302 Mod engine problem question

[blueskyracer]

OK here we go. The first race the boat and motor were perfect at Elk River. After that the motor has been a slug. I have stuck with the same prop thru everything since you are only suppose to change one thing at a time.

Anyway I have played with fuel mixture and it is so sensitive, one click either way and it is to rich or to lean. It will have trouble getting on plan and have half power all the time if it is to rich and if to lean it will take off and at the halfway point down a strait and then it will just slow down and act like it is at half throttle thru the corners with no acceleration till half way down the strait and then it will take off again.

I have gone thru the engine till I am blue in the face. I have checked the reeds and cleaned the carb but it was about as clean as if it was new. Took the head off and checked the head gasket and pistons. No score marks and very clean. Now I am looking over the exhaust and decided to fill in around the filler block with some more epoxy mixture but it was still sealed on the bottom. I have checked the pipe and header and it has no restriction. Everyone at the race said the motor sounds funny compared to usual. Anyone see anything that might help?

Like I said this sucker worked great at the first race so something has changed but what?? Also this is a FIXED pipe system

[Fast Jack]

Mod

Make sure the choke is staying seated with no gas geting past it it

[Boatracer4fun]

Does it wind up on the beach without a load on motor?

[Tim Weber]

I've had a leaky head do strange things. Check the head and make sure its' not warped. And check for any abnormality in the head gasket.

Tim

[DiGia54D]

Did you notice if the pipe is set closer to the manifold then previosly run? Set the pipe back little by little so that it doesnt load up. Mine didnt have a fixed pipe but if it when past a certain point the pipe didnt work at all.

[thepiranhabros]

Check the timing. See this link:

http://yamatoracing.com/technical_entry.php?pid=4

[DeanFHobart]

Float Level

How about the float level???

[blueskyracer]

Float is set at 1.25 per spec and I have made sure the choke is seated closed and removed the lever now. Also the pipe stays seated against the header flange so it cannot move.

I plan to check the timing when I get it back together

[thepiranhabros]

Check also to see you don't have anything else moving around that shouldn't be timing-wise. Your symptoms sound exactly what was happening to our OMC A engine when my son inadvertently spun the hub of the flywheel. We didn't notice the flywheel hub was moving independently of the rest of the casting until we had exhausted everything else and went to take it off to check the stator. Dry fire with no load, test tank, or on the boat under load, the engine would start and run like a pig, then spin up to speed when the timing was right when the flywheel lined up momentarily, then would fall off again when the flywheel shifted timing positions. A new flywheel fixed us up!

[bill van steenwyk]

You might want to check and see if your cooling water discharge hoses have moved so as to be putting water on the pipe now, when they were not before while running, or vice versa. Cooling the pipe with water, when designed for a certain RPM range will make if less effective if it was tuned right to start with. Also check for possible water leaks into the cylinders.

I know you said you checked the gasket but did you pressurize the cooling system while doing so. City water pressure from a hose works well and then inspect the cylinders to see if you have any water droplets present afterwards. Be sure the engine is warmed up while performing this test. Sometimes they won't leak till warm.

Also might check fuel line from tank to carb for obstruction, even if the float level is correct. Also check tank vent to be sure it was open.

ADD: Went back and read your original post again and paid more attention to the part about the needle valve being very sensitive (small amount of adjustment going way lean to rich). This would possibly confirm a fuel starvation problem due to fuel line or filter plugged, tank dirty inside blocking fuel outlet, or vent not operating properly. Is it possible to see the tip of the inlet needle that the float mounts on if it comes thru the top of the carb? If it is disappearing or lowering drastically while the motor is running that could indicate an insufficient fuel supply for various reasons mentioned or others even if float level is correct.

You did not mention whether you changed lower units for any reason, BUT if you had a problem and changed one, engines will act that way with expansion chamber exhaust if the gear ratio is different from one to another. I purchased Yamato racing units some years ago that were stamped 13-15 and they were actually 12-15. Drove me nuts till I finally figured out what the problem was.

[Shep]

Check pipe and make sure the stinger inside isn't broken or loose. Take off pipe and see if it rattles, it shouldn't.

[blueskyracer]

I would like to add that I am the original owner of this motor since I purchased it from RPM marine. Also this is the weird part but the motor has alway run at 30 clicks even when it was a stock motor.

Just about everyone has told me it should be more like 40 clicks but I doubt if this sucker will even run that rich.

[ZUL8TR]

302 problem

Check the flywheel Woodruff key for some shearing signs that is throwing off the timing.
Even small shear sign amount here will effect the performance.

[Tom Cronk]

Pm

Mike
I just sent you a P.M.
Tom

[pro350hydro]

Float is set at 1.25 per spec

On the 102 Mod, we always raised the float about 1/8" to help prevent fuel starvation

the motor has alway run at 30 clicks even when it was a stock motor.

Just about everyone has told me it should be more like 40 clicks but I doubt if this sucker will even run that rich.

Hold up a minute, not every needle is the same!

According to a conversation I had with Ric a long time ago. Not all needles were made the same, and some have different spacing on the outside of the needle for your clicks. What I'm saying is, one needle may require 30 clicks, and another may require 40 clicks to get the motor to run right, but both would be giving the same result as they may not be the same in manufacture. So you wouldn't be comparing Apples to Apples....

Does that make sense?

Other than that get back to the basics. Compression test, spark test, check timing, pressure test the crankcase, pressure test the water cavity, etc. test test test test, then when your done test some more