Increasing carb jets

[Nathan S]

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[R.Johnson]

Re: Increasing carb jets

There should be a jet size chart in your service manual.

 

[TLL]

Re: Increasing carb jets

If the motor was running correctly before the rebuild, it is really not necessary to increase jet sizes just because the cylinders were bored out. With that said, it is common to increase the size of the high speed fuel jets after a rebuild just to assure that the engine won't run to lean, especially on older models that were built before crappy gas hit the market. If you want, increase your jet size by two sizes. For example, if you had 36's go to 38's. Also retard engine timing by 2 deg from factory spec. Before you do this you really need to know why did the engine fail, and then, has that cause been corrected?

 

[Nathan S]

Re: Increasing carb jets

I was reading that I should rejet the carbs to help cool the pistions, but the motor ran fine before failing. I believe I have fixed the problem. The motor dropped a piston ring dowel. I am not sure of the exact cause, but it may have been a combination of things. There was some carbon accumulation on the tops of pistons (I didnt think it was that bad tho) and I have all new wisecos now, there was a faulty check valve, and I had just made a good run at about 5000 rpm (lugging it), although it came loose at idle speed. So my understanding is increase the jets to ensure adequate fuel and lube, but it isnt really necessary. What does retarding the timing help with, and should it be done if the jets are not increased?

 

[TLL]

Re: Increasing carb jets

Retarding the timing by two degress lessens the chance of pre-ignition and detonation, a common cause of outboard engine failure. It is often done upon rebuilding the engine just to cover all the bases and to assure future engine durability. The fuel today is not the quality it was 15 years ago.

 

[a70eliminator]

Re: Increasing carb jets

Run engine to top speed as is and record, jet up 2 sizes and run again under same conditions, speed increase? jet up 2 more until no increase in speed and your golden. You should allow piston rings to seat themselves in before messing around with fine tuning the carb though, and I totaly agree with timing suggestions, less change of detonation just a little buffer till she's broke in good.

 

[modsrx]

Re: Increasing carb jets

make sure to let the engine come fully warm cause your gonna have failure again with those sh it wiseco piston god i hate them ....

 

[modsrx]

Re: Increasing carb jets

carbon on piston will not burn down your engine .....overheating or lean condition(dirty main jet ) will become a major failure so make sure to put a new water pump to be safe and check the carb the piston go caboum ... by the way gaz doesnt lube nothing .... it only keep the piston coool

 

[Nathan S]

Re: Increasing carb jets

Thanks for the advice. I will look into upping the jets from 62 to 64 it may be good insurance. I had one more question about the timing. I read that it hurts the looper motors power, even at 2 degrees. Have you ran into that problem, and if so is it really that much of a loss?

 

[modsrx]

Re: Increasing carb jets

u will not see difference for 2 degree on big engine