Idles high after a hard run

[Johnnydeep]

My 1990 volvo aq131d will idle high for a few minutes after a hard run. I have the single solex 1bbl with no choke(bear to start in cold weather!). My normal idle is 700 rpm and the throttle linkage is not binding, But the engine will idle at about 1200 in nuetral and 850-900 in gear for about 5-10 mins before it drops back down. This is kind of irritating as it seems like I am always trying to maneuver in tight quarters when this happens and that high of an idle really makes the tranny thunk!

 

[outboardguy]

Re: Idles high after a hard run

First I would verify that the throttle cable is returning the throttle to the full closed position.If necessary adjust the cable so that it has a little more throw to close the throttle.Another possibility is that the centrifical advance in your distributor is binding. Thats all I can think of right now Good luck

 

[trog100]

Re: Idles high after a hard run

your variation in idle speed is a little more than mine but i know where u are coming from.. my 3.0L varies by about 200 rpm.. i have fitted electronic ignition.. made sure the throttle is fully back against the stop.. fitted hotter running plugs.. made sure the stop screw aint moving.. lots of fiddlings but i cant seem to fix it.. <br /><br />i can set it running perfectly then the next time i use the boat or later the same time its either running slow on the verge of stopping or running fast about 900 rmp.. if it wasnt for the clunking dog clutch during the 900 rpm periods i woulnt give a rats wotsit about a slightly fast idle sometimes.. but something in me dosnt like that clunk to be any more violent than it has to be.. he he<br /><br />the obviouse thing is some kind of intermittent air leak but mine is a little too consistent to be that..<br /><br />i am pretty sure its a carb problem on my engine.. perhaps a variation in fuel level in the float chamber.. i intend to strip my carb and also fit some kinda spring on the throttle lever just to make sure it always closes.. but i aint certain that this will fix it.. he he<br /><br />i know its not something i can induce or make go away at will.. it plays tricks on me.. after a nice consistant period at say 900 rpm.. i slow the bugger down to say 700 rpm.. we are talking no more than 1/8 turn on the throtthe stop screw here.. u can guarantee that some time sooner rather than later the swine will slow down to 500 rpm and stall on me when i am trying to dock the boat or negotiate a lock.. he he<br /><br />anyways i think your problem is carb and temperature related.. sorry to not be of any more help..<br /><br />trog100

 

[Johnnydeep]

Re: Idles high after a hard run

I know it is not the throttle cable as I have physicaly tried to push it back to idle when it was running fast. If I just stop and drift bring it down to Idle after a hard run it takes about 5 min or so and she will drift back down to normal, It seems to be temperature related but I am lost as to how?

 

[rattana]

Re: Idles high after a hard run

Can you check the vaccum reading? Does it change with the rpm change? Check the timing as well under both conditions. The timing might advance slightly with the rpm but not drastically.

 

[trog100]

Re: Idles high after a hard run

assuming the engine is set up correctly during its normal 700 rpm idle period.. there is only one way it can go another 500 or so rpm faster.. <br /><br />more fuel and more air is getting in to the cylinders somehow.. there really is nothinge else that would make such a difference..<br /><br />course if the engine was running well rich during its 700 rpm period all it would need is more air to make it idle quicker..<br /><br />the too rich at proper 700 rpm idle speeds with an air leak after a thrashing is the more likely of the two.. its easier to imagine it getting more air than to imagine it getting the both.. it aint timing or anything like that.. it cant be..<br /><br />try squirting a little gas (old gas lighter fuel can) around possible air leak sources.. if it is an air leak squirting the gas on it will cause the mixture to richen up and the engine will (momentarily) slow back down..<br /><br />if the mixture was correct without the airleak the oposite would happen.. but either way a change in engine note will occur if u hit the leak with the gas squirt..<br /><br />the other to thing to investigate is just how much of a temperature change happens when u give the boat some stick.. again the engine idling faster when things get hot would only happen if the mixture was a little too weak and praps the engine a little too cold when u are running the boat slow.. this last option aint overly likely thow.. but it is a possibility..<br /><br />dont set fire to your boat.. he he <br /><br />trog100

 

[trog100]

Re: Idles high after a hard run

one other possibility springs to mind.. your plugs are running too cool during slow running and fouling up.. a good blast cleans em up nice only to start to foul up again when things slow down and combustion chamber temps drop.. projected nose plugs are better in this respect..<br /><br />trog100

 

[Johnnydeep]

Re: Idles high after a hard run

I tend to agree trog but why would it happen only when I have been running at about cruising speed? An air leak would be a constant would't it. And I have used carb cleaner judicisly(sp) all around..an air leak should show that way souldn't it??

