125hp idle problems

[wilkin250r]

I've got a 1988 Force 125, but it actually looks like it was possibly pieced together from several Force motors.<br /><br />With a little starting fluid, I can get it to start. Once it starts, I can keep it running as long as I keep the RPMs up, but if it drops below 1200 rpms, it will die.<br /><br />I've tried the obvious idle adjustment screw, i've tried everything from 3/4 turn to 2 1/2 turns, the result is the same. It won't idle.<br /><br />The compression is a solid 135 on each cylinder, the reeds look good, the only thing that seems to help is the timing. If I advance the timing to full advance, it will almost idle. Obviously this isn't the correct mode of operation, but it's the only thing that seems to have a positive effect.<br /><br />Any suggestions on what my problem could be?

 

[Oldsaltydog]

Re: 125hp idle problems

You may want to look into the following possibilities: carb cleaning or rebuilding, fuel filter condition, tight fuel-line connections, choke operation, decarboning the motor, and fuel pump output.

 

[eurolarva]

Re: 125hp idle problems

Also dont use the starting fluid. Use a premix of gas and oil in a spray bottle. Either is real bad for a two stroke

 

[wilkin250r]

Re: 125hp idle problems

Thanks for the suggestions, and I've already tried all of those. Before I posted this question, I have already taken apart the carbs and cleaned them, rebuilt the fuel pump, replaced all the spark plugs, brand new fuel lines and I'm using fresh gas from a separate 5-gallon gas can. The only thing I didn't try was decarbon, but I was told the motor was a fresh rebuild.<br /><br />I've checked the timing according to the manual, and although I can't determine Top Dead Center exactly, I can eyeball it pretty darn close, and the timing seems to be good, at least on the #1 cylinder, which is all the manual covers. Then, just to cover any error I may have in eyeballing TDC, I tried retarding the timing a little, and then advancing the timing a little, and every point in between, and nothing seemed to work.<br /><br />I'm at my wit's end. The motor runs, I'm so close, but this last idling problem has got me perplexed.<br /><br />The only other option I can think of is to check the timing on all other cylinders. But at the risk of tooting my own horn, I hooked up the ignition myself, and I seriously doubt that I wired it incorrectly.

 

[Oldsaltydog]

Re: 125hp idle problems

Sounds like you have covered a lot of territory. For your next step, you could check with themarinedoctor.com.

 

[Scaaty]

Re: 125hp idle problems

Try adjusting the tierod off the tower shaft that runs the bottom carb throttle plate to get the bottom carb open a bit at idle. Make sure that the flat rod going to the top carb is tight and working too. You could loosen everything up and use a couple toothpicks to hold the butterflys open, and go from there. ALSO...MAKE SURE there is a black roller on the bottom carb that follows that cam plate...if thats broke or gone, you won't get the carbs to open without a bunch of throttle. Keep us posted, and good luck (I have a friends 88 125 that has sit for 10 years waiting for me out in the yard..wish ME good luck!)

 

[Scaaty]

Re: 125hp idle problems

see next post

 

[Scaaty]

Re: 125hp idle problems

[QB]

<br />"I've tried the obvious idle adjustment screw, i've tried everything from 3/4 turn to 2 1/2 turns, the result is the same. It won't idle."<br /><br />What you did here is mess up the low speed jets if that (obvious) screw is the angled one facing forward. Turn them in (gently) until closed and then back out 1/1/2 turns. Get those throttle plates set right, then the last thing to do is go back and turn those low speed jets in until a stumble, then back out 1/2 turn...do each seperately

 

[wilkin250r]

Re: 125hp idle problems

Originally posted by Robby6950:<br /> <br />What you did here is mess up the low speed jets if that (obvious) screw is the angled one facing forward. Turn them in (gently) until closed and then back out 1/1/2 turns. Get those throttle plates set right, then the last thing to do is go back and turn those low speed jets in until a stumble, then back out 1/2 turn...do each seperately

I've worked on motorcycles for years, I'm familiar with small carbs, and these are very similar. In fact, they are much simpler, because they use a butterfly valve instead of a slide and needle. They only have two adjustments, the main jet and the idle mixture. Also, I have the manual. Since it throttles up and down just fine above 1500 rpms, it would seem that the main jet is correct. Plus, it coincides with the recommended settings. So I figured the problem was the idle mixture scew. I first tried the recommended 1 1/2 turns out, and that didn't work. I then tried everything from 3/4 turns out to 2 1/2 turns out at 1/4 turn intervals. I should have covered everything from way too lean, to way too rich. It wouldn't idle at ANY idle screw setting. In fact, you would think that 2 1/2 turns out would be WAY too rich. It seemed to run best at 2 1/2 turns out, but it still didn't run correctly.

