Yamato 302 problems

[GuyWithTheCoolBoat]

ok first off im new to the OB racing scene. im in the class c runabout with a yamato 302. i bought my boat, motor, steering and throttle assembly right out of the water after darrel sorensen got done running the top o michigan marathon (please note that this motor ran fine when i got it from him too). ok now for my problem. on day 1 he had epox from his fuel tanks take him out of the race (gummed him up). day two he switched to a plastic tank in the cockpit with him and did just fine. the motor ran strong when i got it from him. we put it on my trailer and drove 6 hours back home to the UP (possibly jarring something in the carb???). i went to put the boat in the water for the first time 2 days later and had my gravity feed tank leaking. so trying to just bypass the problem i ran my 'out' line from my pump directly to the carb. well this worked great for about 1/4 mile . i got a vacuum lock and was forced to call it a day. after repairing the leak in my tank i had good fuel pressure to the carb the following day. i warmed the motor a bit on the trailer just before putting her in (ran fine). but when i got in the water and gave her a yank and jumped on the throttle to plain, all i did was sputter, bog, and eventually crap out. so i pulled her out (with a great deal of coaxing to get back in). checked for a dead cylinder. both good. good fuel delivery (no lock, was fixed when i put the gravity tank back in), threw new plugs in her thinking she was fouled, nothing ran just the same. great on land, terrible in the water. both kill switches were in and snug and my throttle seemed alright (still set where darrel had her for the races). i even pulled the head to see if i had blown a gasket and was getting water in there killing a cylinder. gasket was good. ive called darrel sorensen back quite a few times lately and its really difficult to trouble shoot over the phone (not his fault, hes been more than willing to help). is there anybody out there that has experienced this same problem? or are there any UP michigan racers that are close to the houghton/ hancock area that are willing to help. the boat ran fine when i got it, ran fine until the vacuum lock kicked in all the way and after that hasn't run well at all. im back to the same fuel setup that darrel used in the marathon on day two. coincidence to the vacuum lock that i created by bypassing the gravity tank or did i actually mess something up? if it would be easier to talk over the phone feel free to call my cell anytime. 231-881-4864. any and all help is appreciated.

[seanp3]

Sounds like you're using double kill switches. Make sure both are in good working order. If its running on one cylinder you may think it sounds ok when on dry ground, but in the water under a load won't cut it.

[GuyWithTheCoolBoat]

thanks

when i was trouble shooting with darrel over the phone he said to disconnect hte killswitch directly from the motor and try it in the water and see if that did it but havent gotten that far yet. i did however pull botht he plugs and check the spark by pulling her over and grounding the plugs to the block.. good clean blue spark on both. no weak yellow or missing spark. is the an adequate test or should i still put her in the water and try it without the killswitches to eliminate that possibility?

[Team B&H]

Two kill switches are nothing but a pain. Even if they are not the immediate problem, you'll be much happier with diodes and a single switch. Get it from Tom Johnston or even from your local Mercury dealer.

Most fuel pumps put out too much pressure for the gravity feed Yamato (Mikuni) carbs. You can't hook one up directly to the carb without some tricks to the pump or some sort of pressure regulating device. There are mechanical pressure regulators but most resort to some type of overflow system to limit pump pressure to the carb.

When trouble shooting, it is always a good practice to eliminate things that could be potential problems. Put on a gravity tank and unhook any kill switches and see if it works. If it works then, your issues are in the pump/tank/plumbing system or the kill switch system. If it doesn't work the problem is something in the motor itself- more unlikely.

[bill bob]

had the same problem clean the tank and carb several times to get all epoxy out of system and dont have a tank with epoxyed fuel fittings any more it can cause alot of grief

[bill bob]

remove all epoxy from tank and have fuel fittings welded in by a pro with gas tanks. when the epoxy broke down after a few years i ended up with filters pluged and carbs pluged they ran fine on the beach but like crap under a load hope this helps

[seanp3]

Another thing you should check is for some debris in the bottom of the carb. Usually where this stuff settles in in the banjo nut on the bottom of the carb. It takes a 17mm wrench, remove the nut and check inside the nut. It doesn't take but just a few specs of debris floating around in there to cause the same type of problems your having. If you find stuff in there it wouldn't hurt to remove the top carb cover and pull the float out at this time and clean the bowl out real good. Be sure not to drop or lose any of the washers when you do this or you will have leaks after you put it back together.

