Joe Reeves Need your advice

" Having read this Message Boa

" Having read this Message Board and Boat Motors.com Message Board for the last 18 months I have come to the conclusion you are definitely an OMC expert. I would like your input on the following situation. I have a 1990 25hp rope start Johnson. The previous owner had the marina install a 30hp intake manifold and 30hp carburetor. This motor starts great, but seems to run rich (vibration) for the first 1/3 of the throtle. Once past that 1/3 position motor has good power and runs smooth. Boat (16' Lund Explorer)has no problem getting up on plane. I have installed a new prop, rebuilt carb, used OMC Engine Tune, and replaced fuel pump diaphragm. I am runnig Champion QL82 plugs, gapped @ .030. I have read about Boyesen 2 stage reeds. I was wondering what your opinion is on these reed valves. "

"QL77JC4 plugs,.chaek sync&amp

"QL77JC4 plugs,.chaek sync&link, check WOT timing,
is manual primer on?leaking? What year carb and intake manifold?Correct jets in carb.?What RPM at WOT? does engine warm up/idle temp? Boyesen reeds tend to break if motor sneezes.Zeke Johnson
Evinrude Master Tech with Zeke's Marine Service
Jupiter,Fla.5612-746-1508 or [email protected]"

"Johnnie.... Stick to the regu

"Johnnie.... Stick to the regular metal leaf valves. That is not your problem.

The 25hp and 30hp have the same block, cyl head, crankshaft, rods, pistons, leaf plate, leaf valves etc etc. The differences between the two are:

Of course the throat hole venturi on the carburetor and the manifold is larger on the 30hp than on the 25hp.

30hp rating is hit at 5500 rpm. 25hp is hit at 5000 rpm. Not sure if there's a timing difference between the 25hp and the 30hp.... check with your dealer. Regardless, that would not be your problem.

30hp full throttle rating is 5200/5800 rpm. 25hp full throttle rating is 4500/5500 rpm.

The cam which is attached to the magneto armature plate (cam that rides against the throttle opening arm) is different. The 30hp cam is #326876. The 25hp cam is #334750 (Having the 25hp cam attached to the 30hp intake manifold instead of the 30hp cam could give you a problem).

The orifice at the extreme top front of the carburetors are different. The 30hp is #39 (.039) 334568. The 25hp is #30 (.030) 317473.

The high speed jet, located at the center bottom portion of the float chamber is different. The 30hp is #65D (.065) 327541. The 25hp is #51D (.051) 331567.

Note that the I.D. numbers (#30, #39, #65D, 51D) are actually imprinted on the jets themselves.

If the wrong jets (25hp) were in the 30hp carburetor (even one jet wrong), that would give you a problem.

Can't think of anything else to tell you at the moment. Champion s/plugs, either QL77JC4 or L77JC4 s/plugs should be set at .040 ("Q" is a resistor plug... prefered.

Joe (30+ Years With OMC)"

"Q" on a Champion spa

"Q" on a Champion spark plug is NOT a resister plug. It is a supressor plug. There is about 30K ohms of resistance difference between resister plugs and supressor plugs. Resister plugs should never be run in OMC 2-cycle outboards - according to OMC.

"Bubba..... The "Q" s/

"Bubba..... The "Q" s/plugs are generally refered to as resistor plugs even by OMC factory reps. They are also known to be stated as eliminating and/or quieting down electrical and/or electronic noise. However, they are actually designed to suppress electronic and/or electrical interference.

I'd be very interested in knowing exactly where you read this statement pertaining to "resister" plugs by OMC as I have yet to come across it in any school, seminar, bulletin or service manual. Always looking to learn something new.

Joe "

" Joe: In my part of the count

" Joe: In my part of the country, back in the eighties, a lot of dealers were replacing QL77JC4 Champions with NGK BR9HS-10 plugs because the NGK crossover book said so. At one of the OMC updates that I attended in the early ninties, the difference between resister and supressor was explained. Put an ohm-meter across an NGK BR9HS-10 and then across a BZ7HS-10 (Supressor plug that now crosses over to QL77JC4.) There is quite a difference in resistance. At that same update, there was a page in the workbook that they gave us that said "Don't use resister plugs in OMC outboards! They can cause misfires!" If you know a Bombardier service rep who has been around for a few years, he will remember that update - it was the same all over the country. For some reason NGK charges a lot of money for supressor plugs and not a lot for resister plugs. An NGK catalog might explain it better than I. QL series Champions are supressor plugs. I don't know what Champion calls there resister plugs. I've had no need to use them. A lot of Yamahas run resister plugs, but their ignition systems are very reliable. Some of the early FICHT motors were shipped with NGK BZ (Supressor) plugs, but they got Champion to make them more cheaply. "