EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

[raybow1]

I have a 1992 evinrude v4 90hp and just bought it. I do not know a lot about it so we took compression test and all cylinders tested 145 to 150. When we first started it the motor ran real rough and would not idle and sounded like it wanted to lean out. I took the carbs off and rebuilt them noticing that the float bowl covers were warped. I sanded them flat on a belt sander to get the gaskets to seal and it seemed to work. The boat now runs much better and does idle ok but it wants to backfire and spit and sputter sometimes. It seems to be burning real rich. I put new champion plugs in and gapped to .30 prior to running as well. When I covered upper carburetor with paper it sucked in as if reeds were working properly. When I tested lower carb it seemed to not make any difference when i covered it. It did not seem to suck the paper in and it did not seem to change the way the motor ran. When pulling the plugs to inspect, two looked to be like they were not burning the fuel properly. Could this be reeds or does anyone know what I may need to look at next?

 

[dieselcat]

Re: evinrude 90 hp v4 runs good then backfires

Re: evinrude 90 hp v4 runs good then backfires

Did you check and make sure all cylinders are firing?

 

[raybow1]

Re: evinrude 90 hp v4 runs good then backfires

Re: evinrude 90 hp v4 runs good then backfires

Yes they are all firing. I also checked the resistance on the plug wires and they all tested good. One was a little weaker than the others but was not bad. I also ran motor with removing one plug wire at a time. They all made a fairly moderate difference in the way the motor ran so I know they are all working ok. I have not tested in the water yet, just at house with rabbit ears hooked up. Can a coil cause the motor to occasionally hickup with a miss like this? It will be idleing just fine and then backfire for no apparent reason. It will do it at a higher motor speed as well. It almost sounds like a timing problem to me but it starts great and runs great except for the occasional backfire.

 

[MAW31]

Re: evinrude 90 hp v4 runs good then backfires

Re: evinrude 90 hp v4 runs good then backfires

is there any difference in the running between cold and once its warmed up?

 

[raybow1]

Re: evinrude 90 hp v4 runs good then backfires

Re: evinrude 90 hp v4 runs good then backfires

It actually runs better when it has been run for about 4 to 5 minutes but it still has that occasional backfire or what seems to be a backfire. The motor will be idleing perfect and then it will sometimes die when it backfires. If it is running at a little higher speed than a idle it will sometimes backfire and drop way down in rpm and then pick back up.

 

[raybow1]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

Does anyone think this could be a timing issue?

 

[mrbrink]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

my 30 horse will do the same thing. worse when its cold, never does it in gear. if I turn the mix screw a a hair richer it helps the issue, you might have a carb tuning issue like myself

 

[raybow1]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

I will try and get it into the water tomorrow to test it in gear. The motor does not look like it has any time on it at all. Even the carbs inside looked spotless. It appeared to have sat for quite some time so I changed the needle valves and seats in the carbs and the lower flaoat cover assy gasket. The one thing I did notice was the bowl covers were warped. Is this a common problem? I ended up putting them on a flat sanding machine and basically resurfaced the covers true and flat. I then noticed that when torquing the covers on one out of the two pulled the edges down as I tightened to specs. The parts house was closed so I cannot order till today. That being said it looks like they are working but it obviuosly will be a problem in the future. The float chamber assy part number is 0398544 but is there an updated part number? The reason I ask is I do not want this same kind of chamber assy if there is an improved assy available.

 

[emdsapmgr]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

The crossflow engines in the 1989/1990 time frame came out with the plastic carb bowls. Over time they will all warp and become unuseable. Most of them warp and wind up leaking fuel inside the cowling, esp when the engine is tilted. A few bowls will warp and permit excess air to be ingested into the fuel rod area, causing a lean condition when running high speed-not good. We saw a blown powerhead due to long term scuffing due to leaned out carbs with the plastic bowls. Bombardier used to sell replacement cast aluminum carb bowls kits-you may want to purchase two of them. Your term backfire may be what we call a "lean sneeze." This can occur when the engine idles and is caused by running lean. When the engine idles, the carb butterflys are closed. The only way fuel gets into the powerhead is through the special idle passages in the carb bodies. If these passages get clogged (maybe with dried fuel from an improper winterization, or just old gas) the engine will not idle well and will sneeze. These can be cleaned by spraying an aerosol carb cleaner through them, esp comparing the aerosol flow rate from one carb orfice to the same orfice on the other carb. Also, pull all the jets and visually check them.

 

[dieselcat]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

Also take some copper stranded wire and run it through all the jets wile you have em out,will save you from having to do it later.