 

[Dunaruna]

Re: Idles high after a hard run

Using a fluid to check for vac leaks is a good idea but please don't use anything flammable - brake fluid, soapy water, machine oil even - but not gas or carby cleaner.<br /><br />A vac leak can & will increase/decrease with engine temps, manifolds and carbys expand & contract with heat. Squirt fluid around suspect gaskets and LISTEN for changes in the engine, a non flammable fluid will make it run rough for a couple of seconds - its safer and a much more accurate way to find a vac leak.<br /><br />Have a safe and VERY MERRY CHRISTMAS to all.<br /><br />Aldo

 

[trog100]

Re: Idles high after a hard run

an airleak dosnt have to be constant.. firstly (if in your case it is an airleak)its only a very small airleak.. a big one would have a far greater affect on things.. expansion and contraction of engine parts during temperature changes can make one come and go.. lets assume in your case a small airleak appears during hard engine use.. things warm up..part move..gaps can open up.. a small airleak will not affect high throttle operation in the slightest but it will affect idle speed cos at idle speed the throttle butterfly is damn near closed and there is very little air/fuel mixture entering the engine.. if an airleak is small and its constant a little enrichment of the mixture control screw would make it virtually unnoticable.. but if it comes and goes for whatever reason your engine speed will vary at idle.. fact of life this one no if and buts..<br /><br />to be honest the most common (and the only really obvious one) cause of symptoms like yours would be the throttle linkage sticking a bit and the throttle not closing properly.. but we know it aint that cos thats the first thing u checked.. he he <br /><br />as for soapy water well its 100% safe but its also 100% a waste of time.. okay for air bubbles coming out of something but no good for air going in..<br /><br />the idea of the flamable stuff is that as its sucked into the engine by any possible leak it will alter the fuel/air mixture ratio and in doing so cause a noticable change in engine note.. but i think u already know this..<br /><br />a vacume guage aint gonna show up a very small leak of this nature either.. <br /><br />as i said do not set fire to your boat.. anyone reading this that dosnt feel they could use the method of finding small airleaks i have described without setting fire to either themselves or their boat .. well the answer is simple dont do it..<br /><br />and just bear in mind that i come from an era when gas fitters used their noses and a match applied to pipe joints as a last minute (and very quick) check to make sure there wasnt any leaks.. he he he..<br /><br />honest..<br /><br />trog100

 

[trog100]

Re: Idles high after a hard run

just one more comment the best and safest way to use the flamable (gas) method of checking for possible airleaks is to not use an aerosol or spray can at all.. its to use a small can like an old fashioned oil can (one u sqeeze) with a long narrow spout on it.. u carefully apply a small amount of fuel to each suspected joint/area.. doing it this way gets neat liquid fuel sucked straight into any leak.. and it is reasonably safe if simple precautions are taken.. <br /><br />spaying atomized fuel about is not as good a method (less neat fuel would get sucked in) and definitely more of a fire hazard... so even i would say dont do this..<br /><br />trog100

 

[Dunaruna]

Re: Idles high after a hard run

Trog, <br /><br />First and foremost safety has to be the priority, SPRAYING a flammable liquid into a confined, hot and non ventilated area is a recipe for disaster - this ain't a car.<br /><br />Secondly, jonnydepp may be the most competent tech on the planet or it may be the first time he's ever seen a motor - I don't know, do you? Giving advise needs to be tempered with common sense according to someones capabilities, you may be comfortable turning a bilge into a WMD but are you comfortable advising someone else to do it?<br /><br />Thirdly, using non flammable fluid is not only much safer its also very effective, and by the way, soapy water will get sucked into a vac just as easily as it produces bubbles from a pressure leak. <br /><br />Merry Christmas.<br /><br />Aldo

 

[trog100]

Re: Idles high after a hard run

i know exactly where u are coming from aldo.. and a merry Chrismas to u to..<br /><br />i did say "dont set fire to your boat".. he he.. and i did not say "spray" and if jonnydepp really is looking upon an engine for the first time in his life he certainly shoulnt be messing with it..<br /><br />tell u something about one of the fluids u seem to think is none flamable.. brake fluid.. it causes more engine compartment fires in cars than gas does.. drip gas onto a hot exhaust and it just sizzles.. drip brake brake fluid onto one and it instantly bursts into flames.. <br /><br />add in the fact that this dangerouse and flamable liquid is housed in plastic containers that are just a push fit on top of your master cylinder and easily pop out in the event of an accident and u now know the most common cause of cars going up in flames.. <br /><br />add in the fact that most folks dont even know the stuff is flamable and u really do have a recipe for disaster.. now about "safety" being a priority.. hmmm.. i wonder if the folks that make cars are aware of this..<br /><br />consider the above to be my contribution to the world of "safety".. <br /><br />still.. the world does need folks to point out the "safety" aspect of things.. <br /><br />why does the "gas" method work and the soapy water method not work.. well gas is very thin and it seeps.. it will get sucked into small holes that water would not..<br /><br />for water to affect engine note or speed it would need enough water to be sucked in to actually make the engine mis-fire.. quite a lot.. more than would ever get sucked into the small leak we are looking for.. with gas only a very small amount will do the trick and cause that engine note to alter... <br /><br />course the real problem here is that the method that works carries a certain risk element.. like many methods that work do.. and because of this should not be carried out by mental deficients or those looking at an engine for the first time.. and as u so rightly say we might well just have some of those reading this forum..<br /><br />and for those that really dont know one end of a spanner/wrench from another.. take my tip and leave the mechanics of your boat well alone..<br /><br />be "safe".. but not tooo "safe" and a merry and "safe" christams to all..<br /><br />trog100

