'76 35hp Johnson jolts at full throttle

Hi everyone im new to the forum, but I just bought a 16 john boat with a '76 35 HP Johnson outboard. I've seen that the forum has a lot of knowledgeable people and I have a few questions. At full throttle every 30 seconds or so the motor jolts somewhat violently. At first I thought I hit a log in the water or something. At idle and low speeds it doesn't seem to act up. The motor has new plugs and fuel pump. Q1. What do you suppose is the problem? I called a mechanic and he thought the gears in the lower unit could be shot. I noticed that the fuel fitting is leaking cuz when i squeeze the primer bulb fuel squirts out of the plastic housing. Could the motor be sucking air? I did a search and haven't be able to find anything that resembles this problem. Q2. Should the tell tale be squirting a solid stream of water with the muffs on? I haven't been able to tell the strength of the stream in the lake. Q3. How much should the prop rotate when its in gear? Mine seems to rotate about 1/4 of a turn. Q4. Can you get a water pump and lower unit for this motor if they are shot? Thank you in advance for your response.

Re: '76 35hp Johnson jolts at full throttle

Welcome to iboats!
The condition you describe as a "jolt" is the clutch dog slipping. It can be caused by wear due to incorrect shifting (gently pulling the shifter into gear, instead of a quick snappy shift as one is told to do in the owner's manual), bad shift linkages (worn out), incorrectly adjusted shifter and/or linkages, etc. You should have a solid, hard stream of water coming out of the tattle tail at idle, and water pump impellers are cheap and available. You will likely have to disassemble your lower unit and replace the defective parts which may be limited to the clutch dog at best, or the gear set and clutch dog at worst. You are unlikey to get away with just a shifter/linkage adjustment because even if that was the only problem, your clutch dog is probably damaged at this point. I would just buy a new fuel connector and forget it. They do have seals in them that go bad over time.
Hope this helps,
JBJ

Re: '76 35hp Johnson jolts at full throttle

I just looked up some videos on you tube and it looks like my motor is spitting out about the same amount of water as a motor on there so you can forget about that question. I seems to me like my water pump is still good.

Re: '76 35hp Johnson jolts at full throttle

A1. Check you lower unit oil for any signs of metal particles.
A2. The tell-tale should pump a solid stream as long as the water pump is working correctly.
A3. Yes, the prop will rotate some when in gear and not running, the gears and clutch dog have some tolerance in them.
A4. Yes, water pumps and parts should be available from various sources.

Re: '76 35hp Johnson jolts at full throttle

cbuckla said:

I just looked up some videos on you tube and it looks like my motor is spitting out about the same amount of water as a motor on there so you can forget about that question. I seems to me like my water pump is still good.

Click to expand...

The water pump may very well be working great. However, as a person who has run old, used motors for many years---I drop the lower unit on every used motor I buy and at least take a look at the water pump impeller. They are rubber and can get dry rotted, or harden in a position that will allow them to pump some water, but not enough to prevent overheating. I look for any lack of flexibility, cracks from dry rot, and hardening of the blades in a curved position. The impeller blades should stick out straight when out of the pump body and be nice and flexible.
Good luck,
JBJ

Re: '76 35hp Johnson jolts at full throttle

Also, do not run your motor until you get the clutch dog taken care of. Hopefully, it is just the dog and not the gear, too. The more you run it like that, the more the gear wears...

Re: '76 35hp Johnson jolts at full throttle

Thanks for the responses guys. I will probably just replace the water pump. It's always a good idea and cheap insurance. I ran it that one day for a little while just to check it out and once it started doing that jolting i took it back to the dock and haven't run it since. I drained the oil out of the lower unit and it wasn't milky and didn't have any metal particles in it. I notice a bushing for the shift linkage was worn out, i'm sure that doesn't help matters.

Re: '76 35hp Johnson jolts at full throttle

Plus if i'm in the lower unit I might as well replace the water pump.

Re: '76 35hp Johnson jolts at full throttle

The other thing I noticed is a ground wire for what i believe is the spark advance that is broken off. The advance moves alot and I think it finally borke the wire from bending fatigue. I cant get to the screw to reattach this wire cuz its under the flywheel. Is there anything tricky with removing the flywheel and advance? Also how do you disconnect the shift linkage? Can you disconnect it once you separate the lower unit a little, or is the disconnect up by the power head?

Re: '76 35hp Johnson jolts at full throttle

As a follow up to this post I found out that once I adjusted the shift cable and held all the way down on the shift lever the motor no longer jolted. Seem like it simply wasn't fully engaged in the forward gear.