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40hp seahorse not gaining rpms, not sure where to start - help please?

vandenburgh

Contributing Member
63 electric shift, starts fine, but when throttle advanced, won't get beyond a fast walk. Prop doesn't seem to be slipping, seems to be firing on both cylinders, and fuel bowl seems to be getting fuel from tank. Idles fine. Condition started during a brief outing where we were at 3/4 throttle, running fine, then suddenly we were at fast idle.

Linkage from throttle controls to carb butterfly seems to be working same as when running fine before the episode.

do you folks think this is a fuel issue, or ignition or something else and suggestions where to start? Thank you in advance for your assistance.
 
what rpms are you at when it fails?if its topping out it is probably the prop slipping...pit an inductive timing light in the boat to make sure you are firing on both...check compression...if compression is ok then your decision is it fuel or fire...the timing light should tell you...
 
Engine probably gets to 1500 rpm, but just a guess, no tach. I don't think prop slipping, seems to move forward with power and distance I expect for rpms it is spinning.

Haven't checked compression since this episode/issue occurred.

I will check spark again to make sure I still have on both cylinders. I don't have a timing light, nor do I know how to use, but viewing this engine trouble as an opportunity to learn (a desk educated mechanical engineer by schooling, but little practical knowledge working on engines, so eager to learn from you guys). Will a $30 timing light from China import do the trick and what readings would I be looking for?

if head gasket blown, I assume I would see leaking unburnt fuel on engine head, or could it be obscured from view?

Appreciate the help guys...with the help of this forum I was able to rebuild the lower unit and do the basic carb work, so hopefully can get this issue sorted too! While not the most efficient or environmentally friendly engine, I like the mechanical ingenuity of the 50 yr old technology with no electronics!
 
Thanks. I will check head gasket for any issue. On timing check/ignition system check, need to do a little more research as it is new to me, so will check forums on how to do.

What is on my mind...., does my symptom from running fine at 3/4 throttle to all of sudden being at fast idle, and now not being able to move past a fast idle, sound more like timing/spark issue or fuel and why/why not? Just curious as to the diagnostic logic/thinking?

If I follow, suggestion is check timing first (which I need to learn how to do first, but will give it a whirl), and if that checks out, move onto fuel side. showing my ignorance here..I would have thought if all of sudden magneto system wasn't generating spark properly when throttle control at 3/4 and with throttle butterfly that far open, motor would flood out from too much fuel or cough and sputter and die, which didn't happen. if on other hand, fuel was all of the sudden restricted and remains restricted for some reason, would spark ignition automatically slow as rpm of flywheel would be slowing, and it would be like throttling down smoothly, which is more of what recall happening? Guess I am trying to better understand how system basically operates so I can keep my eyes peeled for what might be ailing my motor. Any thoughts on why you think I have one issue vs the other? Sorry about all the questions, just trying to learn.
 
Thanks papyson and kimcrwbr1 for the replies. Kimcrwbr1, thanks for the suggestion on ohm meter method. Where would the kill wire be...does flywheel need to be removed first to connect lead as in in article you linked, then put back on, or is there another place to connect into point breaker circuit to check timing of open/closing?

unfortunately I don't have access to compression tester for a few days when we go back home, so still working under assumption compression is good until I can check properly.
 
Thanks. R the kill circuit wires are the two black wires just under flywheel on armature plate?

.....Kinda left field question, while I am committed to getting this one running, I am thinking about starting another project boat once this one is sorted. I may have an opportunity to pick up a running (albeit test tank) 89 30hp rude that looks to be in good shape for $500ish. Any thoughts on an 89 rude technology/reliability/serviceability history? If 30hp is running, I would just swap it for my sons ailing 40hp and work on 40hp at my leisure as I enjoy the tinkering/learning. Feel bad about him being beached...
 
On the list above, I think compression is ok, but can't be sure till I get a gauge on it...seems pretty tight when trying to turn by hand, but will check it early next week when I have equipment on hand.

got spark, but still need to check if timing good using multimeter method


Does this logic hold for potential trouble shooting...., again a newbie, but trying to learn....motor starts and idles fine, and sounds like it is firing on both cylinders, wouldn't this be both an indication of good spark and also seems it is getting enough fuel via low speed jet for idle operations. I would have thought that given good idle operations we could rule out ignition issues? True or not true?

Problem is when throttle applied, just goes to fast idle (kinda like when start lever was being applied), never really gains RPMs. Throttle butterfly begins to open just when follower cam hash marks pass pointer on top of carb and fully opens at WOT position, but no real action on engine RPMs, just fast idle. While not an expert by any means, I thought when throttle butterfly opens, increased airflow creates pressure change in carb that draws fuel from float bowl via high speed jet...since I am not getting any engine response, would guess that perhaps high speed jet clogged or float bowl not filling properly with fuel? Am I way off base?
 
I am going to say this ----------------Fact is these motors will run quite well and sound ok to the untrained ear when running on one cylinder.-----------So far all I have read is ---------" seems to have good spark " ----and " seems to have good compression "---" sounds like it is firing on both cylinders "---------------Fact is you need to do some simple testing to find out what is wrong, guessing does not work.-Sorry.
 
I will check compression as soon as I am home with the boat. That said, I did check spark as suggested, that is why I am saying it seems to have good spark. It has spark. it is idling on both cylinders as I did drop test as well where I started engine, pulled top plug wire and it continued to run on bottom, although rough of course. Reconnected top, pulled bottom, and it ran on top.

So yes, actual compression numbers I don't yet know, but based on fact both cylinders are firing while idling, it has spark. Is it strong spark, it jumps 1/4 in gap - is that strong enough?
 
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