The Spark Advance Blues - '86 110hp

[realboats]

Hi Again. I have a number of issues with the throttle linkage and spark advance with my engine, 1986, 110hp, V4 crossflow. I think submitting a separate post for this question keeps the confusion down and I noticed most of the helpful folks responding seldom answer more than one area of the topic in a post.<br /><br />I went through J. Reeves Static Timing procedure to the letter. My timing is specified at 28 degrees BTDC at WOT. I tried to static time my engine at 24 degrees as per Joe's instructions. One problem, though, is that I could not get my timing greater than 20 degrees BTDC unless I moved the timing base lever back (aft, toward back of engine) about an eight to 3/16 inch from the travel stop and was able to get exactly 24. I tried absolutely everything else as far as adjustments go. <br /><br />Just to be sure I understand the procedure:<br />- Instructions said disconnect the spark advance linkage and wire the spark lever against the stop if necessary (towards front of engine). I don't understand how you can time this way if the timer base lever is not connected to the throttle linkage. But that's what I did, and that's when I found moving the lever slightly forward would bring the timing in.<br />- To actually adjust the timing as shown under the timing light, I understand the only way is using the thumb screw on the rod connected to the throttle cam? (Forgot what it's called, but it's the only adjustment besides WOT and idle adjustments)<br /><br />I'me really curious how the spark advance works during throttle movement, but this is a complicated subject. Could someone point me to a link that may explain how the spark advance, throttle cam, etc all work together during increase and decrese of engine rpm under load?<br /><br />I have every workshop manual you can think of, plus some general outboard theory books and even a video tape. Nothing explains how the spark advance works in any detail. In normal operation, I was wondering exactly when the spark advance should start to move and how far (travel distance) should it move; also, at what point does the spark advance stop moving? At WOT?<br /><br />It would help me a lot if I understood how this worked. I assume it must be similar for all two stroke engines, whether they be boat, ATV, motorcycle, etc?<br /><br />Thanks for your patience. It's important for me to understand something well to get it right. Spark advance has always been "in the background" and I never gave it much thought. However, the schmuck who built this engine may have used the wrong length spark advance link, wrong throttle cams, etc. It really has me climbing the walls and I really need the help.<br /><br />SUMMER GOING BY TOOOOO FAST!

 

[R.Johnson]

Re: The Spark Advance Blues - '86 110hp

Your engine peaks at 28 degree's BTDC, That is with wide open throttle. The engine starts, and idles about TDC. As the throttle lever advances, this advances the ignition stator plate into the direction of flywheel travel. Flywheel clockwise, stator plate counter-clockwise. When the plug fires, the piston, or more correctly the crankshaft is 28 degree's before hitting top center. This makes up for lag in mechanical motion, and fuel burn. Maximum burn pressure will be at top center, or very slightly over. The carb, and spark linkage has to be in proper sync throughout this entire series of event's because it is all done mechanically. The spark, and fuel have to be in sync over a range of 28 degree's for smooth operation. As more fuel is delivered to the cylinder, the earlier that plug has to fire to give the proper cumbustion pressure. Spark advance, taken to extreme's, will try to drive the piston back in it's line of travel, causing an uncontrolled explosion, instead of travelling smoothly over the top of center. Does this make sense, ot does it really take me that long to say " I don't know"

 

[clanton]

Re: The Spark Advance Blues - '86 110hp

If is is a 1986 engine , the spark control rod is moved to differetn holes in the rod retainer to change the timing. Small adjustiments can be made with the eccentric screw holding the roller in the slot.Clymer manual B736 page 244/245 fig 52/53.

 

[realboats]

Re: The Spark Advance Blues - '86 110hp

R. Johnson, ha ha, you obviously know what you're talking about. I'm not a combustion engine mechanic and have to admit that I never gave the functioning of the spark advance much thought. You explained it perfectly! Thanks so much for taking the time and effort to explain that. <br /><br />So I feel like I understand the theory, now I need to figure out the mechanics. Is it safe to assume that I need to keep the timer base lever attached to the throttle linkage in order to get an accurate static time? In this case, if the throttle linkage hits the WOT stop before the spark advance is against its own stop, then something will need to be adjusted.<br /><br />Captain Clanton, you are absolutely right. There are different holes in the rod retainer and I did move mine over to the aft hole. The eccentric screw adjustment makes such little difference that I think it's more for adjusting the throttle cams than the timing. <br /><br />Thanks for the pointer to the clymer manual. Unfortunately, I have the factory and seloc manual. I would break down and buy the clymer manual just to understand this one topic; that's how important it is to me.<br /><br />So, if some of you savvy folks can bear with me and read the following painful paragraph to see if I have this sequence of events right?<br />1) During idling, idle screw sits against stop, butterfly plates are closed, spark advance lever is full against its aft stop???<br />2) Throttle is slightly pressed to start accelleration. Cam begins to move, when embossed mark on cam aligns with carb links, butterfly's begin to open. Spark advance is still at 0?<br />3) As throttle continues to increase, cam opens butterfly's more, spark advance begins to adjust timing (at what physical point would it begin to do this?), carbs suck in more air and fuel. <br />4) Throttle reaching WOT. Cam is at very end of travel for carb linkage follower? Spark advance is full against it's stop and has made the full 4 degree adjustment. Butterfly's open full but not past vertical, spark advance lever full open, throttle cam and carb follower are at the end of travel. <br /><br />Does this all sound correct? If so, this means the spark advance linkage should be just the correct length to bring the timer base lever through its full length of travel, but still reach each stop? How would this be adjusted, by bending the linkage rod? <br /><br />What if the carb linkage cam follower rolls off the end of the cam at WOT. Could that happen and what would be the cause?<br /><br />Sorry about all the questions, folks, but I'm still a little rattled over a mishap yesterday that really shook me up, and it's related to this.<br /><br />Many thanks to everyone!