[17W]

Not in the UP....

I am in S.E. Wisconsin. Call me Saturday @ 262-551-8479.

[GuyWithTheCoolBoat]

thanks for the help guys. it was the double kill switches. i may take your advice team b&h and do the diode with the single switch. she runs likes a champ again. thanks again.

[marktrail]

racer winning 302

ok first off im new to the OB racing scene. im in the class c runabout with a yamato 302. i bought my boat, motor, steering and throttle assembly right out of the water after darrel sorensen got done running the top o michigan marathon (please note that this motor ran fine when i got it from him too). ok now for my problem. on day 1 he had epox from his fuel tanks take him out of the race (gummed him up). day two he switched to a plastic tank in the cockpit with him and did just fine. the motor ran strong when i got it from him. we put it on my trailer and drove 6 hours back home to the UP (possibly jarring something in the carb???). i went to put the boat in the water for the first time 2 days later and had my gravity feed tank leaking. so trying to just bypass the problem i ran my 'out' line from my pump directly to the carb. well this worked great for about 1/4 mile . i got a vacuum lock and was forced to call it a day. after repairing the leak in my tank i had good fuel pressure to the carb the following day. i warmed the motor a bit on the trailer just before putting her in (ran fine). but when i got in the water and gave her a yank and jumped on the throttle to plain, all i did was sputter, bog, and eventually crap out. so i pulled her out (with a great deal of coaxing to get back in). checked for a dead cylinder. both good. good fuel delivery (no lock, was fixed when i put the gravity tank back in), threw new plugs in her thinking she was fouled, nothing ran just the same. great on land, terrible in the water. both kill switches were in and snug and my throttle seemed alright (still set where darrel had her for the races). i even pulled the head to see if i had blown a gasket and was getting water in there killing a cylinder. gasket was good. ive called darrel sorensen back quite a few times lately and its really difficult to trouble shoot over the phone (not his fault, hes been more than willing to help). is there anybody out there that has experienced this same problem? or are there any UP michigan racers that are close to the houghton/ hancock area that are willing to help. the boat ran fine when i got it, ran fine until the vacuum lock kicked in all the way and after that hasn't run well at all. im back to the same fuel setup that darrel used in the marathon on day two. coincidence to the vacuum lock that i created by bypassing the gravity tank or did i actually mess something up? if it would be easier to talk over the phone feel free to call my cell anytime. 231-881-4864. any and all help is appreciated.

back to the bacic's
spark, fuel and compression. use gauges, it will be worth your time.
mark trail

[reed28n]

Kill Switch

thanks for the help guys. it was the double kill switches. i may take your advice team b&h and do the diode with the single switch. she runs likes a champ again. thanks again.

There is a kill switch you can probably get from TJ that is fool proof. It has three wires that you can hook up in any order, doesn't matter.

If you open the switch you'll find a button that makes all three contact each other when the switch is tripped. Fail safe and fool proof.

[seanp3]

Another thing about kill switches........I used to have one mounted in a vertical position. If it got wet it would seem to go bad fast because it would not drain the water. I remounted it horizontally where it could drain the water and don't have the problem any longer. Extra kill switches are good to have on hand.

[propnuts]

I'm with Sam

I would start by going gravity feed and eliminate that potentiol issue. We have had people up here try pumps on Yamato's, but the success rate has been not too great. As with most things in racing, simpler is better.

Two kill switches are nothing but a pain. Even if they are not the immediate problem, you'll be much happier with diodes and a single switch. Get it from Tom Johnston or even from your local Mercury dealer.

Most fuel pumps put out too much pressure for the gravity feed Yamato (Mikuni) carbs. You can't hook one up directly to the carb without some tricks to the pump or some sort of pressure regulating device. There are mechanical pressure regulators but most resort to some type of overflow system to limit pump pressure to the carb.

When trouble shooting, it is always a good practice to eliminate things that could be potential problems. Put on a gravity tank and unhook any kill switches and see if it works. If it works then, your issues are in the pump/tank/plumbing system or the kill switch system. If it doesn't work the problem is something in the motor itself- more unlikely.