1989 Force 85 HP dies when accelerating

[tflanigan]

I just rebuilt this engine. Bought it from a guy who hadn't run it in about 2 years because of a bad cylinder. Had cylinders rebored to 0.030 oversize and replaced pistons. Once back together, it started right up, seemed to run well, although rpm's a bit low (about 3500 at full throttle, using tach on dashboard - book says 4500 to 5500 normal). I had idle mix set way too rich for first couple of running hours. Have since corrected the idle mix (set idle screws at recommended 3/4 turn out) and am down to 50:1 oil mix after breakin with 25:1. Problem is that when accelerating from idle, the engine dies. Have to choke to immediately restart, but it starts right up and idles fine. Try accelerating again, same problem. Eventually, after letting it idle for a minute or two, I can get it going if I gun it good. Runs good at high speed. When slowed down from high speed, it is usually OK, but will sometimes die. As long as I keep it idling after a high speed run, it usually will accelerate again without too much trouble (if I gun it). But if I shut it off for a few minutes and then restart (it restarts fine, without choking), it just won't accelerate, and I have to again let it idle for awhile. I pulled the plugs, which were wet fouled. Figured my original rich mixture and 25:1 oil fouled things up. Cleaned and reinstalled the plugs, but had same problem the next outing and they were fouled up again. Also find some fuel puddled in the carburetor air intake housing. Any suggestions on how to systematically troubleshoot and fix this?

 

[sony2001]

Re: 1989 Force 85 HP dies when accelerating

Idle mixtures do not have a fixed setting. Each one is different, but should be set to the richer side of lean. Lean is the highest rpm turning right. Try not to have a dominate cylinder that will drag along other cylindres. Note down the settings to a 16 th of a turn. My Force is 8/16 top and 9/16 bottom

 

[cclemon]

Re: 1989 Force 85 HP dies when accelerating

Hello Tflan,<br /><br />Welcome to the board. In your post you mentioned "a bad cylinder". How were the other cylinders? It would be best if you could determine what caused the bad cylinder. If is was a lean condition caused by a dirty carburator, you don't want to repeat the failure with the new rebuild. If you have not yet rebuilt the carbs, you will want to.<br /><br />The problem you have described sounds like fuel starvation.

 

[Charger183]

Re: 1989 Force 85 HP dies when accelerating

I have an 88/85hp. Check the tank air bleed, disconect the fuel line and check for stuck stuff, disconect the outlet from the fuel pump and blow through the inlet. air should pass. blow through the outlet and no air should pass backwards. If all checks out so far than you must remove all 3 carbs and reset the float levels to the EXACT factory specs. Lastly, the timeing is retarded. Don,t argue just reset it to 28deg wot cranking(plugs out). Once you get it set you can adjust the timeing for the max response on the water. Good Luck. Larry...

 

[tflanigan]

Re: 1989 Force 85 HP dies when accelerating

Sony2001: I will readjust idle mixture and see if it helps. Is there a better way to get the idle mix set right than what my book says? It says to adjust until idle becomes "rough". When I initially tried to set this, it was easy to tell when idle got "rough" on the lean side, but on the rich side, it never seemed to get any "rougher". Also, should I get one carb set, then move to next, or should I do all 3 together?<br /><br />Oil Slick: Bottom cylinder was bad. Carbon buildup blew out the piston ring. Other cylinders were OK, but showed about same amount of carbon buildup. Rebuilt carbs, but may have to do it again. Question on fuel starvation: Seems contradictory that the plugs would be wet if this were the case. Is there something I'm missing here? I thought that I was probably still running too rich.<br /><br />Charger183: Thanks. Will try all of this. I do notice that when I fill the fuel tank and get about half full, I have to add fuel slowly or it overflows (i.e. maybe vent line is restricted). However, if this is the case, I'm confused as to why the plugs are wet fouled. Maybe more than one problem.

 

[sony2001]

Re: 1989 Force 85 HP dies when accelerating

tflan the timing set at 32 degrees and all the WOT's centered on their respective cams. The idle SPEED bolt NOT touching the block at the bottom of the tower shaft. Use one turn on mixture screw as clock positions 12/12. Set the mixture screws 1/4 turn [ 3/12] richer than where you think lean is [counterclock wise] on each carb. Start engine & warm up. At idle, lean a carb to get highest rpm. NOTE setting then return screw to richer setting [3/12]. Do the other two and note setting. Now on all the carbs add 1/12 or 2/12 to their respective lean settings to be on the richer side of lean. These settings will never change. If it stalls going into gear go back to the idle SPEED bolt and raise rpm. Any further rpm change should be done HERE. If you still have gas in one of the carb throats then the float may be set too high to stop the inflow of gas. Let me know how it went!

