120hp v4 fuel problem??

Hey there,

History first... 1990 Johnson V4 120hp, vro capped off. I bought the boat (1978 Wellcraft CC 20' in decent shape) and motor for relatively cheap money. The motor had a complete top end rebuild and the owner couldn't pay for it so the marine service shop owned it for storage. The boat had been sitting for two years after the rebuild and before I bought it. I put it in the water and it ran pretty nice, a little ragged on idle, popping a bit, but smooth as glass on the higher end. Only had it out twice just before the weather turned cold and low end was getting worse, stalling quite a bit, so I took it out one last time to use up some of the fuel (also should note, did a bunch of work to the boat including new fuel tank, lines and filter assbly-used 5/16" line and vented it well). When I took it out that last time, it ran great for a 15 minute run at @ 4000 rpm (didn't want to push it with the new rebuild). I turned it off for a few minutes, it started right up but when I brought it up to speed it ran for about 30 seconds before it bogged down like it ran out of fuel. This happened several times, always restarting well and holding an idle, but would die out if I revved it more than @ 1900 rpm. My first though was that from sitting so long, some crap must have come off the lines in the motor or carbs and plugged up the jets. I let it sit for the winter and just started attacking the problem this spring. I put in a new fuel filter, even though the other had all of an hour's running time, then I pulled the carbs and they were clean as a whistle and in nice shape. I removed and blew out the jets just in case, but they were certainly not plugged (oddly enough, I found one high jet, behind the drain plug that was completely threaded out, the others were fine- thought I found the trouble....). Still didn't fix the problem, but the idle was a little smoother... Next, thinking that there might be a pinched line or vent I checked all that, finding nothing. Then I pulled the fuel pump, thinking it might have some crap in there, but found it nice and clean (also checked all the motor fuel lines which appear to be in good shape). Still dies out at speediing up. Now I'm not sure where to go. It truly seems to me that there is some restriction of fuel so it runs at an idle and when you punch it, it come immediately to speed for a few seconds then dies out like it drained out the bowls faster than they can refill. I would think something like floats but it was an instant problem, worked fine, then not.

I'm planning to test the fuel pump pressure tomorrow, and maybe the cylinder compression just for kicks. The mechanic who did the rebuild is very reputable and seemed to do a good job. I'll eventually turn to him if I can't figure this out, but he's busy and owe's me nothing from the sale.

Soooo, sorry for the long note but I wanted to detail what I had already did/find. Any suggestions??? I have a manual which should have fuel pressure specs, but I'll take any input. Also, if I test the compression, I understand that I should ground out the plugs, just not sure of the best method and will take any tips on that as well...


Thanks for any help!

Evan

Re: 120hp v4 fuel problem??

Sounds like a fuel delivery issue. I would go back to the fuel pump. I suspect a fuel pressure test will point to a worn out pump.

Re: 120hp v4 fuel problem??

check the fuel pump, compression, spark, they can idle, but not pick up if low compression or if not firing, on one. i vote fuel pump, but don't rule out bad coil breaking up.

Re: 120hp v4 fuel problem??

I had an ignition box that ran exactly like that.
Stone cold it ran grat for 10 - 15 minutes than started bogging just like a restricted fuel problem.
Left the engine cover off one day it ran great all around the lake. Put the cover on and within a few minutes it started bogging again.
Once the heat builds within the ignition module it would have to totally cool before it would run good again.
Double check your fuel pump to exhaust all other possibilities, no return on electrical parts.

Re: 120hp v4 fuel problem??

Easy enought to test for a fuel delivery problem to the carb bowls. When she starts to bog out start squeezing the bulb.
Compression test would be a good idea as mentioned and a spark test while shes acting up.

Re: 120hp v4 fuel problem??

I think I may have found it. Even though the fuel system is all new to the fuel pump I decided to rule it out completely by running a new temporary fuel line straight from the tank to the fuel pump. It ran like a top. I then systematically eliminated each component to finding the restriction at the fuel filter. It's a brand new assembly with a new element it must have picked up something from the new tank and plugged the filter housing. I'll pull that housing and check it out. Hopefully that will solve the problem once and for all. If not, I'll run though all the suggestions left here one by one.....

Thanks again for all the help! This forum has been invaluable to me getting this boat in the water on my budget!

Evan

Re: 120hp v4 fuel problem??

Just a word of warning.
If eliminating the fuel filter solved the problem it still may not actually be the filter itself. The filter puts a flow restriction on the system, causing any downstream leaks to have even more effect. In otherwords, by restricting the flow upstream, any downstream leak is more likely to suck air. I leaned this the hard way with a leaky connection on the fuel pump intake. Remove the fuel filter and it ran fine. Put it back in and it didn't. A couple of connectors, clamps, filters and forehead dents later I found the actual problem.

Re: 120hp v4 fuel problem??

Thanks iwombat,

I was thinking of that as well and will check it out. I'm also not convinced that the fuel pump's not weak. I ran out of light the other night after work testing the lines and bypassing the components so I didn't get a chance to throw the tester on the pump or take a close look at those connections. When I removed the pump last week I was thorough in clamping and hose inspection but may have to give it another look if this doen't fix it. I'm going to check the obvious filter assembly first and hopefully I'll find something conclusive and the motor will run well. If not, it's back to testing the fuel pump.

Regardless of this issue, I do seem to get a popping now and then, like a hiccup. That's what first made me think electrical.... I keep telling myself that the motor still has only 3 hrs run time since the rebuild and it's just tight and needs some more running time. We'll see....

Thanks again,
Evan

Re: 120hp v4 fuel problem??

We're gonna file this problem as solved! Thanks to everyone for their suggestions! The problem was the Tempo primer bulb. It seemed to be functioning fine but the it was almost like the springs for the check balls were too strong making it an effort to even blow air through it. The filter housing was clear and lines were good, changed the bulb (to a Napa bulb- need to get over to the boat yard for an OEM as was recommended...) and life was good. I also tried to track down the trouble with the rough idle and ended up checking the sync. and pulling the carbs one more time to check the fuel float levels. They were pretty far from where they should have been, which I suppose could have contributed to the fuel restriction problem as well. I still didn't get a chance to test the fuel pump pressure but it runs like a dream, smooth from idle to WOT. Ran it fairly hard for over an hour and she performed like a champ. I even put it on the dock like I knew what I was doing! It's amazing how much easier that is to do when the motor doesn't stall constantly.....

NOW, maybe I can start chasing those stripers around!!

Thanks again!

Evan

Re: 120hp v4 fuel problem??

watch the pee stream, you don't know when the impeller and T-stat was last changed.