get her where she needs to be and the king mack fishing is almost gone......

chris

Ayuh,.... Here's a run-down of the potential causes of yer problem,....

Good Luck, 'n let Us know what ya find...

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

ok, here is Don's list and my response... thanks for the feedback and let me know if anything else comes to mind. i do have a few of these to check but wont be able to till next weekend when i return from my trip.


1. Fuel condition. Type and Octane possibly old fuel
Brand new Non-E10 marine fuel. we go out often so fuel is never more than a week or 2 old.
2. Propeller pitch or diameter, damaged blades
I suppose i could haul the boat and look at them, we have not hit anything or run shallow where the prop could get damaged so i wouldnt think. pitch and diameter is what it should be according to the prop shop.
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
This is an older tank with no anti-siphon valve. the tanks were flushed and the pickup tubes replaced along with new fuel lines all the way to the carb. New Holley Red label electric pump. we did run it with the F.A. off the carb and i can see that the float bowl isnt running out of fuel when it happens.
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
Oil Level is spot on. just a touch under the full line on the stick.
5. Marine growth on hull and outdrive
Straight inboards so no outdrive but its been a few months since i had the hull cleaned, doesnt look terrible but i suppose a cleaning could help... thing is, the port engine is more than happy to go up to 4400 (WOT) only the starboard is having the issue.
6. Wrong gear ratio in outdrive
No outdrive, 1:1 gear ratio with B/W 71c trans. again, a fine match according to prop shop.
7. Restricted carburetor air intake (clogged flame arrestor)
I did soak and rinse the flame arrestor in mineral spirits but i suppose a swap with the port would tell me a good bit... will try that next weekend.
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
This is a straight unrestricted 3" exhaust system, just a y pipe to the straight exhaust, no muffler or flappers. i suppose a small animal could have crawled up in there and died but i think we would have noticed that the water flow appears to be same as port.
9. Poor cylinder compression Compression Test
tested 150-160 in all cylinders.
10. Carburetor defective, or wrong type.
The Quadrajets are what these engines came with and i ordered exact remanufactured carbs according to the spec of the serial number.
11. Fuel pump pressure and vacuum
Fuel pump pressure is approx 6lbs. dont have a good port to test vacuum off the intake.... can i measure off the vac port of the choke pull off pot? i dont think that is manifold vac though.
12. Boat overloaded, improperly loaded, or improperly trimmed.
right now, no trim, the tabs are there but i have not gotten to restoring that system yet so they are up all the time. 1/2 loaded with fuel, fresh water tanks empty, holding tank empty... 4 people on board... for a 33 footer, i dont think this is over loaded, possibly underloaded still... when sitting in still water, it doesnt list to either side either so i dont thing there is an imbalance there.
13. Engine Overheating
engine running at a steady 170 degrees @ 2500 RPM, it doesnt rise when i push it either.
14. Engine timing and ignition system operation
Timing right on with Don's original suggesting on a different post of mine AND that matches the manual as well. ignition system is working fine (still a question on the plugs but maybe Don can weigh in there?)
15. Remote control cables and linkage for proper travel to open throttle plates fully.
we did check this and the throw to WOT does meet the carbs stops before it meets the controls, secondary plates open all the way.

thanks again. i will also write back in when i test the flame arrestor.

 

[dubs283]

Re: Mercruiser 230 inboard wont go over 3k rpm

the bad thing is, you ditched the t-bolt ignition on the stbd engine, so swapping ignition components is out - unless you swap entire systems (may try that as a last resort)

but... you can start by swapping carbs, fuel pumps, etc... see if the problem moves to the other motor

BTW...what was wrong with the old ignition (t-bolt) system??

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

i will start swapping parts slowly till the issue moves to port (if it moves). the original TB IV ICM died and took the coil with it. merc doesnt make it anymore and the replacement was a complete replacement system. thing is the rpm issue existed with the TB IV and now with the Mallory so i would think ignition isnt the issue... moving onto fuel systems. i will start with the fuel pumps.