 

[wilkin250r]

Re: 125hp idle problems

Having the bottom carb open just slightly is a good idea, I might try that. Anybody else recommend this as a possible fix?

 

[eurolarva]

Re: 125hp idle problems

What elevation are you at in Reno? You may need different Jets on your carb?

 

[wilkin250r]

Re: 125hp idle problems

The manual suggests .101 in the top, and .094 in the bottom, at sea level. It doesn't give jetting for different altitude, but a parts store said .092 for 3000ft, and .090 for 4500 ft. I'm at 4500 ft, and right now I've got .092 in both, but it's certainly not acting rich, so I figure I'm ok. If anything, its actually acting lean, since I get a backfire every once in a while.<br /><br />The main jet shouldn't affect my idle mixture much at all, it's set by the idle mixture screw. The main jet should only affect 1/2 to full throttle. And 1/2 to full throttle, my motor is just fine.

 

[Scaaty]

Re: 125hp idle problems

Just for kicks, put an inline spark checker (Harbor Freight $5) and see if you lose spark dropping down to idle speed. Stators known to go bad, as power packs. But those motors have a complicated system for adjusting the carbs, but as long as you have a manual....? Are you sure you have adjusted the tower shaft idle speed screw properly? The one by the bottom carb? And I have 12 motorcycles and four boats and 45 years wrenching and you should see the mistakes I still make....

 

[wilkin250r]

Re: 125hp idle problems

I haven't tried the inline spark checker, that is a VERY good idea.<br /><br />The idle speed screw was set improperly when I got the motor, so I adjusted it. The carbs were open nearly .10 inch. The carbs should be fully closed at idle, shouldn't they? At zero throttle, the cam should just barely touch the black roller, but it shouldn't put pressure on it and open the carbs at all. If I open them even a fraction, I get 2000 rpm, certainly much too high for an idle. If I open them to .10 inches as previously set, I get well over 2000 rpm, so the idle could not have been set properly when I got the motor.

 

[eurolarva]

Re: 125hp idle problems

YOu are correct. At idle the butterfly should not be open and the cam should just be kissing the cam. Mixture adjustment should be about 1 1/4 turn counterclockwise from fully seated then adjusted either clockwise or counter clockwise by 1/8 turn increments till it is right.

 

[Scaaty]

Re: 125hp idle problems

Originally posted by wilkin250r:<br />At zero throttle, the cam should just barely touch the black roller, but it shouldn't put pressure on it and open the carbs at all.

No wonder it won't idle.<br /> Problem here is that the IDLE SPEED ADJUSTMENT IS ON THE TOWER SHAFT (towards the bottom between the bottom and second cylinders) THAT RUNS THE CAM THAT THE ROLLER TOUCHES! If the roller aint touching, just what in the hell WOULD YOU BE ADJUSTING? You adjust the roller to just touch at the marks, AND THEN ADJUST THE idle speed screw. And the tie-rod needs to be removed for adjustment..same thread both sides. Last post.. good luck...and I am looking at TWO 125 Black Force motors as I type this and they both idle fine. Re-read the manual. Different carbs and set-up on 120, 125, 150..........

 

[Scaaty]

Re: 125hp idle problems

Follow up...the roller is a eccentric screw..you line it up with the marks so as to not go over center at WOT.<br /> And that idle speed screw on the all black motors is so OVERLOOKED (small 1/4 flathead) that most people don't even SEE IT.

 

[Scaaty]

Re: 125hp idle problems

Follow up #2...<br />Bad advise on the spark checker as when the engine dies, OF COURSE the spark will quit. Only applicable on problems with one or more cylinders not firing...not all. Age don't make ya smart, just old.