 

[newport dave]

Re: Idles high after a hard run

Someone earlier suggested checking the centrifical advance. To me, the symptoms seem to be more consistant with this than a vacuum leak. <br /><br />I see a LOT of marine distributors that are moderatly to severly rusted and corroaded on the inside, even though they look decent on the outside. <br /><br />If the advance weights are sticky and not always returning all the way (heat could be a factor hear) the result would be a high idle. In fact broken advance springs are not uncommon, and this could also cause an irratic/high idle.<br /><br />Dave

 

[trog100]

Re: Idles high after a hard run

bob weights staying in the advanced position is not gonna add 500 rpm to an engines idle..????.. all u are gonna end up with is a well over-advanced engine at idle.. this will make the engine run rough.. if it manages to keeps going at all.. but no possuble way could this add 500 rpm to an engines idle speed..<br /><br />an old fashioned way i was taught to set the timing on an engine by hand was to carefully turn the distributor till u find the fastest engine rpm at a fast idle.. similar to how u would tweak the fuel mixture control on a carb..<br /><br />if u go beyond the fastest point advanced-wise the idle will begin to lose its "smoothness" u can go quite a way before it begins to noticeably slow down..<br /><br />going the otherway.. ie.. retarding the timing from the fastest point still produces a nice smooth idle but things just start to slow down..<br /><br />i settle for a point just on the retarded side of the fastest point.. praps 50 to 100 rpm or so.. if the engine runs okay over its full range and normal use i tend to settle for this.. <br /><br />i shouldnt really say this but i have never used any other method to time an engine for the last thirty years.. he he<br /><br />the governing factor really is how much advance an engine will stand before pinking or detonations occur.. there are many things (variables) that can influence this.. and no matter what the manuals say there is no perfect timeing.. too much advance will damage your engine.. too little advance will cause your engine to use a little more fuel and develope a little less power.. but its safe and your engine will last longer..<br /><br />course i am talking within reasonable limits here and not being a mile out.. thow there is a far greater margin of error on the retarded side of things than on the advanced side..<br /><br />trog100

 

[Don S]

Re: Idles high after a hard run

Only thing I can say about that advise trog, is I hope nobody takes it as useful information or fact........

 

[Richard Petersen]

Re: Idles high after a hard run

I must be TOO LOGICAL. The choke - system or logic is assembled- wired- computer programed- 0r the temperature sensor is the wrong type - n.o. instead of a n.c.

 

[Don S]

Re: Idles high after a hard run

The Volvo 131's have no choke, computer program, computer, or temp sensor for operation of the engine............. The only temp sensor is for the gauge.

 

[trog100]

Re: Idles high after a hard run

i am sure they wont take it as advice Don.. not even sure is was meant to be taken as advice.. <br /><br />as to the fact bit.. well it is a fact as regards how i have timed engines over the last thirty years.. its also a fact that it has never done them any apparent harm.. they aways run nicely and behave as engines should else i would have changed my method long ago.. i do learn by experience and mistakes.. <br /><br />as to the some of the other facts.. do u dispute my statement that bob-weights temperorarily sticking in the advanced position cannot cause an engine to gain an extra five hundred as it returns to idle.. ??<br /><br />how about my statement along the lines of an engine being better off being slightly retarded than slightly advance.. is that wrong.. ???<br /><br />i might even go as far as to suggest that the "book timings" that u would quote as correct err on the same principle of better slightly retarded than advanced.. <br /><br />i spose i am a seat of the pants trial and error kinda guy.. thow i do believe books and manuals are a good place to start and i do collect em..<br /><br />i have never used a torque wrench in my life either.. hard to believe for some praps but never the less true and a fact.. he he<br /><br />i recon i was led astray years ago by and old lifetime engine rebuilder.. i am going back forty years..<br /><br />i ask the guy why he never used a torque wrench.. his reply was a simple one.. "if i dont know how tight to tighten a nut or bolt by now i never will".. this was said in a rather scathing fashion.. he he.. mind u it probably did take the guy years to learn.. far easier to use a torque wrench and avoid the learning..<br /><br />he was also the same guy that taught me the timing method i wouldnt advice anybody to use.. cos praps that requires some learning too.. he he<br /><br />forgetting the flamable none flamable thing.. cos that is down to the indiviudal and their aint no real answer to it.. its only a matter of opinion.. <br /><br />be a bit more specific about the rest of my none-facts.. i can stand it and folks might learn something usefull from your comments.. <br /><br />come on Don.. i expect better from u than one liner put-downs..<br /><br />trog100

 

[Don S]

Re: Idles high after a hard run

I started to reply to your comments, but realized it just isn't worth my time.