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low engine rpm

HerbertFriedman

Member III
I have the Universal M25XP and am experiencing a little low maximum RPM, I can only get to 2200 rpm whereas last season, I was able to reach 2500 RPM. I will check to see if the prop is fouled but any other ideas? Could the throttle cable have slipped a little so that with the lever fully extended, I dont get to the max rpm setting? Hate to think of other issues such as valve timing, etc.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
I'd grab the throttle on the engine and see if it will open further. That would eliminate or reveal cable issues.
 

HerbertFriedman

Member III
yes, that was my next attempt. I also have an underwater camera and will look to see if the prop is fouled. I have a diver coming to do the bottom so he will check the prop also. Thanks
 

Glyn Judson

Moderator
Moderator
Limited RPM.

Herbert, If the cables turn out not to be the problem, you might want to consider looking into a partially clogged exhaust elbow as the culprit. Carbon will eventually build up, restricting flow and resulting in reduced power/RPM's. It might be time to change that elbow, a nasty job more easily relegated to someone else. Best of luck, Glyn Judson, E31 hull #55, Marina del Rey CA
 

HerbertFriedman

Member III
yes, my next thought was a clogged exhaust, I need to find out when was the last time that elbow was changed. Do you know of any way of measuring that effect short of pulling out the elbow and visual inspection. Is there any way of bypassing it altogether?
 

HerbertFriedman

Member III
I believe that the exhaust riser/elbow, exhaust manifold and heat exchanger are the original, so they are all 30 years old. I dont have any overheating problems but as I said, I cannot get the engine to rev up past 2200 rpm. Last year I was able to get to 2500 rpm. I will check the prop and cable but several folks have had their elbow, manifold and heat exch. removed and boiled out. Is there any reason to replace the elbow rather than just having a radiator shop boil it out. at least based upon my symptoms?
 

Glyn Judson

Moderator
Moderator
To boil out or replace.

Herbert, Given that it's such a pain to remove the elbow, it's always made sense to me to simply install a new one. Glyn
 

Baslin

Member III
I would start by changing both the primary and secondary fuel filters before i started chasing anything else
 

HerbertFriedman

Member III
Good idea but I did replace both filters about 6 months ago, or about 10 engine hours ago. I did look through the engine log notes from previous owners and found the cryptic comment. "rpm problems, changed exhaust riser, problem solved" That was at 1200 hours, I now have 2400 hours, I wonder.......

My plan is to have the riser removed and either replaced or boiled out (at a radiator shop for example) along with the exhaust manifold and the heat exchanger as long as I am at it. The latter two items are 30 years old and I others have suggested those as good preventative maintenance. Comments welcome and encouraged.
 

supersailor

Contributing Partner
2500 is a rather low RPM for the top end. It sounds like the engine is overloaded in normal usage. Mine spins about 3200 at max and I cruise at about 2500. Has there been a prop change? Is the prop overpitched?
 

Baslin

Member III
I went through this same issue with my engine, Universal 5432, a couple weeks ago. I checked my prop at haulout and cleaned it off to read the size and found it was over pitched. After putting the new prop on of the correct size, I was able to reach correct crusing engine rpm.......This may not be your issue. You may know that the prop has never been changed or that it is in fact the correct one for your setup...What does the engine do in nuetral?? Can you get max engine rpm's??.....If you cannot, then you have an engine issue. Possibly a fuel delivery issue, exhaust restriction as mentioned, or injector, compression issues. If you can reach max rpm's in nuetra but not while in gear, then you most likely have a fouled prop, or transmission drag.
 

HerbertFriedman

Member III
I will try the rev up in neutral idea but the prop has not been changed. I dont actually know what the highest rpm was, only that I was able to easily reach 2500 rpm before. Will let you know what I find.
 

Baslin

Member III
Another thing to look at would be valve lash adjustment. This needs to be checked periodically.
 

HerbertFriedman

Member III
good idea, I am having a good mechanic change the exhaust riser/elbow, should be replaced anyway, its overdue, might as well have him check out the valves too.
 

hodo

Member III
Check to see if you have a bronze fitting in the exhaust hose between the riser and water lift muffler. These have a "flapper" in them, and are known to fail, partially blocking the exhaust.
Harold, S/V Mischief :devil: Maker
 

HerbertFriedman

Member III
I will check about the bronze fitting. It is hard to see where the water lift muffler actually lives. The output exhaust hose from the riser eblow goes a short way behind the engine to a reducer fitting so it probably transitions from 2" hose to 1 1/2" hose, why they did not keep the same hose diameter, maybe the other mavens on this site know. In any case the smaller exhaust hose disappears to the starboard side lazarette and finally out the transom, they have to route the exhaust out from the aft sleeping area. Somewhere in that route I am sure the water lift muffler lives but in anyone can direct me better, please do.

In any case, the riser/elbow was last changed in 1999 at 1243 engine hours again because of an "rpm problem". Kinda cryptic note from a previous owner, but it is 18 years and 1200 engine hours later, so I will change the riser/elbow anyway. I am having trouble breaking loose the exhaust hose from the nipple, I will try breaking the seal with a awl or thin blade but if anyone has any cute tricks, please let me know. A gorilla would be most helpful at this point.

A local mechanic, very highly rated, says if I can undo the three nuts holding the exhaust flange onto the engine and undo the two hoses, and bring him the entire riser and flange, he will swap the riser/elbow easily, if he has to make a "house call" it is a day's labor. So there is cost incentive to get the exhaust hose off. It may be easier to remover the hose at the reducer fitting, better access.
 

Pat O'Connell

Member III
Exhaust Elbow

Hi Herb
Hodo makes a good point. If the exhaust check valve broke in a semi closed position that could be your prob. If you search exhaust check valve Kenneth K has a good picture of what you should look for.
Good Luck
Pat
1981 E28+ Universal 5411
 

HerbertFriedman

Member III
nice photo of the check valve but at least at this point, I cannot find such a part in my exhaust. However, I cannot even find the water lift muffler. On my 1987 E34, the 2" exhaust hose from the output of the riser soon transitions to a smaller diameter hose using a bronze? reducer but as far as I can tell this reducer is just that, no flapper at all. The reduced diameter hose no doubt is probably to fit the muffler but I cannot find it, and it is not small. Does anyone else with an E34 know where this muffler and possible the check valve is? I do not see anything in the transom area where the exhaust thru hull is, just the exhaust pipe.
 

supersailor

Contributing Partner
Herb, the waterlift muffler is at the very front of the cockpit locker on the left side bottom. The water heater towers above it. I can see mine now that I have rearranged the entire front of the locker. The PO was a bit messy. If you should have one of those check valves, get rid of it. The stopping back flow was the good idea but they freeze in the exhaust stream and very rarely in the open position thereby endangering the valves along with diminishing the performance. My PO tried the same thing in the black water hose leaving the Raritan head. Of course, it froze in the closed position causing a blowout of the head seals. Great idea! That's what the Joker Valve is for.
 

HerbertFriedman

Member III
Bob, I assume that that the cockpit locker is on the starboard side of the cockpit, not the transom locker? I will look again but wow is that area ever crowded, with the holding tank, the water heater, a refer compressor, head Y valve plumbing, batter charger, etc.
 
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