89' 90 horse stumbling at 4K - Hey OBJ.

[Marc J.]

I bought this one not running. It was rebuilt by a local shop five or six years ago, but not used at all the last two. Compression ranges from 142 to 150. I fixed the trim motor, new t-stats, gear oil, cleaned the carbs, replaced the L77CJ4s with QL82Cs (gapped @ .035), and replaced the fuel line and bulb. It has a newer 4-wire VRO (which I converted to pre-mix) and fresh fuel/oil in the built in tank. It starts easily and idles smoothly.<br /><br />Today I checked the timing at the ramp, because I noticed the lock nut on the timing advance was left loose. The engine would smoothly advance to just a little over 4K and start to stumble. I set it at 26-27 because I could not reach 4500 rpms. I took it for a short ride afterwards. The engine stopped pulling at 4K and the boat would not plane out with several attempts. I pulled the plugs when I got home and they were really dry and clean considering I mixed the fuel/oil at 32:1 for the first tank. I suspect fuel starvation. I'm gonna try a portable tank tomorrow. Where should I look if this doesn't help?

 

[SpinnerBait_Nut]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

I would first check to see if the throttle plates are going WO at WOT. They might not be opening up all the way, hence, the stop pulling at 4K.

 

[OBJ]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

Good suggestion from SBN. Check the sync and link before the next run.<br /><br />It is also possible that you have a cylinder dropping out. Had a similar problem with my 90 which is an 86'. Idled fine and would come up well until it reached 35 to 4k rpm. #1 cylinder would stop firing. Was lucky to get 4500 after that. If you have someone to go with you, take an inductive timing light and check each cylinder for fire at WOT.

 

[Marc J.]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

The throttle plates open fully (and together), but not easily. The throttle control is taking too much effort at the last 3/4 of it's range. It must need lubricating.<br /><br />Could the use of the non "Q" plugs have damaged the power pack? I haven't had a chance to get back to the ramp. I may borrow the coils of my 87' 88SPL to rule them out. Too bad the power packs aren't the same. What fixed your problem OBJ?

 

[Marc J.]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

^

 

[Marc J.]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

^

 

[OBJ]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

I found a bad wire at one of the amphenol connectors Baja.<br /><br />I was re-reading your original post. Did you set the timing at the dock or while under way? If you were at the dock, you will not have it set right. The boat should be under way at WOT with at least 5K RPM on the tach.<br /><br />Have you checked for spark with the timing light while under way yet? I'm still thinking your dropping a cylinder.<br /><br />Joe Reeves posted a way to set the timing without the boat in the water, here's what ya' do.<br /><br />Pull the spark plugs and connect the spark plug wires to a spark tester so you can connect a timing light to #1 wire.<br /><br />Remove the control cables and move the throttle lever (on the engine) to WOT and tie or wire it against the timing stop. Don't put the engine in gear.<br /><br />Be sure your battery is good and fully charged. With the timing light pointed at the timing pointer, crank the engine. Set the timing 4 degrees less than what's posted on the sticker. If the stickers says 26* BTDC....set it at 22*. The power packs will take care of the other four degrees.<br /><br />Keep us posted as to what's happening.

 

[Marc J.]

Re: 89' 90 horse stumbling at 4K - Hey OBJ.

I checked all the ignition connections and got some resistance readings. One of the coils would give a different reading every time I checked it. It was usually way out of specs (275+/- 50 ohms). I borrowed one off my 87' and it seems to have helped. I managed 5500 rpm at WOT on a test run. Setting the timing at the ramp is still a no go. It will only pull 4K tied to the trailer. I'll use J.R.'s method until I get brave enough to hang off the back at speed. The decal on the breather says 28*, would 26* be easier on the engine?<br />Thanks for the help OBJ.