Low rpms aq125q

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
I have 1985 aq125q /270od. On a 21ft trophy. Starts good,idles good about900 rpms. Starts out fine,get to about 3000rpms and that's it. There is still plenty of throttle travel left. But moving the trottle forward dose not increase speed or rpms? Move it all the way forward and you might even lose just a little speed/ rpms. My friend seems to think it is throttle linkage problem. I feel it my have that and a carb issue.
Thanks for any advice in advance
Edddie
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Re: Low rpms aq125q

What's the speed?You sure the tach is right?Any missing?Plugs burning ok
Get a Tiny Tach and check the readings or a Dwell meter/tach.
Check the comp too.
The fuel system:check the anti siphon valve at the tank.The the tank vent for clogs.
Go for a ride.Un-hook the throttle linkage and try it by hand.J
 

Maclin

Admiral
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May 27, 2007
Messages
6,761
Re: Low rpms aq125q

Is this boat new to you? Has this been happening all along? What was the most recent history and service done to this?
 

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
Re: Low rpms aq125q

Thanks so far! A little more info. Took boat out a week ago ran better than yesterday,still not able to get to wot. Testerdays top speed was only about ten miles a hour. Week before did like twenty one or so. The tac is a new one ,and seems to be working okay? It responds the way it should . Today with the boat out of the water,it has no problem getting up to 4800-5000 rpms? So my problem is when under load. It starts very easy,and runs great for about the first half of the throttle travel . Once it gets to about 3000 rpms ,half thru the throttle travel there is nothing else. It docent bog down ,it dosn't miss os stall nothing. It just won't go any faster and the rpms will not increase.. From what I've read it could be many things. Maybe I'll try the fuel pump. Have a fuel filter separator ,and the gas looks very clean. We did replace the timing belt recently,but that was before I took it out last week.so this seems to have gotten worse. Any help or ideas would be great.
Eddie
 

Maclin

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May 27, 2007
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Re: Low rpms aq125q

Is this boat new to you?

Has this been happening all along?

What was the most recent history and service done to this?

Have you checked the ignition system, condition of points, dwell, timing? Condition of cap, rotor, wires? Spark plugs?

If it was the fuel pump it would be surging bad most likely.

There are some good diagnositics in the stickies at the top of the forum, look thru those (link below). Doing some real troubleshooting and diagnostics will save you having to buy and throw parts at it.



http://forums.iboats.com/showthread.php?t=468654
 

Maclin

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May 27, 2007
Messages
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Re: Low rpms aq125q

I just noticed the timing belt change.

My questions about BEFORE are still pretty valid. Pretend like we only know you from your first post in this thread. Was it running ok before the timing belt broke, include more info like that.

IF all this started after the timing belt, then, hmm...is probably related to cam timing or valve lash or distributor clocking, none of us know if all that work was done properly. BUT even THAT is PURE guessing, doing the diagnostics is the first thing to do.
 

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
Re: Low rpms aq125q

Sorry if I didn't give enough info ,I'll start over.
Boat is new to me. Had mech friend look at it said everthing looked okay.
We took it out the first time,and it would not run well.he was trying to adjust carb and stuff when the timing belt broke.
He replaced the belt,checked the time,set the dwell.adjusted the carb. Seemed okay.
I took the boat out again.it started easy,and ran okay. It would only go about 21 mph. There was still plenty of throttle left . But moving the throttle did not increase speed or mph.
I replaced the tac,added some fuel cleaner and octane boost ,as my friend suggested.
The tac seems to work correctly,the fuel is very clean.
Took the boat out yesterday , started great,ran fine up to 3000 rpm. Here again the throttle response stops,no speed gain or rpm. But this time the speed was only about 10 mph. There is still about half the throttle travel left. But moving the throttle dose nothing dose not start sounding bad or anything but no response. It actually seems to be running fine just won't do anything over 3000rpms that's the top. And only ten mph.
So,today with the boat out of the water.it starts fine runs fine. Climbs all the way up the rpm scale to 5000. That is with the boat in neutral .
So under load it will only do 3000rpm in neutral it will easily do 5000rpm? Sounds good all the time no popping or missing ,surging.
Some of the things I've read here suggest that it is not getting enough fuel under load .some suggest a timing issue.
Thanks for all your help,if you need more info just ask . I will keep checking back.
I do agree that throwing parts at it is not the answer,it will get expensive.
Thanks for the help.
Eddie
 

Maclin

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May 27, 2007
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Re: Low rpms aq125q

New to you, so there is no prior running to compare it to.

The link I gave you at 1:20pm has all the guides you need to follow including the link to low rpms' that Don S gave you in your new post.

I would triple check the ignition points installation. Be sure the points are correctly installed mechanically, meaning correct part and that the spring is strong and they are aligned good when they are closed. And it goes like this....set the dwell then set the timing.

I am not all that familiar with the actual distributor, but it may not be advancing like it should, rusty weights or springs or other problem. The timing check should show that.

It could be clogged mains in the carb still.

Octane boost is a silly suggestion.

You have this queation in 3 places now with the same answer...Revving in neutral give no indication of what it will do in the water!
 

