Low RPM's on '79 Johnson 115hp

[reagon]

I bought a '79 115hp Johnson from a guy and have taken it out a few times but the motor has yet to get over 2,500 rpm's. When I open up the throttle with the warm up lever with the muffs on it gets higher, maybe 3,800 or so, but starts to run rough. The carbs are recently rebuilt. I will do a compression test and spark test and link and sync, but I was wondering if the rough running with the warmup lever was a hint of some kind. Maybe the timing is off? Just wondering what anyone's thoughts were before I launch into it.

 

[tashasdaddy]

Re: Low RPM's on '79 Johnson 115hp

do the test you mention compression, spark. did you remove the jets in the carb a clean them, blow out the ports, and use rebuild kits, replace fuel lines? read here
http://forums.iboats.com/showthread.php?t=299680

 

[reagon]

Re: Low RPM's on '79 Johnson 115hp

spark and compression are good. Compression is 120 across all four. Why would the engine run smooth on the lake with the throttle wide open, but just not go above 2500 rpm? I will move on to link and synk and timing. A question on timing. How do I know what 26 degrees btdc is? I can see the mark on the flywheel for 0, but how do I measure 26 degrees on the flywheel?

 

[emdsapmgr]

Re: Low RPM's on '79 Johnson 115hp

Is the tach on the correct setting? Do the carb butterflies open completely-check with the airbox cover off. Check for good spark on all 4 cyls. A normal inductive timing light will check both the spark and the timing. Once you get the engine to run at least 5000, recheck/verify the timing as it will increase somewhat at high rpm's. Have you got a copy of an original factory service manual?

 

[Chinewalker]

Re: Low RPM's on '79 Johnson 115hp

Do not continue to run it until you verify that A) the tachometer is working correctly, B) that you are getting full fuel to all four cylinders, and C) that you are getting full spark to all four cylinders.

Reason is, if you have a plugged jet or two in the carbs, then those cylinders are not getting lubrication, which is mixed with the gas. Continuing to run the motor with a plugged carb will damage the related cylinders...

 

[reagon]

Re: Low RPM's on '79 Johnson 115hp

The tach is fine. The engine runs smooth but it sounds exactly like 2500 rpms and the boat's moving pretty slow and not planing. How would I check to see if I'm getting full fuel to all four cylinders? Can anyone answer my timing procedure question. How do you tell where the timing is on the flywheel with the timing light without a sticker or something marking the degrees?

 

[emdsapmgr]

Re: Low RPM's on '79 Johnson 115hp

The flywheel is cast/marked with degrees. There is a timing pointer on the front of the block just above the top carb. The airbox should have a gummy label indicating degrees of max timing. That engine was around 28 degrees, set at 5000 rpm.

 

[reagon]

Re: Low RPM's on '79 Johnson 115hp

Thanks emdsapmgr! Exactly what I needed. I don't know why I didn't see it before. I believe I have discovered my throttle problem though, and it doesn't have anything to do with the timing. I opened up the throttle and watched the action of the throttle linkage and realized the throttle high speed arm (I think that's what it's called) wasn't moving at all. The throttle arm would advance, but the high speed arm just sat there. I pushed on it with my finger and it snapped open. It was sticking, probably from sitting for 8 years in the back yard of the guy I bought it from. It's already opening a lot better from me just working it back and forth. Is there a way to grease the throttle arm? Or can I just hit it with WD40? Thanks for all the help.