1955 15 hp Fastwin throttle issue

[dasman7580]

I have replaced all the ignition components, rebuilt the carb, and am getting fire to each cylinder. It starts and idles very well, but will only run approximately 10 mph at full throttle. After running it at full throttle for about 15 minutes it starts to run rough and is hard to start. After 20-30 pulls it will start back up and run smooth again for a little while. In fact, full throttle doesn't sound anywhere close to what it should. Before performing all this work it had this problem until I cleaned the plugs and then it nearly threw me out of the boat. I have not checked the compression yet, but plan on checking it this weekend. Any ideas????

 

[lindy46]

Re: 1955 15 hp Fastwin throttle issue

Yes, check compression, but it sounds like it's only firing on one cylinder - maybe a coil cutting out when it warms up. You did replace the coils?

 

[F_R]

Re: 1955 15 hp Fastwin throttle issue

dasman, you said you replaced all the ignition, so I assume that includes the coils? Your description certainly sounds like the classic bad coils story. But if not....

You need to figure out which cylinder is not firing, then figure out why. Disconnect and ground one spark plug wire and see how it runs. Then do the same thing with the other one. Chances are, it won't make any difference with one, but won't run at all with the other one grounded----that is the good one.

Now that you know which cylinder is missing, you have to figure out why. Recheck your ignition work first. Also check that compression, and check to be sure there is no water getting into the cylinders.

Hate to tell you this last one, but the 1955 Fastwin had problems. Grab hold of the flywheel (not running, duh) and see if you can move it fore and aft. It should not. If it does, you have a junker.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

Yes, I did replace the coils. I have tested the one cylinder theory by only running it on each cylinder individually and it passed. After doing a little more research I think I have a bad head gasket. The plugs appear to be wet each time I've checked them. I've also noticed a greyish oil like substance in the exhaust housing when I changed the impeller. My guess is the water is mixing with fuel/oil in the combusion chamber. It runs smooth (granted it's not full throttle) for the first 15 minutes and then it almost sounds like it is missing. After it sits or is pulled 20-30 times it starts back up and idles great. So, in theory, after running for 15 minutes enough water makes it into the combustion chamber to foul the plugs. This water also mixes with the fuel/oil to create the greyish oil like substance. After pulling it 20-30 times the plugs have dried out enough to fire again. Any thoughts????

 

[kfa4303]

Re: 1955 15 hp Fastwin throttle issue

I think you've found the culprit. Not to worry. It's a fairly easy and inexpensive job. You be able to get the head gasket right here at iboats or on eabay for aobut $20. Do a search here in the forums on installing a head gasket and you'll find tons of links. Be sure you torque the head bolts down to the proper spec, usually in inch/pounds. You might want to re-torque them again after the motor has run for a while and had a chance to warm up. To answer your question; a blown head gasket would allow cooling water into the cylinders and cause the compression to drop drastically. The water and the low compression together are probably to blame for the inability to start easily. Keep us posted.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

Thanks for the help everybody. Not sure I could've have done half the work to the motor without this forum. I'll let keep you posted.

 

[lindy46]

Re: 1955 15 hp Fastwin throttle issue

Before pulling the head, check compression.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

Well I decided not to check the compression and just pulled the head off. After taking a peek inside it would have been a waste of time. There was still about 1/2 table spoon in the bottom cylinder. Now I need some advice. I have the exact same motor in a 56' model. Should I swap all the improvements from the 55' and put them on the 56'??? Or continue with the 55'??? I'll try to get some pictures posted tomorrow.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

It looks like the head gasket has been bad for quite some time judging by the amount of corrosion. There appears to be a little corrosion around the edge of the exhaust plate, but I'm assuming this is from years of pumping water?? What are the odds that the rings are bad?? Unfortunately one of the studs broke off while trying to remove the head. Guess I'll weld a nut a nut on and try to extract it.

 

[Mas]

Re: 1955 15 hp Fastwin throttle issue

Head gaskets are pretty cheap. Fix the bolt as you mentioned, then put it all back together and see how she runs. Do not part her out until you've given her a chance!

Mas

 

[kfa4303]

Re: 1955 15 hp Fastwin throttle issue

agreed. it actually doesn't look to bad. I would clean/clear out all the passages, remove as much of the black carbon deposits from the pistons and head using Deep Creep or Sea Foam, then slap of a fresh head gasket on and fire it up. you might be surprised. these old gems are pretty tough. make sure you do NOT use automotive head gasket sealant as it can lead to electrolysis. you have a great old motor that's well worth the effort. keep us posted.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

I read on maxrules.com to resurface the head with 80 grit sand paper on a flat surface. Then.use a mill file on the block to expose clean metal. A new head gasket is in the mail, so hopefully i'll make a little progress this weekend. Does anyone have a recommendation for a sealant around the water jackets other than OMC brand???
http://maxrules.com/fixtuneitup2.html

 

[Mas]

Re: 1955 15 hp Fastwin throttle issue

Most head gaskets are put on dry...no sealant!


Mas

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

I was unsuccessfull at removing the bolt from the block, so its on to the 56' model. Should have it completely assembled tomorrow. Maybe even a test run on rhe lake. Does anyone know what the compression should be???

 

[Mas]

Re: 1955 15 hp Fastwin throttle issue

I was unsuccessfull at removing the bolt from the block,

Unsuccessful in what way???

Mas

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

I welded a nut onto what was remaining of the bolt that twisted off. After the nut twisted off with a small portion of the bolt 3 times in a row I gave up. I swapped all the improvements over to the 56' model. Just need to bolt up the lower unit, torque the head bolts, and then I should be in business!!! I feel like I could rebuild a fastwin in my sleep now. Anyway, I'll keep you guys posted. By the way, compression was about 75 lbs at each cylinder.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

Finally got every thing back together and it cranked over after about 10 pulls. I think there is still alot of sea foam in the nooks and crannys. I let it run for a few minutes before turning it off. It was really smoking and fogged up the entire yard. Started it a few more times and it started on the second pull each time. The rpms seemed to incease each time I started it, and then slightly decrease. hopefully it will get lined out once I get it on the water and out of the bucket!!!

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

Finally got it out on the water today and the flywheel key sheared in half. Brought it back to the house and scavenged the one off the 55' model. Took it back out and it ran much better but it starts to vibrate at full throttle. I think the timing may be off a little. I set the 0.020" gap in the center of the word "top" on the roller bearing. I've heard to set the gap this way or by using a notch and two lines on the flywheel. Thoughts????

 

[kfa4303]

Re: 1955 15 hp Fastwin throttle issue

hi dasman. glad you got her running. you don't really need to set the timing, assuming you put the flywheel on correctly and set the points to the correct gap, which it sounds like you have. The flywheel key probably sheared because the flywheel wasn't tightened down to the proper torques spec. I believe it needs to be 45 ft./lbs., but someone will correct me if I'm wrong. Assuming the key is aligned with the center line of the crankshaft, the flywheel is torqued to the correct spec, and the points are gaped to .020" you should be all set. You may also want/need to perform a link and sync procedure. just do a search in the forums and you'll find tons of threads.

 

[dasman7580]

Re: 1955 15 hp Fastwin throttle issue

Got eveything torqued down and it runs rough at full throttle. I'm using the recommended 24:1 fuel mixture, but have heard to use 50:1 because of "new oil technology." The plugs appear to have unburned fuel on them. Is this a sign of too much oil???