 

[sycamore]

Re: The Spark Advance Blues - '86 110hp

The ignition stator plate more or less has an opening to travel in, do not consider the ends of the openings as stops. Your only stops are the idle screw stop, and the throttle plate stop when the butterflys are full horizontal.

 

[realboats]

Re: The Spark Advance Blues - '86 110hp

Thanks grandview. So it's safe to assume the spark advance link MUST be hooked up to the throttle linkage for an accurate static time. (DUH, they say there are no dumb questions, but mine are an exception)<br /><br />Please keep in mind what triggered this post is because the person who built the engine, to put it kindly, wasn't very good at what he did. Now I'm worried if the throttle linkage parts are the right ones. Would anyone know the length of the spark advance control rod on the 1986 110hp?<br /><br />Ok, I've reviewed the static timing procedure Joe Reeves so thoughtfully posted for us. The first paragraph says: <br /><br />

Originally posted by Joe Reeves:<br /><br /> To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

I don't think this applies to my engine since I don't believe there is a rubber stop or timer advance screw. I did wire the throttle linkage against the WOT stop (which was set to just before carb butterflies horizontal, carb linkage roll pins vertical) but the spark advance lever was not completely over to the end of its travel (there was a good 1/4" of travel left). Timing light showed that the best I could do was 20°.<br />Moving the spark control rod end over to the next hole (on the nylon piece at the throttle linkage) moved the spark advance lever even further away from the end of its travel. But this did bring it much closer to the 24° I was going for. Close enough for a fine tune, anyway.<br /><br /> Does it sound like the engine is safely timed at this point, or did I do something wrong? <br /><br />I know these questions must seem pretty mundane, but I'm new to these bigger two-strokes and this group is my sole means of support. And, most importantly, I NEED TO GET THIS RIGHT OR BYE-BYE ENGINE! So, a sincere thanks to everyone who has been so helpful. <br /><br />OMC made a very stout engine, built like a tank, but it is absolutely unbelievable the amount of money and sweat I've sunk into this engine so far to keep it running.

 

[djzyla1980]

Re: The Spark Advance Blues - '86 110hp

It sounds to me like theres still something not right with this.... it's either throttle cable, throttle cam, or something else that is mis adjusted. You in reality should be able to advance it over your degree .... either way from your mark. So if everything was in order you could advance it to lets say 32 0r back to 18(not that you want to) <br /><br />"What if the carb linkage cam follower rolls off the end of the cam at WOT. Could that happen and what would be the cause?"<br /><br />I don't think this is right... No Expert so correct me someone please if I'm wrong.... but in WOT your roller should not fall off the cam.. It should come to a rest towards the end of it...but not go over. I BELIEVE...but could be wrong... sounds to me like this area should need a lookin... Something is not adjusted right and I don't think it is in the timing...at this point

 

[TBarCYa]

Re: The Spark Advance Blues - '86 110hp

If your engine is the same as mine, then the linkage between the throttle arm and the timer base should be a fixed length. The throttle arm however is two parts with a spring in the middle. The lower part actually controls the throttle and how far the butterflies are open and the top part controls the timing advance. The bottom part can move further than the top because of the spring in the middle.<br /><br />To set the timing, there is an adjustable stop on the top part of the arm that rests against the block when at idle. This needs to be adjusted so that you are at TDC (or whatever is specified for your engine) when the stop is against the block. <br /><br />Attached to the block and closer to the flywheel, there should be another stop that makes contact with the top part of the arm when at WOT. This one needs to be adjusted so that you have the correct amount of timing when the throttle plates are fully open.<br /><br />From what I can tell by messing with my engine, the top part of the throttle arm should begin advancing timing at the same rate the bottom part opens the butterflies because of the tension on the spring. Once you have reached the max timing advance, the top part of the arm hits the stop and the bottom part is able to continue through it's full range of motion until the butterflies are fully open. <br /><br />I almost forgot that the procedure for synchronizing the linkages (according to Clymer) is that once the timing stops are adjusted, you then make the necessary adjustments to the throttle arm to throttle cam so that the roller lines up with the marks on the cam at both idle and full throttle.<br /><br />I'm also no expert on these things, but this is what I can figure out from the Clymer manual.