'79 Johnson 150 lost 1000 rpm?

[Ganis]

I have a problem i'm having a problem figuring out. O.K. last year, i was turning 5200 rpm @ 53mph, then the impeller went out and no alarm, engine heat ceased up. I tore the motor down and sure enough melted #2 piston, cleaned up the head, had the #2 sleeved (was scratched really bad) and bored .2 over along with the rest of them. All new pistons and rings and while i had it tore down i rebuilt the carbs. Now the motor starts and idles great, smother than ever, runs great all the way up to 4200 rpm. I have about 5 hrs on the break in and trying to figure out why when i go full throttle i can now only get 4200 rpm and about 42 mph. I've done a link and sinc adjusted the timing per the reeves method (it had changed alot from where it was set before) all with no change in wot rpm. I've checked the spark will jump 7/16" on all 6. Checked the compression and got between 94 and 105 on all 6 ( with only 5 hrs on the rebuild, i'm assuming the ring not seated yet). Any suggestion as to what to check now?

 

[emdsapmgr]

Re: '79 Johnson 150 lost 1000 rpm?

A fresh 79 150 with the stock 456/457 heads should get you around 110 lbs compression on all 6 holes. While your current compression is lower, it does not explain the 1000 rpm drop. A couple of things to check: You did not mention doing a sync and link after overhaul. Make sure the carb butterflys are opening fully at full throttle. Take the airbox cover off and visually check them to make sure they are absolutely level when the control box throttle handle is fully forward. They can be misadjusted to overrotate and actually close. Have you retorqued the heads after the first heat/cool cycle? Make sure the middle carb roller is intact. Check the timer base to make sure it moves freely forward with the throttle. It can stick/bind, causing timing issues. Take a timing light with you next time out and check for spark on all 6 wires when the engine is under load in gear. Watch the flashes for misfires or nofires.

 

[killingtime]

Re: '79 Johnson 150 lost 1000 rpm?

Dont no if I can help much but is it taking a lot longer to get up on plane then it did before the overheat, and in neutral can it rev well beyond the 4200RPM.

 

[Ganis]

Re: '79 Johnson 150 lost 1000 rpm?

I've done a sync and link, and the timer base always hits the stop when i advance the throttle. I haven't retorqued the heads yet, i was told to do that at about 10 hr mark. I will try the timing light next time out. As far as getting on plane, it's probably a little slower than it used to be but not much (slower because the motor isn't going wot). I haven't tried to rev it past 4200 in neutral, didn't think that was good for the motor without a load on it.

 

[emdsapmgr]

Re: '79 Johnson 150 lost 1000 rpm?

You are right not to rev the engine. I don't run mine much past 2000 rpm ever in neutral. The fact that the engine will run higher rpm in neutral does not have any bearing on how it will run when under load. It will run 5000 rpm in neutral with only 3 cylinders firing. What full advance timing to you currently have the timing set to?

 

[Ganis]

Re: '79 Johnson 150 lost 1000 rpm?

Using the reeve's method, I set the timing to 22 deg, the sticker on the throttle arm states it's supposed to be 26 deg. I will check it under load when i take the boat out next time.

 

[emdsapmgr]

Re: '79 Johnson 150 lost 1000 rpm?

Take an inductive timing light with you when you get the engine under load. Check all 6 plug wires for spark. Any misfires or weak firing will show up. Also, when at full throttle, cut your ignition and put it in neutral immediately, then check your plugs. They should all look the same-light tan.

 

[Ganis]

Re: '79 Johnson 150 lost 1000 rpm?

Well, took it out this morning and checked for misfires using a timing light, all 6 firing fine. Went wot, shut down motor and pulled the plugs, none were wet. I've given up and took it to the mechanic's. He seems to think it's something with the timing. I'll update you when he figures it out. Thanks for the help though.

 

[Ganis]

Re: '79 Johnson 150 lost 1000 rpm?

Finally heard from the mechanic, it appears there was some trash in the high speed pickup tubes (can't remember what they're called, the two brass tubes that come out of the main body of the carb). He said it was some type of black material but he didn't think it was fuel line material. It was to late to pick up the boat today so i'm gonna pick it up in the morning and hit the river and see if that fixed the problem. I'll post again after i get back an let you know if that fixed the problem.

 

[emdsapmgr]

Re: '79 Johnson 150 lost 1000 rpm?

If you still have some of the original fuel lines on that engine, they could be the problem. These early lines are not made to handle ethanol fuels. The ethanol will gradually break down the fuel hoses. The fuel hose debris will lodge in jets, etc. If the hoses are original, replace them. If you order the original/same hose from Bombardier, the replacement 2010 hoses will be made to handle the ethanol.

 

[Ganis]

Re: '79 Johnson 150 lost 1000 rpm?

Well, picked up the boat and hit the river. Same problem, runs great right up to 4000 rpm and stops. Almost like hitting a rev limiter but not missing. Yes i replaced all the fuel lines with new ones when i rebuilt the motor, and i use ethanol free fuel. The mechanic said he'll have to take it out and load test it on the river to see if he can figure out what it's doing, but i brought the boat home this weekend to do some work on the floor that i'm replacing. The mechanic is stumped so far, he said he's checked spark, fuel, compression, and timing everything so far is good.

 

[emdsapmgr]

Re: '79 Johnson 150 lost 1000 rpm?

Some things you have probably already checked: If you are running off a built-in tank, check for debris in the anti-siphon valve at the fuel tank. Did the mechanic remove all the high speed jets and visually check them to make sure they are clear? Try constantly priming the fuel hose bulb when you get to 4000 and see what happens. Try running it on another (different) 6 gallon fuel tank. Any air leaks in the fuel system? Are you running 3/8" fuel hose and hose bulb? Check for debris on the screen inside the plastic cap on the fuel pumps.

 

[Ganis]

Re: '79 Johnson 150 lost 1000 rpm?

Yes the mechanic did check all the high speed jets, and I've got a all new fuel lines from the tank to the carbs as well as an external tank i've been running. The fuel line between the tank and motor is 3/8, but the fuel line inside the cowl is 5/16, could that be the problem? I can't see 1/16 making that much difference and and it matched what i pulled off the motor. I would think the 2 fuel line "t" would cause more restriction than that. No debris inside the screens on the pumps and the bulb doesn't get soft. I also have installed inline glass fuel filters on the lines between the tank and the motor and they look clean. Next time I take the boat out I'm going to try and use the old "finger in the carb" to see if it is running lean at wot.

 

[emdsapmgr]

Re: '79 Johnson 150 lost 1000 rpm?

It's normal to have 5/16" hose under the cowling.