QL 78YC or L78YC ?? {timing 140 rude 86)

kgw · Mar 3, 2004

still working on bad idle prob 140 rude. could not find QL78YC only L78YC whats the "Q" designate? also is there a setting for timing at idle. manual doesnt show one, linkage to timing plate seems a little sloppy. but i dont know what it was like when new,never had any reason to look at it.thanks again,this place is a great source of info ken

rickdb1boat · Mar 3, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

I don't show an idle timing spec. It does show full throttle timing at 18* BTDC. Idle speed should be 650 RPM's in gear moving on the water. The "Q" designates a resistor plug, similar to the ones used in cars to stop radio interference from the ignition. The L78YC will work fine. Any dealer should have the "Q" plugs if you want them or they can be ordered online here at I-boats.

papasage · Mar 3, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

i got my plugs at wal mart . and have got thim at autoparts stores like N A P A ADVANCE etc.

seahorse5 · Mar 3, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

The " Q " means there is a suppressor, not a resistor, inside the plug and you have to use that style for OMC ignition systems. Idle timing is around 8 ATDC, but the idle speed control changes the timing, so it could end up a bit more advanced than that.

rickdb1boat · Mar 3, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Huummm. My Factory Manual says to use QL77C4's OR L77JC4's for my OMC. Guess the manual is wrong... Actually, that 140 motor calls for a QL77JC4 from 85'-93'...

seahorse5 · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

The only official factory plug reference guide is in the annual Parts and Accessories Catalog that OMC, now Bombardier, publishes every year. Back in '95 or '96, most plugs were changed to a different model. To be up to date you cannot rely on original service literature.

rickdb1boat · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Alrighty, then. So a L78YC will not run in this motor? Would you please recommend the correct plug for my 91' 70 HP rude?

rickdb1boat · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

^^^

kgw · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Seahorse, I ran L77JC4 in this motor for years never had any prob. till now. but I am taking your advice All could find at the boat store was L78YC so I'll give them a try gap at .030. thanks for info on idle timming. I ordered new idle jets .004 over stock to as a last resort to cure my rich idle prob. .004 over never hurt any harley that I have worked on . what do you think ? thanks again the lake is starting to melt.

seahorse5 · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

On those older looper motors, sometimes you had to play with the air jets to make things run better, just like re-jetting a Harley after adding a set of V&H Staggered Big Shots on it. Like others mentioned, try NAPA or another auto parts store for the QL78YC plugs. I've also seen them at Kmart and Walmart and West Marine. Hey RB, Thru 1993, the 70hp motors use a QL77JC4 plug. 1994 and later 70's use QL78YC.

kgw · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Thanks Seahorse,but do you think .004 leaner is to big a jump ? should the "L" 78's be a prob ? Thanks again you guys are great

Cricket Too · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

kgw.....If you ran the L77JC4 for years without a problem the why are you changing to the L78YC? Is it because of the idle problem and the L78YC is a hotter plug? If it is, I would try gapping them at 0.040 instead of 0.030, I do this on all my motors, because I troll alot, and I get a smoother idle and trolling speed. Good luck.

Solittle · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Have you removed the t-stats? Those motors will not idle correctly if they don't get up to operating temp.

kgw · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

mmcpec, thanks for reply,I also troll a lot and all the posts here say the QL78 is now the right plug for my motor I was mainly concerned about the "Q"part of theL77" that I ran.Owners manual listed L77 as alternate for QL77 thanks again ken

seahorse5 · Mar 4, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

About increasing your idle air jet size, it takes about 4 or 5 sizes just to notice a slight difference, because we are talking air here, not fuel. On some motors, going up 10 or more sizes is not unheard of. Years back there was a fix for certain early looper V4's that consisted of drilling a vent hole and installing a hose to eliminate fuel-oil buildup under the lower crank bearing. A problem engine would idle fine for a short time, them blubber and emit a puff of blue smoke, then idle fine again for a time. The fix was thru the factory where they sent the fitting and a template, but I doubt its available any more. Is your water line close to the exhaust ports meaning the engine is deep in the water with a lot of backpressure?

kgw · Mar 5, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Thanks Seahorse,I believe my motor has that fix in the parts book it shows a check valve on the port side with a hose going to the bearing housing the other end of valve going to drain sys.havent acualy seen it be cause its behind vro pump and the weather hasnt been good enough for me to spend a lot of time out side. the exhaust ports are not in the water just the prop. thanks again your help is really appreciated. ken

kgw · Mar 5, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

Seahorse,yes my motor has that fix up to 70 deg today had a chance to give it a good look and decarbed again there is a tee in a line {ceck valve}? one line goes to power head under flywheel 2nd line from fitting goes to lower part of power head under intake manifold 3rd smaller hose goes to tee at the starboard lower recirc. check valve.motor ran fine on muffs at about 1500 rpms it would blubber only occasionly last fall plugs look clean but still a little damp. the real test will be when I can put the prop in the water I'll let you know. thanks again to all ken

kgw · Mar 6, 2004

Re: QL 78YC or L78YC ?? {timing 140 rude 86)

^^^ ken

QL 78YC or L78YC ?? {timing 140 rude 86)

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