Decarb, now fuel problems?

eavega

Lieutenant
Joined
Apr 29, 2008
Messages
1,377
Okay, here is the situation. I have a 1976 Johnson 70 HP which was running pretty good. Carbs were done last year before I acquired the engine, and hadn't had any real problems with it. Spark checked out at 1/4 inch gap with a tester, and compression was 110 and even across all three. Just before the boating season began I did a decarb with seafoam. New plugs after that, and now problems have started. Here is the symptoms.

I get the boat in the water and it starts right up on the second bump of the key with the choke. warmup lever for a couple of min and off we go. idle out of the marina and no problems. WOT throttle run, but motor will only get to about 5K RPM. It was previously running at about 5300 RPM with a 19" pitch stainless steel prop. Met up with some friends on an island on the lake. Cut the motor and beached the boat. Got it ready to pull a tube, jumped in and started it up. Took a couple of tries this time to get it running. Now with the tube behind me I can barely get the motor turning 4700 RPM. I figure maybe the additional drag is lugging the motor. I come back to the beach, switch the prop for a 17" Pitch aluminum. I get back in the boat, star it up put it in gear, and the motor falls flat on its face. It will idle all day long, but as soon as I hammer down it seems to lug then die. The rest of the gang is done on the island and are going to a deeper water anchor to let the bigger kids swim off the boats without the muddy bottom. I re-adjust my Smart Tabs to the 3 hole (previously in the 4 hole) to see if that will make a difference. I'm still gonna try to tow the tube, this time with two little ones so the weight in the tube is less than 100 Lbs. Now it becomes harder to start. a coulple of times it almost starts, but then gives me a sneeze and dies. Once I get it started I raise the warmup lever and the motor revs up at will (don't let it go past 2500 RPM and even that only for a second). The minute I throw it in gear it dies. after a couple of times doing this, I finally get it in gear and it idles along but if I roll on throttle it dies. I let it idle for a few minutes and slowly advance the throttle, and finally it will throttle up all the way. I get to the gang that is anchored and we have some dinner and such. One of the kids asks if he can hydroslide behind the boat. I told him we could try. Again, get it started, let it idle a little, put it in gear, but the moment I hammer down it bogs and dies. I tell the kid that hydrosliding doesn't seem to be in the cards today. I get the ski rope in, and try it again. This time it starts, and again if I cautiously advance the throttle it will eventually go WOT, but only rev to about 4700-4800 RPM with me alone in the boat. We finally decide to head home. Again the problem getting it started. Once started you baby the throttle then it gets up to about 4700 RPM. We make it back to the courtesy dock, unload the boat, and I get it ready to head for the ramp. Won't start. Sneeze. Finally after waiting a few minutes it starts right up, but this time dies while idling.

That was the sum total of the day. Tomorrow I am gonna do another spark and compression test, but it sounds to me like some kind of fuel problem. My question (yes there was a question in all of this) could the Decarb have somehow broken some kind of crud loose in the carbs? Should I also disassemble and re-clean the carbs? Also I am not sure if the fuel lines are ethanol resistant. Could the decarb have done anything to the fuel lines that would cause them to start deteriorating?

My plan of action is: check spark and compression again to make sure those two elements are functioning. If all that checks out, then I am going to tear into the carbs and clean them. I'm also going to make sure the fuel lines inside the motor are the ethanol-resistant lines it should have. Does anyone have any suggestions as to other problems that would cause the above behavior?

any suggestions or comments would be welcome.

Rgds
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Decarb, now fuel problems?

You didn't say what product you used to do the decarb or what method, but if you added it to the fuel, then yes it can break gunk loose from inside the tank, fuel line and carb with chunks possibly plugging things up.

Don't run it in this condition because if it is the carb you can easily destroy the motor.

Clean out the carbs, put on a fuel filter and give it try, it should run OK.
 

eavega

Lieutenant
Joined
Apr 29, 2008
Messages
1,377
Re: Decarb, now fuel problems?

You didn't say what product you used to do the decarb or what method

I mixed half a can of sea foam with 1 gal premix gas, the other half of the seafoam bottle sprayed into the carbs, wait, then run motor with the 1 gal premix/seafoam mix.

So I got out the diagnostic tools this morning to verify what can be verified. Here is what I found.

Compression was 110 - 110 - 105. I had spark on all three (spark tester set at 30K volt gap), but I did see that at times cylinder 3 would occasionally miss. I found that there seems to be a spark leakage on the plug 3 boot. I don't know whether to just replace the spark wire and boot, or replace the whole coil. I'll have to do some more diagnostics on the spark on 3. When running on the timing light, it never seemed to miss a beat, though.

I'm convinced it must be fuel related, so my next plan of action is to replace the fuel lines from the connector through the carbs. I'm also going to clean the carbs. Now, the carbs were rebuilt less than a year ago, and have the newer neoprene gaskets. I'd rather not have to rebuild the carbs with all new gaskets. Will disassembling them and re-cleaning suffice, or do I have to do a full kit on each carb?

Any suggestions or opinions welcome.

Rgds
 
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