 

[Faztbullet]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

You may be chasing a ghost as some engines will "lean spit' on a hose, that engine needs to be run in a barrel or backed into the water to supply some back pressure to engine.

 

[jhumphries]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

I had a similar situation on my 1996 90 hp V4 and it turned out to be one of the floats in the carb needed to be adjusted.
Make sure there is no fuel coming out of the over flow on any of the 4 carbs. If it is then look at the float height on that carb and set it to the top of the bowl gasket give or take 1/32 with the carb inverted .
Good luck!

 

[raybow1]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

emdsapmgr:Thanks guys as I really appreciate all of the input. I did visually inspect all of the jets and actually pulled them out. There was absolutely no buildup of any sort on these carbs inside or out. These things were as spotless as I have ever seen for carbs. I have not seen many outboard carbs but have seen many others and was very impressed with the cleanlyness of this whole motor. I will say that I did not inspect the idle jets in the top end of carb body because I did not know they weree there until looking at a picture diagram. I have not got the manual yet. I found what I believe to be aluminum replacement bowl assys' but am waiting for confirmation before ordering. I will feel much better when these parts are replaced to know I have sufficient pressure on all parts of the gasket internally.

Faztbullet: I am hoping that you are right as the motor other than the occasional backfire seems to idle great right now. It is night and day prior to working on carbs. The problem I have is I just don't like leaving anything for chance and those bowl covers, to say they are suspect, is an understatement in my book. I just don't know much about these motors so I am trying to master and solve all of the basic issues one may assume is ok.

jhumphries: When I get the new float cover assemblies I will pay very close attention to the adjustment on the floats. I did adjust one of them but not like you said. I simply leveled it according to the body of the carb and that may not be the same as you are talking. The good news is before the work on the carbs the body of the motor did have some risidual fuel in it and now it has none and is not leaking at all.

dieselcat: Why do you recomend copper wire? I will do so but was just curious. Is it because of the softness of the wire?

Thanks again guys. Lots of good info in this thread.

 

[raybow1]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

I finally took the boat out today and once in the water it started like a car. A couple revolutions and it fired right up. What I noticed was the fact that the motor actually was not backfiring but rather it would hickup now and then. As soon as we put the motor in gear it all went away. the motor did not hickup or miss at all. We idled around for a few minutes checking the shifting (which seemed very smooth) and then took it up to about 35 mph. The motor at high speed never missed a beat as it really sounded smooth. As soon as we took it out of gear it would occasionally hickup and sometimes not for a couple of minutes. Yet other times it would hickup every 3 or 4 seconds at times. As soon as you put it back in gear it would not do it. Is this normal?
What should I look for next if not?

 

[reelnative]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

sounds like a fuel float adjustment, also did you ck your sink and link

 

[Faztbullet]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

Thats a lean spit, check that the gasket and cover are snug on top of carb, if overtightened the gasket will "bulge" from under cover and cause a lean condition.

 

[raybow1]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

Thanks guys, I actually have new aluminum float assemblies coming as the old ones were warped real bad. I did tighten the cover on top probably too much so I will pull them off and try to find specs on torgue on the screws. I took the old float assemblies and milled them flat just to try to make sure there were no other pending problems but when retightened I noticed one out of the two was warping again. Whatever material was used originally was not good. It appears as if I am narrowing it down thanks to all of your help. Thank you guys so much for your input as it is worth its weight in gold. The float assemblies should be in friday, so I should have it all reworked and tested Saturday. I'm keeping my fingers crossed.

 

[Chinewalker]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

Silly question, but you didn't happen to cross two of the plug wires when you were checking compression & spark? The motor may run like that, but would run erratically like you described...

 

[raybow1]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

Chinewalker:
I will double check that. Boy that would be embarrassing! Would the motor run that good at high speed though?

 

[QuackAddict84]

Re: EVINRUDE 90 hp v4 RUNS GOOD THEN BACKFIRES

It's got a lean spit for sure. Since it runs fine at higher RPM's, you can pretty much rest assured that it's an idle mixture problem. This is best resolved with the engine in the water, because the backpressure on the exhaust system from the water makes a significant difference in performance. Get it warmed up, then start backing the idle mixture screws out a quarter to half turn at a time and see if it quits. If backing one out a full turn does not fix the symptoms, then put it back in it's original place and try the same procedure on one of the other carburetors. They'll probably need to be 2 to 2 and a half turns out from gently seated. You've got a simple problem that just needs a little trial and error to get right.

If you had some plug wires crossed, it would run terribly at high RPM's, and most likely wouldn't idle at all.