 

[tflanigan]

Re: 1989 Force 85 HP dies when accelerating

Charger 183/Sony 2001: I checked the fuel tank vent and fuel pump as suggested. No problems. Reset the timing to 28 degrees (it was actually too advanced) and adjusted the idle mixture. I think I got it where its supposed to be. Also checked compression, which appears to be within specs. Still no change in how it runs. Seems to idle fine and runs fine at high speed, but its almost impossible to get it to run slowly in gear. Put new plugs in after checking compression and they fouled up again. Top and bottom cylinders are fouled worse than the middle, but they all are bad. I'm thinking the fuel recirc system maybe isn't working. It was interesting that immediately after I put the new plugs in, the fast idle speed was significantly higher than it has been (maybe 500 rpm faster). As I idled more and more (and plugs get fouled up), speed came down. Next I plan to remove the drain reed plate to check the recirc system and take the carbs apart again. Any thoughts?

 

[Charger183]

Re: 1989 Force 85 HP dies when accelerating

It is possible the recurc sys is a problem but I tend to think we have a bigger broblem with the fuel delivery. My bet is the float level in the carbs. The timing setting I gave you (28deg)is with the plugs out, in gear using the starter to spin the engine. You can advance the timing on the water by the stop-and-go method later. If you are getting 35-3600 rpm max it is likely your prop is a bit much for the boat. dropping a pitch ie. 19 to 17 will help there. Use the Mercury Power Kleen (or whatever) spray to remove the carbon build-up and always add 1 oz of Quickleen to each 6 gal gas to slow down the production of carbon. The wet plug problem at slow speeds is a common with this engine and the Quickleen helps a lot. With the cover off, have you tried to rev the engine by hand using the carb throttles? If so could you "rump-rump" the engine up to 3500? If so, is there any tendancy to have fuel blow back out the carb throats....bad (loose) reeds?

 

[sony2001]

Re: 1989 Force 85 HP dies when accelerating

tflan are you sure all cylinders are getting a a big spark? 3500 sounds alot like you are on 2 cylinders............... Each of your 2 CD units fire two cylinders, so you have a spare, for when you will need it.

 

[tflanigan]

Re: 1989 Force 85 HP dies when accelerating

Charger183: Timing is at 28 degrees retarded with all plugs out and cranking with wide open throttle. I removed drain reed plate. Orifices look clear, but there was some junk in the screens, although it didn't look like enough to block flow. Will clean and reinstall. Got the carburetors out, but haven't had chance to tear apart yet. Last night, wide open rpm was just over 3000. I previously changed out the prop (went from a 17 to a 16 pitch I think - would have to check again for sure), but that didn't seem to do anything. Have not tried to manually rev the engine - will try that next time out and check for blowback. Also will start using fuel additive as suggested. I did use a little of the Power Tune stuff (OMC equivalent) since I think I've probably already built up quite a bit of carbon. Didn't seem to impact performance. Am going to spray directly into cylinders thru plug holes next time to try to clean up a bit more. One thing I have not mentioned and you might not be aware of - I'm in Denver (5300 ft. elevation). How is that going to affect rpm and are there other adjustments that I need to make for this altitude?<br /><br />Sony2001: Spark looks good on all 3. I believe it is running on all 3 cylinders. When checking the spark, I pulled one plug at a time and it started and ran on 2 cylinders, but you could definitely tell that one cylinder was out. I may try that again though and pay a little more attention to see if I can tell if disabling one of the cylinders is worse than the others. As I mentioned to Charger183 above, I'm at about 5300 ft altitude. How will that affect my performance? FYI - My idle mix settings are 8/12 of a turn open on top, 7/12 open on middle, and 11/12 open on bottom. Bottom cylinder seemed to be more sensitive than the other two. Compression is 110 +/- 2 psig on all three cylinders (I believe that this is right at the minimum spec of 135 psig when adjusted for elevation - approx. 12.4 psia here vs. 14.7 psia at sea level).

 

[Charger183]

Re: 1989 Force 85 HP dies when accelerating

High altitude requires the main jet to be increased 1 size. You have a 74 jet as standard. you will need either the 72 or 70. Part #'s-- F10212 = 074/0-2500' <br />F10213 = 072/2500-5000' <br />F10214 = 070/5000-7500' <br />F10215 = 068/7500-10000'