85 hp evenrude v4 not idling less than 2000 rpm.

[reptileguy]

1980 85 hp evenrude v4 not idling less than 2000 rpm. The carbs are non adjustable and have had rebuild kits put on. Timing was set at 4 btdc but pretty much useless until rpms are down. I can't set it the advance way as under load in water it just backfires and misses a lot when I throttle. I confirmed reed valves are good and installed new manifold to crankcase gasgets and carb gasgets. I did notice one of the check valves was leaking fuel under the carb, further inspection showed it was broken so replaced with a brass check valve as plastic is not available. Now it won't idle at all. Can someone confirm which crankcase vent hoses go where as well just to confirm thanks

 

[reptileguy]

Oh and confirmed strong spark on all 4 cyl they all jump more than 7/16" gap

 

[emdsapmgr]

The idle on that engine is set by adjusting the timing. Nothing to do with the carbs. The idle timing is set when the boat is floating normally in the lake, and in forward gear. Adjust the timing so that the engine idles between 650 and 750 rpm's. You can have a carb issue, causing incorrect idle if the carbs are not set properly. When at idle both sets of carb butterflys must be closed. If one is slightly ajar, it will suck more air and that will cause other jets to provide fuel to that extra airflow. Those plates are adjustable between carbs, so it is possible to have one carb butterflys closed and the other one slightly open. Make sure all 4 butterflys are closed when at idle.

 

[sutor623]

How is the compression on this motor? These V4's can be finnicky in the link and sync department. Did you do a full sync after the carb re-assembly?

How does she run in the upper RPM range? Will it idle at lower RPMs in neutral at all?

 

[reptileguy]

125 lbs each cyl compression, butterfly's closed . I can't get higher rpms because it backfires and misses too much

 

[Bosunsmate]

i cant rememmber where they go but check the four bypass cover nipples have hoses on them and no holes in them.
sounds like an airleak or a blockage behind a jet in one of the small passages

 

[sutor623]

Sounds like a timer base fault to me. You may also have a cracked or misplaced flywheel magnet. Save yourself a lot of guesswork and get a DVA adapter for your multimeter and go to the CDI electronics link in my signature.

Other thing I would do is put a clear line in between fuel pump and carbs to check for air in the system. The fuel pump rebuild kits for these motor are very cheap, so since you rebuilt the rest of the fuel system, I would certainly change out the old pump diaphram.

 

[reptileguy]

In water in gear 1400 rpm is the lowest I can get which of course is bad to shift but I disconnected the throttle cam from the carbs , held butterfly's closed , bottomed out timing and that's the lowest rpm I can possibly get. Adjusted with timing light as well and still can't get lower, I sprayed carb cleaner around crankcase and butterfly's on carbs and no rpmchanges

 

[Tim Frank]

Did this issue just start?

 

[reptileguy]

No, started last fall, went to a marina for work and they couldn't figure it out

 

[sutor623]

A simple test to see if timer base timing is on point is to take the plugs out, get each plug to TDC and mark with a white crayon, the flywheel right where the pointer is for each cylinder (with the corresponding number) Then while the engine is idling, hook a timing light to each spark plug wire and point the gun at the flywheel. You should only see the number show up from which cylinder you are hooked up to. If you see different numbers show up, you have either a bad timer base or magnets in your flywheel displaced.

I really would check the flywheel for a loose magnet. So many people have scratched their heads over these issues. Very hard to diagnose without visual inspection.

 

[Tim Frank]

No, started last fall, went to a marina for work and they couldn't figure it out

But did it come to you like that, or you've owned it for a while, and this just started.
i.e. has this ever run OK for you?

 

[Tim Frank]

A simple test to see if timer base timing is on point is to take the plugs out, get each plug to TDC and mark with a white crayon, the flywheel right where the pointer is for each cylinder (with the corresponding number) Then while the engine is idling, hook a timing light to each spark plug wire and point the gun at the flywheel. You should only see the number show up from which cylinder you are hooked up to. If you see different numbers show up, you have either a bad timer base or magnets in your flywheel displaced.

I really would check the flywheel for a loose magnet. So many people have scratched their heads over these issues. Very hard to diagnose without visual inspection.

^^^ if that actually works (and I am by no means doubting it ) that may be the best single diagnostic tip I've seen in here.
Unfortunately it doesn't apply to any of my O/Bs, but still....

 

[Bosunsmate]

i too imagine your timing is off, might be that the flywheel keys sheared

 

[reptileguy]

Flywheel was pulled a few weeks ago. Key not sheared ,magnets had slight surface rust so cleaned them up and the timing base was not cracked or discolourd or have the oily residue they get when breaking down.no magnets are loose but I will try the tdc thing thanks

 

[sutor623]

^^^ if that actually works (and I am by no means doubting it ) that may be the best single diagnostic tip I've seen in here.
Unfortunately it doesn't apply to any of my O/Bs, but still....

Thanks Tim. I learned that from an old Merc tekkie. Found a couple failing triggers in my day with that trick. It only tells if the trigger/timer base is firing erratically, or not at all (which can be also caused by loose/broken flywheel magnets). Hard to tell if it is over or under-firing on the proper cylinder (although sometimes you can see the light drop out when hunting for a mis-fire.) They do make timing guns with RPM meters on them, which can also help to tell the story.The other aspect that it cannot diagnose is if you are getting ENOUGH voltage for a given revolution. These inductive timing lights are sensitive, and just because it flashes, it doesn't mean there is a strong enough spark. That test is left best for a DVA meter and some test leads off the timer base wires.

From what I understand, a single cylinder can fire multiple times in a single revolution, burning the mixture prematurely, then when that proper firing signal comes around, there is nothing left to burn. Also, the incorrect cylinder firing at the wrong time can slow down the upward traveling piston, causing all kinds of bad running characteristics. Basically, the motor can start to work against itself.

 

[reptileguy]

Haven't Timed just yet after the crayon but noticed cyl 1,3,4 were fouled wet oil soot, cyl 2 has a lil spot on electrode that's it with oil

 

[sutor623]

You have been running a motor that has premix 50:1 at just above idle trying to diagnose an issue, so I wouldn't pay too much attention to the wet plugs.

And visual inspection of timer base is a poor indicator unless you are just looking for cracked magnet/wires. The timer base wires can have issues too. I have seen motors where the wires were breaking down, and they would short out when the throttle was pushed (because the base would spin and the broken down insulated wires would touch.) Once you do the crayon test, if it passes, we will need to see the timer base output on a DVA meter to fully confirm its functionality.

 

[reptileguy]

Ok crayon test worked good. All cyls firing when they should. The engine is very hard to start from cold and only runs on primer fuel until it warms up then runs on its own. Doesn't make sense . This is usually from a dirty carb but they are spotless even took welsh plugs from carb cleaned ports and replaced plugs

 

[sutor623]

Ok crayon test worked good. All cyls firing when they should. The engine is very hard to start from cold and only runs on primer fuel until it warms up then runs on its own. Doesn't make sense . This is usually from a dirty carb but they are spotless even took welsh plugs from carb cleaned ports and replaced plugs

Ok good. Now its time to check all of your voltage values on your ignition system with a DVA meter. The CDI link on my sig will give you a step by step diagnosis. You may just not have enough voltage making it to the plugs to fire the cylinders properly. Only way to test is checking voltage with a DVA right where the powerpack comes into the ignitioncoils.