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
Re: Low rpms aq125q

Maclin,will update you soon. Am going to rebuild the carb. Will run new fuel lines. And try to clear any thing that may be in the vent. If I disconnect the vent line and blow compressed air into the fitting will it hurt the vent? Haven't had a chance to look,is the vent replaceable ?
Thanks again for your help.
Eddie
 

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
Gas vent

Gas vent

How do I tell if the gas vent is working properly? Can I clear it with compressed air? Is it replaceable ?.
I bet the answer is in fuel system thread , I will go back and read it again. Don't remember it saying anything about replacing the vent.
Thank you for your help
Eddie
 

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Re: Low rpms aq125q

That vent won't limit the rpm's each time and immediately. It would run good for a while then act like it was running out of gas. I think it is ignition related, or leftover badness from the belt change.

Here is one thing you can do that is free and does not take much effort....With engine off, take the cap off of the distributor and move the rotor. It should move one way a few (15-20) degrees then snap back. If it does not then the insides of the distributor need looked at.
 

Eddie Ray

Petty Officer 2nd Class
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Jun 8, 2011
Messages
153
Re: Low rpms aq125q

Checked the rotor,it moves and then snaps back. What seems strange to me,is the one week it run in the low twenties . The next week ,it topped out at ten? I thought a timing issue would be the same every time? If there is something else to try please let me know. I will go back and read all the links you gave me and try to figure something out.
Thank you once again for your help.
Eddie
 

Maclin

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Re: Low rpms aq125q

Timing should stay constant, but distributors can fail, so now you know it is probably advancing ok. If the advance mechanism had stuck then one of the symptoms would be low power, i.e. not being able to get over 3000rpm.

Rebuilding a carb, if done properly, is always a good thing. If not done properly then it just adds to the layers of problems.

We still do not know if the points are good or not, the spring has to be strong or they will float and not let you get past 3000rpm. We also do not know the actual dwell, points can move. We do not know the actual static timing setting. Also if the cam is off "a tooth" it would have symptoms like this.

I know you are itching to put a fuel pump on it, but is there always fuel in the carb? Check by working the throttle and looking for accelerator pump spray. You should also check the float setting in the carb next time it is apart. If there is always fuel in the carb then fuel pump is ok for now, but there is a test you can do on that also to verify, see what I mean? You need to do the diagnostics first.
 

Mullin

Petty Officer 1st Class
Joined
May 12, 2011
Messages
256
Re: Low rpms aq125q

considering the timing belt was just changed, double check the gears' timing marks to be sure it didn't jump. It's possible that the tensioner wasn't set correctly and after the first trip out got a little slack and then jumped sometime after, like at the next startup.
Plus its free and easy to check.
 

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
Re: Low rpms aq125q

Maclin,thanks a lot for your help. I have got a tune up kit for the boat,new points ,condenser rotor. Will install saturday. Boat is old,so I'm going to replace fuel lines as well. The old ones are not! CG approved. Also will rebuild the carb .blow out the lines. Temporarily install the clear line to check for air leak and or bubbles. Will pick up the dwell meter and remote starter and tac tomorrow . Have done most of this stuff before,the points long time ago. Will bring the Ipad and your links on the boat for help. If all goes well,will take boat out on Sunday . I will report back after that. I know this might make you laugh. But , the lady at the boat place gave me the fuel pump at cost 50 bucks. Everybody else wanted twice that. So,yea. I'm gonna do that too.. She is an old boat,figured it wouldn't hurt.
Thanks so much again,talk to you on Sunday.

P.S. If you think of any thing else,or I missed something let me know. I'll double check the timing marks too.

Eddie Ray
 

radjaz

Recruit
Joined
Sep 9, 2011
Messages
4
Re: Low rpms aq125q

wow, this is very similar to the issues that i am having with my AQ131. Looks like your last post was in May. I would like to know if you figured it out and what fixed it. I am thinking that there are carb issues with mine. Would really like to know what your fix was.

jaz
 

Maclin

Admiral
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May 27, 2007
Messages
6,761
Re: Low rpms aq125q

jaz,

Eddie started this thread on Sep 4th this year.
 

Eddie Ray

Petty Officer 2nd Class
Joined
Jun 8, 2011
Messages
153
Re: Low rpms aq125q

Mr. Maclin,
We reset the timing,checked the timing marks. New condenser,points, rotor,
New fuel lines,fuel pump lol . Rebuilt carb.
Took her out today,started good ,run nice up to 3000 rpms? Then it topped out there again. My Mech buddy was with me,thought he was gonna pull his hair out. He now thinks ,we could have an obstruction in the exhaust. It did get a little hot maybe200? The water temp is about 90 here in SWFlorida. I slowed it down right away and the temp droped quickly to 180.
Also near the end of the trip the engine jumped time. I think maybe the tensioner is weak,and under enough load it is jumping time. Don't know if that is adding to the problem.but probably.
Anyway the great mystery continues?
Thank you for any help you can offer
Eddie
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Low rpms aq125q

190? is what those engines normally run.
Might want to do a fuel system test, partially plugged pickup or antisiphon valve would sure limit the fuel going to the carb. Hook up an outboard tank to the fuel pump and see if the rpms increase out on the water.
When you did your tuneup, did you make sure the dwell was set correctly, and the timing? Did you verify the timing advance was working correctly? Those engines are very picky about dwell and timing.

Here's a link to the REAL service manual.
http://www.4shared.com/file/89797330/b32e5bf9/AQ125145_AB_Service_Manual.html
 
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