 

[dubs283]

Re: Mercruiser 230 inboard wont go over 3k rpm

if its not fuel consider inspecting your transmission

 

[dgopetactical]

Re: Mercruiser 230 inboard wont go over 3k rpm

I had the same issue, I started going thru Dons list above and when I got to checking my fuel pressure it was only 3 psi, I put a new fuel pump on now I'm at 6 psi and I can get WOT now. What ever your issue is I think it's fuel related.
Denny

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

ok, replaced the fuel filters, replaced the fuel pump (i was getting 2-3 psi but now im getting 5-6) still have the problem. its a tiny bit better, i can get it up to about 3400 before it just drops back down to about 3k and stays there. just to get it up to 3k requires more throttle than the port side and to get it to push to 3400 requires even more. significantly more than the port side and still, it always drops back to 3k and if i leave it there long enough it will start to decline more. the wife says she can smell fuel when im pushin it up there so to me sounds like its running rich at that point...

considering dubs suggestion, i would think that a slipping transmission would allow the engine to rev up not restrict it back to a specific rpm.

being an older (1984) carburetor fed engine, it only has warning alarms on oil pressure and water temp but no "limp" mode of any kind. aside from the ignition system, there isn't anything computerized or electrical that would have a brain to decide to keep it at 3k.

sorry guys, im usually pretty good at figuring these things out being an old 80' certified mechanic.. the engine is right in my line of knowledge but im stumped...

thanks for the help.

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

nothing? does anyone agree that a look at the trans is the way to go here? could it cause this issue?

 

[Don S]

Re: Mercruiser 230 inboard wont go over 3k rpm

Hook up a remote fuel tank (outboard tank) right to the fuel pump and test run the engine.
Then when that works, swap carbs as dubs mentioned. Bet one of those cures your problem.

I know of nothing in those transmission that would cause your problem.

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

OK, sorry its been a while but life tends to get in the way i have fiddled with this quite a few times and swapped them, the problem follows the carb and after careful inspection of the hangers, secondary metering rods i have come to the conclusion that the company who reman'd these were idiots. granted i did order a pair of quads for a mercruiser 305, they obivously threw them together willy nilly. i have not checked the Sec. rod stamped code yet but the hangers are easily seen and i have 2 different hangers. O and J and i believe that they are both wrong.

after giving the port engine (which i can get up to 35 or 3600 RPM) a tune up with new plugs and wires, cap and rotor. its running rich at idle (700 RPM). the plugs that came out where black which of course indicates the same. likely i need a leaner spring for the primary rods. so i have 2 carbs that arent tuned even close to some stock standard where i can start from.

what would really help here is if someone has the specs on what the recommended stock metering rods, jets and PP spring should be so i have a base line to start from. i know im sucking fuel like mad and there has to be tons of room for improvement. both of these engines are stock so nothing souped up. both are 1984 Mercruiser model 230's (GM 305 block) with straight 1:1 inboards and 14x10 3 blade props.

any help would be appreciated, even a link or something pointing me in the direction of the information i need would be great.

thanks!!

 

[Bondo]

Re: Mercruiser 230 inboard wont go over 3k rpm

what would really help here is if someone has the specs on what the recommended stock metering rods, jets and PP spring should be so i have a base line to start from. i know im sucking fuel like mad and there has to be tons of room for improvement. both of these engines are stock so nothing souped up. both are 1984 Mercruiser model 230's (GM 305 block) with straight 1:1 inboards and 14x10 3 blade props.

Ayuh,... The Merc manuals are up in the Adults Only section at the top of this forum,...
I'd think the 84 specs for the SBC/ Rochester carb would be the same,..
Regardless, whether I/O, or inboard...

Btw,... The Edlebrock marine carbs are carbon copies of what Merc is still using today...
Same carbs, Same parts...

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

Excellent, i have retrieved the manual and specs i will do an inventory of what is actually in each carb and order accordingly. BTW, I put the TB IV back on the starboard with a good used ignition module and its running like a champ. i will repost in a week or so when i have done all the tuning with my results. thanks again for all the help.

 

[chrismurr1]

Re: Mercruiser 230 inboard wont go over 3k rpm

thanks everyone for your input. i have resolved my problems and all seems well now. i had to rebuild the carbs, seems National Carbs just slaps these things together. different hangers for the secondary rods, mismatched primary rods to jets, improperly adjusted primary rod stop... you name it, it was wrong. after the rebuild, they fired right up to 800 idle rpm without touching a thing from baseline setting. now to take a cruise and see how the economy is