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We are talking about the exact same problem but you are not grasping what im saying the ski needs to physically be submerged in a body of water in order for the engine to be under load. Running the motor on the hose will give no torque resistance to the motor whatsoever. For some reason 300...

Every 300 with a standard carb that i have owned (i love 300s!) has had this same problem. After searching for air leaks and timing issues and as many other possible causes I could think of i learned that that's just what 300 motors do whenever they aren't under load. I can almost 100% guarantee...

Ebay might be your best bet. I dont think you will find anyone still making or stocking parts for 300s these days. I love 300s and I have built two of them. One has pretty much every bolt-on aftermarket part available to my knowledge and the other is completely stock apart from a 38mm bn carb...

Double check its air escaping from the carb and not a sucking sound. Pull the reeds out and check that all the petals are intact and sitting snuggly down with no gaps its a ten minute job. You may have to replace the gaskets if they are old or damaged. If the reeds are sweet eliminate possible...

A picture would be good to see how your dual cooling is routered. You might want to give it a decent backflush in case there is something stuck in there. Each part should be backflushed individually with water from the hose -compressed air usually wont fix a blockage. Carefull not to fill...

On a two stroke there are always four areas to check. Spark, Compression, Timing and Fuel. It sounds like you have spark and compression covered but do check your plug leads and gaps. If you have recently pulled the motor apart and rebuilt it you most probably would have made sure that you put...

Post a video of it being ridden!

They said they got 37mph out of one and the 300 manual says they do 33mph completely stock. It could be the truth..

Hi sorry for the late reply the gas tank is an Arrow 9 litre Go-Kart tank.

Ok i finally got to take my ski for a test run and the jetting was almost spot on. The .60 pilot was perfect and the 1.0 mainjet was tuned just right at 2 1/2 turns out. I want to go to a slightly bigger main jet to achieve the right mixture at around 1 1/2 turns out and i reckon a 105 main jet...

Check the plugs and see if its running rich now i wouldnt think it would run that much richer that it would have clouds more smoke then before unless the line was leaking alot of fuel before and you would have smelled it. There is the possibility of things being a little more oiled up then...

Thanks for the advise i tightened it right up!. How tight is too tight i dont want it to leak?

The mighty 300 is finally complete and I cant wait to get it wet!

Nah sorry ill give it a run this weekend I only just finished my rebuild

Cool thread cheers for the info! I have a stock 440 with a mariner pipe. What carb and jetting would you recommend to run if I were to port it the same as in your pictures? Would i lose much bottom end performance from the raised exhaust ports? thanks

The motor is all finished and back together im hoping that the new rod will sort my vibration issues out for awhile! I had the top of the head machined to look pretty. Ive got this cool westcoast driveshaft support bolted in now and a bilge pump bracket glued in since my venturi line is used for...

Here are some of the parts I have been painting. The barrel still needs a clear coat. The cases are ready to go back together with the rebuilt crank. The reed block, front cover, flywheel cover and intake manifold have been stripped and now are clear coated aluminium. I have decided to scrap...

I pulled the motor and cleaned the hull up all nice and then cut out of a gym mat some squares of foam to make a flat surface for the gas tank to sit on later on. I also cut a pad out of 25mm thick foam for the waterbox to sit on and glued everything in there with contact glue. I used paint...

This is my js300. You might have seen it in my previous posts. It had always had one of those rock and roll type motors that when running look like they are ready to jump off the motor mounts. The bad vibrations were due mostly to the little end of the rod being a bit worn out and having some...

I set out to do the stock waterbox modd for my 300 but gave up when i measured the cast outlet pipe and found that the internal diameter was only 34mm. The carb is a 38mm the exhaust manifold outlet is 38mm and the end of the kerker pipe is 38mm and also the inside diameter for the inlet pipe to...